NOx In Flue Gas Research Articles

Nitrosamines and Nitramines in Amine-Based Carbon Dioxide Capture Systems: Fundamentals, Engineering Implications, and Knowledge Gaps.

Amine-based absorption is the primary contender for postcombustion CO2 capture from fossil fuel-fired power plants. However, significant concerns have arisen regarding the formation and emission of toxic nitrosamine and nitramine byproducts from amine-based systems. This paper reviews the current knowledge regarding these byproducts in CO2 capture systems. In the absorber, flue gas NOx drives nitrosamine and nitramine formation after its dissolution into the amine solvent. The reaction mechanisms are reviewed based on CO2 capture literature as well as biological and atmospheric chemistry studies. In the desorber, nitrosamines are formed under high temperatures by amines reacting with nitrite (a hydrolysis product of NOx), but they can also thermally decompose following pseudo-first order kinetics. The effects of amine structure, primarily amine order, on nitrosamine formation and the corresponding mechanisms are discussed. Washwater units, although intended to control emissions from the absorber, can contribute to additional nitrosamine formation when accumulated amines react with residual NOx. Nitramines are much less studied than nitrosamines in CO2 capture systems. Mitigation strategies based on the reaction mechanisms in each unit of the CO2 capture systems are reviewed. Lastly, we highlight research needs in clarifying reaction mechanisms, developing analytical methods for both liquid and gas phases, and integrating different units to quantitatively predict the accumulation and emission of nitrosamines and nitramines.

Basic rules of NO oxidation by Fe2+/H2O2/AA directional decomposition system

AbstractBasic rules of NO oxidation by a Fe2+/H2O2/AA directional decomposition system were researched based on the technical background of flue gas NOx removal. Effects of gas‐liquid interfacial area, main gas, and solution parameters on NO oxidation efficiency (η) were analyzed. The results showed that adequate contact area was the precondition for high η by a Fe2+/H2O2/AA system. η decreased with the increase in NO concentration, which illustrated that this method would be efficient in oxidizing NO at a low concentration. η tended to decrease linearly with the growth in gas flow, however, the NO oxidation rate (v) rose with the increase in NO concentration and gas flow. η increased with the initial concentrations of H2O2 and Fe2+, but the amplitude decreased. Controlling the initial concentrations of H2O2 and Fe2+ to achieve reasonable synergies between generation rate and consumption rate of ·OH could weaken the invalid consumption of reactants. η increased with the increase in temperature in the range 30–60 °C, but it nearly did not change with temperature after 60 °C. This oxidation technology and the traditional wet flue gas desulphurization technology exhibited temperature synergy. Under typical pH of wet desulphurization, η and H2O2 consumption rate did not change obviously.

Performance analysis of a steady flamelet model for the use in small-scale biomass combustion under extreme air-staged conditions

Small-scale biomass boiler development is often based on empirical methods resulting in high efforts for experimental test runs using several prototypes. CFD simulations are able to reduce both, development time and efforts for tests and prototypes, supposing that the models reliability is high and its computational effort is low. Extreme air-staging with an initial gasification stage and a subsequent fuel gas burnout in a downstream gas-burner is a promising new method to reduce NOX and PM emissions in small-scale biomass boilers. Gasification conditions in the first combustion stage lead to high accumulation of gaseous tars in the fuel gas contributing challenges for combustion simulation because common CFD models use 2 or 3-step global methane reaction schemes to describe combustion chemistry. In this work, the performance of a computationally inexpensive steady flamelet model (SFM) together with a detailed reaction mechanism (18 species, 42 reactions) was scrutinized. In order to evaluate the performance of the SFM, two furnace designs were examined, running under different load shifts and various excess air ratio. Comparative numerical simulations were performed with classical species transport models. The numerical simulations and the experiments for validation were carried out on a wood-chip boiler with a heat output of 40 kW. Results show that flue gas temperature, flame shape, main flue gas concentrations and NOX can be quantitatively predicted. The SFM shows also reasonable good predictions for CO variation trends. With the present approach, calculation time can be reduced by 90% compared to commonly used models (EDC). The SFM provides sufficiently accurate results within 24 h using a standard processor consisting of six cores (mesh size 1.5 million elements). Thus, the presented model is a perfectly suitable method for applied science and industrial research.

