Selective Non-catalytic Reduction Research Articles

Numerical Simulation Study on Combustion of Low Calorific Value Waste Blended with Biomass.

Numerical simulations of a 600 t/day waste incinerator was carried out using the fluid dynamic incinerator code and Fluent to evaluate the effect of biomass blending on furnace temperature, pollutant generation, and selective noncatalytic-reduction (SNCR) denitrification when treating low calorific-value waste. The results show that as the biomass blending ratio increases, the water content gradually decreases, the calorific value increases, and the maximum temperature of the incinerator gradually increases from 1227 to 1408 K, while the content of exported NOx increases from 579 to 793 mg/Nm3; during the combustion of low-quality waste, the residence time of the flue gas in the high-temperature region (above 1123 K) is 1.62 s. When the biomass blending ratio exceeds 20%, the residence time of the flue gas in the high-temperature region is more than 2 s, which can effectively curb the generation of dioxin. When the biomass blending ratio is 20%, and the normalized stoichiometric ratio (2nurea/nNO) of urea injected into the SNCR is 1.1, the NOx concentration at the outlet is 230.08 mg/Nm3, which satisfies the NOx emission standard of less than 250 mg/Nm3.

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.

Denitration Simulation of SNCR System Nozzles at Different Layout Positions in Coal Powder Boilers

Building a clean, low-carbon, safe and efficient energy system is an overall requirement for the modernization of the energy system, The nitrogen oxides produced by the combustion of fossil fuels need to be effectively treated. The selective non-catalytic reduction denitrification (SNCR) technology in the thermal power industry. It is widely used due to its low cost and mature technology. By using CFD software to simulate and study the coupling of flue gas temperature field and NO concentration field, the SNCR nozzle was set up to study the impact on denitrification efficiency. Simulate multiple layout methods, including sequential arrangement, staggered arrangement, concentrated in the middle and concentrated on both sides. The denitrification efficiency is highest among them, which is concentrated on both sides and further optimized through the NO concentration field in the furnace. After optimization, the denitrification efficiency reached 59.2%, which was 2.4% higher than the traditional uniform layout method. It has important practical guidance significance for energy conservation, emission reduction, and operational optimization.

Potential Risk of Significant N2O Emission without Changing NOx Conversion on Commercial V2O5/TiO2 Catalyst under Working Conditions.

Vanadium-based catalysts play a pivotal role in the emission control of industrial NOx via selective catalytic reduction (SCR) technology. However, little attention has been paid to the potential emission of greenhouse gas N2O under complex working conditions. This work reports that a commercial V2O5/TiO2 catalyst may lead to significant N2O emission without greatly changing the outlet NOx concentration after chromium (Cr) deposition. With a Cr loading of 2 wt %, N2O concentration increased from 27.8 to 199.2 ppm at 350 °C with the value of outlet N2O/(N2O+N2) from 2.5% to 19.4%. Experimental results combined with DFT+U calculations suggest that nonselective catalytic reduction (NSCR) is the main route for N2O formation in a wide temperature range of 250 ∼ 400 °C. It is stemmed from the fact that the covalent interaction between Cr and V species on the V2O5/TiO2 surface accelerates the conversion of V4+ + Cr6+ → V5+ + Cr3+, leading to a larger proportion of surface V5+. More importantly, surface V5+ is highly related to the redox property of the V2O5/TiO2 catalyst, which is beneficial to NSCR reaction rather than the standard SCR process. The work suggests that to better inhibit the emission of greenhouse gases during the NH3-SCR process, monitoring N2O emission should be included along with the NOx concentrations, especially in complex flue gases.

An explainable AI model for power plant NOx emission control

In recent years, developing Artificial Intelligence (AI) models for complex system has become a popular research area. There have been several successful AI models for predicting the Selective Non-Catalytic Reduction (SNCR) system in power plants and large boilers. However, all these models are in essence black box models and lack of explainability, which are not able to give new knowledge. In this study, a novel explainable AI (XAI) model that combines the polynomial kernel method with Sparse Identification of Nonlinear Dynamics (SINDy) model is proposed to find the governing equation of SNCR system based on 5-year operation data from a power plant. This proposed model identifies the system's governing equation in a simple polynomial format with polynomial order of 1 and only 1 independent variable among original 68 input variables. In addition, the explainable AI model achieves a considerable accuracy with less than 21 % deviation from base-line models of partial least squares model and artificial neural network model.

