DeNOx Process Research Articles

The Rôle of Iron in Zeolite Beta for deNOx Catalysis

Selective catalytic reduction with ammonia (NH3-SCR) is a widely used deNOx process, employing zeolitic catalysts. Here, we examine framework substituted and extra-framework exchanged transition metal zeolite catalysts, in the extensively studied Fe – zeolite Beta focusing on the influence of the transition metal cation on the NH3-SCR reaction, and aiming to unravel the underlying mechanisms and their impact on catalytic performance. We use hybrid multiscale density functional theory (DFT)/molecular mechanics to investigate the NH3-SCR at various Fe-BEA active sites including systems with both framework and extra-framework Fe cations. The catalytically active sites under investigation include Fe-FeF-BEA, Fe-AlF-BEA, and Cu-FeF-BEA, (where the subscript F indicates framework species) on which the formation and consumption of key intermediates of both oxidation and reduction half cycles species are analysed. We show the distinctive ability of framework Fe sites to promote the formation of key nitrate and nitrosamine intermediates. Furthermore, we find a strong binding affinity of NH3 with framework Fe systems including Cu(II)-FeF-BEA, Fe(III)-FeF-BEA, and H-FeF-BEA compared to framework Al systems (Fe(III)-AlF-BEA). We explore the reduction potential of the framework Fe3+/Fe2+ in BEA zeolite and establish its feasibility in the presence of a Brønsted acid site. Our calculations clearly predict the bimetallic Cu-FeF system to be the best catalyst which supports a recent experimental report by Yue et al. (Chem. Eng. J. 2020, 398, 125515) for a related FeCu-SSZ-13 (CHA) zeolite. We provide a new understanding of the reactivity of Fe-BEA zeolites, suggesting the advantages of framework Fe over Al sites in NH3-SCR reactions, and establishing a foundation for interpretation of the rôle of framework cations in metal-exchanged zeolites.

Numerical Study on Optimization of Combustion Cycle Parameters and Exhaust Gas Emissions in Marine Dual-Fuel Engines by Adjusting Ammonia Injection Phases

Decarbonizing maritime transport hinges on transitioning oil-fueled ships (98.4% of the fleet) to renewable and low-carbon fuel types. This shift is crucial for meeting the greenhouse gas (GHG) reduction targets set by the IMO and the EU, with the aim of achieving climate neutrality by 2050. Ammonia, which does not contain carbon atoms that generate CO2, is considered one of the effective solutions for decarbonization in the medium and long term. However, the concurrent increase in nitrogen oxide (NOx) emissions during the ammonia combustion cycle, subject to strict regulation by the MARPOL 73/78 convention, necessitates implementing solutions to reduce them through optimizing the combustion cycle. This publication presents a numerical study on the optimization of diesel and ammonia injection phases in a ship’s medium-speed engine, Wartsila 6L46. The study investigates the exhaust gas emissions and combustion cycle parameters through a high-pressure injection strategy. At an identified 7° CAD injection phase distance between diesel and ammonia, along with an optimal dual-fuel start of injection 10° CAD before TDC, a reduction of 47% in greenhouse gas emissions (GHG = CO2 + CH4 + N2O) was achieved compared to the diesel combustion cycle. This result aligns with the GHG reduction target set by both the IMO and the EU for 2030. Additionally, during the investigation of the thermodynamic combustion characteristics of the cycle, a comparative reduction in NOx of 4.6% was realized. This reduction is linked to the DeNOx process, where the decrease in NOx is offset by an increase in N2O. However, the optimized ammonia combustion cycle results in significant emissions of unburnt NH3, reaching 1.5 g/kWh. In summary, optimizing the combustion cycle of dual ammonia and diesel fuel is essential for achieving efficient and reliable engine performance. Balancing combustion efficiency with emission levels of greenhouse gases, unburned NH3, and NOx is crucial. For the Wartsila 6L46 marine diesel engine, the recommended injection phasing is A710/D717, with a 7° CAD between injection phases.

