Gas turbine design and operation training course

وزارة ا��ء وا��ء

إدارة ا��ــ�� ا�داري وا��ــ�ر�ـ�

Gas Turbines

Design & Operation

Training Course

Over 100 Question & answer

Over 200 Pictures

********FULLFULLFULLFULLY ILLUSTURATEDY ILLUSTURATEDY ILLUSTURATEDY ILLUSTURATED********

OPERATION ENGINEER: ABDULLAH ZAMAN ALMERZA

20-24/10/2007

"Gas Turbines design & Operation"– Eng. Abdullah Zaman Al merza 20/10/2007 Mobile: ++9656492894

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Table of Content

Page

Gas turbines general notes ……………………………………………….. 10

Gas Turbine air intake system……………………………………………… 34

Gas turbine compressor………………………..……………………..……… 40

Gas turbine combustion chambers………………………….……………. 69

Gas turbine – turbine section……………………………………………… 94

Gas turbine blade cooling technique…………………………………… 108

General notes in shaft design……………….……………………………. 121

Gas turbine - start up unit………………………………………………….. 133

Gas turbine operation, control & protections…………………….. 138

Gas turbine efficiency & optimization…………………………………... 158

Appendix - a ………………………………………………………………………… 182

References ………………………………………………………………………… 187


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List of questions EـــــــــFGHIـــــــ�ول اK -

�YهW ا��ر�TVR ا��Uز�T وآN�OP QR؟What is the operating principal of gas turbine?

1

�YهY Wا^��P Nر ا��ر�TVR ا��Uز�T ؟Gas turbine history & stages of development?

2

Yــ�هW أgـــ�اع deت ا�^ــــ�ــــاق ا�ـــ�اWFa ؟What are the main types of internal combustion engine?

3

jّP QRآــــــTـــــــ�ز�Uت ا��VRا�ــــ��ر� QV�ًY��l ؟ How can gas turbine classified?

4

آQVjP QR ا��ر�Rـــــ�Vت ا��Uز�ـــــT ا��Y�p�qــــ�F� TـــــRان ؟How aircraft gas turbines is classified?

5

آQVjP QR ا��ر��VRت ا��Uز�T ا��gd TY�p�qج ا��Ts ا��R��Rg�TR وا��TRr؟How can land base gas turbines classified?

6

�Yه� وEK ا��vرT�e uR� Tg ا�^�اق ا��اWFa وT�e ا�^�اق ا��pرWK؟

What is the difference between Internal & external combustion engine?

7

�Yه� وEK ا��vرuR� Tg ا��ر��VRت ا��Uز�T وا��ر��VRت ا��pyر�T ؟

What is the difference between gas turbines & steam turbines?

8

zا {Fl TF|YIا Wه�Y؟WKر�pاق ا�ت ا�^�

What are most common examples of external combustion engines?

9

�vا�� EKه� و�Y؟Tدد�ا�� ur��وا�� Tز��Uت ا��VRا��ر� uR� Tgر What is the difference between gas turbines & reciprocating engines?

10

أ��p�qP uم ا��ر��VRت ا��Uز�T ا��g� TY�p�qج ا��Ts ا��R��Rg�TR؟

Where are land base gas turbines used?

11

ا��Uز�W� T ا��Rqرات؟��ذا �p�qg dم ا��ر��VRت

Why gas turbine doesn't used as car engine?

12

��ذا ��Pزا��ر��VRت ا��Uز�T ��ر��Pع أ�OHره� ؟

Why gas turbines are more expensive than reciprocating engines?

13

�VRا��ر� �VY �VjP W�Fدن ا��Oا�� g uY Tدد�ا�� ur��ا�� VjP d ذا�� V� ضO�P �gأ �Y Tز��Uت ا� TR��Oارة ا�س(ا��yّ�ا� Naاق داارة ا�^�؟) ^

Why reciprocating engines are not made from same materials that gas turbine is made although they are suffer from very high temperature just like gas turbines?

14

�vا�� QRعآ��P؟وا�ر Tز��Uا� TVRا��ر� N�l {Fl How could weather conditions affect gas turbines?

15


4

Tsج ا��g� TY�p�qا�� Tز��Uا� TVRان وا��ر�R�F� TY�p�qا�� Tز��Uا� TVRا��ر� uR� ت��aأه� ا� Wه�Y ا��TRr؟

What is the main deference between land base gas turbines & gas turbine used in aircrafts?

16

�ح ��gم �a�Y ا��اء �W ا��ر��VRت ا��Uز�T؟Explain air intake filter house in details?

17

�Y ه� ا�� و�YهW و�E��R؟What is the main purpose of a compressor?

18

dف اا�} � Naاء ا��ا�^�اق وuY �� ا�} ا��ر�TVR؟��ذا ��gج ا�} ��U ا�

Why do we need to compress air before it is enter to the combustion chamber?

19

�Y هW أ�gاع ��ا�� ا��اء �W ا��ر��VRت ا��Uز�T؟What are the main types of compressors which are used in gas turbine engines?

20

�p�qP d ؟��ذاTز��Uت ا��VRا��ر� W� Tدد�م ا��ا�� ا�� Why reciprocating compressors are not used in gas turbine engines?

21

Centrifugal Compressor ؟ - �Yه� ا�� ذو ا��د ا��آ�يWhat are the operating principals of Centrifugal Compressor?

22

Axial compressor؟ -� ا�� ا��ري �Yه

What are the operating principals of axial compressor?

23

�YهNRq� TRF�l W ا�� ؟What is compressor washing process?

24

�YهW ا��ق ا�aى ا��NRqU� TY�p�q ا�� ؟What are the alternative methods used for compressor cleaning?

25

�Yآ�ي وا�� ا��ري؟د ا��ا�� ذو ا�� uR� Tgر�vا�� EKه� و What is the difference between axial & centrifugal compressors?

26

Axial Compressor Design؟ - �ح �R�jP ا�� ا��ريExplain Axial Compressor in details?

27

R�Y Wه�Yو �R�Vط ا��a TRأه� Wه�Y؟ �Pا� What are the advantages of using blow off lines in axial compressor?

28

�YهO� W ا�|�ا�� ا��TR�R�j ا��R�jP �Vl TY�p�q ا�� ا��ريAxial Compressor؟What are the main design considerations in axial compressor?

29

Axial Compressor ؟ ت ا��اء أ��Vء TRF�l ا��U�gط Fl} ا�� ا��ري �YهR��P Wا

What are the types of air effects during compression process in axial compressor?

30


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List of questions - EـــــــــFGHIـــــــ�ول اK �Y هW ��هة إ��اب ا��اء �W ا�� ا��ري Axial Compressor؟

What is the definition of compressor surge? 31

Axial Compressor ا�� ا��ري W� اء� �Y هW أ�yHب إ��اب ا�What are the main reasons of compressor surge?

32

آ�FU�g QR ��ق ا��Fl TR�R�j} إ��اب ا��اء �W ا�� ا��ري Axial Compressor ؟

How can compressor surge be avoided by improving compressor design?

33

�Y هW وT��s إ��اب ا��اء �W ا�� ا��ري Compressor Surge Protection؟What is compressor surge protection?

34

�YهyY Wـــــ�دئ ا�^ـــــــ�اق؟What are the main principals for combustion?

35

�YهF��Y Wــــ�yت ا�^�اق ا�¤�R ؟What is the requirement for a good combustion?

36

�YهW ا��VO¦ ا��y� Tء ا�^�اق؟What are the important factors for combustion to start?

37

�YهW أ�gاع �ـــف ا�^�اق ا��W� TY�p�q ا��ر�TVR ا��Uز�T ؟What are the main types of combustion chamber which are used in gas turbines?

38

�YهW أ�Kاء ��ـــT ا�^ـ�اق؟What are the main parts of combustion chamber?

39

�اء وا��sد أ��Vء TRF�l ا�^�اق ؟F� �R¤ط ا��aا� TRأه� Wه�Y What is the importance of good mixing between fuel & air during combustion

process?

40

�YهO� W ا��vVط ا��TRF�l W� T ا�^�اق ؟What are the important points to be considered in a combustion process?

41

�YهW أه� ا��OاNY ا��P W�F Fl} ا�^�اق ؟What are the factors that affect combustion process?

42

�YهW ا�I��ل ا��TFO§F� T�F�p أ��Vء ا�^�اق؟What are the different configurations of the flame during combustion process?

43

�Yه� ا��ق �TFO� uR ا��sد ا��Fpط Premix Flame و�TFO ا��sد ا��Oد�diffusion Flame - T؟ What is the difference between Premix flame & diffusion flame?

44

Hybrid Burner؟ uR¤-�Yه�ا�§�N ا��Oم ��Fـّاق ا� What is the general configuration of the hybrid burner?

45

Flame Humming و��ذا ��Rs �Vس E��Rs؟ TــFO§ا� W� Nj�� ي�Fا� uRVه� ا��Y-

What is flame humming & why it is important to measure it?

46

�YهY Wـــا^N ا��اء أ��Vء ا�^ــــ�اق؟What are the stages of the air during combustion?

47


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List of questions - EـــــــــFGHIـــــــ�ول اK NOx emission؟ ��ر��Y TVRهW ¬ق NRFvP إ�Oygث أآ��RH ا��RVوuRK ا�uY T¤P�V �ف ا�^�اق �W ا�

What are the various methods used to educe NOx emission form gas turbines?

48

SOx emission؟ TVRا��ر� W� اقف ا�^�� uY T¤P�Vا� ��y�ا� �RHث أآ��Oygإ NRFvP ق¬ Wه�Y- What are the various methods used to reduce SOx emission from gas turbines?

49

�ًY��l ت�VRا��ر� QVjP QRآ

How can turbines in general are classified?

50

أي �gع uY ا��ر��VRت ��r ا�p�HIام أآ| ا��ر�TVR ا��ر�Axial T أوا��آ��Radial T؟

Which types of turbines is most common radial or axial turbine?

51

Reaction turbine ؟ TVR رد ا��NO و�Pر� Impulse turbine ــ�aا�� TVRر��P ت�RH�Hأ Wه�Y What are the main principals of impulse &reaction turbines?

52

�YهO� W ا�|�ا�� ا��TR�R�j ا��R�jP �Vl TY�p�q ا��ر�TVR ؟

What are the main considerations that used in turbine design?

53

�Yه� وEK ا��vر�P uR� Tgر�TVR ا��Impulse turbine �a و�Pر�TVR رد ا��Reaction Turbine NO؟What is the main difference between impulse & reaction turbines?

54

�YهW ا�I��ل ا��T�F�p ��ر�TVR ا��aــ� ؟What are the different configurations of impulse turbine?

55

g ؟أيTز��Uا� TVRا��ر� W� م�p�q� ت�VRا��ر� uY ع� Which type of turbines is used in gas turbines?

56

�ــح �R�jP ا��ر�VRــT ا��Uز�ــT؟Explain gas turbine design?

57

�YهW ¬ق yP�� ا��® ا��آT وا�|��ـ��F� Tر�VRـT؟

What are the methods used to cool turbine fixed & moving blades?

58

�اء وا��y�� ء؟�� TVRر�® ا��ر� ��yP uR� Tgر�vا�� EKه� و�Y

What is the main deference between air cooled blades & water cooled blades?

59

آ�! ��س آ��ءة ��م ا�� ا��م �� ا��ر�� ا��ز��؟How blade cooling effectiveness is measured?

60

�Yه� OP�Q ا��O�T وا��¯آــF� N�® ا�|��T وا��آW� T ا��ر�TVR ا��Uز�T؟What is the definition of Corrosion & Erosion for gas turbine blades?

61

�د �W ا��ر�TVR؟Kإ {FlI ضO�� ي�Fا� ��Oه� ا��Y

Which part in gas turbine is suffered from the highest thermal stress?

62

�YهW أ�yHب ا��O�T وا��¯آــF� N�® ا�|��T وا��آW� T ا��ر�TVR ا��Uز�T؟What are the main causes of Erosion & Corrosion on turbine blades?

63

�YهW ا��Fل ��NRFv ا��¯آN و^��T ر�® ا��ر�EVY TVR؟What are the methods used to reduce Corrosion & protect turbine blades?

64


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�دات ا��R��Rg�TR ا�O�P W�Fض �� ا��® ا��آW� T ا��ر�TVR ؟KIاع ا�gأ Wه �Y What are the types of loads that exerted on rotating turbine blades?

65

�® Fl} آ��ءة ا��ر�TVRآ�� QR Pاآ� ا�§�اW� �r ا� ؟

How does deposits formation on turbine blade affect turbine efficiency?

66

آQR �� ا��§ّ�° ا��Fي ��ث �W ا��§Fl T} آ��ءة ا��ر�TVR؟

How does the damage to turbine-blades tell upon the efficiency of the unit?

67

ذاة ¦�T�R ؟ وآP QR��ن ا�� Shaft Alignment ��Y TRF�l �Vذاة ا��O ا��وارP ذا�� -

Why shaft alignment process is important & how can we perform this process correctly?

68

��ذا �p�qPم آاWH ا��NR ذات ا��Ovة Journal Bearings دون �Rه� �W ا��ر��VRت

Tز��U؟ا� Tر��pyوا�

Why Journal bearings are used in large turbines?

69

� ا�Oy اaz ؟Y�p�q� d ��VR� د ا��وار��OF� ��م ز�� ا��g ت�VRا��ر� O� م�p�qP ذا��

Why lifting oil is used in some turbines to lift their shafts?

70

WHت آ�VRا��ر� O� W� م�p�q� ذا�� Qjg NR��P WHام آ�p�qg ��VR� �v� �^ري وا��Y NR��P �sُ��O�Y Tدة؟

Why we use only one axial bearing in turbine shaft instead of multiple bearings?

71

�Y هW ا��aت اuR� TRH�HI ا��Oد ا��وار ��Fر�TVR ا��Uز�T وا��ر�TVR ا��pyر�T؟What are the main deference between gas turbine shaft & steam turbine shaft?

72

��ذا ��ن ^¤� ا��ر�TVR ا��Uز�T أآy uY ^¤� ا��ر�TVR ا��pyر��V� T ا�pج؟Why gas turbine is larger than steam turbine for the same power output?

73

�؟�YهW ا�q�lت ا��O� TKد ا��ر�TVR و��ذا yV¤P �VRFl �¤� What is critical speed for turbine rotor & why do we have to avoid it?

74

��O� Saggingد ا��ر�TVR ؟ - �Y هW ا�yHIب ا�TRqRr ��وث ا��vس hogging - وا�ر�pPء

What are the main reasons for shaft Hogging & Sagging?

75

TRqRr ��وث ا�ه��ازات ��l Wد ا��ر�TVR؟�Y هW ا�yHIب ا�

What are the main reasons of shaft vibration in turbine

76

آQR ��ن �l {V�VYم ا��وران وV�VY} ا��ارة وV�VY} ا��W� �U ا��ر�TVR ا��Uز�T ؟

How is the torque, pressure & temperature distribution on gas turbine

77

�Y؟TVRا��ر� W� Tآ® ا��ا� uY ةRaIا TF^ا�� W� T¤P�Vا�ه��ازات ا� NRFv�� م�p�qا�� Nه� ا��

What are the methods used to reduce vibrations at last stage of turbine?

78


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Tز��Uا� TVRا��ر� uY |أآ Tر��pyا� TVRا��ر� N^اY د�l ،ذا ؟��

Why the number of steam turbine stages is larger than gas turbines stages?

79

�YهW أه�TR ا�دارة ا��O� TGR�yد ا��ر�TVR ؟

What is the importance of turning gear operation for turbine rotor?

80

�ز ��ء ا�دارة¤� Tز��Uت ا��VRج ا��ر��P ؟��ذا

Why are gas turbines needs start up unit?

81

�ة �ـ�ء ا�دارة ��Fر��VRت ا��Uز�T ا��W� TY�p�q ا��RراتKاع أ�gأ ؟ �YهW أ�

What are the most common starters which are used in aircraft gas turbine engines

82

�ة ��ء ا�دارة ��Fر��VRت ا��Uز�T ا��g� TY�p�qج ا��Ts ا�Kاع أ�gأ Wه�YTRr��؟ �

What are the most common starters which are used land base gas turbines?

83

ــــT اRH�HIــــــW ا��Rــ�YهKI Tــــ�؟ـــ�ة ا��

What is the main purpose of control system?

84

Tlqاآ� ا�� TRqRrاع ا��gIا Wه�Y/�VRا��ر� W� TY�p�qا�� N؟ا��Tر��pyت ا�

What are the main types of speed/load controller that used in steam turbines?

85

Wه�YNآ� ا�� TRqRrاع ا��gIا/ Tlq؟ا�

What are the main types of speed/load controllers?

86

�R�¤� E ا��ر��VRت ��§�Y Tlqا� �¬�yP Tyqg ن��P أن N�ّ�� ذا�� F�aإ ��Y وا^�ة T�y§� TFjا�� P�OH؟

Why it is preferred to make speed droop setting same for all turbines which are connected to the same network?

87

�YهW أ�gاع ا��اآ� ا��W� TY�p�q ا��ر�TVR ا��Uز�T؟

What are the types of governors which are used in gas turbine?

88

Tز��Uا� TVRا��ر� W� Nز��دة ا�� TRF�l ن��P QR؟آ

Describe the process of increasing gas turbine load?

89

TyqV� ح��Y TVRا��ر� �� Tآ® ا�� أّن ا� uY ��ا� {Fl Tز��Uا��^�ة ا� N�^ ز��دة �R��qg Nه ؟100%

Could we increase the gas turbine load even if compressor inlet guide vanes are fully open?

90

��a uY Tز��Uا� TVRا��ر� ــ�l ��vP �� W�Fط ا��vVا� O� Wه�Y؟

What are some of the factors that may determine the service life of gas turbine components?

91


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TY�p�qا�� Tv�ا�� Wه�YTز��Uا� TVRا��ر� �l ب�q�� ؟

What is the method used to calculate gas turbine service life?

92

-Nا�� {Fl TVRا�} �� ا��ر� Naاء ا��ا�؟ �Yه� R��P درTK ^ارة ا�

What is the effect of compressor inlet temperature on gas turbine output power?

93

a Wه�Y ؟Tز�ــ�Uا� TــVRا��ر� NRU§P ات��

What is the start up sequence of land base gas turbine?

94

TRr�� ؟�YهW أه� ا��sت �W ا��ر��VRت ا��Uز�T ا��g� TY�p�qج ا��Ts ا��

What are the most important protections used in land base gas turbines?

95

vا�� Wه�Y W� ؟�د Tز��Uا� TVRا��ر�

What are the losses in gas turbine?

96

Tز��Uا� TVRا��ر� W� ءة��ق ر�� ا�¬ Wه�Y؟

What are the methods used to improve land base gas turbine efficiency?

97

Axial Compressor؟ �F� T��ّO� Rء�� WF^ا�� yا�� Tv�¬ ن��P ا�� ر ي ��ذا ��

Why compressor intercooling is not wildly used in axial compressors?

98

�Yه�R�Y Wات و�Rlب ا��ق ا��T�F�p ا��y�� TY�p�q�� ا��اء ا��اNa ا�} ا��؟

What are the main advantages & disadvantages of cooling systems which are used for compressor inlet cooling?

99

jP QRـــّآrا��وا QVآــــا��§� ؟ـــT

How combined cycles are classified?

100

�YهW ا�gIاع ا��T��U� T�F�p إ�H�Kع ا��اررة ا��W� TY�p�q ا��ت ا��§�آT؟

What are the main Configurations of heat recovery steam generator?

101


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GAS TURBINE GENERAL NOTESGAS TURBINE GENERAL NOTESGAS TURBINE GENERAL NOTESGAS TURBINE GENERAL NOTES

Tز��Uت ا��VRا��ر� ul TY�l °ــ�yg

MS6001B-G.E.


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�YهW ا��ر�TVR ا��Uز�T وآN�OP QR؟-11-What is the operating principal of gas turbine?

Gas turbine is an internal combustion engine, it is designed to accelerate a stream of gas, which is used

to produce a reactive thrust to propel an object or to produce mechanical power to turn a load, the principal of

operation of the gas turbine can be explained by the following examples:

*-Example (1):

Figure (1)1500AD-Old Style Gas Turbine for BARB-Q not for Power generation!

(The sketch is drawn by Leonardo de Vinci)

Cold air is enter from the hole at bottom of the oven, as its mix with the hot gases that released from the

combustion its temperature will increase & hence its density will drop, then it will move up word & another

cold air will replace hot air with continues action, due to the movement of hot air to the top, it will create a

natural draft that pass through a series of blades that turned the roasting spit so provide power to the attached

mechanism.

*-Example (2):

Figure (2.A) shows a cylinder cross section with a fan on each end, now if the left hand fan is started

via an limited speed electric motor, it will draw air inside the cylinder which will cause the right hand fan to


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rotate at the same speed of the other fan (if we neglect air pressure losses yet velocity losses inside the

cylinder). If we drill a hole in the cylinder surface between both fans & we ignite a continues flame Figure

(2.B), the temperature of the air that passes through the flame will increase & also its specific volume, this will

cause the right hand fan to rotate even faster than the left hand fan (because the air occupied a larger area than

before after being heated since its specific volume increased & hence its volumetric flow rate will increase).

Now, if we disconnect the electric motor that rotates the left hand fan & we connect the left hand fan with right

hand fan by a shaft & we insure a continuous flam Figure (2.C), the right hand fan will produce a mechanical

power that is sufficient to rotate the left hand fan & another applied load.

Figure (2) Simplified gas turbine

Now the idea of gas turbine is clear:

1- The left hand fan represents the COMPRESSOR

2- The right hand fan represents the TURBINE

3- The flame represents the COMBUSTION CHAMBER

4- The electric motor represents the START UP UNIT of the gas turbine.


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5- Another applied load could be an electric generator, pump, or thrust propulsion as in aircraft ….etc.

6- There is additional part of the gas turbine which is the AIR FILTER to insure clean air entrance.

Now if we look to Figure (3) we can realize real gas turbine configuration.

