Turning Acidic Gases Into Solids
Incinerator exhaust can contain acidic gases such as sulfur dioxide and hydrogen chloride. In a scrubber, powdered lime or lime mixed with water is brought into contact with the hot gas. Because lime is alkaline, it reacts with those acids rather than simply masking their smell or letting them pass through.
The reaction changes the pollutants into compounds such as calcium sulfite, calcium sulfate, or calcium chloride. These are salts—solid or dissolved materials that can be separated from the exhaust. In a dry system, the lime and reaction products travel with the gas as fine particles; in a wet system, they are collected in liquid.
The Scrubber Also Has to Catch the Byproducts
Changing a gas into a salt is only part of the job. The resulting particles or liquid must be removed before the cleaned exhaust reaches the stack. Dust-collection equipment can capture the solids, while wet systems separate contaminated liquid for treatment or disposal.
Operators must also supply enough lime and keep it well mixed with the exhaust: too little contact can leave some acidic gas unreacted. The practical benefit is a change in form and a means of capture—pollution that could leave as a gas is converted into material that can be collected and managed as waste.