Effects of MOx modification (M = Mn, Ce, and Fe) on the SCR catalytic properties of the CrOx-WOx mixed oxide catalysts

In this study, a series of MOx-modified (M = Mn, Fe, and Ce) CrOx-WOx mixed oxides were synthesized via the sol-gel technique for the selective catalytic reduction of NOx with NH3. Given the addition of MnOx or CeOx, the availability of the catalyst surface acid sites tended to decline, which negatively affected the proceeding of the deNOx process. Moreover, the retention of oxidative ability by introducing MnOx also favored the over-oxidation of NH3, which accelerated the additional formation of NOx and created a crucial barrier for the increment in the higher-temperature deNOx activity. Apparently, <80 % of the NOx could be effectively eliminated from the working gas within the whole temperature range for the CrCeW and CrMnW samples. By contrast, doping FeOx was able to introduce ample acid sites onto the catalyst surfaces, which was beneficial for the adsorption of NH3 and subsequently the facilitation of the progression of the deNOx process. Furthermore, the weakened oxidizability suppressed the over-oxidation of NH3. Consequently, a broad operating temperature window was obtained for the FeOx-doped catalyst; >90 % NOx conversion efficiency was achieved in the temperature range of 230–450 °C. During the deNOx process, the Eley-Rideal mechanism dominated over the four investigated samples.

Unlocking Mixed-Metal Oxides Active Centers via Acidity Regulation for K&SO2 Poisoning Resistance: Self-Detoxification Mechanism of Zeolite-Confined deNOx Catalysts.

Selective catalytic reduction of nitrogen oxides (NOx) with ammonia (NH3-SCR) is an efficient NOx reduction strategy, while the denitrification (deNOx) catalysts suffer from serious deactivation due to the coexistence of multiple poisoning substances, such as alkali metal (e.g., K), SO2, etc., in industrial flue gases. It is essential to understand the interaction among various poisons and their effects on the deNOx process. Herein, the ZSM-5 zeolite-confined MnSmOx mixed (MnSmOx@ZSM-5) catalyst exhibited better deNOx performance after the poisoning of K, SO2, and/or K&SO2 than the MnSmOx and MnSmOx/ZSM-5 catalysts, the deNOx activity of which at high temperature (H-T) increased significantly (>90% NOx conversion in the range of 220-480 °C). It has been demonstrated that K would occupy both redox and acidic sites, which severely reduced the reactivity of MnSmOx/ZSM-5 catalysts. The most important, K element is preferentially deposited at -OH on the surface of ZSM-5 carrier due to the electrostatic attraction (-O-K). As for the K&SO2 poisoning catalyst, SO2 preferred to be combined with the surface-deposited K (-O-K-SO2ads) according to XPS and density functional theory (DFT) results, the poisoned active sites by K would be released. The K migration behavior was induced by SO2 over K-poisoned MnSmOx@ZSM-5 catalysts, and the balance of surface redox and acidic site was regulated, like a synergistic promoter, which led to K-poisoning buffering and activity recovery. This work contributes to the understanding of the self-detoxification interaction between alkali metals (e.g., K) and SO2 on deNOx catalysts and provides a novel strategy for the adaptive use of one poisoning substance to counter another for practical NOx reduction.

Mechanisms for deNOx and deN2O Processes on FAU Zeolite with a Bimetallic Cu-Fe Dimer in the Presence of a Hydroxyl Group-DFT Theoretical Calculations.

In this paper, a detailed mechanism is discussed for two processes: deNOx and deN2O. An FAU catalyst was used for the reaction with Cu-Fe bimetallic adsorbates represented by a dimer with bridged oxygen. Partial hydration of the metal centres in the dimer was considered. Ab initio calculations based on the density functional theory were used. The electron parameters of the structures obtained were also analysed. Visualisation of the orbitals of selected structures and their interpretations are presented. The presented research allowed a closer look at the mechanisms of processes that are very common in the automotive and chemical industries. Based on theoretical modelling, it was possible to propose the most efficient catalyst that could find potential application in industry-this is the FAU catalyst with a Cu-O-Fe bimetallic dimer with a hydrated copper centre. The essential result of our research is the improvement in the energetics of the reaction mechanism by the presence of an OH group, which will influence the way NO and NH3 molecules react with each other in the deNOx process depending on the industrial conditions of the process. Our theoretical results suggest also how to proceed with the dosage of NO and N2O during the industrial process to increase the desired reaction effect.