Figure(3) open cycle gas turbine

�YهY Wا^��P Nر ا��ر�TVR ا��Uز�T ؟ -2 2- Gas turbine history & stages of development?

a- First successful design for a gas turbine is done by a lot of pioneers at the same time, one of them is Sir Frank

Whittle (England); he make painting for first gas turbine on 1930 but similar patent record in Germany & Italy

on the same year. Whittle developed a working gas turbine engine in April 1937 which was used to drive the

first successful turbojet airplane in Britain; His early work on the theory of gas propulsion was based on the

contributions of most of the earlier pioneers of this field.

b-After the Second World War, the jet engine became the most popular

method of powering aero planes and consequently the gas turbine rapidly

developed to generate electric power.

c-The reason why the gas turbine appeared so much later than other types of

internal combustion engines was because of the difficulty of finding materials

for the working parts, especially the turbine blades, as they would have to

with stand extremely high temperatures of the burning gas without melting or

weakening.

Figure(4) Sir Frank Whittle


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*-The following table summarizes the history of the gas turbines:

Table(1) History of gas turbine development


15

Yــ�هW أgـــ�اع deت ا�^ــــ�ــــاق ا�ـــ�اWFa ؟-3

3-What are the main types of internal combustion engine?

Most popular internal combustion engines:

1-Reiprocating engines

There are two ways in which reciprocating engines classified which are:

a-spark ignition engines (that burn kerosene)

b-compression ignition engines (that burn diesel)

other way of reciprocating engines classification is:

a-Two stroke engines

Figure(5) 4-stroke Reciprocating Engine


16

Figure(6) 2-Stroke Reciprocating Engine

b- Four stroke engines

Figure(7) 4-stroke Reciprocating Engine

2-Rotary Pistons Engine(Wankel Engine)

In wankel engine, the piston has triangular shape & it produce rotating motion rather than reciprocal motion as

in reciprocating engines. Main advantages of Wankel engine are its extremely lower weight compare to its

power output & its low noise & vibration level. Its main disadvantages is higher fuel consumption & higher

pollution level compare to reciprocating engines.


17

Figure(8) Wankel Engine

• Typically, it is more difficult (but not impossible) to make a rotary engine meet U.S. emissions regulations.

• The manufacturing costs can be higher, mostly because the number of these engines produced is not as high as the number of piston engines.

• They typically consume more fuel than a piston engine because the thermodynamic efficiency of the engine is reduced by the long combustion-chamber shape and low compression ratio.

3-Gas turbines


18

؟ T��Y��l آــــــQVjP QR ا�ــــ��ر��VRت ا�Uـــــــ�ز-4

4-How can gas turbine is classified?

Gas turbines can be classified as:

a- Gas turbine that produce mechanical power to drive a load (land base).

b- Gas turbine that produces thrust (propulsion) which is used to move an air planes.

c- Open cycle or closed cycle or combined cycle.

آQVjP QR ا��ر�Rـــــ�Vت ا��Uز�ـــــT ا��Y�p�qــــ�F� TـــــRان ؟-5

5-How can aircraft gas turbine is classified?

Figure (9) Turbojet Engine

Most common gas turbines that used in turbojet aero plane are:

1-Turbojet Engine:

The original concept, the turbojet, is the simplest form of gas turbine and relies on the high velocity hot gas

exhaust to provide the thrust. Its disadvantages today are its relatively high noise levels and fuel consumption.

Figure (10) Turbojet Engine


19

2- Turbofan Engine:

A turbo fan engine is based on the principal that for the same power, a larger volume of slower moving air will

produce more thrust than a small volume of fast moving air. Turbofan engine is the most widely used in aircraft

propulsion.

There are two main types of Turbofan engines:

First type: Low bypass turbofan Engines.

Figure(11) Low bypass turbofan Engine Figure(12) High-bypass turbofan engine

a-In the turbofan or ‘bypass’ engine the partly compressed airflow is divided, some into a central part - the gas

generator or core - and some into a surrounding casing - the bypass duct.

b-The gas generator acts like a turbojet whilst the larger mass of bypass air is accelerated relatively slowly

down the duct to provide ‘cold stream’ thrust. The cold and hot streams mix to give better propulsive efficiency,

lower noise levels, and improved fuel consumption.

Second type: High-bypass turbofan engines.

a-In the high bypass ratio turbofan, as much as seven or eight times as much air bypasses the core as passes

through it. It achieves around 75% of its thrust from the bypass air and is ideal for subsonic transport aircraft.

b-A low bypass ratio turbofan, where the air is divided approximately equally between the gas generator and the

bypass duct, is well suited to high-speed military usage.

3- Turboprop Engine:

As its name implies, a turboprop uses a propeller to transmit the power it produces. The propeller is driven

through a reduction gear by a shaft from a power turbine, using the gas energy which would provide the thrust

in a turbojet. Turboprop engines are generally used on small or slow subsonic aircraft.


20

Figure(13) Turboprop Engine

Figure(14) Turboprop & Turbofan Engines comparison

4- Ramjet Engine:

Figure(15) Ramjet Engine


21

A ramjet, is a type of jet engine. It contains no (major) moving parts and can be particularly useful in

applications requiring a small and simple engine for high speed use; such as missiles. In a ramjet, due to the

high flight speed, the ram compression of air is sufficient to provide the compressed air need for thrust.

4- Scramjet Engine:

A scramjet (supersonic combustion ramjet) is a variation of a ramjet where the flow of the air and

combustion of the fuel air mixture through the engine happen at supersonic speeds. This allows the scramjet to

achieve greater speeds than a conventional ramjet which slows the incoming air to subsonic speeds before

entering the combustion chamber.

Figure(16) Scramjet Engine

5-Pulse jet engine:

A pulse jet engine is an engine where its combustion occurs in pulses and the propulsive effort is a jet.

A typical pulsejet comprises an air intake fitted with a one-way valve, a combustion chamber, and an exhaust

pipe.

Figure(17) Pulse jet schematic. First part of the cycle: air intake (1), mixed with fuel (2). Second part: the

valve (3) is closed and the ignited fuel-air mix (4) propels the craft.


22

Fig (18) Mach number for various aircraft engines

آQVjP QR ا��ر��VRت ا��Uز�T ا��gd TY�p�qج ا��Ts ا��R��Rg�TR وا��TRr؟-6

6-How can land base gas turbines classified?

a-Open cycle gas turbines:

1-Single shaft gas turbine

It's the simplest form of land base gas turbines where compressor & turbine are connected via the same shaft yet

they have the same speed of rotation.

Figure(19) Land Base – G.E. Gas turbine


23

2-Twin spool gas turbine

More complex configuration of gas turbine, in this engine there are two concentric shafts the first shaft

is low pressure shaft & the other is high pressure shaft & both shafts are rotating with different speeds, the main

advantages of this configuration is that the star up torque required to turn the machine is minimized compare to

single shaft with the same load since only high pressure shaft needed to be turned, also compressor surge is

minimized in this configuration, also its is shorter smaller & lighter than single shaft engine & has less number

of blow off lines ,the main disadvantage of this configuration is additional complexity to the design & added

cost.

Figure(20) Twin spool - Gas turbine


24

b-Gas generator & power turbine:

In this configuration, the gas turbine is used as GAS GENERATOR, the gas turbine provide stream of

hot gases which turns the power turbine on the left & the power turbine turns the load.

Figure(21) Gas generator with power turbine configuration

c-Combined cycle gas turbines:

1- Single shaft combined cycle (Steam & gas turbines are on the same shaft via synchro self shifting clutch.

Figure(22) Single shaft combined cycle


25

2-Two shaft combined cycle

Figure(23) Two shaft combined cycle

d-Closed cycle gas turbines:

Closed cycle gas turbines are not so common like open cycles, on these engines the working fluid that is exit

from turbine is goes through heat rejection process & recycled a gain as input for compressor, examples of

working fluid used in this cycles are hydrogen, helium.

Fig (24) Closed gas turbine cycle

�Yه� وEK ا��vرT�e uR� Tg ا�^�اق ا��اWFa وT�e ا�^�اق ا��pرWK؟ -7

7-What is the difference between Internal & external combustion engine?


26

WKر�pاق ا�ا�^� T�e

External Combustion Engine

WFaاق ا��اا�^� T�e

Internal Combustion Engine

1 Heat addition take place outside the engine Heat addition take place inside the engine

2 Ability to burn any fuel Liquid or gaseous fuel are required

3 Complete combustion is insured Cannot utilize all of fuel energy

4 Less pollution since complete combustion More pollution since incomplete combustion

5 Mostly closed cycle (better to fix & control

the properties of the working fluid)

Mostly open cycle

6 Lower heat rate ( more efficient) Higher heat rate (less efficient)

8- Tر��pyت ا��VRوا��ر� Tز��Uت ا��VRا��ر� uR� Tgر�vا�� EKه� و�Y؟

8-What is the difference between gas turbines & steam turbines?

Figure(25) Installation cost of Figure(26) Requirements for water in

gas turbine, steam turbine various power station

& combined cycle stations


27

Tر��pyت ا��VRا��ر�

Steam Turbines

Tز��Uت ا��VRا��ر�

Gas Turbines

1 External combustion engine Internal combustion engine

2 More complex & required more auxiliaries Simple & has much less auxiliaries

3 Start up time is long Startup time is much less

4 Higher efficiency (less heat rate) Lower efficiency (larger heat rate)

5 Installation cost is very expensive Installation cost is cheap in comparison

6 Required large area (more civil work) Can be build any where & less civil work

7 Cannot be portable Portable gas turbine is available

8 Strongly depend on water (cannot build far away

from large water source)

Some configurations does not use water

at all

9 Weather condition has small effect on unit

performance (condenser vacuum in winter)

Strongly affected by weather condition

10 Required long time for installation Shorter installation time

11 Lower noise level Higher noise level

12 Steam turbines are not as flexible as gas turbines (additional cycles cannot be added).

More flexible & has different configurations

13 Long life if good maintenance is applied Shorter life

14 Much larger capacity per unit up to 1800 MW single unit

Smaller in capacity up to 340 MW open cycle

15 Lower operating cost since lower heat rate Higher operating cost since higher heat rate

16 Lower operating temperature Higher operating temperature

17 Can utilize any fuel Mostly depend on natural gas or diesel

18 Load changing is slow in comparison Load changing is very fast

Figure(27)Compare the efficiency of various cycles

9- WKر�pاق ا�ت ا�^�zا {Fl TF|YIا Wه�Y؟

9-What are the examples of external combustion engines?


28

Most famous example of external combustion engine is:

1-steam turbine

2-Stirling engine

�Y-10ه� وEK ا��vرuR� Tg ا��ر��VRت ا��Uز�T وا��ur ا��دّد�T؟

10-What is the difference between gas turbines & reciprocating engines?

��ur ا��دد�Tا�

Reciprocating engines


Gas Turbines

1 Larger size & weight Much smaller in size & weight

2 Higher efficiency for medium range

Only (1-10 MW)

Lower efficiency in medium range but higher

efficiency for range of power >10 MW

3 The engine put in operation very fast Startup time is longer

4 Not affected by weather condition Extremely affected by weather condition

5 Cheap in comparison Very expensive

6 Required reinforced foundation to counter

unbalance force produced from reciprocating

motion

Lower vibration energy because of its direct

rotary motion

7 Produce higher vibration level & noise More smooth (lower vibration level & noise)

8 Practical for low speed - high torque

applications (cannot used in high speed)

preferred for high speed - low torque

applications

9 Lower fuel consumption Higher fuel consumption

10 Useful in application which need higher

power to heat ratio

Useful in application which need lower power

to heat ratio

11 Supplied fuel pressure is lower Supplied fuel pressure is higher

12 Ability to burn even heavy fuels Gas turbines firing heavy fuels is uncommon

13 Fuel consumption is proportional to the power

output

Consume more fuel when they are idling

(compressor work)

14 Can be operated with variable load but with

good fuel consumption

Better fuel consumption in a constant load

rather than a fluctuating load

15 Required higher maintenance cost

(more moving parts)

Required lower maintenance cost

16 Limited power output (up to 15 MW) Much higher power output

(up to 258 MW as land base)


29

��ur ا��دد�Tا�

Reciprocating engines


Gas Turbines

17 Engine exhaust temperature is relatively low

& hence additional firing is required to

produce higher quality steam

Higher turbine exhaust temperature can be

utilizes to produce higher quality steam

18 In reciprocating engine, all 4-processes

(intake-compression-power-exhaust) are

occur in one section (the piston)

Each process has a separate section

19 Igniters are needed at all time of operation Igniter used only one time during speed up

Fig(28-a) Compare between internal combustion engines

أ��p�qP uم ا��ر��VRت ا��Uز�T ا��g� TY�p�qج ا��Ts ا��R��Rg�TR؟-11

11-Where are land base gas turbines used?

Gas turbine is used as prime mover in powers stations, marine propulsion, Helicopters & Tanks.

*-Gas turbines are used for electric power generation in several different ways: 1-used during peak load time 2- Provide stand-by power 3-to provide a power source for black starts 4-to act as base load generating units (Recently only due to the improvement on their design which result in

higher efficiency & also when they are used in combined cycles).


30

��ذا �p�qg dم ا��ر��VRت ا��Uز�W� T ا��Rqرات؟ -12

12-Why gas turbine doesn't used as car engine?

Gas turbine is not used in cars because:

1-They are very expensive.

2-The gas turbine consume a lot of fuel if idling because of added compressor work.

3-Gas turbine are not suitable for variable load application, if the gas turbine is running with 60% of its load, it

will consume around 80% of fuel that used in full load.

4-Start up time for gas turbine is larger that start up time of reciprocating engines.

؟��ur ا��دد��vY �TرTg � ��ذا ��Pزا��ر��VRت ا��Uز�T ��ر��Pع أ�OHره�-13

13-Why gas turbines are more expensive than reciprocating engines?

1- Gas turbine are manufactured by forming process which is much expensive than machining.

2-Gas turbines are subjected to very high temperature, so they are made from nickel & cobalt alloy which are

much expensive than steel.

� O�Pض ��V ا��ارة -14gأ �Y Tز��Uت ا��VRا��ر� �VY �VjP W�Fدن ا��Oا�� g uY Tدد�ا�� ur��ا�� VjP d ذا��

TR��Oاق دا(ا�ارة ا�^�^yّ�ا� Na؟ )�س

14-Why reciprocating engines are not made from the same materials that gas turbine is made

although they are suffer from very high temperature just like gas turbines

a-Because the way that the reciprocating engine operates provide better cooling, when fuel air mixture is enter

the hot pistons after the exhaust stroke, they will cool down the piston since they have much lower temperature

than the piston & engine block although combustion process is complete & all air drawn into the piston is

completely utilized (yet highest temperature form fuel is achieved).

b-Also, the piston & engine block are subjected to heat at small intervals (pulse heating) due to engine

excursive strokes (Intake ,Compression ,Power ,Exhaust).Furthermore, reciprocating engines are cooled by air ,

water & lubricated by oil (relatively cold) which improve overall cooling process & make the average

temperature of the engine around 440ºC. While in gas turbines ,the turbine are subjected to very high

temperature through entire period of operation & cooling techniques use to cool down turbine blades are


31

depend on air only since water cooled blades design are much expensive & additional cost must be considered

(convection heat transfer coefficient for liquids is much larger than it for gases).

N�l {Fl ا��ر�TVR ا��Uز�T ؟ آQR ��ا��v وا�ر��Pع-15

15-How could weather conditions affect gas turbines?

Ideal gas equation of state:

P = ρ*R*T

P= Gas pressure in (KPa) ; T= Gas temperature in ( Kelvin = ºC + 273 ) ; R=Gas constant (KJ/KgK) ;

ρ=Gas density(Kg/m3)

Gas turbine is open cycle, it uses the ambient air as a working fluid, but it is strongly affected by ambient

conditions which are:

1-Ambinet temperature:

*-Ambient temperature is representing compressor inlet temperature for the gas turbine, if the temperature

drops, the air density will increase & hence heaver air will be compressed by the compressor which will

increase mass flow rate, note that compressor work requirements will increase also.

*-As heavy compressed air enter turbine section, it will create extra expansion & more work from turbine will

produced, now to put general statement we can say:

As compressor inlet temperature drop, air density increase, turbine output power will increase but compressor

work will increase, also fuel mass flow to the turbine will increase to handle the increase in air mass flow &

extra turbine work.

Fig(28) Effect of ambient temperature on gas turbine performance


32

2-Ambient pressure:

As ambient pressure increase, air density will increase & the same result in the above point will follows.

3-Relative humidity:

Most people who haven't studied physics or chemistry find it hard to believe that humid air is lighter, or less

dense, than dry air, how can the air become lighter if we add water vapor to it?

*-To see why humid air is less dense than dry air, we need to turn to one of the laws of nature the Italian

physicist Amadeo Avogadro discovered in the early 1800s. He found that a fixed volume of gas, say one cubic

meter, at the same temperature and pressure, would always have the same number of molecules no matter what

gas is in the container.

*-Imagine a cubic meter of perfectly dry air. It contains about 78% nitrogen molecules, which each have a

molecular weight of 28 (2 atoms with atomic weight 14). Another 21% of the air is oxygen, with each molecule

having a molecular weight of 32 (2 atoms with atomic weight 16). The final one percent is a mixture of other

gases, which we would not worry about.

*-Molecules are free to move in and out of our cubic meter of air. What Avogadro discovered leads us to

conclude that if we added water vapor molecules to our cubic meter of air, some of the nitrogen and oxygen

molecules would leave .Remember that the total number of molecules in our cubic meter of air stays the same.

*-The water molecules, which replace nitrogen or oxygen, have a molecular weight of 18.(One oxygen atom

with atomic weight of 16, and two hydrogen atoms each with atomic weight of 1). This is lighter than both

nitrogen and oxygen. In other words, replacing nitrogen and oxygen with water vapor decreases the weight of

the air in the cubic meter; that is, it's density decreases.

* You might say, "I know water's heavier than air." True, liquid water is heavier, or denser, than air. But, the

water that makes the air humid isn't liquid. It's water vapor, which is a gas that is lighter than nitrogen or

oxygen.

4-air density:

*-As air density increases, compressor mass flow will increases & same concept in the first point will follows.

*-The air's density depends on its temperature, its pressure and how much water vapor is in the air.


33

Effect of air density on racing car:

*-More dense, or "heavier" air will slow down objects moving through it more because the object has to, in

effect, move aside more or heavier molecules Such air resistance is called "drag," which increases with air

density.

*- Cool, dense air slows a race car because drag force increases, but some race cars gain from dense air. Cars

designed from the wheels up for racing are really like upside down airplane wings that the air pushes down on

the track, increasing their grip going around curves. Denser air pushes them down harder.

Effect of air density on Aircraft engines:

*- Lower air density effect aircraft engine in three ways: The lifting force on an airplane's wings or helicopter's

rotor decreases(1), the power produced by the engine decreases(2), and the thrust of a propeller, rotor or jet

engine decreases(3).These performance losses more than offset of reduced drag on the aircraft in less dense air.

*- Pilots use charts or calculators to find out how temperature and air pressure at a particular time and place will

affect the air's density and therefore aircraft performance. In general, these calculations don't take humidity into

account since its affects are so much less than the others.

*-When the air's density is low, airplanes need longer runways to take off and land and they don't climb as

quickly as when the air's density is high.

5-Elevation:

Each 100 meter increase in altitude, 1% of gas turbine power will drop since as elevation increase, air density

drops.

16- VRان وا��ر�R�F� TY�p�qا�� Tز��Uا� TVRا��ر� uR� ت��aأه� ا� Wه�YTTRr��؟ ا��Uز�T ا��g� TY�p�qج ا��Ts ا��

16-What is the main deference between land base gas turbines & gas turbine used in aircrafts?

Refer to the table in the next pages.


34

�Pر�TVR ��ز�R�F� Tان

GT for Aircraft

TRr�� Pر�TVR ��ز��gd Tج ا��Ts ا��

GT for power generation

1 Must have aerodynamic shape to reduce drag Can have any shape

2 No air filtration (to avoid blockage) Air filtration is required

3 Use only can type combustion chamber Flexible for any type

4 Must be designed to withstand high vibration

level

Casing & frame are will fixed to the ground

5 Weight & size is very important in design Weight & size is not important

6 Cannot burn any fuel (liquid fuel only) Can burn natural gas or fuel oil

7 Turbine is designed to handle fan &

compressor work only where part of energy is

accelerated in nozzle to provide thrust

Turbine is design to handle Compressor work

& extra mechanical power to the load(shaft

power, electric power)

8 The aim is to produce thrust The aim is to produce mechanical power

9 Turbine & compressor size is much smaller Turbine & compressor size is larger

10 cycle modification cannot be added (weight) Any cycle modification can be added


35

Rolls Royce Gas turbine used in jet aircraft


36

GAS TURBINE AIR INTAKE SYSTEMGAS TURBINE AIR INTAKE SYSTEMGAS TURBINE AIR INTAKE SYSTEMGAS TURBINE AIR INTAKE SYSTEM

Tز��Uا� TVRر��F� ـ�اء ��gم �a�Y ا�

M6001B-G.E.


37

17- Tز��Uت ا��VRا��ر� W� اء�؟�ح ��gم �a�Y ا�

17-Explain air intake filter house in details?

Air Intake system in gas turbines:

Gas turbines consume large mass of air (a 125 MW machine has compressor inlet flow of 438 kilograms

of air per second for 50ºC ambient temperature), thus careful design of the intake system is needed to ensure

that frictional losses are a minimum, and that the noise of the air entering the machine is kept to an acceptable

limit.

Figure (29) Side view of medium side land base gas turbine (SIEMENS-V94.2)

Figure (30) Air intake filter house from inside showing air filter elements before & after installation

& the hole behind each filter is for filtered air exit)


38

Air intake main parts:

a- Air intake filter house

Filter house normally designed to have large shape so to make sure that the pressure drop across it will

minimized (each 10 mbar pressure drop will reduce turbine power by 1%), it contains air filters, air entrance

guide vanes & the implosion doors.

b- Filter element

Air entering compressor must be filtered from any dust or residues that may enter & cause fouling to the which

reduce compressor blades efficiency, the use of series of filters in stead of one big filter is more practical

because design & erection complexity are reduced, also if pressure drop in air intake increases, a set of small

filters can easily be removed in stead of removing the hall big filter.

