Design and experiment on solid heat carrier heating device heated by high temperature flue gas for pyrolysis of biomass

Abstract: Biomass is one of environment friendly and renewable resources, which is considered as an ideally clean energy. In general, the development and utilization of biomass energy aim at converting the solid agricultural and forestry wastes into gaseous, solid or liquid fuels by physical or chemical processing methods. Solid heat carrier heating biomass is one of the process means of preparing bio-oil from biomass pyrolysis. In order to solve the indirect heating slow and low efficiency problems of solid heat carrier heating, a solid heat carrier heating device heated by high temperature flue gas which was generated by fluidized bed combustor was designed, and its structure and principle were analyzed, including high temperature flue gas generator, feeder of ceramic ball, heat carrier heat exchanger, built-in baffle, data acquisition and control system. The device could carry out the solid heat carrier heating performance and the combustion characteristic of fluidized bed combustor. Furthermore, the heat balance analysis of test results was performed. Biomass powder fuel was conducted on proximate analysis, ultimate analysis and determination of low calorific value, the results showed that the biomass powder fuel was a kind of clean energy. By conducting tests of biomass powder fuel combustion on high temperature gas generating apparatus to determine optimum powder concentration was 240 g/m3. The fluidized bed combustion furnace temperature changes were analyzed under optimal wind powder concentration, which indicated that biomass powder burning had ideal effect, the burner could be continuous, stable producing high temperature flue gas. By studying the temperature variation during the heat exchange process of ceramic balls and high temperature flue gas, the convective heat transfer coefficient of ceramic ball and high temperature flue gas and the heat utilization efficiency of the device were obtained. The convection heat transfer coefficient between ceramic balls and the high temperature flue gas was calculated and heat energy utilization of heating equipment was detected. Results showed that the heat utilization efficiency of the heat carrier heater reached by 66.3%. The high temperature flue gas produced by biomass combustion in fluidized bed could satisfy the need of the heating of ceramic balls for biomass pyrolysis. The convection was the main heat transfer in the heat carrier heater and the convection heat transfer coefficient between ceramic balls and the high temperature flue gas was 475 W/(m2·℃). By heat balance analysis and heating capacity theory analysis of the device，it indicated that study results have important guiding significance for solving the biomass pyrolysis technology in the key solid heat carrier heating up issues.