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Posted by Tony Conner on May 20, 2005 at 09:53:31:
In Reply to: steam pressure posted by Tom Looft on May 18, 2005 at 20:03:17:
The "big saving" that is dangled is usually at the boiler itself. Lower steam pressure means lower boiler water temp, which means that the flue gas temp out of the boiler can be lower. The other part is with steam at lower pressure/temperature, the loss from the piping is also reduced.
In practice, there are usually a bunch other problems show up, and I'm not sure that anybody can actually prove much in the way of savings. In any event, most plants don't have enough instrumentation to effectively measure anything - the biggie being the steam meter off the boiler. If a steam meter is not pressure compensated (and the vast majority are not), it'll read high if the operating pressure is lower than it was calibrated for. I've seen people seize this inflated steam production value as the "proof" that dropping the boiler operating pressure has resulted in "big savings". The fact that they now had 125% boiler efficiency didn't seem to give them any concern about the accuracy of their numbers.