Denitration Efficiency Research Articles

Utilizing l-Ascorbic Acid to Inhibit Adverse Oxidation and Enhance Denitration Efficiency during Sulfite Solution Absorption of NO2: Mechanism and Process Parameters

Utilizing <scp>l</scp>-Ascorbic Acid to Inhibit Adverse Oxidation and Enhance Denitration Efficiency during Sulfite Solution Absorption of NO₂: Mechanism and Process Parameters

Application of an integrated device for ultra-low temperature desulfurization and denitration in large rotary kiln

To tackle the problem of excessive nitrogen oxide emissions during the denitration process of the lime rotary kiln at Beitai Iron Mine, it was proposed to integrate ultra-low temperature SCR denitration catalysts and a moving-burden bed reactor into a radial combined desulfurization and denitration device to achieve ultra-low temperature denitration in a low-sulfur state. The self-built integrated device features two desulphurization beds and one denitration bed, through which the flue gas passes successively in a radial flow manner. Industrial test results indicate that the denitration efficiency reached an average of 96.07% at temperatures ranging from 70 to 130°C during a 14-day test period, indicating a good denitration effect. The ultra-low temperature SCR denitration device has been put into use, effectively reducing nitrogen oxide emissions and air pollution, while also promoting the optimization and upgrading of the energy structure. The research results can provide a reference for the environmental management of mining and processing enterprises.

Zr‐doped β‐MnO2 for Low‐temperature Selective Catalytic Reduction of NO by NH3: Preparation, Characterization and Performance

Nanowire‐MnO2 and a series of Zr‐doped MnO2 catalysts with different Zr/Mn molar ratios were successively prepared by hydrothermal and impregnation methods. The Zr‐doped MnO2 catalyst with Zr/Mn molar ratio of 0.04 and calcination temperature of 400°C, proved to be the optimal that possessed the highest low‐temperature denitration efficiency. It showed the NO conversion of ~92% and N2 selectivity of ~80% at 150°C. Characterization results demonstrated that the main active phase of the catalyst was β‐MnO2, Zr atoms interacted with Mn atoms, and Zr doping increased the structural defects, oxygen vacancies and weak acid sites, which effectively enhanced the low‐temperature denitration activity and N2 selectivity of β‐MnO2, also improved the water and sulphur resistance to some extent.

Lewis acid-rich SrFexTi1−xO3/TiO2 to enhance the photocatalytic reduction of nitrate to N2

The photocatalytic reduction of nitrate has received considerable attention due to its high efficiency and environmentally friendly nature. The excessive addition of hole scavengers is the most commonly used method to increase the nitrate reduction efficiency. However, achieving high selectivity in the photocatalytic reduction of nitrate to N2 with low concentration of hole scavengers remains challenging. In this study, the SrFexTi1−xO3/TiO2 S-scheme heterojunction photocatalysts with many Lewis acidic adsorption sites have been developed. The experimental results demonstrated that the incorporation of 6% Fe into SrFe0.06Ti0.94O3/TiO2 (SFTO6) resulted in the nitrate conversion rate of 97.68% and the N2 selectivity reached 96.35% with 25 mmol/L formic acid. Moreover, it also exhibited excellent stability and recycle ability. After 5 cycles, SFTO6 still exhibited a stable photocatalytic denitration efficiency of 92.94%, highlighting its potential for practical application. Through comprehensive mechanistic investigations, enhancing direct reduction process is considered the key to its high reduction efficiency with low formic acid. And the Lewis acidic adsorption sites enhance N2 selectivity by enriching NOx− on the surface of the material. Overall, this study provides a novel approach for achieving efficient photocatalytic reduction of nitrate to N2 under conditions with low concentration of hole scavengers.

