Situating the high-density circulating fluidized bed

Gas-solid flow in high-density circulating fluidized-bed risers differs sig nificantly from that in conventional flow regimes, including fast fluidizat ion and pneumatic conveying. It is shown that when there is no downward flu x at the wall at high suspension densities, and hence no core/annulus struc ture, the flow corresponds to a dense suspension up-flow regime. This flow regime is explained, and ifs key properties given. A lower boundary is also proposed for this new flow regime based on available data.