COMBUSTION OF RESIDUAL BIOSOLIDS FROM A HIGH SOLIDS ANAEROBIC-DIGESTION AEROBIC COMPOSTING PROCESS

A humus consisting of aerobically stabilized anaerobic digester efflue nt was burned in two laboratory test facilities to evaluate possible p roblems in using the humus as Fuel in boilers. An atmospheric circulat ing fluidized-bed combustor (FBC) was used to assess possible bed aggl omeration when using alumina-silicate bed media. A multi-fuel capable entrained flow combustor (MFC) with electrically heated walls simulati ng a boiler was used with air-cooled tubular probes to evaluate potent ial ash deposition on heat exchangers. Low heating value of the humus led to poor temperature control in the FBC when burned alone. Tests of the humus blended 50% by weight with wood were also carried out in th e FBC. No evidence of bed agglomeration was found in the FBC with tith er humus alone or blended with wood at temperatures up to 900 degrees C: the maximum tested. Bed-drain rate was nearly equal to fuel-ash fee d rare to maintain constant bed pressure drop due to the high sand fra ction in the humus. Deposits collected on the probes in the MFC experi ment were enriched in alkali-sulfate, as were the fine fractions of fl y-ash samples. Deposition rates were not established due to particle-i nduced abrasion of deposits from the heavy sand fraction of the fuel, but at least moderate alkali-sulfate deposition can be anticipated if humus is burned in commercial units. (C) 1997 Elsevier Science Ltd.