TiO2 modified limonite for selective catalytic reduction of NO from cement kiln flue gas with NH3

Limonite was used as a precursor and TiO2 as a modifier to synthesize TiO2/Limonite composites through the wet impregnation method. The influences of the TiO2 doping amount, the calcination temperature on the denitration efficiency and the structure and properties of composites were systematically studied. The results showed that the modified catalyst over the Ti/Fe mass ratio was 0.07 and the calcination temperature was 300°C exhibited excellent catalytic activity, good stability, and remarkable resistance to water and sulfur dioxide within reaction temperature of 100 ∼ 240°C. When NO initial concentration was 0.05 % and gas hourly space velocity (GHSV) was 36,000 h−1 and the reaction temperature was 130°C, the NO conversion efficiency reached 100 %, and the N2 selectivity was 99.6 %. When the catalyst was exposed to 10 %H2O at 150°C, it maintained a 100 % NO conversion efficiency. In the presence of 10 %H2O and 50 ppm SO2 at 200°C, the NO conversion efficiency remained at 100 %. The TiO2/Limonite catalyst possessed improved performance due to the introduction of the anatase TiO2, which led to more lattice defects, weak Lewis acid sites, and higher adsorbed oxygen mobility.

Multi-index control strategy from cement calcination denitration system: a model predictive control method for combined control of nitrogen oxide and ammonia escape.

The cement industry is one of the main sources of NOx emissions, and automated denitration systems enable precise control of NOx emission concentration. With non-linearity, time delay and strong coupling data in cement production process, making it difficult to maintain stable control of the denitration system. However, excessive pursuit of denitration efficiency is often prone to large ammonia escape, causing environmental pollution. A multi-objective prediction model combining time series and a bi-directional long short-term memory network (MT-BiLSTM) is proposed to solve the data problem of the denitration system and achieve simultaneous prediction of NOx emission concentration and ammonia escape value. Based on this model, a model predictive control framework is proposed and a control strategy of denitration system with multi-index model predictive control (MI-MPC) is built based on neural networks. In addition, the differential evolution (DE) algorithm is used for rolling optimization to find the optimal solution and to obtain the best control variable parameters. The control method proposed has significant advantages over the traditional PID (proportional integral derivative) controller, with a 3.84% reduction in overshoot and a 3.04% reduction in regulation time. Experiments prove that the predictive control framework proposed in this paper has better stability and higher accuracy, with practical research significance.

Fundamentals of NO reduction by liquid wastes: The first application in hazardous waste incineration

To meet increasingly stringent standards of Nitrogen oxide (NOx), it is highly desirable to develop high-efficiency denitration technology during hazardous waste incineration. Therefore, a state-of-art decoupling combustion technology of liquid hazardous wastes (LHW) has been proposed to achieve low NOx emission. In this technology, LHW is introduced into a low-NOx reactor to reduce NOx generated from solid hazardous waste (SHW) incineration prior to its complete combustion. The present article is devoted to clarifying the optimal conditions for denitration reactions by LHW, so the capabilities of nitric oxide (NO) reduction by reduction by LHW model compounds, namely methanol and methylbenzene, were evaluated in fixed-bed and fluidized-bed reactors. The highest denitration efficiency is 78.9% at 900 °C for methanol and 70.0% at 1000 °C for methylbenzene in the test temperature range. The NO reduction activities were closely associated with cracking characteristics of LHW. The presence of oxygen (O2) exhibited different effects on denitration: it promoted NO reduction at low temperatures due to the generation of more denitration-favored agents but suppressed NO reduction at high temperatures due to the oxidation of denitration-favored agents into CO2 and H2O by excessive O2. Moreover, the fluidized-bed reactor, characterized by good heat transfer, exhibited an approximately 17% higher NO reducing efficiency compared to the fixed-bed reactor at low temperatures, but both reactors demonstrated similar NO reduction efficiencies of around 83% at high temperatures. In addition, methanol and methylbenzene showed higher NO reduction efficiencies than their cracking-produced reducing gases, with the reducing gases accounting for approximately 50% of the overall NO reduction efficiency at 1000 °C. According to the above results, a two-step denitration reaction pathway was proposed in which both cracking-formed free radicals and reducing gases contribute to the overall NO reduction. The results of this study can provide valuable insights for NO reduction in the hazardous waste disposal.

