Combustion in crater beds

A preliminary study of a new type of heat-recirculating particulate bed combustor has been carried out with a view to overcoming some limitations arising in the scaling up of spouted bed combustors. A fountain of particles, somewhat similar to that produced in spouted beds, is raised by a jet of gaseous reactants flowing downward into a crater formed below the bed surface. Reactants are preheated prior to combustion both by heat transfer from the products across the walls of the inlet tube and by the interaction of reactants with the inert particles heated by the flame. Combustion characteristics are studied for single and multiple inlet tubes in small laboratory burners and in a much larger 50 KW system. Crater beds are compared with other two-phase combustors, especially spouted beds. They readily lend themselves to scaling up by the use of multiple jets, from one or from several inlets, and recirculate heat between products and reactants both within the craters and by heat transfer to the inlet tubes. Tests show that they can be used either with gaseous reactants entering through the jet or with only oxidant introduced in that way, fuel being included within the bed. Stability limits established for the laboratory burners show a leaner burning capability than is achievable in spouted or fluidized beds and the device offers several advantages over other circulating two-phase systems.