Estimating gas turbine performance

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Estimating Gas Turbine Performance

The following is a method for estimating gas turbine performance using
performance curves and site data (i.e., elevation, ambient temperature, inlet and
exhaust pressure drops, and the type of fuel). Both full load and part load
performance calculations are described and illustrated. Typical examples are
provided for package power plants.
Performance curves are based on the ISO standard (59°F, 60% relative humidity
and 14.7 psia). Theses curves do not include the water or steam injection for NOx
control due to the many different NOx levels offered. However, the effect of a
known water or steam flow can be calculated separately per the dilutent effects
curves.
This procedure should be used only for the approximation of performance at site
conditions and not for performance guarantees. Performance guarantees for this
proposal are shown in the “Performance Specifications” section. The
performance curves included are to illustrate the calculation
procedure and do not reflect current ratings. Performance curves
applicable to the equipment offered in this proposal are listed under “Turbine and
Generator Performance Curves” in the “Engineering Data” Section.
Nomenclature
D = differential; i.e. DP is pressure drop
fa = inlet DP factor for output
fb = exhaust DP factor for output
fc = compressor inlet temperature factor for output
fd = compressor inlet temperature factor for exhaust flow
fe = compressor inlet temperature factor for heat rate
ff = inlet DP factor for heat rate
fg = exhaust DP factor for heat rate
fh = humidity factor for output
fi = humidity factor for heat rate
HC = heat consumption (fuel consumption in Btu/h)
HR = heat rate (Btu/kWh)
KW = power output (kW)
P = barometric pressure (psia)
Pc = effective pressure (psia) at the inlet flange of a package power plant
Tx = exhaust gas temperature (°F)

Reference GTS–111D page 1

Wx = exhaust flow (lb/h)
EFF = thermal efficiency (%)
(LHV) = based on fuel lower heating value
Subscripts s, i, o
s denotes at site conditions
i denotes at ISO conditions
o denotes at site altitude, actual inlet and exhaust DP’s, and compressor
inlet conditions of 59°F @ 60% RH.

I. Full Load Performance

A. Method
1. Output (KWs) = (KWi) x (Ps/14.7) x fa x fb x fc x fh
2. Heat Rate (HRs) = (HRi) x fe x ff x fg x fi
Note: Altitude has no effect on heat rate
3. Heat Consumption (HCs) = (KWs) x (HRs)
4. Exhaust Temperature (Tx) Read from appropriate curve. Add
temperature increase for additional inlet and/or exhaust pressure
drops.
5 Exhaust Flow (Wxs) = (Wxi) x (Pc/14.7) x fd
Where Pc = Ps – (0.0361 x additional DP (inches of H2O) at inlet)
B. Notes
1. Round off calculations as follows:
Output – To nearest 10 kW or maximum of 4 significant figures
Heat Rate – To nearest 10 Btu/kWh
Heat Consumption – To nearest 0.1 x 106 Btu/h or maximum of 4
significant figures
Exhaust Temperature – To nearest degree F
Exhaust Flow – To four significant figures (lb/h)
2. The ratio Ps/14.7 can be read directly from the altitude correction
curve 416HA662
C. Sample Full Load Calculation
Package Power Plant – MS7001(EA) Simple Cycle Model PG7111(EA)
with an air–cooled generator.


Site Conditions:
Altitude = 600 ft
Barometric Pressure Ps = 14.39 psia (from Curve
416HA662)
Compressor Inlet Temperature = 90°F
Inlet DP = 2.5’ H2O (included in rating)
Exhaust DP = 10” H2O (5.5” H2O is included
in rating)
Fuel = Distillate Oi1
Mode = Base Load

1. Design Conditions (ISO) from Curve 499HA733
Output KWi = 82100 kW
Heat Rate HRi = 10560 Btu/kWh (LHV)
Exhaust Flow Wxi = 2358 x 103 lb/h

2. Calculation of factors.
The ratings for the package power plant include a standard inlet and exhaust
pressure drop as stated with the ratings. Therefore the pressure drops used
to calculate fa, fb, ff, fg, Pc, and exhaust temperature increase are the pressure
drops in excess of the standard pressure drops.
The resulting performance decrease effect of additional pressure drop is
subtracted from unity to obtain the output multiplication factor. The heat rate
percentage effect is added to unity to obtain the heat rate multiplier for
additional pressure drops.

