Carbonization temperature optimization experiment of pilot-scale continuous biomass carbonization equipment with internal heating

Biochar is a solid product generated by low temperature pyrolysis of biological organic material (biomass) in oxygen or anaerobic environment. Biochar can be used as adsorption material and soil conditioner, and also can be used as reducing agent, slow-release fertilizer carrier and carbondioxide sequestration agent etc., in addition, wood tar and wood vinegar as byproduct of biomass pyrolysis, can be used as the chemical raw materials. In recent years, the biomass pyrolysis carbonization technology has aroused widespread attention at home and abroad. Biomass carbonization technology can be differentiated according to the heating process applied and to the continuity of the biomass production. In China, 3 carbonization techniques are used, viz. external heating, internal heating, and spontaneous combustion. External heating indirectly heats biomass materials by hot air flowing around the carbonization chamber, while internal heating directly heats the biomass material through hot gas that is flooding the furnace from the bottom. In this case, hot gas and biomass materials are moving in opposite directions, increasing the heat transfer efficiency. The spontaneous combustion carbonization technique has the highest thermal utilization efficiency. It heats materials directly by spontaneous combustion of small fractions of the biomass materials. In order to analyze pyrolysis carbonization properties of different materials under internal heating and piecewise continuous pyrolysis technology, and verify the influence of carbonization process parameters on biochar physical and chemical properties, biochar yield rate as well as equipment productivity, this study chooses corn straw, corn cob and peanut shell as raw materials, and carries out the experiment of equipment production process. Test results show: When the draft fan speed is 725 r/min, and the furnace negative pressure remains at around 60 Pa by automatically adjusting the opening of the inlet, the biochar physical and chemical properties, equipment productivity and biochar yield rate are obviously different under different carbonization temperatures, especially the fixed carbon content and ash content of the biochar have significant difference (P<0.05), and corn stalk is the most sensitive to process parameters. Through the comprehensive evaluation analysis, the optimal carbonization temperatures are 550-600, 600-650 and 600-650℃ respectively for corn straw, corn cob and peanut shell. Application benefit analysis shows that the technology has good economic benefit and outstanding social and ecological benefits, but biochar industrial chain has some bottlenecks, such as biochar application in agriculture being not wide enough, which influences the straw biochar market sales. This study can provide technical support for the application of continuous biomass carbonization equipment.