Advantages of Venturi Scrubber System for Air Pollution Control

Venturi scrubber systems have high collection efficiencies for particulate pollution, while simultaneously absorbing and neutralizing gaseous pollutants. However, they require large pressure drops leading to higher power requirements.

Dirty air enters a Venturi throat and collides with scrubbing water that atomizes the liquid into tiny droplets that encapsulate and collect dust particles through impaction. Wet cyclone scrubbers can also be used to prevent fire hazards by keeping flammable gases wet.

Efficiency of Venturi scrubbers

The Venturi scrubber system is one of the most efficient types of wet scrubbing systems available. It is particularly effective in collecting particulate pollutants, but can also treat gases. The dirtiest air coming into a Venturi scrubber is forced at high velocity through the scrubber and collides with scrubbing water. The scrubbing water atomizes to produce a fog of tiny water droplets that capture the pollutant particles through impaction and diffusion. The dirty water then is sucked out of the scrubber and is discharged into a recycle tank or is pumped to a mist eliminator to be cleaned before recirculated back through the Venturi section.

The gas stream entering a Venturi scrubber enters a converging section, then passes through the throat section at an extremely high velocity. The gas then flows through the neck of the Venturi tube, where intensive mixing takes place between the gas and scrubbing liquid. The turbulence created in the throat area allows for maximum particulate and gas removal.

Venturis are often used to remove corrosive and sticky contaminants such as carbon dioxide, sulfur dioxide and hydrocarbons from process streams. They are also ideal for removing volatile organic compounds such as acids, alcohols and ketones from coco roasting and can help facilities operating in Ozone Non-Attainment Zones meet clean air requirements.

A Venturi scrubber’s efficiency depends on a number of factors, including the liquid/gas ratio, the velocity of the liquid at the throat section and the length of the throat section. In general, the scrubbing liquid is injected through spray nozzles, which are better for distribution than open-weir injection.

An ejector venturi is another type of wet scrubber that performs at an exceptionally high level in terms of particle collection. It has a simple design that allows it to handle large exhaust flows and high temperatures without plugging or scalding. An ejector venturi has a built-in fan to draw in the air/water mixture and create a turbulent mix inside the Venturi throat. The resulting dust-and-droplet agglomerates are collected by a chevron blade mist eliminator and returned to the sump for reuse or dissolved in sludge form.

Ease of Maintenance

Venturi scrubbers can be used to remove gaseous pollutants, but are most effective at removing particulate matter. They work by injecting a liquid into the throat of a venturi channel, a constriction in the flow path of the air being scrubbed, according to Pollution Engineering. This causes a drop in the relative velocity between the dust particles and the liquid, which results in more contact time and enhanced scrubbing efficiency.

When it comes to removing gaseous pollution, a different set of conditions is required than for removing particulate matter, and venturis are not designed for this application. Instead, the best choice for reducing gaseous pollution is an ejector scrubber or packed bed scrubber.

In order to effectively collect particulate matter, a venturi air pollution control system uses an hourglass-shaped chamber through which exhaust gases pass at high pressure. The scrubbing fluid is introduced into the gas stream at a much lower pressure, turning it into a fine mist that traps the particles. The atomized droplets must be separated from the outlet clean gas stream, and this is typically done by means of entrainment separators.

One of the most common types of venturis is the adjustable-throat model, which features a movable plate that varies the throat area of the scrubber to optimize performance. The design also includes a water-wash spray to wash collected material away from the plate. The adjustable-throat venturi is especially effective when scrubbing abrasive or sticky gas streams.

Another variation on the basic venturi design is the rod deck or rod-type scrubber, which features a grid of longitudinally spaced pipes that form a series of small venturi openings in the throat. This type of scrubber is more effective than the adjustable-throat version, as it is less susceptible to caked-on or abraded materials.

