EXHAUST CONTROL, INDUSTRIAL

Once an undesirable material is created, the most widely used approach to exhaust emission control is the application of add-on control devices (6). For organic vapors, these devices can be one of two types, combustion or capture. Applicable combustion devices include thermal incinerators (qv), ie, rotary kilns, liquid injection combusters, fixed hearths, and fluidized-bed combustors catalytic oxidization devices flares or boilers/process heaters. Primary applicable capture devices include condensers, adsorbers, and absorbers, although such techniques as precipitation and membrane filtration are finding increased application. A comparison of the primary control alternatives is shown in Table 1 (see also Absorption Adsorption Membrane technology). 

Technology Reduction effectivenes s Recovery Waste generation Advantages Dis advantages 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Capture devices are discussed extensively elsewhere (see Airpollution controlmethod). Oxidation devices are either thermal units that use heat alone or catalytic units in which the exhaust gas is passed over a catalyst usually at an elevated temperature. These latter speed oxidation and are able to operate at temperatures well below those of thermal systems. 

A thermal oxidizer is a chemical reactor in which the reaction is activated by heat and is characterized by a specific rate of reactant consumption. There are at least two chemical reactants, an oxidizing agent and a reducing agent. The rate of reaction is related both to the nature and to the concentration of reactants, and to the conditions of activation, ie, the temperature (activation), turbulence (mixing of reactants), and time of interaction. 

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Control of NO emissions from nitric acid and nitration operations is usually achieved by NO2 reduction to N2 and water using natural gas in a catalytic decomposer (123—126) (see Exhaust control, industrial). NO from nitric acid/nitration operations is also controlled by absorption in water to regenerate nitric acid. Modeling of such absorbers and the complexities of the NO —HNO —H2O system have been discussed (127). Other novel control methods have also been investigated (128—129). Vehicular emission control is treated elsewhere (see Exhaust control, automotive). 

Final purification of argon is readily accompHshed by several methods. Purification by passage over heated active metals or by selective adsorption (76) is practiced. More commonly argon is purified by the addition of a small excess of hydrogen, catalytic combustion to water, and finally redistiHation to remove both the excess hydrogen and any traces of nitrogen (see Fig. 5) (see Exhaust control, industrial). With careful control, argon purities exceed 99.999%. 

RCRA incinerator regulations include adrninistrative as weU as performance standards. Administrative standards include procedures for waste analysis, inspection of equipment, monitoring, and facihty security. Steps needed to meet adrninistrative standards are outlined ia the permit apphcation performance standards are demonstrated during a trial bum. Trial bum operating conditions are included in the permit to assure ongoing compliance with the performance standards. Performance standards include destmction and removal efficiency (DRE), particulate emissions limits, products of incomplete combustion emission limits, metal emission limits, and HCl and Cl emission limits (see Exhaust CONTROL, INDUSTRIAL). 

Work in the area of simultaneous heat and mass transfer has centered on the solution of equations such as 1—18 for cases where the stmcture and properties of a soHd phase must also be considered, as in drying (qv) or adsorption (qv), or where a chemical reaction takes place. Drying simulation (45—47) and drying of foods (48,49) have been particularly active subjects. In the adsorption area the separation of multicomponent fluid mixtures is influenced by comparative rates of diffusion and by interface temperatures (50,51). In the area of reactor studies there has been much interest in monolithic and honeycomb catalytic reactions (52,53) (see Exhaust control, industrial). Eor these kinds of appHcations psychrometric charts for systems other than air—water would be useful. The constmction of such has been considered (54). 

Sulfur Dioxide Emissions and Control. A substantial part of the sulfur dioxide in the atmosphere is the result of burning sulfur-containing fuel, notably coal, and smelting sulfide ores. Methods for controlling sulfur dioxide emissions have been reviewed (312—314) (see also Air POLLUTION CONTROL PffiTHODS COAL CONVERSION PROCESSES, CLEANING AND DESULFURIZATION EXHAUST CONTROL, INDUSTRIAL SULFURREMOVAL AND RECOVERY). 

Calcium carbonate is finding increasing use in flue gas desulfurization. This application by a variety of engineering processes traps the sulfur—oxygen compounds produced in the combustion of coal (qv) (see Coal conversion process Exhaust control, industrial Sulfurremoval and recovery). 

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