Scrubbers: An Indoor Pollution Solution?

Scrubbers are devices used to remove pollutants from the air. Wet scrubbers use water or a special solution to capture and neutralise air pollutants. They are highly effective at removing a wide range of contaminants, including organic and inorganic pollutants, and are therefore used in various industries, such as chemical, pharmaceutical, and food production. Wet scrubbers are also used to remove acid gas. Dry scrubbers, on the other hand, use a dry reagent called a sorbent to neutralise or separate acids from the gas. They are more cost-effective and produce less waste than wet scrubbers, but they are not as effective at removing pollutants. So, can scrubbers be used for indoor pollution? The answer is yes. Both wet and dry scrubbers can be used to improve indoor air quality by removing harmful pollutants from the air.

Wet scrubbers can remove organic and inorganic pollutants, including those that cause illness

Wet scrubbers are an effective solution for removing indoor air pollution. They are air pollution control devices that use a liquid, usually water or a water-based solution, to remove pollutants from industrial exhaust streams. Wet scrubbers are highly versatile and can be tailored to address specific pollutants, making them a flexible option for industries with diverse emission profiles.

Wet scrubbers can remove both organic and inorganic pollutants, including those that cause illnesses, deplete the ozone layer, or disrupt ecosystems. They are particularly effective at removing volatile organic compounds (VOCs), which are human-made chemicals produced during specific manufacturing processes, such as those used to make paint, pharmaceuticals, and refrigerants. VOCs can have severe short and long-term health effects, and wet scrubbers help minimize their impact on human health and the environment.

The basic principle of a wet scrubber involves introducing polluted gas into a chamber where it comes into contact with the liquid. The liquid acts as a solvent and a trapping medium, capturing particulate matter and absorbing gases. This process results in cleaner emissions being released into the atmosphere.

Wet scrubbers have different designs depending on the targeted pollutants, and they can be adjusted for height and type to improve the absorption of different pollutants. They are highly effective in removing airborne fumes, vapors, and gases, as well as particulate matter and hazardous air pollutants.

Wet scrubbers offer a contained and efficient solution for eliminating unwanted air contaminants, and they are widely used in industries such as power generation, chemical manufacturing, metal processing, and wastewater treatment. They play a crucial role in helping businesses achieve and maintain compliance with environmental regulations by systematically removing pollutants from industrial emissions.

Wet scrubbers are ideal for particulate-heavy exhaust streams

Wet scrubbers are highly effective at removing pollutants from exhaust gases. They are ideal for particulate-heavy exhaust streams, using water or a special solution to capture and neutralise air pollutants.

Wet scrubbers work by trapping suspended particles in a spray of water or another liquid. The contaminated exhaust gas is funnelled into the scrubber system, where it meets with the scrubbing liquid. The interaction between the two can take place in various ways, depending on the scrubber design. For example, spray towers spray the liquid directly into the gas stream, whereas packed towers pass the gas through a wet packed bed. Venturi scrubbers, which are ideal for particulate-heavy exhaust streams, use a narrow throat to accelerate the gas-liquid interaction, enhancing the efficiency of pollutant capture.

Wet scrubbers are highly effective at removing particulate matter, with Venturi scrubbers achieving the highest efficiency of over 98% for particles larger than 0.5 μm in diameter. They are also capable of removing volatile organic compounds (VOCs) from the air. VOCs are human-made chemicals produced during specific manufacturing processes, such as those used to make paint, pharmaceuticals, and refrigerants.

Wet scrubbers offer several advantages over dry scrubbers. They can process a wider range of pollutants and reduce fire hazards by keeping flammable pollutants wet inside the tower. They are also the only means of pollution control that can remove both particulate matter and gases from the exhaust in the same process. However, the main disadvantage of wet scrubbers is the need to dispose of and treat the liquid waste, which can increase operating costs.

Venturi scrubbers are the most efficient of the wet collectors

Venturi scrubbers are highly efficient wet collectors, achieving efficiencies of more than 98% for particles larger than 0.5 μm in diameter. They are designed to effectively use the energy from a high-velocity inlet gas stream to atomize the liquid used to scrub the gas stream. This type of technology is a part of the group of air pollution controls collectively referred to as wet scrubbers.

Venturi scrubbers bring particulate-laden air streams together with water at high velocities, transferring the particulate into the water stream. The water droplets and particulates are then removed from the air stream through centrifugal separation and mist elimination stages. This process is facilitated by the venturi scrubber's unique design, which consists of three sections: a converging section, a throat section, and a diverging section. The inlet gas stream enters the converging section and, as the area decreases, the gas velocity increases. Liquid is introduced at the throat or the entrance to the converging section, and the high velocity of the gas stream in the small throat section causes it to turbulently mix with the liquid, producing a large number of tiny droplets.

