Abstract:
As the most important unit of coal-to-substitute natural gas (SNG), coal gasification is the key of green utilization of fossil resource, and has been attracting more attention of the chemical process industry, particularly in China, where oil is scare but coal resource is abundant. However, the process still faces some challenges. First of all, a large amount of carbon dioxide is emitted into the atmosphere directly during the process without recycling, increasing the burden of environment. Besides, the product gas of coal gasification is usually used as raw materials for other chemical processes, such as substitute natural gas, methanol and olefins synthesis, which requires a high content of hydrogen in raw materials. To solve these problems, British gas lurgi (BGL) gasification model, the typical coal gasification process, was developed based on chemical process simulation software Aspen Plus. Depending on the simulation, the compositions of gasification agents and preheating temperature were optimized in order to provide reference for actual process. In regular gasification technology, coupling effects of operating parameters on evaluating indexes, including mole fraction of CO and H
2 in product gas, gas production efficiency and decomposition rate of H
2O, were investigated to optimize the compositions and preheating temperature of gasification agents. The result showed the optimal mass ratios of O
2 and H
2O to coal are 0.33 and 0.14 respectively, and the optimal temperature is 220℃. In addition, to solve the problem of CO
2 emission and improve the ratio of H
2 and CO, CO
2 and CH
4 were added to modify the agents respectively. Finally, the compositions of gasification agents were optimized further with
mCO2/
mH2O=0.18 and
mCH4/
mH2O=0.08 by replacing the steam with CO
2 and CH
4 separately.