Synergistic effect of oxygen-containing and nitrogen-containing groups on promoting low-temperature denitration over non-metallic carbon-based catalyst

Oxygen-containing and nitrogen-containing groups on the surface of non-metallic carbon-based catalysts have been regarded as active sites for NH3 selective catalytic reduction (NH3-SCR) of nitrogen oxides (NOx) at low temperature. In this study, series of AC-xO-yN catalysts were prepared via grafting oxygen-containing and/or nitrogen-containing groups on active carbon (AC). The activity test results showed that the denitration efficiency of AC-5O-0 N and AC-0O-4 N catalyst were only 20 and 44 % at a temperature of 120 °C and a GHSV of 4500 h−1, respectively, while the activity of the AC-5O-4 N catalysts reached 97 % at the same condition, indicating that the oxygen-containing and nitrogen-containing groups exhibited a superior synergistic effect in facilitating the low-temperature NH3-SCR denitration reaction. Characterization results revealed that the oxygen-containing groups (mainly carboxyl and lactone groups) contribute to NH3 adsorption and activation, while the nitrogen-containing groups (especially pyridine nitrogen groups) could promote NO adsorption and oxidation. The co-existence of oxygen-containing and nitrogen-containing groups can synergistically advance the low-temperature NH3-SCR denitration reaction on the surface of the AC catalyst via a fast SCR route. This work might provide insight into designing and preparing non-metallic carbon-based catalysts with high denitration performance.

Exploration of the Mn-O coordination regulated reaction stability of manganese oxides in NH3-SCR: Effect of deposited ammonium nitrates

Manganese oxide-based catalysts exhibit excellent low-temperature denitration efficiency, making them potential candidates for application. Herein, the relationship between reaction stability and phase structure for MnO2, Mn2O3 and Mn3O4 was disclosed. The NO conversion for Mn2O3 drastically reduced after 120 h reaction, while minor decline was detected for MnO2 and Mn3O4. Based on dedicate qualitative and quantitative analyses on the deposits over catalyst surface, deactivation trigged by ammonium nitrate (AN) deposition was confirmed. Different from penta-coordinated Mn4+ on MnO2 (110) and tri-coordinated Mn2+, penta-coordinated Mn4+ on Mn3O4 (101), the unique tetra-coordinated Mn3+ on Mn2O3 (200) could stabilize the nitrates and make it difficult to be removed via decomposition or reaction and accumulate continuously, which resulted in the significant deactivation. This research could not only unveil the poisoning mechanism of MnOx based catalysts, but also provide new insights into the relationship between the catalytic stability and surface Mn-O microstructure.

Ce doped V-W/Ti as selective catalytic reduction catalysts for cement kiln flue gas denitration.

In cement industry, the selection of catalyst temperature window and the inhibition effect of dust composition in flue gas on catalyst are the key issues of flue gas denitrification. In this article, a pilot study with Ce doped V-W/Ti catalyst on the removal of NOx by selective catalytic reduction with ammonia (NH3-SCR) from the cement kiln flue gas was presented. Cement kiln dust loading on catalysts obviously decreased the NO conversion in the absence of SO2 and H2O, while the denitration efficiency restored from 75 to 98% at 280 ℃ after SO2 and H2O introduced into the reaction system, which mainly because the SO2 may enhance the acidic site on the catalyst surface, and prefer to be bonded with the coordinated Ca species, releasing the active sites poisoned by dust. The NH3-temperature programmed desorption (NH3-TPD), X-ray photoelectron spectroscopy (XPS), and H2-temperature programmed reduction (H2-TPR) detections were performed to reveal that the appropriate Ce and W ratios catalyst contributed better denitrification activity. The optimum ratio of Ce doped catalyst was amplified to form the standard honeycomb monomer catalyst, and then, the activity of catalyst was verified on the side line of cement kiln. The effect of temperature and space velocity on denitrification efficiency was investigated, and the denitration efficiency reached to 92.5% at 300℃ and 3000h-1 space velocity. Moreover, the life of catalyst was verified and predicted by GM (1,1) grey model. The study realized the innovation from the laboratory data rules to the industrial pilot application, providing positive promoting value for the industrial large-scale demonstration application of the catalyst.

Vanadium in strongly correlated electron system Ni1-xVxWO4: Paradoxically boosted deNOx reaction under SOx environment via modulating electron correlation

The persistent challenge of NOx selective catalytic reduction degradation in the presence of SOx has remained unresolved for decades. In this study, we report a paradoxical boosted denitration performance more than 20% under the SOx environment through controlling the charge state of V utilizing strongly correlated electron systems (SCES) in Ni1−xVxWO4. Substitutional doped V at the Ni site, and the computed charge gap from DFT confirms the SCES. Through the manipulation of the strong correlation between V and Ni, V preserves the between + 2–3 charge state in the presence of SOx. Furthermore, we achieved a stable oxidation/reduction cycle and higher denitration efficiency by altering the oxidation point of (NH4)HSO4-contaminated Ni1−xVxWO4. This results from deliberate decrease in Coulombic repulsion between Ni and V, improving electron transfer for catalytic performance. This revelation offers a resolution of exceptional denitration performance within SOx in industrial exhaust systems, exploiting the foundational principles of SCES.

