we have GE9FA frame machine with DLN2+ COMBUSTION nozzles. Before sending into the combustion chambers we are heating the gas in a performance heater upto 155 deg centigrade. my question is what is the purpose of heating the gas in a DLN system.

 

If "cold" gas fuel is injected into the combustor there is some amount of heat lost in the combustor due to the chilling effect of the temperature of the gas. This somewhat reduces the efficiency of the turbine because it takes a little more fuel to raise the temperature of the combustion gases up to the required value.

So, if there is a source of "cheap" heat that can be used to raise the temperature of the gas fuel before it is injected into the combustor then less heat will be lost due to the chilling effect of the temperature of the gas. This will increase the efficiency of the combustion reaction and of the turbine because it takes a little less fuel to raise the temperature of the combustion gases up to the required value.

I believe we're talking about fractional percentage increases in efficiency, but, over the expected life of a 9FA turbine (approximately 200+ MW) this can add up to substantial savings and improvement in output.

 

In our plant, we used to heat up natural gas with IP economizer water.
It means, flue gas diverted into HRSG heat up water, then we use the same water to heat up natural gas. we have lots of losses while heating up gas with water.

In my opinion diverting cold fuel gas directly to gas turbine is more efficient than heating natural gas with IP economizer water.

Am I wrong?

 

Heating the gas is just to improve the efficiency means, than what it is the necessity to provide runback of GT based on modified wobbe index (wobbe index) which inturn depends on gas temperatures, if gas quality (specific gravity & GCV) are maintaining same?

 

Hi there,

can somebody clear more on wobbe index?

Thanks

 

Dear Vinu,

if GCV/NCV is same, how wobbe index will change with gas temperature, can u please elaborate.

 

Heated gas fuel flows have a different effect on combustion dynamic pressures inside the combustors than "cold" gas fuel flows.

This is all pretty much part of the proprietary nature of the DLN combustion systems that GE designs and sells.

Since this is an F-class turbine, it would be very unusual if the site did not have some kind of Remote Diagnostics or Contractual Services Agreement, so you should be able to contact GE with your queries and they could provide more information.