Abstract: 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 gas-solids 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.

Key words: circulating fluidized bed, pre-lifting, circulation rate, solid concentration