Meghan Hodges
Air pollution control devices are used to prevent gaseous and solid pollutants from entering the atmosphere, primarily from industrial smokestacks. These devices can be split into two categories: those that control the amount of particulate matter escaping into the environment and those that control acidic gas emissions. Devices such as scrubbers, electrostatic precipitators, fabric filters, and cyclones are used to remove pollutants from the air.
| Characteristics | Values |
|---|---|
| Purpose | To reduce or eliminate the emission of harmful substances into the environment or the atmosphere |
| Types | Cyclones, scrubbers, electrostatic precipitators, baghouse filters, catalytic converters, smoke scrubbers, cartridge dust collectors, cyclone separators, fabric filters, incinerators, wet scrubbers, dry scrubbers, spray towers, venturi scrubbers, dynamic precipitators |
| Function | Remove gaseous and solid pollutants from industrial exhaust, smokestacks, flue gases, and the air |
| Pollutants Removed | SOx, VOC emissions, carbon, soot, ash, dust, acidic gases, sulfur dioxide, chlorine, hydrogen sulfide, hydrogen chloride, unburned carbon, fly ash |
| Industries | Manufacturing, processing, power plants, industrial facilities, ceramics, woodworking, fossil fuels |
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What You'll Learn
Fabric filters
Air pollution control devices are used to prevent gaseous and solid pollutants from entering the atmosphere, primarily from industrial smokestacks. Fabric filters, or baghouses, are one such device that can be used to remove dust and other particulate matter from flue gases.
Pulse-jet fabric filters use metal cages to support the bags, which hang from a tubesheet at the top of the filter. The dirty air enters the fabric filter, and the dust or particulate matter collects on the outside of the bags as the air passes through. Reverse air fabric filters, on the other hand, collect dust on the inside of the bags, which are not supported by metal cages. As the dust cake builds up and 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 and dislodge the dust. Shaker baghouses, as the name suggests, mechanically shake the bags to remove the accumulated dust.
The performance of fabric filters can be monitored and evaluated using various indicators, including particulate matter outlet concentration, which can be measured with a particulate matter continuous emissions monitoring system (CEMS) or a bag leak detection system. Other indicators include pressure differential, inlet temperature, temperature differential, exhaust gas flow rate, and cleaning mechanism operation.
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Wet scrubbers
Air pollution control devices are used to prevent gaseous and solid pollutants from entering the atmosphere, especially from industrial sources. Scrubbers are a type of system used to remove harmful materials from industrial exhaust gases before they are released into the environment. Wet scrubbers are a special type of scrubber that uses liquid solvents to remove a variety of pollutants from exhaust gases. They are also referred to as wet adsorption scrubbers or wet collectors.
However, wet scrubbers do have some drawbacks. They require frequent maintenance and are susceptible to severe corrosion. Proper maintenance and venting are necessary to prolong their lifespan. Nevertheless, their versatility and efficiency have made them essential equipment in industries such as chemical, pharmaceutical, and food production.
Overall, wet scrubbers play a critical role in reducing the environmental impact of industrial operations by efficiently removing harmful pollutants from exhaust gases, ensuring compliance with air quality regulations, and protecting public health.
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Dry scrubbers
Air pollution control devices are used to prevent gaseous and solid pollutants from entering the atmosphere, especially from industrial smokestacks. Scrubbers are a type of system used to 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. This text will focus on dry scrubbers.
The basic operations of a dry scrubber involve a few key steps designed to remove pollutants from gas streams without the use of liquids. The process begins with the intake of the polluted gas stream, which typically contains various pollutants, including particulate matter, acid gases, and possibly volatile organic compounds (VOCs). The next step is gas cooling, which is optional. The hot gas stream is potentially cooled before sorbent introduction to optimize scrubbing. Cooling ensures the sorbent's thermal stability, boosts reaction efficiency with pollutants, and safeguards equipment. The gas may pass through a heat exchanger or undergo other cooling techniques to reach a suitable temperature for effective scrubbing. The third step is sorbent injection, which is a key component of the dry scrubbing process. A sorbent material is injected into the gas stream.
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Electrostatic precipitators
An electrostatic precipitator (ESP) is a filterless device that removes fine particles, such as dust, smoke, soot, and ash, from a flowing gas. ESPs are commonly used at fossil-fuel power-generating stations and are highly effective at reducing particle pollution. They can handle large volumes of gas at various temperatures and flow rates, removing either solid particles or liquid droplets.
The basic design of an ESP consists of a row of thin vertical wires and a stack of large flat vertical metal plates. The plates are typically spaced about 1 cm to 18 cm apart, depending on the application. The contaminated gases pass through the passage between the plates, and the particles become charged and adhere to the collection plates. The treated air then passes out of the precipitator and through a stack to the atmosphere.
There are two main types of ESPs: dry and wet. Dry electrostatic precipitators operate above the dew point of the gas stream to remove impurities from smoke and dust. Wet electrostatic precipitators, on the other hand, operate with saturated airstreams that have 100% relative humidity. Wet precipitators are commonly used to remove liquid droplets, including oil, resin, tar, and sulfuric acid mist, from gas streams in industrial settings. They are used when gases are laden with humidity, contain combustible particulates, or have sticky particles.
The collected material on the electrodes of an ESP is removed by rapping or vibrating the collecting plates either continuously or at predetermined intervals. ESPs are highly efficient in their consumption of energy as they apply energy only to the particulate matter being collected. They are capable of collection efficiencies greater than 99%.
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Cyclone separators
The device works by forcing dirty flue gas to enter a chamber containing a vortex, similar to a tornado. The larger particles have greater inertia, causing them to hit the inside wall of the chamber and drop down into a conical dust hopper at the bottom. The cleaned air, on the other hand, swirls upward in a narrower spiral through an inner cylinder and exits through the top. This process separates the particulate matter from the flue gases without the use of filters.
These separators are commonly used in various industrial applications, including pulp and paper plants, cement plants, steel mills, and petroleum coke plants. They are also found in household items such as bagless vacuum cleaners and kitchen ventilation systems. Additionally, cyclone separators are advantageous due to their low installation and maintenance costs, ease of dry waste disposal, and space efficiency. However, a disadvantage is their limited effectiveness in collecting particulate matter smaller than 10 micrometers.
Overall, cyclone separators play a crucial role in air pollution control, particularly in industrial settings, by efficiently removing coarse particulate matter from flue gases.
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Frequently asked questions
There are several devices used to remove pollutants from the air, including:
- Electrostatic precipitators
- Fabric filters
- Scrubbers
- Cyclones
- Cartridge dust collectors
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. Wet scrubbers use a liquid, usually water, to absorb particles or gases from a stream of air, whereas dry scrubbers spray dry reagents into the flue stream to neutralise gases before they enter the atmosphere.
Electrostatic precipitators use static electricity to remove soot and ash from exhaust fumes before they exit smokestacks. They pull out unburned particles of carbon in smoke, leaving clean, hot air to escape.
