Flue gases are byproducts of combustion which are classically vented through long pipes known as flues. These gases are treated as pollutants. Flues can be referred to as “stacks,” and they may be found in the form of chimneys, ducts, or simple pipes. 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 huge percentage of the total generated. These gases are also created whenever people light a wood fire or drive a car.
The contents of flue gases are quite variable. The medium being burned can contribute a number of different compounds, and the conditions under which combustion is occurring can also generate more or less emissions. Incomplete combustion at low temperatures or in poorly managed facilities, for example, tends to generate more pollution.
Some things commonly found in flue gases include: water vapor, carbon dioxide, nitrogen, particulates, oxygen, carbon monoxide, nitrogen oxide, hydrocarbons, and sulfur oxide. Some of these compounds are potentially harmful for the environment, making these gases an issue of concern among environmental advocates. Flue gases can also be hazardous for human health, as might occur if they were trapped in an air inversion which pinned them close to the ground for several days, forcing people in the area to inhale hazardous pollutants which could damage their lungs.
There are a number of ways in which flue gases can be controlled, and processes which produce them are often heavily regulated to force emissions levels down. One of the best methods for control is to avoid generating them at all, either by using alternative technology, improving efficiency levels at a plant, or studying ways in which operating conditions could be improved to reduce the production of combustion byproducts. Gases which cannot be prevented can be trapped using filters and scrubbers which clean the air coming out of flues so that when it is released into the environment, it contains primarily harmless components.
In fact, scrubbing flue gases can even be profitable for a savvy company. For example, the food industry has a use for carbon dioxide, and is willing to pay for purified carbon dioxide extracted from flue gases. This use also resolves the problem of what to do with the pollutant once it has been removed from the flue. Emissions at flues are routinely tested to determine whether or not the gases are being adequately scrubbed before they are vented into the environment.