Cement IndustryCement Manufacturing |
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How is cement made? Cement is made from gypsum, shale or clay, and limestone. 1. Mining the raw material Limestone and clay are blasted from rock quarries by boring the rock and setting off explosives with a negligible impact of the environment, due to the modern technology employed. 2. Transporting the raw material Once the huge rocks have been fragmented, they are transported to the plant in dump trucks or by conveyor belt. 3. Crushing The quarry stone is delivered through chutes to the crushers, where it is reduced by crushing or pounding to chunks approximately 1 ½ inches in size. 4. Prehomogenization Prehomogenization is the proportional mix of the different types of clay, limestones, or any other required material. Limestone (calcium carbonate) 5. Raw material storage Each of the raw materials is transported separately to silos, where it later will be added in specific amounts according to the particular type of cement being produced. 6. Raw material mill This takes places in vertical steel mill, which grinds the material through the pressure exerted by three conical rollers. Which roll over a turning milling table. Horizontal mills, inside which the material is pulverized by means of steel balls, are also used in this phase. 7. Raw meal homogenization This process takes place in silos equipped for obtaining a homogenous mix of the material. 8. Calcination Calcination is the core portion of the process, in which huge rotary kilns come into play. Inside, at 1400 degrees C, the raw material is transformed into clinker: small, dark gray nodules 3-4 centimeters in diameter. 9. Cement milling The clinker is ground by different-size steel balls while it works its way through the mill’s two chambers, with gypsum being added to extend cement setting times. 10. Cement packaging and shipping The cement is then housed in storage silos, from where it is hydraulically or mechanically extracted and transported to facilities where it will be packaged in sacks or supplied in bulk. In either case, it can be shipped by rail car, freighter truck or ship. Under these conditions the raw materials experience chemical and physical changes to form clinker. Clinker and gypsum are introduced to a finish mill where they are ground until a desired fineness is achieved. Changes can be made to the raw materials, burning temperatures and finish mills to create different types of cement such as Type I, Type II, Type III, Type V, and Type N and S Masonry Cements. There are five general types of cement. First, Type 1 cement is general cement for general use, typically the type used in construction. Type 2 cement is still a general cement, but it has resistance to sulfates and heat of hydration. Type 3 cement is for high strength properties in the early stages of the cement's life. I.e., immediately after curing. Type 4 cement is used where very low heats of hydration are desired. And Type 5 cement is used where a very high sulfate resistance is required. Cement is made from a mixture of calcium carbonate (generally in the form of limestone), silica, iron oxide and alumina. A high-temperature kiln, often fuelled by coal, heats the raw materials to a partial melt at 1450°C, transforming them chemically and physically into a substance known as clinker. This grey pebble-like material is comprised of special compounds that give cement its binding properties. Clinker is mixed with gypsum and ground to a fine powder to make cement. Coal is used as an energy source in cement production. Large amounts of energy are required to produce cement. Kilns usually burn coal in the form of powder and consume around 450g of coal for about 900g of cement produced. Coal combustion products (CCPs), such as Fly Ash also play an important role in cement manufacture and in the construction industry generally. Cement is usually gray. White cement can also be found but it is usually more expensive than gray cement. Cement mixed with water, sand and gravel, forms concrete. Cement mixed with water and sand, forms cement plaster. Cement mixed with water, lime and sand, forms mortar. Cement powder is very, very fine. One kilo (2.2 lbs) contains over 300 billion grains, although we haven't actually counted them to see if that is completely accurate! The powder is so fine it will pass through a sieve capable of holding water. Tip: Cement should be stored in a dry area. If it gets wet or damp the powder will turn into a hard lump. |
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Q. Isn't cement manufacturing one of the most energy intensive manufacturing processes? Q. What are the current levels of energy used in the manufacturing of cement? Q. What has the cement industry done to improve its manufacturing process? Q. What is being done about carbon dioxide emissions during the cement manufacturing process? Q. How does the industry compare to others in terms of carbon dioxide emissions? Q. How does the industry plan to reduce carbon dioxide levels? Q. How much recycled industrial byproducts are used in concrete production? Q. What recycled materials are used in cement production? Q. What is cement kiln dust and how is it used in the manufacturing process? Q. How are scrap tires are used in cement production? Q. How is the cement industry's relationship with government agencies? Q. What is the difference between cement and concrete? Q. Why the recent demand for sustainable development? Q. What makes concrete so durable? Q. What is energy efficient about concrete? Q. How does concrete relate to recycling? Q. How does concrete effect the environment compared to wood and steel? Q. What is the urban heat island effect and how does concrete fit in? Q. What are the environmental downsides to using concrete? more click here |