Air Emission Control Devices

Air emission control devices are the engineered units that capture or destroy pollutants in gas streams before they are released to the atmosphere.

Definition

Engineered equipment installed in exhaust or process gas streams that separates particulate matter or removes, converts, or destroys gaseous pollutants to reduce emissions to the atmosphere.

Scope

This topic covers the principal technologies for controlling air emissions at their source. It addresses particulate removal by cyclones, baghouse fabric filters, and electrostatic precipitators, gaseous pollutant control by wet and dry scrubbers and adsorbers, and the chemical conversion of pollutants by catalytic and thermal devices such as catalytic converters. The pollutants being controlled are described in the air pollution area, while the underlying combustion and process sources connect to broader engineering.

Core questions

• How are particulates removed from gas streams?
• How do scrubbers and adsorbers control gaseous pollutants?
• How do catalytic and thermal devices convert pollutants?
• What determines the choice of control device for a given source?

Key theories

Particulate collection mechanisms

Devices remove particles by exploiting inertia in cyclones, filtration in baghouses, and electrical charging and collection in electrostatic precipitators, with collection efficiency depending strongly on particle size.

Gas absorption and catalytic conversion

Gaseous pollutants are controlled either by transferring them into a liquid or solid in scrubbers and adsorbers or by chemically transforming them, as when catalytic converters oxidize and reduce exhaust pollutants to less harmful species.

Clinical relevance

Emission control devices are a primary means of preventing air pollution at the source, reducing the release of particulates and harmful gases; their selection and performance determine how effectively emissions are limited.

Evidence & guidelines

Control-device selection and performance commonly follow established design methods and regulatory emission-limit requirements, described here to explain how emissions are controlled rather than as prescriptive standards.

History

Air-emission control equipment developed rapidly after clean-air legislation of the mid-twentieth century required reductions in particulate and gaseous emissions, driving widespread adoption of precipitators, fabric filters, scrubbers, and catalytic converters.

Seminal works

• cooper2011
• davis2008
• wark1998

Frequently asked questions

How does an electrostatic precipitator remove particles?

It gives particles an electric charge as the gas passes through, then collects them on oppositely charged plates; the captured particles are periodically removed, allowing high efficiency for fine particulates.

What does a scrubber do?

A scrubber brings a polluted gas stream into contact with a liquid or solid that absorbs or reacts with target pollutants, transferring them out of the gas before it is released.