| In recent years, coal consumption for energy supplier in China has continuously dropped. However, coal consumption will still play a major role for quite a long period before sufficient alternatives can economically serve China’s energy needs. The gasification process, as one of the means of efficient and clean utilization of coal, has been extensively investigated on in our country. Nowadays, the normal coal gasification process has encountered with many problems, such as low gasification temperature and tar generation. Furthermore, emissions of CO2 and other greenhouse gases, as a result of extensive use of fossil fuels, have brought serious environmental and climatic concerns. Thermal plasma, a uniform system with characteristics of high temperature, high enthalpy and high energy density, has been widely used in the chemical strengthening process. Coal gasification by CO2 thermal plasma is not only expected to achieve efficient conversion of coal, but also to provide a new way for utilization of CO2. Factors on coal gasification process were investigated using a self-designed rotating arc plasma reactor. Coal gasification by CO2 thermal plasma was proved to be an effective method for the efficient gasification of coal, energy conservation and emission reduction.Four kinds of coal were gasified into syngas by CO2 thermal plasma. Influences of volatile matter content of coal, flow rate of CO2, input power and feed rate on gasification were investigated. Experimental results showed gasification performance had a significantly positive correlation with volatile matter content of coal. The product gas consisted of a high content of CO and H2 as well as small amounts of CO2 and light hydrocarbons. When the flow rate of CO2 increased from 0.77 Nm3/h to 1.37 Nm3/h, both H2 yield and CO yield increased from 63.9% to 73.3% and 60.2% to 83.4%, respectively, with the CO2 content no more than 2.3%. When input power increased, the carbon conversion increased from 77.1% to 83.0%, and the H2 content reached a maximum of 29.3% before it began to decrease. The peak yield of CO and H2 was 82.7% and 71.8% respectively under the optimum condition. Higher feed rate resulted in CO2 reduction and H2 increase. The energy conversion efficiency and carbon conversion reached the maximum of 71.6% and 90.4% respectively at the feed ratio of 18.7.Simulation of thermodynamics and kinetics simulation were conducted using the software of Chemkin and Fluent. The results of thermodynamic simulation did not match with experimental results, indicating that the coal gasification did not reach thermodynamic equilibrium. The dynamic mechanism of coal gasification by thermal plasma was simulated by 41 kinds of elementary reaction and gas-solid reaction between fixed carbon and gasifying agent. The results showed that the temperature of plasma reactor was between 2800K and 3800K, much higher than that of normal gasification process. The variation of gas component content with time showed that the reaction in the coal gasification process occurred in sequence of coal devolatilization, heterogeneous reaction between gasifying agent and volatile, and gas-solid reaction between gasifying agent and fixed carbon. The calculating results of dynamic model provided essential reference for better design of reactor and deeper understanding of coal gasification. |
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