Inlet NO Concentration Research Articles

Optimization of the NO photooxidation and the role of relative humidity

Photocatalysis was recognised as a suitable process for the photoabatement of atmospheric pollutants. The photooxidation mechanism on TiO2 has been widely studied. However, recent studies demonstrated that the very often-assumed photooxidation intermediated by the hydroxyl radical cannot explain all the experimental observations. Indeed, this study contributes for a new understanding of NO photooxidation. First, the adsorption equilibrium isotherms of NO, NO2 and H2O on the photocatalyst, Aeroxide® P25 from Evonik Industries, were obtained. Also, the concentration of hydroxyl radicals was determined by photoluminescence. A comprehensive design of experiments was then followed; NO conversion and selectivity were obtained as a function of the relative humidity, irradiance, NO inlet concentration and residence time, following a response surface methodology (RSM). These results were then used to discuss the photooxidation mechanism of NO.

Elemental mercury removal from flue gas using heat and Co2+/Fe2+ coactivated oxone oxidation system

Oxidation removal process of elemental mercury (Hg0) from flue gas using heat and Co2+/Fe2+ coactivated Oxone oxidation system in a spraying reactor was developed. The effects of several influencing factors and main flue gas compositions on Hg0 removal, and the active species, products, mechanism and mass transfer-reaction kinetic law of Hg0 removal process were investigated. The results show that heat and Co2+/Fe2+ have a significant synergistic effect for activating Oxone to produce free radicals and promote Hg0 removal. Hg0 removal can be improved via increasing Oxone concentration, Co2+/Fe2+ concentration, activation temperature or O2 concentration, and is inhibited with increasing solution pH, Hg0 inlet concentration or NO concentration. Changing SO2 concentration have double impacts on Hg0 removal. SO4− and OH produced from coactivation of heat and Co2+/Fe2+ are the key oxidants, which play a leading role in Hg0 removal. Oxone plays a complementary role in Hg0 removal. Hg0 removal processes using heat/Co2+ and heat/Fe2+ coactivated Oxone systems belong to fast reactions under optimized experimental conditions, and meets a total 2.8-order reaction (i.e. 1.0-order for Hg0, 1.1-order for Oxone and 0.7-order for Co2+) in Co2+/Oxone activation system, and a total 3.0-order reaction (i.e. 1.0-order for Hg0, 1.4-order for Oxone and 0.6-order for Fe2+) in Fe2+/Oxone activation system. Finally, the key mass transfer and kinetic parameters of Hg0 removal processes were also determined.

NO Removal from Simulated Flue Gas with a NaClO2 Mist Generated Using the Ultrasonic Atomization Method

In order to enhance the mass transfer efficiency between gas–liquid interfaces, NaClO2 mist generated by an ultrasonic humidifier was used to remove NO from simulated flue gas. The effects of some key parameters (the gas flow rate, the NaClO2 concentration in the solution, the inlet NO concentration, the NaClO2 solution pH) on NO removal efficiency were investigated preliminarily. The results showed that NaClO2 mist could oxidize NO with a much higher efficiency compared with other mists containing either NaClO or H2O2 as oxidants. With an increase in the gas flow rate from 1.5 to 3.0 L·min−1, the atomizing rate of the NaClO2 solution increased almost linearly from 0.38 to 0.85 mL·min−1. When the gas flow rate was 2.0 L·min−1, a complete removal of NO had been reached. NO removal efficiency increased obviously with an increase in the NaClO2 concentration in the solution. With an increase in the inlet NO concentration, the ratio of NO in the flue gas and NaClO2 in the mist increased almost linearly. Furthermore, the NaClO2 mist exhibited a relatively stable and high NOx removal efficiency in a wide pH range (4–11) of NaClO2 solutions. The reason for the high NO removal efficiency was mainly ascribed to both the strong oxidative ability of NaClO2 and the improved mass transfer at the gas-liquid interface.

