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Transcript of Steam
April 21, 2023 1
Circulation System
April 21, 2023 2
Presentation Plan• Water and Steam circuit diagram• Economiser• Super Heater• De-superheater /Attemperator• Re-heater• IBR• Super Critical Boiler
April 21, 2023 3
FROM BFP DISCHARGE
DRUM
200MW WATER CIRCUIT
Bank I
Bank II
Economizer
April 21, 2023 4
BOTTOM RNG HDR& Z-PANEL 1ST PASS W.W
1ST PASS W.W O/L HDRS ROOF I/L HEADER
2ND PASS UPPER C-HDR 2nd PASS LOWER C-HDRS
LTSH I/L HEADER LTSH O/L HEADER
D.P.I/L HEADER D.P.O/L HEADER
S.H. HEADER R.H.HEADER
2ND PASS ROOF O/L HDR(REAR ECONOMISER
M.S
H.R.HC.R.H
FROM F.R.S
April 21, 2023 5
EconomiserBoiler Economiser are feed-water heaters in which the heat from waste gases is recovered to raise the temperature of feed-water supplied to the boiler.
April 21, 2023 6
Economiser• The economizer preheats the feed water by utilizing the residual heat of the
flue gas.• It reduces the exhaust gas temperature and saves the fuel.• Modern power plants use steel-tube-type economizers.• Design Configuration: divided into several sections : 0.6 – 0.8 m gap
April 21, 2023 7
Tube Bank Arrangement
April 21, 2023 8
Finned Economizers
April 21, 2023 9
Thermal Parameters of Economizer
• Out side diameter : 25 – 38 mm.• Tube thickness: 3 – 5 mm• The water flow velocity : 600 – 800 kg/m2 s• The waterside resistance should not exceed 5 – 8 %.
Of drum pressure.• Flue gas velocity : 7 – 13 m/s.
April 21, 2023 10
6oC raise in feed water temperature, by economizers corresponds to a
1% saving in fuel consumption
Advantages of Economiser
220 C reduction in flue gas temperature increases boiler
efficiency by 1%
April 21, 2023 11
Location and Arrangement
• Ahead of air-heaters • Following the primary super-heater or re-heater • Counter-flow arrangement • Horizontal placement (facilitate draining)• Supported to prevent sagging, undue deflection and
expansion .• Stop valve and non-return valve incorporated to ensure
recirculation in case of no feed-flow• Ash hopper below as flue gas takes a turn
April 21, 2023 12
Type of Construction• Plain Tube : Several banks of tubes with either-in-line or
staggered type formation. Staggered arrangement induces more turbulence than the in-line arrangement. This gives a higher rate of heat transfer and requires less surface but at the expense of higher draught loss.
• Welded Fin-tube : Fin welded design is used for improving the heat transfer.
April 21, 2023 13
Types of Super Heaters
• Pendant type
• Horizontal type
• Radiant Superheater
• Convection
Superheater
• Combined Superheater
April 21, 2023 14
SUPER HEATER• Water is heated to raise steam to higher temperature
• Arranged in 3 stages
LTSH located above economiser.
Radiant pendent type above furnace.
Convective final super heater above furnace
in flue gas path
April 21, 2023 15
Super heaters
• Super heater heats the high-pressure steam from its saturation temperature to a higher specified temperature.
• Super heaters are often divided into more than one stage.• The enthalpy rise of steam in a given section should not exceed
– 250 – 420 kJ/kg for High pressure. – < 280 kJ/kg for medium pressure. – < 170 kJ/kg for low pressure.
April 21, 2023 16
Transfer of Energy
Hot Flue Gas
Thermal Structure SH
Steam
Convection &Radiation HT
Convection HT
Drop in Enthalpyof Flue Gas
Rise in Enthalpy ofSteam
Mechanism of Heat Transfer
Source/Supply Thermal Structure Sink /Demand
April 21, 2023 17
Mechanism of Heat Transfer :
• Rate of heat transfer from hot gas to cold steam is proportional to:
• Surface area of heat transfer• Mean Temperature difference between Hot Gas and Cold
Steam.
