Xinxiang Pan

UV-Enhanced NaClO Oxidation of Nitric Oxide from Simulated Flue Gas

A wet de-NOx technique based on an UV-enhanced NaClO oxidation process was investigated for simulated flue gas of a diesel engine using a bench-scale reaction chamber. The effects of UV irradiation time, initial pH value, and available chlorine concentration of NaClO solution were studied, respectively. The results showed that when the UV irradiation time was 17.5 min and the initial pH value of NaClO solution was 6, NO removal efficiency of UV/NaClO solution was increased by 19.6% compared with that of NaClO solution. Meanwhile, when the available chlorine concentration of NaClO solution decreased from 0.1 wt% to 0.05 wt%, the enhancement in NO removal efficiency of UV/NaClO solution increased from 19.6% to 24%, compared with that of NaClO solution. The reaction pathways of NaClO solution photolysis and NO removal by UV/NaClO process were preliminarily discussed. The results suggested that HOCl might be the most active species that released many UV-induced photooxidants through photolysis reactions, which played an important role in NO removal process.

Nitrogen oxide removal using seawater electrolysis in an undivided cell for ocean-going vessels

As massive nitrogen oxide (NOx) emissions from marine slow speed diesel engines have caused serious health and environmental problems, NOx removal using electro-generated chlorine under seawater electrolysis was studied in a lab-scale scrubbing reactor. Electro-generated chlorine was prepared by seawater electrolysis in an undivided cell. Results showed that active chlorine concentration increased linearly with the increase of current density and electrolysis time. Energy consumption decreased from 83 to 6.1 kW h per (kg [Cl2]) with the salinity varying from 3.2 to 37.8 ppt after 5 min of electrolysis. Onsite generation of active chlorine using concentrated seawater from desalination plants operated on a ship was suggested to be a cost-effective solution with less energy consumption. Then, effects of dilution ratio (seawater/electrolyte), inlet NO and SO2 concentration, and initial pH value of scrubbing solution on NOx removal efficiency were further investigated. NOx removal efficiency of electro-generated chlorine at pH value of 7 decreased from 98.9% to 20.2% with the dilution ratio increasing from 2.4 to 96. The NO absorption rate by HOCl was proved to be higher than that by OCl−. NO absorption rate increased linearly as inlet NO concentration increased. When SO2 concentration increased from 207 to 814 ppm, NOx removal efficiency decreased slightly, but SO2 removal efficiency was almost kept at 100%. The possible reaction mechanism and pathways were discussed by evaluating the pH-dependant NOx removal efficiency using electro-generated chlorine. The proposed method of wet scrubbing using electro-generated chlorine was demonstrated to be a potential after treatment strategy to control NOx emissions from large marine diesel engines.

An investigation of mass transfer-reaction kinetics of NO absorption by wet scrubbing using an electrolyzed seawater solution

The mass transfer-reaction kinetics of NO absorption by wet scrubbing using electrolyzed seawater was studied in a bench-scale bubbling reactor. The effects of active chlorine concentration, solution pH, absorbent temperature, NO and SO2 inlet concentrations on NO absorption rate were investigated. The results showed that the NO absorption rate significantly increased from 0.41 × 10−5 to 1.91 × 10−5 mol m−2 s−1 with the active chlorine concentration increasing from 500 to 3100 mg L−1 [Cl2]. The NO absorption rate greatly increased from 0.25 × 10−5 to 1.58 × 10−5 mol m−2 s−1 with NO concentration increasing from 250 to 1250 ppm. When SO2 inlet concentration increased from 250 to 1250 ppm, the NO absorption rate slightly increased from 1.09 × 10−5 to 1.17 × 10−5 mol m−2 s−1. When the solution pH was in the range of 4–6, the NO absorption rate was about 1.5 × 10−5 mol m−2 s−1. The change of the NO absorption rate was insignificant with the absorbent temperature increasing from 20 to 50 °C. The influential mechanism of the NO absorption rate was also discussed preliminarily. Furthermore, the NO absorption process by electrolyzed seawater was pseudo-first-order reaction with respect to NO concentration. A simplified equation of NO absorption rate was also obtained. The comparison results indicated that the calculated values agreed well with the experimental values.

NOx Removal from Simulated Marine Exhaust Gas by Wet Scrubbing Using NaClO Solution

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.

Effect of microfluidic electrolyte on the photovoltaic performance of ZnO-nanowire-based dye-sensitised solar cells

ZnO-nanowire-based dye-sensitised solar cells (DSSCs) were prepared to investigate the effect of microfluidic electrolyte on the photovoltaic performance of solar cells. At first, long and well-aligned ZnO nanowires were synthesised on FTO substrate via the improved hydrothermal method. The structure and crystallinity properties of ZnO nanowires were characterised by using SEM, TEM and XRD. The photovoltaic characteristics of the assembled DSSCs were measured under various flowrates of microfluidic electrolyte. The results showed that variations of the microfluidic electrolyte had little effect on the fill factor of the cells. However, the photocurrent and photovoltage of the solar cells exhibited systematic changes with the decrease of microfluidic electrolyte: the short-circuited current of the DSSCs decreased while the open-circuit voltage increased. The phenomenon could remain in some extent after cessation of injecting the electrolyte within a short time. The possible influencing mechanism of the microfluidic electrolyte on the photovoltaic performance was discussed.