Pilot-scale study of simultaneous desulfurization and denitration using hexamminecobalt(II) solution

Abstract A pilot-scale wet scrubber was designed and tested for simultaneous absorption of NO and SO2 using hexamminecobalt(II) solution. The effects of inlet NO concentration, SO2 concentration, and hexamminecobalt(II) concentration in liquid on the NO and SO2 removal efficiency were experimentally determined. Results show that the NO removal efficiency increased with increasing NO inlet concentration, but decreased with increasing inlet SO2 concentration. The SO2 removal efficiency also slightly increased, and it could reach 90% and above. The NO removal efficiency increased with increasing hexamminecobalt(II) concentration. The experimental results can provide guidance to the design of a large-scale real industrial facility for simultaneous removal of NOx and SO2 using hexamminecobalt(II) solution.

Synthesis and Performance of Iron Oxide-Coated Ceramsite in a Biotrickling Filter for Nitric Oxide Removal under Thermophilic Conditions.

A novel medium consisting of iron oxide-coated porous ceramsite (modified ceramsite) was investigated for NO removal under thermophilic conditions in this study. We used a surface coating method with FeCl3·6H2O as the modifier. When ceramsite was calcined for 4 h at 500 °C, the surface pH value decreased to 3.46, which is much lower than the isoelectric point of ceramsite, ensuring its surface was electropositive. The surface of modified ceramsite changed from two- to three-dimensional and exhibited excellent adsorption behavior to assist microbial growth; the maximum dry weight of the biofilm was 1.28 mg/g. It only took 8 days for the biofilter constructed from the modified ceramsite to start up, whereas that packed with commercial ceramsite took 22 days. The NO removal efficiency of the biofilter did not decrease apparently at high NO inlet concentration of above 1600 mg/m3 and maintained an average value of above 90% during the whole operation period. Additionally, the morphological observation showed that the loss of the surface coating was not obvious, and the coating properties remained stable during long-term operation. The maximum NO inlet loading of the biotrickling filter was 80 g/(m3·h) with an average removal efficiency of 91.1% along with a quick start-up when using the modified ceramsite filler. Thus, modified ceramsite can be considered a very effective medium in biotrickling filters for NO removal.

A study on simultaneous catalytic ozonation of Hg0 and NO using Mn–TiO2 catalyst at low flue gas temperatures

Mn–TiO2 catalysts were utilized as an ozonation catalyst for the first time to study the simultaneous catalytic ozonation of Hg0 and NO at low flue gas temperatures. BET, SEM–EDS, XRD, XPS, H2-TPR, NO x -TPD and Hg0-TPD were used to characterize the catalysts. The Mn–TiO2 catalyst, in which the molar content of metal Mn was 60%, exhibited the best catalytic activities of Hg0 and NO oxidation, compared with other Mn–TiO2 catalysts. It was found that within the range of experiment, the catalytic ozonation efficiency of Hg0 and NO was higher than that of ozonation or catalytic oxidation. The results also showed that the presence of NO gas inhibited the catalytic ozonation of elemental mercury, and the inhibition was enhanced with the NO inlet concentration, while few elemental mercury molecules did promote the catalytic ozonation of NO. The addition of H2O vapor promoted the catalytic ozonation of Hg0 and NO. In addition, 0.6Mn–TiO2 catalyst demonstrated a good TOS and cyclic stability. The catalytic ozonation of NO and Hg0 on Mn–TiO2 catalyst likely followed the Langmuir–Hinshelwood mechanism, where the hydroxyl radicals reacted with adjacently adsorbed NO molecules and elemental mercury on catalyst surface.

Orthogonal Experiments on Ozone Oxidation Denitration of Sintering Flue Gas

Ozone oxidation denitration process has become the most closely watched sintering flue gas denitration technology currently. In order to investigate the influence of different operating conditions on NO oxidation in practical engineering application of this technology, an ozone oxidation system was built, and sintering flue gas was extracted from the pipeline between the induced draft fan and the desulfurization tower. The influence of flue gas flow and inlet NO concentration on NO oxidation was investigated by orthogonal experiments. The results indicated that NO oxidation efficiency increased with the O3 yield of ozone generator and O3 dosage under any flue gas conditions. Under the same inlet NO concentration, NO oxidation efficiency decreased with the increase of flue gas flow. Under the same flue gas flow and O3 dosage, with the increase of inlet NO concentration, the O3 utilization rate increased while the average oxidation energy consumption of each NO molecule decreased, which was beneficial to promote the NO oxidation efficiency. In practical engineering application, the setting of O3 dosage should take into account both engineering design indicators and economy. Ozone oxidation denitration process could achieve NO oxidation efficiency higher than 90% through reasonable design, indicating a good industrial application prospect in the treatment of sintering flue gas.

