Initial NOx Concentration Research Articles

The synergistic effect of NOx and SO2 on the formation and light absorption of secondary organic aerosols from ο-xylene photooxidation

Both NOx and SO2 are important anthropogenic air pollutants that significantly affect secondary organic aerosols (SOA) formation. However, our understanding of the combined effects of NOx and SO2 on SOA formation is still insufficient. The concentrations, optical properties, and chemical compositions of SOA formed through ο-xylene photooxidation under various NOx concentrations were investigated with or without SO2 in the chamber. It was found that SOA mass concentration increased from 60 to 129 μg m−3 when the initial NOx concentration was increased from 0 to 900 ppb. The presence of 50 ppb SO2 not only enhanced ο-xylene SOA formation by 1.6–2.9 times, but also changed the evolution of SOA with NOx. The enhancement of ο-xylene SOA formation was primarily attributed to acid-catalyzed heterogeneous reactions initiated by nitric acid and sulfuric acid. However, SOA concentration decreased under 900 ppb NOx when SO2 was present, likely due to the decrease in sulfate production because of the competition between NOx and SO2 for ·OH. In addition, nitrogen-containing organic compounds (NOCs) concentrations and mass absorption coefficients (MACλ=365 nm) were promoted by both NOx and SO2. Our research indicates that the promotion of both NOCs formation by NOx, and oligomer formation by SO2 were the main reasons for the enhanced SOA light absorption. The present research provides a scientific basis for understanding the combined effects of both NOx and SO2 on ο-xylene SOA formation, and illustrates that the imbalanced reduction of anthropogenic air pollutants would lead to new characteristics in SOA pollution.

NOx degradation by cement mortar containing B-TiO2/MgAl-CLDH under visible light: Experimental and modeling

In this paper, an advanced photocatalyst, B-TiO2/MgAl-CLDH, was synthesized and applied in cement mortar. The photocatalytic NOx degradation ability of cement mortar containing B-TiO2/MgAl-CLDH under different initial NOx concentrations and flow rates was investigated. The results show that B-TiO2/MgAl-CLDH has stronger visible light absorption, lower recombination rate of electron-hole pairs and narrower optical band gap than commercial nano-TiO2 (P25), resulting in enhanced NOx removal efficiency. Specifically, the maximum NOx degradation ratio of B-TiO2/MgAl-CLDH is 23.4% within 30 min, which is about 5 times that of P25. For photocatalytic mortar, the initial NOx concentration (from 1.0 ppm to 2.0 ppm) and flow rate (from 1 L/min to 3 L/min) were positively correlated with NOx removal amount, while negatively correlated with NOx removal ratio. Based on the internal molecular diffusion properties of NOx, Langmuir-Hinshelwood and the power law kinetic models were used to predict the NOx degradation ability of photocatalytic mortar. The modeling of NOx degradation process presents a reliable prediction of the NOx removal ability of photocatalytic mortar, serving as a valuable tool for assessing the mortar’s NOx removal effectiveness for policymakers and engineers.

Effects of process variables for NO conversion by double-layered photocatalytic mortar with TiO2 nanoparticles

In this study, we prepared the double-layered photocatalytic mortar, where the top-layer has the minimum thickness of 2 mm. We investigated systematically the effects of various process variables (initial NOX concentration, TiO2 addition amount, UV-A radiation, gas flow rate and relative humidity) on photocatalytic conversion of NOX and also the transient NOX conversions for changing ambient conditions of process variables with time. The higher the nano-TiO2 concentration in the mortar or UV-A radiation intensity is, or the lower the NOX gas flow rate or relative humidity is, the higher the NOX conversion efficiency is. As the initial concentration of NOX increases, NOX conversion efficiency decreases, but the amount of NOX conversion increases. It is confirmed that the prepared photocatalytic mortar could convert NOX in the air efficiently for various conditions of process variables. NOX conversion efficiencies in transient environmental conditions were equivalent to those in fixed conditions for the same process variables. This study provides strong basic data to apply the photocatalytic mortar to convert NOX efficiently using solar energy without the use of extra energy and can be easily extended to future applications to infrastructures such as buildings, tunnels, or roads.

