Efficiency of electrostatic precipitators

Other Uses. Other uses include intermediate chemical products. Overall, these uses account for 15—20% of sulfur consumption, largely in the form of sulfuric acid but also some elemental sulfur that is used directly, as in mbber vulcanization. Sulfur is also converted to sulfur trioxide and thiosulfate for use in improving the efficiency of electrostatic precipitators and limestone/lime wet flue-gas desulfurization systems at power stations (68). These miscellaneous uses, especially those involving sulfuric acid, are intimately associated with practically all elements of the industrial and chemical complexes worldwide. 

The efficiencies of electrostatic precipitators, bag filters, and scrubbers are given in Figure 16-3. The costs for installing and operating these devices are given in reference 20. This source also describes some exotic methods, such as the use of thermophoretic or diffusiophorctic forces and sonic agglomeration, that have not yet been commercialized. 

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). 

The amount of emission of radioactive isotopes into the atmosphere through the power plant chimney depends mainly on the efficiency of electrostatic precipitators or other devices used for the cleaning of flue gases. There are two types of coal burning power plants in operation in the world ... 

Ammonia is used in scrubbers to neutralize sulfur oxides in their removal from stack gases in electric power generation and other furnace operations such as smelting. It is also used to improve the efficiency of electrostatic precipitators in the removal of particulate matter. 

The development of electrostatic precipitators was based mostly on empirical work, and it has produced more than 1000 patents covering all aspects of electrostatic air cleaning. From the theoretical point of view, important milestones were papers published by Deutsch as well as White.These papers deal with the collection efficiency of the electrostatic precipitator. The most important early papers dealing with the electrical charging of particles are the ones published by Arendt and Kallmann, Pautheniet and Moreau-Hanot, and White. ... 

In general, electrostatic precipitators have been shown to best suit those applications where high gas flows must be handled and relatively high efficiency is required. It must also be emphasized that the use of electrostatic precipitators is limited to those applications where the explosion risks are minimal. 

This equation, which is called the Deutsch equation, has been shown to be a useful tool for estimating the performance of electrostatic precipitators. An interesting detail in the Deutsch equation is the exponent, which is equal to the collection efficiency of a laminar flow system. The equations based on laminar flow and turbulent flow can be assumed to be the extreme conditions, and the true situation is somewhere in between these two cases (see Fig. 13.1,5). 

A major market which has developed for fabric fillers is for the control ot flue-gas fly ash in the utility industry. This market is primarily at the expen.se of electrostatic precipitators. Fabric filters have the inherent advantage of operating at a high level of collection efficiency tor a wide range of dust and gas conditions. 

Bennett, R.P., Kober, A.E., "Chemical Enhancement of Electrostatic Precipitator Efficiency", Symposium on the Transfer and Utilization of Particulate Control Technology,... 

The collection efficiency of the wire-plate-type of electrostatic precipitator can be estimated by the widely used Deutsch theory [Deutsch, 1922]. To obtain the Deutsch equation, the following assumptions are made (1) because of the turbulent mixing effect, particle concentration at any cross section of the precipitator is uniformly distributed ... 

The removal of electrostatic precipitators can be improved by combining electrical collection with filters either with conventional design in series or via integration of the two technologies. Hybrid systems of this type are being introduced in some industries where very high efficiencies are needed. 

Emissions of sulfur oxides, nitrogen oxides, and particulates from coal combustion are problems of increasing concern and regulation. Coal combustion contributes about 25 percent of the particulate matter, 25 percent of the sulfur oxides, and 5 percent of the nitrogen oxides emitted to the atmosphere. Much of the particulates are derived from the mineral content of the coal, but some particulates also result from sulfur and nitrogen oxides that react to form various sulfate and nitrate salts. A major concern about particulate matter is that the smallest particles are respirable and may pose a health hazard. Particulate matter is recovered in most power plants by the use of electrostatic precipitators, which have been developed to very high efficiencies (>99%). Other methods of particulate removal include baghouses and cyclone collectors. 

Use the Deutsch-Anderson equation to calculate the efficiency of the precipitator. Also, use the modified Deutsch equation with a range of exponents varying from 0.4 to 0.7 (in increments of 0.05) to calculate the efficiency of the electrostatic precipitator. 

Monodispersed polystyrene latex particles 1.049 pm in diameter (std dev = 0.0587 pm) were captured utilizing a radial flow parallel-plate mobility analyzer (Tardos et. al. 1984). The mobility of the particles was determined from measurements of the collection efficiency of the analyzer by sampling particle number density for the inlet and exit flows (Figure 3-10). The principle was fundamentally that of electrostatic precipitation. The particles were charged by a corona discharge. The particles capture efficiency in the mobility... 

The absorption or fixation of solid pollutants and aerosols is generally accomplished on paper, membrane (nitrocellulose), polystyrene or glass-fibre filters. It should be noted that aerosols may also be sampled directly into absorption solutions (similarly as when sampling gaseous pollutants) and with the help of electrostatic precipitators however, these methods are infrequently used in practice. Particular types of filters are selected depending on the type of the pollutants to be determined. The filter quality is considered from the standpoint of the pore size, efficiency of capture. 

An electrostatic precipitator consists of two parallel plates separated by a distance of 0.06 m. The flow of gas through the system at 121°C and 207 X 10 N/m2 pressure has a Reynolds number of lO. Combustion products are anticipated to have log normal distribution with the average log normal length diameter of 6.0 Mm. The solid combustion product has a density of 1282 kg/m3. The electric field is 10,000 N/C with a particle charge of 10" ih c. What is the drift velocity of the average particle, the length of the precipitator needed for capture of this particle, and the efficiency of the precipitator ... 

The quantity ( BpL/AcVfl) in the Deutsch equation carries additional significance. It is essentially the ratio of the collecting electrode surface area over the gas flow rate. Thus, for identical values of Upy, similar particle collection efficiencies will be obtained in two different size precipitators if the value of (BpL/AcVz) is identical. This provides a basis for precipitator scaleup. A survey of the volumes of electrostatic precipitators needed for required gas flow rates is given in Figure 7.3.9 (Soo and Rodgers, 1971). 

The fraction of particles collected is sometimes reported in terms of percent collection efficiency (after multiplication by 100). Values of such efliciencies in a few operating plants are indicated in Figure 7.3.9, which identifies only a few major types of installations. The use of electrostatic precipitators is widespread additional examples of where they are used are cement plants, in the steel industry, in smelting operations, in the chemical industry, the petroleum industry, in carbon black factories, foundries, etc. In such industrial applications, industrial practice suggests techniques other than electrostatic precipitation for particles in the range 0.1-1 pm since the value of is <0.99 and decreases with a decrease in Vp (Donovan, 1985 Eggerstedt et al., 1993). 

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