NUMERICAL STUDY OF EFFECTS OF OPERATION CONDITION FOR OXYGEN BLOWN COAL GASIFIER IN OXY-FUEL IGCC

摘要

In order to reduce CO_2 emission from thermal power stations with keeping high thermal efficiency, a new concept of IGCC system, namely oxy-fuel IGCC, has been recently proposed. Hence CO_2 is recycled in the system, the effect of CO_2 recycle on each equipments should be clarified. In this study, the effect of recycled CO_2 injection on coal gasifier performance was investigated by means of three-dimensional RANS-based numerical simulation. For estimating of coal gasifier performance, coal gasification and water-gas shift reaction are key phenomena. Therefore, the partially active site sharing coal gasification model and detailed chemistry of water-gas shift reaction model were implemented. Calculated gasifier was a commercial scale entrained flow coal gasifier whose coal feeding rate is 70 tons per hour. The gasifier consists of a lower combustor part and an upper reductor part. The effect of coal feeding rate into the reductor, R/T, was investigated. The results show that temperature in the combustor decreases with decreasing R/T. In the lower R/T condition, hence air ratio in the combustor decreases, the reducing atmosphere becomes stronger. As a result, coal gasification which is endothermic reaction in the combustor is promoted. Although coal gasification is occurred in the reductor in higher R/T condition, total coal gasification rate is not so promoted compared with lower R/T condition. Due to the above mechanism, the gasification performance becomes higher with decreasing R/T. The results obtained in this study indicate that it is important that how much the higher gasification reactivity in a gasifier is exploited by optimizing local heat balance.