Emissions control measures

In the early 1970s, air pollution requirements led to the adoption of the double contact or double absorption process, which provides overall conversions of better than 99.7%. The double absorption process employs the principle of intermediate removal of the reaction product, ie, SO, to obtain favorable equiUbria and kinetics in later stages of the reaction. A few single absorption plants are stiU being built in some areas of the world, or where special circumstances exist, but most industriali2ed nations have emission standards that cannot be achieved without utili2ing double absorption or tad-gas scmbbers. A discussion of sulfuric acid plant air emissions, control measures, and emissions calculations can be found in Reference 98. 

Airborne particulate matter emissions can, to a great extent, be minimized by pollution prevention and emission control measures. Prevention is frequently more cost-effective than control and, therefore, should be emphasized. Special attention should be given to pollution abatement measures in areas where taxies and buses associated with particulate emissions may pose a significant environmental risk. 

The WFD, so far, has identified 33 priority hazardous pollutants (PHS), for which Environmental Quality Standards (EQS) have been set. To some extent, these EQS can be met through the establishment of emission control measures. These PHS may originate from several different sources and activities. The main sources of toxic substances to water bodies in Europe may be categorised as agriculture, sewage treatment plants, urban runoff, industry, contaminated lake/ river sediment, soils and landfills. Input via atmospheric transport and deposition has also been identified as an important source both far from and close to source areas. Many of the PS are today banned in Europe, but due to their persistence they are still present in the environment [30]. 

Postformation nitrogen oxide emission control measures include selective catalytic and noncatalytic reduction with ammonia, which between them are used by some 900 power station installations worldwide [51]. The catalytic removal methods are 70-90% efficient at NOx removal, but are more expensive to operate than the noncatalytic methods which are 30-80% efficient. Ammonia or methane noncatalytic reduction of NOx to elemental nitrogen is also an effective method which is cost-effective for high concentration sources such as nitric acid plants (Chap. 11). NOx capture in packed beds is less expensive, but this method is not particularly effective [23]. It is also not a very practical method either for utilities or for transportation sources. Two-stage scrubbing has also been proposed as an effective end-of-pipe NOx control measure. The first stage uses water alone and the second uses aqueous urea. 

Each of the pulping methods—mechanical, chemimechanical (presoak), semichemical, and the kraft and sulfite chemical processes—produce different types of wastes, so that emission control measures for each should be considered separately. Since the mechanical and kraft chemically based pulping methods dominate the world markets (Table 15.1), the discussion will focus on these two processes. Resource use and pollution control problems of the... 

Air emission problems of breweries are relatively minor since mass emission rates are low and discharges are largely nontoxic. Emission control measures focus on containment of process odors. Water scrubbers are used on brew-house stacks to eliminate this potential problem area [7]. If spent yeasts and grains are dried on site, the resulting odors are controlled by afterburner pyrolysis before the dryer vent stacks [18]. 

The new edition has been assembled to make it easy to use on any or all of three levels. Basic principles and theory of each process are discussed initially, followed by more recent refinements and developments of each process, finally supplemented with material which relates to possible process losses and integral and end-of-pipe emission control measures. The user s interest can dictate the level of approach to the material in the book, from a survey of a selection of basic processes to an in-depth referral to one or more particular processes, as appropriate. Chemical reactions and quantitative assessment are emphasized throughout, using worked examples to aid understanding. 

Precautions are being taken against environmental pollution, especially by staie-of-thc-art emission control measures. 

Since the internal combustion engine is the primary source of localized pollutant carbon monoxide emissions, control measures have been concentrated on automobiles and have been very successful in reducing carbon monoxide emissions. Carbon monoxide emissions may be lowered by employing a leaner air-fuel mixture, that is, one in which the mass ratio of air to fuel is relatively high. At air-fuel (mass mass) ratios exceeding approximately 16 1, an internal combustion engine emits virtually no carbon monoxide. Modern automobiles use catalytic exhaust reactors and precise computerized control of engine operation to cut down on carbon monoxide emissions. 

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