Saturday, April 19, 2008

All in a Day's Work: Bottom Ash, Hotwell, DA Storage, Condenser

This is the bottom of the boiler.

This is where the water collects after it condenses after it goes over the turbine.

This is where the cooling water condenses the steam after it goes over the turbine blades.

Friday, April 18, 2008

All in a Day's Work: Furnace Scaffolding

I hope you like this. Possibly I will make more of these little clips.

Monday, April 7, 2008

All in a Day's Work: The Boiler Drum

Ahhhhh.... my least favorite place - anywhere. The drum collects the mixture of steam and water that comes frothing up from the waterwall tubes. The steam goes on to a circuit of tubes that gradually heats the steam until it is dry and has a lot of energy in it (1050 deg F) It then goes down to the turbine. We talked about this in the post on the penthouse.

The drum is about 85 feet long and about 3 feet in diameter inside. Regrettably, it isn't all free space. The top 1/2 or maybe even 2/3 is occupied by steel 'cans' that do the actual separating. So you have the bottom 40% or so to crawl through, but it isn't the real bottom of
the drum, but a shell and so you have less and less space to wiggle through. The drum is about 7" thick and has a small hole on each end to wriggle in and out of. Not only does this construction favor skinny people, it favors short skinny people the most. Enough said. You all know I am neither skinny or short.

I used to think I would like to build a submarine, but a couple of trips through the drum on my stomach changed my mind. Here are a few pictures. Enjoy.

Saturday, April 5, 2008

All in a Day's Work: Scaffold

Every other outage (4 years) we scaffold the boiler cavity in one of the units. This allows us to walk around the edge of the boiler and then they build a big 'dance floor' at the top, right under the platen pendants. Then we put some more scaffolding up around them so that we can inspect and repair them. There isn't a lot more to say. The pictures say most of it.
Looking Across

Looking Down

Looking Up

Thursday, April 3, 2008

All in a Day's Work: The Penthouse

Spending time in the Penthouse sounds a lot more appealing than it is, although as boiler spaces go, it is fairly comfortable.

Boilers are built so that water and steam circulate from the hottest spots, to where the work needs to be done. Forced circulation boilers have big circulating pumps that move the boiler water around. These are common in supercritical plants. Supercritical plants are not plants that are just really grouch, and always complaining about something. They are plants that operate at such high pressures that steam never forms - the water turns to something that isn't water and isn't steam. Then at a pressure drop over a valve, this fluid will flash to steam and drive a turbine.
We have a natural circulation boiler. There is a big fireball area in the cavity of the boiler. It is surrounded by water filled tubes- the water walls. Which is different than the walls of water that you put around your tomato plants. The water boils in the tubes, and the steam that is formed rises, carrying a lot of water upwards with it. The water and steam flows to the steam drum and is separated there. The water falls back down to the cool bottom of the boiler in large pipes called 'downcomers', and the steam starts a path through a series of tubing loops where it becomes progressively hotter and dryer. At each stage there is a really big pipe or 'header' that has all the looping tubes welded to it. The pressure and temperature of each small tube sort of equalizes out in the header, and then the steam is redirected to another set of tubes where it gets hotter yet, until finally it comes out of the secondary superheat header, into the main steam line and goes down from the 19th floor to the 2nd floor where the turbine is.

The place above the boiler roof where all these headers are, and where all these connections are made is called the penthouse. Why I don't know. But there is a lot of stuff going on there. Lots of tubes, lots of pipes. It is really surrealistic to look at, and it takes some time to figure out where everything goes. I think that is enough of a lesson tonight. Here are a few pictures of some of the headers. I end up crawling around in the insulation dust quite a bit, so it is a bit itchy. Still, interesting. I didn't think I would be doing this when I was a little boy.