Novel Low-Cost Process for the Gasification of Biomass and Low-Rank Coals

[摘要] Farm Energy envisaged a phased demonstration program, in which a pilot-scale straw gasifier will be installed on a farm. The synthesis gas product will be used to initially (i) generate electricity in a 300 kW diesel generator, and subsequently (ii) used as a feedstock to produce ethanol or mixed alcohols. They were seeking straw gasification and alcohol synthesis technologies that may be implemented on farm-scale. The consortium, along with the USDA ARS station in Corvallis, OR, expressed interest in the dual-bed gasification concept promoted by WRI and Taylor Energy, LLC. This process operated at atmospheric pressure and employed a solids-circulation type oxidation/reduction cycle significantly different from traditional fluidized-bed or up-draft type gasification reactors. The objectives of this project were to perform bench-scale testing to determine technical feasibility of gasifier concept, to characterize the syngas product, and to determine the optimal operating conditions and configuration. We used the bench-scale test data to complete a preliminary design and cost estimate for a 1-2 ton per hour pilot-scale unit that is also appropriate for on-farm scale applications. The gasifier configuration with the 0.375-inch stainless steel balls recirculating media worked consistently and for periods up to six hours of grass feed. The other principle systems like the boiler, the air pump, and feeder device also worked consistently during all feeding operations. Minor hiccups during operation tended to come from secondary systems like the flare or flammable material buildup in the exit piping. Although we did not complete the extended hour tests to 24 or 48 hours due to time and budget constraints, we developed the confidence that the gasifier in its current configuration could handle those tests. At the modest temperatures we operated the gasifier, slagging was not a problem. The solid wastes were dry and low density. The majority of the fixed carbon from the grass ended up in the solid waste collected in the external cyclone. The volatiles were almost all removed in the gasifier. While the average gas heating value of the collected gas products was 50 BTUs/scf or less, addition a of the second gas exit for combustion gases would increase that value by a factor of two or three. Other changes to the current design such as shortening the gasifier body and draft tube would lead to lower air use and shorter heating times. There was no evidence of steam reforming at the current operating temperature. Likewise there was no indication of significant tar production. Reconfiguration of the gasifier at the on farm site may yet yield more significant results that would better qualify this gasifier for small scale biomass operations.

[发布日期] 2009-03-05

[学科分类] 燃料技术

[关键词] ALCOHOLS;ATMOSPHERIC PRESSURE;BIOMASS;BUILDUP;CARBON;DEMONSTRATION PROGRAMS;ELECTRICITY;ETHANOL;FARMS;FEEDING;FLUE GAS;FLUIDIZED BEDS;GASIFICATION;GRAMINEAE;HEATING;SOLID WASTES;STRAW;SYNTHESIS;SYNTHESIS GAS