SCR Denitration Research Articles

Vanadium Recovery from Spent SCR Denitration Catalyst by Reductive Acid Leaching and Ammonium Precipitation

Vanadium Recovery from Spent SCR Denitration Catalyst by Reductive Acid Leaching and Ammonium Precipitation

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.

Online and Offline Parameter Optimization of SCR Denitration Control in Power Plants

Online and Offline Parameter Optimization of SCR Denitration Control in Power Plants

SO42− immobilization regulated by reaction atmosphere over ABS poisoned α-Fe2O3 catalysts for efficient NOx removal

SO42- immobilization is pivotal for boosting the catalytic performance of iron oxides in NH3-SCR. However, the critical issue related to sulfate species enrichment on α-Fe2O3 is still elusive. Herein, by employing ammonium bisulfate (ABS) as the source of SO42-, we conducted a detailed investigation on the effect of reaction atmospheres (NH3, NO + O2 and NH3 + NO + O2) on the immobilization of sulfate species and their consequence for ABS poisoned Fe2O3/SiO2 (ABS/FeSi) catalysts in NH3-SCR. Results showed sulfate group could be transferred from ABS to FeSi under thermal treatment and the efficiency actually exhibited an atmosphere-dependent feature. The promotion effect from NO/O2 was most prominent due to accelerated consumption of NH4+, whereas NH3 treatment retarded ABS pyrolysis, resulting in reduced sulfate immobilization on FeSi surface. Besides, an unexpected effect on Fe2O3 disintegration was exhibited by NH3, which was detrimental to activity enhancement due to disruption of electronic property. By correlating catalytic performance with adsorption feature, we propose the occurrence of reaction via E-R pathway over sulfated FeSi catalysts. The result of present study can enrich our understanding on the controlled sulfate immobilization for robust SCR denitration.

Halogen modified Cu-Ce-BTC catalyst for NH3-SCR: Combination of NO and Hg0 removal experiments and mechanism analysis

Nitrogen oxides (NOx) and mercury (Hg0) produced from coal combustion are harmful to atmospheric environment. Therefore, the development of high-performance SCR denitration synergistic mercury removal catalysts has practical significance. In this study, a series of halogen-modified Cu-Ce-BTC were synthesized. The structural properties were characterized by SEM-EDS, XRD, FTIR, Raman, BET, XPS, and the synergistic denitration and mercury removal performance were investigated. The results show that, before and after modification, the catalyst still maintain original physical and chemical properties, with the appearance of C-X (Cl, Br, I), indicating that the successful incorporation of halogens into Cu-Ce-BTC. The performance was examined through NH3-SCR, the catalytic activityis followed the order: Cl > Br > I. When Cl was 7%, the removal rates of NO and Hg0 reached 96.19% and 84.64% at 240 ℃. O2 had a significant promoting effect on NO and Hg0 removal. NO had a minor influence·NH3 facilitated NO removal and inhibited Hg0 removal. SO2 and H2O had a certain inhibitory effect on NO and Hg0 removal, with H2O showing a more pronounced inhibitory effect.

Study and management of flow and concentration field problems in 600 MW SCR unit

With the increasingly stringent national requirements for environmental protection, the control of pollutants in coal-fired power plants has been gradually strengthened. In order to meet the NOx emission standard, some coal-fired units achieve ultra-low emissions by excessive ammonia injection, which seriously affects the unit operation economy. This paper takes the SCR denitrification unit of a 600 MW coal-fired unit with a Π-type furnace in China as the research object and studies the distribution of flow and concentration fields inside the unit under a 60% load section by means of CFD numerical simulation. It points out the problems of flow and concentration fields at local locations under current operating conditions and proposes the rectification of the corresponding area of the inflow equipment and the idea of a zonal ammonia injection optimization method. It provides a certain reference value for the optimized management of the denitrification system of coal-fired units in the future.