Reduction of NOx in fluid catalytic cracking flue gas over Mg-Al spinel modified with transition metal oxides

ABSTRACTMg-Al spinel modification with transition metal oxides of CuO, Mn2O3, and Fe2O3 was prepared to catalyze the NO+CO reaction for the DeNOx of fluid catalytic cracking flue gas. Mg-Al spinel modification with CuO showed the best catalytic performance for the easy adsorption of CO on CuO. The Cu+ in amorphous state of the catalyst surface was contributed for the main adsorption site of CO from the characterization results by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy technology. The additive amount of CuO was optimized to 4%, and the excess CuO sintered and converted to crystal phase.

The Acceptor Side of Photosystem II Is the Initial Target of Nitrite Stress in Synechocystis sp. Strain PCC 6803.

Nitrite, a common form of inorganic nitrogen (N), can be used as a nitrogen source through N assimilation. However, high levels of nitrite depress photosynthesis in various organisms. In this study, we investigated which components of the photosynthetic electron transfer chain are targeted by nitrite stress in Synechocystis sp. strain PCC 6803 cells. Measurements of whole-chain and photosystem II (PSII)-mediated electron transport activities revealed that high levels of nitrite primarily impair electron flow in PSII. Changes in PSII activity in response to nitrite stress occurred in two distinct phases. During the first phase, which occurred in the first 3 h of nitrite treatment, electron transfer from the primary quinone acceptor (QA) to the secondary quinone acceptor (QB) was retarded, as indicated by chlorophyll (Chl) a fluorescence induction, S-state distribution, and QA- reoxidation tests. In the second phase, which occurred after 6 h of nitrite exposure, the reaction center was inactivated and the donor side of photosystem II was inhibited, as revealed by changes in Chl fluorescence parameters and thermoluminescence and by immunoblot analysis. Our data suggest that nitrite stress is highly damaging to PSII and disrupts PSII activity by a stepwise mechanism in which the acceptor side is the initial target. IMPORTANCE In our previous studies, an alga-based technology was proposed to fix the large amounts of nitrite that are released from NOX-rich flue gases and proved to be a promising industrial strategy for flue gas NOX bioremediation (W. Chen et al., Environ Sci Technol 50:1620-1627, 2016, https://doi.org/10.1021/acs.est.5b04696; X. Zhang et al., Environ Sci Technol 48:10497-10504, 2014, https://doi.org/10.1021/es5013824). However, the toxic effects of high concentrations of nitrite on algal cells remain obscure. The analysis of growth rates, photochemistry, and protein profiles in our study provides important evidence that the inhibition by nitrite occurs in two phases: in the first phase, electron transfer between QA- and QB is retarded, whereas in the second, the donor side of PSII is affected. This is an excellent example of investigating the "early" inhibitory effects (i.e., within the first 6 h) on the PSII electron transfer chain in vivo This paper provides novel insights into the mechanisms of nitrite inhibition of photosynthesis in an oxygenic phototrophic cyanobacterium.

Emissions and Power Losses due to Biofuel or Biomass Nitrogen: Assessment and Prevention Mechanisms

The impact of nitrogen contained in biofuels and biomass on combustor/boiler performance (throughput and power) is assessed. It is shown that, at 40% excess air, throughput may decrease by more than 6% and power may decrease by ∼5%. Higher feed rates of nitrogen-rich constituents (paper, wood, textiles, tires, leather, biosludge, biomass, animal byproducts) imply higher throughput and power losses. Losses increase with rising conversion factors of fuel-nitrogen to NOx and with excess air (EA). Flue gas NOx flow rates increase almost proportionally to the conversion factor. However, offgas NOx emission rates may increase faster, because of lower residence times and removal efficiencies in the air pollution control system resulting from higher offgas flow rates. Compensation mechanisms are quantified, including manipulation of EA, flue gas recirculation (FGR), and flue gas heat recovery (FHR), independently from FGR and oxygen enrichment (OXE). Offgas NOx emission rates still increase faster than flue gas r...

A simulated rotary reactor for NOx reduction by carbon monoxide over Fe/ZSM-5 catalysts

