Previous work proposed a one-stage wet scrubbing in situ combined with O3 oxidation for simultaneous removal of NO and SO2 from flue gas, and the results showed that wet scrubbing combined in situ with O3 injection could effectively improve O3 oxidant utilization efficiency. In this work, a follow-up research work was carried out to further explore the synergistic effect of dual oxidants of NaClO in the liquid phase and O3 in gas phase. The synergistic effects of O3/NO molar ratio and NaClO concentration in the circulating scrubbing solution on NOx removal performance was investigated systematically. The results showed that when molar ratio of O3/NO was 0.5 and NaClO concentration was 25 mM, NO could be oxidized completely and averaged NOx removal efficiency exceeded 70%. NOx concentrations in outlet gas and anion compositions in the scrubbed solution were analyzed, and the possible reaction paths of wet scrubbing NaClO solution in situ with O3 injection in denitration process were also discussed. When the solution pH was around 6, a relative balance between NOx oxidation and absorption might be achieved, resulting in a high NOx removal efficiency. The temperature of inlet flue gas imposed little impact on NOx removal efficiency due to the quick and efficient cooling effect by wet scrubbing. The increase of initial SO2 concentration led to a slight increase of NOx removal efficiency from 70 to 73.5%. A complete removal of SO2 could be achieved, but coexisting SO2 in flue gas would consume NaClO oxidant and shorten the reaction duration.
After the NaClO solution was used to purify acetylene gas, the solution contained significant amounts of NaCl, Na2SO4, and Na2HPO4. The phase equilibrium data is the most important basic information for recovering sodium salts. In this study, the solubilities and dry-salt phase diagram for the system (Na+//Cl–-SO42–-HPO42–-H2O) were systemically studied. The dry-salt phase diagram contained one invariable point, three univariate solubility curves, and three single salt crystallization regions corresponding to NaCl, Na2SO4, and Na2HPO4·12H2O at 298.15 K and 0.1 MPa. Based on the ELEC-NRTL and Pitzer model embedded in the Aspen Plus, the phase equilibrium data for the ternary subsystem (Na+//Cl–-SO42–-H2O, Na+//Cl–-HPO42–-H2O, and Na+//SO42–-HPO42–-H2O) at 298.15 K and 0.1 MPa taken from the literature were first predicted to verify the applicability of parameters from the default database and literature. Subsequently, the models were optimized by literature solubility data, and then, the obtained parameters can well predict the phase equilibrium data for the ternary subsystem at 298.15 K and 0.1 MPa. All of these will provide basis data for the separation of sodium salt from the Na+//Cl–-SO42–-HPO42–-H2O system.
Zhitao Han,Bojun Liu,Shaolong Yang,Xinxiang Pan,Zhijun Yan
The experiments were performed in a lab-scale countercurrent spraying reactor to study the NOx removal from simulated gas stream by cyclic scrubbing using NaClO solution. The effects of NaClO concentration, initial solution pH, coexisting gases (5% CO2 and 13% O2), NOx concentration, SO2 concentration, and absorbent temperature on NOx removal efficiency were investigated in regard to marine exhaust gas. When NaClO concentration was higher than 0.05 M and initial solution pH was below 8, NOx removal efficiency was relatively stable and it was higher than 60%. The coexisting CO2 (5%) had little effect on NOx removal efficiency, but the outlet CO2 concentration decreased slowly with the initial pH increasing from 6 to 8. A complete removal of SO2 and NO could be achieved simultaneously at 293 K, initial pH of 6, and NaClO concentration of 0.05 M, while the outlet NO2 concentration increased slightly with the increase of inlet SO2 concentration. NOx removal efficiency increased slightly with the increase of absorbent temperature. The relevant reaction mechanisms for the oxidation and absorption of NO with NaClO were also discussed. The results indicated that it was of great potential for NOx removal from marine exhaust gas by wet scrubbing using NaClO solution.
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