Influence of gases pressure on the formation of charcoal in the process of pyrolysis of plant biomass

Abstract

The article discusses the results of an experimental study of the effect of pressure on the formation of charcoal during the pyrolysis of wood, carried out on a laboratory bench at pressures of 1, 3, 5, 7 atm and a temperature of 400 °C. Birch wood in the form of wood chips with a particle size of 17c8c6 mm was used as feedstock. Its moisture content was 14.2 % by weight, its density was 506.4 kg/m 3 , and its ash content was 0.23 % by weight. It was found that an increase in pressure from 1 atm to 7 atm leads to an increase in the yield of charcoal from about 25 % weight. up to about 32 % weight. The carbon content in this case increases from 89.1 % by weight to 96.4 % by weight. The work also experimentally investigated the effect of artificial deterioration of the conditions for the exit of volatile pyrolysis components from the reaction zone on the formation of charcoal and carbon content. The data obtained suggest that the deterioration of the exit conditions of volatile components from the reaction zone leads to their decomposition with the formation of carbon deposited in the pores of the pyrolyzable material and on its outer surface. Experimental data are also presented showing that components of the pyrolysis tar decompose in the presence of charcoal with the deposition of the formed carbon on its surface. The presence of such process is indicated by the difference in masses of identical charcoal samples studied at a temperature of 600 °C in the absence and presence of pyrolysis tar. The final mass of the sample, investigated in the presence of pyrolysis resin, as established in the work, exceeds the mass of the sample, studied in its absence. These results provide indirect evidence of the correctness of the assumption about the decomposition of the pyrolysis components in the pores and on the surface of the pyrolyzable material by a delay in the release of the pyrolysis components from the reaction zone. The results of this study are of interest to specialists developing pyrolysis equipment.