Compressor SelectionNov.13 2006

Thermodynamic calculationEngineering Co. utilize in house data from accumulated vendor information Customer need vendors basic data to performBasic thermodynamic formula with unit conversion Table-1. Parameter for Each Frame Excel spread sheet (Hand over separately)

Sample compressor selection2

Basic thermodynamic formula to be used

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Fundamental Formulas generally usedk -1 / k p = n-1/n Polytropic efficiency k-1 n-1 Td = (Pd /Ps ) n x Ts = (Pd /Ps ) k p x Ts n-1 n Zav R Ts [ (Pd /Ps) - 1 ] n -1 nm

(1)

(2)

H=

=

k-1 Zav R Ts k p [ (Pd /Ps) - 1 ] k -1 k p

= Zav R Ts (r

- 1) / m

(3)

4

k-1

where, r = Pd / Ps,

m=

k

p

(4)

From equation ( 2 ), p and Td p = k - 1 Log( Pd / Ps )

can be back calculated from operation data (5)

k Log( Td / Ts) Td = Ts x r Qd = Qs x r / r Head coefficient can be expressed H = 2 U/gm m

(6 (7)

(8)

D N where U = Ft/ Sec Impeller peripheral velocity ( 9 ) 60 x 12 D : Impeller diameter in Inch, N : Operating speed , rpm 5

Gas power GHP WF x H GHP = 33000 x p where WF is weight flow ( lb / min), From equation ( 1 ), v = Z R T / 12 x 12 P ft /lb 2 where R= 1545.32 /MW, T = = + 460 , P = psia = ( lb/ in ) R F 3 Volume Q (CFM = ft / min) can be expressed: Q = WF x v For multistage centrifugal compressor, operating speed N(rpm) can be approximately expressed: 1300 N= Av. D Total H s x 3

(10 )

( 11)

( 12 )

( 13 )

where s : Number of impellers , Av. D : Average impeller diameter in inch

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Table 1: DATUM DataTable-1: Parameter for each Frame( Value for MU & NH are by writer's experience) Frame 2 4 6 8 10 12Nom.Imp dia, inch

Rev. 1 Nov 2 2

1423.263 10830 10314 83.5 0.53 32000 54368 43.424 109.2

1627 9337 8892 83.5 0.54 43000 73057 50.4 126.7

1831.337 8040 7657 84 0.55 59000 100241 58.5 147.1

2036.372 6925 6595 84 0.55 79000 134221 67.894 170.7

2242.215 5965 5680 84.5 0.55 106000 180094 78.8 198.1

2448.996 5140 4895 84.5 0.55 143000 242957 91.459 229.9

2656.867 4430 4219 85 0.55 193000 327907 106.152 266.9 X

Max. MCS, rpm Max.100% spd Nominal NH, % Nominal MUNom. Flow, ACFM ,AM3/H

Case Rating, Radial psig (kg/cm2G)

Case Rating, Axial psig (kg/cm2G)

Case ID, inch , cm 350 ( 24.6) 400 (28.1) 600 (42.1) 800 ( 56.2) 1200 (84.3) X X X X 1795 (126.2) X X X X 2995 (210.5) X X X X 4995 (351.1) X X X X 7200 (506.2) X X X X 8500 (597.6) 10500 (738.2) X X X X 170 (11.9) 300 (21.1) 350 (24.6) 400 (28.1) X X 600 (42.1) 800 (56.2) 900 (63.2) X X Note: 1.Nominal value of MU is purely by writer's experience. 2. Nominal flow for double flow casing is double of each frame.

9.516 26470 25209 82 0.47 5400 9175 20.617 51.8

11.045 22800 21714 82 0.48 7200 12233 20.617 51.8

12.819 19650 18714 82 0.5 9800 16650 23.93 60.2

14.879 16930 16123 83 0.51 13000 22087 27.774 69.8

17.269 14580 13885 83 0.53 18000 30582 32.235 81.0

20.043 12570 11971 83 0.53 24000 40776 37.414 94.1

X X X X X X X X X X X X X X X X X X X X X X X X

X X X

X X

X X X

X X X X X X X X X X X X X X

X

X X

X X

X X

X X

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Manual CalculationManual Overall Selection( DATUM), Ft/Lbs unitProject number : Customer : Gas : Sour(NACE ) or Sweet gas : Date: By: Barometric pressure: Relative Humidity : Type of Driver: psia % Disch. pressure: psiaCase rating req'd per API(1.25 x Pd-psig)

