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Module 6: Air Pollutants and Control Techniques - Dioxins and Furans - Formation Mechanisms
Contents
Lesson Material
Practice
Problems
Objective
- Describe the basic formation mechanism for dioxin and furan compounds.
The formation mechanisms for dioxin-furan compounds have not been fully identified. It is believed that there are at least three different types of formation mechanisms that are possible. All of these depend on the availability of chlorinated precursor compounds in the fuel and/or waste being burned and the appropriate gas temperature conditions. One of the proposed formation mechanisms for dioxin-furan compounds involves reactions on the surfaces of particles entrained in the gas stream.
Dioxin-furan concentrations appear to increase over the temperature range from 400 to 1,000°F. However, at temperatures well above 1,000°F, dioxin-furan compounds are readily oxidized.
As Figure 1 illustrates, some dioxins and furans form and are destroyed (i.e. oxidized) in the burner flames of combustion chambers. Most of the chlorinated precursor compounds, which originated in the fuel and/or waste, volatilize and move with the gas stream through the combustion process until they reach the temperature range favorable for dioxin and furan formation (400 to 1,000°F). A small percentage of dioxins and furans can form in boilers where the economizers and heat exchange equipment are located. Since most dioxins and furans tend to form in control devices, gas streams leaving combustion processes should be cooled to temperatures below 400°F.
Practice Problems
Dioxins and Furans - Formation Mechanisms
- Instructions:
- Complete the Practice Problems before proceeding to the next section. Click on the button below.