Ejectors Venturi-type

This type of technology is a part of the group of air pollution controls collectively referred to as "wet scrubbers." Venturi scrubbers are also known as venturi jet scrubbers, gas-atomizing spray scrubbers, and ejector-venturi scrubbers. The technology is based on the removal of air pollutants by inertial and diffusional interception. 

Air ejectors (jet pumps) A device injecting high-velocity (pressurized) primary air into the secondary air. It allows air to be moved without passing through a fan, it may be a simple or Venturi-type ejector. 

In bubble columns, agitation of the liquid phase, and hence suspension of the catalyst is effected by the gas flow. The gas is often recycled to cause more turbulence and thus better mixing. Circulation of the liquid is often required to obtain a more uniform suspension. This can either be induced by the gas flow (airlift loop reactor) or by use of an external pump. In the latter instance it is possible to return the slurry to the reactor at a high flow rate through an ejector (Venturi tube). The local under-pressure causes the gas to be drawn into the passing stream, thus affording very efficient mixing. This type of reactor is called a Jet-loop or Venturi reactor. 

The stirred tank, of course, uses the stirrer for mixing, but the performance, even with modem designs of paddles, does little to ensure highly uniform reactions - the main point of stirring (or mixing) the fluid(s) within the pot . The most common types of mixers are in-line units and rotor stator mixers. Other mixer types considered below include variants based upon ejectors, fluidics, types using venturi aeration and ideas based upon spinning discs. 

Venturi-type ejectors (Figure 2-4) are popular for the delivery of chemical solutions. These devices use water pressure through a Venturi to produce a vacuum that draws the chemical solution into the water stream. This stream is then directed into the process water to deliver the chemical. Ejectors are simple and reliable as long as a pressurized water supply is available. It is important to use materials for all of these devices that are compatible with the chemicals being used. 

The powder is supplied to the gun by a powder pump at a uniform and consisfent rate. There are two types of powder pumps ejector type, using the venturi principle, and auger pumps, which use positive displacement. A corona charging system is most widely used to electrostatically charge the powder. The electrostatic spray gun has several functions ... 

Solids Metering The control valves described earlier are primarily used for the control of fluid (liquid or gas) flow. Sometimes these valves, particularly the ball, butterfly, or sliding gate valves, are used to throttle dry or slurry solids. More often, special throttling mechanisms such as venturi ejectors, conveyers, knife-type gate valves, or rotating vane valves are used. The particular solids-metering valve hardware depends on the volume, density, particle shape, and coarseness of the solids to be handled. 

There are two types of two-component nozzles ejectors and injectors. The ejectors are liquid jet aspirators, which operate according to the Venturi principle and with their propulsion liquid jet in the mixing space (diffuser) attain a substantial pressure drop on the gas side. Vacuum is commonly produced by water ejectors (vacuum pumps) in the laboratory and by steam ejectors on an industrial scale. 

Venturi scmbbers, packed columns, ESP (dry and wet types), ejector scrubbers (Fig. 7.5). 

The ejector-based reactor can be constructed in various configurations. Firstly, the jet can be either upflow or downflow, hi this book, only the downflow type is considered. In this type, the venturi loop reactor can be with or without a draft mbe. In case there is a draft tube, there is an additional internal circulation loop within the reactor. An outer circulation loop already exists because the hquid + catalyst slurry is continuously recycled by the external pump through the heat exchanger and the primary nozzle. 

Types of equipment classified as spray contactors include countercurrent spray columns, venturi scrubbers, ejectors, cyclone scrubbers, and spray dryers. The use of spray dryers as absorbers is of particular interest in the removal of sulfur dioxide from hot flue gas (see Chapter 7). 

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