Output : f a + 1.0
ǒ
f b + 1.0 * 0.42 x 4.5
4
Ǔ 1 + 0.9953
100
(curve 499HA733 with additional 4.5” H2 O)
f c + 0.890 (from Curve 499HA734)
f h + 0.9982 (from Curve 498HA697)

Heat Rate : f e + 1.025 (from Curve 499HA734)
f f + 1.0
ǒ
f g + 1.0 ) 0.42 x 4.5
4
Ǔ 1 + 1.0047
100
(curve 499HA733 with additional 4.5” H2 O)
f i + 1.0048 (from Curve 498HA697)


Exhaust Flow : P c + 14.39 psia * 0 + 14.39 psia
f d + 0.930 (from Curve 499HA734)

3. Calculation of Full Load Conditions at Site:

Output KW s + 82100 x 14.39 x 1.0 x 0.9953 x 0.890 x 0.9982
14.7
+ 71063 or 71060kW
Heat Rate HR s + 10560 x 1.025 x 1.0 x 1.0047 x 1.0048
+ 10927 or 10930 BtuńkWh (LHV)

Heat Consumption HC s + 71060 x 10930
+ 776.7 x 10 6 Btuńh (LHV)

Exhaust temperature is calculated by adding the temperature increase
due to pressure drops to the value read from Curve 499HA734:

T x + 1006 ) 1.9 (0 ) 4.5) F
4

T x + 1008.1 or 1008 F

Exhaust Flow + 2358 x 10 3 x 14.39 x .930
14.7
+ 2146.7 x 10 3 or 2147 x 10 3 Ibńh

II. Part Load Performance

Part load output, heat rate and heat consumption are calculated in a similar
manner as base load using the part load heat consumption curve. Before using the
output % off the heat consumption curve, all part load performance must be
referenced to 59°F site performance kWo.
A. Method
1. At site barometric pressure with site inlet and exhaust pressure drops
and at 59°F compressor inlet temperature, calculate the following
base load performance parameters:
Output, kWo
Heat rate, HRo
Heat consumption, HCo
This data then becomes the corrected values on which to base the part
load calculations.
2. Calculate percentage of load:


% load = required load/kWo
3. From the applicable performance curve, at the percent of load
calculated from (2) above and at the compressor inlet temperature,
read the percent of design heat consumption.
HCs = HCo x % design heat consumption.
4. Heat rate at required load:
HRs = HCs ÷ kWs
5. Exhaust flow and temperature are calculated in an analogous manner
as base load using corrected design outputs as shown above, and the
Effects of Modulated Inlet Guide Vanes Curve at the appropriate
ambient. The extreme right hand point of each ambient curve on the
Modulated Inlet Guide Vane Curve represents the full open IGV
position, the knee point in each curve represents the closed IGV
position, Note that this curve is for combined cycle machines only.
Simple cycle machines, which are not normally concerned with part
load Exhaust conditions, operated on a different schedule and can not
be calculated using this curve.
B. Sample Part Load Calculation
The following sample part load calculations are for the MS7001(EA) simple
cycle package power plant used previously.
Site conditions:
Altitude = 600 ft
Barometric pressure = 14.39 psia
Compressor inlet temperature = 90°F
Relative Humidity = 60%RH
Inlet DP = 2.5” H2O (included in
rating)
Exhaust DP = 10” H2O (5.5” H2O is
included in rating)
Fuel = Distillate Oil
Load required = 75 percent base load

1. Calculation of site performance at full load and 59°F at 60%RH:
KWo = KWi x (14.39/14.7) x fa x fb
KWo = 821000 x 0.9789 x 1.0 x 0.9953 = 79990 kW
HRo = HRi x ff x fg
HRo = 10560 x 1.0 x 1.0047 = 10610 Btu/kWh (LHV)
HCo = KWo x HRo


HCo = 79990 x 10610 = 848.7 x 106 Btu/h (LHV)
2. Calculation of site performance for 90°F @ 60%RH:
Site output (base load) = KWo x fc x fh
= 79990 x 0.891 x 0.9983 = 71150 kW
At 75% base load, required load = 71150 x 0.75 = 53360 kW
% load = 53360/79990 = 66.7%

3. From Curve 499HA733 at 66.7% design load and 90°F, % design heat
consumption = 71%

Part load, site heat consumption, HCs = HCo x % design heat rate
HCs = 848.7 x .71 = 602.6 x 106 Btu/h (LHV)

