Dear All,

Please could anybody assist with this?

We operate a frame 6, diesel engine starter gas turbine. It was shut down for gas leaks on one of the combustion cans, but refused to start after repairs.

It cranks with starting attempts but does not start. Fuel filters were replaced and fuel delivery to the injector nozzles were confirmed.

I would be grateful for any lead.
Thanks

 

Can we get some more information please:-

1) Gas turbine model

2) Control system type

You say it was shutdown for gas leaks but it seems that you are trying to start on liquid fuel. Can you start on gas? Do you have Atomizing Air, if yes is AA system OK? Do you see any change in Exhaust Temp. when trying to start.

 

I agree with glenmorangie--there was too little information provided to be of help, and the information provided was not clear.

I suppose "gas leaks" could be "air leaks" (since, technically, air is a gas). But it would have been most helpful if the original poster had told us what fuel the unit was burning when it was shut down, and what fuel they are trying to start on after the shutdown--even if it's the same fuel.

Also, if the site has done any troubleshooting, what was done--and most importantly, what were the results? (It seems some troubleshooting was done, but, precisely what was done and what were the result--precisely?)

Starting (and operating) any internal combustion engine requires the same three things:

Fuel
Air
Spark

The fuel and air have to be in the correct proportions, and when ignited with a spark, there is combustion. For GE-design heavy duty gas turbines, when operating (including starting) the liquid fuel requires atomization for complete combustion, so Atomizing Air is used on most GE-design heavy duty gas turbines to help with breaking down the liquid fuel into smaller particles for more complete combustion.

There are usually two igniters ("spark plugs") which are energized for a brief period during firing (the process of establishing flame in a gas turbine). Only one is required to be working, and the second one is redundant because two redundant devices don't usually fail at the same time (though it has been known to happen). It's a fairly simple matter to, while the unit is at zero speed (on cooldown; at rest) to remove the two igniters, ensure they are solidly grounded (bare metal to bare metal) and then force the logic in the Speedtronic turbine control panel to energize the igniters and observe the spark. (Typical igniters look like normal gasoline engine spark plugs, but most have two "tips" that are very near the center electrode (instead of one like most gasoline engine spark plugs have). The spark generated should be visible to the naked eye, and there should be an audible crackling sound when sparking. Some igniters spark continuously; others ever couple of seconds or so. Igniters do require maintenance (electrode tips wear down; ceramic insulators crack; etc.). Usually, removing the igniters doesn't even require replacing the gasket between the igniter body and the combustion can, but sometimes it does. It's a quick test, and a lot of times it's found that only one of the spark plugs is working properly (something that can't be known/checked during normal operation!) and results in a work order/repair order which can prevent problems later if the other igniter should stop working. Also, a LOT of times the igniter cables are not treated very well during maintenance outages and get kinked or severely dinged when heavy things get dropped on them. And, quite often they are not properly re-installed after maintenance outages, and are left to touch hot casings/combustion cans which will, eventually, cause the insulation to break down and the igniter will not work.

Igniters can become so wet from an excessive, or poorly atomized, liquid fuel flow that they will not spark. So, that's another reason to pull the igniters--especially if starting on liquid fuel--to see if they're wet or dry, and if they're wet, that's an indication of too much, or poorly atomized, liquid fuel.

Air, is pretty easy--as long as the IGVs are at their proper position/angle for starting/firing, the air flow should be adequate. Also, turbine shaft speed should be at or near normal for proper air flow to occur. The exhaust should be free and clear of obstructions (some sites have diverter dampers or other dampers which must be in the proper position(s)).

As for fuel, well, that's a little more difficult. The original poster mentioned replacing fuel filters (which is likely what prompted glenmorangie to ask if the unit was being started on liquid fuel. (Gas fuel can be filtered, but it's a "different" kind of filtering and unless the gas fuel is particularly "dirty"--including entrained liquids--it's not usually done so it's not typical to change gas fuel filters when there's a problem starting.) It would be most helpful to know how the original poster knows there is sufficient fuel flowing to the combustors.

And, if the unit was previously running on gas fuel when it was shut down, how often does the unit run on liquid fuel? And, how often is it started on liquid fuel? (And, to echo glenmorangie, if it was running on gas fuel and is being started on liquid fuel, why isn't it being started on gas fuel?)

If the unit is starting on liquid fuel it most likely has a Booster Atomizing Air Compressor for use during firing, it's often difficult to tell if it's producing sufficient <b>flow</b>--because the pressure is very low. It's often necessary to temporarily install a low-range gauge--with an isolation valve that can be closed after the unit starts to prevent damaging the gauge until it can be replaced.

