The present paper in this series of studies shows the results of testing the new techniques which improve the kiln reduction. So far the design and operation of the so-called ‘throwing-coal method’have been examined in order to prevent adhesion trouble, that is, dam-ring. Previous studies confirmed the fact that immoderate reoxidation of the material bed at the discharge end of the kiln causes adhesion trouble. The present study finds that we can succesfully prevent not only adhesion trouble, but also spalling by adding a little amount of highly volatile coal to the material bed through the discharge end. It also finds that 30 kg coal per a ton of the products is enough for the purpose mentioned above.
Now, the special arrangement of the particle-size of burden material is needed in order to regulate segregation between are and reductant in the process of kiln reduction. We find that segregation is regulated and controlled by arranging the particle-size in such a way that the differences among repose angles of the binary system may be kept within narrow limits, that is, within ab out five degrees.
Ingeneral, since there is a considerable amount of reducing gases inthe exhaust gases of kiln reduction, we make a great deal of heat recovery by injecting air at themiddle part of the kiln shell.
The amount of air theoretically measured for complete combustion of exhaust gases, together with a small amount of excess air, was introduced into the kiln by means of the air fan installed at 55% of the total length of the kiln shell from its discharge end. From thisexperiment we found that reducing gases burned with injection air of 720m3 per an hour, and that the middle part of 46m long kiln was heated up and reached the reduction temperature because of this combustion; as the result, the heat loss amounting to 515×103 kcal had been recovered.
The operation of the kiln under new techniques such as throwing-coal, control of particle-size, and air injection, shows very satisfactory results. The kiln through-putincreased by about 30%; the consumption of fuel oil was reduced by 20%; the residual carbon contained in the products decreased to 2%; the reductant needed in burden was reduced by 7%; and the total heat consumption per a ton of the products decreased by 270×103 kcal to 1840×103 kcal. Furthermore, the new techniques made the operation remarkably easier and freer from dam-ring.
Finally, we test and evaluate other improvements such as:- dust circulation, installation of chains in the feed-end, sectional air injection, installation of ring-dams at the intermediate.