Wet Scrubbing Technology

Greenfield aluminum smelters or smelters that are expanding, are dealing with SO2 emissions from their potrooms. Alumina has the ability to adsorb sulfur oxides on its surface. However, when the reacted alumina is fed into the pots, the SO2 is immediately re–emitted; hence, additional control technology must be applied. The technique of choice is a wet scrubber where water is used to absorb the SO2 and where a reagent is used to neutralize the formed sulfurous acid in the water.

Reducing SO2 emissions from potlines is not something new. It is also not very 'hot' as a smelter typically is a relatively small emitter of SO2 when compared to various other sources around them. Less than 10% of the aluminum smelters in the world have SO2 control systems installed. And of those smelters with the controls, all the SO2 systems are based on a wet scrubbing process.

Danieli Corus commissioned two of the largest wet scrubbers in the world. As part of the Alcoa St. Lawrence Reduction Plant, at Massena, NY, the fume treatment center included two wet scrubbers for the removal of SO2. At that time, these were the largest wet scrubbers ever built at an aluminum plant. They use soda ash (sodium carbonate) as the reagent and the liquid effluent is a sodium sulfate solution. Both wet scrubbers are open spray towers with a low pressure drop and are designed to handle any solids in the liquor.

Scrubbers like these have proven to be very reliable. They continue to be the workhorses for SO2 scrubbing in the primary aluminium industry.