Study On The Internal Effect On Inhibiting Gas And Solids Back-mixing In Fluidized Bed

Gas and solids mixing in fluidized beds ensures excellent ability in the mass and heat transfer, but also results in the back-mixing of desired products which were probably over-converted. Hence, the desire long exists in reducing the disadvantages of back-mixing on reaction while maintaining the desirable efficiency in mass and heat transfer.The author has designed a kind of internal with specific structure that could create dilute phase in the bed, in which the mixing of gas and solids is much weaker than that in dense phase. Through phosphor tracer experiments in 2-dimensional fluidized bed, one can clearly find that particles in the fluidized bed with internals drop from upper zone to lower zone far slowly than the bed with no internals. That shows the restraining effect of the internal on back-mixing. Internal with smaller voidage has stronger effect to inhabit the back-mixing of solids, but should have proper structure to avoid the unexpected choking in the bed, strongly undesirable in the industrialized processes.Yield of aromatics in the reaction of methanol to aromatics in fluidized bed without internal is 10% lower than that in fixed bed reactor, due to the negative back-mixing of gas and solids. It can be increased 4% by the use of internal. And the product profiles of aromatics can be tailored by the used of the internal. It is attributed to the narrow residence time distribution (RTD) of gases, evidenced by the H2 tracing experiment in cold model reactor with the same size. And the H2 tracing experiments inΦ600mm fluidized bed suggested such internal is easily scaled up, which provides the basis on the future application of the internal in industrial scale process.