Energy balance analysis of corn straw continuous distillation

Abstract: Biomass pyrolysis poly-generation technology employs modern biomass distillation technology as the core, and biochar is a kind of solid product generated by low temperature pyrolysis of biological organic material (biomass) in hypoxia or anaerobic environment. Biochar can be used as adsorbent, soil improver, slow release carrier of fertilizer and carbon dioxide sealing agent. It can solve many problems such as agriculture, environment and climate. Pyrolysis gas is a kind of clean fuel, and wood tar and wood vinegar as the byproduct of biomass pyrolysis, can be used as fuel or chemical raw material. In recent years, the biomass pyrolysis poly-generation technology had aroused widespread attention at home and abroad. Compared to batch processing, continuous biomass carbonization technology had many advantages, such as high productivity, good process control and consistent product quality, and therefore it had been the primary focus of applied research and deployment of biomass carbonization technology. However, there are still considerable gaps in knowledge when it comes to carbonization of different biomass, especially non-woody biomass, in continuous units, and to the product characteristics, and energy and mass balances. In order to analyze the pyrolysis characteristics of biomass under the process of exogenous heating and continuous distillation, the biomass continuous pyrolysis experiment was carried out with corn straw, and the influence of process parameters on physical and chemical properties, and composition distribution of the three-state products was tested and analyzed. The pre-processed corn straw was pyrolyzed in a pilot-scale continuous pyrolysis poly-generation unit at the Laboratory of Energy Resource Utilization from Agriculture Residue, Ministry of Agriculture of the People's Republic of China. The unit consists of a sealed feed system, an auger pyrolysis unit, biochar discharge screw with indirect water cooling, secondary cracking unit for pyrolysis vapours and gases, and multi-stage condensation separation system. The core of the poly-generation system was the electrically heated continuous pyrolysis unit with a variable pitch screw to convey material. Heating was provided by a five-segment electric furnace, with independent PID (proportion, integral, derivative) control for each segment. The pyrolysis unit was fed by a rotary feeder connected to a hopper by a system of airlocks to prevent ingress of air. On the basis of above researches, the system calorimetry and energy balance were analyzed. The results showed that the quality of the maize straw charcoal was affected mostly by the residence time of the material in the reaction chamber, and the residence time should be not less than 30 min. The lower calorific value of the pyrolysis gas could reach 15-20 MJ/m3, and the pyrolysis oil's composition was extremely complex. The maize straw charcoal carried the most heat, accounting for 47.88% of the total product energy, and the biogas pyrolysis gas accounted for 36.17% of the total energy of the product; besides, wood tar and light oil accounted for 13.14% and 1.74%, respectively. Energy consumption ratio of continuous pyrolysis system was 0.97, and the energy recovery rate was 75.7%. The research can provide important support for the development and application of the exogenous heating biomass continuous carbonization equipment.