Thot gas,in
Tcold steam,in
Tcold gas,out
T hot steam,out
April 21, 2023 18
Thot gas,in
Tcold steam,in
Tcold gas,out
Thot steam,out
Thot gas,in
Tcold steam,in
Tcold gas,out
T hot steam,out
April 21, 2023 19
Platen Superheater• Platen Superheater : Flat panels
of tubes located in the upper part of the furnace, where the gas temperature is high.
• The tubes of the platen SH receive very high radiation as well as a heavy dust burden.
• Mechanism of HT : High Radiation & Low convection
• Thermal Structure:
– No. of platens
– No. of tubes in a platen
– Dia of a tube
– Length of a tube
April 21, 2023 20
Geometry of Thermal Structure : Platen SH
• The outer diameter of platen SH is in the range of 32 – 42 mm.
• The platens are usually widely spaced, S1 = 500 – 900 mm.
• The tubes within a platen are closely spaced, S2/d = 1.1.
• The number of parallel tubes in a platen is in the range of 15 – 35.
• Design Constraints: Max. allowable steam flow rates.
April 21, 2023 21
Convective Superheater (Pendant)
• Convective super heaters are vertical type (Pendant ) or horizontal types.
• The Pendant SH is always arranged in the horizontal crossover duct.
• Pendant SH tubes are widely spaced due to high temperature and ash is soft.
• Transverse pitch : S1/d > 4.5
• Longitudinal pitch : S2/d > 3.5.
• The outside tube diameter : 32 – 51mm• Tube thickness : 3 – 7mmS1
S2
April 21, 2023 22
Convective Superheater (Horizontal)• The horizontal SH are located in the back pass.• The tubes are arranged in the in-line configuration.• The outer diameter of the tube is 32 – 51 mm.• The tube thickness of the tube is 3 – 7 mm.• The transverse pitch : S1/d = 2 – 3.• The longitudinal pitch :S2/d = 1.6 – 2.5.• The tubes are arranged in multiple parallel sets.• The desired velocity depends on the type of SH and operating steam
pressures.• The outside tube diameter : 32 – 51mm• Tube thickness : 3 – 7mm
S1
S2
April 21, 2023 23
April 21, 2023 24
Superheater Temperature Control
• Basically the control of temperature is to protect the superheater by preventing the metal temperatures reaching a dangerously high level reducing mechanical strength and leading to failure. Water flowing through a tube conducts heat away much more effectively than steam due to its higher specific heat capacity. This means that tubes carrying water have a metal temperature much closer to the fluid passing through it.
• For superheat temperatures alloys of chrome molybdenum steels are used (upto 560oC), difficulties in welding means that there use is restricted to only within the highest temperature zone and a transition piece fitted to connect to remaining mild steel tubing.
• Superheat temperature control is therefore fitted to ensure superheat temperature does not exceed design limits.
April 21, 2023 25
Locating the desuperheater• The preferred location of
desuperheater, especially for temperature above 450 deg C is between sections of superheater. The steam is first passed through a primary superheater where it is raised to intermediate temperature. It is then passed through the desuperheater and its temperature reduction is controlled so that, after continuing through the secondary or final stage of the superheater, the required constant conditions are maintained at the outlet.
April 21, 2023 26
Reheater
• Purpose: Re-heat the steam from HP turbine to 540 deg composed of
CRH header HRH header
Reheater section arranged above goose neck.
Reheating• The optimal way of increasing the steam temperature but not increase
the moisture content in the exiting vapour is to reheat the vapour after it exists the HP turbine and redirect this steam into IP or LP turbine.
April 21, 2023 27
April 21, 2023 28
Procedure to Determine Optimum Reheat Pressure
• Calculate the efficiency of Rankine cycle, Rankine.
• Calculate mean effective temperature of heat addition, Tm,in using
• Find out pressure corresponding to Tm,in and entropy at HP turbine inlet.
• Add reheating at this pressure and calculate efficiency of the Reheat Cycle.
• Repeat above steps for few iterations.
inm
cCarnotEqRankine T
T
,. 1
April 21, 2023 29
Re-heater
• The pressure drop inside re-heater tubes has an important adverse effect on the efficiency of turbine.
• Pressure drop through the re-heater should be kept as low as possible.• The tube diameter : 42 – 60mm.• The design is similar to convective super-heaters.• Overall Heat Transfer Coefficient : 90 – 110 W/m2 K.• The arrangement and construction of a re-heater is similar to that of a super-heater. In large
modern boiler plant, the reheat sections are mixed equally with super-heater sections.
