Air Pollution Controls: Equipment Essentials For Clean Air

Air pollution control equipment is essential for managing emissions from both mobile and stationary sources, with the latter being the focus of most equipment. Pollutants must be captured and removed from the air before they are released into the environment. Common types of equipment include cyclones, scrubbers, electrostatic precipitators, and baghouse filters, with each type of equipment having its own unique pollutant control efficiency. The selection of equipment depends on various factors, such as the characteristics of the pollutant and the exhaust system. The equipment is designed to regulate and remove hazardous emissions, such as particulate matter and gases, produced by manufacturing and industrial processes.

Air scrubbers

There are two primary types of air scrubbers: wet scrubbers and dry scrubbers. Wet scrubbers, also known as wet air scrubbers or wet gas scrubbers, use a liquid solution, typically water, to capture and remove pollutants. The gas stream is directed through a liquid spray or a wetted surface, trapping the pollutants and cleaning the exhaust gas. Wet scrubbers are highly effective at capturing fine particles, acidic gases, and even some heavy metals. They are well-suited for removing odorous compounds and can handle high-temperature and high-humidity environments. However, they tend to consume a significant amount of water and require careful monitoring to prevent the growth of bacteria and fungi.

On the other hand, dry scrubbers, also known as dry air scrubbers or dry gas scrubbers, remove pollutants without using a liquid medium. Instead, they employ dry sorbent materials such as activated carbon or hydrated lime, which chemically react with and capture the pollutants. Dry scrubbers offer advantages such as a smaller footprint, lower maintenance requirements, and reduced energy consumption. They are particularly suitable for industries where water conservation is crucial and for capturing pollutants that are not water-soluble.

The choice between wet and dry scrubbers depends on various factors, including the nature of the pollutants, process conditions, regulatory requirements, and operational constraints. For industries dealing with water-soluble pollutants and strong odours, wet scrubbers are often preferred. In contrast, dry scrubbers may be more suitable when water conservation and a reduced maintenance burden are key considerations.

Heat exchangers

Air-to-air heat exchangers are commonly used in the automotive and air pollution control industries to recover wasted heat energy and direct it toward other processes. They are also used to lower energy costs and condition fresh outdoor air for applications. For example, the automotive industry utilizes heat exchangers to recover heat from incinerators and direct it toward dryers.

Air-to-air plate heat exchangers are another type of heat exchanger that allows industrial facilities to harvest the potential energy found in exhaust air for air pollution control. The heat exchanger attaches to incinerators, kilns, and ovens. The plate collects the heat from the exhaust air and passes it into the clean intake air, while the cooler exhausted air condenses onto the walls and plates. This process results in cleaner exhaust air being vented into the environment.

Overall, heat exchangers play a critical role in reducing energy costs and minimizing industrial air pollution. They are an important tool in the effort to prevent and mitigate various types of air pollution, including volatile organic compounds (VOCs), sulphur oxides (SOx), and nitrogen oxides (NOx).

Cyclones

The basic components of a cyclone include an inlet cylindrical section, a conical section, an outlet gas duct, an outlet dust tube, and a collection hopper. The size of a cyclone is directly related to the volume of gas that needs to be filtered. Larger operations typically require bigger cyclones to handle higher gas volumes. Cyclones can also be configured as multicyclones, consisting of multiple small-diameter tubes in parallel, combining high efficiency with the ability to treat large gas volumes.

One of the advantages of cyclones is their versatility. They can be used as a standalone solution or in conjunction with other pollution control devices. Cyclones are often employed as a pre-treatment step before flue gas enters more advanced pollution control equipment. By removing larger and abrasive particles, cyclones help extend the lifespan and improve the efficiency of downstream collection devices. This makes cyclones a valuable component in air pollution control systems, especially in industrial settings where particulate matter and gases need to be managed effectively.

