| Coal is main energy resource in China, and high-efficiency utilization of coal is an important part of national economic development. For years, coal chemical industry has been regarded as the dominating approach to make full use of coal. According to the processing way of coal, coal chemical industry is divided into carbonization, gasification, liquefaction and chemical synthesis, etc. The coal gas prepared by gasification can be used as raw materials for synthesis of ammonia, methanol and natural gas, etc. However, impurities such as sulfur and carbon dioxide in the gas can cause catalyst poisoning in the process of gasification and synthesis. So removal of acid gas is an essential part of gasification process. And the purification degree of coal gas has a vital influence on subsequent process.The solubility of acid gas in methanol is quite large at low temperature. According to this physical property of methanol, Rectisol process uses methanol as solvent to remove acid gas from feed gas. Comparied with other purification methods, Rectisol process can produce high-purity gases by absorbing a variety of impurities. Moreover, Rectisol process has the advantages of high selectivity and low energy consumption, which is a widely used purification method.According to the raw material conditions and product requirements, this work has designed the Rectisol process and simulated the working conditions by Aspen Plus. Unlike the common coal gas, our feedstock has many special features which make it different from coal gas and other conventional coal gas. It has a few characteristics:one is the various impurities like COS, thiophene, thiol, thioether and benzene besides CO2 and H2S. Secondly, for the low content of CO2 in feedstock, the lower-quality cooling energy is produced in desorption process. So this process need to design the heat exchanger network for recovering more cooling energy. Finally, the feedstock contains much CH4 that can be solved in solvent methanol, which might have influence on the purity of CO2 product.We have designed the process by three steps. Firstly, the Rectisol process has been designed based on the characteristics of the feedstock. Then, the process is divided into four parts and simulated in Aspen Plus. In each section, all the parameters of the equipment are calculated by project experience and analyzed by sensitivity analysis in Aspen Plus for obtaining the most economical working conditions. Finally, we take full process simulation by connecting the four parts and adjusting some parameters for adapting the full process. According to the result of Aspen plus, the composition of the coal gas after purification meet the product requirements (CO2<50ppm, H2S<4ppm, COS<0.5ppm). Besides,97%CH4, 99%H2 and 99%CO are recovered. Moreover, the content of sulfide is below 20ppm in off gas and methanol is below 100ppm in waste water, both meet the emission standards. As a result, the design process can be used as the basis of a factory building. |
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