I was just wondering how much if any damage to the turbine to run with a bleed air valve that is failed and open? Second stage wheelspace upwards of 1200 deg. Power output obviously on the low side because of it.

 

The "dumb operator" is the one who doesn't ask any questions, and assumes that because he's an operator that he knows everything--or is expected to know everything. (It truly is a 50/50 split between those dumb operators who will outright say they know everything about the turbine and auxiliaries--but don't, and those who are so afraid of losing their job for asking a single question because they believe in their heart they are expected to know everything and will be sacked, or ridiculed for asking a question.) So, you've already proven you're NOT a dumb operator simply by asking the question.

What was the wheelspace temperature (the reading from each of the two T/Cs in that wheelspace) before the bleed valve opened?

The turbine shouldn't suffer too much if operated for a couple of hours or so with a compressor bleed valve not fully closed. However, depending on where the extraction for bleed air is taken it might have a serious effect on cooling and sealing air flow to the wheel spaces. If the 1200 deg F you are reporting was reached AFTER the unit had been operated for several hours or longer with a bleed valve not fully closed then some serious damage could have been done to the turbine wheel and/or the seals.

While a bleed valve opening is not usually a turbine trip for a machine with conventional (diffusion flame) combustors, it's incumbent on the operations and maintenance supervision to rectify the situation in a timely manner--that being an hour or two for a prudent response. In an "emergency" situation--that being decided on a case-by-case basis--the unit can be operated longer, <b>BUT</b> if other circumstances--like an extremely high wheelspace temperature (the result of the average of the two wheelspace T/Cs) then prudence dictates the unit be shut down and the issue resolved.

 

I appreciate your time in answering my question. Is it possible to run temporarily with a failed bleed valve isolated or do you need both bleed valves to properly work for "surge" protection?

 

The bleed valves should be open during shutdown and start-up for surge/stall protection. The turbine output is low when any bleed valve is open during loaded operation, which means also that the efficiency is low, so you're getting less power for the same or slightly higher fuel flow-rate.

If the manual isolation valve of a single open bleed valve is closed during loaded operation that is okay--unless the turbine trips. Then the chance of a surge/stall would be higher with a single closed bleed port. If you ran with a closed manual isolation valve and opened it before the unit started decelerating from 100% speed, that would be okay. It's the risk of tripping with the manual isolation valve closed and not being able to open it quickly enough that is the most troublesome issue. In my personal opinion I believe it probably wouldn't be too much risk--but that's a guess, not a fact. I have no experience with a single closed bleed port during a trip.

But, if you NEED the power, you gotta do what you gotta do--trying to minimize the risk as much as possible but recognizing there is some risk. That's what Managers get paid the big bucks to do--recognize risk and decide when to take reasonable risks, minimizing them to the extent possible, and living with the consequences if something does happen.