The reaction characteristics and mechanism of polymer non-catalytic reduction (PNCR) for NOx removal

To overcome the defects of the traditional selective non-catalytic reduction (SNCR) process (e.g., low efficiency, narrow temperature range), a new modified SNCR technology based on the solid complex polymer reducing agents, also called polymer non-catalytic reduction (PNCR), was investigated both in the laboratory and pilot scale to reveal its reaction characteristics and mechanism. The PNCR process demonstrates excellent removal efficiency (about 90%) of NO in furnace in the wide temperature range (850–1150 °C), and possesses promising application feasibility with an average NOx emission concentration of 68.72 mg·m−3 even on unstable industrial operating conditions. The NO removal behaviors influenced by O2, temperature, or water steam illuminate the unique O2-independent and H2O-promoted reaction characteristics of PNCR in the wide temperature range. The thermogravimetric infrared spectra/mass spectrometry (TG-IR/MS) results further reveal a pyrolysis-assisted formation mechanism of active NH2/NH free radicals without the requirement of O2 and high temperature, which avoids the overoxidation of active radicals and accounts for the wide denitrification temperature window, low oxygen compliance and high denitrification efficiency of PNCR process. The excellent NO removal performance as well as the unique reaction characteristics/mechanism of PNCR forebode its broad industrial application prospect in the field of flue gas cleaning.

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.

The influence of organic components in sludge on selective non-catalytic reduction denitrification.

Collaborative disposal of sludge has been applied extensively in cement industry kilns, but the influence of organic components in sludge on the selective non-catalytic reduction (SNCR) denitrification is still in highly demanding. This paper focuses the influence of ethanol, n-octane, benzene, and acetone on the SNCR denitrification, and the influence of ethanol are analyzed on SNCR denitrification under different flue gas condition. The result showed that the presence of organic components reduces the reaction temperature of SNCR. When the temperature of SNCR reaction is at 750 ~ 800 ℃, the denitrification rate of four organic components is ethanol > benzene > n-octane > acetone. The optimum denitrification rate on SNCR can reach as high as 90.377% when the reaction condition is the NH3/NO is 1; the ethanol concentration is 1000ppm; O2 concentration is 2%; and temperature is 750 ℃. The presence of carbon dioxide inhibits the denitrification reaction. With the increase of temperature, the influence of SO2 on the denitrification reaction first increases and then decreases. In this paper, the influence of organic components in sludge on SNCR denitrification will be analyzed, which provides a theoretical basis for the selection of sludge dosing method for cement kiln collaborative disposal.

Computational Fluid Dynamics Simulation of Combustion and Selective Non-Catalytic Reduction in a 750 t/d Waste Incinerator

In this study, a Computational Fluid Dynamics (CFD) approach using Ansys Fluent 15.0 and FLIC software was employed to simulate the combustion process of a 750 t/d grate-type waste incinerator. The objective was to assess the performance of Selective Non-Catalytic Reduction (SNCR) technology in reducing nitrogen oxide (NOx) emissions. Two-stage simulations were conducted, predicting waste combustion on the bed and volatile matter combustion in the furnace. The results effectively depicted the temperature and gas concentration distributions on the bed surface, along with the temperature, velocity, and composition distributions in the furnace. Comparison with field data validated the numerical model. The findings serve as a reference for optimizing large-scale incinerator operation and parameter design through CFD simulation.

Ammonia emission characteristics and ammonia injection control from stationary source in flue gas denitrification system

With the implementation of ultra-low emission of nitrogen oxides, denitrification technologies, such as selective catalytic reduction, selective non-catalytic reduction or selective non-catalytic reduction combined with selective catalytic reduction, have been widely used in gas-fired power plants, cement plants and municipal solid waste incineration power plants. These three denitrification industries have become the main potential fixed sources of ammonia emissions in urban areas, however the studies on ammonia emissions are lacking. In order to study the ammonia emission characteristics and ammonia injection control of gas-fired power plants, cement plants and municipal solid waste incineration power plants, field tests were carried out on five typical denitrification enterprises using three monitoring methods. The multi-form ammonia manual monitoring method proposed in this study distinguished and defined all possible ammonia in the flue gas into filterable ammonia, residual ammonia, condensable ammonia and gaseous ammonia according to the migration and transformation behavior during the collection process. The monitoring results of the multi-form manual monitoring method can more accurately reflect the actual ammonia emission level with the simultaneous collection and monitoring of different ammonia forms. The ammonia emission levels in cement plants (more than 20 mg/m³) were higher than that of gas power plants and waste incineration plants (almost less than 4 mg/m³). The condensed ammonia was the dominant form of ammonia, accounting for 58.4%～88.7%. The humidity and temperature of flue gas at the chimney outlet had significant influence on residual ammonia. For the denitration enterprises using a single denitrification technology, the ammonia emission had a linear negative correlation with that of nitrogen oxide with changing ammonia injection amount, while for that using combined denitrification technology, the degree of collaboration between selective non-catalytic reduction ammonia injection control and selective catalytic reduction ammonia injection control played a decisive role in the control of nitrogen oxide emission and ammonia emission, especially the selective catalytic reduction ammonia injection control.

