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Abstract

The present invention provides an energy conserving process for calcining a clay and apparatus for carrying out the process. A dry pulverized clay powder (1) is fed to a calciner (20) to be calcined therein. The calcined clay product (3) is removed from the calciner (20) and preferably passed in heat exchange relationship with a cooling medium (71) whereby the calcined clay product (3) is cooled and the cooling medium is heated. The hot off-gas (7) discharged from the calciner (20) is passed through an electrostatic precipitator (30) to remove at least a substantial portion of calcined clay product dust (11) entrained in the exhaust gas from the calciner. The clean gas (13) leaving the electrostatic precipitator (30) is passed in heat exchange relationship with a cooling fluid (51) to further cool the gas, and preferably to evaporate at least a portion of the cooling portion to produce a heating vapor (53). In order to improve the dust collection efficiency of the electrostatic precipitator (30), the moisture content of the calciner exhaust gas passing through the electrostatic precipitator (30) should be controlled at a level of at least 12% by volume of the gas. Preferably, the recovered hot calcined clay dust (11) recovered in the electrostatic precipitator (30) is mixed with the clay feed material (1) being supplied to the calciner (20) without substantially cooling the hot calcined clay powder collected in the electrostatic precipitator (30).

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First Claim