I am working in a grinding unit having a vertical roller mill for slag grinding (UBE VRM). Initially this mill is for only slag grinding but we are also able grind clinker. We are getting clinker from various sources. Because of this we are getting different output and power consumption. I want to ask you is this normal to get different output and power consumption? How much influence does the wear rate of table and rollers have on output and power consumption. Also I want to know what are ways to increase the output of the vertical roller mill.

It is normal to get different outputs from the mill with materials from different sources. This will depend on the hardness of individual materials. There are ways to increase the output from a vertical mill. These involve adjustments to the separator and the airflow through the mill. A number of case studies have been reported by Siam Cement where major increases in output were achieved by these means.

NO_x control approaches applicable to the cement industry may be grouped in three categories: process modifications, combustion control, and NO_x reduction controls. One process modification that can be quantified is the CemStar process, which is a small addition of steel slag to the raw kiln feed. Can you provide more information on CemStar?

TXI have published various papers on their patented Cemstar process. The addition of steel slag or air cooled blast furnace slag boosts the output of the kiln with virtually no increase if fuel consumption as the slags have already effectively been clinkered and contains trace elements that mineralise the combination of the kiln feed into the clinker in the kiln. More product with the same amount of fuel burnt inevitably dilutes the NO_x emissions per tonne of clinker produced. The mineralising effect may also lead to lower burning zone temperature, and less thermal NO_x formation in the flame. The real crux of the technology is adjusting the chemistry of the kiln feed to maintain the desired clinker mineralogy when the slags are being added t the kiln inlet. With steel slag the iron oxide input is increased and has to be compensated by increasing the alumina and silca modulii. With air cooled blast furnace slag the material is deficient in lime therefore the LSF of the kiln feed has be increased. This inevitably increases the demand for high CaCO₃ content in limestone and is often the limiting factor.