Operating condition,Sect No

1

2

3

Operating condition,Sect No Leak Loss, HP ( See table * 2)

1

2

3

Ps-psia Ts- F( or F+460 R)MW( Sum of Mol % x Mol Wt of gas)o o

Heat loss(LO&SO), HP(See table *3) BHP=GHP+Heat Loss+Leak Loss D -inch, Imp. diameter from table(*1) MU-pressure coeff. from table(*1) s = Number of Impeller. N=(1300/D) x (H/ s x MU)1/2 , rpmMax. allowable N from table(*1) for the casing

R = 1545/MW Zs Zav= Zs+Zd / 2 Kav WF -Lb/Min or WF=( Nm /H )x MW/610 Svc=Zs RTs/144Ps Qs= Svc x WF, ACFM r = Pd/Ps m =(Kav-1/Kav)/NHNH assumed from table( * 1)3

Selected compressor model U = D N/12x60 , Ft/S: Pai=3.1416 Qs/N Flow Coeff. = 700 Qs/ ND3 MU from CIX curve (MUc) NH from CIX curve(NHc) H = MUc x U2 /g where g =32.14Total Head = H x s, Compare with H req'd

H

m req'd=ZavRTs(r -1)/m

GHP= WF x H /33000 NH Td = Ts x rm:

(Td below 380 F)

o

Qd = Qs rm / r

Remark: If no data of table-1,2 & 3 is available, Use NH= 0.8 for below Frame12, 0.83 below Frame 16, and 0.85 for others. Reasonable MU is in the range of 0.48 through 0.54 except for low head impeller.If low head, MU=0.43 is adequate Head per impeller is 8000 through 12000 Ft-Lbs/Lbs depend on MW. Never be more than 18000 Ft Critical speed(NC1 & NC2) has to be checked for adequate separation margin. Min. separation margin per API

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Sequence of CalculationFrom given Inlet (Ps, Ts, MW & WF) and Discharge condition( Pd), Obtain Head, GHP Speed N and Compressor model using Table 1 attached No inclusion of mechanical loss by bearing for Brake HP No inclusion of leak loss effect nor rotor dynamic

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Ps, Ts, MW, Pd, WF

Head, GHP

Calculate Weight Flow (WF) if not given Calculate Inlet volume Qs = Svc x WFwhere Svc= ZsRTs / 1444 Ps ACFM, WFLB/Min

Calculate H= Zav RTs(r m-1)/m ..FtWhere R= 1545.4/MW, r= Pd / Ps, Zav = Zs +Zd / 2 m= (Kav -1 /Kav) / NH,

GHP = WF H/ 33000 NHAssumed Value: Zs, Zav,

.HP

where 33000= 550 x 60 as 1 HP= 550Ft-lb/Sec Kav, and NH10

ContinuedAssume number of impeller s: Divide total Head by 8000 to 12000 as standard H 8000 Ft/ Impeller Calculate N (rpm)1300 x H N= s D av Where 0.48 to 0.53 corresponding to 800012000Ft/imp. Use 0.5 as standard. D av :Imp Dia by inch

Calculate Td = Ts x r m

R (460+ F)11

Excel Spread SheetSimple program is separately hand over to audience. Lets use this with sample selection

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Ps, Ts, MW, Pd, WF -----------> Head & GHP2 section or 2 casing 1st 2nd 0.511 1.301 88.8 203.4 45 113 573 1.377 214.4 7.61 46663 1715 15600 1 1.35 0.82 0.259 (k-1) / k / E Pd /Ps Td / Ts deg F ACFM ft Ts * (r^m)-460 assuming Zd = 1 0.3162 2.414 1.321 297.1 8535 40 104 564 2.845 427.3 6.25 38013 1397 6650 1 1.35 0.8 0.259 0.3241 2.101 1.272 257.4 4025 117,052 6,193 4,618 Total 235,326 13,687 10,206

