Experimental Study On Simultaneous Desulfurization And Denitrification Over Activated Carbon Fibers

With China's implementation of new environmental standards, research on NOx emissions control has gained widespread attention. SCR technology becomes the technology of choice and has been applied in large coal-fired boilers thanks to its simple process and high NO removal efficiency. As a new catalytic carbonaceous adsorbent material with a large surface area and high adsorption rate, activated carbon fiber can simultaneously remove multi-pollutant, which is promising in terms of providing a cost-effective multi-pollutant removal technology for the industrial boiler or small furnace. Competitive adsorption of different pollutants on the surface of ACF and promoting the removal efficient of NO is the key factor.As implementation of new environmental standards, emission of nitrogen oxides and other pollutants will be more stringent. For large coal-fired units, denitrification renovation has been large-scale implementation, NOx emissions have been basically meet emission requirements. However, for small boilers, a new cost-effective denitrification technology is needed urgently due to the high cost of SCR renovation.Adsorption experiments in a fixed-bed reactor were conducted to investigate the removal of NO over the viscose based activated carbon fibers(ACF). According to the temperature programmed desorption(TPD) analysis, the effects of SO2 on the removal of NO were studied and competitive adsorption between SO2 and NO over the ACF surface was also discussed. Subsequently, ACF pretreated by NO gas was applied to investigate the performance of denitration and desulfurization. It is indicated that in the initial stage of NO/SO2 adsorption, NO and SO2 are adsorbed into the micropores over the ACF surface. As the proceeding of adsorption, –NOX(adsorbed NOX, generally in the form nitrogen groups) is extruded again by continuous entering of SO2 into the micropores. Simultaneously, –NOX provides adsorption sites for SO2 and oxidize SO2 into SO3. In other words, ACF pretreated by NO gases possesses a considerable desulfurization ability. Based on the possible interactions between NO and SO2 during the combined adsorption process, a two-stage purification method was proposed in the paper.ACF coated with Cu2 O using photocatalytic were applied in the experiments to decline the high NO concentration at the inlet of second stage. Meantime, the effects of Cu2 O loading, O2 concentration, the content of water vapor, and the reaction temperature on the removal of NO were respectively investigated. Moreover, the effect of ACF loaded with Cu2 O and Ti O2 using photocatalytic on the removal of NO was also explored. As experimental results, Cu2O/ACF prepared by hydrazine hydrate method was proved to be more effective for the removal of NO in contrast with ACF; moreover, NO removal efficiency was found to increase first and decrease then as the rise of Cu2 O loading; furthermore, Ti O2 significantly enhanced the photocatalytic performance of ACF coated with Cu2O; a higher O2 concentration in the syngases is more suitable for the removal of NO; with increasing content of water vapor, NO removal efficiency was found to increase before 0.5% and decrease after the critical value; temperature has an obvious inhibition to the removal of NO;Moreover, NO adsorption tests were conducted under oxy-fuel combustion especially under conditions of high CO2 concentration. X-ray photoelectron spectroscopy(XPS) technique was used to determine the surface functional groups. TPD analysis was used to investigate the desorption behavior of NO over the porous carbon. Based on such information, denitration mechanism in the presence of CO2 was discussed. CO2 inhibited the adsorption of NO over the ACF surface probably due to:(1) there are competition between CO2 and NO for the limited adsorption sites over the carbon surface;(2) CO2 is not conducive for adsorption of O2 onto the carbon surface, and thus inhibited the production of oxygen functional groups derived from adsorbed O2, such as C-O and C=O, which is beneficial for the removal of NO.