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©Siemens Power Generation 2003. All Rights Reserved

Design of a Gas turbine combustion system Torsten Strand [email protected]

2/9/2006

Power Generation

1

Content

©Siemens Power Generation 2003. All Rights Reserved

z The design requirements, criteria and targets z The overall design process z The gas turbine cycle: Excel calculations z Burner and cooling mass flows: Design calculations z Burner type: lean premixed, diffusion flame or something in between z Combustor heat balance, choice of combustor design: Excel calculations z The component designs z burners z combustor : Excel calculations z fuel system : Excel calculations z Ignition and supervision systems z Operation z Start up z Part load 2/9/2006

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Assumptions

©Siemens Power Generation 2003. All Rights Reserved

z We are going to design a new gas turbine with the shaft power of 35MW for a market consisting of z 60% compressor drivers for pipe line compressors z 40% industrial cogeneration z The first customer segment want a very reliable and robust simple cycle unit for pumping of gas from desolated gas fields in z Siberia ( 0 to -50°C) z Iranian mountains (-20 to +45°C, low ambient pressure) z Saudi Arabian deserts (+10 to +50°C) z Efficiency and emissions are not of prime interest z Fuel is natural gas z The second customer type want an efficient, but still very reliable gas turbine with low emissions and suitable for steam production in waste heat recovery boilers for industries, mainly in the western world. Fuel is natural gas or industrial off gases. 2/9/2006

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Case 1 Gas Turbine in Simple Cycle 63.6 % losses Gas Turbine

©Siemens Power Generation 2003. All Rights Reserved

36.4 % electricity

100 % fuel Pgt Pst Paux Pnet Heat duty Qfired

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44.30 0 0.10 44.20 0 121.4

MW MW MW MW MJ/s MJ/s

Alfa ∞ --Net electrical Powerefficiency Generation 36.4 % Net total efficiency 36.4 %

4

Case 2 Gas Turbine in Cogeneration Cycle 12 % losses

©Siemens Power Generation 2003. All Rights Reserved

1-pressure HRSG

52.2 % process heat

Gas Turbine 35.9 % electricity

100 % fuel

2/9/2006

Pgt Pst Paux Pnet Heat duty Qfired Alfa NetPower electrical efficiency Generation Net total efficiency

43.82 0 0.23 43.59 63.4 121.4

MW MW MW MW MJ/s MJ/s

0.69 --35.9 % 5 88.1 %

Case 3 Gas Turbine in Combined Cycle Steam Turbine (condensing) 12 % losses 520 deg C

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2-pressure HRSG 31 deg C

Gas Turbine

100 % fuel

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Alfa Net electrical efficiency Net total efficiency

31 deg C 15 deg C

27 deg C 35 % losses

35.9 % electricity Pgt Pst Paux Pnet Heat duty Qfired

16.8 % electricity

43.69 20.78 0.70 63.77 0 120.9

MW MW MW MW MJ/s MJ/s

∞ --52.7 % 52.7 %

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Case 4 Gas Turbine in Combined Cycle Steam Turbine (district heating)

11 % losses

11.3 % electricity

©Siemens Power Generation 2003. All Rights Reserved

510 deg C 2-pressure HRSG

78 deg C

42.1 % heat

90 deg C

Gas Turbine

60 deg C 35.9 % electricity 100 % fuel

2/9/2006

78 deg C

Pgt Pst Paux Pnet Heat duty Qfired

43.70 14.18 0.62 57.26 51.1 121.4

MW MW MW MW MJ/s MJ/s

Alfa 1.12 --Powerefficiency Generation 47.2 % Net electrical Net total efficiency 89.3 %

7

Is it possible to use the same design for both applications? z Well, we will try!

©Siemens Power Generation 2003. All Rights Reserved

z The compressor drive requires a variable speed power turbine, so we have to assume a twin shaft unit z The efficiency of the cogeneration unit ought to be in the range of 37% at full load, which means that the heat input is around 95MW

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The core engine 1

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z We have now a basic design. z A critical parameter is the Turbine Inlet Temperature. The higher TIT the better gas turbine cycle, but generally also less robustness and higher turbine cooling flow z Let us assume a conservative TIT = 1300°C z From experience the turbine cooling flow will then be around 16% 95MWth TIT

35MWe

Turbine cooling 2/9/2006

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Turbine Inlet Temperature and emissions

Turbine Inlet Temperature C and NOX

©Siemens Power Generation 2003. All Rights Reserved

1500

200

Ceramics Steam Cooling

Single Crystal Blades

GTX100 Jet Engines 1000

GT200 GT10B/C GT35/GT120

100

Stationary Gas Turbines 500

1940

1960

1980

2000

Year 2/9/2006

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The gas turbine cycle T Tflame

©Siemens Power Generation 2003. All Rights Reserved

p5, t5m

p3, t3

t5

ηct = (t5m - t6)/(t5m - t6s)

p6, t6

ηpt = (t6m - t7)/(t6m - t7s) ηc = (t3s - t2)/(t3 - t2)

p7, t7

p2, t2

s 2/9/2006

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The turbine pressure levels

©Siemens Power Generation 2003. All Rights Reserved

z How are the pressure levels at the compressor and power turbine sat? z The turbine can be seen as a tube with restrictors z In order to pass a certain flow at a certain temperature there is an associated flow area/pressure combination z The flow area is determined by the turbine inlet guide vanes zInner/outer diameter zExit blade angle, which is on gas turbines is generally fairly large, which means that the stage design is of reaction type (the enthalpy drop is divided between vane and blade)

m = A *rot(2*Δp*ρ) = A *rot(2*Δp*p/RT) = Ψ*A*p/rot(RT) For computational purposes the below formula is very useful

m*rot(T)/p = constant 2/9/2006

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Turbine flow The flow capacity of the turbine is determined by the smallest area in the turbine inlet guide vane and the root and tip section diameters the turbine “wideness” the turbine flow number m*rotT/p ©Siemens Power Generation 2003. All Rights Reserved

the ”turbine constant”

The flow capacity of the turbine determines the position of the operating line in the compressor map.