A method of designing an SNCR installation for small pulverized coal-fired boilers on the example of OP-50 boiler

Small pulverized coal-fired heating boilers are popular in heating and industrial applications. Recent changes in emissions limits forced interest in clean-up technologies dedicated for such a boilers, which previously were not included in regulations. The paper presents a method of designing an Selective Non Catalytic Reduction (SNCR) installation for small pulverized coal-fired boilers on the example of OP-50 boiler. Among main challenges during technology development and adjustment injection lances type, position, and operating parameters including reagent type and concentration can be enumerated. The designing process covered mainly following parts: object tests, temperature distribution determination (including balance calculations and computational fluid dynamics (CFD) modelling) leading to lances position determination, injection nozzles designing, installation tuning and calibration. Final measurements confirmed the ability of designed system to reduce NOx concentration in the flue gases below limit given in regulations.

THE TWO-STAGED REDUCTION SELECTIVE NON-CATALYTIC REDUCTION PROCESS OF NITROGEN OXIDES INTHERMAL GENERATION UNIT FLUE GASES

The basic concern of research presented in the article was a development of selective non-catalytic reduction of nitrogen oxides in thermal generation units flue gases. The results of the experiments of two-staged selective non-catalytic reduction of nitrogen oxides with below-stoichiometric urea injection are described. Higher and more stable reducing efficiency with minimal formation of ammonia in treated gases is showed.

Analysis of ammonia combustion for decarbonization followed by selective non-catalytic reduction of nitrogen oxides

This study aimed to investigate the thermodynamics of ammonia combustion at engine conditions and subsequent selective non-catalytic reduction (SNCR) of the products, emphasizing the production of nitrogen oxides (NOX) through the minimization of Gibbs free energy. The results showed a good correlation with existing research about ammonia combustion and SNCR. NOX production increased with temperature, decreased with increasing ammonia equivalence ratio, and was largely independent of pressure. At the conditions with the highest NOX production, the NOX concentration peaked at 21,963 ppm. The ammonia combustion reaction was exothermic at high temperatures and had a reaction enthalpy that decreased with temperature and increased with an increasing ammonia equivalence ratio. Further, the SNCR simulation indicated that reducing large NOX concentrations produced during ammonia combustion could be thermodynamically favorable up to over 98% through selective non-catalytic reduction.

Inhibition mechanism of chlorobenzene on NH3-SCR side reactions over MnOx-CeO2 confined titania nanotubes

The influence mechanism of CB on SCR side reactions including nonselective catalytic reduction (NSCR) and NH3 peroxidation is still a major challenge of current research. The inhibition mechanism was identified qualitatively and quantitatively on MnOx-CeO2 confined titania nanotubes catalyst with good co-remove efficiency. We decoupled NSCR into L-H and E-R mechanism routes and each mechanism were further decomposed into adsorption and reaction steps for the first time. It revealed that CB preferred to inhibit L-H mechanism (99%) and adsorption step (53.5% in E-R and 98% in L-H) in NSCR.CB dominated the inhibition of L-H mechanism and adsorption steps. As for NH3 peroxidation, N2O, NO and NO2 are produced with the increase of oxygen activity. After 240 °C, the inhibition of CB on N2O weakens and starts to inhibit NO and NO2 instead. It can be attributed that CB competitively reacts with higher active oxygen, weakening the oxidization of NH3 to NO/NO2. The inhibition mechanism is that the active oxygen is continuously consumed in CB oxidation process, and the dissociated Cl produced by nucleophilic substitution limits the supplement of the lattice oxygen, finally resulting in the reduction of high valence active centers and the loss of active oxygen.

