Experimental Study On Additives Of Wet Flue Gas Desulfurization

Currently, SO2produced by coal-fired is a horrible threat to the atmosphere environment in our country. Coal-fired power plants are the largest source of SO2emissions. Many desulphurization technologies, especially limestone-gypsum wet flue gas desulfurization (WFGD) process, are applied in many coal-fired power plants, so the SO2emissions has been effectively reduced. However, because of coal shortage and small design margin of desulphurization devices, many problems emerged, such as low desulphurization efficiency and high CaSO3content in desulphurization by-product. The capacity expansion renovation of the desulphurization device must be carried out to satisfy the Emission-standard which the investment is huge.Nowadays researchers focus on adding appropriate additives to the WFGD systems to enhance desulphurization efficiency, reduce investing and operational cost. The new additives for WFGD were screened through investigation of accelerated limestone dissolution and enhanced calcium sulfite catalytic oxidation by additives on the self designed experimental apparatus. The field tests were carried out in two power plants in Heibei to test the effect of the addictives.Compared with inorganic additives, organic additives have the effect of speeding up the limestone dissolving, organic additives are the more effective additives for accelerating limestone dissolution. The most effective additive is adipic acid, which the limestone dissolution ratio increases11.69%when the pH is5.5. On the effect of catalysis on calcium sulfite oxidation, The inorganic additives which contain Mn2+or Fe2+are effective additives for enhancing calcium sulfite catalytic oxidation. The most effective additive is MnCl2, which the calcium sulfite oxidation rate increases2.74times than no additive. Eight compound additives were developed based on the above experimental results. The effects on the limestone dissolution and calcium sulfite catalytic oxidation were tested in laboratory. No.6and No.8compound additives are effective in both accelerating limestone dissolution and enhancing calcium sulfite catalytic oxidation. Especially, No.8compound additive is the most effective additives.Field tests were carried out in WFGD systems of two power plants in Heibei with No.8compound additive. The results indicate that:with the addition of No.8compound additive, desulphurization efficiency of WFGD system has a remarkable improvement and can satisfy the Emission-standard when the inlet SO2concentration is less than1.3times of the design value. With the addition of desulphurization additive, part of slurry circulating pumps can be stopped and the electric current of oxidation fan can decrease. So the energy conservation and emissions reduction were accomplished. Economic analysis shows that the operational cost of a desulfurization device for300MW coal-fired unit can be decreased approximately one million yuan per year with the addition of the No.8additive.