Method for heat treating pulverous raw material calcining combustor

Abstract

A calcining combustor for the suspension preheater of a rotary kiln cement manufacturing plant having a cooler for the clinker comprises an upright furnace vessel having an outwardly spiraling gas exhaust duct at its upper end leading to a preheater gas/meal separator and a mixing portion at its lower end; an inlet for hot combustion air from the cooler into the mixing portion; an inlet for cement meal from the preheater into the mixing portion downstream from the combustion air inlet to entrain the meal in the rising combustion air; and burners for injecting fuel into the air/meal stream downstream from the meal inlet to calcine the meal by heat released by burning of the fuel with the combustion air. The initial calcination temperature is a minimum because the combustion air atmosphere within the combustor is devoid of significant amounts of carbon dioxide and chlorine and alkali vapors typically present in kiln-off gases, and the endothermic calcination reaction absorbs heat energy to limit temperature rise within the combustor so that caking and formation of alkali and nitrogen oxide vapors is minimized. An alternative embodiment has an inlet for hot kiln-off gases into the furnace vessel at a point where substantial calcination has occurred so that both (a) calcining and (b) mixing of the calcined meal/air stream with the kiln-off gases to transfer heat energy thereto occur in a single vessel.