Hello Folks
We have 02 Gas turbine(GE Frame 5) of 18 MW Capacity, and controlling system is MARK-VIe. Recently, we have faced "High Exhaust Spread Problem" twice and we had shutdown the Unit. We cleaned/replace the fuel nozzles twice, and recently we have installed knock out vessel for condensate capturing from Natural Gas. After second time nozzle replacement, Gas turbine performace was much better and spread was around 19 20 Degree C. But now as time is passing on, Exhuast Spread is again increasing and reach to 29 C. The point to be noted that, power load ramained constant and Difference between thermocouple showing lowest temp and TTLT(Low temp trip limit) is almost constant=19-18C.

Need your kind suggestions and comments/recommendations.

Thank you

 

Hi

Did you perform a swirl study /graph to see if the unit present a combustion issue..

 

Yes i studied swirl effects/graph.. We twice replaced fuel nozzles, checked combustion cans. But still the problem is persisting.. Like Exhaust spread is increasing but donot crossing the limit, although the power load is same

 

And the important thing is that the other Gas turbine is normal, and both are running in parallel

 

Are these units operating on simple or combined cycle

 

They are working on combined cycle

 

Hum interesting

 

Maybe load curves are not respected on this plant... Did you check that..

 

IF you replaced the fuel nozzles and spreads improved then it seems the nozzles may be getting fouled by something from the fuel source.
Have you sent out the fuel nozzles for evaluation and flow testing?
What fuel is this unit operating on?
Do inject water or steam for Nox reduction or power augmentation?
It seems to me if you have replaced the fuel nozzles and the problem went away, but then gets bad again over time, then something is fouling the nozzles causing the exhaust spreads to increase.
I would suggest having the nozzles evaluated to determine if something in the fuel is causing the problem.

 

1. inspect the exhaust TC integrity and tip condition
2. check the airline circuit for leaks
3. check the gas line circuit for leaks
4. check hot air leaks in the turbine compartment
5. Sometimes need to install the fuel nozzle as per the gas flow chart in case it is refurbished one
6. if everything is ok and you are not able to find the problem then go to CI (maybe the problem from the crossfire tubes is misplaced or some hot gas path parts are damaged )

 

I have been MANY places where the placement of a gas turbine on a fuel gas supply line has great affects on the operation of the unit. For one example, there was a single 12-inch natural gas main coming into a site with four heavy duty gas turbines. There was a "knock-out drum" (cyclone separator) at the entrance to the site (upstream of the pressure regulating valve). We were upgrading controls and combustion systems on all the units, and as luck would have it, the last unit to be upgraded was the last unit on the natural gas supply line, and all the other units were running when the last unit was being commissioned. We had a LOT of problems with this fourth unit, but one was caused by entrained liquids in the natural gas supply to the site making their way down to the last unit on the supply line and causing primary zone reignitions--lots of them. When we looked at the drain from the knock-out drum, there was very little in it, but there was LOTS of oily residue at the gas fuel y-strainer inlet to the last unit on the supply line. So, the entire plant was shut down, and the knock-out drum was opened up--to find NOTHING inside the knock-out drum. No internals, just an empty pressure vessel with a drain. There was a little oily residue in the knock-out drum, but not much. The internals were located and reinstalled (causing a two-day commissioning delay) we started up again. That drain from the knock-out drum had to be connected to a tanker truck--there was so much liquid coming out of it. The liquids were tested and included compressor lubricating oil, diesel fuel and gasoline. And, STILL the fourth unit was experiencing primary zone reignitions. Until it wouldn't transfer combustion modes any more. And exhaust temperature spreads were VERY high and increasing.
All of the fuel nozzles (primary and secondary) had to be removed and inspected, and lots of debris (rocks; weld slag; sand; broken glass) were found plugging the fuel nozzle orifices. The nozzles were disassembled, cleaned and reassembled and re-installed (after a three-day delay) and commissioning works were re-started. Until the fuel nozzles plugged again.
This time it was decided to get the natural gas supplier to the site and have them witness the issues--and to blow down the supply piping to get rid of all of the dirt and debris and hopefully any liquids in the supply piping, too (we were still finding a lot of oily residue in gas fuel manifold piping of that last unit as well as fuel nozzles).
The point here is that you can have two units sitting side by side, one running just fine and the other having all manner of issues. And, it can just be as "simple" as the way the fuel supply piping is configured. At the site in this example, we had zero indication over several months of commissioning and operation of the previous three units of any kind of issue with entrained liquids and dirt and debris in the supply--until we started running the LAST unit on the supply line. And, then we had nothing BUT problems. (Of course, the Customer blamed the turbine control system, but after three weeks of on-and-off commissioning and getting the gas fuel supplier to rectify their dirty, wet gas issues there were no further problems. On ANY of the four units.
So, simply saying, "The OTHER unit is running just FINE!" doesn't mean a thing, since we don't know the supply configuration. And, this likely IS NOT a controls issue (BUT we don't know what other alarms (Process and Diagnostic) are being annunciated and ignored), but a mechanical issue of some sort. Find out what the source of contamination is and that will resolve MOST of this issue.

 

They are working on combined cycle

Hamza, please contact me at [email protected]/7323435113.