Heat recovery from wet wood waste

Abstract

Overall heat recovery from wet wood waste, particularly sawmill-generated hog fuel, is improved by a process for predrying the fuel. A wet oversize fraction of the fuel is combusted in a fluid bed reactor providing heat for drying the remaining smaller sized fraction of the waste pile to about 10-30% moisture by weight. The gaseous products of the fluid bed burning are contacted with the fuel fraction in, preferably, a rotary dryer. The dried fuel is then screened into coarse and fine fractions. The coarse fraction is fed onto a grate of a wood waste boiler. The fines fraction is injected into the boiler combustion in an air suspension. The amount of fuel fed to the fluid bed reactor is 10-25% of the total fuel flow, depending upon the moisture content of the fuel. The gases fed to the rotary dryer are less than about 1,200.degree. F., to minimize "blue haze," by combining with minimum outside air.

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