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Comment PDF Heat Transfer

Bulk Solids: Operating Direct-Contact Heat Exchangers

By Greg Mehos, Jenike & Johanson, Inc. |

Bulk solids are frequently used as reactants, catalysts or products in chemical process industries (CPI) operations. Often, they must be heated or cooled so that they can be handled safely or processed at a desired temperature. Traditionally, heat transfer to or from powders is carried out using heated or water-cooled screws, fluidized beds or rotating drums. However, a more economical means of heating or cooling bulk solids may be to use a direct-contact, bulk-solids heat exchanger. These devices are designed as hoppers, bins or silos that have been modified to allow for the injection of air or another gas. Heat transfer takes place between the powder and gas when the two streams are fed at different temperatures. The cooling or heating gas can be injected from the bottom of the bulk-solids heat exchanger, such that it passes upward through the moving bed of solids (countercurrent), or it can be injected through the walls of the vessel so that it flows perpendicular to the solids flow (cross-current). Countercurrent and cross-flow designs are shown in Figures 1 and 2. Direct bulk-solids heat exchangers offer a number of advantages over other types of heating or cooling equipment. Because there are no moving parts, capital costs and…
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