2/9/2006

An uncooled turbine has better efficiency than a cooled turbine, which has less good profiles (lower aspect ratio, thick trailing edges) and Power Generation 13 mixing losses from the cooling flows

The gas turbine cycle T Tflame p5, t5m

t5

ηct = (t5m - t6)/(t5m - t6s)

p6, t6

p3, t3

©Siemens Power Generation 2003. All Rights Reserved

ηpt = (t6m - t7)/(t6m - t7s) ηc = (t3s - t2)/(t3 - t2)

p7, t7

p2, t2

s

The next step is to make a simple thermodynamic model of the gas turbine in order to get the conditions for the combustor. We will do it in Excel!

95Mth TIT

35MWe

Turbine cooling Power Generation

2/9/2006

6

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SGT-600, Industrial gas turbine

©Siemens Power Generation 2003. All Rights Reserved

Gas turbine principle & components

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©Siemens Power Generation 2003. All Rights Reserved

The core engine 2 z Now we need to choose the pressure level for the turbine inlet z There is an optimal pressure level for efficiency associated with the turbine inlet temperature, but it is generally quite high which means a low TET. We have also to consider the steam production in the waste heat recovery boiler, so we need a fairly high TET > 520°C ?? z We will try some pressures for TIT = 1300°C z1800 kPa z1700 kPa z1600 kPa z1500 kPa

η=38.3% η=38.0% η=37.6% η=37.1%

TET=509°C TET=517°C TET=526°C TET=536°C

T3=438°C T3=426°C T3=413°C T3=400°C

z The higher the pressure the higher also the compressor exit air temperature T3. That air is zthe combustion air zthe cooling air for the turbine and combustor walls

z For combustion high air temperature is generally better z NOx and combustion pulsations have a tendency to increase with pressure Power Generation

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The combustor 1

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z Now we have basic full load data for the combustor z Air flow to the combustor: 82.8/426/1785 kg/s/°C/kPa z Fuel flow: 2.02 kg/s z Combustor exit flow: 84.8/1300/1700 kg/s/°C/kPa z In order to design the combustor we have to know which type of burner we are going to use 2.02 kg/s 82.8 kg/s 426°C 1785kPa

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84.8 kg/s 1300°C 1700kPa

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Burner 1: types of burners z The conventional combustors were designed for Stoichiometric combustion, using fuel injectors with low air flows Φ ≅1. Water or steam injection were used for NOx reduction z The lean premixed combustors are designed with a high air flow that cools the flame

©Siemens Power Generation 2003. All Rights Reserved

z The low oxygen combustors relay on a combustion process in O2-depleted gas, achieved by recirculation of combustion products NOx ppmv

Diffusion flames

200

Φ = 1/λ

Water Injection 100

Lean Premix Combustion

0. 5

Steam Injection

1.0

1.5

Fuel/Air Equivalence Ratio 2/9/2006

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Diffusion type dual fuel Injector

Water inlet

2100K

STD PARTPOSITIONABLE ELBOW

HCV GAS HOLES

PURGE HOLES

©Siemens Power Generation 2003. All Rights Reserved

STEAM INLET

Air

Gas inlet Oil inlet

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Dual fuel Injector for gas and oil with water and steam injection

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NOx and CO vs Flame Temperature NOx ppm

CO ppm

EV Burner DLE Gas

AEV Burner DLE Gas & Oil

50 ©Siemens Power Generation 2003. All Rights Reserved

NOx 40

40 30

30

CO

Low oxygen burner20

20

Catalytic burner

10

10 1700

2/9/2006

1800 Flame Temp K

1900

- Advanced DLE burners Power - Generation

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Our case

©Siemens Power Generation 2003. All Rights Reserved

z The Oil&Gas customers have presently no high requirements on emissions, but the industrial customers will have a requirement of NOx < 10 ppm z We will try to build a low NOx burner of lean premix type z Our trial choice is a LP burner with a design flame temperature of 1750K z How much air is needed for the combustion? z We will do a heat balance calculation for the flame zone

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The combustor 2

©Siemens Power Generation 2003. All Rights Reserved

z Now we have the basic flow data for the combustor z Air flow to the burner: 65/426/1785 kg/s/°C/kPa z Fuel flow: 2.02 kg/s z Wall cooling flow: 17/426/1785 kg/s/°C/kPa

2.02 kg/s 84 kg/s 65 kg/s

1300°C 1700kPa

17 kg/s 426°C 2/9/2006

1785kPa

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Wall cooling z The burner air is around 65 kg/s out of the 82 kg/s combustion air z We have around 21% of the combustion air for wall cooling, which ought to be enough for a film cooled sheet metal combustor. 438 ©Siemens Power Generation 2003. All Rights Reserved

450

500

850

1477÷1300

If the film cooling air is on the low side Thermal Barrier Coating can be used. If there is more air than necessary for cooling, it can be injected as dilution air in the down stream part of the combustor. 2/9/2006

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Wall cooling designs The shown wall design is the traditional one for film cooled combustors. Several similar designs with improved performance are in use 438

©Siemens Power Generation 2003. All Rights Reserved

450

Impingement

1477÷1300

500

850

Convection

The use of Thermal barrier coatings has been more common. Conventionally only thin TBC (