Research On Co-pyrolysis Of Biomass And Coal In A Free Fall Reactor

The pyrolysis process of solid was divided into primary pyrolysis and second pyrolysis. The reactivity of char obtained in primary pyrolysis was very high in the second reactions of pyrolysis, which significantly influenced the pyrolysis proceedings and product distribution. In this paper, the fast individual pyrolysis and copyrolysis of white pine and sub-bituminous coal were investigated in free fall reactor under nitrogen atmosphere. The study was focused on the effect of char on the second reactions of intermediate product of primary pyrolysis and the synergy effect during copyrolyis of sub-bituminous coal and white pine.The product distribution of individual pyrolysis of white pine and sub-bituminous coal was studied at pyrolysis temperature of600and700℃with and without char bed. The catalytic effect of char on second reactions of pyrolysis intermediate product did not suppress the combination of H free radical with OH free radical into water, but also promoted the combination of H and CH3free radicals with other small free radicals into tar. The catalytic activity of sub-bituminous coal obtained at700℃was higher than that at600℃, while the char of white pine obtained at600℃had better catalytic effect. The effect of char of sub-bituminous coal and white pine obtained at different pyrolysis temperature (600-750℃) was researched. With the pyrolysis temperature increasing, the gas yields of white pine and sub-bituminous coal were increasing while char yields decreased. The highest liquid yield and tar yield of sub-bituminous coal pyrolysis were obtained at700℃, which suggested that the sub-bituminous coal char obtained at70℃showed highest catalytic reactivity to the secondary reactions. As for white pine, the char obtained at600-650℃favored the production of liquid and tar.With char bed, the fast co-pyrolysis process of sub-bituminous coal and white pine were conducted at different pyrolysis temperature (600-750℃) and biomass blending ratio (BR,0.25-0.75). Obvious synergy effect was observed during the copyrolysis process with char bed. Compared to the calculated values according to single pyrolysis, all gas yields increased while char yields decreased. The CH4content in gas composition were all lower than calculated values. The copyrolysis char obtained at lower temperature (600-650℃) and BR (0.25-0.5) had better catalytic effect on the secondary reactions, which could be proved by higher liquid and tar yields than calculated values under that condition. The CH4content at biomass ratio of0.5and700℃were4wt%lower than calculated value, indicating the coyrolysis char promoted the CH3free radical transformation towards tar.The tar from individual pyrolysis and co-pyrolysis of sub-bituminous coal and white pine with and without char bed were separated into water-soluble, acid fraction, aliphatics, aromatics and polar fraction by chemical extraction and column chromatography. FT-IR and GC-MS were also used for quality identification and quantification. The catalytic effect of char on second reactions improves the composition of tar and light compositions in tar increased. The char suppressed the production of poly-aromatic hydrocarbons (such as phenanthrene, fluorine and pyrene) and oxygenated compounds (aldehydes and esters) and promoted the break of long chain alkane and aromatics with alkyal side chain into small or short chain molecules. The contents of decalinnaphthane, naphthane or its derivatives increased, which indicated the catalytic of char and synergy effect during copyrolysis changed the combination of free radicals and promoted the H and CH3free radicals into tar.