Describe the operation of a wet scrubber for fly ash control.

A wet scrubber removes fly ash from flue gas by contacting the gas stream with a liquid, typically water, to capture the particulate matter. The basic principle involves transferring the fly ash particles from the gas phase to the liquid phase. The operation typically involves the following steps: 1) Flue gas entry: The flue gas containing fly ash enters the scrubber. 2) Liquid injection: A liquid, usually water or a chemical solution, is sprayed into the flue gas stream. This liquid can be injected through nozzles to create fine droplets, increasing the surface area for contact with the fly ash particles. 3) Contacting: The fly ash particles collide with the liquid droplets and are captured by them. The efficiency of the contacting process depends on factors such as the size and velocity of the droplets, the gas flow rate, and the design of the scrubber. Different types of wet scrubbers, such as spray towers, venturi scrubbers, and packed bed scrubbers, use different methods to enhance the contacting process. 4) Separation: The liquid droplets containing the captured fly ash are separated from the flue gas stream. This is typically achieved using gravity, centrifugal force, or a demister. 5) Slurry collection: The liquid containing the fly ash forms a slurry, which is collected at the bottom of the scrubber. 6) Water treatment: The slurry is treated to remove the fly ash and other contaminants. The treated water can then be recycled back to the scrubber or discharged according to environmental regulations. 7) Clean gas exhaust: The cleaned flue gas, with significantly reduced fly ash content, is discharged to the atmosphere. Wet scrubbers are effective at removing fly ash and other pollutants, such as sulfur dioxide (SO2), from flue gas. They are commonly used in power plants and other industrial facilities to meet air quality standards.