hello everyone

I want to talk about a event occur with me.

I am a shift supervisor in gas plant. the last week, I approved a PTW for instrumentation technician to purge inlet (suction) FI for BLC606C compressor driven by MS5002C from GE controlled by MARK 5, because it was indicate 0 although the machine was on service. when he open the purge valve, these events occur DDS Activate, anti-surge valve opened, and the GT entered under CONTROL TEMPERATURE (exhaust temperature reaches 535 c).

I want to ask, is the purge of FI caused these phenomenon? or the increase of temperature?

if the first answer, how to purge this FI with the machine on service?

best regards

 

zaidhrm,

Although you use abbreviations and acronyms every day at your site, many of the acronyms are not known to everyone, and many sites use different words/terms/abbreviations/acronyms for the exact same component or piece of equipment. So, when using abbreviations/acronyms please take the time to explain their meaning at your site.

It would seem to me that if the Mark V was being controlled by flow-rate through the compressor and if someone depressurized the flow-measuring instrument the inlet flow-rate indication would decrease to zero which would tell the Mark V, "Go, baby! GO!" Or, when the anti-surge valve opened the load on the gas turbine suddenly decreases which caused the exhaust temperature to go high because the fuel valves weren't able to close fast enough to prevent a high exhaust temperature because of the sudden loss of load.

When the Mark V wants to increase flow (or pressure) through the compressor it increases the fuel flow-rate to the turbine, which in turn increases the exhaust temperature. Or, when the load on the GT is suddenly lost it takes a split-second for the fuel valves to close and limit fuel flow-rate to limit the exhaust temperature; this is normal on a sudden loss of load (also called a load rejection), and sometimes even results in both a high exhaust temperature followed by a loss of flame trip as the fuel valves close too far and flame is extinguished.

I would suggest that proper operating procedures were not followed for this operation, or that it had never previously been done and a proper analysis and consideration of the consequences of purging the compressor inlet flow sensing device(s) was not done. I would also suggest that such a critical sensor would be redundant, that is, it would have more than one flow sensor, and that it's possible the technician depressurized all the flow sensors instead of just one at a time.

If there is only one flow sensor, then I suggest that before performing maintenance on it that the mode of operation of the gas turbine and compressor be switched to something other than flow (if possible) to prevent this kind of event from occurring again.

But, there should be written operating and/or maintenance procedures for activities like this on any well-managed site to prevent what happened from happening. If there is/was no written procedure then it's suggested the appropriate parties (operation; maintenance; I&C) form a team to analyze what happened and why, and develop a procedure for safely performing this activity--if it's even possible. Again, depending on the compressor controller and the available modes of operation and the level of redundancy of flow sensors it may not even be possible until such time as appropriate modifications to the system are made.

Hope this helps!