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Posted by Jeff fisk on November 03, 2004 at 18:43:30:
In Reply to: Proper air/fuel requirments in a wood fired boiler posted by Chris B on October 29, 2004 at 08:48:40:
: We burn wood dust and shavings primarily made up of Red Oak at about 7% moisture. I'm looking for some help in determing proper air/ fuel mixtures. We have firebox temps. in excess of 2000F and causing fusion. The ash comes out in chuncks not a powder like it should. Under grate temps are around 300 to 350F. and the grates are covered with a hard layer of ash. The refractory side walls get a glazed look and the over fire air nozzles get covered with the melted ash.
First thing you should do is get a lab to perform (ultimate) fuel anaysis for you. Tell them are are having problems with your ash melting. They will be able to provide you with all kinds of information which will tell you some very specific things about your ash. (ie the point at which it starts to become sticky, the point it melts etc) They will also give you a complete chemical breakdown of you fuel.
You MUST have this infomation....otherwise your only guessing.
Next take this info with your problems to whoever manufactured your furnace. They will be able to tell you how much theroretical and exess air you require per pound of fuel. (they would have done this....but give them new data)
More specifically, they will tell you what percentages of your total air should be flowing through what windbox. After this....you should be able to figure everything out on your own. (providing you've done your homework, and have some way of measuring your combustion temps)
As mentioned by someone else....make sure there is nothing else in your fuel. Waste oils.....or anything at all. (garbage in...garbage out) Also 7% sounds very low...even for dust and shavings.
Without knowing more about the furnace its hard to say. Likly your problem is something simple like your running too much underfire air, or not enough overfire air.
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