A sequential cycle of coal gas production with high heating value consisting of reduction and oxidation reactions

摘要

A sequential cycle of coal gas production with high heating value was developed consisting of reduction and oxidation reactions. Steam and air are used as gasification agents in the reduction zone while the reaction between char and air in the oxidation zone is exothermic and provides heat for the reduction zone. Coal ash and unburned char are circulated between the two zones and heated in the oxidation zone. The reduction zone and the oxidation zone form a circulation system, and high heating value coal gas can be produced in it continuously. The feasibility of the proposed cycle was verified by preliminary experiments; and a system model was built with Aspen Plus software, in order to evaluate the operation conditions, to get accurate parameters for the cycle and provide a design basis for a serial production of large equipment. The simulation results show the effect of air-to-coal ratio in the reduction zone (R_(a-red)) and steam-to-coal ratio (R_s) over some parameters, like lower heating value (LHV), production rate (m) and compositions of coal gas. In addition, pilot experiments were carried out based on the model; coal gas LHV was established between 8.40 and 9.24 MJ/N m~3. The simulation results were according with the experimental data under the same operation conditions in 3 different cases. As a result, coal gas LHV was increased by more than 87.50%, comparing the experiment with the typical Winkler fluidized bed gasifier, which uses air and steam as gasification agents as well.