When considering the use of cyclones, it is important to evaluate the specific requirements and characteristics of the application. Cyclones work best with flue gases that contain a high concentration of large particulate matter. Their efficiency decreases with an increased presence of lighter particulate matter. Additionally, the overall efficiency of cyclones can be influenced by factors such as capture efficiency, gas stream flow rates, temperature, humidity, and the surface area of the cyclone itself. Regular maintenance and servicing are crucial to maintaining the performance and longevity of cyclone equipment, ensuring optimal pollutant removal.

In summary, cyclones are a vital tool in the arsenal of air pollution control equipment. Their ability to effectively separate and collect particulate matter from contaminated gas streams makes them a versatile and cost-effective solution. Cyclones can be employed as a preliminary treatment step or used in conjunction with other technologies to enhance their performance. By understanding the strengths and limitations of cyclones, industries can make informed decisions about their air pollution control strategies and contribute to improved air quality.

Electrostatic precipitators

There are four basic types of electrostatic precipitators (ESPs): plate and wire (dry), flat plate (dry), wet, and two-stage. ESPs provide a large air volume, can operate at various temperatures, and require minimal maintenance. However, they have limitations, including their physical size, operation expenses, and inconsistent collection efficiencies.

Wet electrostatic precipitators (WESPs) are a type of ESP that can collect finer particulate matter than other technology, as well as aerosols. They are commonly used to remove liquid droplets, including oil, resin, tar, and sulfuric acid mist, from gas streams in industrial settings. WESPs have been used in the metallurgical industry for nearly 100 years and are often integrated with other air pollution control equipment to remove multiple pollutants.

Overall, electrostatic precipitators are an important tool for cleaning up flue gases and reducing particle pollution, particularly in industrial settings.

Baghouse filters

Air pollution control equipment is used to regulate and remove potentially hazardous emissions, such as particulate matter and gases, produced by manufacturing and industrial processes. One such equipment is the baghouse filter, also known as a fabric filter, which is a highly effective solution for controlling emission of air pollutants. Baghouse filters are used by power plants, steel mills, pharmaceutical producers, food manufacturers, chemical producers, and other industrial companies to control air pollution.

Baghouses came into widespread use in the late 1970s after the invention of high-temperature fabrics capable of withstanding temperatures over 350 °F (177 °C). They are designed to capture fine particulate matter and hazardous particles entrained in gas released from commercial processes, ensuring safer and cleaner air in industrial environments. These filters can capture particles as small as 2.5 micrometers (PM2.5), which are particularly harmful to human health. The captured pollutants and dust accumulate in a hopper, which is designed to prevent their escape back into the environment.

The primary component of a baghouse filter is the filter bags, which are typically made of woven or felted fabric, though they can also be made of non-woven materials. These bags are suspended inside a housing or casing, with fans on the outside blowing the dirty or polluted air through the filters. The bags allow the formation of a layer of particulate matter, called a dust cake, which continues to build until it restricts airflow, at which point the bags are cleaned. Cleaning can be done while the baghouse is either online or offline, depending on the type of baghouse.

There are several types of baghouses, including mechanical-shaker baghouses, reverse-air baghouses, and pulse-jet baghouses. Mechanical-shaker baghouses use tubular filter bags that are fastened to a cell plate at the bottom and suspended from horizontal beams at the top. The dirty gas enters the bottom of the baghouse and passes through the filter, with the dust collecting on the inside surface of the bags. Cleaning is accomplished by shaking the top horizontal bar to create vibrations that shake off the dust cake. Shaker baghouses can be small, handshaker devices or large, compartmentalized units that operate intermittently or continuously.

Reverse-air baghouses have similar space requirements to shaker baghouses but have greater maintenance needs. In pulse-jet baghouses, individual bags are supported by a metal cage fastened to a cell plate at the top, with dirty gas entering from the bottom and flowing from the outside to the inside of the bags. The bags are cleaned by a short burst of compressed air injected through a common manifold, which travels through the entire length of the bag and causes the bag surfaces to flex.

Frequently asked questions