Cement manufacturing equipment needs to withstand the heat and the abrasive material from which cement is made. Making cement involves combining raw materials including limestone, clay, and shale, which are milled into a very fine powder after being mined. These materials are then mixed with other ingredients according to their end-use. This mixture is then fired in a kiln at temperatures between 2732-2912˚F (1400-1500˚C).
Modern Cement Manufacturing Process
Mainly made from limestone and clay, mining these raw materials entails blasting or drilling using heavy mining equipment to extract them from quarries. Once these raw materials are extracted, they are processed further with cement manufacturing equipment onsite or taken to a plant that turns them into usable cement. Manufacturing equipment such as crushers and mills are used to break these materials down. Once processed, they go on to a finishing mill.
The four stages for manufacturing cement involve:
Crushing and grinding raw material,
Blending materials in correct proportion,
Kiln drying to drive certain elements to form clinker, and
Grinding the clinker into a finished product.
Crushing & Grinding
During this stage of cement manufacturing, equipment first crushes the harder materials into smaller particles. This usually happens in two stages, using a vertical roller (or other similar types of) mill to grind the material down. Depending on the exact process used for cement production, the material will be either wet or dry. When using dry grinding, raw materials are first dried in cylindrical rotary dryers. Meanwhile, softer materials go through wash mills, where they are vigorously stirred in water to produce a fine slurry that then passes through screens to remove oversized particles.
Blending
These raw mixes seek to approximate the needed chemical composition for particular types of cement as they are crushed and ground. Different batches of cement are stored in silos when using dry processing techniques or in slurry tanks when using wet processing. To reach the right mixture, compressed air circulates through the dry material in silos to agitate it. The wet process uses either compressed air or mechanical means to stir the slurry tanks. From here, the material is then fed into the kiln.
Burning
Modern rotary kilns are used most widely today to make cement. These can reach up to 660 feet (200 meters) long and 20 feet (6 meters) wide. They consist of a cylindrical shell lined with heat-resistant materials – either cast or brick – to protect the outer shell of the kiln. Rotating slowly on an axis, the raw material is fed from the upper end, sliding slowly down to the lower end where it is fired with fuel, most commonly natural gas, petroleum, or crushed coal. Temperatures within the kiln range from 2460-2820°F (1350-1550°C), producing a substance called clinker, which has a lumpy consistency. It then passes through coolers that use incoming air to cool the product. This material can then be ground immediately into cement or stored for later processing.
Grinding
Clinker and gypsum are ground together into a fine powder before being milled further. This mixture passes through the mill, though the process may include separating coarser material that is then returned for further grinding. Sometimes the grinding process uses small amounts of specific mineral compounds to aid grinding, such as silica dioxide, calcium oxide or tricalcium silicate. This finished cement then gets pumped into bulk containers or paper bags.
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