DISTINCTIONS BETWEEN LOW-DENSITY AND HIGH-DENSITY CIRCULATING FLUIDIZED-BEDS

While many fundamental studies have been carried out in relatively low density circulating fluidized beds (LDCFB), there has been little rep orted fundamental study of the high density (including high solids flu x and/or high solids concentration) circulating fluidized bed (HDCFB), although many commercial CFB setups are operating under high density conditions. Catalytic gas-phase reactions tend to require higher gas v elocity and higher solids flux and/or concentration than gas-solids re actions, and therefore it is necessary to make a distinction between t he two types of operations. The study of hydrodynamics and other funda mentals of HDCFB will help in understanding the fundamentals and thus improving the design and operation of existing HDCFB reactors such as FCC risers, and may also lead to other applications requiring even hig her solids/gas feed ratios and/or higher solids concentration in the r iser. On the other hand, high density operation can only be achieved b y properly choosing the gas blower, solids feeding system and CFB geom etry to avoid the instabilities resulting from insufficient pressure h ead from the gas blower and downcomers.