Pollution control equipment can reduce emissions by cleaning exhaust and dirty air before it leaves the business. A wide variety of equipment can be used to clean dirty air. DNR engineers carefully study and review how these controls may work and the methods and requirements are put into a permit - a major duty performed by the DNR.

How common control equipment works is explained below:

• Bag Houses or Fabric Filters
• Scrubbers or Wet Collectors
• Adsorbers
• Cyclones
• Vapor Condensers
• Electrostatic Precipitators
• Flares
• Afterburners
• Catalytic Oxidizers

There are other ways to reduce emissions besides using pollution control equipment--prevent emissions to begin with. Air quality permits help minimize, reduce or prevent emissions as much as possible by placing requirements on how things are done.

Permits can specify the quantity, type, or quality of fuel or other substance used in a process. For example, a permit might specify the maximum percent of sulfur that can exist in the coal to reduce sulfur dioxide emissions. A permit may specify the quantity of volatile chemicals in paint, solvent, adhesive or other product used in large quantity during manufacturing. Permits can also help reduce the impact of emitted pollutants on local air by specifying smokestack height and other factors.

Engineers can also set combustion specifications to minimize emissions. For example, to help reduce nitrogen oxide formation, the combustion conditions in the furnace can be altered. The flame temperature can be lowered or raised, the amount of time air remains in the combustion chamber can be altered, or the mixing rate of fuel and air can be changed. These options are often reviewed, studied and best choices made depending upon cost, plant design and many other variables.