SOx scrubbers, also known as flue gas desulfurization (FGD) systems, are used to remove sulfur dioxide (SO2) from the exhaust gases emitted by power plants, industrial boilers, and other sources that burn fossil fuels containing sulfur. The working principle of an SOx scrubber involves the following steps:

1. Flue Gas Contact: The exhaust gas containing sulfur dioxide is directed into a scrubber vessel. Inside the vessel, the gas comes into contact with a liquid solution or slurry, typically a mixture of water and a sorbent, such as limestone (calcium carbonate) or lime (calcium oxide).

2. Absorption: The sulfur dioxide present in the flue gas reacts with the liquid solution or slurry in the scrubber. In the case of limestone-based scrubbers, a chemical reaction occurs where the sulfur dioxide reacts with the calcium carbonate to form calcium sulfite (CaSO3) and water.

3. Reaction and Conversion: The calcium sulfite formed in the previous step is further oxidized to calcium sulfate (CaSO4), commonly known as gypsum. This oxidation process can occur naturally or with the aid of an oxidizing agent, such as oxygen or air.

4. Separation: The solid particles, mainly gypsum, are separated from the liquid solution or slurry using various separation techniques, such as settling tanks, filters, or centrifuges. The separated gypsum can be further processed for various applications, such as construction materials.

5. Recirculation and Disposal: The liquid solution or slurry, depleted of the absorbed sulfur dioxide, is recirculated back to the scrubber for further use. In some cases, a portion of the liquid may need to be discharged and treated to remove impurities before disposal, depending on local regulations and environmental requirements.

SOx scrubbers are efficient in reducing sulfur dioxide emissions, helping to mitigate air pollution and comply with emissions regulations. However, it is important to note that the use of SOx scrubbers can also introduce other environmental considerations, such as the disposal of the generated gypsum and the energy requirements for operating the scrubber system.