Effect of Pr/Zr atomic ratio on the activity of catalytic oxidation denitration of PrxZr1−xO2−δ

AbstractThe PrxZr1–xO2–δ catalyst with different atom ratio of Pr/Zr was prepared by the sol-gel to catalytic oxidation denitration. Results showed that the efficiency of catalytic oxidation denitration increased initially and decreased afterward with the ratio of Pr atom increased. And the optimum denitration activity could achieve 94.62% at 250 °C when the atom ratio of Pr/Zr was 5:5. The catalysts were characterized by SEM, N2 adsorption-desorption, XRD, XPS, H2-TPR, and FT-IR. The results illustrated that the catalyst (Pr0.5Zr0.5O2–δ) with the best activity has a “layered” morphology, many pores on the surface, and it has a large specific surface area and pore volume of 77.74 m2/g and 0.66 cm3/g, respectively. Furthermore, the crystalline phase transforms from c-ZrO2 to Pr2Zr2O7 with the increasing of Pr atom. XPS and H2-TPR results showed that the surface chemosorption oxygen and surface Pr4+ oxides increased, and the rising of Pr atom ratio was beneficial to produce oxygen vacancy (Vӧ) site which advantageous to improve the efficiency of catalytic oxidation denitration. FT-IR characterization results indicated that Pr0.5Zr0.5O2–δ solid solution had better NO selectivity, which was conducive to the catalytic oxidation of NO. The anti-SO2 and H2O toxicity experiments showed that Pr/Zr atomic ratio at 5:5 had better anti-toxicity than other ratios. In addition, using IC to analysis absorption products, the result showed that NO2– and NO3– were the main products in the absorption solution.

Microwave assisted synthesis of ZnO-TiO2 and its visible light catalytic denitrification activity

Comparing the composite TiO2 prepared by hydrothermal sol gel method and microwave-assisted sol gel method, the microwave-assisted sol gel method with shorter time and better crystallinity was finally used to prepare ZnO-TiO2 materials with different composite ratios. The specific surface area, pore volume and pore size of ZnO-TiO2 composite are significantly larger than those of TiO2. The surface acidity of ZnO-TiO2 composite is stronger. The band structure is conducive to the efficient separation of electrons and holes, and the catalytic reduction activity and selectivity are stronger. The best composite ratio of ZnO and TiO2 is optimized to be 0.2 through photocatalytic denitration experiments. For NOx with an initial concentration of 6.83 mg/m3, under the light source condition irradiated by 65 W energy-saving lamp, the visible photocatalytic removal efficiency is as high as 85%. When the NOx concentration is increased to 13.67 mg/m3 and the ammonia nitrogen ratio is 1:1, the denitration efficiency is as high as 96%, which is 43% higher than that of pure TiO2. According to mechanism analysis, the whole reaction can be divided into adsorption and photocatalysis. Adsorption is the speed control step of the reaction. NO is oxidized to NO2 under the action of adsorbed oxygen, and photogenerated electrons can further reduce NO2 to N2. After NH3 is introduced, NH3 and photogenerated electrons work together to improve NOx removal efficiency.

Integration of dedusting and denitration in V2O5-WO3/TiO2/PTFE-based catalytic bag-filter materials: Lab- and pilot-scale testing and development of SCR models

