Pollution control device, effects

The demand for environment-friendly fuels requires the removal of organosulfur compounds present in crade-oil fractions. SO2 or SO3 contribute to the formation of acid rain and have an effect on pollution control devices [9]. Very stringent environmental regulations will limit the sulfur levels in diesel fuels in EU to less than 10 ppm by the end of 2010 [10]. The conventional sulfur-compound... 

For effective volatilization using an enclosed mechanical aeration system, contaminated soil is mixed in a pug mill or rotary drum. The gasoline components are released from the soil matrix by the churning action of the air/soil contact. The induced airflow within the chamber captures the gasoline emissions and passes them through an air pollution control device (e.g., a water scrubber or vapor-phase carbon adsorption system) before they are discharged through a properly sized stack. 

U.S. EPA has shown that 90% of process water can be recycled to the front end of the system for slurry preparation, and the rest must be treated on site or transported to an off-site facility.80 During the aerobic process, some contaminated air may be formed and emitted from the reactor. Depending on the air characteristics, a compatible air pollution control device may be used, such as activated carbon. Slurry biodegradation has been shown to be successful in treating soils contaminated with soluble organics, PAHs, and petroleum waste. The process has been most effective with contaminant concentrations ranging from 2500 mg/kg to 250,000 mg/kg. 

Both fossil fuels and hazardous waste fuels used in Southdown cement kilns contain metals. The raw materials (limestone, clay, sand) used to make cement clinker also contain metals. In fact, certain metals, such as iron and aluminum, are essential components of the final product. While metals cannot be destroyed, the Southdown cement kiln process effectively manages them in the following ways (a) cement kiln operators limit emissions by carefully restricting the metals content in wastes accepted for recycling (b) dust particles containing metals are returned to the kUn through closed-loop mechanisms, where metals are chemically bonded into the cement clinker (c) particles not returned to the kiln are captured in state-of-the-art pollution control devices and (d) small amounts are emitted from the stack in quantities strictly hmited by USEPA s BIF mle. 

The physical characteristics of individual particles also are of environmental significance. For example, the smaller particles (diameters on the order of 1 micrometer of less) generally are most important in that they have very long atmospheric residence times (18), are least effectively controlled by pollution control devices (19), are preferentially deposited in the pulmonary regions of the lung (20,21), and may be most enriched in toxic species on a specific concentration (iig/g) basis (22-24). 

The surface layer composition may influence the effectiveness of pollution control devices. For example, it is apparent that a surface region highly enriched is alkali-alkaline earth sulfates may enhance the fly ash particle collection efficiency of electrostatic precipitators (11, 12, 51-53). 

Accurate knowledge of compositions of particles released by pollution sources is required by receptor modelers, e.g., for Chemical Mass Balances (CMBs). To improve model calculations, we have developed a source-composition library of data from journals, reports, and unpublished work. The library makes the data readily available and also helps to identify what new data are most needed. The library includes data for 21 studies of coal-fired plants. These data were used to investigate effects of coal type, pollution control device, and particle size on plant emissions. 

A comparison of fine and coarse particle compositions supports this hypothesis. Figure 4 shows EFcrust values for fine and coarse particles from six eastern-coal-burning plants equipped with ESPs. (We wanted to emphasize size-fraction differences without the additional effects of coal type and pollution control device.) For... 

We now further examine the effects of coal type and pollution control device on plant emissions. Table III gives individual values from each of 18 studies for the important elements S, As, and Se. As expected from the results in Table II, coal type has some effect on emissions of these elements, but the presence of a scrubber vs. an electrostatic precipitator (ESP) has a far greater influence. Except for the anomalous Radian(2) plant, and despite some overlap between the two groups, scrubber-equipped plants generally emit far more As, Se and, especially, S than do plants with ESPs. The total particulate mass emitted by plants with scrubbers ( 25 mg/m3 sulfate 4 mg/m3) is comparable to that emitted by plants with ESPs ( 47 mg/m3 sulfate 0.5 mg/m3), so scrubber-equipped plants release much more primary sulfate than do plants with ESPs. Scrubbers are designed to remove gas-phase S02 They accomplish this partly by converting SO2 to sulfate droplets or particles, some of which escape from the plant. 

Using a source-composition library containing data from 21 studies of coal-fired power plants, we have investigated the effects of particle size, coal type, and pollution control device on the composition of particles emitted from coal-fired power plants. 

All of the surface effects listed above must be considered in the design of effective pollution control regulations. It is apparent that most current control devices may be poorly equipped to remove the particles with the greatest potential for deleterious environmental effects. 

The effect of burning tires or TDF in waste-wood (hog fuel) boilers in pulp and paper mills was generally unfavorable on the emissions. Particulates increased in every series of tests when the TOF percentage was increased. The reason for this is pr ably due to the type of emissions control devices used on hog fuel boilers venturi scrubbers. The effectiveness of venturi scrubbers decreases as the particle size in the emission decrease. Zinc oxide is used in the manufacture of tires, and is present in significant quantities in scrap tires. Zinc oxide has a relatively low vaporization temperature and is vaporized when tires are burned. When zinc oxide vapors condense, they form sub micro-sized particles that are too small to be removed with a venturi scrubber. This is verified by comparing the zinc emissions in hog-fuel boilers to baseline. Zinc emissions increased in most cases 300 percent (and in one case, almost 50 times the base line emission rate). The effect of burning tires on other pollutants was mixed, and distinctive trends could not be determined. 

The combination of modern electrochemical techniques with the breakthrough in microelectronics and miniaturization has enabled the introduction of powerful analytical devices for effective process or pollution control. 

Electrostatic precipitation is perhaps the most versatile and cost effective of all particulate collecting devices and can be applied to any process where there is a need to remove solid particulate and mist of fume sized particles from the gas stream, whether it be for recovery or pollution control duties. It can be designed to deliver any efficiency for any gas flow rate and temperature and has a low pressure drop and a life span of more than 20 years. 

Thermal oxidizers and incinerators are extremely expensive to purchase, install, operate, and maintain. However, they are one of the most effective methods of handling toxic and etiologic agents. The operational aspects of these devices are beyond the scope of this book. Also, their application to fume hoods has historically been rare. When considering this method of pollution control, an expert should be called to assist. 

The removal of particulate matter from gas streams is the most widely practiced means of air pollution control and is very important in sustaining the quality of the atmosphere. A number of devices that differ widely in effectiveness, complexity, and cost have been developed for this purpose. The selection of a particle removal system for a gaseous waste stream depends on the particle loading, nature of particles (size distribution), and type of gas scrubbing system used. 

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