Another example of a successful scrubbing system that is specifically designed to address difficult-to-clean substances is the Monroe Dual Throat Venturi Scrubber. This type of scrubber was installed at a coco plant operating in an Ozone Non-Attainment Zone, and it was able to efficiently and economically remove water soluble volatile organic compounds (VOCs) and odors from the coco roasting process.

Ease of Installation with Venturi scrubbers

A venturi scrubber system is one of the easiest air pollution control systems to install. Unlike stacked tower scrubbers and chemical absorption systems that require a large amount of space for the scrubbing solution to be stored, venturi air scrubbers are compact and easy to assemble. They are also a cost-effective alternative to other air pollution control methods, such as ductwork dampers and blast gates.

The venturi scrubber works by forcing the dirty gas at high velocity through a narrow throat section that collides with scrubbing water. The rapid collisions between the scrubbing water and dirty gas create small water droplets that capture the contaminants through impaction and diffusion. The scrubbing water is collected in a sump tank and then pumped back to the scrubbing throat or through a mist eliminator. The scrubbing solution is continuously purged to limit the concentration of solids and to ensure that enough liquid is available to maintain efficient operation.

Two primary types of venturi scrubbers are available: the wetted approach type and the non-wetted approach type. The non-wetted venturi scrubber is best suited for low gas temperatures and high humidity levels. The wetted approach venturi scrubber, on the other hand, has an inlet section where the gas does not make contact with the scrubbing solution until it enters the throat section. This type of scrubber can be used in a variety of gases, including vapors and particulates.

Both types of venturi scrubber systems are available in a variety of construction options. They can be designed for vertical or horizontal flow and can have the scrubbing liquid injected at the inlet section of the Venturi throat or through the convergent throat. Monroe Venturi scrubbers can also include a separate scrubbing vessel for the recirculation of wash water and freshwater, which reduces maintenance and cleaning. An additional Clean-In-Place manifold system can also be included to provide continuous blow-down of the scrubbing solution and freshwater makeup, which decreases the frequency of cleaning.

Venturi scrubber systems are often used in combination with a cyclone separator to remove the heavier solids from the scrubbing solution. This increases the efficiency of the scrubbing process and also allows for a lower energy demand from the system fan.

Versatility of Venturi scrubbers

Venturi scrubbers can be used to collect both gaseous and particulate pollutants. When a dirty gas enters the Venturi scrubber, it is forced at high velocity through a throat and collides with scrubbing water. The liquid drops that are formed capture the pollutants through impaction and diffusion. The scrubber is often followed by a mist eliminator to remove the dirty water and recirculate it back into the Venturi section. This system is typically easier to maintain than filters and can handle a wide range of fluids.

A rectangular Venturi scrubber can be adapted to operate with varying gas flow rates and scrubbing liquid flow rates. This versatility can improve scrubbing efficiency. The throat size and type of the venturi can also be varied to accommodate different types of gas flow conditions.

The nozzle and throat of the Venturi scrubber must be made from wear-resistant materials due to the high gas velocities. A spray nozzle or open-weir liquid injection is commonly used because these provide better distribution of the liquid droplets in the throat area than a simple venturi. The use of a spray nozzle can also reduce the amount of liquid carryover into the gas stream, which may increase scrubbing efficiency. However, spray nozzles can easily plug with the abrasive particles from the gas stream and must be regularly cleaned. If the scrubbing liquid is a heavy liquid slurry, it may be preferable to use an open weir injection instead of a spray nozzle to prevent plugging.

Venturis have the highest collection efficiencies (especially for small particles) of any wet particulate scrubber. The equipment is particularly effective in removing fine PMs such as those found in the chemical, ore, timber, cellulose and paper, rock and solid waste incinerator industries.

Ejector Venturis are unique in that they can move the process gas with the scrubbing liquid without using a fan or blower. This is beneficial for clog-prone or explosive gasses and environments where the presence of a fan could pose safety risks. The scrubbing action of the nozzle creates a partial vacuum in the side duct and draws the process gas through the scrubber throat, similar to water aspirators used in laboratory testing.