A novel method for removing NOx from simulated marine exhaust gas in wet absorption system using Na2SO3/THS composite solution

AbstractSince it is difficult to deal with high‐concentration nitrates in scrubbed wastewater onboard vessels, the application of traditional wet denitration technology is limited to some extent. Here a novel method for removing pre‐oxidized NOx by using Na2SO3/THS composite solution is proposed with the aim to obtain high NOx absorption efficiency and low nitrate concentration in scrubbed wastewater simultaneously. The effects of Na2SO3 concentration, THS concentration, NOx oxidation degree, coexistence of SO2 and O2 in flue gas, initial pH value and temperature of absorption solution on denitration performance were discussed in detail. The results showed Na2SO3 could reduce NOx to nitrate, nitrite, and N2. The addition of THS could promote NOx absorption greatly by forming complexes with SO32−. When initial NOx concentration was 1000 ppm with a NOx oxidation degree of 50%, O2 concentration was 8%, Na2SO3 and THS concentrations were 25 and 20 mmol/L, a NOx absorption efficiency of 87% could be achieved, while nitrate and nitrite concentrations were 32.97 and 14.19 mg/L, respectively.

Photocatalytic NOx mitigation under relevant conditions using carbon nanotube-modified titania

Although a majority of photocatalysts exhibit improved NO conversion to NO2, the performance in the oxidation of NO2, the more toxic form of NOx, to nitrate remains a challenge; in addition, the performance of hybrid photocatalysts under practical conditions is unclear. This study demonstrates the use of carbon nanotube-TiO2 (CNT-TiO2) photocatalyst films for effective transformation of NOx into nitrates. Using the objective figure of merit for NOx abatement, DeNOx index, the catalyst performance in a laminar-flow reactor was evaluated under simulated conditions that are relevant in abating NOx. The conditions probed include relative humidity (RH), initial NOx concentration, reactor geometry (headspace distance), and state of the catalyst (fresh vs. recycled). Our results reveal CNT-TiO2 significantly outperforms P25 despite exhibiting comparable NO conversion at low RH. P25 experiences a 66% reduction in DeNOx at high RH compared to low RH while CNT-TiO2 only incurs a 27% reduction. For recycled photocatalysts, this disparity becomes even more pronounced; CNT-TiO2 experiences a 49% reduction in DeNOx at high RH, whereas P25 experiences a 134% reduction. In addition, mass transfer from the bulk airflow limits NO conversion when the reactor headspace is too large (>3 mm), due to limited diffusion of NOx to the photocatalyst surface. Our findings highlight the importance of headspace distance, a parameter that has mostly been overlooked in reactor design for photocatalytic oxidation of NOx, but which dictates the optimal catalyst configuration for flue gas treatment. The remarkable DeNOx activity of CNT-TiO2 over a wide range of RH levels is rationalized based on the ratio of physisorbed-to-chemisorbed water on the photocatalyst surface.

Removal of NOx using electron beam process with NaOH spraying

Nitrogen oxides (NOx; NO and NO2) are major air pollutants and can cause harmful effects on the human body. Electron Beam Flue Gas Treatment (EBFGT) is a technology that generates electrons with an energy of 0.5–1 MeV using electron accelerators and effectively processes exhaust gases. In this study, NOx was removed using an electron beam accelerator with spraying additives (NaOH and NH4OH). NO and NO2 were 100% and more than 94% removed, respectively, at an electron beam absorbed dose of 20 kGy and an additive concentration of 0.02 M (mol/L). In most cases, NOx was removed better with lower initial NOx concentrations and higher electron beam absorbed doses. As the irradiation strength (mA) of the electron beam increases, the probability of electron impact on the material accordingly rises, which may lead to increase removal efficiency. The results of the present study show that the continuous electron beam process using additives achieved more effective removal efficiency than either individual process (wet-scrubbing or EB irradiation only).