4. Site heat rate HRs = HCs ÷ kWs
HRs = 602.6 x 106 ÷ 53360 = 11290 x Btu/kWh (LHV)
5. Entering the Modulated Inlet Guide Vane Effects Curve (516HA129)
at the 66.7% output calculated in Step 2 and, for the 90°F ambient
curve;
Exh Temp. = 990°F
Wexh % design = 75.5%

Wexh = Wi x % design
Wexh = 2358 x .755 = 1780 x 103 lb/h

Performance With Water or Steam Injection

The amount of steam or water injection required to meet a given NOx emission
level is not available from a curve because of the many variables impacting this
value. In fact, the exact flow is typically not finalized until the field Emissions
Compliance Testing. However, given a specific flow value, the resulting effect on
output and Heat Rate can be determined using the Injection Effects Curves.
For example, taking the “dry” Output and Heat Rate Performance calculated
from Example I and, assuming GE has reported (for the specific conditons given)
an estimated steam flow to meet 65 ppmvd @ 15% O2 NOx of 42590 lb/h (11.83
pps); The resulting output and Heat Rate would be:


KW = 71060 x (1 + 0.059) (from curve 499HA899A)
= 75250 KW

HR = 10930 x (1 – .0275) (from curve 499HA900A)
= 10630 Btu/Kw–h (LHV)


SI and Metric Units Conversion

The following is a list of conversion factors most
commonly used for gas turbine performance calculations.
Conversion Factors
To Convert To Multiply By
atm kg/cm2 1.0333
atm lb/in2 14.7
bars atm 0.9869
bars lb/in2 14.5
Btu/h kcal/h 0.2520
Btu/h kJ/h 1.0548
Btu/hph kJ/kWh 1.4148
Btu/lb kJ/kg 2.326
°F °R °F + 459.7
°C °F (°C x 9/5) + 32
°C °K °C + 273.2
ft3/min l/s 0.4720
ft3/min m3/min 0.02832
gal/mln l/s 0.06308
in. of mercury kg/cm2 0.03453
in. of water
(at 4°C) kg/cm2 0.00254
in. of water
(at 4°C) lb/in2 0.03613
J Btu 9.478 x 10–4
kg lb 2.205
kg/cm2 lb/in2 14.22
kg/m3 lb/ft3 0.06243
kW hp 1.341
lb/in2 Pa 6894.8
l/min ft3/s 5.886 x 10–4
l/min gal/s 0.004403
scf Nm3 0.0268
W Btu/h 3.4129


GENERAL ELECTRIC MODEL PG7111(EA) GAS TURBINE
ESTIMATED PERFORMANCE – CONFIGURATION: NATURAL GAS & DISTILLATE
Compressor Inlet Conditions 59 F (15.0 C), 60% Rel. Humidity
Atmospheric Pressure 14.7 psia (1.013 bar)

FUEL NATURAL GAS DISTILLATE
DESIGN OUTPUT kW 83500 82100
DESIGN HEAT RATE (LHV) Btu (kJ)/kWh 10480 (11060) 10560 (11140)
DESIGN HEAT CONS (LHV) X10–6 Btu (kJ)/h 875.1 (923.5) 867.0 (914.6)
DESIGN EXHAUST FLOW X10–3 lb/h (kg)/h 2351 (1066) 2358 (1070)
MODE: BASE LOAD PPB 061088

NOTES:
1. Altitude correction on curve 416HA662 REV A
2. Ambient temperature correction on curve 499HA734 REV A
3. Effect of modulated IGV’s on exhaust flow and temp. on curve 516HA129
4. Air cooled generator 7A6
5. Humidity correction on curve 498HA697 REV B – all performance
calculated with specific humidity of .0064 or less so as not to
exceed 100% relative humidity.
6. Plant performance is measured at the generator terminals and includes
allowances for excitation power, shaft driven auxiliaries, and
2.5 in. H2O (6.2 mbar) inlet and 5.5 in. H2O (13.7 mbar) exhaust
pressure drops.
7. Additional pressure drop effects:
%Effect on Effect on
Output Heat Rate Exhaust Temp.
4 in. H2O (10.0 mbar) inlet –1.42 0.45 1.9 F (1.1 C)
4 in. H2O (10.0 mbar) exhaust –0.42 0.42 1.9 F (1.1 C)

130
0F
HEAT CONSUMPTION – PERCENT DESIGN

120
59 F
110

100
120 F
90
80

70

60
50

40

30
20

10
0 10 20 30 40 50 60 70 80 90 100 110 120 130
GENERATOR OUTPUT – PERCENT DESIGN

DATE: 10/17/89 499HA733
DA JAQUEWAY REV A


Effect of Compressor Inlet Temperature on
Output, Heat Rate, Heat Consumption, Exhaust Flow
And Exhaust Temperature at 100% Speed

