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Module 6: Air Pollutants and Control Techniques - Sulfur Oxides - Characteristics
Lesson Material
Practice Problems
Objective
- Describe the basic characteristics of sulfur dioxide and sulfuric acid.
Sulfur oxides include sulfur dioxide (SO2), sulfur trioxide (SO3), and sulfuric acid (H2SO4).
The major sources of sulfur dioxide are shown in Figure
1. Combustion of fossil fuels for generation of electric power is
clearly the primary contributor of sulfur dioxide emissions. Industrial
processes, such as nonferrous metal smelting, also contribute to sulfur
dioxide emissions.
Sulfur dioxide is a colorless gas, which is moderately soluble in water and aqueous liquids. It is formed primarily during the combustion of sulfur-containing fuel or waste. Once released to the atmosphere, sulfur dioxide reacts slowly to form sulfuric acid (H2SO4), inorganic sulfate compounds, and organic sulfate compounds.
Some of the sulfur dioxide in high temperature processes is oxidized to form sulfur trioxide as shown below.
Sulfur trioxide remains in the vapor state while the combustion gases are very hot. As the gases cool, sulfur trioxide adds a water molecule and forms sulfuric acid as indicated by the reaction below.
Below 500 to 600°F, most of the sulfur trioxide, which is extremely hygroscopic, reacts with water molecules to form sulfuric acid.
Sulfuric acid is a strong acid. In addition to the sources mentioned above, sulfuric acid can also be released from plants that manufacture batteries.
Sulfuric acid vapor in moderate concentrations (2 to 8 ppm) is very beneficial to electrostatic precipitators because it adsorbs onto particle surfaces and creates a moderate resistivity. High concentrations can be detrimental to precipitator performance. High sulfuric acid levels can also cause significant corrosion problems for precipitators, fabric filters, and other control devices. The temperature of flue gases should be kept well above the dew point for sulfuric acid to prevent condensation on ductwork surfaces and components in the air pollution control system.
Practice Problems
Sulfur Oxides - Characteristics
- Instructions:
- Complete the Practice Problems before proceeding to the next section. Click on the button below.