Numerical simulation of two stage entrained flow coal gasifier with recycled CO₂ injection

In order to reduce CO₂ emission from thermal power plants with keeping high thermal efficiency, a new concept of IGCC system, namely oxy-fuel IGCC, is recently proposed. CO₂ is recycled in this system, hence the effect of CO₂ recycle should be clarified. In this study, the effect of recycled CO₂ injection on coal gasifier performance was investigated by means of three-dimensional RANS-based numerical simulation. In calculation of a coal gasifier, coal char gasification and water-gas shift reaction are important phenomena, therefore, the partially active site sharing coal gasification model and detailed chemistry of water-gas shift reaction model were implemented. The results show that recycled CO₂ injection promotes coal gasification for the lower oxygen concentration condition in which gaseous concentration temperature is relatively high. On the other hand, for higher oxygen and CO₂ concentration condition in which gaseous temperature level is relatively low, it is important that how much the higher gasification reactivity in a gasifier is exploited by optimizing local heat balance. It is essential to locally control exothermic gaseous and endothermic heterogeneous reaction in order to take advantage of recycled CO₂ injection in the O2/CO₂ blown gasifier system.