The effects of operating conditions of superficial gas velocity,system storage capacity,butterfly valve opening,pre-lifting gas volume on solids circulation rate in a cold apparatus of circulating fluidized bed were investigated using air and FCC equilibrium catalyst,and the causes of influence were also analyzed.Meanwhile,this paper conducted a thoroughly comparative study about the impacts of pre-lifting outlet on solid fluxes as well as axial and radial solids concentration distribution inside the bottom section of riser.The micro-flow pattern in the gas-solids confluent zone was proposed.The results show that the solids circulation rate increases with increasing gas velocity and more intensive gassolids contact.The pressure needed for supporting gas-solids flow in riser is from storage vessel and butterfly valve.Increasing particle reserves and decreasing butterfly valve pressure drop also helps boost solids circulation rate.Injection of pre-lifting gas helps to push solids upwards in case of particle deposits at the bottom.When the solids flux provided by storage vessel is large enough,increasing pre-lifting outlet position could change the gas-solids flow structure in the gas-solids confluent zone by preventing solids downwards and pushing solids upwards.Besides,the different pre-lifting structures have limited influence on solids concentration in either axial or radial distributions in riser.%以催化裂化平衡剂为固体介质、常温空气作为流化气体,在循环流化床冷态模拟试验装置上分别考察了表观气速、颗粒贮量、下料蝶阀开度、预提升气量等操作条件对循环流化床反应器催化剂循环速率的影响,并探讨了产生这种影响的原因;同时,深入研究了预提升出口位置对系统内催化剂循环速率、提升管底部轴向、径向颗粒浓度分布的影响,并描述了气固两相交汇点处的微观流动结构.结果表明:随着操作气速的升高,气、固相之间的相互作用增强,颗粒循环速率提高;伴床及蝶阀通过提供足够的压力支持提升管内的两相流动,增加颗粒贮量或减小蝶阀压降可有效提高颗粒循环量;通入预提升气可增大颗粒向前运动的推动力,避免颗粒发生坍落而沉积于床层底部;当伴床向提升管提供足够的颗粒循环速率时,预提升出口位置的提高破坏了颗粒的向下流动,迫使颗粒进入中心快速向上的气固流动区,从而改变气、固相交汇点处的流动结构;另外,不同预提升结构对颗粒浓度的影响有限,并未从根本上改变轴向、径向颗粒浓度的分布规律.
展开▼