Promotion effect of Ce and Ta co-doping on the NH3-SCR performance over V2O5/TiO2 catalyst

NH3-SCR (SCR: Selective catalytic reduction) is an effective technology for the de-NOx process from both mobile and stationary pollution sources, and the most commonly used catalysts are the vanadia-based catalysts. An innovative V2O5-CeO2/TaTiOx catalyst for NOx removal was prepared in this study. The influences of Ce and Ta in the V2O5-CeO2/TaTiOx catalyst on the SCR performance and physicochemical properties were investigated. The V2O5-CeO2/TaTiOx catalyst not only exhibited excellent SCR activity in a wide temperature window, but also presented strong resistance to H2O and SO2 at 275 ℃. A series of characterization methods was used to study the catalysts, including H2-temperature programmed reduction, X-ray photoelectron spectroscopy, NH3-temperature programmed desorption, etc. It was discovered that a synergistic effect existed between Ce and Ta species. The introduction of Ce and Ta enlarged the specific surface area, increased the amount of acid sites and the ratio of Ce3+, (V3++V4+) and Oα, and strengthened the redox capability which were related to synergistic effect between Ce and Ta species, significantly improving the NH3-SCR activity.

Optimization of Combustion Cycle Energy Efficiency and Exhaust Gas Emissions of Marine Dual-Fuel Engine by Intensifying Ammonia Injection

The capability of operational marine diesel engines to adapt to renewable and low-carbon fuels is considered one of the most influential methods for decarbonizing maritime transport. In the medium and long term, ammonia is positively valued among renewable and low-carbon fuels in the marine transport sector because its chemical elemental composition does not contain carbon atoms which lead to the formation of CO2 emissions during fuel combustion in the cylinder. However, there are number of problematic aspects to using ammonia in diesel engines (DE): in-tensive formation of GHG component N2O; formation of toxic NOx emissions; and unburnt toxic NH3 slip to the exhaust system. The aim of this research was to evaluate the changes in combustion cycle parameters and exhaust gas emissions of a medium-speed Wartsila 6L46 marine diesel engine operating with ammonia, while optimizing ammonia injection intensity within the limits of Pmax, Tmax, and minimal engine structural changes. The high-pressure dual-fuel (HPDF) injection strategy for the D5/A95 dual-fuel ratio (5% diesel and 95% ammonia by energy value) was investigated within the liquid ammonia injection pressure range of 500 to 2000 bar at the identified optimal injection phases (A −10° CAD and D −3° CAD TDC). Increasing ammonia injection pressure from 500 bar (corresponding to diesel injection pressure) in the range of 800–2000 bar determines the single-phase heat release characteristic (HRC). Combustion duration decreases from 90° crank angle degrees (CAD) at D100 to 20–30° CAD, while indicative thermal efficiency (ITE) increases by ~4.6%. The physical cyclic deNOx process of NOx reduction was identified, and its efficiency was evaluated in relation to ammonia injection pressure by relating the dynamics of NOx formation to local combustion temperature field structure. The optimal ammonia injection pressure was found to be 1000 bar, based on combustion cycle parameters (ITE, Pmax, and Tmax) and exhaust gas emissions (NOx, NH3, and GHG). GHG emissions in a CO2 equivalent were reduced by 24% when ammonia injection pressure was increased from 500 bar to 1000 bar. For comparison, GHG emissions were also reduced by 45%, compared to the diesel combustion cycle.