Removal of dust and NOx from flue gas is highly significant for air pollution control, and integration of these two functions in one unit can greatly improve process efficiency. In this study, a functional catalytic bag-filter material (CBFM) was fabricated from commercial PTFE felt and cheap catalyst V2O5-WO3/TiO2 via a simple immersion-fixation procedure. The attachment of catalysts on PTFE was confirmed, and the material properties of CBFM of various loadings were determined. Their denitration and dedusting performances were investigated individually in lab-scale experiments. Compared to the original PTFE, CBFMs exhibited superior denitration activities, which were positively correlated with temperature (60–90% under 150–210 °C) and negatively correlated with filtration velocity (50–90% under 0.5–0.9 m min−1). On the other hand, introduction of catalysts in PTFE felt did not compromise its filtration efficiency, and almost complete dust removal was achieved. A simplified kinetic model was developed based on Eley-Rideal mechanism, to correlate the materials' denitration efficiency with various operational conditions. The model's accuracy was verified in both lab and pilot environments, where real flue gas from a waste incineration plant was treated with a scaled-up CBFM. In a six-day continuous test, the CBFM maintained >70% NO removal and >99.8% dust removal, confirming its stability and applicability in industrial settings. Therefore, this study offers a low-cost and functional bi-functional filter material capable of efficient simultaneous dedusting/denitration, as well as a simple and practical procedure for its manufacture. In addition, the kinetic model could be applied to speed up production and process optimization, and direct future application of similar materials in real environments.

Effect of Zr Modification on NH3-SCR Reaction Performance of Cu-Ce/SAPO-34 Catalysts

Molecular sieve catalysts containing transition metals have been attracting attention for their potential applications in various fields, including environmental and industrial catalysis. A Cu-Ce-Zr/SAPO-34 series of molecular sieve catalysts were prepared by the impregnation method, and the effect of Zr introduction on the selective catalytic reduction of NO by Cu-Ce/SAPO-34 molecular sieve catalysts was explored. Through various characterization methods, the physical and chemical properties of the catalysts were analyzed, and the denitration mechanism of the molecular sieve catalyst was discussed. This study found that the total acid content of the acid sites on the catalyst surface decreased with the introduction of Zr, leading to a decrease in the denitration efficiency of the catalyst. At 350–400 °C, the denitration efficiency of the 4Cu-4Ce-4Zr/SAPO-34 catalyst was over 80%, and at 400–500 °C, it was over 99%. Moreover, excessive metal Zr could destroy its CHA structure and decrease the denitration efficiency of the catalyst. This study analyzed the reaction mechanism of NH3-SCR of Zr-modified polymetallic zeolites and the effect of Zr modification on the NH3-SCR reaction results. This study contributes to the understanding of the performance of molecular sieve catalysts containing transition metals. Reliable conclusions were obtained, which offer data support for future research in the field of NH3-SCR.

Performance evaluation of NOx absorption by different denitration absorbents in wet flue gas denitration

BackgroundDeveloping efficient denitration absorbents transforming the NOx of flue gas into nontoxic species are critical for wet flue gas denitration (WFGD). MethodPerformance of various denitration absorbents and their unique mechanisms were investigated by a laboratory-scale apparatus, and the denitration efficiency was quantified via response surface method. ResultsThe denitration efficiency were Na2SO3>Na2S>(NH4)2SO3>TEA>KI>Na2S2O3>NaOH>CO(NH2)2>NH3∙H2O>H2O. Na2SO3, Na2S, (NH4)2SO3, TEA, KI and Na2S2O3 removed NO2 by reducing it into NO2− ion, where the denitration efficiency showed positive correlation with reducing ability. The CO(NH2)2 eliminated NO2 by reducing it into nontoxic N2, but the efficiency was limited due to its low reactivity at low temperatures. The alkaline reagents including NaOH and NH3∙H2O promote NOx absorption via acid-base neutralization mechanism leading to both NO2− and NO3− ions formation. For Na2SO3 with highest denitration efficiency, pH significantly affects its efficiency by changing the proportions of its hydrolysate, oxygen weakens the NOx absorption capacity of absorbent by oxidizing SO32− into inert SO42−, and the accumulation of NO2− ions greatly suppresses the denitration efficiency, whereas NO3− ions had negligible effect. The quadratic regression model could accurately quantify and predict the effects of various factors on denitration efficiency.

