Saturday, March 29, 2008
All in a Day's Work: Backpass Inspection
The dreaded outage has begun. Unit 2 came off line last night about midnight and things cooled down enough for us to get in and do a backpass inspection this afternoon. I have a few more pictures for you too look at. The backpass in Unit 2 is the same as in Unit 1, so there really isn't a lot new here.
This is a roomy and comfortable hole know as the 'economizer'. After the steam has gone over the turbine and condensed back to water, that water is pumped back into the boiler to be used again, as it is very pure. But is is also very cold compared to the boiler and would cause problems if it were pumped directly back into it. So it goes through a series of feedwater heaters (more on these later) that use waste and low quality steam to preheat the water. The last heater is actually in the coolest part of the gas path and the water picks up quite a bit of heat that would otherwise be wasted. Walking around in the Economizer is tricky, and the pipe is covered with slippery ash, kind of the consistency of flour. So you can appreciate the care that is taken by each of us as we walk around on these tubes.
Here is a little hole to let us go from the top parts, to the lower parts. Beneath this is a pipe called a sootblower lance. Periodically the soot blower shoots steam out of the end of this pipe as it rotates it slowly, and pushes it into the space. The steam knocks ash of the tubes and that lets them transfer heat more efficiently.
One thing that we didn't do last time, on the short outage, was to wash the boiler cavity and remove all the clinkers and ash so that work can begin down below without worry of a boulder sized clinker falling 18 floors and smashing you flat. We have tried several different methods to remove these clinkers, and this time we are washing them out with a water cannon. This is a fancy nozzle that you can hook two 2-1/2" fire hoses to.
Well, that is about it. More adventures tomorrow. We are both tired at the start. It might be a really long month.