Negative effect of industrial waste residue additives (IWRA) on NOx reduction by selective non-catalytic reduction (SNCR) in cement plant: A comparison between copper slag and iron-ore slag

The rapid development of cement plants necessitates the involvement of IWRA to improve the production performance of cement, which leads to the suppression of SNCR de-NOx process. However, the specific performance and mechanism of iron-rich waste materials on SNCR remain unclear. This study specifically addresses the effects of iron-ore slag (Fe2O3) and copper slag (Fe3O4) on the SNCR de-NOx process using fixed bed reactor in a simulated precalciner atmosphere ranging from 400 to 1000 °C. The results show that iron-ore slag had a strong inhibitory effect on the SNCR de-NOx process at low-medium temperatures (400 ∼ 800 °C), whereas copper slag could promote the NOx reduction reactions under slightly excessive NH3/NO ratio (NSR) conditions (NSR = 1.3). Both types of slag exhibited a more significant restraining effect on SNCR as ammonia concentration increased. In addition, the influence of trace elements in IWRA is not significant, which proved IWRA has incomparable substitutability and better economy than traditional catalysts. Consequently, these findings offer theoretical guidance for the subsequent implementation of IWRA in actual cement production processes. Additionally, it is advisable to avoid using Fe2O3-containing IWRA and ensure that ammonia injection points are positioned in the high-temperature region (900 ∼ 1000 °C) to achieve higher de-NOx efficiency.

Mechanistic insights into the adsorption and dissociation of nitrogen oxides on nickel phosphide (Ni2P) catalysts

The escalating concern regarding nitrogen oxides (NOx) emissions, linked to environmental challenges like smog, acid rain, ozone depletion, and global warming, necessitates effective strategies for their mitigation. DeNOx processes, including selective catalytic reduction (SCR), offer potential solutions, but costly precious metal catalysts hinder a widespread implementation. Alternatively, earth-abundant element compounds, particularly transition metal phosphides (TMPs), such as nickel phosphides (Ni2P), have garnered interest due to their promising catalytic performance. This study employed first-principles density functional theory (DFT) methods to investigate the catalytic properties of the (0001) Ni2P surface concerning NOx adsorption and dissociation. Both NO and NO2 are found to exhibit strong reactivity towards Ni2P-(0001)’s surface at the hollow triple-Ni sites, forming stable conjugated structures. Bader charge analysis indicates significant charge transfers during NOx adsorption from the interacting surface to the NOx, resulting in elongated N–O bond lengths, confirmed by vibrational frequency analyses. The dissociation process of NO2 was found to be both thermodynamically and kinetically favorable, with more heat being released than the subsequent NO dissociation’s activation barrier, resulting in a self-sustaining overall reaction. These insights provide valuable knowledge for designing efficient and sustainable Ni2P-based catalytic systems to address NOx emissions in environmental and industrial applications.

SNCR deNOx process by urea decomposition system and evaluation of CO2 reduction

SNCR deNOx process by urea decomposition system and evaluation of CO2 reduction

New approach into NOx removal from flue gas by carbohydrazide

Selective non-catalytic reduction (SNCR) is a proven technique to reduce nitrogen oxide (NOx) emissions from stationary sources. The process utilizes NH3 or urea as a reducing agent, which is only effective in a narrow and high temperature range with the maximum NOx abatement falling with the increase of the O2 content. In large industrial boilers, the effectiveness of the deNOx process may be decreased with boiler load variations and excess O2. This study investigated carbohydrazide as a reagent to improve SNCR performance. NO reduction by carbohydrazide was experimentally investigated in a pilot-scale flow reactor. The effect of reaction temperature, molar ratio of NH2 to NO (normalized stoichiometric ratio, NSR) on the NO reduction was determined. Moreover, the promotion effect of carbohydrazide on the reactivity of NH3 and urea was also investigated. The experimental results indicated that NO reduction by carbohydrazide occurred in a relatively low temperature range of 650–850 °C, and the optimum reaction temperature was about 730 °C at NSR of 2.0, the O2 content of 11.5%–16.6% and the initial NOx concentration of 635 mg/m3. After adding a small amount of carbohydrazide to an NH3 or urea solution, the data showed that carbohydrazide could shift the temperature window of NH3 to the left, but had no positive effect on urea deNOx and the NO conversion efficiencies of NH3 deNOx. Consequently, carbohydrazide is a potential reducing agent for NOx, but was not adapted to improve the deNOx performance with NH3 and urea.

