Scrubber systems (eg chemical scrubbers, gas cleaners) are a diverse group of air pollution control devices that can be used to remove some particulates and/or gases from industrial waste streams. The first air scrubber was designed to remove carbon dioxide from the initial airborne submarine, Ictineo I, a role that continues to be used today. Traditionally, the term "scrubber" refers to a pollution control device that uses liquid to wash unwanted pollutants from the gas stream. More recently, the term has also been used to describe a system that injects reactants or dried slurry into a dirty exhaust stream to "cleanse" acid gas. Scrubber is one of the main devices that control gas emissions, especially acid gas. Scrubber can also be used for heat recovery from hot gas with exhaust gas condensation. They are also used for high flow in diesel, PV, or LED processes.
There are several methods to remove toxic or corrosive compounds from the exhaust gases and neutralize them.
Video Scrubber
Burning
Burning is sometimes the cause of dangerous exhaust, but, in most cases, combustion can also be used for cleaning of exhaust gases if the temperature is high enough and enough oxygen is available.
Maps Scrubber
Wet scrubbing
The exhaust gases from combustion may contain substances that are considered harmful to the environment, and scrubbers may remove or neutralize them. Wet scrubber is used to clean air, gas or other gas from various pollutants and dust particles. Wet scrubbing works through contact of target or particulate compounds with scrubbing solution. Solutions may be water (for dust) or reagent solutions that specifically target specific compounds.
The exhaust process may also contain water-soluble gases and/or corrosive gases such as hydrochloric acid (HCl) or ammonia (NH 3 ). This can be removed very well by wet scrubbers.
The efficiency of pollutant removal is increased by increasing the residence time in the scrubber or by increasing the surface area of ​​the cleaning solution by the use of spray nozzles, packed towers or aspirators. Wet scrubber can increase the proportion of water in the gas, resulting in visible clumps of piles, if gas is sent to the pile.
Wet scrubber can also be used for heat recovery from hot gas with exhaust gas condensation. In this mode, called condensation condensation, the water from the scrubbing drain is circulated through the coolant to the nozzle at the top of the scrubber. The hot gas enters the scrubber at the bottom. If the temperature of the gas is above the water dew point, it is initially cooled by evaporation of water droplets. Further cooling causes moisture to condense, increasing the amount of water that circulates.
Water condensation releases large amounts of low temperature heat (more than 2 gigajoules (560 kWh) per ton of water), which can be recovered by refrigerant for eg. purpose of district heating.
Excess condensed water should continue to be excreted from circulating water.
The gas leaves the scrubber at its dew point, so even if large amounts of water may have been removed from the cooled gas, it will likely leave a visible water vapor stack.
Dry scrubbing
Dry or semi-dry scrubbing systems, unlike wet scrubbers, do not meet the flow of exhaust gases that are being treated with moisture. In some cases no water vapor is added, while on the other only the amount of vaporized water vapor in the smoke gas without condensation is added. Therefore, dry scrubbers generally do not have steam steam vapor or wastewater treatment/disposal requirements. Dry scrubbing systems are used to remove acid gases (such as SO 2 and HCl) especially from combustion sources.
There are a number of dry type scrubbing system designs. However, they all comprise two main parts or devices: a device for introducing an acid gas absorber into the gas stream and a particulate matter control device for removing reaction products, excess sorbents and the existing particulate matter in the flue gas.
Dry scrubbing systems can be categorized as dry sorbent injectors (DSIs) or spray drier sprays (SDAs). Spray dryer absorber is also called semi-dried scrubber or spray dryer.
Dry scrubbing systems are often used to remove corrosive and odorous gas from wastewater treatment plant operations. The medium used is usually an active alumina compound impregnated with a material to handle specific gases such as hydrogen sulfide. The medium used can be mixed together to offer various removal for other odorous compounds such as methyl mercaptan, aldehydes, volatile organic compounds, dimethyl sulfide, and dimethyl disulfide.
Dry sorbent injection involves the addition of an alkaline material (usually hydrated lime, soda ash, or sodium bicarbonate) into the gas stream to react with the acid gas. Sorbents can be injected directly to several different locations: combustion process, exhaust channels (in front of particle control devices), or open reaction chamber (if any). The acid gas reacts with the alkali sorbent to form the solid salt expelled in the particle controller. This simple system can only achieve limited acid gas drain efficiency (SO 2 and HCl). Higher collection efficiency can be achieved by increasing the moisture of the exhaust gases (ie, cooling using a water spray). This device has been used in medical waste incinerators and some city waste incinerators.
In the spray dryer sprayer , the exhaust gas is fed to the absorber tower where the gases are contacted with fine atomized alkaline slurry. Acid gas is absorbed by a slurry mixture and reacts to form a solid salt emitted by the particle controller. The heat of the smoke gas is used to evaporate all the water droplets, leaving the unsaturated smoke gas out of the absorbent tower. Spray dryers are capable of achieving high efficiency (80%) of acid gas drainage. This device has been used in industrial boilers and utilities and urban waste incinerators.
Adsorber
Many chemicals can be removed from the exhaust gases also by using the adsorber material. The exhaust gas is passed through a cartridge filled with one or more adsorbers and has been adjusted to the chemical properties of the component to be removed. This type of scrubber is sometimes called a dry scrubber. The adsorber material should be replaced after the surface is saturated. Note: adsorption is a surface phenomenon, absorption involves the entire material. Ex: Activated carbon is an adsorbent, used for the adsorption of odorless compounds.
Mercury removal
Mercury is a highly toxic element commonly found in coal and city waste. Wet scrubber is only effective for removing dissolved mercury species, such as oxidized mercury, Hg 2 . The mercury vapor in its elemental form, Hg 0 , does not dissolve in the abrasive slurry and is not removed. Therefore, an additional conversion process of Hg 0 is needed to complete mercury capture. Usually halogens are added to the exhaust for this purpose. The type of coal burned as well as the presence of a selective catalytic reduction unit affect the ratio of the element to the oxidized mercury in the flue gas and hence the extent to which mercury is removed.
In July 2015, one study found that some mercury scrubs mounted on coal-fired power plants inadvertently capture PAH (polycyclic aromatic hydrocarbons) emissions as well.
Products scrubber waste
One of the side effects of scrubbing is the process of simply removing undesired substances from the flue gas into liquid, solid paste or powdered form. This should be disposed of safely, if not reusable.
For example, mercury removal produces waste products that require further processing to extract raw mercury, or should be buried in special hazardous waste disposal sites that prevent mercury from leaking out into the environment.
As an example of reuse, limestone scrubbers in coal-fired power stations can produce adequate quality synthetic gypsum that can be used to produce drywall and other industrial products.
Bacteria spread
Scrubber that is not well maintained has the potential to spread disease-causing bacteria. The problem is the inadequate cleaning results. For example, the cause of 2005 Legionnaires disease outbreak in Norway is only a few scrubbers infected. This outbreak causes 10 deaths and more than 50 cases of infection.
See also
References
Further reading
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Source of the article : Wikipedia
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