Fuel Gas Composition

[ppmsb]

Hi,

The GTG is designed based on certain composition of gas. Currently we don't have monitoring device to check the gas composition entering GTG. What is the impact to GTG if there is significant changes on the gas composition?

ppm

 

[gtsim]

Higher the methane (CH4) content, which also increases the lower heating value (LHV) of the fuel, increases the GT power output and reduces heat rate. Also, NOx emissions decrease. The higher the CH4 content, greater is the water vapour in the products of combustion. This improves the engine performance (water vapour has a higher cp). The higher water vapour also suppresses the peak combustion temperature and therefore lower NOx emissions.

If the fuel composition is outside the OEM spec and this results in a significant decrease in LHV, CO, smoke and (free) carbon emissions can increase due to insufficient residence time in the combustor. Burning carbon can destroy the turbine, due localised high temperatures in the turbine section.

 

[dcasto]

Unless the composition is changing in the butanes and heavier, there should not be a big change in performance or burning characteristics.

 

[gtsim]

If you have a change in the inerts (CO2, N2, etc) there will be a noticeable change in LHV, performance and NOx emissions.

 

[MJCronin]

ppm,

What are you burning ?

Digester gas ? Landfill gas ? Pipeline quality natural gas ?

What is the impact of a significant change in composition ?

Well, if you dont have enough methane in your fuel and/or you run out of the range of your fuel combustion equipment, the machine will stop....

-MJC

 

[abeltio]

From other posts, seems like you have GE units.

If the LHV varies significantly from the original design, the consequences are as follows:

LHV > design

The unit will input too much thermal power and it may overspeed during start-up
Or, the base load FSR will be much lower than expected.

LHV < design
The unit may not reach base load and may have difficulty firing

The problem is in the Speed Ratio and control valve(s) sizing with significantly different LHV different sizes may be needed.
OEM engineering should determine whether the gas fuel nozzle need change due to Wobbe Index changes.

Base load MW and FSR% change are the most noticeable indication of gas fuel composition change, with due consideration to changes in other conditions like ambient, steam injection, inlet filter pressure drop, etc.

saludos.
a.

 

[Feric]

Hi there:

Here is a URL for an online calculator dealing with the gas turbine technical performance:

http://members.aol.com/engware/calc3.htm

Thanks,

Gordan

http://engware.i-dentity.com