Preheater cement

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The suspension preheater is the basis of all modern systems. Rawmix in dry powder form is injected into hot kiln exhaust gas in a vertical duct. The upward gas velocity is sufficient for the powder to be picked up and lifted up the duct "in suspension" in the gas. Because heat exchange occurs over the vast surface area of the individual mineral particles, the gas and rawmix reach a common equilibrium temperature in a fraction of a second. The solids and gas are then separated in a cyclone. This process is repeated a number of times - typically three to six - by stacking "riser" ducts and cyclones on top of one another in a tower. By repeated heat exchange, most of the heat in the kiln exhaust gas can be captured, while heating the rawmix to calcination temperature. Such heat as escapes the preheater is used to heat the rawmill.