Smokestack scrubbers

Over the past decades, advances have been made that reduce environmental impacts of coal burning in large plants. Some arc standard and others experimental. Limestone (mainly calcium carbonate) scrubber smokestacks react with the emitted sulfates from the combustion and contain the chemical products, thereby reducing the release of SO., into the atmosphere by a large factor (of ten or more). Pulverization of coal can also allow for the mechanical separation of some sulfur impurities, notably those in the form of pyrites, prior to combustion. Currently deployed—with more advanced versions in the development stage—are various t yies of fluidized bed reactors, which use coal fuel in a pulverized form, mixed with pulverized limestone or dolomite in a high temperature furnace. This technique reduces sulfate release considerably. There are... 

The most common form of fluoride added to municipal drinking water today is hydroflusiliric acid, H2SiF6, which is obtained from the antipollution smokestack scrubbers of the phosphate fertilizer industry. What are the advantages and disadvantages of this system If water fluoridation were banned, what... 

The market for higher-sulfur coal is on the rise, since advanced filtering units called scrubbers are in use by a growing number of electric generating companies. Scrubbers are multistory facilities that are built adjacent to smokestacks. They capture sulfur as the coal exhaust billows through the smokestack and sequester it for storage before it can be cleaned. 

Another important use of lime is in pollution control. Many factories release harmful gases into the atmosphere through smokestacks. Lining a smokestack with lime allows some of these gases to be captured. The lime is known as a scrubber. Lime captures one harmful gas, sulfur dioxide (SO2), which is a contributor to acid rain (a form of precipitation that is significantly more acidic than neutral water, often produced as the result of industrial processes) ... 

To try to prevent the formation of SO, (and subsequently FI,SO ), one or both of two procedures are used. One procedure is to wash the coal first to reduce the amount of sulfur impurities. The other procedure is to install scrubbers in the smokestacks of power plants. The scrubbers... 

The sulfur gas produced by burning coal can be partially removed with scrubbers or filters. In conventional coal plants, the most common form of sulfur dioxide control is through the use of scrubbers. To remove the SO2, the exhaust from a coal-fired power plant is passed through a mixture of lime or limestone and water, which absorbs the SO2 before the exhaust gas is released through the smokestack. Scrubbers can reduce sulfur emissions by up to 90%, but smaller particulates are less likely to be absorbed by the limestone and can pass out the smokestack into the atmosphere. In addition, scrubbers require more energy to operate, thus increasing the amount of coal that must be burned to power their operation. 

Utilities have a great deal of flexibility as to how they reduce their sulfur oxide emissions. One way to cut emissions is to use low-sulfur coal, or to remove sulfur from coal before burning it. Sulfur is removed from coal by crushing the coal to a powder and washing it with water, resulting in a 50% sulfur reduction. Another way to cut emissions is by removing the sulfur dioxide from the exhaust. Fhie gas scrubbers can be installed in power plant smokestacks. These scrubbers spray a mixture of water and limestone into the exhaust, trapping the... 

We will also see that calcium compounds still figure in mortar formulations. Figures 13.10 and 13.11 summarize many of the commercial aspects of calcium chemistry. Figure 13.10 shows the uses of limestone, CaC03. Some of these have been mentioned elsewhere, but the Solvay process, smokestack scrubbers, and Portland cement need further explanation. 

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