Production of gaseous fuel in circulating fluidized bed gasification process employing refuse-derived fuels

A fuel gas production system involving gasification of refuse-derived fuel (RDF) in a circulating fluidized bed (CFB) was explored. The pyrolysis behavior of three kinds of RDF and the particle motion in a cold model CFB were experimentally studied to contribute to the design of a CFB gasification system and to clarify operation factors for optimum control as the first step of R&D on the proposed system. A rise in pyrolysis temperature improved the yield of the combustible gas components and/or the energy recycle efficiency from RDF, but the highest heating value of pyrolysis gas was obtained at temperatures of 873 to 973 K. The total gas yields could be expressed as a function of temperature and volatile matter content in raw materials regardless of the type of RDF. The gas flow rate in the pneumatic valve of the CFB was found to be an important factor to control the circulation rate and the holdup of particles in the cold model riser. For silica sand whose median diameter was 100 mum, a dense bed was formed at the bottom of the riser in the superficial gas velocity explored in the present work, 1.65-2.12 m/s. A gas velocity of 1.65 m/s increased the holdup significantly in the dense bed and could maintain the residence time of RDF needed for the conversion by gasification of the RDF. The pyrolysis test of RDF in CFB was carried out, and inflammable gas with 23.6 MJ/m(3) yielded under the riser temperature 1030 K.