Gravel Bed Combustor for Solid Fuel Fired Gas Turbine

Abstract

A fixed bed, downdraft combustor for solid fuels applicable to gas turbine cogeneration or combined cycles is described. The combustor has a refractory gravel bed, with fuel placed on top of the gravel and burning at the fuel-gravel interface. The gravel retains fuel particles in the combustion zone, preventing carryover of unburned char. Combustion temperature is held below the ash fusion temperature by using high excess air through the bed, thereby minimizing particulate ash agglomeration. Previous work on fixed bed, downdraft combustors and coal fired gas turbines is reviewed. Recent results from test firing a 480 cm2 (0.5 ft2) gravel bed combustor at atmospheric pressure with 2 cm (0.75 in.) wood chips are presented. Heat release rates of 3500 MJ/hr m2 (300,000 Btu/hr ft2) and higher were obtained. Carbon carryover in the exhaust was negligible. Approximately 85 percent of the particulate ash emissions was less than 10 microns.

The direct observation of alkali vapor species in biomass combustion and gasification

“…These provide some guidelines for conditions that will cause fo uling and stagging in turbines. Hamrick (1991) and Ragland (1989) have both operated turbines on hot gases from biomass combustors. Neither used gasification.…”

“…Ragland's system comprised a downdraft combustor and an Allison 250-C20B gas turbine (Ragland 1989). This system has no cyclone, and significant deposition was found.…”

“…The deposits on the nozzles were loosely attached and flaked off, but those on the turbine were more firmly attached and required soaking to remove. The system was run on primarily yellow poplar for 130 hours at bed outlet temperatures of 327-699°C (Ragland, 1989). However, temperature data for four out of the 26 runs were missing so temperatures may have exceeded this range.…”