The high relative velocity between the droplets and the particulates is a key factor in the efficiency of Venturi scrubbers. This is achieved by injecting water into the throat of a venturi channel—a constriction in the flow path—through which particulate-laden air passes at high speed. The pressure drop in the venturi scrubber, which is the change in pressure as the gas travels through, is another important factor influencing efficiency. Venturi scrubbers are designed to operate at different pressure drops, with most operating with pressure drops in the range of 50 to 150 cm of water.

The liquid-injection rate, or liquid-to-gas ratio (L/G), is another critical factor in Venturi scrubber performance. The proper amount of liquid must be injected to provide adequate coverage over the throat area and compensate for any evaporation losses. Most Venturi scrubber systems operate with an L/G ratio of 0.4 to 1.3 L/m3. Maintaining the correct L/G ratio ensures that there are enough liquid targets to capture the particles and prevent them from being entrained in the outlet gas stream.

Venturi scrubbers are widely used in various industries due to their ability to handle large inlet volumes at high temperatures. They are particularly attractive for applications such as cement kiln emission reduction and control of emissions from basic oxygen furnaces in the steel industry. Venturi scrubbers are also effective in controlling fly ash and sulfur dioxide emissions from industrial and utility boilers.

In summary, Venturi scrubbers are the most efficient of the wet collectors due to their ability to utilize high-velocity gas streams, their unique design, and the careful consideration of factors such as pressure drop and liquid-injection rate. Their versatility and high efficiency make them a popular choice for reducing particulate emissions in a wide range of industrial applications.

Packed tower scrubbers are suited for gaseous pollutants

Packed tower scrubbers are ideal for removing gaseous pollutants. They are designed to force exhaust gases through a tower filled with packing material, maximising contact between the gas and the scrubbing liquid. This type of scrubber is particularly effective for corrosive vapours, unwanted mists, and noxious and odiferous gases.

Packed tower scrubbers are often used in industries such as chemical, pharmaceutical, energy, metals, mining, hazardous waste, electronics, pulp and paper, and food processing. They are well-suited for removing a wide range of gaseous pollutants, including:

• Corrosive gases such as acetic acid, hydrochloric acid, nitric acid, and sulfur dioxide
• Basic gases like ammonia and amines
• Halogens and halogen compounds, including chlorine, chlorine dioxide, fluorine, bromine, and iodine
• Specialty toxic gases such as silanes, ethylene, and propylene oxide
• Water-soluble organic compounds like ethanol, methanol, and formaldehyde
• Odorous gases, including hydrogen sulfide and methyl mercaptan

The design of a packed tower scrubber can be customised to meet specific requirements. For example, for low solubility gases, the scrubber can be engineered with extra depth or multiple packed beds with intermediate step chemical treatment. The packing material and bed depth can also be adjusted to meet the desired absorption efficiency.

Packed tower scrubbers offer several advantages. They provide a high level of removal efficiency for gaseous pollutants, and their design can be tailored to suit specific applications. Additionally, they have a relatively low capital cost compared to other pollution-minimising solutions.

Spray tower scrubbers are a straightforward and effective method for a wide range of applications

Scrubbers are devices that use liquid solutions to capture and remove pollutants from the air. Wet scrubbers are a type of scrubber that uses water or a water-based solvent to remove pollution from the air or liquid. They are highly effective in removing air pollutants and are used across a wide range of industries.

Spray tower scrubbers are a type of wet scrubber that uses a spray of water or liquid to trap suspended particles. They are a straightforward and effective method for a wide range of applications.

The design of a spray tower scrubber is simple: it consists of an empty cylindrical vessel made of steel or plastic, and nozzles that spray liquid into the vessel. The inlet gas stream usually enters at the bottom of the tower and moves upward, while the liquid is sprayed downward from one or more levels. This countercurrent flow exposes the outlet gas with the lowest pollutant concentration to the freshest scrubbing liquid.

Spray tower scrubbers can be very effective in removing pollutants, especially if the pollutants are highly soluble or if a chemical reagent is added to the liquid. For example, spray towers are used to remove HCl gas from the tail-gas exhaust in the manufacturing of hydrochloric acid. They are also used in the production of superphosphate, a key component in manufacturing fertilizer, to vent SiF4 and HF gases.

Spray tower scrubbers are also used for odor removal in the bone meal and tallow manufacturing industries by scrubbing the exhaust gases with a solution of KMnO4. Due to their ability to handle large gas volumes in corrosive atmospheres, spray towers are used in flue-gas desulfurization systems as the first or second stage in the pollutant removal process.

Spray tower scrubbers are low-energy scrubbers, making them a cost-effective solution. They are also advantageous due to their completely open design, which eliminates many of the scale buildup and plugging problems associated with other scrubbers.

Overall, spray tower scrubbers offer a straightforward, effective, and cost-efficient method for removing pollutants across a wide range of applications.

Frequently asked questions