Studies of solid-solid mixing behaviors in a downer reactor

Abstract

Downer reactor has the very short residence times, narrow residence time distributions and uniform solids holdup distributions with the aid of gravitational acceleration. As a result, it has become an attractive alternative to its counterpart, the riser reactor, for certain classes of chemical reactions. These include gasification reactions, fluid catalytic cracking, Fischer-Tropsch reactions and others. In particular, in downer reactor, high reaction efficiencies and low tar formation can be achieved in fast pyrolysis of coal or biomass. The flow behavior of solids is a key to the successful operation of the reactor within the downer, because it determines the contacting pattern as well as the extents of mixing between different phases of materials. Despite the research efforts that have been invested towards both experimental and numerical studies of hydrodynamics and flow behaviors in downer reactor systems, current understanding of such systems is far from complete. In particular, relatively little attention has been given towards the studies of mixing behaviors between two or more types of solids within a downer reactor. Our work will focus on the characterization of the mixing between two types of solids through both experiment and numerical studies.