Gas Purge Valves

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Thread Starter

Fazal

When Gas Turbine is running on Gas Fuel what happens if the gas purge valve opens?

There may be back flow of flue gases into the air manifold. What type of damage can be occur and What action should we take to prevent the damage?
 
A bit more information would be useful, Frame size, DLN or not. Simply you will get some damage to fuel nozzles at least. I've had purge valves causing problems with secondary fuel nozzles on DLN1 systems, mainly due to limit switch settings and purge valves not fully closing. As for remedial actions, firstly you need to establish why the purge valve opened.
 
Gas Turbines Frame 7001E, Control is Mark V. Normally these GTs running on Gas fuel. There may be any cause of opening the gas line purge valves. It is Sure that vent valve remains open and any leaking flue gases will vent. But my question is that what type of effects would be on the other systems.
 
The units will trip on "gas purge valve trouble" alarm.
There is possible damage of internal parts such as nozzles. Actually this very dangerous because of facing of hot air coming from the last stage of Gas turbine compressor with about 300 degree Celsius and fuel gas. The mixing of two (air + fuel gas) will be in gas manifold.
I hope that I answered your question.
 
i am sorry for first reply from me i answered it quickly. the below is the right answer.

The units will change over to Light fuel oil unless receive "gas purge valve trouble" alarm. Which Causing by limit switch problem. I hope that I answered your question.
 
Please have a look at the Gas Fuel or Fuel Purge Piping Schematic (P&ID) drawing to see the details of the gas fuel purge valve<b>S</b>.

If you have a standard GE-design Frame 7E or 7EA machine, then there is--or should be--a double block and bleed valve in the gas fuel purge line. This puts two valves in series (and "back to back") with a vent between the two valves.

When you are running on gas fuel, both valves should be closed and the vent between the two valves should be open. The vent line is not usually very large, because the piping volume between the two valves is not very large.

There is a pressure switch monitoring the pressure between the two valves as well.

If either closed valve leaks, the leak should not get through the second valve. If the leak (of either the purge air (CPD) valve or the gas fuel valve is severe enough then the vent line won't be able to vent the pressure (either CPD or gas fuel) quick enough and the pressure will rise and the pressure switch will alert a conscious operator to the condition.

Again, the idea behind a double block and bleed valve arrangement is that a failure of both valves at the same time should be very unlikely, so the protection you seek against a failed valve should be provided by the other block valve. The system is designed to be as reliable as possible, and to provide protection against the worst condition which would be for fuel gas to enter the combustion wrapper/compressor discharge area where such a failure could be catastrophic. (Remember, fuel gas pressure must be higher than CPD, in order to have fuel gas flowing into the combustors through the fuel nozzles during normal operation. So if there was a failure of both valves simultaneously then gas fuel, at the higher pressure, would enter the combustion wrapper/compressor discharge area.)

The Piping Schematic Drawings (P&IDs) can be found in Vol. III of the Service Manuals provided with the unit. Please become familiar with them as they are very necessary to understanding how the gas fuel purge valve<b>S</b> work.

There should also be a description of the gas fuel and purge systems in Vol. I of the Service Manuals. While probably not entirely accurate, they are an excellent to place to learn about systems and intended operation.
 
J
> A bit more information would be useful, Frame size, DLN or not. Simply you will get some damage to fuel nozzles at
> least. I've had purge valves causing problems with secondary fuel nozzles on DLN1 systems, mainly due to limit switch
> settings and purge valves not fully closing. As for remedial actions, firstly you need to establish why the purge valve opened.

I'm concerned with a persistent gas smell from the top commercial buildings presumably from the flue gas vent. Surface gas leak survey and survey of above ground piping has ruled that possibility out. The building would have a boiler(s) plus water heating devices with a total max. btu input of 5 mil to 10 mil.

My email address is [email protected]
thanks
 
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