Numerical Simulation of Selective Non-Catalytic Reduction Denitrification Process in Precalciner and the Effect of Natural Gas Injection on Denitrification

Cement production is the third largest source of nitrogen oxides (NOx), an air pollutant that poses a serious threat to the natural environment and human health. Reducing NOx emissions from cement production has become an urgent issue. This paper aims to explore and investigate more efficient denitrification processes to be applied in NOx reduction from precalciner. In this study, firstly, the flow field, temperature field, and component fraction in the precalciner are studied and analyzed using numerical simulation methods. Based on this, the influence of the reductant injection height and amount on the SNCR was studied by simulating the selective non-catalytic reduction (SNCR) process in the precalciner. The effect of natural gas on the NOx emissions from the precalciner was also investigated. The simulation results showed that, with the increase in height, the NOx concentration in the precalciner decreased, then increased, then decreased, and then increased again. The final NOx concentration at the exit position was 531.33 ppm. In the SNCR denitrification process, the reductant should be injected in the area where the precalciner height is 26–30 m so that the reductant can fully react with NOx and avoid the increase of ammonia escape. The NSR represents the ratio of reductant to NOx, and the results show that the larger the NSR is, the higher the denitrification rate is. However, as the NSR approaches 2, the denitrification rate slows down and the ammonia escape starts to increase. Therefore, according to the simulation results, the NSR should be kept between 1 and 1.6. The denitrification rate reached the maximum value of 42.62% at the optimal condition of 26 m of reductant injection height and 1.6 of NSR. Co-firing of natural gas with pulverized coal can effectively reduce the NOx generation in the furnace. The denitrification rate reached the maximum value of 32.15% when the natural gas injection amount was 10%. The simulation results of natural gas co-combustion and SNCR combined denitrification showed that combined denitrification was better than natural gas co-combustion or SNCR denitrification. Under the condition of NSR of 1 and natural gas injection of 10%, the denitrification rate increased by 29.83% and 31.64% compared to SNCR-only or co-combustion-only denitrification, reaching 61.98%, respectively. Moreover, less reductant is used in co-denitrification, so the problem of excessive ammonia emissions can be avoided. The results of this study provide useful guidance for denitrification process development and NOx reduction in cement production.

Effects of swirl intensity on flame stability and NO emission in swirl-stabilized ammonia/methane combustion

Ammonia is an attractive clean fuel for its potential to reduce CO2 emission and fossil fuel consumption. However, ammonia combustion has been mainly discouraged by the low flammability and the high fuel NOx emissions. This study numerically investigates the effects of swirl intensity on combustion characteristics in swirl-stabilized ammonia/methane combustion. Large eddy simulation was performed by using OpenFOAM, and the accuracy of numerical results was validated by the experiment. The results show that swirl intensity will significantly affects the flow field and flame structure, and flame stability decreases with the swirl number increasing. The high swirl intensity leads to extinguishing at the flame root, while the low swirl intensity cannot generate the central recirculation zone to stabilize the flame. Selective non-catalytic reduction of NO (SNCR) is the key to controlling NO emission, the decrease of temperature will promote the reduction of NO, while the decrease of residence time will inhibit the reduction of NO. Meanwhile, SNCR will weaken the correlation between NO and OH in ammonia/methane combustion. NO emission will decrease with the swirl intensity increasing. In a word, medium swirl number (S ≈ 0.76) is proper to control NO emission and ensure flame stability.

The impact of hydrogen substitution by ammonia on low- and high-temperature combustion

