niazbibiyana,

People will start talking (as people will do) if you keep using 'Dear' also.

My colleagues call me CSA. (That's one of the nicer things they call me.)

 

Ok. CSA.

Can I get your Linkedin/Twitter/Facebook Profile ID?

 

Dear CSA,

I am not a control engineer... would like to understand the functionality of purge valves in DLN 1 frames Three GCV arrangement.

I want to know the purge valve open close position during different combustion modes.

I mean just tell me position of VA-13/VA-14 during primary, Lean Lean, Secondary and premix mode....

My understanding is that these are continuously purging during premix mode....

Regards
Novice

 

Novice,

Is the unit dual-fuel (gas/distillate)?

Regards,
CSA

 

Dear Novice,

It is helpful when you start a new thread rather than continue a thread from several years ago that may or may not be the same type of unit that you are working with.

I assume this is a DLN1 combustion system independent valve configuration running on a GE Frame 7 or GE Frame 9 unit.

You indicated you want to know the desired position of valves VA13 and VA14 during the different combustion modes. I believe you missed some numbers as there should be more numbers and all should start with VA13-X. You need to clarify if you are talking about VA13-1, VA13-2, VA13-3 or VA13-4 and we can then best answer.

 

Novice,

I don't have access to any P&IDs as I write this. The topic of GE-design heavy-duty gas turbine fuel purge systems has been covered many times before on control.com (there is a 'Search' feature at the far right of the Menu bar at the top of every desktop control.com webpage).

Gas fuel purge systems have primary and "follow-on" functions. The primary function is to make sure there is no fuel in the fuel supply lines to the fuel nozzle(s) so that hot combustion gases cannot ignite the fuel and cause damage or an explosion. (Gas fuel liquids, as well as other combustible liquids which might be entrained in or condense in supply piping need to be purged as well as any combustible gases.) Second, the flow of purge air also serves to provide some cooling to the fuel supply lines and fuel nozzles so that hot combustion gases don't damage them. Third, the flow of purge air prevents hot combustion gases from flowing backwards into the fuel nozzle and supply piping. But, the primary purpose is to make sure there is no combustible gases or liquids in the fuel nozzles and the fuel supply lines to the fuel nozzles. (While you didn't ask about liquid fuel purge, the purpose and follow-on functions are similar--except one of the most important things about purging liquid fuel out of the supply piping and nozzles is to prevent the liquid fuel from "carbonizing" ("cooking" and hardening) in the liquid fuel supply piping and liquid fuel nozzles.)

The purge systems on a DLN-I unit (well, most of them, except maybe for those designed and built and implemented by GE Belfort, France) use axial compressor discharge air flowing continuously through the supply piping and nozzles of the fuel system which is NOT in use to push the combustible gases or liquids out of the fuel system and nozzles and to also ensure that hot combustion gases do not flow back into the nozzles and supply piping. And, because axial compressor discharge air temperature is less than the internal combustor temperature in the area of the fuel nozzles the flow of purge air also provides some cooling effect to the nozzles, in particular.

The DLN-I combustion system (on most GE-design heavy duty gas turbines equipped with DLN-I combustion systems) have three, sometimes only two, fuel supply systems. The three are Primary, Secondary and Transfer. Some units do not have a Gas Fuel Transfer Valve and are therefore referred to as "transfer-less" DLN-I combustion systems. (It sounds as if your unit may have only an SRV, GCV and Gas Fuel Splitter Valve--and no Gas Fuel Transfer valve, making it a transfer-less DLN-I gas fuel system.)

When a unit with DLN-I combustors is starting it is usually only flowing fuel through the Primary fuel supply lines and nozzles; there is no fuel flowing through the Secondary or Transfer fuel supply lines or nozzles. In this case, purge air would be flowing through the Secondary fuel supply piping and nozzles (and in some cases the Transfer fuel supply piping and nozzles). When the unit transitions to Lean-Lean combustion mode as it is loaded after start-up the purge air into the Secondary supply piping and nozzles is stopped (because there will be fuel flowing soon in the Secondary supply piping and nozzles). So, when there is fuel flowing through the Primary- and Secondary fuel supply piping and -nozzles there will be NO purge air flowing to the combustors.

When the unit transitions to Premix combustion mode, if there is purge air for the Transfer supply piping and nozzles, that purge air will be stopped as the unit transitions from Lean-Lean to Premix combustion mode (as there will temporarily be fuel gas flowing in the Transfer supply piping and nozzles). Very shortly after the transition to Premix combustion mode is complete if there is Transfer purge air, it will be re-admitted to the Transfer supply piping and nozzles.

As the unit is unloaded and transfers from Premix to Lean-Lean there will be no need for purge air for the Secondary or Primary fuel supply piping and nozzles (because fuel is flowing through both of them). As the unit is unloaded further and transitions to Primary combustion mode purge air to the Secondary fuel supply piping and nozzles will be readmitted.

If the unit is dual fuel (gas/liquid), there will usually be a purge air system for the Primary gas fuel supply piping and nozzles, which will ONLY be used when the unit is operating on liquid fuel (fully on liquid fuel). If the unit is operating

VA13-1 and -2 are for the Primary gas fuel supply piping and nozzles (and would only be used when the unit is operating on liquid fuel), and VA13-3 and -4 are for the Secondary gas fuel supply piping and nozzles and nozzles. (It's possible that the packager re-numbered the Secondary gas fuel purge valves as VA14-1 & -2; who knows these days.)

So, to recap: When the unit is running on gas fuel, there should be NO purge air flowing in the Primary gas fuel supply piping and nozzles. If the unit is running on gas fuel AND the unit is Primary combustion mode, there should be purge air flowing in the Secondary gas fuel supply piping and nozzles. If the unit is a dual-fuel unit and it is running on liquid fuel (fully on liquid fuel), there should be purge air flowing in both the Primary- and Secondary gas fuel supply piping systems and nozzles.

Hope this helps!