Abstract:
The coal consumption of power generation in China is nearly 2 billion tons annually. Although SO_2 emissions have been controlled at ultra-low emission level by the wet limestone-gypsum flue gas desulfurization( WFGD) technology,the problems of large consumption of H_2O as well as the difficulty in disposing the low-value by-product CaSO_4 make traditional WFGD technology face the sustainable development dilemma. By contrast,SO_2 removal based on carbon materials is regarded as one of alternative technologies to WFGD due to the advantages of low H_2O consumption,less water consumption,recycling of pollutants,eco-friendliness as well as high-value utilization of by-product. Herein,the research progress of sulfur removal and resource utilization based on the adsorption and catalysis of carbon materials was reviewed. The key technical links in the process of desulfuration by using carbon materials were discussed. Finally,the directions for future research for sulfur removal and resource utilization were proposed. The mechanism of SO_2 adsorption catalytic reaction and the product migration path in carbon materials were discussed. The effects of pore structure,functional group and metal oxide loading on the adsorption and conversion of SO_2 as well as by-product migration were discussed. The results show that the adsorption and conversion of SO_2 as well as by-product migration can occur in hierarchical pore; Doping non-carbon elements such as nitrogen and oxygen can change the electronic structure of carbon surface and further adjust the processes of adsorption as well as catalytic oxidation of SO_2 in carbon materials. Therefore,oriented construction of hierarchical pore structures and functional groups is an efficient method to strengthen the adsorption and transformation of SO_2 and improve the desulfurization performance of carbon materials. The regeneration of saturated carbon materials and the pathways of sulfur resource utilization were analyzed. Particularly,the factors that may influence the conversion of SO_2 to sulfur by carbothermal reduction were discussed. Thermal regeneration faces the problems of high energy consumption and serious loss of quality. Washing regeneration has the problems of low efficiency and poor cycling desulfurization capacity. Efficient regeneration requires effective matching of pore structures of different sizes to enhance the diffusion and transportation processes. Among all kinds of desulfurization by-products,sulfur owns the advantages of low quality,high value,convenient storage and transportation,which is an ideal goal of resource recovery. The regulation of the activity and selectivity of carbon-based reductant is the key to achieve efficient sulfur generation. Low-cost preparation methods of high-performance coal-based activated coke was analyzed. The method that could prepare activated coke with hierarchical pore structures was particularly discussed. The preparation of traditional columnar activated coke has complicated preparation process and high cost and microporous distribution of pore structure. The prepared columnar activated coke only owns micropores,leading to the problems of large internal diffusion resistance,low internal surface utilization,and poor SO_2 removal and regeneration performance. The preparation of broken or granular activated coke is able to reduce the cost of preparation of activated coke and achieve deep regulation of the pores of activated coke,but the improvement of structural stability( strength) is the key for its application. Through catalytic activation,coal blending and catalytic graphitization,the desulfurized active coke with both high activity and high structural stability is expected to be prepared.