| Coal staged utilization is the background in this thesis by the extraction of coal using supercritical carbon dioxide (SCCO2) with co-solvent. Interaction between supercritical carbon dioxide and co-solvent was explored. Physical and chemical properties of extract and coal residues were characterized. The gasification reactivity of residues was investigated. Supercritical carbon dioxide (SCCO2)-coal tar-N-methyl-2-pyrrolidinone (NMP) mixed solvents were used to upgrade low rank coal in a semi-continuous supercritical extraction device. The effects of process conditions (operating temperature, pressure, solvent ratio, low rank coal particle size, etc.) on the composition of liquid extract and the physical and chemical properties of upgraded coal were studied. The differences between the raw coal and upgraded coals in the elemental composition, microstructure and reactivity were investigated. Supercritical carbon dioxide (SCCO2)-N-methyl-2-pyrrolidinone (NMP) or alcohol solvent were used to upgrade coal and petroleum coke in a semi-continuous supercritical extraction device in this study. The effect of many factors(temperature, pressure and solvent, etc) on the the physical and chemical properties of upgraded coal were studied. The differences between the raw coal and upgraded coals in the elemental composition, functional group and reactivity were investigated. The construction of lignite modification and gasification process system has been proposed in this paper. The main contents and results are summarized as follows:(1) Different co-solvents were used in the SCCO2 extraction of coals. The role of supercritical carbon dioxide and co-solvent was studied. The effects of coal, temperature, pressure and solvent ratio on the extraction rate were investigated. Physical and chemical properties of the extracts and residues were characterized. Result shows that extraction yields of mixed solvent are higher than those of pure SCCO2 and DMF solvent. The maximum values occur at the 1:1 volume ratio of two solvents. The extraction yield increases with the increase of pressure. But the effect is gradually weakened after the pressure exceeds 11MPa. The extraction yield increases with the increase of temperature. The effect is gradually weakened after the temperature exceeds 150℃. The extraction yields of lignite and bituminous coals increase first and then decrease with the increase of carbon content of coal. When the carbon content is 85.12%(daf), the extraction yield reaches a maximum. The gasification reactivities of raw coal and residues were also investigated. The extract is rich in hydroxyl and oxygen-containing functional groups (lipid, phenols, ketones and so on). With the addition of SCCO2, the extraction of hydroxy rich matter is enhanced while the aliphatic matters in extracts decrease. Crystallite structure in extracts is similar to the raw coals, but they hardly contain minerals. Their graphitization degree is lower. The surface of coal particles is damaged by the mixed solvent and the pore structure changed with the declines of BET surface area and the increase of pore size. Average stacking height of coal crystallite is reduced after extraction. Gasification rate is enhanced for all extracted coals and the gasification rate tends to increase with increasing extraction yield.(2) Xiao Longtan lignite was modified with the SCCO2-coal tar-NMP mixed solvent. Result shows that BET surface area and BJH adsorption pore volume of upgraded coal increase about 2 times, adsorption average pore size decreases about 20%. The slurry ability of the modified lignite is improved. Maximum slurry concentration increases from 46% to 56%, rheological index changes from 0.66 to 0.55 around, the pseudoplastic of coal slurry increases, the thixotropic loop area increases 4.5 times and the upgraded coal water slurry has good stability. The gasification activity index of upgraded coal increases twice due to the improve of the coal gasification reactivity with the increase of temperature and pressure.(3) The coal and petrol coke was modified with the SCCO2-NMP or alcohol solvent. Result shows that the supercritical CO2 single solvent or mixed solvent extraction has the effect of desulfurization and de-ashing. Ash decreases 5-10%, sulfur content decreases by 0.2-0.4 percentage points. The gasification activity of modified coal and petroleum coke has been improved. The improvement of the gasification activity of Jinling petroleum coke is higher than that of India petroleum coke. Compared with the petroleum coke, the modification effect of the mixed solvent on coal gasification activity is more obvious. The supercritical CO2-NMP solvent is better than the supercritical CO2-ethanol solvent.(4) The construction of lignite modification and gasification process system has been proposed in this paper. The process system simulation based on the Xiao Longtan lignite modified results and the opposed multi nozzle coal water slurry gasifier was carried out. The difference of coal gasification results was compared. The influence of operating conditions on the gasification results was investigated. Result shows that compared with the raw coal, modified coal is 26% lower in coal consumption and oxygen consumption decreases by 41%. With the modification coal slurry concentration increases, the coal consumption and oxygen consumption decreases slowly. Effective gas production of 1kg coal increases by 26%. The concentration of CO increases from 26.32% to 34.38%, the concentration of H2 increases from 33.68% to 37.56% and the concentration of CO2 decreases from 38.44% to 26.61%. |
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