GB709845A - Method of drying and roasting or roasting and sintering - Google Patents

Abstract

High melting silicates, oxides, carbonates and other substances such as clay or mixtures of substances such as lime and sand with a similarly high melting point are dried and roasted or roasted and sintered when mixed with fuel and return material and in layer heights of up to 30 cms., by a downward blast roasting process characterized in that in order to recover return material only from the lowermost layer of the material undergoing treatment, said lowermost layer is prepared from raw material without the admixture of fuel or return material and consists of particles of such a size that it goes completely into the return material on screening. It is preferred to establish a ratio of 1 : 2 to 1 : 4 between the amounts of raw material present in the fuel-free lower layer and the fuel-containing upper layer. Pulverulent raw material may be mixed with water, dusted with more raw meal, nodulized and, if desired, dried before roasting, the maximum grain size being adjusted to pass through, e.g. an 8 mm. sieve. The invention also applies to the production of cement and in the example raw cement meal is sprinkled with water in a worm mixer to give granules having a water content of 16.5 per cent.; these are dusted with 1.7 kg. of raw meal for 5kg. of said granules, and nodulized to give firm nodules with 11.5 per cent. water content. Roasting after drying is performed with a layer height of 30 cms., of which 5 cms. is taken up by the lower layer. 8 per cent. of coke slack, and return material in a 1 : 1 ratio is added to the upper layer.ALSO:Raw materials for the preparation of cement are dried and roasted or roasted and sintered when mixed with fuel and return material and in layer heights of up to 60 cms., by a downward blast roasting process characterized in that in order to recover return material only from the lowermost layer of the material undergoing treatment, said lowermost layer is prepared from raw material without the admixture of fuel or return material and consists of particles of such a size that it goes completely into the return material on screening. It is preferred to establish a ratio of 1 : 2 to 1 : 4 between the amounts of raw material present in the fuel-free lower layer and the fuel-containing upper layer. Pulverulent raw material may be mixed with water, dusted with more raw meal, nodulized and, if desired, dried before roasting, the maximum grain size being adjusted to pass through, e.g. an 8 mm. sieve. In the example raw cement meal is sprinkled with water in a worm mixer to give granules having a water content of 16.5 per cent.; these are dusted with 1.7 kg. of raw meal for 5 kg. of said granules, and nodulized to give firm nodules with 11.5 per cent. water content. Roasting after drying is performed with a layer height of 30 cms., of which 5 cms. is taken up by the lower layer. Eight per cent. of coke slack, and return material in a 1 : 1 ratio is added to the upper layer.