Research On No Ozonation Process & Double Swirl Gas Mixer & Denitration Model In Spray Absorber Based On Numerical Simulation

Along with the large-scale haze becoming more serious in urban agglomeration, simultaneous removal of air pollutants from flue gas has been widely concerned by researchers. In this thesis, a systematic study was carried out onto a two-step process that combined a rapid oxidation by using ozone with a subsequent wet absorption process. The thesis studied the effectiveness of NO2 and N2O5 generation using CHEMKIN, together with a numerical simulation of spay cooling for a 35 t/h boiler based on Euler-Lagrange equation. Furthermore, a new double swirl gas mixer that was suitable for NO ozonation was also developed. Eventually, a mass transfer model including a chemical absorption was established to simulate the absorption process of NO2 and the simulation results of different cases were executed to explore the influences of operating conditions.Firstly, a kinetic mechanism for O3 and NOX reaction involving 20 new reactants and 76 reaction steps was proposed. The generated NOx concentrations in experiments were quantitatively measured by using a Fourier Transform Infrared (FT-IR) spectroscopy, the results of which together with published references have effectively proved that the proposed kinetic mechanism was accurate and the corresponding model was reliable. The relationship between NOx production rate and operating parameters, such as residence time, reaction temperature and molar ratio of O3/NO, was also studied. Simulation results indicated that the increase in residence time was beneficial for the enhancements of NO2 and N2O5 generations. The effect of temperature on NO2 generation could be neglected. However, for N2O5, the optimized temperature was 373K. The desired molar ratio of O3/NO was at about 1.0 for NO2 generation, whilst for N2O5, the molar ratio was at 1.75.Secondly, a spray cooling system to control flue gas temperature for a 35 t/h boiler was studied based on the Euler-Lagrange equation. The results showed that single-hole spraying lances worked better than two-holes spraying lances. Moreover, the suitable layout for single-hole spraying lances was a distributed arrangement at Z = 3m. The parameters such as the diameters of droplets, the water flow rate, the gas temperature and the gas flow, had greatly affected the spray cooling efficiency, where the temperature of spraying water had little effect. The designed cooling system could meet the requirement for the 35 t/h boiler.Thirdly, on the basis of swirling flow mixing mechanism, a new double swirl gas mixer was developed in assistance of computational fluid dynamics. Numerical simulations for structural parameters including inner connector, L/D, nozzle length and angle of vane were carried out using the FLUENT software and the influences on flow field and pressure loss were also investigated. In the experiments, the flow field was detected by using PIV method and the pressure loss was observed from micro pressure gauge. Experiment data declared that the model was suitable and accurate to simulate the static mixer. When L/D was equaled to 4, the coefficient of variation (COV) was less than 5%. The installment of inner connector was beneficial for gas mixing, but would enlarge the energy consumption. The nozzle length should be set at 4 cm and the optimal angle of vane should be at 45°. It has been demonstrated that the developed double swirl gas mixer could get a good mixing in a short distance and its pressure loss was lower than that of commercial products.Finally, a mass transfer model for denitration process in spray tower was proposed. Experimental results indicated that the developed mass transfer model was suitable to simulate the NO2 absorption process where simulation results indicated that the inlet flow velocity had nearly no effect on NO2 absorption but the L/G, NO2 concentration and solution concentration could greatly influence on the absorption process. This result well described the influences of operating parameters on NO2 absorption, which makes the developed mass transfer model be a powerful tool to verify the influences on the NO2 absorption in spray tower.