| Coal is the dominant fossil energy in China, of which 70% is used through combustion. The contrast of the pollution of SO2 and the demand of sulfur resources are intense. The coal mines are mostly located in the west of China, where is lack of water resources. Consequently, flue gas desulfurization (FGD) used activated coke could realize sulfur resources recovery. The cost of activated coke limited the popularization and application of FGD using activated coke. The rapid preparation technology of powder activated semi-coke by one-step activation was developed in this paper. The powder activated semi-coke was prepared within about 5-20 seconds from pulverized coal by flue gas activation which could be conditioned by air and steam according to the differences in coal rank at about 900℃ on entrained bed reactor. In order to promote the popularization and application of rapid preparation technology of powder activated semi-coke, the basic research of this preparation technology was investigated. The SO2 adsorption capacity of powder activated semi-cokes which were prepared respectively from lignite, bituminous coal and lean coal by different activation agents was studied. Based on lean coal, the evolution mechanism and controlling factors of pore structure and surface chemical characteristics was studied. The relations between the SO2 adsorption capacity and the physical and chemical characteristics were also investigated. Based on theoretiacl research, the pilot test system of powder activated semi-coke was established. The rusults obtained in pilot test system could verify the results of the mechanism experimental and guide the design and operation of the engineering application of powder activated semi-coke preparation tecnology.Based on lignite, bituminous coal, and lean coal respectively, the influence of activation agents and temperature on the SO2 adsorption capacity of activated semi-coke prepared by one-step rapid pyrolysis/activation was investigated, which could provide basic data to the design of pilot test. The SO2 adsorption capacity of powder activated semi-coke prepared by original flue gas activation was mainly determined by the coal rank, preparation temperature and activation agents. The SO2 adsorption capacity of lignite based powder activated semi-coke gradually increased with the temperature rising. When the preparation temperature reached to 1200℃, the particle surface was densely covered and pore structure was clogged due to the formation of pellets which are formed by ash fusion. The SO2 adsorption capacity of bituminous coal and lean coal based powder activated semi-coke first increased with temperature increasing and then decreased, and the maximum capacity was achieved at 850℃. When the oxygen concentration reached to 6%, the activated semi-coke prepared from three ranks of coal achieved largest SO2 adsorption capacity. Steam conditioning flue gas activation could significantly increase the SO2 adsorption capacity of activated semi-coke prepared from bituminous coal, but not have obivious influences on it from lean coal or lignite.Based on lean coal, the influences of temperature, reaction atmosphere and residence time to the pore structure and surface morphology characteristics of lean coal based powder activated semi-coke have been studied. Both the pore surface roughness and the influence of pore structure on the SO2 adsorption capacity of activated semi-coke were investigated employing the fractal theroy. On the basis of the investigation of pore structure characteristics and surface properties of activated semi-coke under different process conditions, the evolution mechanism of pore structure in the preparation process of lean coal based powder activated semi-coke was discussed. The controlling factors of pore structure formation druing the preparation process of activated semi-coke included temperature, reaction atmosphere and residence time. There were two obvious evolution paths of the pore structure of powder activated semi-coke due to the different activation agents. In the oxygen-free atmosphere (N2/H2O), the pore structure of the activated semi-coke showed macropore and mesopore, and the surface of particle presented a sparse macroporous structure. When the activation agents contained oxygen, the pore structure formation was promoted because of the high reactivity of oxygen. The fractal dimension of activated semi-coke showed positive correlation with the SO2 adsorption capacity. The fractal dimension increased with the increase of micropore volume and micropore surface area. The adsorption active sites of activated semi-coke was mainly distributed on micropore.The elements content and amorphous carbon such as C, H, O, changing along with devolatilization was studied by ultimate analysis. The surface functional groups of different activated semi-cokes were analyzed by thermogravimetric analysis according to the different decomposition temperatures of oxygen-containing functional groups. The evolution mechanism of the benzene ring polymerization extent, content of C=O functional group, branched degree and branched chain length of different activated semi-cokes were researched by FITR. The relationship between the pore structure evolution and the surface functional groups evolution characteristics were discussed combined with the pore structure parameters. The O/C ratio of the activated semi-coke first increased, then decreased with the increase of temperature. Compared to other activation agents, the O/C ratio of activated semi-coke prepared by single oxygen activation was higher. When using steam as the single activation, the O/C value was low. When using mixed oxygen and steam as activation, the polymerization degree of the aromatic ring of activated semi-coke was low. The content of the C=O structure oxygen-containing functional groups of the activated semi-coke had a favorable linear relationship with the specific surface area of micropore. The DT850-O7S15 with larger specific surface area of micropore contains more C=O structure. With the polymerization degree of the aromatic ring increasing, the specific surface area of micropore gradually decreased, and they had a favorable linear relationship.To obtain the main parameters about the rapid preparation technology of the activated semi-coke by one step activation, a pilot test system was set up based on the theoretical researches of the activated semi-coke preparation. In this experiment, a local bituminous coal was used as the metrials to prepare the activated semi-coke. The power activated semi-coke was prepared from the loal bituminous coal by different activation agents which could be adjusted by oxygen and steam followed by the SO2 adsorption capacity investigated, which can provide a theoretical foundation for industrial application. The SO2 adsorption capacity of the activated semi-coke undergoing 2 hours was about 38mg/g which was perfectly agreed with the expected. The activated semi-coke had a high porous structure and the porous were mainly microporous and mesopores. The total surface area of the activated semi-coke which was prepared in the atmosphere of air and steam conditioning was about 121m2/g and the micropore surface area was about 80m2/g. |
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