Carbon monoxide could be used to reduce NOx to N2 over zeolite catalysts. But the NOx reduction efficiency is highly inhibited by oxygen present in the flue gas. In this research, a rotary reactor was proposed for the treatment of NOx in oxygen-rich flue gases. In the proposed rotary reactor, an adsorption zone and a reduction zone were configured in such a way that the flue gas stream, containing NOx and oxygen, and the reducing gas stream, containing CO, are introduced into the reactor separately. Loaded catalysts were rotated between the two zones to adsorb NOx from the flue gas in the adsorption zone and then reduce the adsorbed NOx by CO in the reduction zone. The performance of the rotary reactor was investigated in a fixed bed reactor loaded with Fe/ZSM-5 catalysts synthesized in the lab, and the dynamic adsorption-reduction process was simulated by switching the inlet gas stream. The results showed that the simulated rotary reactor could well remove and reduce NOx from oxygen containing flue gases. NOx removal efficiencies were very stable in the investigated temperature range, i.e., 250–400°C. Higher CO concentration could significantly enhance both NOx removal and reduction efficiencies. The amount of CO slipping into the adsorption zone was very low even though CO is in great excess. In order to explore the reaction mechanism, in situ DRIFT study was performed. It was found that CO could occupy the active Fe sites, promoting NOx desorption and the subsequence NOx removal in the adsorption stage. But the active intermediates for NOx reduction is not effectively formed during CO purging, resulting in a lower NOx reduction efficiency.

Influences of SO2, NO, and CO2 Exposure on Pore Morphology of Various Rank Coals: Implications for Coal-Fired Flue Gas Sequestration in Deep Coal Seams

Carbon dioxide (CO2) sequestration in deep coal seams with enhanced coal-bed methane recovery is a promising way to store the main anthropogenic greenhouse gas, CO2, in geologic time. Recently, injection of CO2 mixed with coal-fired flue gas components, i.e., SO2 and NOx, into coal seams has gained attention because it offers great advantages in reducing the cost of CO2 capture, flue gas desulfuration, and denitration. As a preliminary investigation on the feasibility of coal-fired flue gas sequestration in deep coal seams, the influences of SO2, NO, and CO2 exposures on the pore morphology of various rank coals are addressed in this work. Considering the optimum coal reservoir conditions for flue gas sequestration, the interaction of CO2 with coals was studied at a temperature of 45 °C and a pressure of 12 MPa. The results show that both CO2 exposure and SO2 exposure lead to decreases in both the specific surface area and pore volume of micropores of various rank coals. The micropore morphology of both H...

NH3 selective catalytic reduction of NO: A large surface TiO2 support and its promotion of V2O5 dispersion on the prepared catalyst

A titania support with a large surface area was developed, which has a BET surface area of 380.5 m2/g, four times that of a traditional titania support. The support was ultrasonically impregnated with 5 wt% vanadia. A special heat treatment was used in the calcination to maintain the large surface area and high dispersion of vanadium species. This catalyst was compared to a common V2O5-TiO2 catalyst with the same vanadia loading prepared by a traditional method. The new catalyst has a surface area of 117.7 m2/g, which was 38% higher than the traditional V2O5-TiO2 catalyst. The selective catalytic reduction (SCR) performance demonstrated that the new catalyst had a wider temperature window and better N2 selectivity compared to the traditional one. The NO conversion was >80% from 200 to 450 °C. The temperature window was 100 °C wider than the traditional catalyst. Raman spectra indicated that the vanadium species formed more V-O-V linkages on the catalyst prepared by the traditional method. The amount of V-O-Ti and V=O was larger for the new catalyst. Temperature programmed desorption of NH3, temperature programmed reduction by H2 and X-ray photoelectron spectroscopy results showed that its redox ability and total acidity were enhanced. The results are helpful for developing a more efficient SCR catalyst for the removal of NOx in flue gases.

Novel effect of SO2 on selective catalytic oxidation of slip ammonia from coal-fired flue gas over IrO2 modified Ce–Zr solid solution and the mechanism investigation

The slip ammonia from selective catalytic reduction (SCR) of NOx in coal-fired flue gas can cause degeneration of the utilities and environmental issues like aerosol. To achieve selective catalytic oxidation (SCO) of slip ammonia to N2, novel IrO2 modified Ce–Zr solid solution catalysts were synthesized and tested under various conditions. It was found that IrO2/Ce0.6Zr0.4O2 (PVP) catalyst displayed outstanding catalytic activity for slip ammonia and the removal efficiency was higher than 98%. Interestingly, the effect of SO2 on NH3 oxidation was bifacial, which the presence of SO2 could result in slight deactivation of catalyst but also improve the N2 selectivity of oxidized products to as high as 100% with coexistence of SO2 and NH3. The mechanism of NH3-SCO process over IrO2/Ce0.6Zr0.4O2 (PVP) was evaluated through various techniques, and the results demonstrated that NH3 oxidation could follow both NH mechanism and internal SCR (iSCR) mechanism at different temperature regions. And the dominant pathway is the iSCR mechanism, in which adsorbed ammonia is firstly activated and reacts with oxygen atoms to form the HNO intermediate. Then, the HNO could be oxidized with atomic oxygen from O2 to form NO species. Meanwhile, the formed/adsorbed NO could interact with NH2 to N2 with N2O as by-product, and the presence of SO2 can effectively inhibit the production of N2O and NO. Also, the mechanism of SO2 effects was also evaluated and determined reasonably.

