Study On Removal Of Sulfur Dioxide From Flue Gas Using Semi-Steel Slag

The concept of “cleaner production” has been adopted in many industrial fields worldwidely today. Due to high energy consumption and serious pollution, the cleaner production in iron and steel industry has been received more and more attentions. After the “Cleaner Production Promotion Law of the People’s Republic of China” was formulated, cleaner production has been adopted and developed in China and a lot of achievements related to cleaner production have been made during these ten years.The cleaner production emphasizes on reducing pollution at the source and reducing or avoiding the generation and discharge of pollutants during production. Meanwhile, the cleaner production also refers to effective treatment of the wastes after production. Currently, most of iron and steel enterprises in China treat sintering flue gas after production. Although the sulfur dioxide emissions from sintering flue gas meet the requirements, the cost of flue gas desulfurization is increasing dramatically due to more and more stringent national and local standards.In these years, steel production capacity is over the required amounts, thus, the environmental protection activity performed in the iron and steel enterprises has become the basic line for them to survive. The production activity has to be stopped without meeting the environmental standards, which is the fact that the iron and steel enterprises have to face. The higher flue gas desulfurization cost has become the burden on the iron and steel enterprises. In addition, a large amount of solid wastes are generated in steel production, and their utilization rate is very low. Dealing with these solid wastes needs a lot of costs for transportation and storage, which generally cannot be paid back.In order to reduce the sintering flue gas desulfurization cost, fully utilize solid wastes, achieve environmental goals, and fulfill the purpose of treating wastes by wastes, this study review the state-of-the art status of the cleaner production, air pollution control, solid waste disposal, sintering flue gas desulfurization in iron and steel industry. This study also describes the details on the special production process of vanadium steel, semi-steel slag disposal and utilization, flue gas desulfurization in Chengde Iron and Steel Pte Ltd of Hebei Iron and Steel Group(hereinafter referred as Cheng Gang). Furthermore, the optimal conditions for sulfur dioxide removal from flue gas using semi-steel slag are determined by designing the experimental procedures, performing the experiments, and analyzing the experimental results. The cost reduction of desulfurization using semi-steel slag is analyzed.Cheng Gang employed the circulating fluidized bed semi dry desulfurization process for the old steel sintering machines, and the limestone gypsum wet desulfurization process for the new sintering machines. The concentration of sulfur dioxide in the flue gas after treatment is below 200 mg/Nm3, which meets the requirements. On the other hand, Cheng Gang produces semi-steel after extracting vanadium steel from molten iron liquid containing vanadium. The semi-steel slag contains 27.52% of calcium oxide and 12.75% of magnetic iron oxide.In this study, semi-steel slag is used as a desulfurization agent to remove SO2 in flue gas. Several comparison experiments and an orthogonal experiment based on the wet desulfurization process are performed in this study. Experimental results show that, semi-steel slag displays a capability to removal SO2 from the flue gas. When SO2 concentration is 500 mg/Nm3, the emission concentration is less than 200 mg/Nm3 after treatment. The higher desulfurization efficiencies were observed when the flows of the flue gas and slurry are countercurrent and the semi-steel slag without magnetic separation is used. Increasing the ratio of liquid to gas significantly improves the desulphurization efficiency. After further analysis, the semi-steel slag can be potentially used in real production, which ensures to meet the discharge requirements.Considering the sinter production and the existing desulfurization agent cost, the desulfurization costs using limestone, quicklime and semi-steel slag are compared based on the experimental results in the semi dry and wet conditions. If semi-steel slag is used to replace semi dry limestone, the desulfurization cost can be reduced by 0.94 yuan per ton of sinter. If semi-steel slag is used to replace wet lime, the desulfurization costs can be reduced by 1.86 yuan per ton of sinter.