Cement preparation By Kamran wazir


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Cement preparation

Published in: Engineering, Business, Technology

Cement preparation By Kamran wazir

  1. 1. Lecture # 2 Manufacturing process of Cement
  2. 2. Traditional Process of Cement Manufacturing 1- Aspdin mixed and ground hard limestone and finely divided clay into a slurry 2- The slurry was calcinated in a furnace till CO₂ was expelled 3- The calcinated mixture was then ground to a fine powder perhaps at a lower temperature than the clinkering temperature by Aspdin.
  3. 3. Later in 1845 Isaac Charles Johnson burnt a mixture of clay and chalk at clinkering temperature to make better cement .
  4. 4. Modern ways to Manufacture Cement The process is divided into 4 main parts – Quarrying and Grinding the raw materials – Mixing them in a intimately in certain proportions depending upon their purity and composition – Burning the proportioned mix in a kiln at 1300 ⁰C to 1500 ⁰C also called clinkering – Grinding of clinker and adding of gypsum
  5. 5. 1-Quarrying of Raw materials – The raw materials required are calcareous materials like chalk or limestone and argillaceous materials such as clay, marble or shale – Local availability of raw material is an important concern setting up a cement factory in order to reduce the transportation cost . The quarried materials are crushed, then mixed at the plant to be fed to the kiln
  6. 6. 2-Mixing and storage of feed Mixing is carried out by the either of the following processes – Wet Process – Dry Process
  7. 7. i) Wet Process The materials in the wet process are mixed with a water content of about 35% to 50%
  8. 8. ii) Dry Process In this process the materials are mixed in the powdered form using compressed air. The powdered material behaves like a fluid when exposed to compressed air in a chamber and mixing becomes possible This is the most widely used method in the recent years It reduces the fuel consumption as the slurry is already dry unlike wet process.
  9. 9. Burning or clinkering (wet process) • A typical kiln is a large refractory lined steel tube 165 m long inclined to the horizontal with capacity of 1050 tonnes/day • At the lower end of tube there is a burner and raw meal is fed from the other end • The kiln rotates slowly at about 20-86 rph passing material to the lower end • The water from the slurry needs to be driven off prior to the calcinating process
  10. 10. Zone 1: 0 - 35 min, temp is 800 – 1100 C o Decarbonation. Formation of 3CaO• Al2O3(C3A) above 900 Co. Melting of fluxing compounds Al2O3 and Fe2O3. heat CaCO3 → CaO + CO2
  11. 11. Zone 2: 35 - 40 min, 1100 – 1300 Co Exothermic reactions and the formation of secondary silicate phases as follows: heat 2CaO + SiO2 → 2CaO•SiO2
  12. 12. Zone 3: 40 - 50 min, 1300 - 1450 – 1300 Co Sintering and reaction within the melt to form ternary silicates and tetracalcium alumino- ferrates: heat+time 2CaO.SiO2 + CaO → 3CaO•SiO2 heat+time 3CaO.Al2O3 + CaO + Fe2O3 → 4CaO•Al2O3•Fe2O3
  13. 13. Zone 4: 50 - 60 min, 1300 – 1000 Co Cooling and crystallisation of the various mineral phases formed in the kiln. The cooler : Immediately following the kiln is a large cooler designed to drop the temperature of the clinker (as the fused material is now called) from 1000o C to 150 Co. This is achieved by forcing air through a bed of clinker via perforated plates in the base of the cooler. Like cement, the clinker will react with water and harden, but because it is composed of 1-3 cm diameter fragments it is too coarse to be used.
  14. 14. Cement milling To produce the final product the clinker is mixed with gypsum (CaSO4•2H2O), which is added as a set retarder, and ground for approximately 30 minutes in large tube mills. The cement flows from the inlet to the outlet of the mill (a rotating chamber), being first ground with 60 mm then 30 mm diameter steel balls. The first grinding breaks up the material and the second grinds it to a fine powder.