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A variety of devices are used to move pollutants, depending on the type of pollutant and the context in which it is being used. For example, in the context of air pollution control, devices such as scrubbers, electrostatic precipitators, fabric filters, and cyclones are commonly used to remove gaseous and solid pollutants from industrial emissions before they are released into the atmosphere. In the context of indoor air pollution, solar water heaters, improved ventilation designs, and low-emitting consumer products can help reduce pollutants. Additionally, specific devices such as cartridge dust collectors and mist collectors are used to remove airborne dust and moisture from the air.
| Characteristics | Values |
|---|---|
| Air pollution control devices | Cyclone separators, scrubbers, electrostatic precipitators, fabric filters, baghouses, cartridge dust collectors, mist collectors, incinerators, biomass stoves, solar water heaters, catalytic converters |
| Cyclone separators | Use the principle of inertia to remove particulate matter from flue gases; dirty flue gas enters a chamber containing a vortex, and due to the difference in inertia between gas particles and larger particles, the gas particles move up the cylinder while larger particles drop down |
| Scrubbers | Remove harmful materials from industrial exhaust gases before they are released into the environment; there are two main types, wet scrubbers and dry scrubbers, which use liquid or dry reagents respectively to absorb particles or gases from a stream of air |
| Electrostatic precipitators | Create an ionized field to remove charged particles; can also be used with water for cleaning, in which case they are referred to as wet ESPs |
| Fabric filters | Simple method that can be used to remove dust from flue gases; can also remove acidic gases if they utilize basic compounds |
| Baghouses | Use fabric filter bags to capture and remove airborne dust and other particulates |
| Cartridge dust collectors | Similar to baghouses but use cartridge filters instead of fabric filter bags; can achieve higher filtration efficiencies than baghouses but are more sensitive to condensation |
| Mist collectors | Remove moisture and vapour from gas streams such as smoke, oil mist, and other liquid droplets using fine mesh-like filters |
| Incinerators | Convert VOC emissions into carbon dioxide and water through combustion |
| Biomass stoves | Can be equipped with secondary combustions, fans, or insulated combustion chambers to burn off unused fuel and ventilate remaining pollutants |
| Solar water heaters | Cut the necessity of solid fuel consumption |
| Catalytic converters | Used to control gaseous pollutants |
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What You'll Learn
Scrubbers
There are two main types of scrubbers: wet scrubbers and dry scrubbers. Wet scrubbers use a liquid, usually water, to absorb particles or gases from a stream of air. They are highly effective at removing water-soluble toxic and corrosive gases like hydrochloric acid (HCl) or ammonia (NH3). Wet scrubbers can also be used for heat recovery from hot gases by flue-gas condensation.
Dry scrubbers, on the other hand, do not saturate the flue gas stream with moisture. They work by spraying dry reagents into the flue stream, neutralizing gases before they can enter the atmosphere. Dry scrubbing systems can be further categorized into dry sorbent injectors (DSIs) and spray dryer absorbers (SDAs). Spray dryer absorbers are also called semi-dry scrubbers or spray dryers. They are used for the removal of odorous and corrosive gases from wastewater treatment plant operations.
Wet scrubbers generally achieve a higher level of pollutant removal than dry scrubbers. They are also more versatile, with various scrubbing agents and solutions available to remove and neutralize specific pollutants. However, dry scrubbers have their advantages too, such as not requiring stack steam plume or wastewater handling.
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Cyclone separators
In a cyclone separator, dirty flue gas is fed into a chamber that creates a spiral vortex, similar to a tornado. The lighter components of this gas have less inertia, making it easier for them to be influenced by the vortex and travel up. On the other hand, larger components of particulate matter have more inertia and are not as easily influenced by the vortex. These larger particles then hit the inside walls of the container and drop down into a collection hopper. The chambers are shaped like an upside-down cone to promote the collection of particles at the bottom of the container.
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Electrostatic precipitators
An electrostatic precipitator (ESP) is a filterless device that removes fine particles, such as dust and smoke, from a flowing gas using the force of an induced electrostatic charge. This device was first patented in 1907 by Professor Frederick Gardner Cottrell, a chemistry professor at the University of California, Berkeley. ESPs are highly efficient in their energy consumption as they apply energy only to the particulate matter being collected.