Influence of Dissolved Metals on N-Nitrosamine Formation under Amine-based CO2 Capture Conditions.

As the prime contender for postcombustion CO2 capture technology, amine-based scrubbing has to address the concerns over the formation of potentially carcinogenic N-nitrosamine byproducts from reactions between flue gas NOx and amine solvents. This bench-scale study evaluated the influence of dissolved metals on the potential to form total N-nitrosamines in the solvent within the absorber unit and upon a pressure-cooker treatment that mimics desorber conditions. Among six transition metals tested for the benchmark solvent monoethanolamine (MEA), dissolved Cu promoted total N-nitrosamine formation in the absorber unit at concentrations permitted in drinking water, but not the desorber unit. The Cu effect increased with oxygen concentration. Variation of the amine structural characteristics (amine order, steric hindrance, -OH group substitution and alkyl chain length) indicated that Cu promotes N-nitrosamine formation from primary amines with hydroxyl or carboxyl groups (amino acids), but not from secondary amines, tertiary amines, sterically hindered primary amines, or amines without oxygenated groups. Ethylenediaminetetraacetate (EDTA) suppressed the Cu effect. The results suggested that the catalytic effect of Cu may be associated with the oxidative degradation of primary amines in the absorber unit, a process known to produce a wide spectrum of secondary amine products that are more readily nitrosatable than the pristine primary amines, and that can form stable N-nitrosamines. This study highlighted an intriguing linkage between amine degradation (operational cost) and N-nitrosamine formation (health hazards), all of which are challenges for commercial-scale CO2 capture technology.

Room temperature efficient reduction of NOx by H2 in a permeable compounded membrane – Catalytic reactor

A permeable compounded membrane-catalytic reactor is proposed and evaluated to remove NOx in simulated flue gas by H2. The flue gas denitrification could be achieved at room temperature spontaneously without extra energy input. In the reactor, the reducing agent H2 is recycled and separated from the simulated flue gas containing NO by a compounded membrane embedded with Pt–C catalyst, through which only H2 could permeate to efficiently reduce NO. The relevant experimental data show that the NO removal could reach close to 100% at room temperature with the influent concentration from 218ppm to 985ppm, with a very short residence time of 0.09s. The transmission electron microscopy (TEM) illustrates that the Pt nanoparticles are uniformly dispersed on carbon as cluster. The prepared Pt–C catalyst is described by Raman spectra, and further electron transfer from Pt to substrate carbon is observed via X-ray photoelectron spectroscopy (XPS). It is proved via both experimental data and DFT calculations that the electronic structure of Pt is modified due to the strong interaction between Pt and carbon in the prepared catalyst, at the same time, the high surface area of carbon ensures efficient capture NO and H2, which gives rise to synergetic chemical coupling effect accounting for the surprisingly performance of Pt/C catalyst coated on carbon paper. The effects of the operating parameters on the removal for the proposed reactor, such as the residence time, initial NO concentration, and NO:H2 flow rate ratio, are also analyzed.

Controlling Nitrosamines, Nitramines, and Amines in Amine-Based CO2 Capture Systems with Continuous Ultraviolet and Ozone Treatment of Washwater

Formation of nitrosamines and nitramines from reactions between flue gas NOx and the amines used in CO2 capture units has arisen as a significant concern. Washwater scrubbers can capture nitrosamines and nitramines. They can also capture amines, preventing formation of nitrosamines and nitramines downwind by amine reactions with ambient NOx. The continuous application of UV alone, or a combination of UV and ozone to the return line of a washwater treatment unit was evaluated to control the accumulation of nitrosamines, nitramines and amines in a laboratory-scale washwater unit. With model secondary amine solvents ranging from nonvolatile diethanolamine to volatile morpholine, application of 272-537 mJ/cm(2) UV incident fluence alone reduced the accumulation of nitrosamines and nitramines by approximately an order of magnitude. Modeling indicated that the gains achieved by UV treatment should increase over time, because UV treatment converts the time dependence of nitrosamine accumulation from a quadratic to a linear function. Ozone (21 mg/L) maintained low steady-state concentrations of amines in the washwater. While modeling indicated that more than 80% of nitrosamine accumulation in the washwater was associated with reaction of washwater amines with residual NOx, a reduction in nitrosamine accumulation rates due to ozone oxidation of amines was not fully realized because the ozonation products of amines reduced nitrosamine photolysis rates by competing for photons.

