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Posted by Tony Conner on June 08, 2002 at 06:43:25:
In Reply to: how much steam can be produce from fueloil and natural gas posted by zaib on June 07, 2002 at 23:33:12:
I doubt very much that you're actually getting 90% eff. Probably much closer to 80%. Pull out your steam tables, and find the BTU/lb of the steam generated. Subtract the BTU/lb of the feedwater. This will be the amount of heat added to each lb of water entering the boiler to make steam.
Now it's a matter of the heating value of each fuel. Natural gas will be about 1,000 BTU/ cu ft, oil (depending on what type), maybe 140,000 to 160,000 BTU/ US gallon. Typically on oil, you'll need to run higher combustion air flow, possibly have steam atomizing, steam to preheat it, and blow soot. This won't affect the actual boiler eff, but does have an impact on operating costs.
A pretty good rule of thumb for industrial package boilers is that the boiler will add about 1,000 BTU to each lb of feedwater. This means at 80% eff, the burner will have to supply about 1,250 BTU per lb of steam generated. Remember to allow for blowdown when figuring total heat input required by a boiler. You're heating that water in the boiler, but it doesn't leave as steam to do work. 10% of steam production would likely be a safe number for CBD & bottom blow down.