Is it necessary to close all the gas fuel purge valves while first firing?

Thanks.

 

David,

We know that you know what kind of combustion turbine(s) you have at your site and what combustion system you have at your site.

But, you should also know that we don't know what you know and we have never been to your site.

Unless you tell us.

When posting to a forum like this, we need as much information about the problem you are experiencing or the question you are having (we don't deal in doubts). Because there are no avatars on this site (where people would provide information about themselves and the equipment at their site for others to refer to when attempting to provide information or assistance) we don't have any idea about the units at your site and their configuration.

If you're referring to the very first firing of a turbine being commissioned, the answer would be the same as for the 2,347th start: The as-supplied sequencing or application code in the control system should be programmed to operate the purge valves as desired. "First fire" is no different from 2,347th fire, except that everyone has their fingers and toes crossed (a good luck wish in many parts of the world) hoping that the flame will be established successfully and maintained throughout acceleration without high exhaust temperatures, or high exhaust temperature spreads, or flickering flame indications.

If the turbine(s) at your site have been running properly for any period of time since the original commissioning with the as-installed sequencing or application code, then the purge valves are properly configured and programmed to operate as necessary.

If the valves have recently been refurbished or have been replaced or there has been a maintenance outage recently that has resulted in some problem with firing or valve positions, then it's likely the problem lies with the refurbishment or the re-installation or the gas valve LVDT feedback "calibration".

What alarms are being annunciated while starting?

Are you trying to start on liquid fuel or gas fuel?

We don't the nature of your question, what has caused you to post it here. Are you experiencing problems establishing flame while starting the turbine? When did this problem begin? Are you trying to find information to help you program a control system? Are you just curious about purging of gas fuel systems?

For GE-design heavy duty gas turbines with gas fuel purge valves, the purge air comes from the axial compressor discharge, which is very low pressure air during starting and firing. Also, the compressor bleed valves are open during starting, which further reduces the axial compressor discharge pressure.

Most of the gas fuel purge valves on GE-design heavy duty gas turbines have pneumatic (air) actuators, and the pressure source for those actuators is also compressor discharge pressure, which is nowhere near the pressure required to actuate the purge valves. (Many of the newer F-class GE-design heavy duty gas turbines and a lot of them that are being used in combined cycle power plants are using or are switching to plant instrument air for air-actuated valves, but the sequencing or application code is no different for this different pressure source.)

But, we still don't know exactly what question you are asking, nor for what equipment (turbine, control system, combustion system, fuel(s), etc.). Help us to help you by providing as much information as possible in order to get the most concise response possible in the shortest period of time.

 

Thank you CSA,
I am sorry for give you less information.I am referring to the first firing of a turbine being commissioned. GE said that all the gas fuel purge valves should be closed before DLN turning.