Experimental And Mechanism Study On Multi-pollutants Control By Ozone And Active Molecule

Primary energy consumption is increasing continuously with country's economy development in which coal accounts for about 70%. Pollutants from coal combustion are endangering human health and global environment. High environmental benefits with relatively low cost can be obtained by using one technology or two combined to remove multi-pollutants simultaneously. Issues about multi-pollutants control using ozone and active molecule were investigated experimentally and theoretically in this work which included soluble NOx removal in wet scrubber, pollutants oxidation by catalytic flue gas integrally and comparation with ozone, quantum chemistry study on some reactions with unknown mechanism or reaction rate, NO oxidation by catalyzing O2 to produce active molecule heterogeneously.Soluble NOx removal is the last and most important step. When O3/NO molar ratio is low, NO2 is the main product. S(Ⅳ) concn and pH value of absorption solution directly affected removal efficiency. Reactions of NO2 with SO32-,HSO3- were favorable for NO2 removal by increasing absorption rate. NO2 removal increased with pH value at the same S(Ⅳ) concn. NO2 removal was around 70% in the typical wet FGD condition with initial concn 300ppm. NO2-was the main solution product. Mutual effects of NO2 and SO2 were that absorption of SO2 made pH value decline and S(Ⅳ) concn increase resulting in decrease of NO2 removal and that absorption of NO2 also resulted in both pH value and SO2 removal decreasing and the SO42-concn increasing. When O3/NO molar ratio was over 1, NO2 removal increased drastically even to 90% with NO3- concn increasing because of NO3 and N2O5 formed in gas.Oxidation of Hg0 and NO was studied by catalytic flue gas integrally (NTP and UV) separately. Active molecules were produced to oxidize Hg0 by catalytic flue gas using DBD-NTP. O/O3 affected the oxidation rate of Hg0 directly. Hg0 could be oxidized to some extent with OH produced by NTP when vapor existed in gas without oxygen. Small amount of vapor was favorable to Hg0 oxidation with oxygen coexisting, but it hindered the oxidation when concn was beyond a certain value because OH didn't only oxidize Hg0 but also increased the consumption of O and O3. HCl could promote the oxidation producing soluble Hg2+species. NO was oxidized by UV catalytic flue gas. Ozone produced was consistent with NO oxidized. Vapor favored NO oxidation. SO2 couldn't be oxidized by O2 in UV, but coexistence of vapor promoted the reaction apparently. NTP and UV could both catalyze flue gas to produce O3, O and OH et al active molecules oxidizing pollutants effectively. However, they consume much more energy than ozone injection which is enough to oxidize inorganic contaminations efficiently with low cost. Reactions involving O3 and NO3 are characterized by oxygen-extract and-transfer. The activation energy of SO2 reaction with O3 obtained by quantum chemistry calculations is 9.68 kcal/mol which is 3.5 times as high as NO with O3. Rate constant of the former is 1/105 of the latter at 150℃, so NO could be selectively oxidized by O3. The reaction rate of H2O2 with SO2 is also very low, which means SO2 conversion in gas is difficult. NO3 could react with O3 or itself producing NO2 and O2. Activation energy of reaction of NO3 with O3 is 8.85kcal/mol. Two paths were found for reaction of two NO3 molecules. The triplet path is one step reaction and activation energy is 34.6kcal/mol. There are two transition states and one intermediate in singlet path and energy barriers are 1.36kcal/mol,2.38kcal/mol, respectively. Reaction of two NO3 molecules mainly occurs through singlet pathway. It was found by kinetics analysis that two NO3 molecules reaction was the major cause for NO3 consumption at 150°C and low temperature benefited NO3 survival. NO3 consumption will not pose a competitive challenge to oxidation of Hg by NO3 because the rate of NO3 reaction with Hg is large and Hg concn is much lower than NOx in flue gas.This work proposed an idea that using solid catalyst to absorb and activate oxygen in flue gas oxidizing pollutants by combining with wet scrubber to achieve multi-pollutants control, during which active oxygen species could be produced on catalyst surface. Catalysts could enhance the reactivity of O2. Heterogeneous catalytic oxidation of NO and characterization of catalysts were investigated. An excellent oxygen storage material (CeO2) was chosen as support. Co and Mn were used as active components. Catalysts were made by sol-gel method. The optimum calcining temperature was 400℃for CoCeOx and 500℃for MnCeOx. The best catalytic activity was reached when the molar ratio of metal dopped and Ce was about 1:2. Metals dopped were highly dispersed in catalyst support forming solid solution phase. About 50%-90%of NO would be oxidized in 200-300℃. La-doping could hance MnCeOx activity. The catalytic mechanism was described as follows. Oxygen interacts with surface of catalyst to induce active oxygen species (Ox) that is more reactive than O2 molecule by bulk lattice oxygen and surface oxygen species migrating to surface lattice oxygen vacancy sites, gas O2 absorption on surface lattice oxygen vacancy sites or absorption sites. Intermediate is formed by integration of NO molecule and O atom of Ox*. After NO2 aparted from the intermediate lattice oxygen vacant sites and surface absorption sites are formed for further adsorption of O2 and migration of surface or bulk oxygen species.