|
An ejector or venturi scrubber is an industrial pollution control device, usually installed on the exhaust flue gas stacks of large furnaces, but may also be used on any number of other air exhaust systems. This type of technology is a part of the group of air pollution controls collectively referred to as wet scrubbers. Like a spray tower an ejector venturi scrubber uses a preformed spray. However, in an ejector venturi scrubber only a single nozzle is used instead of many nozzles. This nozzle operates at higher pressures and higher injection rates than those in most spray chambers. The high-pressure spray nozzle (up to 689 kPa or 100 psig) is aimed at the throat section of a venturi constriction. The ejector venturi is unique among available scrubbing systems since it can move the process gas without the aid of a fan or blower. The liquid spray coming from the nozzle creates a partial vacuum in the side duct of the scrubber. The partial vacuum is due to the Bernoulli effect, and is similar to water aspirators used in chemistry labs. This partial vacuum can be used to move the process gas through the venturi as well as through the facility's process system. In the case of explosive or extremely corrosive atmospheres, the elimination of a fan in the system can avoid many potential problems. The energy for the formation of scrubbing droplets comes from the injected liquid. The high pressure sprays passing through the venturi throat form numerous fine liquid droplets that provide turbulent mixing between the gas and liquid phases. Very high liquid-injection rates are used to provide the gas-moving capability and higher collection efficiencies. As with other types of venturis, a means of separating entrained liquid from the gas stream must be installed. Entrainment separators are commonly used to remove remaining small droplets. ==Particle collection== Ejector venturis are effective in removing particles larger than 1.0 µm in diameter. These scrubbers are not used on submicrometer-sized particles unless the particles are condensable (1977 ). Particle collection occurs primarily by impaction as the exhaust gas (from the process) passes through the spray. The turbulence that occurs in the throat area also causes the particles to contact the wet droplets and be collected. Particle collection efficiency increases with an increase in nozzle pressure and/or an increase in the liquid-to-gas ratio. Increases in either of these two operating parameters will also result in an increase in pressure drop for a given system. Therefore, an increase in pressure drop also increases particle collection efficiency. Ejector venturis operate at higher L/G ratios than most other particulate scrubbers (i.e., 7 to 13 l/m³ compared to 0.4-2.7 l/m³ for most other designs). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ejector venturi scrubber」の詳細全文を読む スポンサード リンク
|