Figure (31) Air intake filter house

Fig(32) Compressed air lines for filters purging & pulse air outlet can be seen

Pulse air header pressure is 7.5 bar & each pulse has a pressure of 3 bar


39

c- Air intake silencer

Due to the high speed of air entering air intake filter house, a large noise level will produced & silencer must be

used to reduce noise level. The silencer contain sound absorbent baffles & these baffles are covered with

perforated sheets & filled with high quality heat & moisture resistance mineral wool, this mineral wool is

covered by a glass fiber which gives an additional mechanical protection for the absorbent material.

d- Filter element purging system

As air passes through filter elements for a long period, the filters become dirty & thus the pressure drop

across them will increase, to overcome rapid increase in pressure drop either filter elements is replaced with

new elements or air filter must be purged.

*The filter purging system is compressed air that provided from separate air compressor, if the pressure drop

across any one of the filters raw increase to more than normal limit, this compressor will start to provide

compressed air for cleaning these filters.

*-The compressed air will released via small holes on the air lines located behind each filter ,there are solenoid

valves that operate with respect to each raw of filters to release that compressed air.

*-Compressed air releasing process will done by pulsing ,so some time filters cleaning system may named as

pulse air system ,complete purging process may take 84 pulses (30 minutes duration ) & the cleaning process

will start from top of the air intake to the bottom so that we avoid dust to sucked again by upper filter raw.

Activation of pulse air system (Example from SIEMENS V94.2 Gas Turbine):

Pulse air system aim is to clean the dirty filters & to do so there are two ways to activate this system which are:

a- high pressure drop across filters raw signal

b- High ambient air relative humidity signal (humidity > 80% signal)

a- high pressure drop across filters raw signal

During gas turbine on load, the control system will monitor air intake filter house pressure drop via two

pressure sensors:


40

First sensor is to measure air pressure before & after filters raw (this sensor activates pulse air system).

Second sensor is to measure air pressure drop across air intake filter house (this sensor not activates pulse air

system & it is associated with gas turbine protection only).

Figure (33) Schematic diagram of pulse air system

If the second sensor indicate very high pressure drop, a gas turbine trip will initiated by the following steps:

1-As air intake pressure drop increases, the air pressure after silencer decreases, this will create a local vacuum

area,

2-Due to the vacuum inside air intake filter house, the implosion doors (4 to 6 doors) will be sucked in

3-There are limit switch on each door so for any door reach full open position, this mean that the limit switch

will send open signal which will initiate gas turbine trip to protect gas turbine from operating with air intake

filter house is blocked. Implosion doors are designed to make sure that the pressure inside air filter house is

equalized to the atmospheric pressure to avoid air intake damage.

* If the gas turbine on load, normally pulse air system will activated only due to pressure drop signal


41

Figure (34) Pressure sensors used in air intake filter house

b- High ambient air relative humidity signal (humidity > 80% signal)

*There is humidity sensor on air intake filter house entrance to measure ambient humidity, if humidity is raise

to 80%, a signal will go to activate pulse air system, and complete purging process may take 168 pulses (1 hour

duration), this is to insure dry filter & avoid condensation which may block the filters during gas turbine

operation.

*Normally pulse air system activated by humidity sensor only when the unit is off load, pressure drop sensor

will not sense any pressure drop because air is not entering inside filter house at high speed (no pressure

difference).


42

GAS TURBINE GAS TURBINE GAS TURBINE GAS TURBINE ----AIR COMPRESSORAIR COMPRESSORAIR COMPRESSORAIR COMPRESSOR

Tز��Uا� TVRا��ر� ��

MS6001B-G.E.


43

�Y ه� ا�� و�YهW و�E��R؟ -18

18-What is the main purpose of a compressor?

The compressor is located at the front behind the air intake. It consists of a spinning fan with a number

of fixed blades arranged in several rows. Air is drawn into the engine from its surroundings by using

compressor fans. These fans are driven from the turbine by a shaft. This air is heated by being compressed and

is led into one of several combustion chambers. The Compressor can reach typical pressures up to 40 times

higher than atmospheric pressure.

19- ��ذا ��gج ا�} ��U ا��اء ا��اNa ا�} �ف اd^�اق وuY �� ا�} ا��ر�TVR؟

19-Why do we need to compress air before it is enter to the combustion chamber?

Gas turbine efficiency will increase whenever pressure ratio increases. Refer to Fig (29).

Figure (35) Pressure ratio versus gas turbine efficiency

؟ �W ا��ر��VRت ا��Uز�Tا��Y TY�p�q هW أ�gاع ��ا�� ا��اء-20

20-What are the main types of compressors which are used in gas turbine engines?

In general compressors are classified in two main groups:

1-Positive displacement compressors (in which air pressure is increased by reducing its volume)


44

2-Dynamic compressors (in which air pressure is increased by increasing its speed)

The following table summarizes compressors classification.

Figure (36) Compressors Classification

*Most common compressors used in gas turbine are:

1- Centrifugal Compressor.

2- Axial Compressor.

Note that both of them are of dynamic type.

21-Tز��Uت ا��VRا��ر� W� Tدد�م ا��ا�� ا��p�qP d ؟ ��ذا

21-Why reciprocating compressors are not used in gas turbine engines?

Reciprocating compressors are not used in gas turbine due to:

a- They have higher vibration level due to pulsation (coming from changing rotary motion reciprocal motion to

rotary motion.

b- They produce very high pressure

c- As gas turbine size increase, the size of reciprocating compressor must be increased & due to its heavy parts

it will require larger power.

d- They provide small air flow compare to centrifugal or axial compressors.

e- They have a lot of moving parts (pistons, connecting arms, crank shaft, and intake & discharge valves).

f- Relatively inefficient (20% - 45%).


45

g- High power consumption.

h- High maintenance requirement since more moving parts are involved compared to other types of

compressors.

I -Good for service air application.

Figure (37) Reciprocating Compressor

Centrifugal Compressor؟ �Y- - 22ه� ا�� ذو ا��د ا��آ�ي

22-What are the operating principals of Centrifugal Compressor?

Figure (38) Centrifugal Compressor


46

Centrifugal Compressor is a dynamic compressor, it increases air pressure by accelerate it, the air enter

centrifugal compressor at the center of compressor impellers & thrown out by centrifugal force to compressor

discharge which is located at compressor casing arc (Direction of air flow discharge is perpendicular to the axis

of rotation). Acceleration of the air is obtained through the action of one or more rotating impellers; the

discharge air is free from pulsation.

Figure (39) Centrifugal Compressor Diffuser Figure (40) Multistage Centrifugal Compressor

Figure (41) Multistage Centrifugal Compressor

Axial compressor؟ -�Yه� ا�� ا��ري -23

23-What are the operating principals of axial compressor?

All modern high output gas turbines use axial flow compressors, the principles of operation are shown in


47

Figure (43). The air enters at the left and is speeded up by a set of revolving blades. The air leaves the first set

of revolving blades and enters a set of stationary blades, where the air is slowed down and its kinetic energy

converted to pressure energy. This process is repeated by a lot of stages depend on the desired output pressure.

(The direction of flow is parallel to the direction of the rotation).

Figure (42) Axial Compressor, the lower picture showing axial compressor of SEMENS -V94.2 gas turbine

& the first six stages are coated with Aluminum Pigment


48

Figure (43) Axial Compressor pressure & speed curves

Refer to Fig (43):

a- Moving blades accelerate air.

b- Fixed blades slow down air & hence change kinetic energy of air into pressure energy.

c- Discharge velocity should equal suction velocity.

*-The design of compressor blades are different than turbine blades, compressor blades divergent profile which

works as diffuser to increase air pressure, while turbine blades have convergent profile which is works as nozzle

since turbine is reducing air pressure by changing its pressure energy into kinetic energy. Refer to Fig (44)

Figure (44) Turbine & Compressor blades profile


49

*-Note that compressor blades are suffer from high stress but with lower temperature while combustion

chamber suffer from high temperature but with relatively lower stress.

*-In axial compressor, design of moving blades are significance to provide aerodynamic shape with minimum

losses, also blade tip clearance must be as minimum as possible to improve moving blade efficiency &avoid

blade tip leakage. Normally compressor moving blades have blade clearance of 7 mm to minimize blade tip

losses.

*-During humid weather, high humidity may occur only on the first sex stages of compressor because air is

heated so rapidly & condensate may occur. To overcome pitting damage to compressor blades, the first six

stages are coated with Aluminum pigment.

*-Air enter compressor may contain dust or dirt (even if its passes through air intake system) & such dust or

contaminations will stick into compressor blades which will affect compressor performance because:

a- It will reduce compressor stage efficiency since accumulation of dirt on the moving blade will cause change

in discharge angle of blade by 7º which will result in changing output velocity direction to the next stage &

hence reduce blade efficiency.

b- Dirt or dust when stick on compressor blades will form a hot spots, recall that compressor blades will be

heated during compressor operation due to friction coming from high rotation. Dirt or dust will generate high

temperature spots on the blade because they have different thermal conductivity than steel,(compressor blades

are made from steel),so these hot spots will produce thermal stresses on the blade which will result on blade

failure if the dirt is not removed or washed.

c- Compressor blades fouling may produce turbulence to the flow; produce vibration & increase discharge

temperature which will result in reduce blade efficiency.

*-Most of gas turbine compressors have compressor washing unit in which compressor blades are washed with

a mixture of demineralized water & special agent to remove any dirt or dust on compressor blades, washing

process can be performed either when the gas turbine is running(on-line washing) or when gas turbine is stand

by (off- line washing).


50

Figure (45) Compressor blade fouling

�Y -24هNRq� TRF�l W ا�� ؟

24-What is compressor washing process?

*-The aim of compressor cleaning process is to remove deposits from blades that have caused a decline in

output and efficiency of Gas Turbines.

*-Pollution of the ambient air cannot be completely removed by the air intake filter system.

*-compressor washing are mainly two types online & off line washing.

*-Compressor washing is carried out by using detergent solution and demineralized water for the final flushing.

Both fluids are sprayed onto the compressor blades through two types of nozzles:

a- Jett nozzles which are consisting of two jet nozzles which inject water at high speed

Jet nozzles are used for off load washing only since them inject high speed water jet which will be

harmful to the blades of compressor which are rotating at synchronizing speed-3000 rpm. The effect of

one droplet of water will become like a bullet.

b- Spray nozzles which are uniformly spaced around the circumference of compressor inlet, upstream

of the variable compressor inlet guide vanes, each producing a gentle jet of water.

*-Compressor cleaning skid is consisting from a tank & pumping unit, a centrifugal pump draws the cleaning

solution and demineralized water from portable tank and feeds it through a hose to the jet or spray nozzles. The

cleaning solution / demineralized water are delivered at a pressure of about 10 bars. Isolation valves are used to

change over from the jet nozzles to the spray nozzles and vice versa. Refer to Fig(48).


51

Figure (46) Compressor washing nozzles

Figure (47) Compressor Washing Skid

�YهW ا��ق ا�aى ا��NRqU� TY�p�q ا�� ؟ -25

25-What are the alternative methods used for compressor cleaning?

*-Alternative methods for compressor cleaning include:

a- Dissemble the compressor partially to clean the blades of the rotor, this method gives excellent result but

it required long time outage.

b- Injection of crushed walnut shells, Injection of rice & Injection of concentrated carbon.

The second method should not be used in modern gas turbines because:

a- Fire hazard.


52

b- Oil system contamination & blockage.

c- Result in blade cooling system fouling.

d- Early hot component failure.

Figure (48) Types of compressor washing nozzles

�Y -26ه� وEK ا��vرuR� Tg ا�� ذو ا��د ا��آ�ي وا�� ا��ري؟

26-What is the difference between axial & centrifugal compressors?

ا�� ا��ري

Axial Compressor

ا�� ذو ا��د ا��آ�ي

Centrifugal Compressor

1 Higher efficiency (82% - 90%) Lower efficiency (72%-82%)

2 Larger in size Smaller in size

3 Has higher isentropic efficiency Has lower isentropic efficiency

4 Longer in size Shorter in size

5 Good for medium pressure/flow application Good for low pressure / large flow application

6 Used in higher speed application

(aircraft engines)

Used in high speed application

(land base gas turbines)

7 Its performance will reduces as dirt is

contaminated on its blades surface

Not liable to loss its performance due build up

of dirt on its blades surface

8 Multistage configuration is done with no

pressure losses

As number of stages increases pressure losses

will increases

9 More expensive Less expensive


53

Figure (49) Compressors operating range

Axial Compressor Design؟ 27- -ح �R�jP ا�� ا��ري �

27-Explain Axial Compressor in details?

Axial compressor consists of:

1-Stator & Guide Blade Carrier 2-Rotor 5-Blow off Lines

3-Inlet Guide Vanes 4-Exhaust Diffuser

Figure (50) SIEMENS-V94.2 Gas Turbine Longitudinal section (Compressor section)


54

1-Stator & Guide Blade Carrier:

*-Compressor stator consists of three guide blade carrier, they are separated from each other to provide good

control in blade tip clearance, guide blade carrier position can be adjusted using eccentric bolt which provide

flexibility to guide blade carrier movement in all direction except axial direction by 3 mm.

*-There are gaps on compressor stator which provide passages to blow off air.

*-Blade tip clearance is measured by six peep holes located on compressor stator.

*-There are carbon rings fitted in segments around the shaft to protect moving blades from rubbing compressor

stator on the event of rotor misalignment.

*-Usually compressor stator is made up from steel alloys.

2-Compressor rotor:

*-The rotor is consisting of a serious of rotor disks which are joined to gather by Hirth Coupling, refer to

Fig(50) & Fig(51) .Rotor disk is holding the moving blades of the compressor.

*-Rotor disks are hollow from inside & there are central tie bolt which insure that they are hold into position,

note that there is a gap between rotor disks ( about 3 mm) & central tie bolts, this gap is to provide passages for

extracted air from compressor to cool down hot components (combustor & turbines).

*-Damper rings are used to reduce vibration of central tie bolt by supporting it with rotor disks.

*-Rotor is supported by radial & axial bearings (journal bearings).

*-Compressor rotor is made up from steel alloys & its blades generally made by machining process.

Figure (51) Compressor Rotor Disk


55

Figure (52) Hirth Coupling

3-Compressor variable inlet guide vanes (I.G.V.):

*-Most of modern gas turbine contain Variable Inlet Guide Vanes, They normally set to be open for 40% when

the unit is stand by, once the gas turbine starts they put under control to being used to provide the air necessary

for the given load & also to control turbine outlet temperature & avoid increase in temperature by increase

I.G.V. opening position to increase compressor flow to cool down turbine.

*- I.G.V. is used to control compressor flow for a given load & to control boiler inlet temperature in combined

cycle, also I.G.V. is set at 40% open during gas turbine start up to reduce compressor inlet flow which will

reduce stresses on first stage moving blade of compressor (longest moving blade in compressor) during start up.

The movement of inlet guide vane is done via electric motor which is attached to guide vane mechanism see

Fig(53).

*-As the gas turbine load increases, IGV opening position will increase until it reach 100% open & at this time

the unit is said to be under base load operation (i.e. compressor flow is maximum) ,note that additional fuel

input to the gas turbine will increase turbine inlet temperature to higher value & extra power can be supplied

but in this case the unit is said to be under Peak load operation since turbine outlet temperature is higher than in

case of base load operation due to I.G.V. cannot open more (100% already) to provide necessary cool down to

the turbine.


56

Figure (53) Compressor variable inlet guide vanes (I.G.V.)

4-Exhaust Diffuser:

*- Exhaust Diffuser is used to provide further increase in air pressure also to remove vortices from air & make it

more laminar since air direction is being changed along the entire compressor stages & hence its turbulence

increased.

*-Number of compressor stages is more than turbine stages since increasing air pressure from axial compressor

(dynamic compressor) required either increasing the size of stages or increase number of stages to produce the

desired pressure.

5-Blow off Lines:

*-Blow-Off Systems are designed to Control the Pressure / Flow Ratio, During Low Speed Running, such as

star up period.

*-Axial flow compressor contain blow off line (or bleed lines) to blow out some of the air entering the

compressors during start up to the exhaust (by pass the combustion chamber & turbine), this help to eliminate


57

compressor surge during low speed operation (start up).On each of this lines there are blow off valve normally

butterfly type & its operates by compressed air from compressor extraction.

*-Blow off lines usually placed at 30% & 60% through the compressor, For axial compressor having 10 stages,

one blow off valves are required & large axial compressor need three lines, not that compressor surge associated

only with dynamic compressors & positive displacement compressor do not need blow off valve.

Figure (54) Compressor Blow off Lines


58

� ؟-28Pا�R�Y Wه�Yو �R�Vط ا��a TRأه� Wه�Y

28-What are the advantages of using blow off lines in axial compressor?

*-Advantages of blow off lines:

1- They blow off air is used as anti icing to prevent blockage due icing in air intake filter house in cold

weather, this bleed air (warmer than outside air) is re circulated to compressor inlet again.

2- Bleed air is used as purge air for furnace in combined cycle.

3- Blow off lines Dissipate Energy in Event of Trip, Preventing Over-speed.

4-If the speed is reduced to less than under frequency limit, blow off valves will open to prevent

compressor surge.

*-Refer to Fig(54) There are two blow off lines on 30% of compressor length (stage#5) & one blow off line on

60% of compressor length (stage#10),the reason why there are two blow off line at 30% of compressor length is

because the air pressure at this stage is not high so its volume is bigger, this means that we need to blow a lot of

air out ,but in 60% length of compressor (stage#10) air is pressurized so only little amount of air must be sent

out & hence one blow off line is enough.

*-Note that:

Blow off valves of at stage #5 will closed at 38Hz (2280rpm)

Blow of valve at stage #10 will closed at 49Hz (2940 rpm)

Fig(55) Blow off lines

*-Compressor must supply two types of air:

1- Air that discharge from last stage of compressor & enter combustion chamber to being utilized for

combustion.

2- Air that is extracted from compressor at different location via hidden passages & sent to provide film cooling

for the hot component of gas turbine (combustion chamber & turbine section).


59

*-Each 1% of air extraction from compressor will reduce turbine power by 2% because extracted air is used to

cool down hot component but not as air for combustion.

�Y -29هO� W ا�|�ا�� ا��TR�R�j ا��R�jP �Vl TY�p�q ا�� ا��ري Axial Compressor؟

29-What are the main design considerations in axial compressor?

1-Back Work Ratio (B.W.R.):

It is the ratio of compressor work (Wc) to turbine work (Wt)

B.W.R.= Wc/Wt

Compressor mechanical power required to compress air is supplied by the turbine, for large gas turbines back

work ratio greater than 0.5 can be found. The gas turbine must provide additional mechanical power to drive its

compressor. Therefore, the turbine used in gas turbine is larger than those used in steam turbine for the same net

power output.

Fig (56) Back Work Ratio

2-Pressure Ratio(rp):

Pressure ratio is the compressor discharge pressure over compressor inlet pressure, for modern gas turbines this

ratio exceeds 20.

Fig (57) for a fixed value of compressor inlet &turbine inlet temperatures, an increase in pressure ratio will result in increasing turbine work to maximum then it will decrease


60

3-Hub/Tip Ratio:

This is the ratio of the diameter of the hub into which the blades are fitted (Stator) to the diameter over the tips

of the blades (the outside diameter of the whole rotor at that section).

Hub/Tip Ratio= R1/R2

Fig(58) Hub/Tip Ratio

*-Hub/tip ratio has an effect on compressor design. A low value permits a slightly smaller overall compressor

diameter, but increases the blade height.

*- At the intake end the hub/tip ratio is not normally less than about 0.5, while at the exit end of the compressor

its value is 0.9 (i.e. blade length is minimum).

4-Aspect Ratio:

The aspect ratio of the blade is given by


61

Fig(59) Terms Used in Describing Compressor Blade design

A high value of aspect ratio gives a higher efficiency of the compressor. However, the blade height is

fixed by the mass flow of air at the stage being considered, and changes in the aspect ratio can only be made by

changing the chord length, so to increase aspect ratio we have to lower chord width. The disadvantage is that

the blades are thinner and hence blade vibration problems will occur.

5-Mean Blade Diameter:

As the air passes along the length of the compressor, its specific volume decreases, and since the flow

velocity parallel to the longitudinal axis remains approximately constant (land base gas turbine have constant

speed (synchronizing speed at all load intervals), it follows that the cross-sectional area needed to reduce to

compensate decreasing in air volume. Methods to reduce area is tapering down the inside diameter of the outer

casing. Also, increasing the rotor outside diameter while holding the stator inside diameter constant.

Furthermore, these two methods can be combined by increasing the rotor diameter & reducing the diameter of

the casing.

*-Note that axial flow compressor is design to have constant flow speed if its shaft speed is constant from no-

load to full load. However, this is not the case in gas generator & power turbine configuration.

*-the speed of two spools (HP & LP shafts) are mechanically independent but a strong aerodynamic coupling

exists.


62

Fig(60) Methods of Decreasing Compressor Cross-sectional Area to

Compensate for Decrease in Specific Volume of Air as Pressure Increases Along

Length of Compressor

Hint: The above notes are simplification about compressor design; major compressor design will be determined

by a lot of complex factors.

*-Refer to Fig(60) which shows three types of reducing compressor cross-sectional area. In (a) the mean

diameter decreases as the air moves through the compressor. In (b) the mean diameter increases and in (c) the

mean diameter remains constant. Generally the effects of blades mean diameter are that:

(a) Can generate very high pressure ratios (b) limited to pressure ratios of about 14(c) Offers a useful solution

since it can handle pressure ratios up to about 24.

6-Compresosr blade twist:

Compressor blade must be twisted in order to maintain same blade velocity vector (blade speed is

maximum at tip & minimum at root), the velocity vector will be different at each radius of the blades &


63

hence the angles of the blade necessary to meet the air stream correctly will vary at each radius of the blade

which will represent poor design to the blade, so compressor blades must be twisted to obtain correct angle for

all blade radii. you can see clearly blade twist on Fig(61)

Fig(61)Compressor blade twist

*-Note that compressor blade twist decrease as we move along compressor length since at these stages

compressor blade length is decreasing so blade twisting is reduced.

