Removal of SO2 with hydrated lime in aluminum smelter

由于用于生产阳极的原材料(主要是焦炭，但也包括沥青)中存在硫，所以在铝生产过程中会排放二氧化硫(SO2)。由于铝产量增加和原材料质量下降，二氧化硫排放量继续上升。目前，电解排放的二氧化硫和氟化氢(HF)是在气体处理中心用氧化铝处理的。然后，氢氟酸被回收回电解槽。然而，HF和SO2的吸附是竞争的，随着HF的吸附，SO2被解吸。因此，氧化铝对SO2的脱除效果不是很好。因此，在气体处理中心之后安装第二个气体净化装置，它将使用消石灰作为试剂，可能是一个可行的解决方案来消除二氧化硫。石灰和其他化学品用于不同的过程，如火力发电厂，以消除二氧化硫。然而，这些工艺的操作条件和气体成分与铝电解槽出口的操作条件和气体成分有很大的不同。在一些冶炼厂，使用湿法二氧化硫捕集工艺；但是，这些技术使用的是基于钠的解决方案，并且有几个缺点，如成本高、大量的废品不可能被有价化、需要回收所用的溶液等。力拓(RT)已经尝试了使用熟石灰从工厂的废气中脱除二氧化硫的中试装置。结果是有希望的，但当时没有进行基础研究，这一过程也没有得到最大限度的开发。在拟议的项目期间，将对在该工艺特定条件下使用消石灰从铝电解废气中脱除SO2的效率进行基础性研究。实验室和工厂将研究温度、湿度、颗粒大小、颗粒孔隙率、SO2浓度、气体中HF的存在、消石灰颗粒在过滤器表面的积累以及气体流量对消石灰捕获SO2的影响。吸收SO2的动力学将通过实验确定。

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.