"Before you diagnose yourself with depression or low self-esteem, first make sure that you are not, in fact, just surrounded by assholes." - William Gibson
This year's outage is just about over. It's been a minor one - about two weeks in length. As is usually the case, we found a couple of issues that were unexpected, and still managed to correct them inside the two-week time window. All it took was expediting some special high-pressure, high-chromium pipe here from Texas, and 50 pounds of welding rod :)
Below: A section of piping that drains condensation out of the superheater during start-up. This is P22 Chrome-Moly steel with 2 inch wall thickness. They don't keep this sort of stuff in stock at the local pipe supplier.
Yesterday I spent the morning on top of the boiler, on a temporary scaffold platform, wearing a safety harness. I was using a slugging wrench to close up a steam attemporator that had been disassembled for inspection. Below, a slugging wrench being used to tighten up a fitting.
The fitting I was working on looked something like the photo below. I hope it doesn't leak.
When performing maintenance on the boiler, it's necessary to segregate it into two different components: The Hot Gas portion, and the Steam/Water portion. The Hot Gas portion is the part of the boiler that the gas turbine exhausts into, and this requires a completely different equipment clearance than the steam and water part of the boiler.
Below: A cutaway of a General Electric 7FA Gas turbine. Images below are looking into this machine from the right side.
Yesterday it was time to perform a final inspection of the Hot Gas side, and then close it up. To go inside, you have to sign onto the equipment clearance, place a lock on the box that holds the keys to reactivate the equipment, and use a Confined Space Permit. The confined space permit ensures that the air is safe to breathe, and logs who has entered and left the space. It's all good safety practice, even if it is a pain in the butt.
Below, inside the boiler, looking at the gas turbine exhaust. The ladder and I are there for scale, and also to install the cover plate. To my left and right are a couple of ten inch (25 cm) holes.
In the image above, the opening above and right of my head is the access manhole to reach the aft gas turbine bearing. This bearing supports and aligns the aft end of the gas turbine shaft. The bearing housing sits in a stream of 1100 degrees F (593 C) hot exhaust gas when the turbine is operating. The housing is heavily insulated, and it is also cooled by blowers forcing cool air through it. Cool air enters from the tube on the upper right, and exits out the tube on the upper left. There is a third tube behind the ladder, and the bearing oil supply and drain lines are inside of it, as well as some instrumentation and fire suppression connections.
Below, a closer view of the gas turbine exhaust arrangement. Furthest away are the third stage turbine rotating blades, and you can see the struts that support the front end of the bearing housing. Exhaust thermocouple housings are the little spikes sticking in around the circumference. The bearing access cover plate has been reinstalled in this photo.
Below: The yellow deposits are sulfur compounds. Residual sulfur is in all fossil fuels. No matter how much the fuel stream is processed upstream, some traces of sulfur will always get by - since no process is perfect. This is why we have food specifications on the number of insects allowed per quantity of food. LOL.
Help meeeee!
Below, the holes mentioned in one of the images above.
Explanation of the holes: When the gas turbine is not up to full speed, the compressor is moving a great deal more air than the turbine needs. This excessive air has a tendency to snuff out the flame, and also cause surging issues - which I made a post about here. In order to avoid surging during start up and shut down, this excess air is routed around the turbine through bypass lines. Once the turbine breaker shuts, the bypass valves go shut, and all of the air goes through the turbine. These holes are where the excess air re-enters the exhaust after bypassing the turbine.
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