选择性催化氧化吸收耦合生物还原法脱除烟气中NOx的机理研究

Biological reduction method plays an important role in the NOx removal field, but its application is limited by the two critical problems that are the impossible anaerobic condition and the low NO mass transfer efficiency. To solve both problems, a new selective catalytic oxidation absorption–biological reduction integrated method is proposed to remove NOx. Effects of some factors such as different absorbents, the concentration of absorbent and oxidation degree on the absorption efficiency and product are investigated to determine the optimal absorption system after the NOx oxidation. On the basis of optimizing the denitrifying bacteria, a biological reduction system is built, and the NOx removal characteristic in the selective catalytic oxidation absorption–biological reduction integrated system are studied emphatically: Effects of operating conditions on the NOx removal performance are surveyed to identify the critical parameters for ensuring stable operation of the integrated system. The change rule of microbial community and population in different operation stages or under changing operational parameters are clarified through PCR-DGGE and high-throughput sequencing methods. Dominant species in the integrated system are isolated to construct the population of aerobic denitrifying bacteria which is further applied in the system to realize the effective removal of NOx. The existing forms of NOx in the gas phase, liquid phase and biological phase, and the aerobic denitrifying pathways of microbe are investigated to clarify the NOx removal mechanism. The research results can provide an environment-friendly method for actual DeNOx technologies.

生物还原法在NOx处理领域发挥着重要作用，但厌氧条件难以实现以及NO传质效率低成为限制其应用的两个关键问题。为解决这两个问题，本项目提出了选择性催化氧化吸收—生物还原法相耦合的NOx处理新思路。考察不同吸收剂、吸收剂浓度、氧化度等因素对吸收效率及产物的影响，确定NOx氧化后的最佳吸收体系。在优选反硝化菌群的基础上建立好氧生物还原体系，并研究选择性催化氧化吸收—生物还原耦合体系的NOx去除特性：研究不同操作条件对NOx去除性能的影响，明确耦合体系稳定运行的最优参数；运用PCR-DGGE和高通量测序等技术明确不同运行阶段和改变运行参数时的微生物群落及种群变化规律，从中分离优势菌种并构建好氧反硝化菌群，应用于耦合体系以实现NOx的高效去除；通过弄清NOx在气相、液相、生物相之间的存在形态，以及微生物的好氧反硝化路径，阐明耦合体系中NOx的去除机理。研究结果将为实际脱硝提供一种环境友好的借鉴方法。

生物还原法在NOx处理领域发挥着重要作用，其核心是在微生物的反硝化作用下将NOx还原为无毒无害的N2。然而，其工业应用受到两个关键问题的限制：厌氧条件难以实现且NO传质效率低。为解决这两个问题，本项目基于新型好氧生物还原技术，建立了调节NOx氧化度协同化学吸收–生物还原（CABR）新工艺用于脱除模拟烟气中的NOx。.在优选好氧反硝化菌群、NOx氧化度及吸收体系的基础上建立了稳定CABR脱硝系统，确定了最佳NOx氧化度和吸收体系，分别为50%及0.02 mol/L的NaHCO3。并在此基础上考察了不同操作条件对CABR系统NOx去除性能的影响，结果表明CABR系统在50 °C高温下仍能有效去除98%以上的NOx。当NOx浓度为500 ppm，在氧气浓度为0−10 vol%的范围内，系统脱硝效率超过94%。入口NOx浓度升高至800 ppm时，系统对NOx去除效率高于98%。烟气中通入的SO2浓度高达800 ppm时，不会影响系统的脱硝效率。每天更换50%的吸收液即可同时满足NOx高效去除和微生物生长的氮源需求。吸收液的流量在30−50 L/h的范围内，NOx的去除效率可保持在99%以上。.同时运用气相色谱法、质谱法以及水中含氮化合物定量检测方法研究了NOx在气相、液相和生物相之间的存在形态及转化路径，并结合酶活及氮元素平衡实验结果发现进口NOx中约59%的氮通过微生物反硝化作用以N2的形式排出，37%的氮转换为微生物生长所需的生物质氮，只有1.1%的氮积累在液相中，这进一步表明CABR系统中NOx的去除主要取决于微生物的反硝化作用和同化作用。.通过本项目的研究发现CABR脱硝系统在研究范围内高温、高氧含量、高入口NOx浓度及SO2浓度高达800 ppm仍能实现NOx的高效脱除，这就为NOx治理提供一种环境友好的借鉴方法，也为实现生物脱硝技术的工业应用提供重要的理论支撑。