1

GAS TURBINE GENERATOR Site power demand: 23MW

Make – Siemens

Model – SGT- 400 (3+1 Units)

Rating: 13.9 MW (ISO), 10.2MW site rating @45°C.

DLE combustors

Speed – 9500 RPM

2 – SALIENT FEATURES OF MAIN EQUIPMENT, PROBLEMS, DECISIONS

Footer can be customized2

Typical Gas Turbine

Typical Gas Turbine

Gas Turbine Combustor

Footer can be customized3

Blue Lines represents Compressed Air from Axial compressorRed Lines Represents Fuel Gas and Hot Gases

DLN / DLE Combustor

Comparison of Flame Speeds

Footer can be customized4

Flame Speed

Ar-Ratawi Fuel Gas composition

Footer can be customized5

Footer can be customized6

Heavier Hydrocarbon, Flash back

H2, Flash back

Inert Gases, Blown Out

Fuel Gas Mapping

• High hydrocarbon fuels are significantly more reactive and energetic (Similar to H2) compared to natural gas.

• Wobbe Index: The index defines the heating value of a quantity of gas that will flow through a hole of a given size in a given amount of time. The higher the index the higher the heating value.

Footer can be customized7

Blown Out. Blown out occurs when the flame becomes detached from the location where it is anchored and is physically “blown out” of the combustor. Due to low WI, Mass flow rate of fuel through injector will increase (As it is required to provide the same Heat release) resulting in Pressure drop with possible flame detachment Result : Dynamic Pressure Amplitudes Solution : Changing the Fuel Injector Nozzle design (High inert gas components)

Flashback. Flashback occurs when the turbulent flame speed exceeds the flow velocity (Gas Velocity of gas before combustion), allowing the flame to propagate upstream into the premixing section (Which is not designed for higher temperature). (High Hydrogen and Higher Hydrocarbons components)

When Flashback occurs acoustic oscillations in the premixer section causes fluctuations in the fuel and/or air supply rates, thus producing a reactive mixture whose equivalence ratio changes periodically in time. Result : Mixture fluctuation is transferred to the flame where it produces heat release oscillations that drive the Combustion instability.

Combustion Instability. Combustion instabilities are characterized by large amplitude pressure oscillations that are driven by unsteady heat release

Due to Heavier Hydrocarbons / Hydrogen in fuel composition will Increase the flame speed and change flame Centre of Mass (Increasing the Burner Metal Temp.). Chances of Hot spot due to shorter convection time in the combustor.

Footer can be customized8

Modified Wobbe Index (MWI): By increasing the fuel supply temp wobbe index is altered from ISO conditions. The fuel supply temperature impacts the actual volumetric fuel flow.

“All gas mixtures that have the same Wobbe number will give the same amount of heat.”

MWI=LHV/(SG * Tgas) 0.5

LHV = Lower heating value of the gas in Btu/scf

SG = Specific gravity of the gas fuel related to air

Tgas= Absolute temperature of the gas fuel in oR

Ethane content vol % 10 15 20 25 30 35 40 45 50

Min Supply Temp C 2.5 3.0 11.0 20.0 29.0 37.0 46.0 54.0 63.0

Dew Point C < -20 < -20 < -20 < -20 < -20 < -20 < -20 < -20 < -20

Temp Corr Wobbe Index kj/m3 48214 48939 48991 48957 48926 48975 48946 48993 48965

Wobbe Index @ iso kj/m3 47156 47909 48650 49380 50101 50811 51513 52205 52888

For standard SGT-400 operation, Siemens generally accept fuels within a MWI range 37 – 49MJ/m3.

SOLUTION 1 : Heating the Fuel Gas (Heavier Hydrocarbon)

Footer can be customized9

SOLUTION 2: RIG TESTING OF COMBUSTORS (High Calorific value High H2)

COMBUSTORS

Footer can be customized10

TEST ARRANGMENT

Footer can be customized11

TYPICAL RESULTS