Experimental Study On Lignite Pyrolysis In A Fluidized-bed Reactor

Lignite plays a very important role in energy resource. Since lignite has high moisture and high volatile matter, how to make rational use of lignite becomes a hot research area. The multi-products technology based pyrolysis in a fluidized-bed is a new clean way to use lignite with high efficiency. The characteristics of lignite pyrolysis in a fluidized-bed is meaningful for the design and operation of multi-products plant, and the yield and characteristics of pyrolysis products (gas\semi-char\tar) determines the economics and stability of whole system. In this paper, Xiaolongtan lignite was chose as material, and the characteristics of lignite's pyrolysis are systemically researched by TG-FTIR, DSC, a small fluidized-bed reactor and a 1MW multi-products system. The effect of temperature on characteristics of lignite pyrolysis in a fluidized-bed was focused on.Through the TG-FTIR research, the weight loss and gas generation during pyrolysis were known more exactly, and find that final weight lost increase with final pyrolysis temperature linearly. Through the DSC research, find that pyrolysis is endothermic before 700℃, and then become exothermic.The effect of temperature on the pyrolysis products of XiaoLongTan lignite was studied in a fluidized-bed reactor. When reaction temperature rose from 550℃to 750℃, the semi-char yield decreased, the gas yield increased, maximum tar yield and pyrolysis water yield was obtained at about 650℃, the yields of H2, CH4 and CO increased evidently, the content of H2, CH4 and CO also increased, but the content of CO2 decreased substantially, the gas production increased markedly, and the gas heat value increased a little. With the temperature increased the volatile matter in semi-char decreased evidently, Oxygen and Hydrogen element decreased markedly, and the removal rate of nitrogen and sulfur increased evidently, when temperature is higher than 700℃, the rate could get 57% and 63% respectively. Most pore in semi-char was middle pore, and the number increased with pyrolysis temperature. The temperature has little influence on combustion characteristics of semi-char, with the temperature increased the semi-char were harder to catch fire.When Xiaolongtan lignite was chose as material,1MW multi-products system ran successfully, and tar and gas product were got. The gas had high effective composition, when temperature raised from 550℃to 750℃, the concentration of H2 increased from 12% to 31%, the concentration of CO increased from 12% to 23%, and the concentration of CH4 decreased from 22% to 13%; the heat value is between 16-18Mj/m3, and decreased with temperature; but the yield of gas is between 24-247m3/ton and increased with temperature substantially. Effects of temperature on H2/CO concentration and gas yield were the same with those got from small fluidized-bed reactor; but effects of temperature on CH4 concentration and gas heat value were different. Effects of temperature on content of saturated hydrocarbon\aromatics\ non-hydrocarbon were complex, when temperature was low, the contents increased with temperature, but when temperature was high, the contents decreased by decomposition. The content of asphaltene increased with temperature continually, indicated that asphaltene was more stable and hard to decompose when temperature was high. The tar yield increased firstly, and then decreased, and got its maximum at 600℃.