No abstract

Both cyclic and noncyclic scrubbing experiments were conducted to remove NO from simulated flue gas in a lab-scale countercurrent spraying reactor. The effects of various operating parameters (initial solution pH, NaClO concentration, absorbent temperature, and inlet NO and SO2 concentrations) on NO removal efficiencies were investigated in the noncyclic scrubbing mode. The results showed that NO removal efficiency increased greatly with the decrease of the initial pH value. However, there was a drop in NO removal efficiency, possibly due to the NO2 absorption in the gas phase. NO removal efficiency increased gradually with the increase of the NaClO concentration. Complete removal of NO was achieved when the NaClO concentration was 24 × 10–3 mol·L–1. However, the NO removal efficiency obviously decreased with the absorbent temperature increasing from 303 to 343 K. This could be mainly ascribed to the decrease of the water solubility of NO2 and the absorption reaction of NO2 with water vapor. Furthermore, NO removal efficiency increased quickly with the increase of the inlet NO concentration. The coexisting SO2 in the simulated flue gas had little effect on the NO removal efficiency. Both NO and SO2 could be removed simultaneously with a SO2 removal efficiency of 100% and a NO removal efficiency of >93%. More importantly, the results of cyclic scrubbing experiments indicated that an average NO removal efficiency of 74% had been obtained for the whole cyclic scrubbing duration. The utilization of NaClO oxidant was calculated to be approximately 83%. The ion chromatographic analysis showed that there was no ON2 – in the spent liquor. The results demonstrate that NaClO is a low-cost high-efficiency oxidant for NO removal from exhaust gas and that it has great potential for industrial applications.

The experiments were conducted to investigate the NO removal by wet scrubbing using NaClO2 seawater solution in a cyclic scrubbing mode. Results show that, when the concentration of NaClO2 in scrubbing solution is higher than 10 mM, a complete removal of NO can be achieved during the cyclic scrubbing process. The breakthrough time for seawater with 15 mM NaClO2 is enhanced by 34.3 % compared with that for NaClO2 freshwater. The extension of the breakthrough time for NaClO2 seawater is mainly ascribed to the improved utilization of NaClO2 in the solution. The good buffering ability of seawater could suppress the acidic decomposition of NaClO2 into ClO2 effectively. The analysis of reaction products indicates that the main anions in the spent liquor are chloride ions and nitrate ions. The calculation of NaClO2 utilization according to the ion chromatography also agrees well with the experimental results of breakthrough times.

Ultraviolet irradiated sodium chlorite (UV/NaClO2) solution was introduced to remove nitrogen oxide (NO x ) from simulated flue gas in a bench-scale scrubbing reactor. Effects of UV irradiation time, NaClO2 concentration, NO inlet concentration, pH value, and O2 concentration were investigated separately. Results showed that NaClO2 solution with UV pretreatment achieved a remarkable promotion in NO x removal efficiency. The ClO2 produced from photodecomposition of NaClO2 in aqueous solution substantially improved the NO absorption process. The NO x removal efficiency by UV/NaClO2 solution increased from 28 to 77% as the UV irradiation time increased from 0 to 600 s. When the NaClO2 concentration increased, the NO x removal efficiency by UV/NaClO2 solution increased, whereas the enhancement factor decreased. The NO absorption rate by UV/NaClO2 solution increased with NO inlet concentration. The NO x removal efficiency by UV/NaClO2 solution was higher than that by NaClO2 solution without UV pretreatment at a pH range of 3–12. The reaction mechanisms of the NO removal process were suggested to be different in acid and alkaline media. The UV/NaClO2 process was demonstrated to significantly improve NO x removal efficiency, which might be developed to be a potentially cost-effective method for removing NO x from flue gas.

The mass transfer reaction kinetics of NO absorption by UV/chlorine advanced oxidation process were investigated in a lab-scale photochemical bubble reactor. Effects of several parameters on NO absorption rate were studied, including UV power, NO inlet concentration, SO 2 concentration, active chlorine concentration of electrolyzed seawater, and reaction temperature. Results showed that NO absorption rate increased gradually with the increase of UV power, NO inlet concentration, and active chlorine concentration of electrolyzed seawater, but was almost independent of SO 2 concentration and reaction temperature (below 313 K). The absorption process is a pseudo-0.2-order with respect to NO, as well as a pseudo-0.6order with respect to active chlorine. The mass transfer process is the main rate-determining step for the NO absorption by UV/electrolyzed seawater process. The established NO absorption model is in good agreement with the experimental values.