35. The process of burning cement clinker

36. Procedures for burning cement clinker

Cement is obtained by pulverizing clinker and gypsum. Clinker - a product of uniform firing to the sintering of the homogeneous raw mixture of limestone and clay specific composition, ensuring the predominance of calcium silicates.

When grinding clinker introduced additives gypsum SaSO4 ∙ 2H2O to control setting time, up to 15% of active mineral additives (pyrite cinders, flue dust, bauxite, sand, [flask] and [Tripoli] s) to improve certain properties and reduce the cost of cement .

Calcination of the raw mix is ​​carried out at a temperature of 1450 + ... + 1480 ° C for 2-4 hours in long rotary kilns (3,6 × 127 m, 4 × 150 × 4.5 m and 170 m) from the internal heat exchanger devices, for simplification synthetic minerals required cement clinker. The material is calcined there are complex physical and chemical processes. Rotary kiln can be divided into zones:

• heating (200 + ... + 650 ° C - and burn organic matter begins the process of decomposition and dehydration of the clay component). For example, kaolinite decomposition occurs according to the following formula: Al2O3 ∙ 2SiO2 ∙ 2H2O → Al2O3 ∙ 2SiO2 + 2H2O; further at temperatures of +600 ... + 1000 ° C decomposes aluminum silicates and oxides metaprodukty.

• decarbonization (900 + ... + 1200 ° C) takes place decarbonisation of limestone components: CaCO3 → CaO + CO2, while continuing disintegration of clay minerals on oxides. The interaction of the main (CaO, MgO) and acidic oxides (Al2O3, SiO2) in the same zone start processes tvёrdofazovogo synthesis of new compounds (CaO ∙ Al2O3 - abbreviated CA account that at higher temperatures react with CaO and at the end of liquid-phase synthesis is formed C3A), proceeding in steps;

• exothermic reactions (1200 + ... + 1350 ° C) completes the process tvёrdofazovogo sintering materials are fully completed the process of formation of such minerals as the C3A, S4AF (F - Fe2O3) and C2S (S - SiO2) - 3 of 4 main clinker minerals;

• sintering (+ 1300 → + 1480 → + 1,300 ° C) partial melting material, into the melt moving clinker minerals except C2S, which interacts with remaining melt CaO forms alite mineral (S3S - solid solution trёhkaltsievogo silicate and a small amount (2 -4%) MgO, Al2O3, P2O5, Cr2O3 others);

• Cooling (1300 + ... + 1000 ° C) temperature drops slowly. Part of the liquid phase crystallizes with separation of crystals of clinker minerals, and the part solidifies in the form of glass.

37. Decarbonizators with upward vertical gas flue.

Furnace system with calciner as a rising vertical flue height ~ 80m received in recent years, most rasprostranenie.Dekarbonizator is ascending flue with a turn down, which takes most of the heat capacity of clinker reaction - decomposition of limestone. To accelerate the dissociation temperature after obych¬no calciner maintained at 850 ... 880 ° C. In circuits with calciner the raw meal from the cyclone of stage IV-directed to the lower part of the calciner, where entrained in the upward, where the intense heat exchange between the gas and the material. After passing the calciner, flour enters the cyclone V-th stage and then fed into a furnace, the degree of decarbonation of the material reaches 95%. The calciner is burned ~ 60% of total fuel. Tertiary air is supplied for combustion izgolovki oven at about 950 ° C. Skhe¬my advantages lie in the simple design of the calciner, niz¬kom flow resistance and high temperature of the tertiary air. The use of fossil fuel deposits depends strongly on the price and availability. In the cement production of natural gas used in the mainly hard coal, brown coal, oil shale and oil.