*-Compressor blade airfoil is vary in shape depend on air speed inside compressor, refer to Fig(63).

Axial Compressor ؟ �YهR��P Wات ا��اء أ��Vء TRF�l ا��U�gط Fl} ا�� ا��ري-30

30-What are the types of air effects during compression process in axial compressor?


64

Fig (62) Types of air circulation in axial compressor Fig(63)Compressor blade airfoil Design

Z=Chord thickness/Chord length

(a)-Subsonic Blades (M<0.7; Z=45%)

(b)-Transonic Blades (1.3 >M >0.7; Z=65%)

(c)-Supersonic Blades (M >1; Z=85%)

Air flow effects on axial compressor:

*-We think that air passing in a steady stream through the blades, and not deviating from its path, this is not

correct. Even between the root and tip of a blade considerable differences can occur. One test on a good

performance compressor using special instrumentation show a difference in air temperature between the root

and the tip of 5 °C, change in temperature will affect air properties.

*-Fig (62) shows some of the flows which can occur between two blades. Point (a) show the eddies produced

by air leaking between the stator blades and the rotor, point (b) shows vortices arising from the trailing edges of

blades. These are similar in type to the vortices which can sometimes be seen at the wing tips of aircraft in

damp weather (High humidity). Point (c) shows the circulation patterns which arise due to the Coriolis

acceleration acting on the airflow. (Coriolis acceleration arises when a body moves radially outward while


65

rotating circumferentially). All these flow components cause losses which reduce the efficiency of the

compressor.

إ��اب ا��اء �W ا�� ا��ري �Y هW ��هة-Axial Compressor 31؟

31-What is the definition of compressor surge?

Compressor Surge/Stall:

*-Compressor surge is a phenomena occur on axial flow compressor, this phenomena occur when compressor

operates at incorrect pressure ratio & mass flow rate (i.e. they are not matching to gather) & the result is

compressor flow instability & reversed air flow which will produce high vibration on the blades (extremely at

the last stages blades) which may result in blade failure.

Refer to Fig(64) which shows compressor flow instability,

Fig(64) Compressor flow instability

(a)Full stall [chocked] (b) Leading edge tip stall (c) Trailing edge root stall

(d) Full flow (e) Trailing edge tip stall

*-Axial compressor is designed to run at a design point at which it will operate most efficiently, with the air

flow in each stage approaching the blades at the correct angle throughout the machine, and the flow velocity

parallel to the axis of the machine will be constant along the length of the machine, and at a maximum value.

*-Most of the compressor running should be at, or near, this point (design point). If at a given speed, the mass

flow or the pressure ratio is changed, the balance of flow will be disturbed.

*-If the pressure ratio increases to more than a certain point, the axial velocity of the air will fall and the blades

will stall because the flow will now approach the blades at an incorrect angle. The compressor will then

probably surge, with flow alternatively building up and breaking down, and with a possible complete of air

delivery. This situation may be notes on the machine by high noise, and in bad cases, by physical damage to the


66

machine. Similarly, if the pressure ratio is reduced too far, the axial velocity will increase and the blades will

again stall.

*-The first condition described is referred to as positive shock stall and the second as negative shock stall.

Operation under both these conditions must be avoided. If pressure ratio is plotted against mass flow a curve

named as "compressor operating curve" will be obtained. Refer to Fig(65).

Fig(65) Compressor operating curve

�Y هW أ�yHب إ��اب ا��اء �W ا�� ا��ري-Axial Compressor 32؟

32-What are the main reasons of compressor surge?

*-Reasons of compressor surge could be:

1- Drop on the speed of rotation while compressor is operating at its rated flow.

2- Blow off valves are closed two early (before rated speed is reached).

3- Blockage on compressor discharge lines which increase compressor discharge suddenly.

4- Sudden drop of compressor discharge pressure.

*-Since compressor surge must be avoided, compressor surge protection must be installed.


67

Fig(66) Compressor surge is a result on excessive angle of attack

Axial Compressor ؟ ا��ري آ�FU�g QR ��ق ا��§Y {Fl TR�R�j�TF إ��اب ا��اء �W ا��-33

33-How can compressor surge be avoided by improving compressor design?

Compressor surge can be avoided by using the following methods:

(a) Install variable inlet guide vane to control the angle of the incoming flow to the required angle so that it

matches the angle of the first row of moving blades.

(b) Make the angle of the first few rows of static guide vanes variable. This can be controlled automatically,

and ensures that the blade angle matches the flow angle so that stalling does not occur.

(c) Provide controlled air bleed off from the compressor so that the stages after the bleed off point receive less

air, and the velocity is relatively reduced.

In many cases all three of the above solutions are being used together.


68

Fig(67) Methods of Controlling Axial Compressor surge

؟ Compressor Surge Protection �Y هW وT��s إ��اب ا��اء �W ا�� ا��ري -34

34-What is compressor surge protection?

*-Compressor surge protection provide excellent monitoring for surge phenomena in the compressor, This

protection if activated will trip the gas turbine to avoid compressor blade damage which caused by reverse air

flow due to surging.

*-This protection is consist of differential pressure indicator & two pressure sensors, one of these sensor is

placed at air intake filter house inlet to measure ambient pressure (point#1) & the other pressure sensor is placed

just at compressor entrance before the inlet guide vanes (point#2) refer to Fig(68)

Fig(68) Compressor Surge Protection


69

*-Note that total pressure is summation of static pressure & dynamic pressure, static pressure is the result of the

force exerted by the of air when it is at rest & dynamic pressure is the result of the force exerted by t of air

when it is moving (velocity pressure):

Total Pressure (TP) = Static Pressure (ST) + Dynamic Pressure (DP)

So total pressure at point (1):

TP1= ST1 + DP1

Note that:

Static pressure on point (1) is the ambient pressure.

Dynamic pressure on point (1) is approximately equal zero since air speed is very slow.

and total pressure at point (2)

TP2= ST2 + DP2

Note that:

*-Static pressure on point (2) is less than static pressure on point (1) due to vacuum created by compressor

suction.

*-Dynamic pressure on point (2) is much higher than Dynamic pressure on point (1) due to higher speed of air

because of compressor suction.

*-Now to put it clearly:

Static pressure at point (1) at normal operating condition must be greater than static pressure at point(2),so

Compressor surge protection is set so that:

Differential Static Pressure (∆Ps)= SP1-SP2 must be at least greater than 40 mbar.

i.e. Static pressure at point(1) must be at least grater than static pressure at point(2) by 40 mbar.

*-Note that if (∆Ps) less than 40 mbar this means that static pressure at point(2) approach static pressure at

point(1) which mean that compressor is no longer sucks air even if it is operating at its rated speed & flow(i.e.

compressor is surged).

*-Compressor surge differential pressure sensors is normally have three channels to provide redundancy, if two

of these channels an out put signal that tells ∆Ps <40 mbar, then gas turbine trip will be initiated by gas turbine

controller .

*-If for any reason compressor surge protection is not activated during machine prepares to start, gas turbine

start is blocked.

*-Compressor surge protection is active only when the speed is (42 Hz, 2520 rpm) and above.

*-If gas turbine speed is drop during its normal operation, then the following will happen:

a-At turbine speed of (47.5 Hz 2850 rpm), compressor variable inlet guide vanes (I.G.V) will close to

75% to reduce compressor flow & hence avoid compressor surge due speed drop.

b-At turbine speed of (47 Hz 2820 rpm), gas turbine will trip by under frequency protection.


70

Fig(69) Air flow through aircraft engines


71

GAS TURBINEGAS TURBINEGAS TURBINEGAS TURBINE----COMBUSTION COMBUSTION COMBUSTION COMBUSTION

CHAMBERCHAMBERCHAMBERCHAMBER

W� اقف ا�^��

Tز��Oا� TVRا��ر�

MS6001B-G.E.


72

35-yY Wه�Y اق؟ـــــــ�دئ ا�^ـــــ�

35-What are the main principals for combustion?

1-Fuel: any material that can be burned (oxidized) to release energy is called fuel; most common fuels are

consisting of hydrocarbon flues. Hydrocarbons exist in all phases (solid, liquid, gaseous) examples are coal,

gasoline & natural gas. Most fuels are consists of mixture of hydrocarbons composites & exists as complex

hydrocarbon nodes ,for simplicity most common fuels are treated as single hydrocarbon, for example:

a-Gasoline is treated as Octane (C8 H18).

b-Gas oil (Diesel) is treated as Dodecane (C12 H26).

c-Kerosene is treated as (C12 H24 )

d-Natural Gas (mixture of 90% Methane CH4 & 10% Ethane C2 H6) is treated as Methane (CH4).

Fig(70) Simplified distillate tower

2-Oxidizer: any material that is rich in oxygen is called oxidizer, most common oxidizer used in combustion

processes is air because it is free oxidizer & located any where, Pure Oxygen however is used in special


73

applications such as cutting & welding were air cannot be used.

3-Combustion: a chemical reaction during which a fuel is oxidized & a large quantity of energy is released.

4-Combustion reactants: Components that exists before combustion.

5-Combustion products: Components that exists after combustion, any hydrocarbon fuel when it has complete

combustion, it will produce Carbon dioxide, water vapor & Nitrogen.

*-Note that Nitrogen is generally inert gas it is enter & exit from the reaction with out reacting with other

chemical elements .However, as combustion temperature is increased to more than 1300ºC such as in internal

combustion engines, Nitrogen start to react with other elements, most hazardous product of Nitrogen reactant is

when it is react with Oxygen forming Nitric oxide (NO) &Nitrogen dioxide (NO2) .

*-Note also that Nitrogen is represent 78% of air that is used for combustion ,so it is enter combustion chamber

in large volume at low temperature & exit at a higher temperature & hence it will absorb a large portion of the

chemical energy released during combustion.

Fig(71) Combustion temperature vs. NOx & CO emission

6-NOx: an expression that represent the mixture of Nitrogen oxides (NO & NO2).

7-Sox: an expression that represent the mixture of Sulfur oxides (SO2 & SO3).


74

8-Dry air composition: dray air (on volume basis) consist of 20.9% Oxygen, 78.1% Nitrogen, 0.9% Argon &

0.1% is represent small amount of carbon dioxide, Helium, Neon and Hydrogen.

9-Theoretical air: minimum amount of air that is necessary for complete combustion.

10-Excess air: amount of extra air that is added to the combustion process to insure complete combustion or to

cool down combustion chamber.

11-Complete Combustion: it is a combustion process in which all carbon on the fuel is burned (oxidized) to

carbon dioxide (Co2) & all Hydrogen on the fuel is burned (oxidized) to water (H2O) & all Sulfur on the fuel (if

any) is burned (oxidized) to Sulfur dioxide (SO2) in the product.

12-Incomplete Combustion: It is combustion in which combustion products contain unburned fuel or

component such as carbon(C), Hydrogen (H2), Carbon Monoxide (CO) or Hydroxide (OH).

*-Many reasons are responsible for incomplete combustion, major reasons are:

a- Available air is not enough for complete combustion to take place (Insufficient Oxygen).

b-Insufficient mixing in the combustion chamber burners during the limited time that the fuel & oxygen

are in contact (even if the combustion is take place with excess air!).

c-Dissociation which become important at high temperatures. At high temperatures, the main products

of combustion will decompose or dissociate into other species. For example, complete combustion of

hydrocarbons with air gives CO2, H2O, N2 (as products. But dissociation of these and reactions between

the resultant species from the dissociation may lead to many other species, for example O, H, OH, N,

NO, and others.

*-Oxygen is more strongly attracted to Hydrogen than Carbon. Therefore, the Hydrogen in the fuel is normally

burned completely & yet forming H2O even when these is less Oxygen than needed for complete combustion

Some of the Carbon ends up as Carbon monoxide or just as Carbon particles in the products.

13-Flash Point Temperature:

The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture with


75

oxygen. At this temperature, the vapor may continue to burn when the source of ignition is removed. Fire point

is a slightly higher than flash point temperature.

*-The flash point is used to describe the characteristics of liquid fuel, but it is also used to describe liquids that

are not used intentionally as fuels (like lubrication & insulation oils).

*-Petrol (gasoline) is used in spark ignition engines. The fuel should be premixed with air within its flammable

limits and heated above its flash point, then ignited by the spark plug. The fuel should not pre-ignite in the hot

engine. Therefore, gasoline is required to have a low flash point and a high auto-ignition temperature.

*-Diesel is designed for use in compression ignition engines. Air is compressed until it has been heated above

the auto-ignition temperature of diesel; then the fuel is injected as a high-pressure spray, keeping the fuel-air

mixture within the flammable limits of diesel. There is no ignition source. Therefore, diesel is required to have a

high flash point and a low auto-ignition temperature.

Fuel Flash Point (ºC) Gasoline > -45 ºC Diesel > 62 ºC Jet fuel > 38 ºC

Table (1) Flash Point Temperature for common fuels

14-Fire Point Temperature:

The fire point of a fuel is the temperature at which the fuel continues to burn after ignition for at least 5 seconds.

At the flash point, a lower temperature, a substance will ignite, but vapor might not be produced at a rate to hold

the fire. Auto ignition temperature is always higher than flash point.

15-Auto-ignition Temperature:

The lowest temperature at which the fuel will ignite in a normal atmosphere, without an external source of

ignition, such as a flame or spark if mixed with Oxygen, note that in order to ignite a fuel, it must be exposed to

higher temperature than its ignition temperature, note also that to ignite a fuel either we introduce a spark or

flame, or we compress mixture of air & fuel to very high pressure until mixture temperature become above fuel

ignition temperature. Some of famous fuels minimum ignition temperatures at atmospheric air pressure are

shown in table below.


76

Fuel Ignition Temperature ºC Gasoline 260 ºC Carbon 400 ºC Hydrogen 580 ºC Carbon monoxide (CO) 610 ºC Methane (CH4) 630 ºC Sulfur 243ºC Acetylene (C2H2) 482ºC Ethane (C2H6) 538ºC Diesel 210 ºC Jet Fuel 210 ºC

Table (2) Ignition temperature for common fuels

-Note:

*-To start a combustion not only we have to perform spark or flame in a mixture of fuel & air, the percentage of

the fuel into the air the must be in the proper range of combustion, for example natural gas will burn only if the

ratio of the gas into the air is between 5% to 15% (by volume), for Hydrogen the ratio is 4% to 76% (by

volume).

16-Adiabatic flame temperature:

Maximum temperature that could be achieved in a combustion process if we assume that there is no heat losses

from combustor to the surrounding. The table below shows some common fuels flame temperature.

Fuel Flame Temperature ºC* Propane in air 1980 ºC Butane in air 1970 ºC Natural Gas in air 1950 ºC Acetylene in air 2500 ºC Acetylene in Oxygen 3100 ºC Methane in air 1950ºC

*-assuming initial atmospheric conditions (1 bar and 20°C)

*-Adiabatic flame temperature is affected by the percentage of air that used in the combustion, for example if

Gasoline (Octane -C8 H18) is burned with:

a-Theoretical amount of air ,then the resultant adiabatic flame temperature is 2122ºC.

b-400% excess amount of air amount ,then the resultant adiabatic flame temperature is 689ºC.


77

c-Only 90% of theoretical air(or 10% deficiency air) ,then the resultant adiabatic flame temperature is 1936ºC.

-Note:

*- Adiabatic flame temperature is always maximized when the fuel is burned with theoretical amount of air.

*-In case (b) adiabatic flame temperature is extremely reduced because of excess air used is four times greater

than the amount of air needed for complete combustion.

*-The following table shows some of common fuels flame temperature (for constant volume basis) & also

compare between using air or oxygen as oxidizer for combustion

15- Heating Value of the Fuel:

The total amount of heat released when a fuel is burned completely & the products of combustion are returned

to their temperature before being burned.

Fuel Oxidizer Adiabatic flame temperature(°C)

Acetylene (C2H2) air 2,500

Acetylene (C2H2) Oxygen 3,100

Butane (C4H10) air 1,970

Butane (C4H10) Oxygen 2,718

Methane (CH4) air 1,950

Natural gas air ~1,950

Propane (C3H8) air 1,980

Propane (C3H8) Oxygen 2,526


78

16-Higher Heating Value of the Fuel (HHV):

The total amount of heat released when a fuel is burned completely & the water in the product is in liquid form.

17-Lower Heating Value of the Fuel (LHV):

The total amount of heat released when a fuel is burned completely & the water in the product is in vapor form.

*-Most of power plants analysis is depend on LHV not HHV.

*-The relation between HHV &LHV is : HHV= LHV + m*hfg

m (Kg) = mass of water from combustion products ; hfg (KJ/Kg) = Latent heat of vaporization of the water at the

temperature of the products.

Table(3) Calorific vales for fuels compared to gasoline

Table(3-a) Atomic weight for some substances


79

Table(4) Calorific vales for common fuels

Table(5) Common fuels compositions


80

18-Air/ Fuel Ratio: It is the ratio of the mass of air to the mass of fuel for a combustion process. It is used to

determine how much Kg of air needed to burn 1 kg of the selected fuel. Larger air fuel ratio reduces flame

temperature (increase flue gas losses) & vise versa .Careful selection for this ratio must be made to over come

incomplete combustion.

EXAMPLE:

CH4 + O2 =CO2 + H2O

Equation after balancing: CH4 + 2O2 =CO2 + 2H2O

N=m/M ; N= # of Kilo moles, m= mass in Kg, M= Molecular mass in Kg/Kmol

a-Mass of CH4 = N*M=1* [ (4*1) + (12) ] =16 Kg CH4

1 Kmol CH4 = 16 Kg of CH4

b-Mass of O2 needed in combustion = 2*[ (16*2) ]=64 Kg of O2

-Air is consisting of 21% Oxygen so the amount of air we need it is:

64*(100/21)= 305 Kg of theoretical air is needed to burn 16 kg of CH4

-Air Fuel Ratio= mass of air/ mass of fuel= 305/16=19

So for each 1 Kg of CH4 to burn completely we need 19 Kg of air (theoretical air).

19-Excess Air Ratio(λ): It is the ratio for available air over theoretical air ,it is very important design parameter

For combustion analysis.

*-There is no combustion process so perfect that it is need only theoretical air for complete combustion, all

combustion processes required excess air to insure complete combustion, other reasons to provide excess air for

combustion could be reduce combustible products temperature to the desired temperature.

*-Note that combustion process which use theoretical a mount of air will have excess air ratio λ=1.


81

*-Gas turbine are known to have very high excess air ratio (SIEMENS V94.2 has average excess air ratio of

λ=2.1 so the exhaust air from chimney).

Fig(72) Effect of excess air on combustion products

؟ا�^�اق ا�¤�Y �RهF��Y Wــــ�yت -36

36-What is the requirement for a good combustion?

Good combustion required:

a-Good mixing between fuel & air.

b-Combustion must be carried out with excess amount of air to insure complete combustion.

c-Combustion products must be completely burned to reduce pollution.

d-Carbon deposits on burners must be avoided.

e-Losses of air pressure that is enter the combustion chamber must be minimized.

g-Combustion must be in smallest possible space ( to minimize radiation heat transfer losses).

f-Combustion must be stable with uniform temperature distribution .

؟ �YهW ا��VO¦ ا��y� Tء ا�^�اق-37

37-What are the important factors for combustion to start?


82

For combustion to take place there are three basic conditions need to be satisfied these are:

a-The presence of Oxygen

In the 'chemistry' of burning (combustion) we require the fuel to combine with oxygen. Therefore, if no

oxygen is present combustion will not take place. In a practical situation the oxygen source is air. Air

contains 21% oxygen by volume and is readily available.

b-The correct temperature

A fuel will only ignite if its temperature is raised above its self ignition temperature in the presence of

oxygen.

c-The presence of a source of ignition

The burning process can only occur when the fuel, in the presence of oxygen and at or above the ignition

temperature, is ignited by an ignition source, this source can be a spark, flames, glowing embers or red

hot metal. Other method of fuel ignition could be compress a mixture of air & fuel top very high

pressure until the temperature of the mixture raises above fuel ignition temperature.

d- Percentage of the fuel into the air is in the proper range of combustion

Natural gas will burn only if the ratio of the gas into the air is between 5% to 15% (by volume), for

Hydrogen the ratio is 4% to 76% (by volume).

؟ ا��W� TY�p�q ا��ر�TVR ا��Uز�Tف ا�^�اقـــ �YهW أ�gاع �-38

38-What are the main types of combustion chamber which are used in gas turbines?

Types of Combustion Chambers are:

1-Can type -combustion chamber

Please refer to the next paper.


83

Fig(73) Can type combustor, the red line represent

Air used for combustion & the blue line represent

Cooling air

*-Flame holder must be used in the combustor to a void extinguishing the flame due to discharge air flow. flame

holder is hollow perforated piece of metal.

Fig(74) Flame Holder

*-Advantages & Disadvantages of Can type Combustors:

Please refer to the next paper.


84

Can type

Combustor

Advantages Disadvantages

1 Light & small so its used in air craft High pressure losses

2 Its surrounding gas turbine which reduce

machine dimension & improve aerodynamic

shape of the jet engine

Malfunction of one can could damage turbine

Since heat distribution will disturbed

3 Easy in maintenance Uneven heat distribution

4 Minimum radiation heat transfer losses More suitable for centrifugal compressor where

the flow is divided into separate streams in the

diffusers.

Fig(75) GE-gas turbine with annular type combustors

2-Annular type -combustion chamber

Fig(76) Annular type-Combustion Chamber, Flame tube is shown (ceramic layer)


85

Fig(77) First stage gas turbine for annular type-Combustion Chamber

*-Advantages & Disadvantages of Annular type Combustors:

Annular

Combustor


1 Completely surrounding the gas turbine Turbine suffer from heat since turbine blades are

exposed to flame ( heat transfer by radiation)

which reduce turbine life

2 Pressure losses is reduced Broken of any ceramic block inside the

combustor will hit directly turbine blades result

in catastrophic failure to turbine parts

3 Reduce the size of the machine Possibility of turbine parts burned out

4 Uniform heat distribution (turbine inlet

temperature)

Cooling holes in Flame tube wall is more likely

to have blockage

5 Provide best aerodynamic shape therefore it

is most combustor used in air craft

Difficult in maintenance

3-Silo type (Cylindrical) -combustion chamber

Silo type combustors have two main configurations: single combustor & double combustor.


