33. Reaction with cooling

An important process is the preparation of cement clinker it is cooled. From the rotary kiln clinker cooling zone out at a temperature of 1100 ... 1300 0C. Final cooling is carried out in its refrigerators.

Cooling the clinker has a significant effect on the structure, the mineralogical composition, grindability and thus the quality of the cement produced from it.

Primarily clinker cooling rate affects the ratio of crystalline and glassy phases. Slow cooling crystallization occurs, and with rapid - it slows down the formation of crystals and substantial portion of the melt solidifies in the form of clinker glass. The proportion of clinker melt in the rotary kiln is 20 ... 25%.

The rate of cooling affects the consistency of clinker cement volume change. Rapid cooling becomes large amounts of MgO in the glassy phase remain a microcrystalline state (grain size up to 5 ... 8 m). On slow cooling crystals of MgO increase in size, up to 30 ... 150 microns, which causes uneven changes in the volume of cement hardening. With a sharp firing and rapid cooling of the clinker formed small crystals alite, which increases the strength of the cement stone.

clinker cooling process also causes the chemical resistance of cement. Rapid cooling of the clinker increases cement sulphate. This is because C3A determining resistance clinker towards sulfate aggression by rapid cooling generally proceeds in a glassy form and becomes less sensitive to the effects against sulfates.

Grindability clinker depends on many factors, including the and the cooling rate. Comparison of grindability data quickly and slowly cooled clinker indicate that the clinker is cooled (slowly) in a drum cooler, requires higher energy consumption for grinding than clinker is cooled (fast) in a grate cooler. A higher content of the glassy phase and the small size of the crystals of clinker minerals grindability increases rapidly cooled clinker compared with cooled slowly. These data demonstrate the need for rapid cooling clinker.

34. Homogeneity of the raw meal

In the clinker burning process and fuel consumption affect the chemical composition, fineness of grinding, crystal size, nature of raw materials, the type and amount of impurities, the homogeneity of raw muki.Himichesky composition of the raw meal has a significant impact on the required firing time. It is defined as the time it takes to during firing the raw material mixture at a certain temperature the content of free CaO in the clinker should not exceed 2%. Oxides of alkali metals in larger amounts (about 2.5%) retard (inhibit) binding of lime during firing, while the content of MgO (about 2.0%) accelerates the firing.

The homogeneity of the composition of the raw meal is a necessary condition for the uniform clinker mineralogical structure and uniform operation of the kiln system. To do this, you must make sure that the raw material mixture in the smallest volume in the range (<1 mm3) is representative of a composition (thoroughly mixed, homogeneous). If the meal is poorly mixed, the clinker having "nest" of different phases, for example, free lime and belite clusters that formed in non-uniform material with valuable tricalcium silicate - alite. Using mineralizers (such as fluorspar, zinc oxide, manganese sulfide), the firing temperature can be lowered, and thus, can be achieved energy savings in the production of clinker.