Experimental Study On Wet Desulfurization Of Industrial Wastes

At present, coal-burning thermal power generation has a dominant position in the electric power industry because coal is the primary energy sources in our country. Wet flue gas desulfurization has been used in most coal-fired thermal power plants due to its mature technology and high efficiency. Recently, a mass of industrial wastes are exhausted. Using these wastes in desulfurization can not only reduce the environmental contamination but also decrease the cost. Thus, it can contribute a lot to the environmental protection and economic benefits. Based on industrial application of wet flue gas desulfurization, the dissolution characteristics and desulfurization characteristics of industrial wastes are studied in this paper.Industrial wastes such as alkali slag, salt slurry, white clay, carbide slag and solid waste in water treatment from the chemical industries; smelting iron slag, red mud and magnesium dross from the metallurgy industries; fly ash and coal—burning slag from the electric power industries were selected to be experimental materials. The limestone and the magnesite were selected to be the contrast materials.Firstly, the fundamental desulfurization characteristics of these experimental materials were studied. The industrial wastes with preferable desulfurization abilities were screened out by comparing their desulfurization efficiency, desulfurization saturation time and composition. The results indicate that carbide slag, white clay, magnesium dross, salt slurry, alkali slag and magnesite have higher desulfurization efficiency, which can be used as wet desulfurizers; red mud is inappropriate because it creates a lot of solid deposition although it has high efficiency; fly ash, coal-fired slag, smelting iron slag and wastes in water treatment can not be used as wet desulfurizers because of their lower desulfurization efficiency.Secondly, the dissolution characteristics and desulfurization characteristics of the industrial wastes used as desulfurizers were studied. In order to ascertain the best operating parameters, the influences of pH value, temperature, particle diameter, entrance concentration of SO2 and ratio of liquid to gas were researched, aiming at desulfurizers own characteristics and environment of wet desulfurization systems. The results indicate that when the pH value of alkali slag are chosen between 5.5～7.5, magnesium dross are chosen between 5～7.5 and white clay, salt slurry, carbide slag and magnesite are chosen between 4～7.5, the desulfurizers have higher efficiency. The absorption temperature of alkali slag and magnesite should be controlled between 60℃～90℃, salt slurry, white clay and magnesium dross should be controlled at 60℃and carbide slag should be controlled between 30℃～60℃. The higher of the entrance temperature, the lower desulfurization efficiency is. The higher ratio of liquid to gas is propitious to enhance the desulfurization efficiency because of bigger effective contact area. However, equipment investment and operating costs increases with the enhancement of ratio of liquid to gas. Thus, the ratio of liquid to gas should be reduced properly when the higher efficiency can be guaranteed.Finally, the influences of magnesium sulfate and adipic acid to the desulfurization abilities were studied. The results indicate that magnesium sulfate and adipic acid can not only enhance desulfurization efficiency but also slower the fall of pH value. In the process of desulfurization by wastes, the fall of pH value can be divided into three stages, namely, high stage, middle buffer stage and low stage. However, the pH value can stayed at middle buffer stage and low stage when magnesium sulfate and adipic acid are added. The dissolution of wastes is accelerated by magnesium sulfate. Along with the reaction, Mg²⁺ can come into being MgSO₃⁰ with strong activity, which contributes a lot to the enhancement of desulfurization efficiency. When the pH value is lower, adipic acid has a distinct effect, because it can slower the fall of pH value.