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Before the hazards of mercury emissions were fully recognized, actual emissions from mercury cells were as high as 3 kg per metric ton. Mercury emissions from chlorine production have dramatically declined in response to tighter regulations, better housekeeping, and technology improvements. However, there are considerable variations in the estimated mercury emissions from chlorine manufacture (Ayres 1997). Production of sodium carbonate from trona ore also creates emissions of carbon dioxide, a suspected greenhouse gas. Emission factors for carbon dioxide emitted from this process are given in Table 6-6. Additional carbon dioxide may be emitted as sodium carbonate is processed in other manufacturing processes (glass-making, water treatment, flue gas desulfurization, soap and detergent production, pulp and paper making). Data is listed on releases of carbon dioxide from these processes. According to a recent study (EIA 1998), approximately 113 metric tons of carbon are released for every 1000 metric tons of soda ash consumed in glass manufacturing or flue gas desulfurization. The same source indicates about 97 million metric tons of carbon released for every 1000 tons of trona ore produced annually for sodium carbonate production. In 1997, reported annual emissions of carbon dioxide from manufacture of sodium carbonate were 1.08 million metric tons; emissions from use of sodium carbonate were 0.86 million metric tons (EIA 1998). More than 88 percent of emissions from the use of sodium carbonate were associated with flue gas desulfurization. Controlled and uncontrolled emissions of filterable and total particulate matter from sodium carbonate production processes are shown in Table 6-7. Emissions of particulates from calciners and dryers are most often controlled by venturi scrubbers, electrostatic precipitators, or cyclones. The high moisture content of exiting gases makes it difficult to use baghouse-type filters. Control of particulates from ore and product handling systems, however, is often accomplished by baghouse filters or venturi scrubbers. These are essential to the cost- effectiveness of the process as they permit capture and recovery of valuable product. Varying Estimates of Mercury Emissions per Ton of Chlorine Manufactured 0.6 gram/metric ton (EPA 1992b) 0.47 gram/metric ton (Habersatter 1991) 2.47 gram/metric ton (Manzone 1993) 2.50 gram/metric ton (Euro Chlor 1995) 3.00 gram/metric ton (SRI 1989) Brine preparation and caustic evaporation processes release emissions through the combustion of fuels in process heaters and in boilers that produce process steam. When operating in an optimum condition and burning cleaner fuels (e.g., natural gas, refinery gas), these heating units create relatively low emissions of SOx, NOx, CO, particulates, and volatile hydrocarbon emissions. A table of emission factors for combustion of fossil fuels in fired heaters and boilers is provided in Chapter 7, Supporting Processes. During the production of sodium carbonate, particulate emissions are created from ore calciners, soda ash coolers and dryers, ore crushing, screening and transporting, and product handling and shipping. Combustion products (SOx, NOx, CO, particulates, and volatile hydrocarbons) are also emitted from direct-fired process heating units (ore calcining kilns, soda ash dryers). Little data is available on combustion products from these units, although emissions from similar equipment are categorized by the U.S. Environmental Protection Agency for the mineral industries, in AP 42 Chapter 11, Mineral Products Industry. 194PDF Image | The Chlor-Alkali Industry
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