| Coal made huge contribution to the economic development of our country during the past thirty years since reform and open, the coal industry developed much faster in recent years than ever before, the coal production and consumption ranked the first in the world in the year2010. However, coal development brought lots of environment issues which limited our economic healthy development. The harm of sulfur in coal can’t be ignored, influencing people’s production and life, poisonous gases such as hydrogen sulfide and sulfur dioxide can be produced in the process of coal consumption. If the sulfur in coal could be removed, this will reduce the emission of sulfurous gas efficiently and achieve the goal of clearing production. In addition, the coal with high sulfur accounts for a large proportion in our country, so, it was the top priority to look for an effective desulfurization technology before combustion.Among all the desulfurization methods, microwave desulfurization was one of the most used ways with the advantages of heating speed, selective heating, efficient non-polluting, simple operation as well as work under normal temperature. The sulfur in coal was easy to change after absorbing microwave irradiation, while the coal matrix will not absorb, so it is not easy to damage the coal structure. Ultrasonic irradiation could produce local high temperature and pressure which made the weak chemical bond of organic matter in coal rupture and reduced the activation energy of desorption reaction. Meanwhile, cavitation of the ultrasonic wave can significantly improve the interaction between sulfur group and solvent.Extraction and Oxidation method combined with microwave and ultrasonic irradiation technology were applied to sulfur removal experiments of coal samples from Qinyuan and Xiongshan. This paper studied microwave irradiation time, microwave power, ultrasonic irradiation, ultrasonic power, oxidant ration as well as the desulfurization efficiency with the microwave and ultrasonic. The results showed the desulfurization rate two kinds of coals had a big difference, for Xiongshan coal, the optimum conditions for desulphurization were100min,490W under microwave irradiation and30min,500W under ultrasonic irradiation in the process of extraction, reaching10.36%and3.10%, the optimum conditions for desulphurization were50min,490W, nHAc:nH2O2was1:1under microwave irradiation and30min,500W, nHAc:nH2O2was1:1under ultrasonic irradiation in the process of oxidation, reaching21.04%and18.42%; for Qinyuan coal, the optimum conditions for desulphurization were60min,490W under microwave irradiation and50min,400W under ultrasonic irradiation in the process of extraction reaching22.10%and19.88%, the optimum conditions for desulphurization were30min,490W, nHAc:nH2O2was 1:3under microwave irradiation and50min,400W, nHAc:nH2O2was1:3under ultrasonic irradiation in the process of oxidation reaching32.75%and33.98%, it is not effective for desulphurization rate with the methanol added; the desulfurization rate increased with longer irradiation time and power. This indicated that longer reaction time could increase the direct contact time between the coal and the solution, and the power could supply more energy per unit time to improve desulphurization rate. For the desulphurization rate, microwave-ultrasonic was better than ultrasonic-microwave, combined effect was better than alone, which indicated that ultrasound could assist microwave to improve desulfurization. For the desulphurization rate, oxidation-extraction was better than extraction-oxidation,the desulphurization rate for Qinyuan coal was41.78%and for Xiongshan was23.31%, explaining more organic sulfur bond was opened in the process of oxidation, which made it easy to remove because of easier dissolve in tetrachloroethylene.Compared the two sulfur forms before and after coal desulfurization through XPS spectrum, the results showed that the major sulfur forms of the two kinds of coal were thiophene and pyrite sulfur, both of the ultrasonic and microwave irradiation had good effect for the coal desulfurization, while a part of thiophene changed to sulfone and two sulfur oxide continued to exist in coal. Extraction didn’t have obvious effect for the inorganic sulfur removal, while have little effect for the organic sulfur. However, oxidation removed almost all of the inorganic sulfur and part of organic sulfur. In order to deeply explore desulfurization, this paper studied mechanism of swelling of two coals. The results showed that the equilibrium swelling degree increased with the higher temperature of two coals, and the equilibrium swelling degree increased under the ultrasonic irradiation, declaring two kinds of coals could reach balance quickly with ultrasonic. Equilibrium swelling degree of Qinyuan coal was much higher than the Xiongshan coal, swelling degree might have certain relationship with desulfurization rate by compared to the desulfurization rates. The apparent activation energy of ultrasonic was lower than the normal condition, showing that ultrasonic irradiation could reduced the swelling activation energy of the two coals, which could change the structure of two coals more easily, part of the sulfur structure was easier to change and was more likely to be removed and through the BET analysis found:surface area and pore volume increased, but the pore size decreased under ultrasonic irradiation, because much more pore be produced under ultrasonic irradiation, the average pore diameter decreased。... |
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