> Modern central stations have "economisers"- huge rotating rooms 
 > about 40 feet
 > diameter. The exhaust gases thus preheat the incoming combustion 
 > air. Don't
 > ask me to describe the design. The design object is, recover lotsa 
 > heat
 > without requiring more fan power. These furnaces usually have Forced 
 > draft
 > fans to blow the combustion air into the flame, and Induced draft 
 > fans to suck
 > the burned gases out again. Any gadgets along the way [such as 
 > precipitators,
 > flue gas washers] demand more fan HP thus more fuel consumed.
They have home-sized gadgets that do the same thing for modern, well-sealed 
houses.
A friend recently retired from Detriot Edison, where he worked at a 
coal-fired generating plant. He said that he often wondered how they had 
enough electricity left over to sell after all they used in-house to run 
fans, pumps, etc. Nuclear plants can't start up from 'dark' without outside 
help; their emergency generators are just enough to perform a graceful 
shutdown.
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