Determining an Effective Layout for Injectors in a Wet Scrubber

Raw phosphate contains fluoride is small doses - around 2-4%. Phosphate processing plants process raw phosphate into water soluble phosphate using sulfuric acid. This operation releases the fluoride in a gaseous form, which is toxic when it's eventually emitted into the air. In the past, fluoride gas, even in small doses, was responsible for scorched vegetation, crop destruction and harm to livestock. Now wet scrubbers are used to remove, or "scrub," fluoride prior to venting. However, due to the hazardous conditions and gases in such environments, physical testing of the process is impossible. As such, CFD simulations offer an excellent solution to optimizing wet scrubber applications. 

We first conducted experimental testing on two FullJet nozzles using our patternation table. Using this instrument we can visually and statistically illustrate the fluid distribution across each nozzle's spray pattern. Using this data, we then assessed two nozzle injector layouts for our customer's wet scrubber. Our design considerations included the diameter and height of the wet scrubber vessel, the fluid volume required to scrub the gas, the gas flow at the inlet and the outlet and any mounting restrictions set by the customer. Using this collected data, we were able to increase the application's effectiveness by maximizing the spray surface area and obtaining a more uniform distribution across the vessel.

Comparing a three nozzle layout and a four nozzle layout revealed that the four nozzle layout most effectively evaporates and scrubs the incoming fluoride gas. While both layouts adequately evaporated the gas in the time and space allowed before the gas reached the outlet, the temperature of the four nozzle design was much lower, resulting in a better overall result. In the end, selecting the correct nozzle and optimal nozzle placement is critical to the success of wet gas scrubbing. 

Measuring both spray concentration and temperature revealed that drop size has significant impact on efficient liquid-vapor interaction. Furthermore, optimizing the spray's surface area coverage and distribution across the vessel enhances the liquid-vapor interaction resulting in a better overall result. Because the four nozzle layout maximized both surface area and distribution coverage, this was the best option for our customer. Furthermore, we're able to validate the major role CFD simulations play in determining nozzle selection, layout and operating parameters for a successful wet scrubber application.