Cement manufacturing

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. 

The black, nodular clinker is stored on site in silos or clinker domes until needed for cement production. Clinker, gypsmn and other process additions 

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Silica and Alumina. The manufacture of Pordand cement is predicated on the reaction of lime with siUca and alumina to form tricalcium sihcate [12168-85-3] and aluminate. However, under certain ambient conditions of compaction with sustained optimum moisture content, lime reacts very slowly to form complex mono- and dicalcium siUcates, ie, cementitious compounds (9,10). If such a moist, compact mixture of lime and siUca is subjected to steam and pressure in an autoclave, the lime—silica reaction is greatiy accelerated, and when sand and aggregate is added, materials of concrete-like hardness are produced. Limestone does not react with siUca and alumina under any circumstances, unless it is first calcined to lime, as in the case of hydrauhc lime or cement manufacture. 

Portland Cement Manufacture. The second greatest use of limestone is as raw material in the manufacture of Pordand cement (10). The average limestone factor per ton of Pordand cement is 1.0—1.1 t of pulverized limestone. The limestone, calcined to lime in the cement rotary kiln, combines with siUca and alumina to form tricalcium siUcate and tricalcium aluminate and other lesser cementing compounds (see Cement). Most cement companies operate captive limestone quarries. 

E. E. Berry, L. P. MacDonald, and D. J. Skinner, E.xpenmentalBurning of Waste Oil as a Fuel in Cement Manufacture, Environment/Canada Report No. EPS 4-WP-75-1, Ottawa, Canada, June 1975. 

In 1991, Goodyear began working with Cadence Environmental Energy (Indiana) to market a whole tine feed system to supplement fuel for cement kilns. The system is used by several cement manufacturers. In 1992, Goodyear furnished tines for a Tennessee Valley Authority (TVA) test bum at a Memphis power plant. The electric utiUty used tine-derived fuel (TDE) to supplement coal fuel in a cyclone boiler. These tests were successflil. 

Part 403 general pretreatment regulations for existing and new sources of pollution Part 411 cement manufacturing point source category Part 413 electroplating point source category... 

Industrial by-products are becoming more widely used as raw materials for cement, eg, slags contain carbonate-free lime, as well as substantial levels of silica and alumina. Fly ash from utility boilers can often be a suitable feed component, because it is already finely dispersed and provides silica and alumina. Even vegetable wastes, such as rice hull ash, provide a source of silica. Probably 50% of all industrial by-products are potential raw materials for Pordand cement manufacture. 

ASTM C845 Type E-I (K) expansive cement manufactured ia the United States usually depends on aluminate and sulfate phases that result ia more ettriagite formation duriag hydration than ia normal Portland cements. Type K contains an anhydrous calcium sulfoaluminate, C A SI. This cement can be made either by iategraHy burning to produce the desired phase composition, or by intergrinding a special component with ordinary Portland cement clinkers and calcium sulfate. 

In the past 30 years, the ready-mixed concrete industry became the primary customer for cement manufacturers. In 1990 more than 72% of the cement shipped was sold to the ready-mixed concrete industry, compared with 63% in 1975. The other primary uses are in building materials, concrete products, and highway constmction. 

Diffusion of ions or molecules in solids is preliminary to reaction. It takes place through the normal crystal lattices of reactants and products as well as in channels and fissures of imperfect crystals. It is slow in comparison with that in fluids even at the elevated temperatures at which such reactions have to be conducted. In cement manufacture, for instance, reaction times are 2 to 3 h at 1,200 to 1,500°C (2,192 to 2,732°F) even with 200-mesh particles. 

Particulate matter emissions are the primary concern with cement manufacture. Fugitive emissions and uncontrolled kiln emissions are shown in Table 30-23. 

Ail Pollution Emission Factois for Portland Cement Manufacturing without Controls... 

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

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

The ASTM specifications provide for five types of Portland cements Types I, II, III, IV and V they are manufactured for use at atmospheric conditions [165]. The API Classes A, B and C correspond to ASTM Types I, II and III, respectively. The API Classes D, E, F, G, H and J are cements manufactured for use in deep wells and to be subject to a wide range of pressures and temperatures. These classes have no corresponding ASTM types. 

Marland, G., Boden, T. A., Griffin, R. C., Huang, S. F., Kanciruk, P. and Nelson, T. R. (1989). Estimates of CO2 emissions from fossil fuel burning and cement manufacturing, based on the US Bureau of Mines cement manufacturing data. Rep. ORNL/CDIAC-25, NDP-030, Carbon Dioxide Information Analysis Center, Oak Ridge Natl. Lab., Oak Ridge, TN. 

Use of wastes as raw material or secondary fuel in cement manufacture... 

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. 

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)... 

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