Industrial emissions, scrubbing

To prevent the emission of SO2 into the atmosphere, industrial processes scrub the gas to remove the SO2. The exhaust gas flows through stacks lined with calcium carbonate that, when heated, capture sulfur oxides in the form of calcium sulfate dust. 

While the use of low-sulfur fuels is one mechanism to reduce sulfur dioxide emission, alternatively most approaches focus on scrubbing or ridding the emissions in smoke stacks of sulfur dioxide gas. A number of different types of scrubbers, i.e., sulfur dioxide removal systems, are available for industry. One system sprays the flue gas into a liquid solution of sodium hydroxide. The hydroxide combines with SO2 and O2 to form the corresponding sulfate which can be removed from the aqueous solution ... 

Uses. In construction materials manufacture of steel, aluminum, and magnesium as a scrubbing agent to remove sulfur dioxide emissions from smokestacks manufacmre of glass, paper, and industrial chemicals in fungicides, insecticides, and lubricants... 

The Alka/Sorb air pollution control system is designed to remove dioxin, furans, toxic metals, acid gases, and particulates from industrial and medical incinerator off-gas. The Alka/Sorb system consists of a dry treatment/wet scrubbing process during which incinerator off-gas is cooled, contacted with an alkaline powder, injected with a sorbent, filtered by a baghouse and then wet-scrubbed for final removal of trace acid gases. Two central parts of the Alka/Sorb system include a wet-acid scrubber and a patented sorbent called Diox-Blok, which prevents the formation of dioxins and furans in air emissions. 

The detrimental effects of acid rain are a major reason why legislation such as the Clean Air Act places strict limitations on sulfur and nitrogen emissions. It is also a reason why low sulfur coal is preferred over high sulfur coal. To reduce sulfur dioxide emissions, industry also uses a technique call scrubbing. Industrial scrubbers employ a variety of physical and chemical processes to remove sulfur dioxide from emissions. Another technique used to combat acidification of lakes is to treat these systems with lime. The lime acts to neutralize the acid, but such techniques are usually costly and are only a temporary remedy for combating the problem. 

Dust (especially from industrial activities) and salt spray will also exacerbate atmospheric corrosion (Section 16.4). In enclosed industrial premises, atmospheric corrosion could be minimized by preventing noxious emissions, filtering the air to remove particulate matter, and scrubbing the air with water to remove SO2 and other objectionable gases, although the humidity should itself be kept as low as possible (e.g., steam leaks should not be tolerated). On the global scale, however, the cost to the public of atmospheric corrosion could be substantially reduced by sharply limiting SO2 and, to a lesser extent, NO. emissions from power plants, smelters, automobiles, and other industrial functions. This is an aspect of the acid rain threat (Chapter 8) that is usually overlooked. 

In other fuel markets, coal liquids can be more competitive. Industrial boilers presently are not amenable to stack gas scrubbing. The same is true of smaller utility plants. In particular, peak load units require a clean, storable liquid fuel as an alternative to natural gas. However, the high viscosity of primary coal liquefaction products is undesirable for many of these applications. Also, their residual sulfur and nitrogen contents may be excessive as emission standards become more stringent. 

Utne and coworkers [36] measured the emissions of carbonyl sulfide from industrial cells during normal operation. High levels of COS were found in the undiluted/unoxidized anode gas amounts corresponded to 3.3-10.2 kg tonne-1 of aluminum produced. Most of the sulfur emitted from the cells appears to originate from sulfur in the anodes. However, the COS is oxidized as the anode gasses leave the cell. After the gasses pass through dry and then wet scrubbing, the COS content corresponds to 0.21-0.26 kg tonne-1 Al. 

Industries use a variety of techniques to cut back on emissions of solid particles. Physical methods include filtration, centrifugal separation, and scrubbing, which, as Figure 17-9 shows, involves spraying ga.seous effluents with water. Another method, electrostatic precipitation, shown in Figure 17.10, is energy-intensive but more than 98 percent effective at removing particles. 

Major CO2 emissions sources are generated by fossil fuel combustion within the power and industrial sectors. Storage of the greenhouse gas in empty gas fields and aquifers could be a solution. To store CO2 underground it should be captured first. The most currently used post-combustion technology is absorption columns by means of an organic hquid. The flue gases are scrubbed in several reactors in which the CO2 is bound by... 

Measures taken to control atmospheric pollution include (a) scrubbing industrial waste gases to remove SO2, and (b) reduction of NO in motor vehicle emissions. Explain how these are achieved and write balanced equations for relevant reactions. Are they catalytic processes ... 

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