Estimation of cold gas efficiency and reactor size of low-temperature gasifier for advanced-integrated coal gasification combined cycle systems

Abstract

In order to achieve power-generation efficiency higher than those of integrated coal gasification combined cycle plants, advanced integrated coal gasification combined cycle systems have been developed. Here, we developed a triple-bed combined circulating fluidized bed gasifier model using the commercial process simulator Aspen Plus® (version 8.6) and Excel®. The heat balance and reaction kinetics, including the inhibition of steam gasification by H2, were simulated for a combustor temperature of 950 °C using porous alumina particles as heat-carrying particles. The theoretical maximum cold gas efficiency of the triple-bed combined circulating fluidized bed gasifier model was 85.0% for a gasification temperature of 800 °C. However, when the temperature was increased to 900 °C, the efficiency decreased to 80.9%. This indicates that, for triple-bed combined circulating fluidized bed gasifiers, a relatively low gasification temperature is suitable for ensuring higher cold gas efficiency and reducing the amount of circulating heat-carrying particles needed. On the other hand, gasification temperatures lower than 850 °C resulted in significantly higher bubbling fluidized bed gasifier volumes even when an effective Ca-based catalyst was used. The cold gas efficiency can be increased further by 8.6% by converting and recovering the missing hydrogen as H2 gas. Hence, there is a trade-off between the cold gas efficiency, gasifier size, and heat-carrying particle/coal ratio. The optimal gasification temperature for triple-bed combined circulating fluidized bed gasifier is 850 °C.