Synthesis and Performance of Iron Oxide-Based Ceramsite in a Biotrickling Filter for Nitrogen Oxides Removal

A novel medium containing iron oxide-based porous ceramsite (modified ceramsite) and commercial ceramsite was used in two bench-scale biotrickling filter for nitrogen oxides removal to evaluate the performance of the modified ceramaite. In this study, we adopted the method of surface coating by choosing FeCl3·6H2O as modifier. Under the calcination time was 4 h at the temperature of 500°C, the modified filler presented excellent adsorption for microbial growth and the mass dry weight of biofilm reached a peak of 1.28 mg/g. Results showed that the density increased by 17% and porosity increased by about 15%, and the isoelectric point PI increased more than 4 times, while the surface pH value reduced to 3.46. The surface of pH is much lower than the isoelectric point, to ensure that its surface is electropositive, besides, the modified ceramsite had a more rough surface compared with ceramsite and changed the two-dimensional rough surface into three-dimensional surface. It only took 8 days for the biotrickling filter to start up with the modified ceramsite while the commercial ceramsite was about 22 days, which greatly shortened the start-up period. Packing with the modified filler, the NO removal performance stayed quite stable and efficient, the removal efficiency of NO did not apparently decrease under high inlet concentration of NO and basically maintained an average value of 92.8% during the whole operation period of treatment. While the commercial ceramsite presented an obvious removal decrease comparing with the modified, especially with the high NO inlet concentration of above 1600 mg/m3 and the removal efficiency was less than 80%. The iron oxide-based ceramsite proved to have the capability for improving the performance of the biofilter for NO removal. Furthermore, the fall off of the surface coating is not obvious under the experimental condition and the property of the coating is relatively stable in a long period of operation. Thus, our findings support the modified filler of iron oxide-based ceramsite as a material for use in filter media in in a biotrickling filter for pollutant gas removal.

Removal of NOx and SO2 from simulated ship emissions using wet scrubbing based on seawater electrolysis technology

This paper proposed a promising method for removal of NOx and SO2 from simulated ship emissions by wet scrubbing using electrolyzed seawater. Several factors were investigated on removal efficiencies of NO and NOx in a semi-continuous bubble column reactor. Results showed that NOx removal was enhanced with the increase of active chlorine concentration, NO inlet concentration, reaction temperature, and concentrations of coexisting gases (CO2 and O2), but was inhibited with increasing gas flow rate. The pH of the electrolyzed seawater had a significant impact on the NOx removal. Then, simultaneous removal of NOx and SO2 in both single stage and double stage reactors were studied preliminarily. Maximum removal efficiencies of NOx and SO2 from simulated ship emissions (NOx 1000ppm, O2 15%, CO2 5%, SO2 751ppm) were 92% and 100% respectively under optimum conditions. Final products (NO2− and NO3−) of the process effluent were analyzed by the ion chromatography, and reaction pathways were also discussed.

Kinetic modelling of NO heterogeneous radiation-catalytic oxidation on the TiO2 surface in humid air under the electron beam irradiation

Abstract Theoretical study of NOx removal from humid air by a hybrid system (catalyst combined with electron beam) was carried out. The purpose of this work is to study the possibility to decrease energy consumption for NOx removal. The kinetics of radiation catalytic oxidation of NO on the catalyst TiO2 surface under electron beam irradiation was elaborated. Program Scilab 5.3.0 was used for numerical simulations. Influential parameters such as inlet NO concentration, dose, gas fl ow rate, water concentration and catalyst contents that can affect NOx removal efficiency were studied. The results of calculation show that the removal efficiency of NOx might be increased by 8-16% with the presence of a catalyst in the gas irradiated field.

