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Environmental Pollution and Management 25 Fig. 4.1a. Daily variation of NO emissions of a rotary kiln Fig. 4.1b. Daily variation of NO emissions of a rotary kiln (over a long period)
26 Technology, Energy Efficiency and Environmental Externalities of the Cement Industry 4.1.3 Solid waste The major solid waste from cement industry is the dust collected from the air pollution control equipment. In addition, used refractories are also to be disposed of. 4.2 Current Pollution Abatement Strategy and Technologies 4.2.1 Air pollution control Pollution abatement in cement industry involves mainly prevention of air and water protection. By early 1980’s the average specific heat consumption for cement manufacture steadily decreased due to the change over to energy-saving preheater kilns and to waste heat utilization techniques. In contrast with the heat consumption, the specific electric power consumption slightly increased. This is due, among other factors, to the newly built coal grinding plants and to the increasingly stringent requirements to be fulfilled by environmental protection. Thus, these factors should be considered when deciding the environmental standards. The overall dust emission values can be steadily reduced with the aid of advances in dedusting technology and of process engineering changes. It has been proved that the dust emission levels can be reduced not only during normal plant operation, but more particularly also during start-up and shut-down (Kroboth et al, 1987). For example, in the case of grate pre-heater kilns, the auxiliary chimney as a source of emission has been eliminated. Instead, while the grate is stopped, the hot kiln exit gases are so conditioned with added air and water that even during heating-up and cooling-down of the kiln they can be dedusted in the kiln’s dust collecting unit. A remarkable decrease in dust emissions in the vicinity of cement plant can be attained by elimination of the so-called diffuse dust sources. For this, enclosed buildings and silos for clinker storage have to be build up. 4.2.1.1 Dust collecting devices It is the physical characteristics, such as total dust load, particle size distribution, bulk density, electrical resistivity and gas volume which normally determine the selection of suitable and efficient collection system, as some of these characteristics limit the power input and collection efficiency. Dedusting equipment in the form of filtering or of electrostatic precipitating units to reduce dust emission is employed in the cement industry. Inertia-force separators are now used only for pre-cleaning purposes, e.g., for protection of fans, or are integrally incorporated in the filter or precipitator systems. Formerly, cyclone collectors were considered adequate for both kiln stack and cooler stack (principal particulate emission sources) because they prevented nuisance dust-fall conditions. Now, however, opacity and discharge weight require more efficient collection equipment. Fabric filters are generally used for the dedusting of primary crushing operations, materials handling, raw meal blending and silo discharge operations, whereas grinding and drying installations (including those for coal) are dedusted with electrostatic precipitators or with
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The Asian Institute of Technology (
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