Mechanism And Key Factors Of NO_x Removal From Flue Gas Using Chemical Absorpeion-biolgocial Reduction Integrated Approach

With the development of the national economy and the increasing emission amount of NOx, the pollution caused by NOx becomes more serious and receive increasing attention of more people. Current technologies for NOx removal from flue gas have associated with some problems, such as high cost on investment and operation, producing secondary pollutant and low removal efficiency. So, to exploit a new technology which has advantages of low cost environment-friendly and high efficiency for NOX removal from flue gas is becoming an extremely urgent issue, presently.A chemical absorption-biological reduction integrated approach is employed to achieve the removal of nitrogen monoxide (NO) from the simulated flue gas with the advantages of low cost, completely reduction of NO and high removal efficiency. The development of the integrated technologies includes two aspects:1) complex absorbent regeneration;2) NO bioreactor process control. In this dissertation, the key factors and mechanism of Fe(II)EDTA-NO reduction was investigated; the effects of carbon source, nitrogen cycle on this system were discussed; the feasibility of biological packed column with the integrated process was studied; through the analysis of biological reduction rates and NO absporption rates of NO process, the kinetic model was established. The main original conclusions of this dissertation are:Glucose is suitable for the heterotrophic bacteria as the carbon source and electron donor to remove NO from simulated flue gas by the integrated chemical absorption-biological reduction system. In the range of0-10%oxygen concentration, the reactor can achieve long-term stable operation, and the removal efficiency of NO can be maintained above86%. The reduction of Fe(Ⅲ)EDTA mainly depends on the carbon source supplied. The studies on carbon source metabolites showed that the concentration of the accumulative acid determines whether the reduction of NO and Fe (Ⅲ) EDTA was inhibited. However, long-term stable operation of bioreactor could be achieved when there is acetic acid accumulation under aerobic conditions. The distribution of the carbon source degradation was also examined here with17%existed in the form of VFA, while50%total carbon source was consumed in the form of CO2. In addition, it was also found that glucose added into bioreactor within a certain range of oxygen concentrations will not be accumulated in the reactor, which keeps the operation stable.After a run of93hours operation by chemical absorption-biological reduction integrated approach, about66%of the nitrogen discharged in the form of N2. The accumulation of nitrogen in the biological and liquid phases was18%and4%, respectively. The nitrogen in the liquid phase is mainly present in the form of NO3-, and there is no N2O presence of in the exhaust gas. Only a small amount of nitrogen present in the form of NO2and CH4. About5%of the nitrogen is in the form of other types or experimental error.The reaction rate of NO absorption capacity by ferrous EDTA (Fe(II)EDTA) solution and reduction by microorganism were studied in an scrubber-bioreactor system.The results show that the order of the four reaction rates in reactor is as follow: Fe(II)EDTA-NO reduction rate> Fe(II)EDTA oxidation rate>Fe(III)EDTA reduction rate> NO absorption rate,so the NO absorption process and Fe(III)EDTA reduction are key steps for NO removal efficiency in this integrated system.The microbial community structure in the biological packed tower was analyses with the PCR-DGGE technology. The microbial species at the top of the tower was least due to water erosion, while the bottom layer had the largest micro-organisms and less species. The similarity of microbial community structure increased with the increase height of packed bed. The preliminary analysis results indicated that the microorganisms in the biofilm belonged to β-Proteobacterium and Pseudomonas. The denitrifier was dominanted in the biofilm.Investigate the influence on the NO removal efficiency of some elements such as the concentration of O2, NO, SO2, flow rate of inlet gas and absorbents. that the result of the influence on NO removal efficiency of the concentration of O2, NO, SO2, flow rate of inlet gas and absorbents was obtained. The results showed that the Fe(II)EDTA /Fe(Ⅱ)Cit mixed system has the best technical parameters and economic benefits.