There is 20MW mark-v (GE) gas turbine.

Its atomizing air compressor failed but turbine is yet running. I found its main compressor discharge pressure 8kg/cm2 and the atomizing air pressure 7.5 kg/cm2 at a moment. There is no way to meet the power demand. That's why we didn't shutdown the unit.

It is running fine at 19.5MW since last 2 days.

Any suggestions...??

 

From the very little information provided, it's presumed the unit is running on gas fuel at the moment, because there isn't likely sufficient atomizing air pressure available to run on liquid fuel. (You forgot to tell us what fuel the unit is running on.)

When the unit is running on gas fuel, the Atomizing Air compressor is bypassed (somewhat) in order to reduce the load and improve power output of the gas turbine when running on gas fuel. The Atomizing Air is only used to purge and cool the Atomizing Air nozzle tips and passages; it's not required for operation, though it does slightly help with gas fuel combustion. (The amount of air flowing in the AA passages when running on gas fuel is factored into gas fuel nozzle tip sizing, but it's a negligible number, really.)

So, while you may be running (at a slightly reduced load) on gas fuel with no Atomizing Air pressure/flow you may also suffer a catastrophic failure due to nozzle failure caused by overheating of the nozzle tips. Or, when you next perform maintenance on the nozzles you may find damage from overheating of the tips.

It's generally not a good idea to run on gas fuel without Atomizing Air pressure/flow for cooling and purging. But, if you need the power you gotta do whatcha gotta do. And pay for it later, if necessary.

If the unit is running on liquid fuel with Atomizing Air pressure below compressor discharge pressure--and it's running without smoking (black smoke--then you are lucky indeed. But, you could still find damaged nozzles when you do next perform maintenance, if not before. Again, because with no Atomizing Air pressure/flow there is no cooling or purging of the Atomizing Air tips and passages.

I have heard, but never seen, units that had glowing red Atomizing Air pigtails and/or manifolds because of circulating combustion gases back-flowing through the Atomizing Air nozzles into the pigtails and manifold piping.

Again, it's risky and not really recommended. You should have someone monitoring the Atomizing Air pigtails and manifolds--whether operating on gas- or liquid fuel--as long as you are running without Atomizing Air pressure flow. And shut down if you notice anything out of the ordinary.

Please write back, though, and tell us what fuel the unit is operating on while running without Atomizing Air.

 

Hi,
Is unit running on liquid fuel?

How do you know atomizing air compressor failed?

What is the spread valve?

G.Rajesh