Experience with producing high-alumina cement by calcination in a shaft furnace

Abstract

The aim of the investigation was to explain whether it is possible to obtain high-alumina cement from clinker calcined in shaft furnaces used for firing chamotte made from fireclays. The preliminary studies were done in small shaft furnace designed by the Institute.* The granules produced by the Dorogobuzhsk nitrogen fertilizer factory and prepared on a granulator at the Institute were fired in the trials.Together with adequate mechanical strength, preventing damage during firing in a shaft furnace, granules should have a uniform grain-size composition ensuring a uniform firing. The granules from the Dorogobuzhsk factory had a low strength and heterogeneous composition: there were marked variations in the apparent density of granules of the same size (with sizes of 15-20 mm it ranged from 1.3 to 1.6 g/cm3). Therefore we carried out a study to obtain granules with properties ensuring normal operation of the shaft furnace, It is known that the strength of moistened granules depends on their moisture content, and is determined by the forces of capillary action and surface tension of the thin water films, and the strength of the dried granules is provided by colloidal films of substances cementing the grains [i]. According to [2], good granulation occurs not only in finely milled materials but also in granular materials if they contain an adequate content of fractions minus 30 ~m, capable of enveloping the coarser grains.The granules were prepared from a mixture of unmilled alumina and finely milled chalk. The optimum moisture content of the batch was selected so that the granules were not broken down during operation of the granulator, and had a uniform grain-size composition. The granules with the maximum strength were those that had a moisture content of about 4%~In order to obtain seedings the mixture was moistened by spraying witha 2% solution of methyl cellulose and this was then passed through a screen with apertures of 2 ram; the rolling of the granules on the seeds was done with a mixture moistened through a jet using 25% solution of sodium lignosulfonate. The properties of the granules are shown in Table i. The strength of the raw granules rolled in the Institute was double that of the granules from the Dorogobuzhsk factory. The granules with the additions of surface-active substances have a somewhat higher density and strength. Such granules withstand loading in the furnace and firing without considerable damage.Both types of granule were fired in the shaft furnace. Since the Dorogobuzhsk granules had an irregular form and variable sizes, we selected granules measuring not less than I0 mm for calcination. The properties of the calcined granules are shown in Table 2 The Institute's granules calcined at 1450~ had a moderate concentration of calcium dialuminate, and after firing at 1600~ were mainly fused on to each other. The Dorogobuzhsk granules in the main were white in color, and some even at 1430~ were fused. Thus, the cal-*Designed for firing corundum briquet.