86

*-Advantages & Disadvantages of Silo type Combustors:

Silo

Combustor


1 Minimum pressure losses Large size result in larger radiation heat transfer

losses

2 Easy in maintenance Not suitable for aircraft engines

3 Higher efficiency &Long life Higher noise level

4 Connected to the turbine by single flange to

reduce heat transfer by conduction

Occupy much larger size compare to can or annular

combustors

5 Burning is carried out at lower temperature (lower

NOx emissions)

More fuel piping are required

Fig(78) Various Silo type-Combustor configurations


87

؟�اقـT ا�^ـــ �YهW أ�Kاء ��-39

39-What are the main parts of combustion chamber?

Combustion chamber mainly consists of:

1-Combustor Casing 2-Flame holder 3-Igniters (provide ignition spark)

4-Flame Tube (reduces radiation heat transfer & distributes air flow between the primary & dilution zones)

5-Burners 6-Fuel supply valves & piping 7-Flame detector

�اء وا��sد أ��Vء TRF�l ا�^�اق ؟ -F� �R¤ط ا��aا� TRأه� Wه�Y 40

40-What is the importance of good mixing between fuel & air during combustion process?

*-The importance of good mixing between fuel & air can be described by the flowing example:

Fig(79-a) Bunsen Burner

Refer to Fig(79-a), If the air inlet at the bottom of the burner is closed ,long flame will results, point(a).

If the inlet is opened so that the air and gas are thoroughly mixed before leaving the burner, a short, sharp flame

is produced, point (b). The various zones of the flame are shown in Figure 9(c).

؟ �YهO� W ا��vVط ا��TRF�l W� T ا�^�اق-41

41-What are the important points to be considered in a combustion process? 1-Flame Color: *- The various colors in the flame are due to the difference in the temperature of the particles, the higher the

temperature of the particles, the whiter the flame.


88

Fig(79-b) Temperature distribution of candle flame Table(6) Relation between flame color & temperature

*-For a given amount of high volatile fuel burned, a short flame will generally mean rapid and complete

combustion, a longer flame means delayed combustion and a very long flame means poor combustion.

*-There is a relationship between the color of the flame and its temperature. If the flame length is also

considered, better knowledge about flame can be obtained. Refer to table (4).

2-Flame Speed and Back Firing: *-Imagine a tube containing a flammable mixture of gas and air. If the mixture is ignited at one end of the tube,

the flame will travel through the mixture initially at a constant velocity, and then, under suitable conditions, at

an increasing velocity. This is particularly so if there is turbulence present.

*-It has been determined experimentally that hydrogen has a flame speed about seven times greater than that of

both carbon monoxide and methane. The importance in practice of these various speeds of flame propagation is

that they determine the tendency of a flame to back fire.

*-If the velocity of the fuel entering a furnace is the same as the velocity of flame propagation, the point of

ignition will remain a set distance from the burner. However, if the speed of backward propagation of the flame

exceeds the velocity of flow of the air/fuel mixture, then back firing will occur. Fuels rich in hydrogen tend to

back fire because their flames have a high speed of flame propagation.


89

*-The air velocity does not normally vary with gas turbine load because the compressor is operating at constant

speed

؟ �YهW أه� ا��OاNY ا��P W�F Fl} ا�^�اق -42

42-What are the factors that affect combustion process?

The rate at which fuel is burns and the efficiency of the burning will depend on:

a-Time b-Temperature c-Turbulence

�YهW ا�I��ل ا��TFO§F� T�F�p أ��Vء ا�^�اق ؟ -43

43-What are the different configurations of the flame during combustion process?

The actual burning happens in two main forms:

1. Laminar diffusion flame, where a sheet of flame is formed between the fuel and the air. This is the type of

combustion seen in a candle flame, and occurs around a fuel droplet. (DIFFUSION FLAME)

Fig(80) Diffusion Flame Fig(81) Premix Flame

2. The second type is the pre-mixed laminar flame, which occurs when the fuel and air are already mixed

together before the fuel burned.(PREMIX FLAME),note that premix flame include tertiary air which help to

reduce flame peak temperature yet reducing NOx emission.

- Diffusion Flame ؟ Tد��Oد ا��sا�� TFOو� Premix Flame - �ًvyqY ط�Fpد ا��sا�� TFO� uR� قه� ا��Y - 44

44-What is the difference between Premix flame & diffusion flame?


90

*-Modern Gas turbine have hybrid burners in their combustors, these hybrid burners have two different flame in

one burner, the diffusion flame & the premix flame, each flame is supplied with fuel by individual pipes.

*-When the gas turbine firing use diffusion flame, then the gas turbine is said to be under Diffusion Mode, &

when the gas turbine is using premix flame, the, then the gas turbine is said to be under Premix Mode.

*-Both flames are consuming the same amount of fuel for a given load, but the difference between them is on

the way of mixing air &fuel.

*- Designers choose premix flame as the main flame for gas turbine base load operation because of lower NOx

level in this flame. The main characteristics of these flames are shown on the following table.

Fig(82-a)Compare between Diffusion flame & Premix flame)


91

Fig(82-b)Compare between Diffusion flame & Premix flame)

Diffusion Flame Premix Flame

1 Strong & stable flame, used during gas turbine

start up until 60% of the load

Weak & instable flame since it does not have (peak

temperature)

2 Temperature profile is not linear Linear temperature profile provide excellent heat

distribution

3 Non visible flame Visible short flame

4 Much higher NOx emission Much lower NOx emission

5 Bad air fuel mixing Excellent air fuel mixing

6 Flame is far from burner metal Flame is closed to burner metal so burner

temperature monitoring is required

7 Used during fuel change over Cannot be used during fuel changeover

8 Since diffusion flame is strong flame ,it will not

be affected by flame humming

Fast change over to diffusion mode is required when

the premix flame suffer from fuel gas pressure

fluctuating while flame humming monitoring is

response

9 No pilot flame is required Pilot flame to stable premix flame is required

Hybrid Burner؟ 45 –uR¤ - �Yه�ا�§�N ا��Oم ��Fـّاق ا�

45-What is the main configuration of the hybrid burner?


92

*-A hybrid burner is a burner that design to have two different flames which are diffusion & premix flames,

each flame has its own air & fuel supply passages within the burner, also each flame has its own swirler. Most

of modern Gas turbines (Europe) is using this burner in their gas turbines, the main advantage of this burner is

the lower NOx level if the gas turbine is operated under Premix Mode. Other designers (U.S.A) tend to use

water injection on the burners to reduce flame temperature & yet reduce NOx emission.

Fig(83)Hybrid Burner on Silo type combustor


93

Fig(84) Hybrid Burner Assembly (Diffusion-Premix Burner)


94

�E ؟ــ�س ��RsــRs �Vـــّـّو��ذا � Flame Humming 46 –FO§ا� W� Nj�� ي�Fا� uRVه� ا��Y ــ T-

46-What is flame humming & why it is important to measure it?

*-Flame humming can be defined as pressure fluctuations of the flame in the combustion chamber. During

load changes, the fuel flow will be changed which will case fluctuating in flame position & temperature jump, a

flame with temperature jump will produce pulsation pressure. The variation of the flame pressure will have a

certain frequency

*-Flame frequency range must be within the safe operating limits, if flame humming increases, then the

vibration level in combustion chamber will increase, and hence flame tube which consist of combination of

blocks may collapse by time & the broken brick pieces fall down & mix with the flow stream that enter the

turbine which is rotating at high speed, the resultant is catastrophic failure to the gas turbine. Monitoring of

flame humming is so important to avoid such cases.

Fig(85)Flame tube for Silo type combustion chamber, the picture on the left is showing maintenance

procedure for each brick by using transparent paper with a black X painted on it, good brick condition is

checked in a way that any crack must not be inside the black X and if the cracks elongated & reach the

black x, the corresponding brick must be replaced to avoid its failure during gas turbine in operation


95

*-Flame humming is measured by vibration sensor that works on the principal of piezoelectric concept. The

output signal is a pressure signal (mbar), Piezoelectricity concept can be shown on the following figure.

Fig(86) Piezoelectricity is voltage produced by squeezing crystals of certain substances (pressure)

*-If flame humming is increased to more than 30 mbar, Gas turbine load increasing is blocked until Humming

sensor is rested (removed).

47–N^اـــY Wه�Y ء�Vاء أ��اق؟ــــ ا�^ ا�

47-What are the stages of the air during combustion? Combustion occurs in three zones: (1) Primary zone, where most of the fuel is burnt in a vortex movement in which the fuel re-circulates a

number of times, allowing time along the spiral paths for the burning to become complete.

(2) Secondary zone, where further air is added to provide a condition of excess oxygen in which all the other

combustion components can be fully burned.

(3) Tertiary zone, where still more of the air from the compressor is added to reduce the temperature of the

products of combustion to a temperature which the turbine can withstand. A major function of this tertiary zone

is to ensure that the mixing is complete so that a uniform flow is passes to the turbine, with no hot areas.

Fig(87) Dividing of air into combustion air & cooling air


96

*-In gas turbines, air enters the combustion chamber traveling at about 150 meters per second. The velocity at

which a flame is propagated in a typical fuel/air mixture is about 7 meters per second. Comparing these figures,

we can see that, we have to reduce air velocity to avoid flame immediately blown out.

Fig(88) Addition of flame tube distribute air flow between the primary & dilution zones

*-In order to provide the necessary conditions for stable burning, two main

Measures are taken:

1-Air flow is slowed down by increasing the cross-section of the combustion chamber just after air entry

2-Air flow is divided into three zones (primary, secondary and tertiary), to provide controlled air to help in

different purposes (part for combustion & part for cooling).

NOx emission؟ �Vا� uRKو�RVا� �RHث أآ��Oygإ NRFvP ق¬ Wه�YPTVRا��ر� W� اقف ا�^�� uY T¤ Tز��U48 - -ا�

48-What are the various methods used to educe NOx emission form gas turbines?

*-Method of reducing NOx generation includes:

1-Reduce flame peak temperature to less than 1300ºC & this can be achieved by introducing tertiary air

on the flame (Premix flame) - Preferred by Europe Gas turbine Manufacturer -.


97

2-Modify Combustion chamber design so that a small portion of the burning is occur under theoretical

amount of air where the flame temperature is highest.

3- Dilute the flame using water or steam injection on the burners , this will prevent 80% of uncontrolled

NOx formation-Preferred by U.S.A. Gas turbine Manufacturer-, note that add steam injection will raise

gas turbine power output by 6%.

4-Inject ammonia (NH3) in the exhaust of the gas turbine to react with NO in present of catalyst. Since

solid catalysts have a short life, a more stable wet de-nitration process using liquid ammonia is generally

employed. By mixing exhaust gases with ammonia, NOx is converted to harmless nitrogen and water.

The reaction is expressed as follows:

NOx + NH3 + (catalyst) --> N2 + H2O

*-The running cost of a liquid ammonia process is high, so NOx measurements before and after the

operation of NOx removal is important to control (minimize) the amount of ammonia that is injected.

*-NOx generation in fuel-rich flame is quit low, then as air approaches theoretical air NOx generation increases

& reach maximum at excess air, then as excess air is added to cool down the flame, NOx generation is reduced.

*-Note that permissible NOx generation worldwide recent standard is varying from 28 to 60 ppm.

SOx emission؟ TVRا��ر� W� اقف ا�^�� uY T¤P�Vا� ��y�ا� �RHث أآ��Oygإ NRFvP ق¬ Wه�Y Tز��U49 - -ا�

49-What are the various methods used to reduce SOx emission from gas turbines?

*-Sulfur oxides result from the burning of the sulfur in the fuel with oxygen from the combustion air, and are

generally referred to as 'SOx'.

*-These substances are very undesirable since they are major components of acid rain, which causes

environmental damage, and they can also cause severe corrosion of equipment.

*- Method of reducing SOx generation includes:

1-Reduce the amount of Sulfur on the fuel is most famous solution.


98

2-Operating at low excess air ratio is the best solution to minimize Sox emission ,note that this solution

is not practical in combined cycle gas turbines since the excess air is needed to burn any extra fuel added

to the heat recovery steam generator(supplementary firing).

*-Note that Sulfur can be removed from the fuel by some treatment but Nitrogen cannot be removed from air!

Fig(89) Siemens hybrid burner Fig(90) G.E. burner -water injection

(Diffusion-Premix burner)

Axial & diagonal swirlers are clearly shown


99

GAS TURBINE GAS TURBINE GAS TURBINE GAS TURBINE ––––TURBINE SECTIONTURBINE SECTIONTURBINE SECTIONTURBINE SECTION

TـــــــVRا��ر�

MS6001B-G.E.


100

50- �ًY��l ت�VRا��ر� QVjP QRآ

50-How can turbines in general are classified?

Turbines can be classified by:

*- the action of flow on the turbine blades:

1-Impulse. 2-Reaction. 3-Impulse and reaction combined.

*-The number of step reductions involved:

1-Single stage. 2-Multi-stage.

*-The direction of flow:

1-Axial. 2-Radial.

*-Reheat or non reheat.

*-Tandem compound or cross compound (this configuration is for steam turbine only)

Fig(91) Radial & Axial flow gas turbine

Fig(92) Tandem & cross compound configuration


101

Fig(93) Gas Turbine with reheat

؟ Radial Tآ��أوا�� Axial 51- Tا��ر� TVRا��ر� ام أآ|�p�HIا �r�� ت�VRا��ر� uY ع�g أي

51-Which types of turbines are most common radial or axial turbine?

*-Most gas turbines engines use axial flow turbines. However, Radial flow turbines can handle small mass flow

applications more efficiently than axial flow turbines & they are used widely in turbocharger for reciprocating

engines.

Fig(94) Conventional Super Charger used in reciprocating engine


102

Impulse turbine و�Pر�TVR رد ا��Reaction turbine NO ؟ �YهW أ�RH�Hت �Pر�TVR ا��aــ� - 52

52-What are the main principals of impulse & reaction turbines?

*-Principals of Impulse & reaction Turbine:


103


104


105

Fig(95) Impulse & Reaction turbines comparison Fig(96) Velocity ratio for various turbines

�YهO� W ا�|�ا�� ا��TR�R�j ا��R�jP �Vl TY�p�q ا��ر�TVR ؟-53

53-What are the main design considerations that used in turbine design?

1-Degree of Reaction (D.O.R):

It is a ratio = (the enthalpy drop across the moving blade) / (enthalpy drop across stage)

*-If D.O.R= 0 %, its pure impulse

*-If D.O.R= 10 %, its impulse stage with small reaction

*-If D.O.R= > 10 %, its reaction stage


106

Note that pure impulse is occur at the root of the blade & as we go further along the blade, degree of

reaction will increase.

2-Velocity Ratio (VR):

It is = (blade speed /Flow speed)

Impulse turbine has highest efficiency at 0.5 VR & Reaction Turbine at 0.9 VR. Note that VR will increase

as blade wheel become larger that's why reaction blades are used in low pressure turbines (such as steam

turbines) because it develops its highest efficiency at higher velocity ratio.

�Yه� وEK ا��vر�P uR� Tgر�TVR ا��Impulse turbine 54-�a و�Pر�TVR رد ا��Reaction Turbine NO؟

54-What is the main difference between impulse & reaction turbines?

KLMــOPQا STUVر

Impulse Turbine

XـــYZQرد ا STUVرKL

Reaction Turbine

1 Has much higher speed since pressure drop per stage

is high

Lower speed since pressure drop per stage is small

2 Power output is higher (for same no. of stages) Lower power output (for same number of stages)

3 Less efficiency since work is done only on the fixed

blade

Higher efficiency since work is done in both fixed &

moving blades

4 Blade tip leakage is far less since its moving blade

does not reduce flow pressure (lower moving blade

leakage factor)

Suffer from blade tip leakage since its moving blade

produce pressure drop (higher moving blade leakage

factor) so careful design must be made to keep pressure

drop per stage to minimum

5 Its moving blade produce lower axial thrust since it

does not reduces flow pressure

Its moving produce high axial thrust since it reduces flow

pressure

6 Used as first stage in HP steam turbine to:

produce larger pressure drop to reduce leakage losses

at first stage, also to reduce thrust & minimize

number of reaction stages needed on HP turbine

Depend on impulse turbine as first stage to enhance

overall turbine design

7 Less number of stages is needed for given load Higher number of stages are needed for a given load

8 Small labyrinth gland sealing (high pressure) Larger labyrinth gland sealing (Low pressure)

9 Has higher flow velocity, friction losses is high Lower flow velocity, friction losses is minimized

10 Less pressure drop in moving blades minimize

leakage & sealing devices around moving buckets of

the turbine

Higher pressure drop in moving blades maximize &

sealing devices around moving buckets of the turbine


107

Fig(97) Impulse & Reaction turbines blade geometry & profiles

�YهW ا�I��ل ا��T�F�p ��ر�TVR ا��aــ� ؟ -55

55-What are the different configurations of impulse turbine?

Impulse turbine has three main configurations which are:

a- Pressure Compound.

b- Velocity compound.

c- Velocity & pressure compound.

The various configuration of impulse turbine is shown in the figures below.


108

Fig(98) Pressure Compound impulse stages Fig(99) Velocity Compound

Fig(100) Combined Velocity & Pressure Compound

أي �gع uY ا��ر��VRت ��p�qم �W ا��ر�TVR ا��Uز�T؟ -56

56-Which type of turbines is used in gas turbines?

*-The selection of turbines is never clear, but in general most designers used combined impulse & reaction

configuration, most gas turbine uses reaction turbines with the first fixed stage is impulse.


109

57- jP حــ�VRا��ر� �Rز�ــ��Uا� TــT

57-Explain gas turbine design?

Fig(101) SIEMENS- V94.2 gas turbine

*-Turbine stator is surrounded with shroud & there is a gap between them to minimize conduction heat transfer.

*-Turbine rotor disks has small gaps for cooling air that extracted from compressor at various stages in such

way that each turbine stage receive suitable cooling air temperature. This cooling air is used to cool moving

blades. Turbine stator blades are also cooled from compressor extractions.

*-There are no peep holes on turbine section since blade tip clearance can be measured from combustor side or

exhaust side (for gas turbine using silo type combustor only).

*-Thrust direction of turbine is opposes compressor thrust direction & has higher value.


110

*-Gas turbine bearing is placed down of the hot stream to reduce heat level (refer to the figure below), turbine

bearing also is sealed from hot stream by seal air from compressor extraction, that air also provide cooling for

gas turbine bearing & it is either exist from bearing bores to mixed with the exhaust or it mixed with lube oil

that is back to oil tank.

*-Lubricating oil is enter with higher flow than other bearing to provide cooling to turbine bearing & to avoid

high temperature from hot steam that passes through the bearing.

Fig(102) Hot gases leaves turbine through diffuser& gas turbine bearing is placed down to the hot stream

*-Turbine stator is made from a mixture of alloys & globolitic cast iron. Turbine inner casing is made of

mixture of alloys mainly nickel & chromium.

*-Turbine blades is made from expensive alloys to with stand high temperature, Air craft Boeing -757 is made from the following compositions :

Titanium (38%), Nickel (37%), Chromium (12%), Cobalt (6%), Aluminum (5%), other alloys (2%)

*-Note that air craft must be as light as possible to reduce its weight, this is tell you way titanium content on

aircraft turbine blade is so high. Modern land base gas turbine blades are made mainly from Nickel, Chromium


111

& Cobalt along with other alloys.

*- Both moving & fixed blades of turbine are cooled by air-cooling, air is enter inside moving blade & at the

root also there are extracted air that provide sealing & avoid hot gases to enter the hollow section of the rotor

(inter stage seals).the sealing air also provide cooling for turbine rotor disks.

*-First & second fix blade of gas turbine normally coated with ceramic to reduce thermal stresses.

*-Each increase in turbine inlet temperature will increase turbine power by 1.7% & thermal efficiency by 0.5%.

Fig(103) Gas turbine blades &bearing carbon rings fitted in stator are clearly shown

Fig(104) Turbine Rotor Disk & hirth coupling also shown


112

Fig(105) First stage of silo type combustor

Fig(106) Gas turbine first stage moving blade

Fig(107) GE- Gas turbine rotor & moving blade which have first two stages coated with ceramic


113

GAS TURBINE GAS TURBINE GAS TURBINE GAS TURBINE ––––BLADE COOLING BLADE COOLING BLADE COOLING BLADE COOLING

TECHNIQUESTECHNIQUESTECHNIQUESTECHNIQUES

Tز��Uا� TVRر�® ا��ر� ��yP TRVـvـP

MS6001B-G.E.


114

58- �F� Tوا�|��ـ Tآ® ا��ا� ��yP ق¬ Wه�Y؟TـVRر��

58-What are the methods used to cool turbine fixed & moving blades?

*-Turbine inlet temperature will depend on:

a- Material of the blades b-Fuel c-Cooling technique

*-Most component that suffer from high temperatures, high stresses and chemical attack is turbine first fix

stage, (normally it is coat with ceramic to provide extra protection).

*-Main reasons of high thermal stress on turbine moving blades are:

a-High rotational speed

b-Uneven temperature distributions on different blade cross sections

c-Static & pulsating gas forces that may give raise to dangerous vibration stresses

d-Temperature changes which occur during start up & shutdown

e-Normal & up normal load changes which affect turbine inlet temperature (unlike steam turbine which

have constant inlet conditions for various load profile.

*-Turbine blades are hollow so that coolant can be circulating through.

*-Blade root is called (leading edge) & blade tip is called (trailing edge).

*-Turbine blades must be cooled to protect them from melting due to high turbine inlet temperature, highest

turbine inlet temperature raised to 1370 ºC in new designs. There are two main techniques used to cool down

turbine blades which are air cooling & water cooling (steam).

*-The range for air cooling technique is up to turbine inlet temperature of 1150 ºC & for water cooling

technique is up to turbine inlet temperature of 1315 ºC . In some hybrid designs both technique are used where

water cooling is used for turbine first fixed stage & air cooling is used for the other blades.