Investigation of Mg-doping effect on the activity and P tolerance of V2O5-MoO3 /TiO2 catalysts for NH3-SCR

V2O5-MoO3/TiO2 catalyst modified by Mg was studied to obtain higher NOx SCR activity and higher P, SO2, and H2O resistance than the V2O5-MoO3/TiO2. The results show that Mg modification can promote the denitration activity of V2O5-MoO3/TiO2 catalyst, and the maximum NOx removal efficiency of Mg1-SCR catalyst was 97.5%; the optimum reaction temperature and flow rate were 350℃ and 1200mL/min, respectively. Mg doping can broaden the reaction temperature window of the catalyst, and the denitration efficiency can reach more than 87% at 300℃. P2O5 solution was prepared as poisoning precursor and mixed with catalyst to simulate the process of catalyst P-poisoning. The step-wise study showed that Mg0.5-SCR and Mg1-SCR catalyst displays higher durable resistance to P, SO2, and H2O than original catalyst. The degree of denitrification efficiency reduction of Mg1-SCR is 4% smaller than that of Mg0-SCR after passing SO2. Mg0.5-SCR catalyst achieves 88% denitrification efficiency at 350°C after simulating phosphorus poisoning. The catalysts have been characterized by X-ray diffraction, Brunner - Emmet - Teller, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscop, programmed temperature desorption, and programmed temperature reduction. The obtained results suggested that the Mg doping made the active components more dispersed on the surface of the supports, improved the thermal stability of the catalyst, promoted the transition of VOx from monomeric state to polymerized state, inhibited the interaction between P and V, and protected the acid site.

Study on Denitration Performance of Mn-Ce/TiO2 Low-Temperature SCR Catalyst

Low sintering flue gas temperatures and large temperature fluctuations require the development of low-temperature and efficient SCR (selective catalytic reduction) catalysts suitable for the sintering process. It has been shown that modified Mn-Ce/TiO2 catalysts have good denitration capability and have potential commercial use. In this experiment, TiO2-loaded Mn and Ce SCR catalysts were prepared using the impregnation method, and a series of characterizations of the samples were carried out to illustrate the effect of the active material on the denitration efficiency. The kinetic analysis provides theoretical as well as data support for the subsequent optimization of the SCR catalysts. The results show that the denitration efficiency of the catalysts can reach 93.86% when the Mn content is 10% and the Ce content is 3%. The doping of active substances can increase the specific surface area, total pore volume and average aperture of the catalysts and improve the adsorption capacity of the catalysts.

Performance and kinetics of rotating drum biofilter aerobic simultaneous purifying SO2 and NOx

ABSTRACT The rotating drum biofilter (RDB) was investigated as a biological process for purifying SO2 and NOx. After 25 days of film hanging, the inlet concentration was less than 2800 mg·m−3, and the NOx inlet concentration was less than 800 mg·m−3, with greater than 90% desulphurisation and denitration efficiency. Bacteroidetes and Chloroflexi were the dominant bacteria in desulphurisation, while Proteobacteria were the dominant bacteria in denitrification. The sulphur and nitrogen in RDB were balanced when the SO2 inlet concentration was 1200 mg·m−3 and the NOx inlet concentration was 1000 mg·m−3. The best results were obtained SO2-S removal load was 28.12 mg·L−1·h−1 and NOx-N removal load was 9.78 mg·L−1·h−1. when SO2 concentration was 1200 mg·m−3, NOx concentration was 800 mg·m−3, and empty bed retention time (EBRT) was 75.36 s. The liquid phase dominated the SO2 purification process, and the experimental data fit better with the liquid phase mass transfer model. NOx purification was governed by the biological and liquid phases, with the modified biological-liquid phase mass transfer model fitting the experimental data better.

Integrated technology for dust removal and denitration of high-temperature flue gas in coal-fired power plants

A new integrated technology of high-temperature dust removal and denitration, which solves the catalyst problems of wear, blockage, and poisoning caused by the operation of selective catalytic reduction (SCR) denitration systems in coal-fired power plants under high concentrations of particulate matter, is developed. A pilot plant was established for the integrated technical performance test research based on the actual engineering flue gas. The test research results agree well with the design indicator values. The maximum denitration efficiency and potential of the high-temperature dust removal and denitration integrated pilot plant were no <88.445 % and 2.97, respectively. The removal efficiency of sulfur trioxide was > 60 %, and the efficiency improved with the addition of alkaline substances. The removal effect of NaHCO3 on sulfur dioxide was higher than that of calcium hydroxide. The mercury concentration in the flue gas at the outlet increased with an increase in the filtration velocity. The test results provide a reference for the optimization and engineering application of the developed integrated technology and equipment.