Characterization of secondary products formed through oxidation of reduced sulfur compounds

Dimethylsulfide (DMS) and dimethyldisulfide (DMDS) are precursors to products, like sulfuric acid and methanesulfonic acid (MSA), which are important to secondary aerosol formation. The formation and yields of particulate MSA and sulfuric acid from the oxidation of reduced sulfur compounds is not well understood. In this study, a 37.5 cubic meter Teflon environmental chamber was utilized to study the oxidation mechanism and aerosol forming potential of DMS and DMDS under dry conditions. Experiments were conducted in both the presence and absence ofNOx, using hydroxyl radical, nitrate radical, as well O(P3) as an oxidant. With initial NOx concentrations of 100 part-per-billion, relatively low for laboratory oxidation experiments, O(P3) dominated oxidation of the reduced sulfur precursor and resulted in aerosol mass yields of greater than 40%. Hydroxyl radical oxidation of DMS and DMDS in the absence of NOx resulted in aerosol yields of 6% and 13%, respectively, while nitrate radical oxidation in the presence of NOx resulted in yields of 8% and less than 1%, respectively. Evidence of sulfuric acid formation was present during all particle-forming experiments, as was evidence of additional unknown sulfur-containing organic particulate. There was no evidence of MSA formation in the gas- or particle-phase throughout this study. The absence of MSA formation in the presence of NOx has not been reported in previous studies and indicates a lack of understanding of the MSA formation mechanism. The observations made during this chamber study diverge from observations made during previous studies conducted under high precursor and NOx concentrations, emphasizing the importance of atmospherically relevant initial conditions.

A prospective absorption system for marine NOx removal from simulated gas using Na2SO3/urea composite absorbents in bubble reactor

The large amount of NOx emitted from ships causes great harm to the environment and to health. Due to the strict regulations on NOx emission, it is urgent to develop a marine NOx absorption technology with efficient NOx removal and less nitrate residue in scrubber water. This paper proposed a novel composite Na2SO3/(NH2)2CO absorption system that could efficiently absorb NOx from ships. The NOx absorption process was studied in combination with a bubble reactor. Na2SO3 could react with NOx to convert the N into nitrite and N2, and (NH2)2CO could reduce the nitrate, nitrite, and NOx to N2. The main key parameters such as Na2SO3 concentration, (NH2)2CO concentration, SO2 concentration, oxygen concentration, NOx oxidation degree, initial NOx concentration, initial pH, and temperature were investigated experimentally. The Na2SO3 concentration had great effects on the NOx absorption efficiency. The nitrate concentration was significantly affected by the absorbents concentration, the NOx oxidation degree, the temperature, and the O2 concentration (0%–8%). Acid condition was not conducive to NOx absorption. A NOx absorption efficiency of 92.3%, a nitrate content of 13.1 mg/L, and the nitrite content of 21.3 mg/L were achieved under the optimal conditions in which, Na2SO3 was 0.25 mol/L, (NH2)2CO was 0.4 mol/L, SO2 was 700 ppm, NOx oxidation degree was 20%, initial NOx was 1000 ppm, and O2 was 12%. The Na2SO3/(NH2)2CO absorption system satisfied the regulations on NOx removal efficiency and nitrate concentration of scrubber water and therefore showed excellent application prospects on ships.