Comparison of the Mechanisms of deNOx and deN2O Processes on Bimetallic Cu–Zn and Monometallic Cu–Cu Dimers in Clinoptilolite Zeolite—A DFT Study Simulating Industrial Conditions

This paper presents two mechanisms for the deNOx process and for the deN2O process (in two variants). The processes were carried out on a clinoptilolite zeolite catalyst with a deposited Cu–Cu monometallic dimer and Cu–Zn bimetallic dimer with bridged oxygen between the metal atoms. Analyses were performed for hydrated forms of the catalyst with a hydrated bridging oxygen on one of the metal atoms. Calculations were performed using DFT (density functional theory) based on an ab initio method. The analyses included calculations of the energies of individual reaction steps and analysis of charges, bond orders and bond lengths as well as HOMO, SOMO and LUMO orbitals of selected steps in the mechanism. Based on the results obtained, it was determined that the most efficient catalyst for both processes is a Cu–Zn bimetallic catalyst with a bridged hydroxyl group. It shows higher efficiency in the limiting step (formation of the -N2H intermediate product) than the previously studied FAU and MFI zeolites with a Cu–Zn bimetallic dimer. In addition, the possibility of using the catalytic system from the deNOx process in the deN2O process was presented, which can benefit SCR installations. In addition, it was proved that the order of adsorption of NO and N2O has significance for further steps of the deN2O process. In order to improve the comparison of FAU, MFI and CLI zeolite catalysts with a Cu–Zn dimer, further studies on the deN2O mechanism for the first two zeolites are needed. This study allows us to propose a bimetallic catalyst for the deNOx and deN2O processes.

Boosting the H2O resistance and NH3-SCR activity over sulfated FeCe0.5 SmaTi4Ox-S catalysts by Sm modification

In this work, a series of Sm modified sulfated FeCe0.5Ti4Ox-S catalysts were successfully prepared by a concise one-step co-precipitation method for application in flue gases denitrifications (de-NOx) generated from high sulfur content coal-fired power plants. The catalysts were carried out by XRD, Raman, N2 adsorption and desorption, TEM, EDS spectroscopy, NH3-TPD, H2-TPR, XPS, and in-situ DRIFTS characterization. Among these catalysts, FeCe0.5Sm0.3Ti4Ox-S showed the best catalytic activity, maintaining 100% NO conversion in 260–450 °C, high N2 selectivity and good resistance to water and SO2 poisoning. The results demonstrated that the addition of appropriate amount of Sm promoted the interaction between Sm, Ce, Fe and Ti, which increased the oxidation capacity and L-acid sites on the catalyst surface, improving the catalytic activity. Additionally, the increase of L acid sites also contributed to the improvement of water resistance of the catalyst. In-situ DRIFTS studies also indicated that the Sm addition promoted NH3 adsorption in the presence of water due to the reaction of special surface sulfates with H2O to form additional B acid sites, which may be the reason for the negligible effect of water on the catalytic activity. Based on various characterizations, the NH3-SCR de-NOx processes are proposed over FeCe0.5Sm0.3Ti4Ox-S in presence of H2O.

Low-temperature DeNOx characteristics and mechanism of the Fe-doped modified CeMn selective catalytic reduction catalyst

Low-temperature deNOx selective catalytic reduction (SCR) catalysts are of great significance to prolong catalyst life and reduce flue gas temperature. In this work, the low-temperature deNOx performance of different zFeCexMny catalysts was investigated on a simulated flue gas fixed-bed experimental bench. BET, XRD, XPS, NH3-TPD, and in situ FT-IR were used to characterize the physical-chemical properties of the samples. The optimum ratio and deNOx mechanism of the catalysts were explored. The results show 4FeMn7Ce3 doped with 4 wt% Fe based on Mn7Ce3 has the best deNOx performance. Its deNOx efficiency is over 90% at 120–220 °C and GHSV = 50,000 h−1, with the peak value of 98% at 150 °C. The Fe doping makes the oxide distributed uniformly on the catalyst's surface, promotes the valence cycle of the catalyst, yields more Mn4+ and Ce3+ species, and prompts the optimal deNOx temperature to the low temperature direction. Meanwhile, Lewis acid sites on the catalyst's surface are enhanced, which can promote the amide species formation that is beneficial for the deNOx reaction. Combined with in situ FTIR, the E-R mechanism and the L-H mechanism coexist in the deNOx process of zFeCexMny catalysts. These findings are helpful for the development of high-performance low-temperature deNOx catalysts.

