Flue Gas

Definition - What does Flue Gas mean?

Flue gas is the byproduct of combustion, normally vented through long pipes known as flues, which exhaust gases from fireplaces, ovens, furnaces, boilers or steam generators. These gases are treated as pollutants.

Flue gas often refers to the combustion exhaust gas produced at power plants.

Large amounts of flue gases are generated around the world on a daily basis, with heavy industry and the power industry in particular being responsible for a large percentage of the total generated. These gases are also created by wood fires and vehicle exhaust.

Corrosionpedia explains Flue Gas

Flues, also known as stacks, may be found in the form of chimneys, ducts or simple pipes. The contents of flue gases are quite variable. The composition depends on what is being burned, but usually consists of mostly nitrogen (typically more than two-thirds) derived from the combustion air, carbon dioxide (CO2) and water vapor as well as excess oxygen (also derived from the combustion air). It further contains a small percentage of a number of pollutants, such as particulate matter (like soot), carbon monoxide, nitrogen oxides and sulfur oxides.

At power plants, flue gas is often treated with a series of chemical processes and scrubbers which remove pollutants. Electrostatic precipitators or fabric filters remove particulate matter and flue-gas desulfurization captures the sulfur dioxide produced by burning fossil fuels, particularly coal.

Flue gas desulfurization (FGD) involves the removal of sulfur dioxide (SO2) contained in gases produced by the combustion of fossil fuels such as coal, oil, municipal solid waste, automobile tires and many industrial processes such as gasoline refining, cement, paper, glass, steel, iron and copper production.

Sulfur dioxide emissions are a primary contributor to acid rain and have been regulated by every industrialized nation in the world. Emissions at flues are routinely tested to determine whether or not the gases are being adequately scrubbed before they are vented into the environment. Scrubbing can lead to meaningful recovery of sulfur for further industrial use.

Flue gas analysis offers a means of determining pollutant concentrations and adjusting heating installations for maximum efficiency.

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