NOx Emission Reduction by Advanced Reburning in Grate-Rotary Kiln for the Iron Ore Pelletizing Production

The NOx reduction in the iron ore pelletizing process becomes an important environmental concern owing to its role in the formation of photochemical smog and acid rain. Thus, it is essential to develop new technologies for reducing NOx emissions in order to contribute to the cleaner production of pellets. In this paper, NOx reduction by advanced reburning ingrate-rotary kiln for oxidized pellet production was performed on a laboratory-scale gas kiln. Temperature and NH3/NOx molar ratio (NSR) were the key factors affecting the reduction of NOx. A better denitrification effect can be obtained on flus gas with higher initial NOx concentration, at temperature = 900 °C, NSR = 1.2, and reaction time exceeds one second. NOx reduction rate had reached 55–65% when the initial NOx concentration was above 400 ppm, and exceeds 70% when the initial NOx concentration was around 680 ppm. Urea solution has the best denitrification effect compared with NH3·H2O and NH4HCO3 solution. As for additives, the denitrification effect of the vanadium-titanium catalyst was better than that of ethanol and NaCl, while NaCl plays a promotive role at low NSR. Finally, a series of denitrification measures that include advanced reburning technology for achieving NOx ultra-low emission in the oxidation pellet production was proposed.

Prediction of voltage required for nonthermal plasma based diesel exhaust treatment for removal of nitrogen oxides.

A prior prediction of voltage required for the nonthermal plasma (NTP)-based diesel exhaust treatment toward removal of nitrogen oxides, i.e., NOX (sum of NO and NO2) would help the researchers to plan for the resources required for the treatment. In this present study, experimental data set of 4032 number of input-output pairs have been collected by taking flow rate (Fr), temperature (T), discharge gap (Dg), initial NOX concentration (NOXi), and NOX removal efficiency (ηr) as the 5 inputs and the voltage required for the treatment (Vrt) as the output. Then, an attempt has been made to predict Vrt for achieving particular ηr, while other input parameters have fixed values, using multivariable linear and quadratic polynomial regression techniques. The performances of these two predictive models have been assessed during training and testing. The root mean square error (RMSE) between experimental and predicted values of Vrt with both the models has been compared, where quadratic polynomial regression-based model has been found to be performing well with an RMSE of 0.85kV for a test data of 1210 sets. This study shows that the voltage required for the treatment, to achieve a particular amount of NOX removal from the exhaust, can be predicted with very good accuracy so that the necessary arrangements for the treatment can be made by the researchers.

Low temperature, medium temperature and high temperature performance of the continuous regenerative diesel particulate filter assisted by electric regeneration

A model is established to investigate low temperature (<300 °C), medium temperature (300–550 °C) and high temperature (>550 °C) performance of the continuous regenerative diesel particulate filter (CR-DPF) assisted by electric regeneration regarding to balance point temperature, regeneration speed and outlet temperature respectively and relevant influencing factors. Results show that inlet PM concentration and inlet flow rate are positively correlated to balance point temperature and vice versa for initial soot loading and intake NOX concentration. Increasing intake NOX concentration and flow rate increase rapid continuous regeneration speed. At low and medium temperatures, rapid thermal response tends to increase passive regeneration speed and the trend is more with decreasing wall thickness and channel density. In the high temperature range, outlet temperature increases and temperature gradients presented in the early stage of regeneration become steeper with decreasing channel density and wall thickness. However, “L/D” has limited impact on low, medium and high temperature performance.

Effects of NOx, SO2 and RH on the SOA formation from cyclohexene photooxidation

We performed a laboratory investigation of the secondary organic aerosol (SOA) formation from cyclohexene photooxidation with different initial NOx and SO2 concentrations at low and high relative humidity (RH). Both SOA yield and number concentration first increase drastically and then, decreased when the [VOC]0/[NOx]0 ratio changed from 30 to 10 and from 10 to 3. Though the presence of SO2 could increase the SOA number concentration, the SOA yield could only increase under [VOC]0/[NOx]0 = 10 and high RH, and [VOC]0/[NOx]0 = 3 and low RH experimental conditions, while decreasing under [VOC]0/[NOx]0 = 10 and low RH conditions. In the presence of SO2, the high RH and high NOx conditions were keys to efficient sulfate formation and could promote the SOA formation. The chemical composition of SOA was characterized using hybrid quadrupole-orbitrap mass spectrometer equipped with electrospray ionization (ESI-Q-Orbitrap-HRMS), and few organosulfates were identified. A visible enhancement of organosulfates and the formation of high molecular weight organic compounds were observed at high RH conditions, and this seemed to be the reason for the SOA yield increase at high RH.