Simultaneous Absorption of NOx and SO2 Using Magnesia Slurry Combined with Ozone Oxidation

To achieve simultaneous removal of NOx and SO2 in flue gas, an effective technology combined with ozone oxidation was explored in this paper. The simulated flue gas was initially oxidized by ozone (O3), turning NO into NO2 or N2O5, and then absorbed by alkaline slurries to achieve simultaneous removal of NOx and SO2. It was found that the MgO slurry was a suitable absorbent for the simultaneous removal of NOx and SO2. The operating parameters, such as the pH of the liquid phase, initial SO2 concentration, and MgO concentration, were investigated for the NO2 removal efficiency of the MgO slurry, where the optimal NO2 removal efficiency (at ca. 75%) was obtained with the pH value at 6.5 and the MgO concentration at 0.02 mol/L. In the case of N2O5, the absorption efficiency of the MgO slurry was maintained at a high level because of the rapid reaction between N2O5 and H2O. Furthermore, it was noted that the absorption efficiency of SO2 could be at a high level (i.e., approaching 100%) when the pH of the MgO ...

Effects of the outer secondary air cone length on the combustion characteristics and NOx emissions of the swirl burner in a 0.5 MW pilot-scale facility during air-staged combustion

Cold air experiments using a centrally fuel-rich pulverized-coal swirl burner model were performed within a laboratory-scale facility to study the effects of the outer secondary air cone length on the aerodynamic fields. The divergent angle of the air jet and the size of the central recirculation zone were found to increase with increasing outer secondary air cone lengths. The 0.5 MW pilot-scale facility was also used to optimize the length of the outer secondary air cone by measuring the flue gas temperature, and O2, CO and NOx concentrations, at different cone lengths. As the cone length was varied from 0 to 49 mm, the NOx emissions rapidly fell from 778 to 458 mg/m3 (O2 6%), while the unburned carbon content in the fly ash decreased from 5.83% to 3.51%, and CO concentration decreased from 1355 mg/m3 (O2 6%) to 99 mg/m3 (O2 6%). Based on these results, the optimum length of the outer secondary air cone was determined to be 49 mm.

Simultaneous suppression of PCDD/F and NOx during municipal solid waste incineration

Thiourea was tested as a dioxins inhibitor in a full-scale municipal solid waste incinerator with high capacity (34th−1). The suppressant, featuring a high S- and N-content, was converted into liquor and then injected (35kgh−1) into the furnace (850°C) through the inlets already used for Selective Non-Catalytic Reduction (SNCR) of flue gas NOx. The first results show that thiourea reduces the dioxins in flue gas by 55.8wt.%, those in fly ash by 90.3wt.% and the total dioxins emission factor by 91.0wt.%. The concentration of PCDD/Fs was 0.08ngTEQNm−3, below the national standard of 0.1ngTEQNm−3. The weight average chlorination degree of dioxins decreases slightly after adding the inhibitor, indicating that it suppresses both the formation and the chlorination of dioxins. Analysis of fly ash by scanning electron microscope (SEM) suggests that the particle size becomes larger after adding the inhibitor. Further analysis using an energy dispersive spectrometer (EDS) reveals that the sulphur content in fly ash rises, but the chlorine content declines when adding thiourea. These results suggest that poisoning the metal catalyst and blocking the chlorination are probably responsible for suppression. NOx reduction attains 42.6wt.%. These tests are paving the way for further industrial application and assist in controlling the future emissions of dioxins and NOx from MSWI.

Recycle Sewage Sludge Char as Flue Gas De-NOx Catalyst within Low Temperature Ranges

Sewage sludge chars produced at four different pyrolysis temperatures (550, 650, 750 and 800oC) were investigated to check their CO and SO2 emissions in a hot flue gas flow; and then their catalyst effect on De-NOx process with hydrazine hydrate as reductant was studied. It was found that the chars produced at 750 and 800 oC were highly temperature- and oxidant-resistant and their CO emissions were considerably inhibited in the temperature range of 100 to 400 oC with oxygen level of 5∼10%, at the same time, De-NOx efficiencies were increased by 25% to 50%, suggesting those chars are proper De-NOx catalysts. Chars obtained at pyrolysis temperatures of 650, 750 and 800 oC were also checked their possibilities for absorbing NOx in flue gas, and it was found that they can achieve 20%∼30% of De-NOx efficiency by adsorption within a temperature range of 100∼250 oC at oxygen level around 8%. When hydrazine hydrate was used as a reducing agent together with char catalysts, the De-NOx efficiency was greatly affected by O2 pressure and lower O2 is benefit for the improving De-NOx efficiency. Moreover, it was found that char obtained at 750 oC had the best ability to remove NOx both as an absorbent and as a catalyst.

