Gas-Phase Filtration: Is It the Solution for Your Business?

Indoor air quality is an urgent and ongoing concern for businesses whose practices produce airborne contaminants. Particulates generated by manufacturing or industrial processes can be removed from the air with filtration designed to physically capture and hold those tiny pieces of material. Removing gases, fumes, and combustion by-products from the air, however, requires a more specialized type of filtration system. Gas-phase filtration is effective at cleaning indoor air of chemicals, odors and other intangible materials that other filters cannot remove.

What Is Gas-Phase Filtration?

Gas-phase filtration is the process of using specialized filter media and chemical substances to remove gaseous pollutants from the air. In most gas-phase filtration systems, a substance called a sorbent is used to literally absorb chemical substances and remove them from indoor air. The most common type of sorbent is activated carbon or charcoal, which are very effective at capturing vapors, gases, odors and chemicals.

Gas-phase filtration systems are usually installed in the ductwork of the building’s heating or cooling system. There, the air circulating through the furnace or air conditioner enters a pre-filter that removes solid particulates. The air continues into the gas-phase filter where airborne chemicals are removed or destroyed before continuing on their normal path within the HVAC equipment. The air circulation and filtration cycle keep indoor air as clean as possible.

There are two main filtration processes used in a gas-phase filtration system:

• Adsorption: Adsorption occurs when the molecules of the airborne substance are physically pulled into contact with the surface of the adsorbent material. Different types of adsorbent material are more likely to attract certain types of chemicals and molecules while leaving other types of substances in the air. Adsorption is most effective at lower temperature and humidity levels. Common adsorbent materials include activated charcoal, silica gel, activated alumina and porous clay minerals.
• Chemisorption: Chemisorption relies on a chemical reaction between either the sorbent itself or with chemicals contained within the sorbent. The chemical reactions form chemical compounds that stick to the sorbent media, or that are converted into harmless materials, such as carbon dioxide or water. Sometimes the chemisorption process can convert airborne gases and vapors into substances that can be easily adsorbed by other materials in the system.

Depending on the application, the system may be either deep bed or thin bed.

Deep bed systems most often are used where the concentration of airborne contaminants is high. Filters in these systems are thicker and are designed to allow more exposure to the sorbent media. They also can be used in pressurized filtration systems. Thicker filter media also last longer before they must be replaced.

Thin bed systems are appropriate in environments where levels of contaminants are lower. They often are used in systems that recirculate air or where pressurized filtration is needed.

Common Applications of Gas-Phase Filtration

Gas-phase filtration most often is found in industries where vapors, fumes, and chemicals are released into the air during normal operations. This includes manufacturing facilities, waste treatment plants, paper and pulp operations, oil refineries and agricultural storage facilities.

Gas-phase filtration also is appropriate for business and commercial environments where air quality is critical, such as computer clean rooms, data centers, food processing facilities, museums and libraries.

In general, gas-phase filtration systems are not commonly used in homes. This is because of factors such as:

• expense of the initial purchase of a gas-phase system.
• the impractical physical size of the filtration equipment.
• expense of adapting a gas-phase system for residential use.
• need to change filters frequently to maintain performance.
• limited filter lifetime.
• cost of filters.

Our goal is to help educate our customers about plumbing, HVACR, fire protection and alarm systems in mechanical, commercial and residential settings. For more information on gas-phase filtration and how it can be used in a commercial or industrial setting, or to view projects we’ve worked on, visit our website!