OCR Text |
Show solids. Hot solid materials, the limestone and hot metals, would constantly strike the burning tire carcass, reducing it to small bits. Preheated air would be introduced uniformly through the distributor to be utilized as combustion air throughout the first-stage combustion chamber. Noncombustible solid refuse, like metal or glass belts and steel beads, would agglomerate into pellet-like masses. The first-stage combustion chamber would have a slightly tilted distributor, which would enable the fused pellets to "walk" across the distributor, "drain" through a downcomer, and collect as spent bed material. To simplify hot material handling and to recover the residual heat from the spent bed material, an air stream would be introduced through the downcomer which would flow countercurrently against the descending spent bed material. This pellet-like bed material could then be collected to recover the steel and glass. The surface of the fluidized bed inside the first-stage combustion chamber would be controlled by an overflow weir. Solid hot-bed materials, mostly limestone and ashes from tire burning, would be "sucked out" of an eductor (an ejector-like device) by the up-flowing air. The mixture of hot bed material and air would then be transported to the second-stage combustion chamber. This air-bed material pipeline would serve two purposes: one, it would transport the bed material from the first stage to the second stage; two, it would preheat the incoming air by intimate solid-air mixing inside the air lift. The solid-air mixture would then be separated in an over-bed cyclone inside the second-stage fluidized bed and the solids would be discharged into the second stage combustion chamber. The heated air would then be fed back to the first-stage combustor through the plenum or wind box, passing through the distributor into the first combustion chamber. This arrangement would eliminate the use of air preheaters and increase thermal efficiency. The volatile matter and fines from the first-stage combustion would enter the second-stage combustion chamber through the distributor. Second-Stage Fluidized-Bed Combustion In this second-stage fluidized-bed combustion chamber, vigorous mixing and continued combustion would occur and the volatile matter (gases and vapors) and carbon fines from the first stage could be burned to completion. The bed height could be controlled by adjusting the amount of bed material flow from the first-stage combustion chamber. Not shown in figure 6, a down-comer would also be provided to control the bed height. In the second stage, in-bed and over-bed heat transfer surfaces would be provided to take advantage of the excellent heat transfer rate available due to the fine size of the bed materials; the heat transfer coefficient improves with the decreasing bed material size(3). The second stage would also serve as a fluidized-bed particulate filter, trapping particles inside the fluidized bed and providing residence time sufficient to burn them to completion. 11-31 |