Some dual fuel gas turbines have solenoid-operated valves in the Atomizing Air lines which can sometimes get stuck in the wrong position and cause problems during firing. Also, many Booster AA Compressors are properly maintained and moisture collects in them and causes problems when they do run (which is only during starting). So, a check of all valves in the AA lines is often necessary, especially if the unit doesn't run on liquid fuel very often.

Another thing which is critical to proper liquid fuel operation--especially during starting--is liquid fuel check valve condition. If they don't open at the proper pressure (particularly if they open at too low a pressure, called the "cracking" pressure) then the fuel will not be properly atomized by the fuel nozzle (prior to being further atomized by Atomizing Air).

And, lastly, if the unit is dual fuel there is usually a liquid fuel purge system which uses check valves which quite often fail when the unit is not operated very often on liquid fuel. Failure of these liquid fuel purge check valves results in low liquid fuel pressure to the affected combustor/nozzle, and also in liquid fuel flowing out of the Tell-Tale Leak-off (usually located on the right side of the Turbine Compartment, under the walkway grating) into the gas turbine drains tank.

If the unit is being started on gas fuel, it's important that the P2 pressure (the pressure between the Stop-Ratio Valve and the Gas Control Valve) be correct, and that the GCV be open to the proper position to allow the proper flow-rate of gas fuel to the nozzles. P2 pressure is usually on the order of about 2 barg (approximately) during starting/firing, and the pressure downstream of the GCV is usually only about 0.2-0.3 barg (barely readable on most GCV discharge pressure gauges).

So, without a LOT more information--and trying to "fill in the blanks"--once again, it's simply FUEL, AIR and SPARK (and in the case of liquid fuel, Atomizing Air). There's no magic to this--it's the same for every internal combustion engine, including GE-design heavy duty gas turbines (and gas turbines made by every other manufacturer).

Look, if somebody you didn't know rang you on your mobile phone and said, "After picking my watch up from the floor, it's not working. What could be the problem?" how would you respond? You would have to ask a lot of questions to find out how the watch came to be on the floor; if it shows signs of visible damage; if it's an analog watch or a digital watch; if it's a mechanical mechanism or an electronic watch; if the second hand (if present is working while the minute/hour hands are not moving); if there is anything visible on the display or not; and on, and on, and on. Whereas if the caller had told you it's a digital watch and that it had fallen to the floor from a second story balcony, that the watch face was cracked, that only a part of the LCD display was readable you would not have had to play "Twenty Questions" to help the person understand why the watch "wasn't working" and what could possibly done to repair it.

It's the same when you post to a World Wide Web forum like this--we're not there alongside you; we don't anything about the turbine at your site and how it's operated. We may have seen GE-design Frame 6 heavy duty gas turbines (perhaps even a lot of them), and we may have experience with troubleshooting and operating them. But, not every Frame 6 is like every other Frame 6 (in fact, there are Frame 6<b>B</b> gas turbines, and there are Frame 6<b>FA</b> gas turbines--and the two are VERY different in many respects--and we don't really know which "Frame 6" you have at your site....) and not every problem like this can be solved with a one sentence, or one paragraph answer--though the more we know about the situation, the equipment, the operating conditions, what troubleshooting has been done and what the results were--the shorter and more concise our response can be.

I'm not trying to discourage anyone from posting--I'm just simply trying to say the same thing as glenmorangie: The more information you can provide in your original post the simpler and more concise the response can be, and the fewer questions we'll have to ask and wait for the response to until we can get at the solution to your problem.

And, again--the problem in this case is the fuel and air are not in the correct proportions (including atomization of liquid fuel--if that's what's being burned during starting), or there is no or insufficient spark. It's as simple as that. Now, a better understanding of gas turbines and their systems (using the P&IDs) will always help in troubleshooting problems, but, in the end, it will likely come down to one or more of the three essentials being absent or in the wrong "quantity" (including a weak or missing spark). A valve is in the wrong position, or has failed, or one or both of the igniters isn't working properly or is excessively wet, and so on. This, again, is where a good working understanding of the systems and components comes into effect.

Please write back with the requested information, and also write back to let us know if you were able to solve the problem with the information provided!!!

And, do write for help with other problems--but remember, tell us as much as you can in the original post for the simplest and most concise response. Gas turbines are pretty simple devices, but the auxiliaries and nuances can be intimidating at first.

Best of luck--and, do write back!!!