We are facing a problem in bringing the whiteness of material that is close to cement composition in our R&D trials. We would like to know the effect of each oxide and cooling method on whiteness of the material.

The principal colouring oxides are those of the first row of the transition metals. In cement the most likely to cause problems are iron, manganese and chromium in that order. The cooling of the clinker is absolutely fundamental to achieving the desired whiteness. You must
(i) burn the clinker as close to the nose ring as possible to eliminate the possibility of oxidation ofFeO to Fe2O3 in the kiln, and
(ii) immediately quench cool the clinker in water.
Air-cooled blast furnace slag can be added to the inlet of the cement kiln in the patented Cemstar process developed by TXI cement in the USA. I know a number of US cement companies are doing this. This is in the manufacture of cement powder. Another use is as an aggregate in the manufacture of concrete.

What is the effect of cooler dust on flame?

Air-cooled blast furnace slag can be added to the inlet of the cement kiln. The effect of dust recirculating from the cooler in the secondary air is potentially disastrous. I have seen occasions where the dust keeps increasing until the kiln is full of dust and the firing has to stopped while the kiln is emptied of dust. The dust affects the combustion of the fuel in the flame and the problems tends to intensify in a vicious circle. Potential causes are poor combustion in the flame or elevated sulphate content in the clinker. (See the April 2003 issue of International Cement Review for an article about dust formation with pet coke firing in cement kilns).