Dynamic NOxPrediction Model for SCR Denitrification Outlet of Coal-Fired Power Plants Based on Hybrid Data-Driven and Model Ensemble

Dynamic NO<i>_x</i>Prediction Model for SCR Denitrification Outlet of Coal-Fired Power Plants Based on Hybrid Data-Driven and Model Ensemble

Application of SCR Denitration in Treatments of Nitrogen Oxides in the Air

This article mainly introduces the background of nitrogen oxides in air pollution and SCR technology in detail. SCR has become a very wide range of pollution control technology in recent years, because it saves energy, produces no pollution, and is easy to operate. The article clearly lists the reaction mechanism, reaction materials and matters needing attention when SCR is applied. As a problem that has plagued people for several years, air pollution has always existed in our daily life. If SCR technology is well applied, air pollution will be effectively controlled in the near future.

Variations in the physicochemical properties of spent honeycomb V2O5-WO3/TiO2 catalysts from PC and CFB boilers SCR denitration systems

The massive production of spent honeycomb V2O5-WO3/TiO2 catalysts has caused serious environmental hazards. Revealing the physicochemical property variations of the spent catalysts is of great significance to clarify the deactivation mechanism of catalysts and the recovery of the spent catalysts. This study focused on the changes of typically spent catalysts, selected from pulverized coal (PC) and circulating fluidized bed (CFB) boiler deNOx systems, morphologies, pore structure, chemical composition, carrier, and active components properties, etc. The activities of most spent catalysts could be to more than 95% at 300–400 °C after vibration cleaning. The pore blockage caused by fly ash and sulfur deposition is the major deactivation factor of the catalysts from the two furnace systems. The catalysts from CFB furnaces are more easily deactivated, which is owing to they are more prone to occur severe pore structure loss. The transformation of anatase to rutile TiO2 as one of the major factors causing the pore structure loss would form the irreversible deactivation of the catalysts. The valence state of the active component V has shifted. The spent catalysts from PC systems typically exhibit higher V4+/Vn+ ratios. However, those from CFB systems display a noticeable decrease, which may be attributed to the formation of CaWO4, resulting in the destruction of dispersed active sites on the surface. Finally, the deactivation mechanism of the spent catalysts from different furnaces of coal-fired power plants was summarized. This research is beneficial for further modification of SCR catalysts under different application conditions and provides valuable insights into the classification and recycling of the spent catalysts.

Low temperature SCR denitration with NH3 by highly dispersed Ni–Cu Sites: An insight into surface acidity and redox ability

Surface acidity and redox ability are critical factors affecting the NH3 and NO adsorption-activation in the selective catalytic reduction of NOx with NH3 (NH3-SCR). Herein, CuyNi3-yAlOx (y represents the Cu/Al ratio) mixed oxides with highly dispersed Ni-Cu dual active sites were constructed from the layered double hydroxide precursors to optimize the acidity and redox ability. Compared with other CuyNi3-yAlOx (<80%), Cu1.5Ni1.5AlOx delivered a NOx conversion as high as 90% at 200 °C. Moreover, Cu1.5Ni1.5AlOx possessed superior N2 selectivity (92% above 200 °C), catalytic stability (64 h), and H2O and SO2 resistance. Characterization demonstrated that Cu and Ni species in CuyNi3-yAlOx had interactions, and the interactions were derived from the electron transfer and influenced by the Ni/Cu ratio, inducing the formation of highly dispersed Ni–Cu sites. Cu1.5Ni1.5AlOx with a Ni/Cu ratio of 1 achieved the strongest interaction. That interaction could inhibit nanosheet agglomeration, increase surface acidity, and improve low-temperature reducibility, in favor of NH3 and NO adsorption/activation. It was discovered that the Ni–Cu sites participated in the NO and O2 activation, respectively, and accounted for the NH3 adsorption-activation, synergistically. More active intermediates (NH3/NH4+, bridging/bidentate nitrate) were produced by Langmuir-Hinshelwood and Eley-Rideal mechanisms over Cu1.5Ni1.5AlOx. This study offered light on fabricating effective functionalized active sites to promote NH3-SCR performance.

