Cement Energy and Environment

the splash box of the calciner reduction zone extending down to the kiln gas riser. All these symptoms cause unstable kiln operation and loss of output. All sound familiar and can be related to excessive sulphur recirculation in the kiln leading to ring and build-up formation , late decomposition of calcium sulphate leading to high free-lime, and reduced flux viscosity resulting in excessive dust return from the cooler. Once again the solution is likely to lie in increasing the momentum of the main burner to improve the mixing of the combustion air and fuel. Clinker balls In a third case, a cement factory in the Antipodes was suffering from periodic formation of clinker balls. When these balls were broken open they were found to be filled with uncombined raw meal. This factory was burning alternative fuels in lump form in the gas riser from kiln inlet to calciner. Some of the alternative fuel was falling into the kiln inlet and burning in the charge, creating local reducing conditions and increased recirculation of sulphur, in turn leading to the formation of large clinker balls. Sulphate build-up In a fourth instance, a cement factory in Southeast Asia introduced the burning of whole motor tyres in the inlet of the kiln. This kiln was heavily loaded with sulphur and the local reducing conditions in the kiln inlet lead to massive recirculation of sulphur and the formation of very hard build-up through the calciner and bottom stage of the preheater. Build-up necessitating a kiln stoppage of six days duration while the rock- hard sulphate build-ups were cleared from the system. Free lime fluctuations Perhaps the most interesting case was in Western Europe where a cement factory with very consistent kiln feed chemistry was suffering from wildly fluctuating clinker combination and free lime content. This factory was attempting to burn more than 50 per cent alternative fuels with ncr bypass installed in the kiln . The fluctuations in clinker content could not be directly related with the clinker sulphate content. This is where the combined cycles of sulphate and chloride become important. As the chloride cycle in the kiln intensifies with changing chloride content of the alternative fuels so the potassium in the kiln is increasingly combined with chloride as KCI. Less potassium remains available for combination with sulphate as K 2 so 4 , leading to increasing formation of calcium sulphate. Calcium sulphate that can decompose after the charge has passed under the flame and is too late to be recombined into the clinker resulting in high clinker free-lime content. In this case not only the circulation of sulphate but also the circulation of chloride needs to be brought under control. Only then will the variations which the process is imposing on the clinker composition be brought under control. Understanding kiln chemistry In 2008 at the Cemtech Singapore conference a workshop was conduqted on cement kiln chemistry. The main proposition of that workshop was that detailed knowledge and understanding of cement kiln chemistry is becoming ever more important as the fuels used to fire cement kilns evolve. This remains the case today, as illustrated by the above case studies from cement factories in different parts of the world. The chemistry doesn't change dependent on where the cement kiln is operating. Knowledge of cement kiln chemistry is critical whether you are operating in Western Europe, the Middle East, Southeast Asia , Latin America , West Africa or anywhere else for that matter. Of course what is changing is the personnel who are operating these kilns and their knowledge and understanding of cement kiln chemistry. I can't think of a better reason for people to study the CemNet Cement Kiln Chemistry course! Courtesy: . International Cement Rev1ew, March 2011 , Pp43-44. liT-MADRAS, LAFARGE TO PARTNER IN CEMENT RESEARCH PROJECT Indian Institute of Technology-Madras (liT-M) and French cement major Lafarge Group's research arm have launched a joint project which will conduct research to test the durability of concrete as a building material in different climatic conditions. This will be the first joint project between th~ two and is expected to start soon. The cement major's research arm, Lafarge Research Centre, and liT-M have signed a Memorandum of Understanding, last year under which the liT's civil engineering department would set up a laboratory to carry out joint research programmes. Lafarge Research Centre has funded the 6