The combustion behaviour of ammonia has attracted intermittent interest with the original patent by Lyon (US3900554A) relating to its use for nitric oxide reduction through selective non-catalytic reduction (SNCR) a focal point. The recent interest in ammonia stems from its use as a hydrogen rich energy carrier with practical use requiring a much wider parameter space. The corresponding challenges (e.g. Kobayashi et al., Proc. Combust. Inst. 37 (2019) 109–133) include different flame dynamics and high emissions of oxides of nitrogen. The current paper explores the complex nature of ammonia oxidation and provides a reduced size reaction mechanism that enables application, without approximation, to the computation of turbulent flames through a joint-scalar transported probability density function (JPDF) method. Comprehensive validation suggests similar accuracy to a reference mechanism (Glarborg et al., Prog. Energy Combust. Sci. 67 (2018) 31–68) and highlights some uncertainties. The selected turbulent flame configuration features auto-ignition stabilised flames supported by a coflow of hot combustion products. The base case features a H2/N2 fuel jet that permits flame stabilisation at 1045 K corresponding to the onset of the SNCR temperature window. The impact of a gradual substitution of hydrogen by ammonia on flame stabilisation, emissions of oxides of nitrogen and the flame structure is quantified. It is shown that ammonia substitution leads to more prevalent local extinction, a more distributed flame structure and requires substantially increased coflow temperatures to achieve a similar flame stabilisation point. A lowering of the coflow temperature to operate within the SNCR regime substantially reduces NOx and leads towards a homogeneous/distributed reaction mode. The reduced fuel reactivity highlights the importance of turbulence-chemistry interactions leading to complexities in the design of practical devices.

Investigation on co-disposal technology of sludge and municipal solid waste based on numerical simulation

Rapidly growing municipal sludge (sludge) with a low calorific value and high nitrogen content leads to high treatment difficulties. This study uses numerical simulations to simulate the steady-state combustion process of waste and sludge (40% moisture content) blending in a 750 t/d waste incinerator, to analyze the effect of sludge blending ratio on the combustion characteristics and to optimize the selective non-catalytic reduction (SNCR) spray gun structure. It was found that 13% is a suitable maximum sludge blending rate for the incinerator, satisfying the 3 T principle. Combining denitrification efficiency, NOx distribution uniformity, and modification feasibility, five spray guns are a more suitable SNCR solution with a denitrification efficiency of 45.40%. The results provide support and reference for the subsequent optimization of the working conditions of the waste incinerator and the optimal design of the incinerator.

Influence and mechanism of the adsorption and reactions of residual NH3, NO, and O2 on coal ash after the selective noncatalytic reduction process

NH3 as reducing agent in selective noncatalytic reduction (SNCR) is widely used for the deNOx of coal-fired boiler flue gas, where fly ash significantly influences the conversion of residual NH3 that does not participate in deNOx. However, few studies have been conducted on the exact nature of this influence. The adsorption and reaction of NH3, NO, and O2 on the fly ash at 50–850 °C were investigated in this study. At 50–350 °C, NH3, NO, and O2 co-adsorbed on the coal ash surface, and the presence of NO and O2 reduced the physical adsorption of NH3 on the ash and promoted its chemical adsorption on the ash. At 450–850 °C, coal ash catalyzed NO reduction by NH3 and NH3 oxidation by O2. In the presence of O2, the oxidation reaction became dominant and the reduction reaction was inhibited. The mechanism of adsorption and reaction of coal ash showed that NH3 was adsorbed on the Brönsted and Lewis sites on coal ash and NH3 at the Lewis site could be dissociated into *NH2 and *NH. The NO ad-species in coal ash were mainly nitrate and nitrite. *NH2 reacted with NO to form NH2NO, which desorbed as N2 at 450–850 °C. The main oxidation intermediates for NH3 ad-species were monodentate nitrate and bridged nitrate, which desorbed as NO at 450–850 °C. The results provide a theoretical basis for adjusting the migration and conversion of residual NH3 and reducing ammonia slip from power plants.

Nitric oxide (NO) and nitrous oxide (N2O) emissions during selective non-catalytic reduction and selective catalytic reduction processes in a pulverized coal/Ammonia Co-fired boiler

The global warming and climate change are accelerated by the emissions of CH4, chlorofluorocarbon, and N2O gases along with CO2 resulting from the use of fossil fuels. Recently, a new combustion technology that combines carbon-free ammonia (NH3) fuel and coal has been proposed to reduce CO2 emissions from thermal power plants. In this study, we examined the emission levels of NO and greenhouse gas N2O from the existing coal-fired and future carbon-neutral coal/ammonia co-fired thermal power plants. As a result, a correlation between the amounts of NO and N2O gases generated during combustion in the furnace of a thermal power plant was established, and possible relationships between NO and N2O emissions during the selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR) of NOx were experimentally analyzed. In addition, a linear correlation between the CO and N2O concentrations was observed. The air-staged combustion during SCR (300 °C, urea) produced the lowest total emission concentration of NO and N2O (9 ppm) under the utilized conditions. The findings of this study can help control the emission levels of air pollutant NO and greenhouse gas N2O throughout the entire process of thermal power plants.