Understanding the temperature-dependent H2O promotion effect on SO2 resistance of MnOx-CeO2 catalyst for SCR denitration

Understanding how H2O affects SO2 tolerance of SCR catalysts at different working temperatures is of great importance. Herein, we reported that H2O addition at ultra-low temperature of 100 °C induced a significant promotion on SO2 tolerance of MnOx-CeO2 catalysts. Sole SO2 led to serious activity loss from 100% to 20%, while H2O coexistence alleviated the deactivation and an admirable activity of 60% was reserved. Combining experimental characterizations with DFT calculation, we demonstrated that H2O promoted hydroxyl formed on defect sites, which promoted more sulfite formation and retarded sulfates with strong electron-withdrawing capacity disturbing active Mn sites. In comparison with sulfates, sulfites exhibited less interference in adsorbed species, ensuring the occurrence of Eley-Rideal and Langmuir-Hinshelwood mechanisms. The present study discloses the unique temperature-dependent effect of H2O on SO2 tolerance, which is expected to deepen our understanding on the role of H2O in modulating surface species and catalytic behaviors of SCR catalysts.

Experimental research on the volatilization and condensation of ammonium bisulfate as SCR byproduct

Abstract In this paper, the research progress of ammonium bisulfate (ABS) volatilization in coal-fired power plants the SCR denitrification process was reviewed. Combination with self-made experiments, SEM, flue gas analyzer and TG-DTG curves of ABS and ion chromatography. The volatilization and condensation characteristics of ABS were investigated carefully. Results show that as the temperature increased by 50 oC, the ABS/AS volatilization rate increased by an order of magnitude. The decomposition process of ABS should have a two-step reaction. The reaction in the initial volatiliza-tion stage is ABS dehydration turned into (NH4)2S2O7. The reaction in the rapid volat-ilization stage is (NH4)2S2O7 decomposed into NH3, N2, SO2 and H2O. There is an inter-section in the reaction temperature range (especially 300 oC) between the two-step re-action. This research provides an experimental basis for temperature control of ABS to avoid air pre-heater fouling.

Application progress of small-pore zeolites in purifying NOx from motor vehicle exhaust

• Small-pore SSZ-13 and SSZ-39 zeolites have unique advantages in purifying NOx. • Pd/zeolites as PNAs present the superior low-temperature NOx adsorption activity. • Non-precious metal Co/zeolite is an ideal substitute for Pd/PNAs to reduce the cost. • Cu/zeolites possess the excellent high-temperature NH3-SCR catalytic activity. • Fe/Mn/Ce doped Cu/zeolites can broaden the NH3-SCR active temperature window. Lean-burn mode results in the high NOx emission of diesel vehicles despite its high fuel economy. NOx can be effectively removed by the SCR unit during normal operation, however, elimination during the cold start period needs to be addressed soon. Passive NOx adsorber (PNA) was proposed to adsorb and store NOx emitted during the cold start period. With the increase of exhaust gas temperature during normal operation, the adsorbed NOx will be quickly released and efficiently converted to N 2 when flowing through the downstream SCR catalyst. After years’ investigation, small-pore zeolites such as CHA and AEI have been found to possess superior hydrothermal stability and NOx selectivity compared with medium and large pore zeolites, and the former’s eight-membered ring structure effectively exclude large hydrocarbons from entering the zeolite channels, making them play a prominent role in NOx purification via both PNA and SCR units. SSZ-13 and SSZ-39 zeolites, which belong to CHA and AEI topologies respectively, has been confirmed to exhibit excellent low-temperature NOx adsorption performance and high-temperature SCR denitrification performance. In the field of purifying NOx from the diesel vehicle exhaust, the review simultaneously focused on the application of SSZ-13 and SSZ-39 zeolites in NOx purification from two aspects of PNA and SCR in recent decades. In addition, the unique advantages of their modified form of loading Pd/Co as PNAs, or loading Cu doped with Fe/Mn/Ce as SCR catalysts were systematically clarified, in order to provide some advanced guidance for the researchers in the purification of NOx from the diesel engine exhaust.