115

Fig(108-a) Cooling passages of turbine rotor blade

Fig(108-b) Methods of turbine blades cooling


116

Fig(109) Cooling air flows at turbine section & cooling air to gas turbine bearing is clearly shown

Fig(110) Air extraction temperature must be suitable with gas temperature along turbine

*-Note that turbine inlet temperature must be identified as per ISO condition since first stage fixed blade is

cooled from inside by air & hence there will be a temperature drop for hot gases at entrance.


117

Fig(111) Definition of Turbine Inlet Temperature as per ISO- 2314

Blade Cooling methods:

Fig(112) Types of blade cooling

There are four main typed of cooling methods, some blades may have two method or three involved, these

methods are:

1-Convectin Cooling

Most common technique used in gas turbine where the air flow is entreat the root of the blade & travel

through multiple passages before leaving blade at the tip (air always flow in parallel with the axis of the

blade cross section.


118

2-Impingment Cooling

It is a form of convection cooling but here air is blasted on a blade surface at high velocity (air is flow

parallel & perpendicular to the axis of the blade cross section. This technique can be limited to desired

sections of the blade, for example the root of blade required more cooling than the middle or the tip of

the blade. Cooling air is impinged at the root of the blade to improve the cooling in this section.

3-Film Cooling

It is a very effective cooling method in which cooling air flow from the root & exit at the tip and at

holes around the blade surface, this air will surround the blade with a thin layer which insure maximum

blade cooling efficiency.

4-Transpiriation Cooling

Transpiration Cooling is some how similar to film cooling, in this method blade cooling is done by

passing the cooling air through the porous wall that formed over the blade. The air flows on these pores

& exit from the blade after cool it being down. The disadvantages of this methods is that it required

large cooling airflow, also the porous blades are easily damaged.

Fig(113) Cooling air move around series of passages before exit

*-The amount of cooling air needed may represent to 5% of the total compressor output for small units to 16%

for large units to cool the gas turbine blades. This air is not, of course, available for combustion, and hence


119

represents a power loss. The pressure of the cooling air may need to be varied to match the pressure in the

various zones of the turbine.

ersus cooling effectiveness forv ) kη(y Cooling efficienc )114(Fig Various blade cooling methods

Fig(115) Types of blade Cooling

5-Water Cooling

*-water cooling technique is used for higher turbine inlet temperature, as gas temperature exceeds 1150

ºC, the percentage of extracted air (air that is by pass the combustion chamber) to cool turbine parts


120

is increase to unacceptable value& the use of water cooling is more preferred (Each 1% of air extraction

from compressor will reduce turbine power by 2%), the air extraction in water cooling is eliminated.

*-Test have been made in both techniques shows that for air cooling the blade temperature is below

900ºC while in water cooling the blade temperature is well below 450ºC.

*- Cooling water must be heated enough before entering turbine blades to avoid thermal shock. The

fixed blades are normally having closed cooling water loop while the moving blade have open cooling

water loop. In this case the water enters from blade root & allows to be boiled then it will thrown out

form blade tip by centrifugal force as steam.

*-Water has much higher heat capacity & heat transfer capability than air but it is not used so common

because of the added complexity to the design. This technique is suitable only for large land base

turbines which have high turbine inlet temperature & in these machines water is used to cool down first

fixed stage while other stages are cooled by air extraction, the main aim of this hybrid designs to reduce

air extraction from compressor flow which may be up to 16% of total flow (Each 1% of air extraction

from compressor will reduce turbine power by 2%).

*-Unvaporized water moves radialy by centrifugal force & may be collected by water collectors which

are installed on the outer inner casing of the turbine, refer to the figure below.

Fig (116) Water cooled gas turbine moving blade with water collector at the circumferential


121

�اء وا��y�� ء؟-59�� TVRر�® ا��ر� ��yP uR� Tgر�vا�� EKه� و�Y

59-What are the main deference between air cooled blades & water cooled blades?

\QاءاK^Q_V `abc

Turbine cooling by air extraction

Qء\ا_dQ_V `abc

Turbine cooling by water

1 Extracted air that bypass combustor reduce total

flow that enter turbine which represent a loss in

turbine efficiency (5-6% of compressor discharge

for medium range units & up to 16% for large units)

No need for air extraction from compressor

2 Easy design & lower cost More complex design & higher cost

3 For open type air cooling system, mixing of air with

hot stream will reduce hot gases temperature at each

stage which will reduce the work done by each stage

For open type water cooling system, mixing of

water with hot stream will reduce hot gases

temperature at each stage but since water will

evaporates to steam which have larger expansion

than air, there will be extra power out put on the

turbine which will offset the reduction of hot gas

temperature

4 Air extraction temperature must be suitable with the

desired cooled stage temperature to avoid thermal

shock

Water must be heated before entering blade to

avoid thermal shock

5 Common technique for gas turbine blades cooling Un common technique

*-Note that a hybrid technique which includes both water & air cooling is done by GE-gas turbines.

آ�! ��س آ��ءة ��م ا�� ا��م �� ا��ر�� ا��ز��؟-60

60-How blade cooling effectiveness is measured?

*-Blade cooling efficiency is given by the ratio of the actual drop in temperature achieved to the maximum

theoretical temperature drop achieved.

*-Cooling effectiveness (εb) = (Tg - Tb) / (Tg – Ta )

Where, Tg= Hot gas temperature


122

Tb = Mean blade surface temperature Ta = Cooling air inlet temperature

؟ا��ر�TVR ا��Uز�F�T�® ا�|��T وا��آW� T ا��O�T وا��¯آــOP � N��Y Qه-61

61-What is the definition of Corrosion & Erosion for gas turbine blades?

*-Turbine blades suffer from high temperature corrosion & erosion.

Erosion: Loss of material of the blades due to abrasion of a moving fluid.

Corrosion: Material removal due to chemical reaction.

Normally first three stages are coated with special material to avoid corrosion.

�د �W ا��ر�TVR؟-62Kإ {FlI ضO�� ي�Fا� ��Oه� ا��Y

62-What is the component in gas turbine which is suffered from the highest thermal stress?

The part on turbine that greatly suffers from stresses & high temperature is turbine first stage fixed blade, these

blades are coated with ceramic to reduce thermal stresses. Refer to the figure below.

Fig (117) Gas turbine first fixed blades suffer from corrosion & erosion


123

Fig (118) Overheated gas turbine blades

ا��ر�TVR ا��Uز�T؟ |��T وا��آ�Y W� TهW أ�yHب ا��O�T وا��¯آــF� N�® ا�-63

63-What are the main causes of Erosion & Corrosion on turbine blades? *-The main reason of turbine hot corrosion is associated with the contents of the fuels & more clearly the

contaminations present in the fuel. Also, pollution from the air that enter compressor.

*- The main agent in this type of corrosive attack is sodium sulphate, arising from the combination of sulphur

and sodium present in the fuel.

*- Normally the melting point of sodium sulphate is sufficiently high that it is not deposited on the blade

surfaces. However, the presence of small amounts of secondary substances, such as vanadium pentoxide, lowers

the melting point of the sodium sulphate below the blade surface temperature with resultant deposits on the

blade. Once deposited the sulphates combine with the blade materials, attacking the surface of the blades and

forming metallic sulphides.

*- Because the air/fuel ratio is very high in gas turbines, there is extra oxygen available in the blade zone to

oxidize these sulphides(air contain 21% air by volume & at turbine exhaust air represent 15 % of hot gases by

volume). The sulphur is then released to attack the next layer of blade surface.

*-Other sulphates, such as lithium and potassium sulphate which are present on the fuels, will have the same

effect on turbine blade & above process will be repeated.


124

�YهW ا��Fل ��NRFv ا��¯آN و^��T ر�® ا��ر�EVY TVR؟-64

64-What are the methods used to reduce Corrosion & protect turbine blades? There are various methods of controlling corrosion that Resulting from Fuel contaminations, these methods include: 1-Eliminating the substances causing corrosion from the fuel and air:

*-Some of the harmful substances in fuels, such as sodium sulphate, are water soluble and can be washed out by

water. The wash water, with the dissolved out impurities, is then removed by centrifuging. Impurities such as

vanadium and heavy metal compounds are not water soluble compared with oil and cannot be eliminated in this

way. Combustion air can be filtered to remove solid particles.

*-Air also contain some of the harmful substances, even if the air is passes trough air intake filter house, the

harmful gases cannot be removed by filters.

2-Protecting the blades themselves from corrosion attack:

By forming the blades from mixture of strong alloys or by coating.

Fig (119) Corrosion effect on turbine blades


125

3-by using corrosion inhibitors in the fuel:

Fuel additives are available which assist in preventing hot corrosion via sulphates. One such additive is

magnesium. In the presence of this metal, magnesium sulphate is formed instead of sodium sulphate.

Magnesium sulphate remains solid at the temperatures found in the hottest parts of the gas turbine, and hence

liquid deposition and corrosive attack do not occur.

4-by using ceramic blades (or a complete ceramic turbine rotor):

This method is still experimental in both gas turbine (to reduce blade temperature) & reciprocating engines (to

reduce heat loss to surrounding).

�دات ا��R��Rg�TR ا�O�P W�Fض �� ا��® ا��آW� T ا��ر�TVR ؟ -65KIاع ا�gأ Wه �Y

65-What are the types of loads that exert on rotating turbine blades?

*-Type of loads in a turbine blade:

a-Flow load which try to bend the blade.

b-Centrifugal force which try to pull out the blade in tension.

c-Vibration loads because the blade is subjected to steam pressure at blade intervals ( since there is a

difference in pressure in the blade, maximum pressure occur at root and minimum at tip & hence

result in blade vibration).

آ�� QR Pاآ� ا�§�اW� �r ا��® Fl} آ��ءة ا��ر�deposits formation on turbine blade 66-TVR ؟

66-How does deposits formation on turbine blade affect turbine efficiency?

*-About 500 grams of deposits distributed on the blade can bring down turbine efficiency by 1%.

Fl} آ��ءة ا��ر�TTVRا��§�� ا��§ّ�° ا��Fي ��ث �W آQR -67 ؟

67- How does the damage to turbine-blades tell upon the efficiency of the unit?

*-The damage to blade profiles changes the geometry of flow path and hence reducing the efficiency of the unit.


126

GENERAL NOTES ON GENERAL NOTES ON GENERAL NOTES ON GENERAL NOTES ON

TURBINETURBINETURBINETURBINE ––––SHAFT DESIGNSHAFT DESIGNSHAFT DESIGNSHAFT DESIGN

�R�jP ت�RH�Hأ ul TY�l ت�Y�FOY ا��Oد ا��وار

MS6001B-G.E.


127

T�R�¦ ن ا��ذاة��P QR؟ وآ Shaft Alignment ��Y TRF�l �Vذاة ا��O ا��وارا ��ذ-68P -

68-Why shaft alignment process is important? & how can we perform this process correctly?

Alignment of shaft bearings:

*-The rotors of a modern turbine are bolted up with solid couplings, so that they form a single long shaft, and

this is supported in a number of bearings. However, we must not think of this shaft as rigid, since it will bend

under its own weight.

*-If we put all the bearings at the same height, then the shaft will be forced into a deflected shape as shown in

the figure below part (a), and this alignment is incorrect because in this case the faces of the rigid coupling

(unbolted) would not lie parallel to each other.

*-The bearings must be set as shown in part (b) with the centre pair lower than the two outer bearings, in order

that the shaft shall be able to lie in a continuous curve . This setting permits the two faces of the rigid coupling

to lie parallel to each other. The basic goal of this arrangement is to have zero shear force and zero bending

moment at the coupling bolts.

Fig (120) Shaft Alignment

*-On large turbines the centre bearings may require to be set 12 mm lower than the outer bearings in order for

the shaft to be able to deflect and to form this continuous curve.


128

Fig (121) Typical Shaft Alignment for large turbo generator

؟ �Tدون �Rه� �W ا��ر��VRت ا��Uز�T وا��pyر Journal Bearings ��ذا �p�qPم آاWH ا��NR ذات ا��Ovة -69

69-Why Journal bearings are used in large turbines?

*-Plain white metal journal bearings are widely used because of their high loading capacity, their long life and

the low rate of wear.

*-The long life of these bearings is due to the fact that, when the shaft is rotating at speed, a continuous high

pressure film of oil is automatically formed between the white metal and the shaft.

*-The oil film ensures that no metallic contact takes place and consequently no wear occurs. Oil is supplied to

the bearings from the lubrication system.

*-Journal bearings are designs to carry rotor radial forces but there are also axial forces that generates from

thrust. To keep the shaft in correct axial position, axial bearing is used.

� ا�Oy اaz ز�� ا�� OFد ا��وار ��gم ��ذا �p�qPم �O ا��ر��VRت -70Y�p�q� d ��VR؟�

70-Why lifting oil is used in some turbines to lift their shafts?


129

*-Lifting oil is used to lift the shaft during start up to reduce wear on bearings metal since the oil film is no yet

established, This system is used to reduce the cost of using strong bearing material which withstands wear

during low speed by replacing these bearings with less cost bearings materials.

�O� W ا��ر��VRت آ��Y NR��P WHري وا^� ��p�qg ��VR� �vم آا�sُ Qjg NR��P WH��O�Y Tدة؟ �p�qما � ��ذ-71

71-Why we use only one axial bearing in turbine shaft instead of multiple bearings?

*-Because turbines shafts are joined to gather by bolted joints (rigid coupling) & hence the axial thrust of single

shaft will push the hall turbine shaft, but if there is a reduction gear between the shafts, then each shaft will have

its own axial movement & hence each one must has axial bearing.

ا��وار ��Fر�TVR ا��Uز�T وا��ر�TVR ا��pyر�T؟ �Y هW ا��aت اuR� TRH�HI ا��Oد-72

72-What are the main deference between gas turbine shaft & steam turbine shaft?

Tز��Uا� TVRر��F� د ا��وار��Oا�

Gas turbine shaft

Tر��pyا� TVRر��F� د ا��وار��Oا�

Steam turbine shaft

Due to high operating temperature, the shaft must be

hollow from inside to provide passages for cooling air

Most of steam turbines shafts are solid

Since the shaft size is small & short so it expand &

shrink less so their is no shell expansion & differential

expansion monitoring

shell expansion & differential expansion monitoring

is required since the shaft & its shell is large & heavy

yet they expand & shrink more relative to each other

Most gas turbines depend on temperature sensors that

embedded on bearing metal to detect wear instead of

thrust wear detector.

Thrust wear power failure is required in some

designs due to slower rate of heating ( Slow thermal

expansion in steam turbine in comparison).

Manufactured from complex materials, alloys &

surface coating is required in some parts

Manufactured mainly from steel (steel base alloy)

with 11-13% of chromium for large units

Blade is manufactured by forming & casting (very expensive) Its blades are manufactured by machining

Gas turbine processes simulate internal combustion

engine

Steam turbine simulate a wind mill

Temperature is lowest at the beginning of the rotor Temperature is highest at the beginning of the rotor

Much higher operating temperature Lower operating temperature


130

73-yأآ Tز��Uا� TVRن ^¤� ا��ر��ج؟ ��ذا �pا� ��V� Tر��pyا� TVRا��ر� �¤^ uY

73-Whay gas turbine is larger than steam turbine for the same power output?

*-Because gas turbine compressor extract mechanical power from turbine the valve of this mechanical power

around 50% to 67%.

*-Note that steam turbines required 2% of rated steam flow when they are idling (full speed no load condition)

& this flow is only to resist bearing friction & windage losses, while gas turbines required 60% - 67% of full

load flow when they are idling, this flow is to resist bearing friction , windage losses & compressor work.

�؟ -74yV¤P �VRFl �¤� و��ذا TVRد ا��ر��O� TKت ا��lqا� Wه�Y

74-What is critical speed for turbine rotor & why do we have to avoid it?

In order to understand shaft critical speeds, the following definitions must be recognized.

A-Types of vibration:

*-Vibration, in general, reduces equipment life and, in extreme cases, can result in equipment damage or even

catastrophic failures. Thus vibration must be observed to avoid damage to the turbine. There are three types of

vibrations in terms of the direction of motion and deformations experienced by the vibrating object which are:

1- Lateral

Lateral vibration is the most common. It occurs when the object deflects/bends laterally to its

longitudinal axis. Most turbines vibration sensors sense lateral vibration.

2-Axial

Axial vibration occurs when the object is subjected to pulsating axial forces. This type of vibration is

difficult to notice & special sensors must be involved in order to monitor this type of vibration.

3- Torsional

Torsional vibration occurs when the object goes through a pulsating angular motion around an axis of

reference, usually its own longitudinal axis.

B-Critical Speed:

*-Critical speed is the speed of a rotating shaft at which one of the natural frequencies of the rotor-bearing-

foundation system equals the forced frequency that corresponds to the rotational speed. The term rotor-bearing-

foundation system reflects the fact that the rotor natural frequencies are affected by the stiffness of its support.

*-Critical speed is the speed at which resonance occur.


131

C-Natural frequency:

*-Natural frequency is a frequency at which the object would vibrate after the initiating force is removed and

the object is left on its own. This type of vibration is referred to as free or natural vibration. In practice, due to

friction and energy transmission to surrounding objects, the amplitude of free vibration decreases until the

object comes to rest.

*-What causes natural vibration to continue after the initial disturbance has been removed? It is a combination

of the object's inertia (an object with higher inertia will have lower natural frequency) and stiffness or rigidity

(the stiffer the object the higher natural frequency will result).

*-The concept of natural frequencies is important for prevention of excessive vibration. To avoid resonance, we

should avoid situations where a forced frequency (shaft speed) equals a natural frequency. We must therefore

know the factors affecting the values of natural frequencies.

D-Damping:

Vibration damping is dissipation of the mechanical energy of a vibrating object. In free vibrations, damping

reduces the amplitude of vibration to zero.

The main sources of damping are:

1- Internal friction in the material of the vibrating object.

2- Friction between sliding surfaces of the vibrating object and some other object.

3- Friction between the object's surface and the surrounding fluid (fluid damping).

Although fluids, in general, provide some damping, sometimes they cause vibration.

E-Resonance:

Very high vibration occurs when rotor speed is synchronies with natural frequency the rotor. Resonance is

potentially dangerous because it can produce excessive vibration.


132

Fig(122) Resonance can raise vibration amplitude dramatically when damping is low. *-When the machine is running at a critical speed, the resonance will increase vibration, particularly if damping

is small. From the above figure, you can see that vibration will increase not only at the single value of a critical

speed but also at a speed range around it.

*-Operation at or near critical speed should be avoided because vibration will increase and may become

unacceptable. This condition means that normal operating speed must be sufficiently far from the nearest critical

speeds (minimum ±20%).

*-In some machines like turbine generators and high-speed pumps and compressors, the normal operating speed

is above the lowest critical speeds. These machines pass through the critical speeds during run-up and rundown.

This is perfectly safe as long as sufficient damping exists (In rotating machinery, damping is usually provided

by the oil film in the bearings, by the cast iron casing and by the concrete foundation).

*-Normally any rotor has one or more critical speeds which may be below or above its operating speed.

*-During rolling up turbine rotor care must be taken when passing near rotor critical speed & in many control

system the rate of speed will increased more than normal when passing near critical speed to minimize

resonance & protect rotor from excessive vibration.

*-Each rotor on the turbine has its own critical speeds; they are mainly lateral critical speeds & tensional critical

speeds.

*- Critical speed decreases as rotor shaft length increase or rotor diameter decrease.


133

*-Factors that affecting critical speed:

1-Length of the shaft 2-Diameter of the rotor

3- distance between rotor bearings 4-rigidity of the rotor support

TVRد ا��ر��O� ؟ Sagging pPء وا�ر� - hogging -TRqRrب ا��yHIا Wه �Y س�vوث ا�� - 75

75-What are the main reasons for shaft Hogging & Sagging?

F-Shaft Hogging: Hog is an upward bending of the rotor and it is s happen when the top of the shaft is hotter

then the bottom.

*-This temperature differential is produced by the fluid around the rotor. That is, the colder and therefore

heavier fluid collects at the bottom, while the warmer and hence lighter fluid is pushed to the top. This process

takes place when the turbine rotor is left stationary (with out put it under turning gear operation) for cooling

down or when start the turbine without being warmed up.

*-Hogging is a fast process; it may take only several minutes to bow the shaft enough to close some radial

clearances in the machine. An attempt to turn the rotor in this condition could damage the machines internals

(i.e. turbine blades) and bearings through rubbing.

*- Note that hogging also affects turbine casing. However, the rotor is our primary concern, because its bowing

introduces a mass unbalance, which does not affect the casing and secondly, because rotor hogging is faster and

larger than casing hogging. The reason for this is that the rotor changes its temperature faster than the casing

which is heavier and therefore needs more heat transfer to change its temperature. (also because rotor it is

smaller yet expand &shrink faster).

G-Shaft Sagging: Down word bending of the shaft under its own weight

*-Note that very small, sag is present during normal shaft rolling operation because the rotor is not infinitely

rigid. But when the rotor is stationary, sag increases because the same part of the rotor is subjected to a constant

stress for an extended period, the top half is in compression, while the bottom half is in tension.

*-Unlike hogging, sagging is a slow process and it takes days rather than minutes to develop to a troublesome

level. Another term that is closely associated with hogging.


134

*-Note that shaft sagging is slow process (several days to affect the shaft & can be removed by put the shaft

under turning gear operation to adjust shaft eccentricity.

Fig(123) Shaft hogging & sagging

H-Shaft Eccentricity: Eccentricity is a measure of the rotor deflection from the perfectly straight line; this

measurement is unavailable when the rotor is stationary.

*-Reasons of shaft eccentricity:

1-Shaft hogging 2-Shaft sagging 3-Rubbing of rotating parts with stationary parts in the rotor

4-Rapid heating or cooling for the rotor

�Y هW ا�yHIب ا�TRqRr ��وث ا�ه��ازات ��l Wد ا��ر�TVR؟ -76

76-What are the main reasons of shaft vibration in turbine?

