Nowadays, to improve air quality, governments, industry, and the public need to understand the interconnected components of an air quality management system. Machines that will be used to minimize particulate matter incorporate electrostatic precipitators, dust cyclones, and wet scrubbers. A recent advancement in air quality control systems, particularly in wet scrubbers, involves eliminating pollutants from gas streams as they flow through a cleansing liquid. As a rule, these wet scrubbers are used in industries such as fertilizers, steel, and acid plants. Various designs incorporate spray nozzles, misters, cyclonic action, venturi dispersion, and/or wet impingement configurations to capture the dust.

A venturi scrubber typically employs venturi-shaped construction and a spray nozzle on the inlet, which accelerates the water to break it into a fine mist. The higher the velocity, the more efficient the collector becomes. As this occurs, the pressure drop through the system also increases sharply. Design airflow must be maintained constantly or filtration efficiency will drop. Maintaining a clean- or recycled water supply is important with scrubbers. The concentration of dust particles in the scrubbing fluid must be kept at less than 5% to maintain operating efficiency. In the case of combustible metals, the amount allowed to accumulate in the discharge vats is prescribed in NFPA 484: Standard for Combustible Metals.

A key benefit of wet scrubbers is that when flammable dust particles are trapped in the scrubbing liquid, they are separated from oxygen, thereby managing the combustible dust risk. Many metal dust, however, is reactive with water and other metals and may produce hydrogen gas. This should be considered before selecting a wet scrubber. Also, many specks of dust can be considered hazardous, and disposing of wet materials may be costlier than disposing of dry materials due to regulations. Dry media collectors are inherently at higher risk of a combustible dust explosion. As a result, they require more ancillary explosion-protection equipment to meet NFPA standards and control the hazards. Dry collectors typically can scale up to very large airflows and heavy dust loads whereas wet collectors would require multiple systems to handle larger airflows. Heavy dust loading with a wet collector also means more water consumption and treatment. Sometimes the choice between a wet or dry media system will not be clear-cut. Dust testing is the first step in the decision-making process.

Redwood Technology presents a new type of wet scrubber – the Scroiler. The Scroiler can be used to remove dangerous gases, particulate matter, vapors, and other contaminants from the air to meet EPA and OSHA requirements. Scroiler uses up to 10 times less cleaning liquid than a typical wet scrubber and it has no scale-up issues. This water- and reagent-saving device has found wide applications in wet flue gas desulfurization (WFGD).