Ozone and Secondary Organic Aerosol Formation of Toluene/NOx Irradiations under Complex Pollution Scenarios

Toluene is one of the most important precursor contributors to ozone and secondary organic aerosol (SOA), both of which greatly affect the air quality and human health. In this study, the effects of toluene on ozone and SOA formation were investigated in the presence of NOx in the CAPS-ZJU (Complex Air Pollution Study-Zhejiang University) smog chamber. Three comparison groups of experiments were conducted under the gas-phase environments of toluene/NOx, toluene/isoprene/NOx, and toluene/ethylene/NOx. The ozone concentration and physical properties of SOA such as mass concentration, aerosol yield, effective density, extinction and scattering were measured simultaneously. A toluene-dependent mechanism of ozone formation was found at ratios of toluene and NOx between 3.1 and 11.3 with the initial NOx concentration about 30 ppb. With further increase of the toluene concentration, the maximum value of ozone concentration remained almost stabilized. The maximum SOA yields decreased with increase of toluene, while the SOA effective density was concentrated at 1.3–1.4 g cm–3. The presence of isoprene or ethylene can promote the formation of ozone and SOA. The SOA nucleation was delayed under different initial toluene concentrations and the yield was reduced at the same mass concentration. A linear increase of extinction and scattering was observed with the increase of SOA mass concentration in both the toluene/isoprene/NOx and toluene/ethylene/NOx systems. A rapid increase of single scattering albedo reflects the process of SOA nucleation and growth. In addition, organic aerosol oxidation products tend to carboxylic acids in toluene/isoprene/NOx system according to Van Krevelen.

Characteristics of O3 Oxidation for Simultaneous Desulfurization and Denitration with Limestone–Gypsum Wet Scrubbing: Application in a Carbon Black Drying Kiln Furnace

The special process for producing carbon black precludes the application of traditional, mature flue-gas treatments (e.g., SNCR and SCR) to reduce NOx emissions. However, simultaneous removal of sulfur and nitrogen by the combination of ozone oxidation with limestone–gypsum wet scrubbing is suitable for the conditions found in carbon black flue gas. This article presents the first industrial-scale deployment of this technology in a 100000 t/year carbon black production line (flue-gas volume of 60000 Nm3/h). Optimizations were performed by studying the effectiveness of desulfurization and denitration for various operating parameters such as O3/NOx molar ratio, spray-tower liquid/gas ratio, initial NOx concentration, and forced oxidation. The results showed that (1) the O3/NOx molar ratio is the determining factor in denitration efficiency, (2) both forced oxidation and increasing initial NOx concentration improve the denitration efficiency but reduce the desulfurization efficiency, and (3) increasing the l...

Molecular characterization of brown carbon (BrC) chromophores in secondary organic aerosol generated from photo-oxidation of toluene.

Atmospheric brown carbon (BrC) is a significant contributor to light absorption and climate forcing. However, little is known about a fundamental relationship between the chemical composition of BrC and its optical properties. In this work, light-absorbing secondary organic aerosol (SOA) was generated in the PNNL chamber from toluene photo-oxidation in the presence of NOx (Tol-SOA). Molecular structures of BrC components were examined using nanospray desorption electrospray ionization (nano-DESI) and liquid chromatography (LC) combined with UV/Vis spectroscopy and electrospray ionization (ESI) high-resolution mass spectrometry (HRMS). The chemical composition of BrC chromophores and the light absorption properties of toluene SOA (Tol-SOA) depend strongly on the initial NOx concentration. Specifically, Tol-SOA generated under high-NOx conditions (defined here as initial NOx/toluene of 5/1) appears yellow and mass absorption coefficient of the bulk sample (MACbulk@365 nm = 0.78 m(2) g(-1)) is nearly 80 fold higher than that measured for the Tol-SOA sample generated under low-NOx conditions (NOx/toluene < 1/300). Fifteen compounds, most of which are nitrophenols, are identified as major BrC chromophores responsible for the enhanced light absorption of Tol-SOA material produced in the presence of NOx. The integrated absorbance of these fifteen chromophores accounts for 40-60% of the total light absorbance by Tol-SOA at wavelengths between 300 nm and 500 nm. The combination of tandem LC-UV/Vis-ESI/HRMS measurements provides an analytical platform for predictive understanding of light absorption properties by BrC and their relationship to the structure of individual chromophores. General trends in the UV/Vis absorption by plausible isomers of the BrC chromophores were evaluated using theoretical chemistry calculations. The molecular-level understanding of BrC chemistry is helpful for better understanding the evolution and behavior of light absorbing aerosols in the atmosphere.