FUEL: NATURAL GAS & DISTILLATE OIL
DESIGN VALUES ON CURVE 499HA733 REV A
DESIGN MODE: BASE LOAD
EXHAUST TEMPERATURE (DEG. F)

1040
1030
1020
1010
1000
990
980
970
960
950
940
130

125

120

115
PERCENT DESIGN

110

105 HEAT RATE

100

95

90
EXHAUST
FLOW
85
HEAT CONS.
80
OUTPUT
75

70
0 10 20 30 40 50 60 70 80 90 100 110 120
COMPRESSOR INLET TEMPERATURE (DEG. F)
DATE 10/17/89 499HA734
DA JAQUEWAY REV A



Effect of Modulated Inlet Guide Vanes on Exhaust Flow and Temperature
As a Function of Output and Compressor Inlet Temperature.

FUEL: NATURAL GAS & DISTILLATE OIL
DESIGN VALUES ON CURVE 499HA733 REV A
DESIGN MODE: BASE LOAD
1100
EXHAUST TEMPERATURE (DEG. F)

1050
1000
950
900
0F
850
30 F
800
59 F
750
90 F
700
120 F
650
600
550
500
EXHAUST FLOW – PERCENT DESIGN

115
110
105
100
95
90
0F
85
30 F
80
59 F
75
90 F
70
120 F
65
0 10 20 30 40 50 60 70 80 90 100 110 120 130
GENERATOR OUTPUT – PERCENT
DATE 10/17/89 516HA129
DA JAQUEWAY


GENERAL ELECTRIC GAS TURBINE
ALTITUDE CORRECTION FACTOR
ALTITUDE VS ATMOSPHERIC PRESSURE
AND
ALTITUDE VS CORRECTION FACTOR
FOR GAS TURBINE OUTPUT AND FUEL CONSUMPTION

NOTES:
1. Heat Rate and Thermal Efficiency are not affected by altitude.
2. Correction Factor = P(atm)/14.7

15.5 1

15 0.95
CORRECTION FACTOR

14.5 0.9

14 0.85

13.5 0.8

13 0.75

12.5 0.7
ATMOSPHERIC PRESSURE

12 0.65

11.5 0.6

11 0.55

10.5 0.5
0 1 2 3 4 5 6 7 8 9
ALTITUDE – THOUSAND FEET
4/24/90 416HA662
F.J. BROOKS REV A


GENERAL ELECTRIC MS6001, MS7001 AND MS9001 GAS TURBINES
CORRECTIONS TO OUTPUT AND HEAT RATE
FOR NON–ISO SPECIFIC HUMIDITY CONDITIONS
For operation at base load on exhaust
temperature control curve

1.01

1.009
ISO SPECIFIC HUMIDITY
0.0064 lb. water vapor/lb. dry air
1.008

1.007

1.006
HEAT RATE
1.005

1.004
CORRECTION FACTOR

1.003

1.002

1.001

1

0.999
POWER OUTPUT
0.998

0.997

0.996

0.995

0.994
0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.03
SPECIFIC HUMIDITY (lb. water vapor/lb. dry air) 5

10/10/89 498HA697
DA JAQUEWAY REV B


GE MODEL PG7001(EA) GAS TURBINE
EFFECT OF STEAM INJECTION ON OUTPUT
BASE LOAD – NATURAL GAS / DISTILLATE

12

11
100F

10

9
PERCENT INCREASE IN OUTPUT

59F
8
45F

7
0F

6

5

4

3

2

CURVE 499HA899A
1
KH CONWAY 4/14/89

0
0 2 4 6 8 10 12 14 16 18 20
STEAM INJECTION – LB/S


GE MODEL PG7001(EA) GAS TURBINE
EFFECT OF STEAM INJECTION ON HEAT RATE
BASE LOAD – NATURAL GAS / DISTILLATE

6.0

5.5

5.0
100F
4.5
PERCENT DECREASE IN HEAT RATE

4.0
59F
3.5 45F

3.0 0F

2.5

2.0

1.5

1.0

CURVE 499HA900A
0.5
KH CONWAY 4/14/89

0.
0 2 4 6 8 10 12 14 16 18 20
STEAM INJECTION – LB/S


Estimating gas turbine performance

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