Design of the multi-chamber equipment for corn straw in-situ returning carbonization

In-situ returning carbonization can directly convert the straw into biochar in the field. It is of great significance to improve the soil structure and soil fertility. The costs of collection, storage, and transportation can be reduced to solve the slow decomposition, low emergence rate, as well as serious pests and diseases in straw directly returning to the field. Previous research focused mainly on carbonization returning equipment. It is still lacking in the reactor section in large-scale production, uneven carbonization, operational stability, and production efficiency in the current equipment of carbonization returning. This article aims to develop multi-chamber equipment for corn straw in-situ returning carbonization, according to the precise oxygen and temperature control carbonization. A precise structure of air distribution was adopted to innovate a vertical multi chamber in the limited area of the carbonization reactor using the early prototype. The spiral disturbance component was designed to enhance the directional flow of materials. ANSYS software was used to simulate the structural optimization. The heat-transfer properties of metal were used to develop a clean combustion system for pyrolysis gas, together with a high-temperature flue gas heat exchange and reuse. In addition, the systems were further integrated, such as picking and crushing, silo conveying, continuous carbonization, flue gas cleaning and reuse, as well as the control. The vertical multi-chamber equipment was innovatively designed for the corn straw in-situ returning carbonization. A 20 kW/h generator was equipped to provide the energy consumption for all motors, in order to meet the needs of field work. The continuous transportation and carbonization of materials were achieved in the carbonization reactor. The high-temperature flue gas reuse was improved to reduce the equipment energy consumption for high carbonization and operational efficiency. In addition, a carbonization experiment was conducted using corn straw as the raw material. The equipment was also operated for one hour to collect the produced biochar and flue gas. The results show that the capacity of straw processing was 500 kg/h, the biochar yield was 125 kg/h, the fixed carbon content was 50.30%, and the system energy utilization rate was 70.66%. Industrial and elemental analysis of the biochar showed that the total carbon content reached 61.32%, whereas, the metal contents of Cu, Zn, and Pb were lower than those in the standard range of DB21/T 3314-2020. The biochar fully met the first-class standard of biochar returning. The concentrations of particulate matter, NOx, and SOx substances in the combustion smoke were 16%, 164.2%, and 32.6%, respectively, which were lower than the concentration standards for various substances in GB 13271-2014. And simulation analysis was conducted on the disturbed components, where the received stress was far less than the yield limit of the material. The maximum deformation was ignored relative to the overall size, where the structure and material of the disturbed components fully met the design requirements. The entire system operated stably, fully meeting the design standards, indicating environmentally friendly and pollution-free carbonization and returning to the field. This finding can provide theoretical, technical, and equipment support to the direct carbonization and return of straw to the field.