Ps Ps Ts Ts Ts Pd Pd MW WF WF Q Zs k

M Pa G psia degC deg F deg R M Pa G psia

Ts+460

kg/h lb/min ACFM

efficiency: E (k-1)/k m r r^m Td Qd H

Z*(1545.4/MW)*(460+Ts)*(-1+r 118,274 WF * H / 33000 / E 7,494 5,588

GHP hp kw

K-value (approx) H2, N2, Air : 1.4 CH4, NH3, CO2 : 1.3 C2H4:1.24, C2H2: 1.23, C2H6 : 1.19, C3H6:1.15, C3H8: 1.13

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A Compressor Operating ConditionWeight Flow, kg/s ( Lb/Min) Inlet Pressure, kPa ( Psia) Inlet Temperature, 0C ( 0R) Relative Molecular Weight Discharge Pressure, kPa (Psia) 3.025 (400) 118 (17.1) 34.2 ( 553.5) 38.8 377(54.7)14

A Compressor selection resultQs= 3580ACFM, s = 27815/8000=3.5 Operating speed N(rpm)When s=3, N =1300/11.045 (27815/ 0.5x 3)0.5= 16027 rpm When s=4, N =1300/11.045 (27815/ 0.5x 4)0.5= 13880rpm

Select D4R Frame, D=11.045 Either 3 or 4 Impeller

H= 27815Ft , GHP=411 HP , Assume 420BHP with 2% loss

Conclusion: Either D4R3S at 16000rpm with 420BHP or D4R4S at 13900rpm DRs program for precise selection is D4R4S with 436BHP at 13581rpm. Our Nazri will present later.15

B Compressor operating conditionWeight Flow, kg/s, (Lb/Min) Inlet Pressure, kPa A (Psia) Inlet Temperature, 0C (0 R) Relative Molecular Weight Discharge Pressure, kPa (Psia) 6.898 (911.4) 2,912(422.3) 34.6 ( (554.3) 19.91 9,513 (1379.8)

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B Compressor selection resultQs= 645ACFM Smallest compressor D2R is

good for Max. flow of 5400ACFM, Min.1000ACFM resulting no suitable quote by centrifugal unit H= 60441Ft, GHP= 2038HP with centrifugal. Better go to Recip solution!

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C Compressor-2 Section with inter coolerDescriptionWeight Flow, kg/s (Lb/Min)

Stage 1 21.873(2890) 273(39.6) 33.5 24.8 1239(179.7)

Stage 2 21.873(2890) 1170(169.7) 60 24.8 5294(767.8)18

Inlet Pressure, kPa( Psia) Inlet Temperature, 0C (0R) Relative Molecular Weight Dis. Pressure, kPa ( Psia)

Sample calculationQs=17464ACFM H=61631FT S= 7.7 at 8000Ft/imp or 5 at 12000Ft/imp GHP=6510

D12R

Qs=4427ACFM H=67083Ft S= 8.4 at 8000Ft/imp or 6 at 12000Ft/imp GHP=7261

WF= 2893Lb/Min, Total required impeller is 16 at 8000Ft/imp or 11at 12000Ft/imp. Try to squize to 10 imp/case or 2 casing Total GHP= 13771HP, Total BHP 14,050 BHP with 2% loss D12R10B, D=20.043 , N= (1300/20.043)(127814/10x 0.52)0.5= 10245rpm D14R10B, D=23.263 , N= (1300/23.263)(127814/10x 0.52)0.5= 8792rpm D16R10B D=27.0 , N= (1300/27)(127814/10x 0.52)0.5= 7575rpm19

ContinuedCompressor selection either D12R10B,D14R10B or D16R10B is depend on rotor dynamic. DRs precise program resulted to D16R10B at 14628BHP at 8044rpm. Refer Nazri presentation Note: More than 10 impeller/case is not recommended due to Rotor dynamic problem.

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Description Weight Flow, kg/s (wet) Inlet Pressure, kPa Inlet Temperature, 0C Relative Molecular Weight Discharge Pressure, kPa

Stage 1 41.13 131 -36 44.1 537

Side stream inlet 1 12.25 537 4.2 44.1 1219

Side stream inlet 2 31.55 1219 35 44.1 219721

Selection by DRs ProgramGhazali Nazri presentation

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