Grant: Collaborative Research and Development Grants

Sulfur dioxide (SO2) is emitted during the production of aluminum due to the presence of sulfur in raw materials (mainly coke, but also pitch) used in the production of anodes. As a result of increased aluminum production and declining raw material quality, SO2 emissions continue to rise. Presently, SO2 and hydrogen fluoride (HF) emissions coming from electrolysis are treated with alumina at the gas treatment centers. HF is then recycled back to the electrolysis cells. However, adsorption of HF and SO2 is competitive, and SO2 is desorbed as HF is adsorbed. Therefore, the removal of SO2 with alumina is not very effective. Thus, the installation of a second gas purification unit, which will use hydrated lime as a reagent, after the gas treatment center could be a viable solution to remove SO2. Lime and other chemicals are used in different processes such as thermal power plants to remove SO2. However, operating conditions and gas compositions of these processes are quite different from those at the outlet of aluminum electrolysis cells. In some smelters, a wet SO2 capture process is used; but, these technologies use a solution based on sodium and have several disadvantages such as high cost, large quantity of waste product with no possibility of valorization, need for recuperating the solution used, etc. Rio Tinto (RT) has already tried a pilot unit in which the hydrated lime is used to remove SO2 from the effluent gases in the plant. The results were promising, but no fundamental study was carried out at the time, and this process is not exploited to the best of its potential. During the proposed project, a fundamental study will be carried out on the efficiency of SO2 removal from the effluent gases from the electrolysis of aluminum using hydrated lime under the conditions specific to this process. The effects of temperature, humidity, particle size, particle porosity, SO2 concentration, presence of HF in the gas, accumulation of hydrated lime particles on the filter surface, and gas flowrate on SO2 capture by hydrated lime will be studied in the laboratory and at the plant. The kinetics of SO2 uptake will be determined experimentally.