Evaluation of NO&lt;sub&gt;X&lt;/sub&gt; Removal from Simulated Flue Gas by "Absorption-Oxidation-Reduction" Method

This paper presented a new method of absorption-oxidation-reduction which used ferrous sulfate solution as absorbent, oxygen as oxidizer and urea as reducer to remove NOX from flue gas based on the properties of Fe2+, NO, [Fe (NO)]2+ and urea. These properties included that Fe2+ and NO could produce [Fe (NO)]2+, furthermore [Fe (NO)]2+ was easy to be oxidized by O2, as well as urea can reduce HNO2 and HNO3 in the absorption liquid. This research was to discuss its absorption and removal mechanism with the influence of the initial urea concentration, pH value, initial NOX concentration and gas flow rate on the NOX removal efficiency. The results showed that the removal efficiency of NOX would increase when the initial concentration of urea and NOX increased, while the pH value and gas flow rate decreased.

Wavelength and NO&amp;lt;sub&amp;gt;x&amp;lt;/sub&amp;gt; dependent complex refractive index of SOAs generated from the photooxidation of toluene

Abstract. Recently, secondary organic aerosols (SOAs) generated from anthropogenic volatile organic compounds have been proposed as a possible source of light-absorbing organic compounds, "brown carbon," in the urban atmosphere. However, the atmospheric importance of these SOAs remains unclear due to limited information about their optical properties. In this study, the complex refractive index (RI, m = n-ki values at 405, 532, and 781 nm of the SOAs generated during the photooxidation of toluene (toluene-SOAs) under a variety of initial nitrogen oxide (NOx = NO + NO2) conditions were examined by photoacoustic spectroscopy (PAS) and cavity ring-down spectroscopy (CRDS). The complex RI-values obtained in the present study and reported in the literature indicate that the k-value, which represents the light absorption of the toluene-SOAs, increased to shorter wavelengths at &lt;532 nm, and the n-value also increased to shorter wavelengths from 781 to 355 nm. The k-values at 405 nm were found to increase from 0.0018 to 0.0072 with increasing initial NOx concentration from 109 to 571 ppbv. The nitrate to organics ratio of the SOAs determined using a high-resolution time-of-flight aerosol mass spectrometer (H-ToF-AMS) also increased with increasing initial NOx concentration. The RI-values of the SOAs generated during the photooxidation of 1,3,5-trimethylbenzene in the presence of NOx (1,3,5-TMB-SOAs) were also determined to investigate the influence of the chemical structure of the precursor on the optical properties of the SOAs, and it was found that the light absorption of the 1,3,5-TMB-SOAs is negligible at all of the wavelengths investigated (405, 532, and 781 nm). These results can be reasonably explained by the hypothesis that nitroaromatic compounds, such as nitrocresols, are the major contributors to the light absorption of the toluene-SOAs. Using the obtained RI-values, mass absorption cross sections of the toluene-SOAs at 405 nm were estimated to be 0.08–0.52 m2g−1 under typical conditions in an urban atmosphere during the daytime. These results indicate that light absorption by the SOAs potentially contributes to the radiation balance at ultraviolet wavelengths below ~400 nm, specifically when the mass concentrations of the anthropogenic SOAs are significant compared with other light-absorbing particles.