Low-temperature NOx capture and reduction via NO oxidation by O3 on Cu-CHA

We studied the transient reduction of NOx with NH3 over Cu-exchanged CHA zeolite (Cu-CHA) assisted by the catalyst-free oxidation of NO by O3. The room-temperature catalyst-free oxidation of NO by O3 yielded NO2 at low O3/NO ratio and N2O5 as the main product at higher ratios. DFT calculations verified the reaction of NO2 +O3 to N2O5 proceeding with low activation energies. Transient operando IR measurements demonstrated that Cu-CHA exposure to NO+O3 at 100 °C resulted in the storage of NOx as NO3− on the Cu2+ site. The stored NOx reacted with NH3 to yield N2 and NH4NO3. Preadsorbed NH3 on Cu-CHA was oxidized by O3 to yield N2 and N2O. The reaction of preadsorbed NH3 with NO+O3 caused the selective formation of N2. The obtained results may aid in developing a new O3-assisted unsteady-state lean De-NOx process involving reactions of captured NOx with NH3 or reduction of NOx with stored NH3.

Chemical mechanism of ammonia-methanol combustion and chemical reaction kinetics analysis for different methanol blends

As a carbon-free fuel, ammonia is considered as an attractive alternative fuel for internal combustion engines. However, ammonia has the problems of high ignition temperature and NOx emissions while using in engines. Methanol as liquid fuel is easy to store and transport. Ammonia-methanol blended fuel is probably-one of the most appropriate methods to solve the problem. However, there are few studies of chemical mechanism for the combustion of ammonia/methanol dual fuel. Moreover, it is important to study ammonia-methanol combustion by chemical reaction path analysis. In this paper, a chemical reaction mechanism of ammonia-methanol blends with 60 species and 399 reactions was developed. This mechanism can accurately predict the laminar burning velocity (LBV) and ignition delay time (IDT) in a wide range of equivalent ratios (Φ) and methanol blends. By using this chemical reaction mechanism, the effects of methanol addition on ammonia combustion and emissions at different equivalent ratios were numerically studied. Results showed that the addition of methanol significantly improves the chemical reactivity of ammonia, and blending a small amount of methanol can greatly reduce the IDT. However, the accumulation of radical HO2 caused by ammonia production enhances the fuel NOx path of NH2 → H2NO, which, together with high temperature and oxygen enrichment, leads to a NOx peak of 12500 ppm at equivalent ratio of 0.8. However, with the increase of equivalent ratio, NOx emission will decrease, which is only 2500 ppm at equivalent ratio of 1.4. Due to the existence of cross reaction of NH2 + CH3OH = NH3 + CH2OH and NH2 + CH3OH = NH3 + CH3O between ammonia and methanol, NH2 is difficult to participate in the thermal DeNOx process in the premixed combustion process, resulting in high NOx emissions. In addition, it is also found that after equivalent ratio of 1.1, H will replace OH as the most important chain propagation carrier.

