Monitoring and control system development for pilot-scale moving bed biomass carbonization equipment with internal heating

Abstract: Biochar is a pyrolysis solid product of biological organic material (biomass) in anoxic and anaerobic conditions, It can be widely used in carbon emission reduction, water purification, adsorption of heavy metals and soil improvement, etc., so it can partly provide solutions for the focus issues of global concern, such as climate warming, environmental pollution and soil degradation. The production and application of biochar have aroused wide attention of researchers both at home and abroad. According to the continuity of production process, two types of biomass carbonization techniques have been developed in China, which are respectively fixed bed carbonization technique and moving bed carbonization technique. The fixed bed carbonization techniques can be divided into kiln carbonization technique and retort carbonization. Accordingly, the kiln carbonization technique commonly adopts spontaneous combustion heating method, its corresponding equipments have the features of simple structure and low-cost, so this technique has been used widely in China. The retort carbonization technique adopts external heating method, so its corresponding device has more complicated structure than the kiln carbonization technique, this technique can commonly realize the poly-generation of biochar and other byproducts. The moving bed carbonization technique is upgraded from the fixed bed carbonization technique, and according to flowing the direction of material, this technique can be divided into transverse flow moving bed carbonization technique and vertical flow moving bed carbonization technique. Continuous producing is the remarkable feature of the moving bed biomass carbonization technique, and it has higher automation level and lower labor intensity, compared with the fixed bed carbonization technique. The moving bed carbonization technique represents developing direction of China's biomass carbonization technique. Aimed at the problems of low productivity, high energy consumption as well as difficulty in control of process parameters with biomass carbonization equipment, based on the development of moving bed biomass carbonization equipment with internal heating, monitoring and control system was developed by using the software platform of Kingview, and feedback control mechanism and cascade control technology the system are adopted. The monitoring and control system mainly includes feeding control system, the carbonization environment monitoring system, biochar discharging control system, and other auxiliary software system, etc. The main and deputy controllers for monitoring carbonization temperature and furnace pressure are respectively positional PID and incremental PID. Production test results show that monitoring and control system is stable and reliable, which can realize orderly control of equipment operation and directional control of carbonization environment. Compared with no monitoring system, equipment productivity increases by 18.3%, and the carbon yield increases by 2.3 points. Development and application of the monitor and control system provides technical support for the industrialization promotion of related equipments.In automatic work mode of the monitoring and control system, control mechanism and the control algorithm are the main influence factors in order to realize directional process control of the biochar. On the one hand, we need further optimize process parameters of different materials through a lot of production test under internal heating condition, on the other hand, we need further analysis the influence of control parameters (such as negative pressure, the air inlet opening, air inlet position, etc.) on the carbonization environment (such as carbonization temperature, heating rate, catalyst, etc.), and optimize the environment of coking equipment control mechanism and algorithm.