【作者】 姜树栋；

【导师】 周俊虎； 岑可法； 王智化；

【作者基本信息】 浙江大学 ， 热能工程， 2010， 博士

【摘要】 随着经济发展我国一次性能源消费将不断上升,煤在一次能源中占了70%的比重。煤燃烧释放的各种污染物威胁着环境和人类的健康。利用一种技术或者两种技术结合同时脱除多种污染物可以以较低的成本获得较高的环境收益。本文对利用臭氧和活性分子实现多种污染物协同脱除的相关问题进行了实验和机理研究,主要研究内容包括可溶性NOx的湿法脱除,烟气整体催化氧化污染物研究及与臭氧氧化对比,若干未知速率和未明机理反应的量子化学研究,异相催化氧气产生活性分子氧化NO研究。将可溶性NOx湿法脱除是氧化性方法协同脱除污染物的最后也是重要的一步。采用臭氧喷射技术,NO2是O3/NO摩尔比较低时的产物。吸收液中S(Ⅳ)和pH值直接关系着NO2的脱除效率。NO2可与吸收液中的SO32-、HS03-反应,增大吸收速率,提高脱除效率。相同S(Ⅳ)浓度下,NO2脱除率随pH值升高而增大。在典型脱硫塔液相条件下,300ppm NO2的脱除效率约为70%,亚硝酸根是其主要的液相产物。NO2、SO2的相互影响为：SO2造成喷淋液中pH值下降和S(Ⅳ)上升,综合结果使NO2脱除率略有下降；NO2的吸收使喷淋液的pH值和SO2的脱除率下降,吸收液中硫酸根浓度上升。在O3/NO摩尔比大于1时,因气相生成NO3、N2O5,NOx脱除急剧上升,可以达90%以上,同时液相NO3-浓度上升。采用两种烟气整体催化方式(NTP、UV),分别氧化Hg0和NO。利用DBD-NTP对烟气整体催化产生活性分子氧化Hg0。O/O3是氧化Hg0的重要物质,氧化率与O3浓度直接相关。当模拟烟气中无O2单独水汽存在时,NTP中产生的OH会一定程度上氧化Hg0。当H2O与O2共存时少量水汽可促进Hg0氧化,超过一定浓度则阻碍氧化,原因是有O2存在OH对Hg氧化有两面性：一是OH自身可以氧化Hg0,二是OH能促进O、O3等的消耗。模拟烟气中的HCl可促进Hg氧化,生成可溶性Hg2+物质。利用UV光催化烟气产生活性分子氧化NO。UV催化烟气产生臭氧量与NO氧化量基本一致,水汽加入可以明显改善NO氧化。在UV下烟气O2不对SO2产生氧化作用,有水汽出现后氧化效果明显。与臭氧氧化对比：NTP与UV均可对烟气整体催化,产生O3、O、OH等多种活性分子有效氧化污染物但整体化催化方式更加耗能,就无机污染物处理方面臭氧喷射方式足可以实现高效低价脱除。所有涉及到O3、NO3的反应均为氧抽取转移反应。SO2与O3反应活化能量子化学计算结果为9.68 kcal/mol,为NO与O3的3.5倍,150℃下的反应速率常数为后者的105分之1,所以O3可以选择性氧化NO.H2O2与SO2反应速率同样很慢,SO2在气相中的转化比较困难。NO3可分别与O3和NO3发生反应,生成NO2、O2。NO3与O3反应活化能为8.85kcal/mol。NO3自身碰撞消耗反应可以通过两条路径实现,三重态路径活化能为34.6 kcal/mol,单重态路径上有两个过渡态、一个中间体,活化能依次为1.36 kcal/mol,2.38 kcal/mol,反应主要通过后一路径实现。反应动力学模拟表明,150℃下NO3自身碰撞分解反应是NO3消耗的主要反应,低温利于NO3的生存。N03与Hg共存的动力学模拟表明,NO3分解不会对NO3氧化Hg构成竞争,原因是NO3与Hg反应速率极快、Hg浓度远远低于烟气中NOx。本文提出了利用固体催化剂吸附活化烟气中的氧气,产生表面活性氧物种,氧化多种污染物,与湿法洗涤结合可实现协同脱除。O2分子本身反应活性很低,与催化剂表面作用后可提高反应活性。首先对固相催化O2氧化NO进行了试验研究和催化剂表征。采用的载体是具有优良储氧功能的CeO2,活性组分为钻和锰,溶胶凝胶法制备,最佳煅烧温度分别为400℃(CoCeOx),500℃(MnCeOx),掺杂金属与载体铈摩尔比约1∶2时,达到最好交互作用,催化效果最好,金属高度分散在载体中形成固溶。在200-300℃范围内可以达到50-90%的NO氧化率。La掺杂可提高MnCe氧化物催化剂的活性。催化机理可简述为,通过体相晶格氧和表面氧物种向表面氧空位迁移、气相O2分子向表面氧空位和吸附位吸附,诱导产生比O2更具有反应能力的活性的氧物种(Ox*),Ox*与被吸附的NO分子发生反应,NO分子结合一个氧原子生成中间体,中间体释放NO2分子,NO2从表面脱离后,遗留下氧空位和表面吸附位,以进行下一次O2分子吸附和催化剂表面或体相氧物种迁移。更多还原

【Abstract】 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.更多还原