Pilot-scale studies on NOx removal from flue gas via NO ozonation and absorption into NaOH solution

Abstract The paper presents results of experimental studies on removal of NOx from flue gas via NO ozonation and wet scrubbing of products of NO oxidation in NaOH solutions. The experiment was conducted in a pilot plant installation supplied with flue gas from a coal-fired boiler at the flow rate 200 m3/h. The initial mole fraction of NOx,ref in flue gas was approx. 220 ppm, the molar ratio X = O3/NOref varied between 0 and 2.5. Ozone (O3 content 1÷5% in oxygen) was injected into the flue gas channel before the wet scrubber. The effect of the mole ratio X, the NaOH concentration in the absorbent, the liquid-to-gas ratio (L/G) and the initial NOx concentration on the efficiency of NOx removal was examined. Two domains of the molar ratio X were distinguished in which denitrification was governed by different mechanisms: for X ≤ 1.0 oxidation of NO to NO2 predominates with slow absorption of NO2, for X &gt;&gt; 1.0 NO2 undergoes further oxidation to higher oxides being efficiently absorbed in the scrubber. At the stoichiometric conditions (X = 1) the effectiveness of NO oxidation was better than 90%. However, the effectiveness of NOx removal reached only 25%. When ozonation was intensified (X ≥ 2.25) about 95% of NOx was removed from flue gas. The concentration of sodium hydroxide in the aqueous solution and the liquid-to-gas ratio in the absorber had little effect on the effectiveness of NOx removal for X &gt; 2.

Experimental and Kinetic Study of the Effect of Additives on the Ammonia Based SNCR Process in Low Temperature Conditions

An experimental and kinetic study of the influence of additives on the selective noncatalytic reduction (SNCR) process is presented. Experiments were performed on a lab-scale reactor suitable to investigate the influence of important operating parameters (flue gas temperature, residence time, amount of reducing agent, initial NOx concentration, etc.) on the SNCR efficiency. Several chemical compounds such as CH4, C2H6, C2H4, C2H2, CH3OH, C2H5OH, and CO, which are usually used in the literature as additives for the SNCR process, have been evaluated. The experimental results prove that the use of such additives allows the NO reduction process to be more efficient at lower temperatures. Furthermore, they induce a downward shift up to more than 100 K of the optimal temperature window for the reduction process. Four detailed kinetic mechanisms available in the literature have been tested to model our experimental results. The one that presents the better agreement between experiment and modeling has been optimized to explain the kinetic influence of the additives on the classical SNCR process. The main reaction pathways involved have been pointed out, illustrating the important role of OH radical.

Microwave Effect in the Simultaneous Removal of NOx and SO2 under Electron Beam Irradiation and Kinetic Investigation of NOx Removal Rate

NOx and SO2 were removed from an air mixture in a flow process combining electron beam (EB) irradiation with microwave (MW) irradiation in order to improve the NOx removal efficiency. The addition of the MW irradiation considerably decreased the required EB doses compared to a single EB irradiation: for 80% removal efficiency the removal rate was increased by 21.1% to above 117.4% at initial NOx concentrations ranging from 250 to 1000 ppm. The increased NOx removal efficiency due to the MW irradiation addition was attributed to an intrinsic kinetic rather than a thermal effect. The removal process of SO2 and NOx with a stoichiometric ratio (M) addition of NH3 showed high removal efficiencies, as they were converted into main final products of NH4NO3 and (NH4)2SO4. The rate form of NOx removal (−rNOx = k[NOx][NH3][R•]) in the simultaneous removal of SO2 and NOx could be converted to a second-order rate according to the EB dose, instead of the irradiation time, and linear testing of this rate form with experimental data showed a good correlation, depending on the M value. The amount of NOx removed in the simultaneous removal of SO2 and NOx exhibited the following linear correlation: ΔC = k[NOx]o + ko with k = aDm + b and ko/Dn = aD + b.