Optimization study on operation conditions of an industrial-scale circulating fluidized bed coal gasification

Abstract

This research was carried out on a new industrial circulating fluidized bed (CFB) gasifier with output power of 111 MW. In order to realize stable operation and improve economic benefits, a series of experimental studies were carried out during the hot commissioning of the gasifier. The effects of O2/coal ratio, oxygen concentration and secondary gasification agent on gasification indices were investigated. The boundary conditions for the safe and stable operation of the gasifier were obtained, which provides a strong support for the commercial operation of the gasifier. The results showed that, the gasifier can operate stably between 940 and 970 ℃. As the O2/coal ratio increases from 0.31 to 0.36 Nm3/kg, the dry gas yield increases from 2.5 to 2.8 Nm3/kg, carbon conversion rate increases from 78.1 to 82.1% and cold gas efficiency increases from 68.9 to 71.5%, while the effective gas composition (CO, H2 and CH4) decreases from 51.9 to 49.3% and heat value of gas decreases from 6.6 to 6.3 MJ/Nm3. With the increase of oxygen concentration, the effective gas composition and heat value of gas increase. When the oxygen concentration of gasification agent reaches 25%, the temperature is about 960 ℃ and the heat value of gas can reach 6.2 MJ/Nm3. The introduction of secondary gasification agent (O2 + H2O) makes the riser temperature more uniform, but it will reduce the effective gas content and gas heat value to a certain extent.