Dears,

We had an issues with exhaust temperature high spread for one of our Fr-9E machines.

Unit was running with normal spread around 12 deg.C with gas fuel operation. after unit transferred to liquid fuel due to gas low, temperature spread was increased to 24 deg.C. when unit was running on liquid fuel, spread around 10 deg.C.

What could be the cause for spread increase after fuel change over to liquid fuel?

Take care
G. Rajesh

 

Dear,

The topic of exhaust temperature spreads has almost as many threads as that of droop speed control (it's certainly the second-most gas turbine-related thread).

Gas fuel flows out of one set of orifices in the fuel nozzles, and liquid fuel flows out of another, different, set of orifices in the fuel nozzles.

Troubleshooting exhaust temperature spreads while running on liquid fuel is MUCH simpler than troubleshooting exhaust temperature spreads when running on gas fuel. Why? Because there are ten (10) individual fuel lines running from the liquid fuel flow divider to each of the ten liquid fuel nozzles on each of the 10 combustors. And, there's that manual selector valve and gauge. (I know--it takes a human being to turn the handle and another one to write down the individual pressures for the ten (10) liquid fuel lines.) Any pressure that is more or less than 10% of the average of all the liquid fuel pressures indicates some problem with the liquid fuel flow to that combustor (or combustors).

What can the problem be? A failed liquid fuel check valve. A failed liquid fuel purge air check valve (which can also be indicated by a flow of liquid fuel coming out of the Tell-tale Leak-off (see the Liquid Fuel or Fuel Purge P&ID; it's usually located on the right side of the turbine compartment, under the walkway.) A blocked liquid fuel nozzle, or a liquid fuel nozzle whose internal components have loosened.

The gas fuel system doesn't have nearly as many possible causes, and because one can't measure the individual pressures to each of the ten (10) sets of gas fuel nozzle orifices it's more difficult to find the problem fuel nozzle. (This is where a swirl angle chart comes in handy--and, no; I don't have one to send to anyone. They vary by machine, and by combustor type (diffusion; DLN; MNQC; etc.).

If the unit has water- or steam injection for NOx emissions reduction a problem with the spray nozzles can also be a cause.

But, if the spread differs between fuels the problem is not likely related to combustion liner and/or transition piece cracks or holes or some other hardware problem.

Hope this helps!

 

you can check which liquid fuel purge air check valve failed primary or secondary when machine stop by remove one air check valve from primary and fabricate air hose connect to primary air manifold blow air and check for fuel liquids com out from Tell-tale Leak-off , use same technique for secondary system to know the leak from which one