Joint Removal Research And Scale-up Experiment Of Multiple Pollutants In Coal Fired Flue Gas Based On Modified Activated Carbon Fiber

The human health and survival environment are being damaged by the pollutants such as SOx, NOx, VOC (volatile organic component), and Hg0which discharged from coal fired flue gas, and now, this situation will never be able to continue. Efficient and joint removal are two unmatched advantages for the technologies used in cleaning up the coal fired flue gas based on ACF (activated carbon fiber), and even there are potential probability in recycling the acidic components in the flue gas.This study mainly utilized the methods of acidic and basic compounds, electrochemistry, heating, and UV (ultraviolet) to modify the ACF samples, and explored the removal effect of the modified ACF samples on the pollutants SO2, NO, VOC, and Hg0under single or multiple gaseous components. Simultaneously, we investigated the action mechanisms of the various factors including the functional groups on the ACF sample surface in deep. Based on these small-scale mechanism experiments, the method of joint removal and cycling the acidic flue gas compounds in the coal fired flue gas were designed, and for this consideration, constructed a lab-scale joint removal system.The physical and chemical properties of all modified ACF samples were obtained by the BET (Barrett-Emmett-Teller) and XPS (X-ray photoelectron spectroscopy) methods. Experiment results showed that the powerful oxidant such as KMnO4and H2O2obviously raised the content of acidic surface functional group on the ACF samples, while these oxidants destoried the pore structure of the samples modified by themselves because of lacking the capability of constructuring micropores. However, the modification methods with KOH, NaOH, ammonia, and high temperature not only eliminated the acidic surface functional groups, but also had the capability of constructuring micropore. After modification by these methods, the BET surface area dicreased, but the everage micropore diameter also decreased rather than usual increase.On the ACF sample surface, the removal of SO2, NO, and Hg0mainly depended on chemical adsorption, but at low temperature, even if the flue gas containing O2, the removal of VOC mainly was still regarded as physical adsorption. Both acidic and basic functional groups played importmant roles during adsorption tests. Among the oxygen functional groups, parts of the carboxyl and lactone groups (COO), which act as active sites and belong to the typical acidic groups, were not easy to interact with SO2and NO directly, but these oxygen functional groups had the sepcial capability to decomposite the strong oxidizing substances such as O2and NO2in the simulated flue gas to realese the powerful oxidant0*free radical, and whereby promoted the adsorption and oxidation of SO2and NO to form H2SO4and HNO3. As for the phenolic (-OH) and carbonylic groups (C=O), there were no appropriate test reslults to demonstrate their role and effect, and many researchers regarded them as acidic groups, but others ascribed them to basic. Nevertheless, the test results proved that the ether (C-O-C) and quinone groups acted as active sites for the adsorption of SO2and NO, and these two groups generally were considered as basic. The nitrogen functional groups mainly included pyridine and pyrrole functional groups, and these two groups played a role of active sites and can adsorb SO2and NO directly. There were a bit differences between the adsorption progresses of SO2/NO and Hg0. Simplely said, the difference was that the Hg0atom can be captured by the defective sites or active sites to form the C-Hg covalent bond, centainly, these active sites should contain the surface oxygen functional groups.Except for the oxygen functional groups, all the flue gas components should interact with each other. During the adsorption tests, so long as there were no direct or indirect chemical reaction between these flue gas components, these flue gas components would presented an inhibiting effect between themselves. According to our reserach results, NO showed weak inhibiting effect on SO2, but SO2hindered the adsorption of NO obviously. HC1promoted the Hg0adsorption tremendously due to the chemical effect of direct or indirect, but shown the opposite effect on the adsorption removal of SO2. O2and NO2had positive effect on the adsorption of SO2, NO, VOC, and Hg0in different degrees, the reason was that the surface oxygen functional groups can decomposite the O2and NO2molecules to realese the powerful oxidant O*free radical. But at low temperature (<100℃), the oxidizing effect of NO2or O2was poor on VOC according to our test results, and to the Hg0oxidization, NO2showed stronger oxidability than O2.In addition, the experiment results obtained from a middle-small sized experiment system made sure that the ACF sorbent can realize the purpose of simutaneous and efficient removal to the SO2, NO, VOC, and Hg0in coal fired flue gas. Within valid24hours for the the system running, the removal average efficiencies of SO2arrived at over95%, over80%for NO, over95%for total Hg, and54.17%for VOC. In summary, these resullts went better than expected.