I have a question about the mode of operation of quaternary valve. can it be disabled in speedtronic during premix stready state operation and can some one explain exact mode of its operation in 6FA gas turbine?

 

In general, one should direct this question to someone with the original equipment manufacturer (GE?) since they would be able to access information about your specific application.

The Quaternary gas control valve is used for several functions, depending on the type of fuel(s) used or even whether or not the fuel is heated. It can be used to control emissions, and it can be used to control or limit dynamic pressures in the combustors--or even some combination of the two.

Decisions about the Quaternary gas control valve and its operation are usually made by the OEM during initial commissioning of the unit, and even during subsequent DLN tuning after maintenance outages.

Changing the fuel splits in any DLN combustion system can have very serious consequences, over and above having an adverse effect on exhaust emissions. Consult with the OEM prior to making any changes in the operation of your DLN-II combustion system to protect the turbine and personnel.

 

The quaternary gas control valve is used only during PMSS, and is used for quieting dynamics. The quat system was an after thought by GE and the very early DLN 2.0 systems were shipped without them, but subsequently retrofitted. However, it has been learned that many units espcially the DLN 2.6 systems, can get by with out quat gas. If you wish to call I have a copy of the DLN 2.0 tuning manual that I can discuss with you.

Jeff Fassett
IEM Energy Consultants Inc.
320-846-5255

 

Hello Sir,
This is one more question I had asked earlier and luckily I got 2 replies.There are 2 turbines here 6FA in one of our site have both of quatarnary valves disabled which was not known to customers,later on I found out during maintanance and thereafter start-up of turbine that this valve is not operating,it is kept disabled by placing LFALSE in the sequence,mentioning a comment that it is disabled due to finding of high tone during Tuning turbine.Our customers have asked BHEL-GE for their explanation but no reply since then.

Best Regards,
Everblue

 

It is exactly as Mr. Fassett says; admitting gas fuel through the Quaternary pegs/nozzles can calm unwanted dynamic pressure pulsations in the combustors during Premix Steady-State (PMSS) operation. Quaternay systems are also often enabled when heated gas fuel is used.

However, "afterthought" is a strong description; it was developed as a means of reducing combustor dynamics which can cause premature failure of hot gas path components. The Quaternary gas fuel system is now always provided with DLN 2.x combustion systems. During DLN tuning (during initial start-up/commissioning and after maintenance inspections) it can be put into service--if necessary--to quiet combustor dynamics.

Just because it's not in service at this time does not mean the unit is not being operated properly; it simply means it was determined during DLN tuning that Quaternary gas was not required.

After some future maintenance inspection it may be determined that Quaternary gas is required to reduce combustion dynamics, and it will be enabled and tuned at that time as required.

So, not to worry--it can be considered a good thing for the Quaternary system to be disabled, an indication that combustion dynamics are low and Quaternary gas is not required to reduce them.

Enabling Quaternary gas when it's not required will not improve turbine operation or efficiency or output. Fuel admitted through the Quaternary system will be "shifted" from other systems as the total amount of fuel will not differ if the Quaternary system is enabled or not. Also, enabling Quaternary gas when it's not required can also induce unwanted combustion dynamics.

The proprietary details of GE DLN combustion systems are extremely closely guarded by GE, and most Business Associates (companies who build turbines under license from GE) find themselves on a "need to know" basis. GE has invested huge sums developing DLN systems; they are not obliged to divulge any more than is absolutely necessary.

One thing you can be certain of when dealing with GE: They have never been known to shy away from problems. While some criticize them for their lack of "forthrightness" they have continually demonstrated their commitment to maintaing their reputation for quality heavy-duty combustion turbines. They may not always tell you what they're doing or why, but they will always "do the right thing" when it comes to their turbines. They couldn't remain in business if they didn't.

markvguy

 

Dear Sir,

I accept what is written by Mr. Fassett.
But I have a suggestion to whom so ever is doing such modification during the DLN tuning, that if they don't want the quartanary valve to open during premix steady state mode, why not completely isolate or remove the servo valve regulator from io.asg and not by just placing a LFALSE in the rung? The reason being during recent maintanance, unknowingly the valve was stroked as normal valve stroke checks and this valve got stuck in half open position, and then we had to change the servo valve which adds to extra expense on the maintenance cost.

Specially when turbines are based in remote deserted areas and remotely operated 750 kms far, only dln tuning takes place may be 3-4 yrs, i mean NOX measurements don't have any significance.

rgds,

everblue

 

In the future, you will know to ask the commissioning engineer to disconnect the servo if that will be your or your customer's practice for unused servo-operated devices. However, doing so causes Diagnostic Alarms to be annunciated--unless one disable the servo-valve output in the I/O Configurator. So, there are several things which must also be done in conjunction with disabling the output. And all of this complicates returning the system to service if it's deemed necessary.

A failure such as the one you experienced is not common at all. The response you have is not unusual; "Why do they do that?!?!!??!!" is a common refrain after one is made aware of something which was not obvious or explained previously. You should be directing your comments to the turbine supplier, who will most likely respond that this is a common, though undocumented, practice and that the failure you experienced, while regrettable, is unusual.

Some conventional combustor-equipped units with dual fuel capability experience failures of the back-up fuel supply system components when they aren't used/exercised regularly. In this author's opinion, keeping oil flowing through a system when it's not in service prevents other potential problems when it's time to put a system which has not had oil flowing through it back into service. So, it's just a matter of perspective. You were wise to stroke the valve, but unfortunate in your experience.

Perhaps the real problem is Lube Oil conditioning and maintenance? Such failures as the one you describe can be attributed to varnishing and/or contamination of the Lube Oil.

As for NOx measurements not meaning anything, large changes can be indicative of combustion problems, and even high dynamic pressures which can cause premature combustion hardware failures. Dry Low NOx (DLN) units are MUCH more "sensitive" than their conventional combustor equivalents. Conventional combustor-equipped units "take a licking and keep on ticking" (to use a phrase from an old advertisement campaign), meaning they are much less susceptible to lesser combustion problems than are DLN combustor-equipeed units.

Don't fall into the trap of thinking that just because emissions aren't "important" in arid locales that sudden changes, or even gradual ones in some cases, don't indicate other much more dangerous problems.

markvguy

 

Dear Friends,

We have the GE DLN-114 tuning kit in stock. Would you know if it can be used on GE 6FA engines?

Jaroslav Najman
LDAP
[email protected]
+420 602 210638