cement mixer machine used in the cement making plant

Cement is a hydraulic powder material, which reacts with water to produce strength-bearing lattices. The mixture of aggregates, cement and water is concrete. The strength and durability of concrete makes it one of the most useful materials developed by man. The chemistry and mineralogy of cement is complex. In simple terms, cement is a manmade mineral structure created at high temperatures, mainly comprising lime, Silica and oxides of aluminium and iron . People has pay more and more attention to the cement making plant in recent years.

The cement making process can be divided; first "clinker" is made at temperatures of 1400 oC. Then the clinker is milled with other minerals to produce the powder we know as cement.

The raw materials, used to produce clinker includes some naturally occurring minerals and some materials available as waste streams from other industries. The most common combination of ingredients is limestone (for calcium) coupled with much smaller quantities of clay, shale and sand (as a source of silica, aluminium and iron) in the cement clinker grinding plant . Other "alternative" raw materials such as mill scale, fly ash and slag are brought in from other industries. Plants generally rely on nearby quarries for limestone to minimise transport.

Rock blasted from the quarry face is transported to the primary crusher where large "run of mine" rocks are broken into pieces of approximately 100mm. Generally the other raw materials do not require crushing. The raw materials are then proportioned to the correct chemical balance and milled together to a fine powder, "rawmeal. To ensure high quality of cement, the chemistry of the raw materials and rawmeal is very carefully controlled. Kiln exhaust gases are used in the raw mill to dry the raw materials used the cement mixer machine. In some gases with wet materials, additional heat sources are required for drying.

Materials are also homogenised to ensure consistency of product quality.

Preheater:

Rawmeal is the feed material for the high temperature process in the kiln system. "Preheating" is the first part of this system. A pre-heater is a series of vertical cyclones. As the raw meal is passed down through these cyclones it comes into contact with the swirling hot kiln exhaust gases moving in the opposite direction and as a result heat is transferred from the gas to material. This pre-heats the material before it enters the kiln so that the necessary chemical reactions will occur more quickly and efficiently. By retaining energy from the exhaust gases, energy is saved. Depending on the raw material moisture, a kiln may have 3 to 6 stages of cyclones with increasing heat recovery with each extra stage.

The calciner is a combustion chamber at the bottom of the preheater above the kiln back-end. Up to 65% of the total energy needs of the kiln system can be supplied to the calciner. Calciners allow for shorter rotary kilns and for the use of lower grade alternative fuels. Calcination is the decomposition of CaCO3 to CaO, which releases CO2. These process emissions comprise 60% of the total emission from a cement kiln. The combustion of the fuel generates the rest.