Mechanism of the selective catalytic oxidation of slip ammonia over Ru-modified Ce-Zr complexes determined by in situ diffuse reflectance infrared Fourier transform spectroscopy.

The slip ammonia from selective catalytic reduction (SCR) of NOx in coal-fired flue gas can result in deterioration of the utilities or even the environmental issues. To achieve selective catalytic oxidation (SCO) of slip ammonia, Ru-modified Ce-Zr solid solution catalysts were prepared and evaluated under various conditions. It was found that the Ru/Ce(0.6)Zr(0.4)O2(polyvinylpyrrolidone (PVP)) catalyst displayed significant catalytic activity and the slip ammonia was almost completely removed with the coexistence of NOx and SO2. Interestingly, the effect of SO2 on NH3 oxidation was bifacial, and the N2 selectivity of the resulting products was as high as 100% in the presence of SO2 and NH3. The mechanism of the SCO of NH3 over Ru/Ce(0.6)Zr(0.4)O2(PVP) was studied using various techniques, and the results showed that NH3 oxidation follows an internal SCR (iSCR) mechanism. The adsorbed ammonia was first activated and reacted with lattice oxygen atoms to form an -HNO intermediate. Then, the -HNO mainly reacted with atomic oxygen from O2 to form NO. Meanwhile, the formed NO interacted with -NH2 to N2 with N2O as the byproduct, but the presence of SO2 can effectively inhibit the production of N2O.

Effects of flue gas compositions on nitrosamine and nitramine formation in postcombustion CO2 capture systems.

Amine-based technologies are emerging as the prime contender for postcombustion CO2 capture. However, concerns have arisen over the health impacts of amine-based CO2 capture associated with the release of nitrosamines and nitramines, which are byproducts from the reactions between flue gas NOx and solvent amines. In this study, flue gas compositions were systematically varied to evaluate their effects on the formation of nitrosamines and nitramines in a lab-scale CO2 capture reactor with morpholine as a model solvent amine. The accumulation of N-nitrosomorpholine in both the absorber and washwater increased linearly with both NO and NO2 for concentrations up to ∼20 ppmv. These correlations could be extrapolated to estimate N-nitrosomorpholine accumulation at extremely low NOx levels (0.3 ppmv NO2 and 1.5 ppmv NO). NO played a particularly important role in driving N-nitrosomorpholine formation in the washwater, likely following partial oxidation to NO2 by O2. The accumulation of N-nitromorpholine in both the absorber and washwater positively correlated with flue gas NO2 concentration, but not with NO concentration. Both N-nitrosomorpholine and N-nitromorpholine accumulated fastest in the absence of CO2. Flue gas humidity did not affect nitrosamine accumulation in either the absorber or the washwater unit. These results provide a basis for estimating the effects of flue gas composition on nitrosamine and nitramine accumulation in postcombustion CO2 capture systems.

Mechanisms and reaction pathways for simultaneous oxidation of NOx and SO2 by ozone determined by in situ IR measurements

Ozone (O3) oxidation combined with wet scrubbing is a promising method for the simultaneous removal of SO2 and NOx in flue gas. In this study, the O3 oxidation processes of NO and SO2, as well as their coexistence, were investigated using an in situ IR spectrometer. Experimental results showed that the O3 concentration and the reaction temperature played critical roles in the O3 oxidation process of NO. Around 80°C, when inlet molar ratio of O3/NO was less than 1, NO was mainly oxidized to NO2, while when the ratio was greater than 1, NO would be further oxidized to NO3, N2O5, and HNO3. NO3 was the key intermediate product for the formation of N2O5 and HNO3. However, the subsequent reactions of NO3 were temperature dependence. With the increase of reaction temperature above 100°C, the concentration of NO2 increased whereas the concentrations of N2O5 and HNO3 decreased. The oxidation of SO2 by O3 was negligible and SO2 had little influence on the oxidation of NO in the simultaneous oxidation of NO and SO2. Finally, based on the in situ IR results, the oxidation mechanism is discussed and the reaction pathways are proposed.