process for reducing the content of alkaline substances in the cement clinker and to obtain dust rich in alkaline substances in combustion plants, cement

摘要

946,872. Preheating cement clinker. POLYSIUS G.m.b.H. Feb. 6, 1961 [March 21, 1960], No. 4409/61. Heading F4B. [Also in Division C1] The content of alkalies, i.e. Na 2 O and K 2 O, in cement clinker is reduced and alkali-rich dusts are recovered in cement kilns operating with exhaust gas temperatures of 100-300‹C., e.g. Lepol travelling grate rotary kiln, by preheating the cement raw material by heat exchange with the hot exhaust gases, from the kiln which are withdrawn from the preheating at a point where their temperature is such that the sublimed alkalies in the gases begin to be deposited as a solid, the dust in the withdrawn gases are extracted, the dust-free gases returned to the preheating and the extracted dust is separated into an alkali-rich fraction used, e.g. as a fertilizer, and an alkali-poor fraction which is mixed with the raw material. The dusts may be separated by a wet method, e.g. by flotation in a solution saturated with alkali. Raw cement is fed via shoot 1 to travelling grate 2 and rotary kiln 5. Hot exhaust gases from 5 are fed to heating chamber 4 and through the cement on 2 to chamber 4SP1/SP which contains dust collectors 6. Gases from 6 pass via trunk 7 to drying chamber 3 and through the cement on 2 to chamber 3SP1/SP where fan 8 feeds a final dust separator 9. The dust collected is taken by conveyer belt 11 to be separated into the two fractions, the alkali poor fraction returning on to grate 2 via shoot 1. Specification 874,818 is referred to.