ESPs are made up of four main components: a power supply unit, an ionizing section, collection surfaces, and rappers. The power supply unit provides high-voltage DC power, while the ionizing section imparts a charge to particulates in the gas stream. The charged particles are then attracted to collector plates carrying the opposite charge, where they build up and are later removed from the air stream. The collection plates can be flat and parallel, or they can be tubular, consisting of cylindrical collection electrodes. The particulate removal process can be done mechanically or by using water, with the latter being referred to as wet ESPs.
ESPs are capable of collection efficiencies greater than 99%, and they can handle large volumes of gas at various temperatures and flow rates. They are widely used in minerals processing operations and are important tools in cleaning up flue gases. ESPs can also be used to clean the air in shipboard engine rooms, removing flammable oil fog accumulations and returning collected oil to the gear lubricating system.
The performance of ESPs can be measured by the particulate matter outlet concentration, opacity, secondary corona power, secondary voltage, and secondary current, among other indicators. ESPs are available in various sizes and types, designed for different dust and water droplet characteristics, as well as gas volume flows.
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Fabric filters
Air pollution control devices are used to prevent various pollutants, both gaseous and solid, from entering the atmosphere, especially from industrial smokestacks. Fabric filters, also known as baghouses, bag filters, or dust collectors, are an effective solution for capturing pollutants.
The design of fabric filters has evolved over time, with the market now offering a range of collection equipment for different applications. The main difference in designs lies in how the filter bags are cleaned. Pulse-jet fabric filters, for example, use metal cages to support the bags, which hang from a tubesheet at the top of the filter. As dirty air enters, dust accumulates on the outside of the bags, and when a sufficient pressure drop occurs, the cleaning process begins. Reverse air fabric filters, on the other hand, collect dust on the inside of the bags, and when the dust cake cuts off the inflow of dirty air, a reverse flow of clean air is used to remove the dust, causing the bags to partially collapse.
The performance of fabric filters can be monitored through various indicators, including particulate matter outlet concentration, opacity monitoring, pressure differential, inlet temperature, and exhaust gas flow rate. These indicators help ensure the effectiveness of the fabric filters in reducing pollutant emissions.
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Cartridge dust collectors
Air pollution control devices are used to prevent gaseous and solid pollutants from entering the atmosphere, especially from industrial smokestacks. One such device is the cartridge dust collector, which captures and removes airborne dust and other particulates. These collectors function similarly to baghouses but use cartridge filters instead of fabric filter bags.
The Donaldson Torit® range offers a variety of cartridge dust collectors, including the Downflo® Evolution, which combines cartridge technology with an integrated fan and electrical controls. The Downflo® Oval is a compact, high-efficiency unit that uses oval-shaped filters suited for filtering submicron dust. The Donaldson Torit® Workstation is designed for areas of dirty and/or noisy operations, applying no restrictions to worker movements or visibility. The Donaldson Torit® Bin Vent is another example, applying cartridge dust collector technology to continuous duty, venting applications that displace air and harmful products into silos and bins.
Other air pollution control devices include scrubbers, which remove harmful materials from industrial exhaust gases before they are released into the environment. There are two main types of scrubbers: wet scrubbers and dry scrubbers. Wet scrubbers use a liquid, usually water, to absorb particles or gases from the air, while dry scrubbers spray dry reagents to neutralise gases before they enter the atmosphere. Mist collectors, or moisture eliminator filters, are designed to remove moisture and vapour from gas streams, using fine mesh-like filters to separate liquid particles.
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Frequently asked questions
There are several devices used to move pollutants, including:
- Scrubbers
- Cyclone separators
- Electrostatic precipitators
- Fabric filters
Scrubbers are a type of pollution control device that removes air pollutants like sulfur dioxide, chlorine, hydrogen sulfide, and hydrogen chloride from industrial exhaust. There are two main types of scrubbers: wet scrubbers and dry scrubbers.
A cyclone separator is a device that uses the principle of inertia to remove particulate matter from flue gases. Dirty flue gas enters a chamber containing a vortex, similar to a tornado. The difference in inertia between gas particles and larger particulate matter causes the gas particles to move up the cylinder while larger particles hit the inside wall and drop down.
Electrostatic precipitators (ESPs) are air pollution control devices that create an ionized field to remove charged particles. ESPs typically feature multiple collecting plates to enhance their filtration capacity.
