Chrome-Free, Magnesia-Spinel Brick Used in Burning Zone of Cement Rotary Kilns

摘要

As of February 2002, five cement kilos had begun to use as part of their linings the chrome-free brick we developed in 2001. In July 2001, the first set of this product was installed in the high temperature region of the burning zone of a kiln, which was dismantled in January 2002. Some of the bricks of the dismantled lining were retrieved and used as samples for this study. Examination of this kiln when it was stopped for relining revealed that the new chrome-free brick was as durable as magnesia-chrome brick. It also revealed that cement coating had adhered well to the brick surface, and at the sport where the coating had come off, only a thin piece of brick had come off with it. Analysis of the used brick samples permitted us to conclude that wear around the hot faces was due to mechanical wear combined with chemical wear. The former had been caused by texture deterioration as a result of the penetration of alkali salts, mainly that of KCl, and the thermal cycle. The latter was attributed to the reaction at high temperatures between main brick components, i.e., magnesia and spinel, and cement components. These wear patterns were the same as those of conventional spinel brick. Distinctly different wear patterns, however, were found between a sample of the new product located in one ring and a conventional chrome-free brick located in the adjacent ring; the two materials exhibited a marked difference in the wear of the hot face and the depth of alkali salt penetration. We believe it highly possible that this difference was due to the difference in the fundamental design between the two bricks; Young's modulus and thermal conductivity of the new chrome-free brick were made less than those of the conventional product and closer to those of Mg-Cr brick. We will, however, reserve judgment on this point until the results of the performance of the new product in other kilos become available. We believe that total replacement of Mg-Cr brick with chrome-free bricks in the cement kiln will require several kinds of chrome-free bricks that would meet different performance criteria at different locations within the kiln. The new chrome-free brick presented in this report was not developed as a replacement for the conventional chrome-free brick but as one of a series of chrome-free bricks suitable fur the locations where chrome-free bricks have not been used. Our work will continue toward the goal of making the entire lining in the cement kiln chrome-free.