Kinetics of Nitric Oxide Absorption from Simulated Flue Gas by a Wet UV/Chlorine Advanced Oxidation Process

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, SO2 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 SO2 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-0.6-order 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.

Removal of NOx by Cement Raw Meal and Biochar Admixture

Many studies have indicated that carbon can be reduced to nitric oxide. This paper reports an experimental study of NO reduction by mixed materials of biochar or active carbon with cement raw meal. The proportion of mixed materials was 95 wt.% cement raw meal and 5 wt.% biochar or active carbon. A mixture loading amount and gas flow rate study quantifying the effect of carbon amount and gas residence on the reduction of nitric oxide was carried out. The experiment was performed in a fixed bed reactor at the temperature of 800°C, with O2 concentration of 1%. The inlet NO concentration was 1000 ppm. The characterization of structure and properties of biochar and active carbon was conducted by SEM-EDS, BET. The results show that different carbon materials have different NO reduction effect. The NO conversion rate increases with the increase of the amount of mixture loading. This method of removing NO is practically feasible.

Photocatalytic abatement of NOx pollutants in the air using commercial functional coating with porous morphology

Titanium dioxide is the most important photocatalyst used for purifying applications. The purpose of this study was to investigate the photocatalytic activity of the commercial product Protectam FN2, containing Evonik P25 titanium dioxide nanopowder, with regard to NO and NO2 abatement. Photocatalytic experiments on the photocatalytic coatings on concrete and plaster substrates were carried out in two types of flow reactors, namely one with laminar flow and another with ideally-mixed flow, under “real world conditions” of temperature, relative humidity, irradiation intensity and pollutant concentrations. The results showed that the photocatalytic process significantly reduced the concentration of both nitrogen oxides in the air. The reaction rate, i.e., the decrease in the concentration of NOx achieved in the steady-state for the inlet concentration of NO and NO2 of 0.1ppmv, which corresponds to highly polluted urban air, was up to 75 and 50μmolm−2h−1, respectively, at the flow rate of 3000cm3min−1 and relative humidity of 50%. Further, even two years after their application to the surface of concrete walls along a busy thoroughfare, the photocatalytic coating maintained high effectivity.

Nanoflower-like Mg-doped MnOx for facile removal of low-concentration NOx at room temperature

Nanoflower-like Mg doped MnOx (Mg/MnOx) is synthesized via a facile and scalable redox reaction strategy for facile removal of low-concentration NOx at room temperature. The optimized sample Mg/MnOx exhibits good activity, giving 100% NO removal efficiency at room temperature for 10h under extremely high space velocity of 120,000mL−1g−1h−1 and low NO inlet concentration of 10ppm. The Mg/MnOx is found to gradually get inactive resulted from the generated NO2 and large amount of adsorbed NO covering active sites based on the results of characterizations and performance. Furthermore, the superior monolithic catalyst indicates great potential in actual application.

Nitrogen Oxide Removal from Simulated Flue Gas by UV-Irradiated Sodium Chlorite Solution in a Bench-Scale Scrubbing Reactor

Ultraviolet irradiated sodium chlorite (UV/NaClO2) solution was introduced to remove nitrogen oxide (NOx) 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 NOx removal efficiency. The ClO2 produced from photodecomposition of NaClO2 in aqueous solution substantially improved the NO absorption process. The NOx 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 NOx 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 NOx removal efficiency by UV/NaClO2 solution was higher than that by NaClO2 solution without UV pretreatment at a pH r...

