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Why are limestone and lime used in wet scrubbers?
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In the context of flue gas desulfurization (FGD), limestone and lime are used in wet scrubbers as chemical reactants to neutralize sulfur dioxide, a primary pollutant from fossil-fuel power plants.1
The process works through chemical reactions that trap the sulfur:
- Limestone scrubbing: Sulfur dioxide reacts with limestone (calcium carbonate) particles in the slurry to form calcium sulfite and carbon dioxide.1
- Lime scrubbing: Sulfur dioxide reacts with slaked lime (calcium hydroxide) to form calcium sulfite and water.1
Depending on oxidation conditions, the resulting calcium sulfite can further react to form calcium sulfate, also known as gypsum. Because these reaction products have low water solubility, they can be precipitated out of the slurry for removal. While this process is essential for mitigating acid rain by reducing sulfur dioxide emissions, it generates significant quantities of sludge that require careful disposal.1