*-Main reasons of turbine vibration:

1-unbalanced parts 2-poor alignment of parts 3-loose parts

4-rubbing parts 5-lubrication troubles 6-Flow instability

7-foundation troubles 8-cracked or excessively worn parts 9-vibration result from blades

10- Running the rotor near its critical speed.

*-Note that regard case#10 we have to make sure that the vibration of the rotor is caused by critical speed & not by some other trouble.


135

�W ا��ر�TVR ا��Uز�T ؟ وV�VY} ا��ارة وV�VY} ا��U آQR ��ن �l {V�VYم ا��وران-77

77-How is the torque, pressure & temperature distribution on gas turbine?

*-The highest torque occurs between compressor last stage & turbine first stage.

Fig (124) Torque distribution & output power in V94.2-SIEMENS gas turbine

(125) Temperature & pressure distribution on twin spool gas turbine with power turbine configuration which was in shuwaik power station (Rolls Royce& Curtiss wright)


136

Fig(126) Single spool axial flow turbo jet aircraft engine

�Yه� ا��N ا��p�qم ��NRFv ا�ه��ازات ا�W� T¤P�V ا��^TF اRaIة uY ا��® ا��آW� T ا��ر�TVR؟ -78

78-What are the methods used to reduce vibrations at last stage of turbine?

One modification is to join the blade segments together at the shroud band.

Fig (127) SIEMENS- gas turbines last stage (lift side steam turbine & right side gas turbine)


137

Fig(128) Toshiba- steam turbine last stage on left & GE-gas turbine turbines last stage on the right

-Tز��Uا� TVRا��ر� uY |أآ Tر��pyا� TVRا��ر� N^اY د�l ،ذا ؟�� 79

79-Why is the number of steam turbine stages is larger than gas turbines stages?

Steam turbine has more stages than gas turbine because Steam turbine inlet pressure is much higher than gas

turbine inlet pressure hence more stages are required in steam turbine for added flow expansion.

�YهW أه�TR ا�دارة ا��O� TGR�yد ا��ر�TVR ؟ -80

80-What is the importance of turning gear operation for turbine rotor?

*-Turning gear operation is very important after the turbine is shut down to prevent uneven temperature

distribution for the shaft which may cause shaft, a motor-driven turning gear is engaged to the turbine to rotate

the spindle and allow uniform cooling. If shaft hogging stay for large time period, a catastrophic failure for the

shaft may result & at that time the shaft cannot be recovered & hence must be replaced.


138

GAS TURBINE GAS TURBINE GAS TURBINE GAS TURBINE ––––START START START START UP UNITUP UNITUP UNITUP UNIT

Tز��Uا� TVRر��F� و^�ة ��ء ا�دارة

MS6001B-G.E.


139

�ز � -81¤� Tز��Uت ا��VRج ا��ر��P ؟�ء ا�دارةــ��ذا

81-Why are gas turbines need start up unit?

*-Most of internal combustion engine required start up system, in reciprocating engine there is a starter which is

mish with the fly wheel that is connected to crank shaft, also gas turbine need start up unit but the point here is

that gas turbine required longer time before reaching its stable operating speed.

*-Care must be taken when designing the start up system, for example a land base gas turbine (SIEMENS

V94.2) will start ignition at 600 rpm & the start up device will stop at 2200 rpm & the gas turbine will by its

own power will accelerate to nominal speed (3000 rpm), this process take at least 4 minutes hopefully if there is

no operating troubles during shaft acceleration.

*-There are various method of starting gas turbine, the choice of the start up system will depend on the

condition of the engine, for example a military air craft requires the engine to be started in the minimum time &

when possible to be completely independent of external equipment. A commercial aircraft however requires the

engine to be started with the minimum disturbance to the passengers & by the most economical means.

�ة �-82Kاع أ�gأ ؟ �ء ا�دارة ��Fر��VRت ا��Uز�T ا��W� TY�p�q ا��Rراتـ �YهW أ�

82-What are the most common starters which are used in aircraft gas turbine engines?

*-Most common methods that used to start aircraft engine:

1-Electric started (DC-motor)

Used in some turbo-prop & turbojet engine, the electric power for the motor is supplied from aircraft onboard.

2-Cartridge starter

*-Cartridge starting is sometimes used in military engines & provide a quick independent method of starting,

the started consist of impulse turbine that driven from hot gases which generates from electrically fired

detonator called cordite (detonator that burn without smoke resulting).

3-Compressed air starter

Used in most modern commercial and some military jet engines. It has many advantages over other starting

system as it is light, simple & economical to operate. Air is supplied from an external ground supply to rotate


140

the air turbine.

4-Small Gas Turbine as starter

In this method small gas turbine is used as starter for the main engine. It has its own fuel and ignition system,

starting system, usually electric motor or hydraulic pump with hydraulic turbine).

5-Hydraulic starter

Hydraulic turbine receives high pressure oil from electric pump to rotate the main engine.

Fig(129) Start up sequence of typical turbojet engine

83-TRr��ة ��ء ا�دارة ��Fر��VRت ا��Uز�T ا��g� TY�p�qج ا��Ts ا��Kاع أ�gأ Wه�Y ؟

83-What are the most common starters which are used land base gas turbines?

1-Reciprocating engine:

*-Many old gas turbine use Reciprocating engine to provide starting torque to accelerate the gas turbine until

disengage speed, a reduction gear must be installed between reciprocating engine output shaft & gas turbine

shaft normally called (accessory gear).

*-The old gas turbines in Doha East PowerStation (manufactured by HITACHI) & in Zour South power station

(manufactured by MITSUBISHI) have this method of starting.


141

2-Compressed air starter:

*-In this method, compressed air is used to rotate air turbine & the output torque is used to turn the main engine.

*-The old gas turbine which were in Showaik power station (manufactured by Rolls Royce & Curtiss Wright)

was using this method, compressed air was supplied to the air turbine by auxiliary compressor at 500 to 1000

psi (34 bar to 68 bar).

3-Hydraulic oil starter:

In this method high pressure oil is injected to turn start up turbine to rotate the main engine.

4-Electric motor starter:

*-In this method electric motor was used to supply the required start up torque to the main engine.

5-Start-up Frequency Converter -S.F.C.:

*-In this method the generator of the gas turbine is used as starting motor, note that synchronous generator has

the same operating principal of synchronous motor, after gas turbine reach its stable operation speed, the S.F.C.

will shut down & gas turbine will accelerate until nominal speed. The new gas turbines (manufactured by

SIEMENS) in Zour gas turbine power station is using this method.

Fig(130) ABB-Gas turbine using eclectic motor as starter


142

Fig(131) Start up Frequency Converter


143

GAS TURBINE GAS TURBINE GAS TURBINE GAS TURBINE

OPERATION, CONTROLOPERATION, CONTROLOPERATION, CONTROLOPERATION, CONTROL

& PROTECTIONS& PROTECTIONS& PROTECTIONS& PROTECTIONS

Tز��Uا� TVRا��ر� W� ��ا�� T��gأ

MS6001B-G.E.


144

ــــT اRH�HIــــــW ا��Rــ �Yه-84KI Tــــ�؟ـــ�ة ا��

84-What is the main purpose of control system?

The main function of governing system is:

1-Limit the speed raise to an acceptable limit during load rejection

2-Control the output power

3-Control the speed during start up, synchronizing & loading

4-Match the power generated to the power that is required by the load

85- Wه�Y Tlqاآ� ا�� TRqRrاع ا��gIا/Tر��pyت ا��VRا��ر� W� TY�p�qا�� N؟ا��

85-What are the main types of speed/load controller that used in steam turbines?

Min type of turbine governors:

1-Mechanical Hydraulic governor (refer to Appendix-A)

2-Electrical Hydraulic governor (refer to Appendix-A)

Fig(132) Basic fly ball governor


145

Fig(133) Mechanical Hydraulic Governor

Fig(134) Electro hydraulic governor

*-Note that gas turbine need to control the fuel flow & Compressor inlet guide vanes position in order to

increase or decrease its load, while steam turbines need to control the position of the steam control valves only.


146

86- Wه�Y آ�� TRqRrاع ا��gIاNا/ ا�� Tlq؟� 86-What are the main types of speed/load controllers? There are two types of prime mover speed governor: 1- Isochronous Governor (Constant speed governor)

2-Droop Governor

*-First we have to define speed droop:

Fig(135) Isochronous Governor curve Fig(136) Droop Governor curve

1- Isochronous Governor (Constant speed governor)

*-the operation of the isochronous governor (0% speed droop) can be explained by comparing speed versus load. As

shown in figure above. If the governor were set to maintain the speed represented by line- A and connected to an

increasing isolated load, the speed would remain constant. The isochronous governor will maintain the desired

output frequency, regardless of load changes if the capacity of the engine is not exceeded.

*-Paralleling turbine with isochronous governor to an infinite bus would be impractical because any difference

in speed setting would cause the generator load to change constantly. A speed setting slightly higher than


147

the bus frequency would cause the engine to go to full-load position. Similarly, if the speed setting were slightly

below synchronous speed, the engine would go to no load Position.

*-If more than one generator is connected on the same network, they cannot have droops with zero slopes.

because the system would be unstable. A very small frequency disturbance would cause one of the machines to

grab the whole load. The result would cause hunting of the governors and rapid load swings between the

generators.

*-Note that prime movers having isochronous governor is not desiarable since they will not automatically increase

their loads when system frequency & vise versa.

*- With isochronous governor, in order to provide load in response to a drop in frequency, the operator must

increase the load set point manually to the desired load.

2-Droop Governor

*-The speed-droop governor has a similar set of curves, but they are slanted as shown in the figure above. If a speed-

droop governor was connected to an increasing isolated load, the speed would drop (until the maximum engine

capacity is reached.

*-Now let us imagine that we connect the speed droop governor (slave machine) to a utility bus so large that our

engine cannot change the bus frequency (an infinite bus),remember that the speed of the engine is no longer

determined by the speed setting but by the frequency of the infinite bus. In this case, if we change the speed setting,

we would cause a change in load, not in speed. To parallel the generator set, we are required to have a speed setting

on line A (figure above) at which the no-load speed is equal to the bus frequency.

*-Once the set is paralleled, if we increase the speed setting to line B. we do not change the speed, but we pick up

approximately a half-load. Another increase in speed setting to line C will fully loaded prime mover. If the generator

set is fully loaded and the main breaker is opened, the no-load speed would be 4% above synchronous speed. This

governor would be defined as having 4 % speed droop.

*-Note that normal range for turbine governor droop settings is between 2% to 5% , to low droop setting means

very sensitive & unstable governor to a load change & to high droop setting means less sensitive governor to a

load change.

*-good governor is that which have lower droop settings (4% droop governor is more sensible than 6% droop

governor).

*-Note that droop setting is some thing associated with prime mover (turbine) NOT generator set.


148

87- P أن N�ّ�� ذا��§�Y Tlqا� �¬�yP Tyqg ن��Eوا^�ة T�y§� TFjت ا��VRا��ر� �R�¤� �P�OH ��F�aإ ��Y ؟

87-Why it is preferred to make speed droop setting same for all turbines which are connected to the same network?

Turbines which are connected to the same network must have the same droop settings for their governors to

provide equal share of load for each unit with respect to its size during system disturbance, the following

example.

Fig(137) Two generator have different droop settings

*-In the figure above, first generator (G1) has less of a droop than second generator (G2). It will react to load

changes more than G2, which has the lower droop. Both generators have capacity of 600 MW & they are loaded

with 350 MW for each. The frequency of the network is 60 Hz.

*- Some disturbance happen on the network due to unit's trip & system frequency therefore drop to 59.5 Hz & a

system load increase of 350MW is needed to restore normal operating frequency.

*-In this case the amount of load increase for system stability will be shared between both generators, G1 will

handle 250MW extra load (because its droop setting is less yet it will sense frequency drop faster than G2) and

G2 will handle extra 100MW.


149

*-Note that In actual practice with many generators feeding the large system, it would take a major load

disturbance to drop the system frequency that much (59.5 Hz) but we take it here only as for demonstration of

the effect of different droop setting. However, all large generators connected to the grid should have the same

droop setting. With the same setting, they will equally share the load according to their capabilities and equally

share in stabilizing the load during system disturbances.

*-Now imagine that G1 have a capacity of say 400 MW only & it was running with 350 MW & G2 have

capacity of say 800 MW & it was running with 350 MW. With same droop settings & with same load increase

to restore system frequency, G1 will go to full load & it will increase its load from 350 to 400 MW(full load

operation) while G2 which is much larger capacity will increase its load from 350 MW t0 450 MW( only in

56% of its full load) .

*-Both generators will recover 50+100 =150 Mw only from the required load increase & other 200 MW shall

be taken from other generators on the network, you can see that large generator such as G2 operates with only

56% of its full load while much smaller G1 operates with its full load in response to load demand to restore

system frequency. This is because larger generator has poor droop setting while small generator have higher

setting & hence, all generators must have same droop setting so that they equally share load.

*-Note that constant speed governors will never increase their load to restorer system frequency. They will only

stay at the desired load set point which is set by the operator.

�YهW أ�gاع ا��اآ� ا��W� TY�p�q ا��ر�TVR ا��Uز�T؟-88

88-What are the types of governors which are used in gas turbine?

The gas turbine controller is designed on the master/slave principal to provide redundancy in case the master

controller has unrecoverable fault during gas turbine in operation. The gas turbine controller is responsible for

controlling all of the following controllers:

1-Run up Ramp Function

Its aim is to control the startup of the gas & the start up unit. This controller is active when we push start

up button of the gas turbine until the gas turbine become self standing (the starter device is disengaged

& the gas turbine depend on its own power).


150

2-Speed /Load Controller:

Speed /load controller is a two variable controller; it controls the speed and the electric power under the

following conditions:

1-No-load speed to rated speed

2-synchronizing with the electric grid

3-Loading of the turbine

4-Load rejection

5-Shutdown of the gas turbine

*-Speed controller (first variable) is active from start up until generator synchronizes. Then the speed

load controller is shift to the second variable (electric load),The range of operation of the load controller

is from synchronizing until compressor inlet guide vane (I.G.V) position is 100%

3-OTC Controller (Turbine Outlet Temperature Controller)

*-Its aim is to maintain turbine outlet temperature to the designed value, if we have high turbine outlet

temperature, this means that turbine inlet temperature is exceeded, to avoid this, the OTC- controller is

monitoring turbine outlet temperature by means of temperature called OTC (outlet turbine calculated

temperature).This temperature is theoretical temperature (i.e. it is a result from equation).

*- the OTC temperature depends on turbine average outlet temperatures, constant taken for the weather

& compressor inlet temperature, the equation used by OTC-controller is:

OTC=OT-(K1+K3*TC1)*TC1

Where, OT= average turbine outlet temperature K1&K2 are constants for weather condition

K1=0.37 K2=0.007 TC1=compressor inlet temperature

Putting all together the equation will be:

OTC= OT-(0.37+0.007*TC1)*TC1


151

*-The OTC-controller is try to maintain this temperature to the designed value.

*-example: for SIEMENS gas turbine V94.3 this value is:

OTC=534 for Natural Gas firing

OTC=520 for Gas Oil firing

*-The OTC controller range of operation is when ever I.G.V reaches 100% position, if I.G.V. for

example 99%, then the control system turns to load controller.

*-Note that all gas turbines install temperature monitoring systems in the exhaust of the gas turbine not

on its inlet, this is because:

1- Turbine inlet temperature is very high & hence the thermo couple to withstand this high temperature

has short life & also costly.

2-If one of the temperature sensor that is installed in turbine inlet is broken, then it will fall down &

taken by the flow stream into turbine blades which result in catastrophic failure to them while if these

sensors install in the exhaust, then there is no danger.

4-Load Limit Controller

To protect turbine section from over load, load limit controller will activate when gas turbine load is

more than a certain value (example: SIEMENS V94.2 gas turbine maximum permissible load is 173

MW). Its aim is to abort any increase in gas turbine by increase load set point by the operator .This is

done to protect turbine section from over load.

5-Generator Load Limit Controller

To protect generator from over load limit controller will activate whenever generator is load to more

than a certain value (example: SIEMENS V94.2 gas turbine generator maximum permissible load is 204

MW).

6-Compressor Pressure Ratio limit controller

The aim of this controller is to insure that compressor outlet pressure is not exceeding the maximum


152

design value to avoid compressor overload &compressor surge (since high pressure is required with the

same speed).

7-I.G.V. Temperature Controller

Its aim is to reduce exhaust temperature by opening the I.G.V. to increase air flow.

8-Compressr I.G.V. Position Controller

Its aim to provide control to the I.G.V. position.

9-Valve Lift Controller

Its aim is to control the control valve of the selected fuel system for various gas turbine loads.


153

Fig(138) Operating screen for modern gas turbine


154

-Tز��Uا� TVRا��ر� W� Nز��دة ا�� TRF�l ن��P QR89 ؟ آ

89-Describe the process of increasing gas turbine load?

Gas turbine load increase process:

1-Load set point is manually increased by the operator.

2-Load controller sends a signal to the selected fuel control valve to increase its open position.

3-Due to the increased fuel flow, turbine inlet temperature will increase & hence the gas flow will

expand more & additional mechanical power is added.

4-As turbine inlet temperature is start to increase, the exhaust temperature will increase & the controller

will open the inlet guide vane of the compressor to increase its air flow to match the requirement of load

increasing & to decrease down turbine exhaust temperature.

5-As I.G.V. position increase, compressor output flow will increase & hence addition mechanical power

(in the form of additional torque) must be supplied to compressor from turbine, so fuel control valve will

open more than what the added load required to satisfied compressor requirement.

This process is describing the load increase in the gas turbine, but what happens in generator is another

story:

1-As the mechanical torque from the turbine increasing, it will counter act the electric torque in generator stator

which is opposes turbine torque direction.

2-As generator counter torque is shifted by turbine torque, the load angle increases & the line of magnetic filed

produced by the rotor now is being cut at large angle than before & hence a higher current flow on the stator

will result (Induction low).Note that turbine mechanical torque must be greater than generator stator electric

torque for load increase process & vise versa.

3-Due to the higher current in the stator, the terminal current of generator stator will increase.

4-As higher terminal current generated in the stator, the electric power will increase (P=V*I) while generator

terminal voltage will drop (due to armature reaction & self inductance of generator coils effect.

5-If the Automatic Voltage Regulator is put into auto mode ,it ill increase generator rotor excitation current to


155

restore the magnetic field of the rotor & to increase the voltage of the generator to its original value.

Fig(139) How electric power generated

؟%100 ا��Uز�Fl T} ا�� uY أّن ا� �® ا��آT �� ا��ر��Y TVRح �TyqV ه�R��qg N ز��دة ^�N ا��^�ة-90

90- Could we increase the gas turbine load even if compressor inlet guide vanes are fully open?

*-Gas turbine can be loaded to more than its base load operation (base load operation means than the

compressor inlet guide vanes is fully open supplying full compressor flow).

*-This mode of operation is called "peak load operation", in this mode the turbine inlet temperature is increased

by increasing fuel flow, the result is extra megawatts generated to the power system even if I.G.V. is 100%.

*- This method can be done by increasing OTC-controller temperature setting to higher value (example

Siemens V94.2 OTC setting for peak load operation is 560°C).


156

91- W�Fط ا��vVا� O� Wه�YTز��Uا� TVRا��ر� ــ�l ��vP �� a uY ؟

91- What are some of the factors that may determine the service life of gas turbine components?

*-Factors to be considered for estimate gas turbine life are:

1-Number of starts and stops

2-load and temperature swings (load rejection)

3-running hours (Base load operation or peak load operation).

4-whether components have protective coatings

5-material creep strength

6-endurance limit for fatigue strength evaluation

7-method of blade cooling

8-effect of steam injection

9-erosion wear noted during inspections

92-Tز��Uا� TVRا��ر� �l ب�q�� TY�p�qا�� Tv�ا�� Wه�Y ؟

92-What is the method used to calculate gas turbine service life?

*-The method is calculating the equivalent operating hours of the gas turbine by equation contain many

variables.Equavalent operating hours that result from this equation is not true hours, instead these hours are

theoretical hours, They are a function of many variables & they are related to the condition of the gas turbine,

fuel type, fuel deposits, number of starts & so many other variables. The equation is described in the following

paper (used for SIEMENS V94.2 gas turbines).It is good to mention that:

1-each start up will add 10 hours to the age of the gas turbine.

2-Each load rejection happen will increase the equivalent operating hours up 50.

3-Each base load trip will add 125 hours.

4-Each peak load hour will add 4 hours.


157

93- Nا�� {Fl TVRا�} �� ا��ر� Naاء ا��ا�؟�Yه� R��P درTK ^ارة ا�

93-What is the effect of compressor inlet temperature on gas turbine output power?

*-As we know from the earlier discussion that as compressor inlet temperature decrease, the air density will

increase & hence compressor output flow increases & additional flow will enter the turbine which result in

increase in output power (note than compressed air velocity is almost constant no matter the dense the air, this is

because the shaft speed is constant at various loads-Synchronous generator operates at constant speed-).

*- The GT performance is a function of The ambient temperature (compressor inlet temperature) & as a result

any drop in the ambient temperature will lead to increase the available load for the GT (each 1 degree drop will

result in increase GT available load by 1.24 MW).However, it is good to mention that the GT load is not fixed

at the rated capacity all the time (unlike steam turbines).


158

Fig(140) Gas turbine load variation with ambient temperature

*-The following diagram & table is for V94.2 -SIEMENS gas turbine located at Azzour Power Station , there

are important assumptions to introduce this table & reading which are:

1-The maximum load that could be exported in this table is calculated under the assumption of unity

power factor

2-Since there are 8 GT's in the station which definitely have different performance & also they have

different OTC-settings, do not expect that all the GT's will produce same maximum load for the given

ambient temperature.

3- Since load limit controller is restrict GT load to maximum 173MW,even if the ambient temperature is

5ºC degree for example, GT load could not increased to the corresponding maximum load (175MW in

this case) due this reason.

4-If National Control Center (N.C.C) request from Azzour GT staff to increase GT load to maximum

expected load, this is definitely means that the corresponding GT will auto changed to OTC-Controller

when the IGV open to100%.


