GB797487A - Improvements in methods of and apparatus for heating cement raw material or the like - Google Patents

Abstract

797,487. Preheating furnace charges. SMIDTH & CO. AKTIESELSKAB F. L. Nov. 20, 1956 [Nov. 29, 1955], No. 35477/56. Class 51 (2). Cement raw materials, lime or ore to be burnt or sintered in a rotary kiln is preheated by the passage of gases from the kiln downwardly through a bed of the material on a gas-permeable support, the fresh material forming a lower layer of the bed and material through which the gases have already passed forming an upper layer, part of the bed, including some at least of the upper layer being fed into the kiln and the remainder being wholly or partly used to form the upper layer. Hot gases from a rotary kiln 1, Fig. 1, pass downwardly through material on a chain grate 5. Fresh raw material from a hopper 10 forms a bottom layer on the grate and a second hopper 11 feeds material to form an upper layer. A horizontal blade 12 extending the whole width of the grate divides the bed into an upper part which passes to the kiln 1 and a lower part which drops through a hopper 30 to an elevator 13 and conveyed to the hopper 11. Fine particles which pass through the grate 5 and fine particles removed in the hopper 30 are delivered to the kiln by a conveyer 31. The inclination of the blade 12 is made adjustable to vary the amount of material returned. Raw material and fine particles returned from below the chain grate may be passed to a nodulizing drum feeding the lower layer to the grate. Fine particles screened from the partly heated material being fed to form the upper layer are also returned to the nodulizing drum. The raw material may be in the form of slurry, which may be passed over a vacuum filter before feeding it to the nodulizer. In a modification, Fig. 4, an inclined grate 22 with alternate bars reciprocated passes the bed of the material from the hoppers 10, 11 to kiln 1. Fines passing through the grate is fed to the kiln 1 together with the upper part of the bed. In another embodiment, Fig. 5, a plough-like device 29 divides the bed of material of the grate 5 vertically.