MIPPV TOPIC 6

• Cement


  A basic material for building and civil engineering construction, a finely ground, non-metallic, inorganic powder that when mixed with water forms a paste that sets and hardens

  
• Output from the cement industry is directly related to the state of the construction business in general and therefore tracks the overall economic situation closely
• Hydraulic hardening


  The setting and hardening of cement primarily due to the formation of calcium silicate hydrates as a result of the reaction between mixing water and the constituents of the cement
• Portland cement, the most widely used cement in concrete construction, was patented in 1824
• Cement


  A binder, a substance that sets and hardens and can bind other materials together, with principal constituents for constructional purpose being compounds of Ca (calcareous) and Al + Si (argillaceous)
• Chemical composition of cement

  • Lime (63%)
  • Silica (22%)
  • Alumina (6%)
  • Iron Oxide (3%)
  • Gypsum (1 to 4%)
• The cement industry is an energy intensive industry with energy typically accounting for 30-40% of production costs (i.e. excluding capital costs)
• Emissions caused by cement plants

  • Nitrogen Oxides (NOx)
  • Sulphur Dioxide (SO2)
  • Dust
  • Carbon oxides (CO, CO2)
  • Volatile Organic Compounds (VCOs)
  • Polychlorinated dibenzodioxins (PCDDs)
  • Dibenzofurans (PCDFs)
  • Metals
  • Noise
• Calcination process


  Decomposition of calcium carbonate (CaCO3) at about 900 °C to leave calcium oxide (CaO, lime) and liberate gaseous carbon dioxide (CO2)
• Clinkering process


  The calcium oxide reacts at high temperature (typically 1400-1500 °C) with silica, alumina, and ferrous oxide to form the silicates, aluminates, and ferrites of calcium which comprise the clinker
• Four main process routes for the manufacture of cement

  • Dry process
  • Semi-dry process
  • Semi-wet process
  • Wet process

  
• Winning of raw materials

  1. Rock drilling

  2. Blasting

  3. Excavation

  4. Hauling

  5. Crushing
• Raw materials preparation


  • Controlling the feed into the raw grinding plant to achieve chemical homogeneity
  • Pre-blending by stacking and extracting cross-sections
  • Storing and preparing materials with potentially harmful properties according to specific requirements
• Grinding of raw materials, dry and semi-dry kiln systems

  The raw materials, in controlled proportions, are ground and mixed together to form a homogeneous blend with the required chemical composition
• Tube mill


  A type of grinding mill consisting of revolving cylinders with hard balls inside, used to grind materials into a fine powder
• Vertical roller mill


  A type of grinder used to grind materials into extremely fine powder, an energy efficient alternative to a ball mill

  
• The fineness and particle size distribution of the product leaving a raw grinding system is of great importance for the subsequent burning process

  
• Clinker burning


  The raw meal (or raw meal slurry in the wet process) is fed to the rotary kiln system where it is dried, pre-heated, calcined and sintered to produce cement clinker
• Clinker burning


  • Maintain kiln charge temperatures of between 1400 to 1500 °C and gas temperatures of about 2000 °C
  • The clinker needs to be burned under oxidizing conditions
• Kiln firing


  The fuel introduced via the main burner produces the main flame with flame temperatures around 2000 °C, with the flame shaped and adjusted by the primary air
• Long Rotary Kiln


  Can be fed with slurry, crushed filter cakes, nodules or dry meal and are thus suitable for all process types, producing around 3600 tonnes/day using the wet process

  
• Grate Preheater Technology


  Allows part of the clinkering process to take place in a stationary installation outside the kiln, reducing heat losses and increasing energy efficiency
• Suspension Preheater Technology


  Preheating and even partial calcination of the dry raw meal takes place by maintaining the meal in suspension with hot gas from the rotary kiln, allowing almost complete heat exchange
• Storage of cement


  1. Pneumatic and mechanical conveying systems used for cement transport to storage silos

  2. Different cements stored separately in silos, with compressed air used to initiate and maintain the cement discharge process

  
• configurations currently used for cement

  storage are:

  • single cell silo with discharge hopper;
  • single cell silo with central cone;
  • multi cell silo
  • dome silo with central cone.
• Parts of rotary kiln:

  • Burner
  • Discharge Chute
  • Discharge Breeching
  • Riding Ring
  • Drive Motor
  • Trunnion Base
  • Refractory Lining
  • Gear/Sprocket Guard
  • Leaf Seal
  • Drive Base
• Applied Processes and Techniques:

  • Calcination Process
  • Clinkering Process