Simulation and Optimization of BGL Coal Gasification Based on Different Gasification Agents

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 H₂ in product gas, gas production efficiency and decomposition rate of H₂O, were investigated to optimize the compositions and preheating temperature of gasification agents. The result showed the optimal mass ratios of O₂ and H₂O to coal are 0.33 and 0.14 respectively, and the optimal temperature is 220℃. In addition, to solve the problem of CO₂ emission and improve the ratio of H₂ and CO, CO₂ and CH₄ were added to modify the agents respectively. Finally, the compositions of gasification agents were optimized further with m_CO2/m_H2O=0.18 and m_CH4/m_H2O=0.08 by replacing the steam with CO₂ and CH₄ separately.