Removal of elemental Mercury from flue gas using wheat straw chars modified by K2FeO4 reagent

ABSTRACTIn this article, wheat straw (WS) char, a common agricultural waste and renewable biomass, was pyrolyzed and then modified by K2FeO4 reagent to develop an efficient sorbent for removal of Hg0 from flue gas. Brunauer–Emmett–Teller, scanning electron microscopy with energy spectrum and X-ray diffraction (XRD) were employed to characterize the sorbents. The effects of K2FeO4 loading, reaction temperature, Hg0 inlet concentration and concentrations of gas mixtures O2, NO and SO2 in flue gas on Hg0 removal were investigated in a fixed-bed reactor. The results show that K2FeO4-impregnation can improve pore structure of WS char and produce new active sites, which significantly enhance Hg0 removal. Increasing Hg0 inlet concentration significantly decreases Hg0 removal efficiency. O2 in flue gas promotes Hg0 oxidation by replenishing the oxygen groups on the surface of modified chars. The presence of NO obviously promotes Hg0 removal since it can oxidize Hg0 to Hg(NO3)2. SO2 in flue gas significantly decreases Hg0 removal efficiency due to the competition adsorption between SO2 and Hg0. The increase in reaction temperature has a dual impact on Hg0 removal.

New Experimental Results of NO Removal from Simulated Flue Gas by Wet Scrubbing Using NaClO Solution

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, ...

Removal of nitric oxide from flue gas using sulfate/hydroxyl radicals from activation of oxone with cobalt and high temperature

A simple and efficient method for removing NO from flue gas using sulfate and hydroxyl free radicals from activation of Oxone with cobalt and high temperature has been developed. A comparison of NO removal efficiencies and the yields of sulfate and hydroxyl free radicals in several reaction systems were carried out. Co2+ concentration, Oxone concentration, solution pH, flue gas flow rate, stirring rate, solution temperature, and NO inlet concentration were evaluated as the key factors impacting on NO removal efficiency. The highest removal efficiency of 94.9% for NO was achieved under optimal conditions. The sulfate and hydroxyl radicals as the major reactive species which are responsible for removing NO were determined using ESR spectrometer. The NO is finally oxidized to nitric acid through a series of redox reactions. The chemical reaction mechanism of NO removal has also been proposed. These results prove the feasibility of this new NO removal technology. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1013–1021, 2017

Kinetic model for the reversible deactivation of a Pt/Al2O3 catalyst during NO oxidation

Microkinetic approach is used to develop a kinetic model for the reversible deactivation of a Pt/Al2O3 catalyst during NO oxidation. The model predicts the dependence of temperature on the transient evolution of NO conversion. Consistent with literature, it is shown that for low and high temperatures, it takes a few minutes to achieve steady state, whereas for intermediate temperatures (>130°C and <250°C), the time taken is of the order of a few hours. The model explains the inverse hysteresis phenomenon reported in the literature. In contrast to other works, the effect of NO2 as well as O2 on the catalyst deactivation is considered. The restoration of catalyst activity is explained by the reduction of Pt oxides by NO at low temperatures and the thermal decomposition of Pt oxides at high temperatures. The effect of inlet NO concentration, gas hourly space velocity, and temperature ramp rates on the light-off behavior is captured accurately by the model. The effect of gas composition during cooling, maximum temperature during heating, minimum temperature during cooling, and catalyst exposure to various gases at a fixed temperature on the NO oxidation activity in the subsequent runs is predicted. Consistent with the literature, the model predicts that cooling in the presence of N2 only can result in a significant restoration of the catalyst activity, provided that the catalyst has been exposed to high temperatures (>300°C) before the start of cooling. This has been attributed to the enhanced decomposition of Pt oxides at high temperatures. It is also shown that exposing the catalyst to NO at low temperatures for long time periods can result in a regain of the catalyst activity.

Preparation of porous carbon nanofibers with controllable pore structures for low-concentration NO removal at room temperature

Porous carbon nanofibers (PCNFs) with controllable pore structures for removing low-concentrations of NO at room temperature were prepared from electrospun polyacrylonitrile nanofibers by oxidative stabilization, carbonization and steam activation. The PCNFs had high surface areas and abundant micropores, which were favorable for the adsorption and catalytic oxidation of NO at ambient temperature. The diameter of the fibers and their pore structure were tailored by adjusting the concentrations of polyacrylonitrile, and the spinning and activation parameters. Their performance in the removal of low-concentration NO was strongly dependent on their pore structure and fiber diameter. The highest NO removal ratio for PCNFs activated at 900 °C, which had an average diameter of 175 nm, reached 29.7% when the inlet NO concentration was 20 ppm.