GB1251572A - - Google Patents

Abstract

1,251,572. Heating and cooling pulverulent materials; drying pulverulent material. F. L. SMIDTH & CO. A/S. 2 Sept., 1970 [2 Sept., 1969], No. 43349/69. Headings F4B, F4G and F4U. Pulverulent material is heated or cooled or dried whilst passing down a shaft 1 in counterflow to upflowing gases. In one form, the refractory lined shaft is provided with at least one helical rib 15, which is preferably uninterrupted and of constant pitch, and which has an upper surface that slopes downwardly by between 0 and 70 degrees. Baffles 17 extend at least partly between adjacent turns of the rib, to stop the upflowing gases, which pass through a central " free space " comprising between 25 and 50% of the cross-sectional area of the shaft, from taking a helical flow path. Where, as shown, the baffles only partly extend between adjacent turns of the rib, which in this case has a pitch of about 40 degrees, the descending material gets trapped in gas eddies which form at the upper edge surfaces of the rib and travel down along it to the bottom of the shaft whilst the material undergoes extensive heat exchange within the eddies. Alternatively when the baffles fully extend between adjacent turns of the rib, stationary eddies are formed, the material falling from one eddy to another as each upper eddy becomes saturated with material. In a modification (Fig. 5, not shown) a central gas return pipe or solid core is located within the shaft, the " free space " being defined in the annulus between the pipe or core and the shaft. The helical rib(s) may alternatively be formed on the outside of such pipe or core (Fig. 3, not shown), the baffles between adjacent turns being wholly or partly replaced by vertical partitions projecting inwardly from the shaft wall. The shaft may be used to preheat cement materials passing to a rotary kiln 2.