The rotary kiln consists of a tube made from steel plate, and lined with firebrick. The tube slopes somewhat (1–4°) and slowly rotates on its axis at between 30 and 250 revolutions per hour. Rawmix is fed in at the upper end, along with the rotation on the kiln causes it gradually to move downhill to the other end of your kiln. At the other end fuel, in the form of gas, oil, or pulverized solid fuel, is blown in through the “burner pipe”, producing a large concentric flame in the lower part in the kiln tube. As material moves under the flame, it reaches its peak temperature, before dropping out on the kiln tube into the cooler. Air is drawn first through the cooler and then through the kiln for combustion of the fuel. In the cooler the air is heated by the cooling clinker, so that it may be 400 to 800°C before it enters the kiln, thus causing intense and rapid combustion with the fuel. grinding mill
The moist course of action along with the dry course of action
From the earliest times, two different methods of rawmix preparation were used: the mineral components were either dry-ground to form a flour-like powder, or were wet-ground with added water to produce a fine slurry with the consistency of paint, and with a typical water content of 40~45%.
The moist method suffered the obvious disadvantage that, when the slurry was introduced into the kiln, a large amount of extra fuel was used in evaporating the water. Furthermore, a larger kiln was needed for a given clinker output, because much with the kiln’s length was used up for the drying process. On the other hand, the wet course of action had a number of advantages. Moist grinding of hard minerals is usually much more efficient than dry grinding. When slurry is dried in the kiln, it forms a granular crumble that is ideal for subsequent heating in the kiln. In the dry method, it is very difficult to keep the fine powder rawmix in the kiln, because the fast-flowing combustion gases tend to blow it back out again. It became a practice to spray water into dry kilns in order to “damp down” the dry mix, and thus, for many years there was little difference in efficiency between the two processes, and the overwhelming majority of kilns used the wet system. By 1950, a typical large, moist process kiln, fitted with drying-zone heat exchangers, was 3.3 x 120 m in size, made 680 tonnes per day, and used about 0.25–0.30 tonnes of coal fuel for every tonne of clinker produced. Before the energy crisis with the 1970s put an end to new wet-process installations, kilns as large as 5.8 x 225 m in size were making 3000 tonnes per day.
. It became a practice to spray water into dry kilns in order to "damp down" the dry mix,
and thus, for many years there was little difference in efficiency between the two processes,