April 21, 2023 30
Safety Valves
Device attached to a boiler for automatically relieving the pressure of steam before it becomes great enough to cause bursting. The common spring-loaded type is held closed by a spring designed to open the valve when the internal pressure reaches a point in excess of the calculated safe load of the boiler. Safety valves are installed on boilers according to strict safety norms and IBR recommendation
April 21, 2023 31
Safety Valve Settings of a Typical 200 MW Boiler
Locacation Set Pressure (Kg/sq cm
Reliving Capacity T/Hr
Drum 175.8 177.1
179.3 180.6
181.1 182.5
Super Heater
163.3 154.0
Re-heater –inlet
45.0
45.5
46.3
Re-heater outlet
42.70
April 21, 2023 32
Indian Boiler Regulations• History• Scope (cover regulations on):
– Electric-Resistance-Welded Steel Boiler And Super-Heater Tubes
– Boiler Tubes Subject To External Pressure – The Working Pressure To Be Allowed On Various Parts
Of Boilers – Welded And Seamless Forged Drums For Water Tube
Boilers And Super Heaters – Requisite Mountings, Fittings and Auxiliaries
April 21, 2023 33
Indian Boiler Regulations (Continued)
– Boiler And Super Heater Tubes, Headers And Other Pressure Parts Tubes
– Steam-Pipes And Fittings – Registration Of Boilers And Inspection Of Boilers – Safety Of Persons Inside Boilers – Qualification Tests For Welders Engaged In
Welding Of Boilers – Feed Water For Boiler
April 21, 2023 34
Why supercritical pressure
Increasing the pressure will mean increase in saturation temperature at which steam evaporates thus increasing the average temperature of heat addition.
A Boiler operating at a pressure above critical point is called ‘SUPERCRITICAL BOILER’
A point where boiling water and dry saturated lines meet so that associated latent heat is zero, this point is called Critical Point.
April 21, 2023 35
Critical condition
Definition “CRITICAL” is a thermodynamic expression
describing the state of a substance beyond which there is no clear distinction between the liquid and gaseous phase.
• The critical pressure & temperature for water are • Pressure = 225.56 Kg / cm2• Temperature = 374.15 C
April 21, 2023 36
T S DIAGRAM
Boilin
g W
ater
Dry Saturated Steam
Entropy KJ / Kg K
Tem
pera
ture
( 0
C )
-2730
24’0c
A
B C
D
E
F
OUTPUT INCREASEBasic Rankine Cycle
April 21, 2023 37
256 Kg/cm2
0
100
200
300
400
500
600 540’C568’C
ENTROPY
TEMP
SUPER CRITICAL BOILER CYCLE WITH SH,
RH & Regeneration of SIPAT 3 x 660 MW
Steam flow :2225 T/HrSteam temp : 540 ‘cSteam Pres : 256 kg/cm2RH pre : 51.6 Kg/cm2RH Temp : 568’cFeed water Temp : 291’c
April 21, 2023 38
Supercritical boiler
• Supercritical pressure boiler has no drum and heat absorbing surface being, in effect, one continuous tube, hence called
‘once through Supercritical pressure boilers.’• The water in boiler is pressurized by Boiler Feed Pump, sensible
heat is added in feed heaters, economizer and furnace tubes, until water attains saturation temperature and flashes instantaneously to dry saturated steam and super heating commences.
April 21, 2023 39
Pressure Parts Material
SA210C, T12, T23ReheaterTube Final
Section
Economizer Tube SA210C
Spiral SA213T22 EvaporatorTube/Water Wall
Vertical SA213T22
Primary
SA213T23, T91
Secondary
SA213T12, T23, T91SuperheaterTube
Final SA213T23, T91, T92
Primary
SA213T23, T91 SUPER304H
Separator SA302CSH outlet SA335P91
Header RH outlet SA335P91
SIPAT
500 MW PlantMaterial Oxidation Criteria,
℃
SA-210C 454
SA-213T2 482
SA-213T12 552
SA-213T22 593
SA-213T23 593
SA-213T91 649
SA-T92 649
SUPER304H 760
April 21, 2023 40
THANK YOU