Role of iron-based catalysts in reducing NOx emissions from coal combustion

Nitrogen oxide (NOx) pollutants emitted from coal combustion are attracting growing public concern. While the traditional technologies of reducing NOx were mainly focused on terminal treatment, and the research on source treatment is limited. This paper proposes a new coal combustion strategy that significantly reduces NOx emissions during coal combustion. This strategy has two important advantages in reducing NOx emissions. First, by introducing iron-based catalyst at the source, which will catalyze the conversion of coke nitrogen to volatile nitrogen during the pyrolysis process, thereby greatly reducing the coke nitrogen content. The second is de-NOx process by a redox reaction between NOx and reducing agents (coke, HCN, NH3, etc.) that occurred during coke combustion. Compared to direct combustion of coal, coke prepared by adding iron-based catalyst has 46.1% reduction in NOx emissions. To determine the effect of iron-based additives on de-NOx performance, demineralized coal (de-coal) was prepared to eliminate the effect of iron-based minerals in coal ash. The effects of iron compounds, additive dosages, and combustion temperatures on de-NOx efficiency are systematically studied. The results revealed that the NOx emission of the coke generated by pyrolysis of de-coal loaded with 3% (mass) Fe2O3 decreases to 27.3% at combustion temperature of 900 °C. Two main reasons for lower NOx emissions were deduced: (1) During the catalytic coal pyrolysis stage, the nitrogen content in the coke decreases with the release of volatile nitrogen. (2) Part of the NOx emitted during the coke combustion was converted into N2 for the catalytic effect of the Fe-based catalysts. It is of great practical value and scientific significance to the comprehensive treatment and the clean utilization process of coal.

Effect of spray operation conditions on Nox emission control in a power station

Adequately mixing of reactants is an important factor for efficient deNOx process in power station NOx emission control system. In this study, an experimental validated CFD simulation is conducted to investigate the effect of spray operation conditions on the mixing uniformity of reactant ammonia vapor in deNOx process occurring in a power station’s furnace. According to the CFD simulation results, it is found that spray momentum ratio, initial droplet size and initial ammonia concentration all affect the mixing uniformity of ammonia vapor. Overall, a larger spray momentum ratio, larger initial droplet size and lower ammonia concentration contributes positively to the mixing uniformity. By comparing the same spray momentum ratio but different nozzle inlet velocity and furnace inlet velocity, it is found that the impact of spray momentum ratio mainly comes from furnace inlet velocity not nozzle inlet velocity. In addition, gravity should not be neglected. In the end, the method described in this study could provide a systematic way to study the effects of nozzle operation conditions on deNOx process.

Stability and emission characteristics of ammonia-air flames in a lean-lean fuel staging tangential injection combustor

The present work suggests the stability and emission characteristics of an ammonia-air tubular flame in a fuel staging tangential injection combustor. Owing to the development of a large inner recirculation zone induced by a high swirling motion, the ammonia tubular flame exhibited wide operational flexibility at an ambient temperature condition. With ammonia fuel staging, we confirmed that the Thermal DeNOx process significantly mitigates NO emissions when the exit temperature of the primary region is close to the threshold for active NO reduction. In this study, fuel multi-stage technology was used for pure ammonia-air combustion, and the result effectively challenges the existing paradigm of the NO reduction strategy: Rich-Quench-Lean staging configuration. Thus, our results demonstrate the potential use of ammonia as a fuel in a dry low-NOx system.

A Comparative Study of NOx Emission Characteristics in a Fuel Staging and Air Staging Combustor Fueled with Partially Cracked Ammonia

Recently, ammonia is emerging as a potential source of energy in power generation and industrial sectors. One of the main concerns with ammonia combustion is the large amount of NO emission. Air staging is a conventional method of reducing NO emission which is similar to the Rich-Burn, Quick-Mix, Lean-Burn (RQL) concept. In air-staged combustion, a major reduction of NO emission is based on the near zero NO emission at fuel-rich combustion of NH3/Air mixture. A secondary air stream is injected for the oxidation of unburned hydrogen and NHx. On the other hand, in fuel-staged combustion, NO emission is reduced by splitting NH3 injection, which promotes the thermal DeNOx process. In this study, NOx emission characteristics of air-staged and fuel-staged combustion of partially cracked ammonia mixture are numerically investigated. First, the combustion system is modeled by a chemical reactor network of a perfectly stirred reactor and plug flow reactor with a detailed chemistry mechanism. Then, the effects of ammonia cracking, residence time, and staging scheme on NOx emission are numerically analyzed. Finally, the limitations and optimal conditions of each staging scheme are discussed.