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Posted by Dick Bishop on June 03, 2003 at 16:53:40:
In Reply to: stack economizers posted by m white on July 23, 2002 at 09:29:32:
: does anyone have an opinion on stack economizers?
: this would most likely be for a 100bhp firetube boiler, burning #2, and total operating hours for the year are estimated to be 1300-1400 hours. is it worth it or am i just setting myself up for a major maintainence issue?
I would run from the economizer idea for this size of boiler espically burning fuel oil. Fuel oil has a lot of sulfer, which if the temperature of the flue gas falls below the sulfer's dew point the sulfer liquifies (to Sulfuric Acid) and eats everything. Depending on the pressure the boiler is operating will effect the temperature of the flue gas leaving the boiler. Typically for a boiler to be efficient the flue gas should not exceed 150 degrees above the steam temperature
If you are making low pressure steam, around 15psi. the steam temperature is about 250 degrees the gases should be no more than 400 degrees entering the economizer, if you are not preheating the feed water and it is entering the economizer at approxametly 50 degrees it can asorb enough heat to cause the temperature of the gases to fall below 260 degrees and your breeching and stack collapase in a matter of months. Do some reasearch be cause an economizer can work but the type of fuel, the steam pressure and temperature the temperature of the feed water will have an effect. For an example natural gas usually does not have sulpher but has Nox2 getting below the dew point can be hazardous and can cause a fire as well. I would think your money would best be spent keeping traps in good repair and insulating allsteam and condensate line.