159

5- The assumption for this table is made for dry weather (i.e. low relative humidity <35%)

6-The assumption for this table is made for Natural Gas firing; the situation with Gas Oil fuel is different

since the OTC- settings are less in case we run the Gas Turbine with Gas Oil.

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20 25 30 35 40 45 50 55 60

Ambient Temperature

Expected max. load (MW)

Fig(141-a) Gas turbine electric power output versus compressor inlet temperature

Fig (141-b) Effect of ambient temperature on gas turbine output power


160

ambient Max. ambient Max.

temp. expected temp. expected

(ºC) load (MW) (ºC) load (MW)

7 173 33 141.08

8 171.8 34 139.84

9 170.6 35 138.6

10 169.4 36 137.36

11 168.2 37 136.12

12 167 38 134.88

13 165.8 39 133.64

14 164.6 40 132.4

15 163.4 41 131.16

16 162.16 42 129.92

17 160.92 43 128.68

18 159.68 44 127.44

19 158.44 45 126.2

20 157.2 46 124.96

21 155.96 47 123.72

22 154.72 48 122.48

23 153.48 49 121.24

24 152.24 50 120

25 151 51 118.76

26 149.76 52 117.52

27 148.52 53 116.28

28 147.28 54 115.04

29 146.04 55 113.8

30 144.8 56 112.56

31 143.56 57 111.32

32 142.32 58 110.08

Table(7) Variation of gas turbine electric power with ambient temperature(compressor inlet)

�Yه��a Wات NRU§P ا��ر�VRــT ا��Uز�ــT؟-94

94-What is the start up sequence of land base gas turbine?

*-Please refer to the following table which describe gas turbine start up, loading & shut down.


161

Table(8) Gas turbine start up, loading & shutdown:

STEP SGC-GAS TURBINE STEP FUNCTION SGC-GAS TURBINE NUM. MBY01EC001

ST(01) SFC-Unit Start Selected From ST(01)

ST(02) Hydraulic Oil Pumps ON Preparation for Gas

ST(03) Compressor Blow Off Valves OPEN Turbine Start Up

ST(04) Generator Cooling System ON

ST(07) Prepare SFC To ST(07)

ST(08) Start Up Of Selected Fuel System

ST(09) Acceleration GT until SFC-OFF if Speed > 38.6 Hz From ST(09) To ST(11)

ST(10) GT Acceleration To Nominal Speed Monitoring Run Up

ST(11) GT At Full Speed No Load (FSNL) Behavior of GT

ST(12) Excitation Switched ON From ST(12)

ST(13) Generator Synchronizing To Grid Synchronizing Generator

ST(14) Waiting for generator on load signal 3 to Grid & Load Increase

ST(16) Normal Gas Turbine Operation To ST(16)

ST(51) Unloading GT to < 8 MW From ST(51)

ST(52) Unit Auxiliaries Has Transferred (Not Applicable)4 Unloading the Gas

Turbine

ST(53) Unloading GT to < 1.5 MW & Disconnecting

Generator

ST(54) Disconnecting Generator From Grid from Grid

ST(55) Excitation Switched OFF To ST(55)

ST(56) SHUT DOWN of Selected Fuel System

ST(57) Shaft Running Down From ST(57) Gas Turbine

ST(58) Set Release Memory For Restart To ST(58) Running Down

ST(59) Turning Gear Operation START if GT Speed < 3 Hz From ST(59)

ST(60) Generator Cooling system SHUT DOWN Start Turning Operation

ST(61) Hydraulic Oil Pumps OFF & active turn Program

ST(62) Ready to Start Up the Gas Turbine (Restart) To ST(62)

ST(0) SGC-GAS TURBINE in Manual Mode

(1)-During GT running with natural gas premix mode, there are some situations that required either fast or normal change over to diffusion mode. however, fast change over to diffusion mode is required when: a-natural gas pressure drop to minimum or fluctuating, b- rapid change in natural gas pressure & Humming Monitoring is response , c-pilot gas valve has a fault, d- load fluctuating during premix natural gas firing. Note that there is a fast change over to diffusion while running with fuel oil premix mode put with out additional steps on the SGC-F.O. (2)-In case Fuel change over, there are additional steps that the corresponding SGC should do. (3)-If generator on load signal received, then the automatic paralleling device will switched OFF. (4)-This step is not available for az-zour GT & its applied only for units having their generator CB before Unit Service transformer Branch & hence the unit auxiliaries need to feed power from neighboring units in case their

unit shut down.


162

95-TRr�� ؟ �YهW أه� ا��sت �W ا��ر��VRت ا��Uز�T ا��g� TY�p�qج ا��Ts ا��

95-What are the most important protections used in land base gas turbines?

Most Important gas turbine protections when it is on load & in which will trip the gas turbine if activated are:

1-Compressor surge protection

2-Exhaust temperature high

3- Air intake filter house differential pressure high

4-Fuel supply pressure high/low

5-Gas detection system inside turbine hall activated (during firing with fuel gas)

6-Gas turbine fire protection system activated

7-Turbine over speed protection system #1 or #2 activated

8-Bearing vibration high

9-Beraring temperature high

10-Gas turbine controller fault

11-Flame detector has fault

12-Any protection from generator required gas turbine trip

13-Any protection from generator transformer required gas turbine trip

14-Luberecation oil pressure low


163

GAS TURBINE GAS TURBINE GAS TURBINE GAS TURBINE ––––EFFICIENCY EFFICIENCY EFFICIENCY EFFICIENCY

& OPTIMIZATION& OPTIMIZATION& OPTIMIZATION& OPTIMIZATION

��ءة ا��ر�TVR ا��Uز�T¬ق uRq�P آ

MS6001B-G.E.


164

96- W� د�vا�� Wه�Y ؟ Tز��Uا� TVRا��ر�

96-What are the losses in gas turbine?

Gas turbine losses include:

1-Bearing friction losses 2-Mechanical losses

3-Bleed air for cooling turbine blade losses (5% to 6% of compressor flow for mid range gas turbines & 16%

for large gas turbines)

4-Exhaust losses (Most larger- 67%) 5-Auxiliaries power losses (0.5% only unlike steam turbine)

*-Over the past years, gas turbine efficiency is well improved due to the moderate techniques &improvement of

high temperature alloys to withstands higher turbine inlet temperature.

*-Gas turbine efficiency is lower than steam turbine since gas turbine connected to compressor which use large

part of the generated load(two third).Also, the exhaust temperature of steam turbine is much lower than it in gas

turbine, so large amount of energy in the form of heat is lost in the chimney. Furthermore, the percentage of

extracted air to cool down hot parts (by pass air) is another reason for lowering gas turbine efficiency.

*-During full speed no load condition (idling), steam turbine need 2-3% of full load flow while gas turbine required 67% of full load fuel during idling.

Fig(142-a) Snakey diagram for SIEMENS-V94.3A gas turbine


165

Fig(142-b) Thermodynamic diagrams for open cycle gas turbine (Ideal Bryton Cycle diagrams in the top)& (actual Bryton cycle diagram at the bottom)

Fig(143) Gas turbine compressor work


166

97-Tز��Uا� TVRا��ر� W� ءة��ق ر�� ا�¬ Wه�Y ؟

97-What are the methods used to improve land base gas turbine efficiency?

The following points describe the methods used to improve gas turbine efficiency:

1-Increase turbine inlet temperature

2-IncreaseThe efficiency of turbo machinery components

3-Gas turbine with regenerator

4-Compressor Inter cooling

5-Turbine Reheat

6-Evaporative cooling for compressor inlet

7-Fogging system (high pressure water spray)

8-Chilling water system for cooling compressor inlet air (Mechanical Chilling)

9-Water or steam injection

10-Increase the pressure ratio (rp)

11-Supercharging

12-Combined cycle gas turbine

13-Humid air Turbine cycle

14-Fuel consideration in gas turbine

These methods are described in details in the next pages.


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Fig(143-a) Bryton cycle for gas turbine (T-s thermodynamic diagram)

1-Increase turbine inlet temperature:

Turbine inlet temperature has been improved from 540ºC (1049s) to 1425ºC today, as turbine inlet temperature

increases, the output power & the efficiency of the gas turbine will increase. The main factors that limit this

choice are that the development of super alloys to withstand such high temperatures & the extra NOx as turbine

inlet temperature increases. As turbine inlet temperature increased by 56ºC will increase turbine power by 10%

& thermal efficiency by 1.5%.


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*-Using steam as coolant for turbine blades allow lower average turbine blade (steam has better heat removing

capability than air-almost wise).

*-To increase turbine inlet temperature, we have to consider blade material, fuel type & cooling technique.

*-The disadvantages of increasing turbine inlet temperature are the shorter life to turbine parts which will

require more frequent maintenance.

2-IncreaseThe efficiency of turbo machinery components:

Old gas turbine has poor blade aerodynamic but to day with computer aided design, these blades has optimum

efficiency with minimum losses.

3-Gas turbine with regenerator:

*-In this method the hot gases from turbine exhaust is recovered to increase compressor outlet temperatures, the

effects of this method is reduce heat input by the fuel & increase the efficiency of the cycle, note that this

modification is applicable only for gas turbines with low pressure ratio so that the difference between

compressor outlet & turbine outlet temperatures are large to get benefits.

*-For gas turbines with large pressure ratio, the additional of regenerator may reduce cycle efficiency (since

compressor outlet will be higher than turbine exhaust).

Fig(144) Gas turbine with regenerator

*-The disadvantages of this method is the decrease in turbine specific power output(KJ/Kg) as a result of added

pressure losses on the regenerator, also regenerator will produce back pressure losses on the turbine(just like car

engine exhaust with super charge).


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Fig(145) Efficiency versus compressor pressure ratio Fig(146) Specific power versus pressure ratio

Of gas turbine showing effects of turbine inlet for a gas turbine showing effects of turbine inlet

Temperature & regeneration temperature & regeneration

*-Addition of regenerator to the gas turbine cycle will increase the back pressure of the turbine (each 2.5

increase in back pressure will reduce gas turbine load by 0.3%, the same result will be obtained when using gas

turbine combined cycle, the hate recovery stream generator tubes will be just like barrier to the hot gases flow &

the result is increase the back pressure on the gas turbine & reduce its load by 1% to 2%.

4-Compressor Inter cooling:

*Compressor work can be reduced if the compression process takes place at constant flow temperature with

same pressure ratio across each stage of compression.

*-To minimize compression work during two stage compression, the pressure ratio across each stage of

compression must be the same, when this condition is satisfied, compression work across each stage will

become identical (i.e. Compressor stage #1 work=compressor stage#2 work).

*-The temperature of the compressed flow will increase across each stage of compression & to reduce this

temperature inter cooling process is used between stages (by cooling water).

*-This method is effective in reciprocating engines (positive displacement compressor) & used also in

centrifugal compressor but it is impractical in axial compressor.


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Axial Compressor؟ ��ذا P��ن ¬�Tv ا��y�� ا��^WF ��ء�R ��F� T��ّO ا��ري-98

98-Why compressor intercooling is not wildly used in axial compressors?

Because in axial compressor, the direction of the flow is always parallel to the axis of rotation, introduce an

intercoolers between its stages require change in the flow directions by improving compressor casing design,

the additional pressure & velocity losses will limit the benefit of interfolding (unlike centrifugal compressors

which already have to redirect the flow from each stage too the new stage since they are radial flow

compressors.

*-Note that velocity losses is important in axial compressor since it is increases flow pressure by accelerate it (dynamic compressors).

Fig (147) Centrifugal compressor must change its flow direction

Fig (148) Axial Compressor intercooling

*-Note that compressor intercooling will reduce compressor work & hence increase turbine output power &

thermal efficiency, but it will increase heat input by the fuel slightly but the offset is increase in thermal

efficiency.

*- Compressor intercooling will optimize cycle efficiency if it is used combined with turbine .


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Fig(149) Gas turbine with compressor inter-cooling, turbine reheat& regeneration

5-Turbine Reheat:

*-Reheat configuration will increase gas turbine power, note that flue gases exhaust from first turbine will have

high % of air so a second combustion system will be added to inject more fuel & allow the hot gases to expand

again in the second turbine resulting in maximizing gas turbine power output.

Fig (150) Turbine Reheat

*-Note that in air craft gas turbines ,the same method is used to increase engine thrust but it is not called reheat

process, in stead this method is commonly named as afterburning or after burner.

*-After burning is used only for military fighter in order to increase fighter climb rate while striking on the sky

& also during short take off, the additional thrust from after burner will allow the fighter to take off in shorter

distance.


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Fig (151) Principal of after burner

Fig (152-a) Effect of increasing number of reheats & compression intercooling on gas turbine cycle

performance

6-Evaporative cooling for compressor inlet:

*-Recall that gas turbine power can be increased by lowering compressor inlet temperature, in evaporative

cooling system, water is sprayed into tilted surfaces that design to absorb the water (made of cartoon or wool),

air is pass through these surfaces & vaporize some of this water, the air lost some of its heat (latent heat of

vaporization of the water) yet it cools down almost to the wet-bulb temperature of the air.


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Fig (152-b) Evaporative cooling concept as it shown in psychometric Chart

Fig (152-C) Effect of ambient temperature on gas turbine output power


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Fig (153) Evaporative cooler section for gas turbine compressor inlet

*-The advantages of this system is simplicity & lower cost compare to chilling water system, the main

disadvantages is that this system it suitable only for hot & dray regions (as ambient relative humidity increases,

the efficiency of evaporative cooling concept will drop since air wet bulb temperature will approach dry bulb

temperature & hence, no further drop in air temperature by this concept).

Fig (154) Effect of relative humidity on increasing

Gas turbine load when using evaporative cooling or fogging systems


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7-Fogging system (high pressure water spray):

In this system, a series of water spray nozzles are installed in the air intake filter house (of course after the filter

elements to avoid blocking them by condensate), by spraying water in the flow stream, the temperature of the

air reduced to the wet bulb temperature of the air(evaporative cooling concept).

Fig (155) Fogging system

The main advantaged of this system is:

1-Increased Output by to 20 % 2-Reduces NOx Emissions up to 30 %

8-Chilling water system for cooling compressor inlet air (Mechanical Chilling):

*-This system is some how independent of weather condition effect (humidity effect).

Fig (156) Fogging system arrangement with nozzles


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*- compressor inlet air is enter through cooling coils installed in their intake house with Chilled water flow

inside the pipes from chiller output .Condensers of these chillers is either air cooled or water cooled.

*-Centrifugal chiller used for gas turbine intake air cooling has capacity between 1500 to 4500 Ton (required

very large electric power), example:

-for 185 MW gas turbine with ambient conditions of 40ºC dray bulb temperature / 26 wet bulb

temperature & the cooled air is leaving at 13ºC is approximately need water chiller of 5700 Tons

capacity. The electric power required to run this chiller is about 8.6 MW!

Fig(157) Mechanical chilling system for gas turbine compressor inlet cooling application

*-The main disadvantages of this system is very high installation & operation cost compare to other methods.

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99-What are the main advantages & disadvantages of cooling systems for compressor inlet?

*- Cooling compressor inlet flow will result in increasing turbine output power, increasing heat input by the fuel

& increasing compressor work requirement but the offset is increasing gas turbine power & efficiency.

*-The following table summarizes the main advantages & disadvantages of compressor inlet cooling

techniques.


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Table (9) Comparison between all methods used to reduce gas turbine compressor inlet temperature

9-Water injection:

*-water is either injected in compressor stages or compressor discharge or directly into the burner.

*-In this method, water is injected into the compressor & evaporates as the air temperature raises during

compression process, the latent heat of vaporization gained from the air will reduce its temperature resulting in

decrease compressor work (just like intercooling processes which described before).

*-Water injection is used in some aircraft engines to improve engine efficiency. At high altitude, the air density

drop & hence engine thrust will drop. This methods is affective if used at high altitudes and/or high ambient

temperature. To improve the thrust, a mixture of water & methanol or water only is sprayed either at

compressor inlet or injected into combustion chambers, addition of methanol is due to its anti freezing


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properties. The resultant boost in thrust can be used to increase the speed of the aircraft or to boost take off

thrust.

*-When water injection in used along with regeneration, more improvement to the cycle efficiency can be achieved.

*-Water flow is inert the injector in a value that make compressed air to be saturated, (i.e. Relative

Humidity=100%),more injection for water will result in liquid flow with compressed air, although this liquid

water will increase turbine work but it will affect the turbine more than the saturated air because of local service

temperature difference & associated thermal stresses.

*-The increase in turbine work due to water injection is due to the increase in the total mass flow that enters the

turbine (hot gases + water vapor), with out corresponding increase in compressor work. Note that water mass

flow does not enter the compressor in this case,(steam has higher specific heat (Cp) than air, almost twice) .

Fig(158-a) Gas turbine cycle with regeneration & water injection at compressor discharge

*-The main advantages of this method are increasing turbine metallurgical efficiency & its output power.

*-For each 1% in weight of steam added to the air (assume 100% in terms of weight in the axial compressor

flow), turbine power will increase by 3.5% with only 1.6% increases in fuel flow. Note that 1% of steam

injected contains higher energy level than air. Also, specific heat of steam is almost twice that of air.

*-It has been found that the injection of water will reduce NOx formation in the gas turbine to half.

*-The amount of steam or water injected is limited to about 12%, this amount will increase the power output by

25%.


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Fig(158-b) Gas turbine with steam injection

10-Increase the pressure ratio (rp):

As pressure ratio is increase, gas turbine efficiency will increases

Fig (159) Effect of pressure ratio in gas turbine work & cycle efficiency


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*-Increasing pressure ratio(compressor size-stages) while fixing turbine inlet (firing rate) will cause turbine

power to increase, reach a maximum & after that it will drop, refer to the above figure.

11-Supercharging:

*-In this system large fan is installed up stream of gas turbine compressor intake to increase intake pressure.

The output power will increase by 20% but the fan required 1/4 of the gas turbine power, so the net increase in

power is 15%.

*-Due to the heat generated from the fan, supercharging method is more effective if it is used combined with

evaporative cooling system.

Fig(160) Super charging combined with evaporative cooling

12-Combined cycle gas turbine:

*-One of the most successful & widely used method in power plant engineering is to recover the exhaust gases

of the gas turbine in a heat recovery steam generator (HRSG), the generated steam will used either for steam

turbines or for heat process or combined.


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100-How Combined cycle is classified?

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*-Combined cycle has so many configuration, there are two main ways of classification which are are:

A-Classification depend on the cycle parameters:

1-Single shaft or two shafts

2-Single pressure or dual pressure or triple pressure

3-With Supplementary firing or without

4-With auxiliary boiler or with out

B-Classification depend on the process involved on the cycle:

1-Combined cycle (HRSG steam output is fed to steam turbine)

1-Cogeneration cycle (HRSG steam output is fed to a heat process)

2-Combi-cogeneration (HRSG steam output is fed to a steam turbines & heat process)

3-Combined cycle with supplementary firing (Fuel input after turbine exhaust- no fans are required)

4-Combined cycle with auxiliary burners (HRSG steam is superheated in auxiliary boiler)

101-What are the main Configurations of heat recovery steam generator?

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Fig(161) Principal of heat recovery steam generator

Fig(162) Types of heat recovery steam generator


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Fig(163) Heat recovery boiler with supplementary firing

Fig(164-a) Main parts of heat recovery steam generator(Horizontal Configuration-single pressure)


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Fig(164-b) Main parts of heat recovery steam generator(Horizontal-triple pressure type)

*-The following pictures summarize some of combined cycle configurations:

Fig(165) Cogeneration cycle Fig(166) Combined cycle


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Fig(167) Combined cycle –single pressure with Supplementary firing

Fig(168) Combi-cogeneration cycle


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Fig(169) Combined cycle –dual pressure with Fig(170) Cogeneration cycle with auxiliary boiler

Supplementary firing

Fig(171) Sankey diagram for combined cycle


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Fig (172) in combined cycle each gas turbine will have its own heat recovery unit

Fig (173) Triple pressure combined cycle with reheat


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13-Humid air Turbine cycle:

Fig (174) Humid air gas turbine cycle

*-In this cycle air & steam both are representing the working fluid, an intercooler and after cooler recover the

heat from compressor (reducing compressor work requirement) and transfer it to fee water. The heated feed

water and compressor discharge air are combined in the saturator (like steam drum in boiler) which produce a

mixture of steam & air (humid air), this mixture is heated into waste heat recovery unit before enter combustion

chamber.

*-Tests on this cycle shows that it has 4% higher efficiency than equivalent combined cycle.

14- Fuel selection considerations in gas turbines:

*-The products of combustion come in direct contact with turbine blading. This requires using fuels which has a

combustion products does not cause high-temperature corrosion or oxidation, erosion, and deposition of ash on

blades.

*-Preferred fuels are natural gas, and distillate oils. Most other liquid fuels require external treatment to remove

harmful vanadium and sodium. Vanadium pentoxide and sodium sulfate are the principal ash components

formed at higher temperatures. This ash adheres to blades and causes corrosion on the blades.


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Fig (175): Economic comparison of various power generation technologies


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APPENDIXAPPENDIXAPPENDIXAPPENDIX----AAAA

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MS6001B-G.E.


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*-SIEMENS V94.3A land Base Gas Turbine


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*-The World Largest Land Base Gas Turbine Build by SIEMENS:

SGT5-8000H


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*-Combined Axial &Centrifugal Compressor


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*-Rover-Jet1 gas turbine Vehicle


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*-Motorcycle power by gas turbine


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References

1- Power plant technology -M.M. ELWakil

2- Power Generation hand book -Philip Kiameh

3- Standard hand book of power plant engineering -Robert C. Elliott

4- Power plant engineering -Jeffrey M. Smith

5- The jet engine -Rolls Royce Limited

6- Gas turbine theory –H. Cohen

7- Gas turbine – Nuvo Pignone

8- thermodynamics – Yunus A. Cengel

9- Reactor fundamental -CANDU reactor

10-Combined cycle training –National Power

11-Combined cycle training – Innogy

12- Modern Power Plant Practice – P. Hampling

13- Wikipedia- the free encyclopedia

Gas turbine design and operation training course

Engineering

Transcript of Gas turbine design and operation training course