Measurement of retention times in cement burning systems with the aid of radionuclides

The retention time distributions in various rotary kiln systems were determined in three series of investigations using In-113m. The results confirm the predicted shortening of the overall time of passage in a short and rapidly rotating kiln with precalciner as compared with a kiln without precalcining equipment, namely, from about 35-40 minutes to about 20-25 minutes. An investigation in detail reveals, however, that the precalcined meal flour flows much more slowly - both absolutely and in relation to the speed of kiln rotation - than feed material does during calcination. This information is of particular importance in discussing the effects of the heating-up rate on clinker formation and quality. (orig./HP)