Removal of SO2 with hydrated lime in aluminum smelter

在铝的生产过程中，由于阳极生产中使用的原材料（主要是焦炭，但也有沥青）中存在硫，因此会排放二氧化硫（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，来自电解的SO2和氟化氢（HF）排放物在气体处理中心用氧化铝处理。HF然后再循环回到电解槽。然而，HF和SO2的吸附是竞争性的，并且SO2随着HF的吸附而解吸。因此，用氧化铝去除SO2不是很有效。因此，在气体处理中心之后安装第二个气体净化装置（将使用熟石灰作为试剂）可能是去除SO2的可行解决方案。石灰和其他化学品用于不同的过程，如热电厂，以去除SO2。然而，这些过程的操作条件和气体组成与铝电解槽出口处的操作条件和气体组成有很大不同。在一些冶炼厂中，使用湿法SO2捕集工艺;但是，这些技术使用基于钠的溶液，并且具有若干缺点，例如高成本、大量废物且不可能实现价值回收、需要回收所使用的溶液等。Rio Tinto（RT）已经尝试了一个试验装置，其中使用熟石灰从工厂的废气中去除SO2。结果是有希望的，但当时没有进行基础研究，这一过程没有充分发挥其潜力。在拟议的项目中，将进行一项基础研究，研究在该工艺的特定条件下使用熟石灰从铝电解废气中去除SO2的效率。将在实验室和工厂研究温度、湿度、颗粒尺寸、颗粒孔隙率、SO2浓度、气体中HF的存在、过滤器表面上熟石灰颗粒的积累以及气体流速对熟石灰捕获SO2的影响。将通过实验确定SO2吸收的动力学。

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.