Flow of materials in rotary kilns used for sponge iron manufacture: Part II. Effect of kiln geometry
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I.
INTRODUCTION
THEpresent work was conducted in order to investigate the effect of length to diameter (L/D) ratio of a rotary kiln on the flow of materials. The work was in continuation of the earlier investigation ~ in which the effect of several operational variables like inclination, rotational speed, and exit end dam height on the flow of the charge was studied. The effects of the kiln LID ratio on the residence time, filling degree, and volumetric kiln loading were studied by varying the feed rate (0.25 Kg per minute to 1.25 Kg per minute), exit end dam geometry (blanking off 10 pct to 50 pct of kiln diameter), and LID ratio (3.3 to 16). II.
E X P E R I M E N T A L APPARATUS AND P R O C E D U R E
Different kilns used in this part of the work, with varying length and diameter, were all made from 6 mm thick mild steel plates. In the first stage of this work, five kilns of different diameters but having the same length were used. The lengths of these kilns were fixed at 2000 mm while the diameter varied from 200 mm to 600 mm, resulting in L/D ratios of 3.3 to 10: 1. These five kilns were mounted for experimentation on two stands with the help of an overhead hoist; the set-up is shown in Figure 1. In the second stage of this work, kilns having a fixed diameter of 300 mm and lengths varying from 2000 mm to 4800 mm were used, resulting in L/D ratios of 6.67 to 16:1. The inclination angle, rotational speed, and feed rate alteration arrangements, as well as the method of introducing the dams at the inlet and outlet end of the kiln for all the kilns were the same as described earlier, j A circular dam which covered 50 pct of the kiln diameter was always used at the inlet end of each kiln to avoid back-spillage. The circular dams used at the exit end of the kilns blanked off between 10 to 50 pet of the kiln diameter; the details of the dimensions of the circular dams as well as their nomenclature are given in the earlier work. ~ With this arrangement, it was possible to ensure a certain minimum bed depth within the kiln; a typical configuration is shown in Figure 2. AMIT CHATTERJEE, formerly Joint Director, Research and Development, TISCO, is now Managing Director, [pitata Sponge Iron Ltd., Jamshedpur 831001, India. A. V. SATHE, Project Coordinator, and P. K. MUKHOPADHYAY, Assistant Engineer, are with Research and Development Division, TISCO, Jamshedpur 831001, India. Manuscript submitted March 20, 1981. METALLURGICALTRANSACTIONS B
The procedure adopted for determining the residence time, kiln hold-up, and bed depths at different positions within the kiln has been discussed in the first part of this work. ~ A series of experiments was performed in all these kilns of different diameters and lengths with varying feed rates and exit end dam geometries to determine the values of these variables.
III.
RESULTS AND D I S C U S S I O N
A. Prediction of the Residence Time Different operating variables which govern the material flow in a rotary kiln under steady state conditions were correlated with the help of dimension
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