Cement manufacturing process

In the portland cement manufacturing process, three steps occur. First, raw materials are crushed and mixed. The raw materials are powdered limestone, alumina, iron, and silica. Second, the raw materials are fed to an inclined rotary kiln in which they are heated to at least 2700 F. A rock-like substance called clinker is formed, which exits the kiln and is cooled. Third, the cooled clinker is finely crushed, and about 5 percent gypsum is added to produce finished cement. Details of the process are explained below. 

This section presents a brief account of the concrete-producing materials, namely cement, fine and coarse aggregate, water, air and admixtures. The cement manufacturing process, the composition of cement, type and gradation of fine and coarse aggregate, and the function and importance of the water and air are reviewed. The reader can refer to books and papers on concrete such as the selected references at the end of this section. 

Understanding what one observes in powder mount, polished section, or thin section requires an appreciation of not only the cement manufacturing process but also the varied effects of light as it passes through or is reflected from crystals and amorphous materials. Formal training or extensive experience in microscopy is required. For example, when viewing crushed clinker in cross-polarized light in refractive-index oil on a microscope slide or a thin section, one must be aware that the interference colors are dependent mainly on four factors ... 

The main raw materials used in the cement manufacturing process are limestone, sand, shale, clay and iron ore. The main material, limestone, is usually mined on site while the other minor materials may be mined either on site or in nearby quarries. Another source of raw materials is industrial by-products. The use of by-product materials to replace natural raw materials is a key element in achieving sustainable development. 

Goh CL, Gan SL (1996) Change in cement manufacturing process, a cause for decline in chromate allergy Contact Dermatitis... 

Changes in the cement manufacturing process by using slag as a substitute for clinker, proportionally decreases the Cr(VI) concentration of cement. This phenomenon is considered to be one of the reasons for the decline in the prevalence of cement dermatitis among construction workers in recent years in Singapore (Goh and Gan 1996). 

X-ray fluorescence spectrometers can be used independently for occasional analyses or for simple analysis programs or be incorporated as an integral part of a process control system associated with computer equipment. The output data may take the form of pulse rates, concentrations (% by weight), moduli and lime standard, or be utilized in some other form for process control at the raw material end of the cement manufacturing process (e.g., for raw mix proportioning feed control). 

The object of grinding is, more particularly, to increase the specific surface of the material - while conforming to a desired particle size distribution - to such an extent as to obtain adequate reactivity for the next stage in the cement manufacturing process or adequate reactivity in the finished product (the cement) itself. 

Collaboration on policies, programs and projects geared toward further enhancing energy efficiency and reducing the GHG emissions of the cement manufacturing process. 

Portland cement is manufactured by two basic processes, the wet process and the dry process. The dry process uses approximately 25% less energy per ton of Portland cement and is used to produce about 68% of the U.S. Portland cement. Both processes start by mixing selected raw materials, cmshed and/or milled to approximately s in. (1.9 cm) diameter, in the correct ratios to give the final desired chemical composition. 

Mineral Products (e.g.. Cement Manufacturing, Coal Cleaning, and Stone Quarrying and Processing)... 

The development of electrostatic precipitators soon led to new applications, including the separation of metal oxide fumes. This was followed by various metal manufacturing processes such as the lead blast furnace, ore roaster, and reverberatory furnace. Electrostatic gas cleaning was soon applied also in cement kilns and in several exotic applications, such as recovering valuable metals from exhaust gases. 

Figure 1-4. Pictorial flow diagram establishes key processing steps Cement manufacture. By permission, E-M Synchronizer, Electric Machinery Mfg. Co.

In the manufacture of Portland cement, many otherwise-waste materials can be used either as a substitute for the traditional raw material, or as a secondary fuel (e.g., used tires) [334,1577]. In particular, drilling wastes can be introduced in the clinker burning process [878]. For both waste disposal and cement manufacturers, a mutual benefit will emerge. The cement manufacturing companies reduce their demand for traditional raw materials and save the limited capacity of landfills and other waste-treatment industries. 

Industrial furnaces are enclosed units that are integral parts of a manufacturing process and use thermal treatment to recover materials or energy from hazardous waste. These units may use hazardous waste as a fuel to heat raw materials to make a commodity (e.g., a cement kiln making cement) or the unit may recover materials from the actual hazardous waste (e.g., a lead smelter recovering lead values). The following 12 devices meet the definition of an industrial furnace12 ... 

Howden An early flue-gas desulfurization process using a lime or chalk slurry in wooden grid-packed towers. The calcium sulfate/sulfite waste product was intended for use in cement manufacture, but this was never commercialized. The key to the process was the use of a large excess of calcium sulfate in suspension in the scrubbing circuit, which minimized the deposition of scale on the equipment. The process was developed by Imperial Chemical Industries and James Howden Company in the 1930s and operated for several years at power stations at Fulham, London, and Tir John, South Wales, being finally abandoned during World War II. British Patents 420,539 433,039. 

Mineral products (e.g., cement manufacturing, coal cleaning, and stone quarrying and processing)... 

Market and actors In Germany approximately 32 m. tons of cement are manufactured, of which about 16% are processed manually, 31% are used in factory manufacture of concrete parts and 53% are used in the manufacture of ready-mixed concrete. Around 5.5 m. tons are imported. The cement industry operates in a Fordist stmctured market for mass products (lengthy product cycles, dominated by price competition) with trends towards monopolies. Raw materials suppliers and downstream businesses (e.g. cement transportation enterprises) are also being controlled increasingly by the cement manufacturers. 

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