Exploring the effect of calcination temperature and sulphuric acid impregnation treatment on the NH3-SCR activity of cold-rolled sludge

In recent years, sulphate materials have received more and more attention because of high activity in the selective catalytic reduction of nitrogen oxides with ammonia (NH3-SCR). In this paper, a series of catalysts for NH3-SCR were prepared by sulphuric acid impregnation and calcination at different temperatures of cold-rolled sludge which main component is iron oxide. The performance of cold-rolled sludge catalyst was measured by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), temperature programmed-reduction of hydrogen (H2-TPR), temperature programmed desorption of ammonia (NH3-TPD) and X-ray photoelectron spectroscopy (XPS). It was demonstrated that the increase of iron sulphate and Fe3+ content can be observed in the cold-rolled sludge after sulfuric acid impregnation and low temperature calcination (300 ℃), which leads to the improvement of SCR denitration performance. The results show that 100% denitration conversion can be achieved at 280 °C via the modified cold-rolled sludge, with 94% of the performance was retained after the introduction of SO2 and H2O for 5 h. There are minor morphological structural changes in the catalyst, while the redox properties and acidity of the catalyst changed significantly after the treatment process of sulfuric acid impregnation and calcination. This means that the enhanced redox properties and acidity of the catalyst play a key role in improving the activity of NH3-SCR.

Research progress in the SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; resistance of denitration catalysts in low-temperature NH&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;-SCR reactions

<p indent="0mm">NH₃-SCR reaction is one of the most widely used denitration technologies at present, and the catalyst is the core of the NH₃-SCR technology. Because of its low-temperature activity and easy deactivation in the presence of SO₂, the research on the low-temperature sulfur-resistance of denitration catalysts becomes a hot spot. In this review, the deactivation mechanism of NH₃-SCR catalysts in the presence of SO₂ is reviewed. It is found that the deactivation of the catalysts is mainly due to the reaction of SO₂ with NH₃ and metal-active sites; the formation of ammonium sulfates or ammonium bisulfates will block the pores of the catalysts and affect the efficiency of the catalysts; the metal sulfates will lead to the deactivation of the active sites of the catalysts and cause the irreversible deactivation of the catalysts; the competitive adsorption of SO₂ and NO will also cause the deactivation of the catalysts. Based on the known mechanism of catalyst deactivation, some effective strategies for improving the SO₂ tolerance are proposed: reducing the adsorption and oxidation of SO₂, constructing sacrificial sites to protect active sites and promoting the decomposition of sulfates. It is found that the sulfur resistance of the catalysts can be improved by some methods: such as metal modification, the special structure of catalysts, the influence of supports, acid catalysts. Finally, the development prospect of low-temperature sulfur-resistant NH₃-SCR denitration catalysts is prospected.

Study on denitration performance of multi element modified MIL-101 (Fe) at low temperature

MIL-101 (Fe) was modified by amino group and doped by Cu and Co elements by microwave hydrothermal method. The effect of SCR denitrification at low temperature was investigated with high concentration of NOx as adsorption object. The results show that when the flue gas temperature is 200 °C and the NOx concentration is up to 1640 mg/m3, the removal efficiency of NOx can reach 86% under the optimal conditions, which is 1.5 times higher than that before modification. In addition, the characterization results indicated that the specific surface area of the modified catalyst increased, the thermal stability was good at low temperature, the selective adsorption capacity of NO was enhanced, and the doping played a synergistic catalytic role. It can be used for flue gas denitration in various industries.

Synthesis of Cu-BTC by room temperature hydrothermal and its low temperature SCR denitration

In this paper, the room temperature hydrothermal synthesis method was used instead of the traditional solvothermal synthesis method to successfully prepare Cu-BTC, the growth of Cu-BTC was studied, and it was successfully applied to SCR flue gas denitration. The physic-chemical properties of catalyst samples were characterized by multiple techniques, such as SEM, XRD, FTIR, XPS and BET. The results showed that: (1) Cu-BTC prepared at different reaction times maintained its unique hexagonal prism crystal structure. As the reaction time increased, the purity and specific surface area of Cu-BTC gradually increased, up to 1521.320 m2/g. (2) Cu-BTC-30 h catalyst had a high Oα/(Oα+Oß) ratio and could act as an electron acceptor to react with NO. The surface of the catalyst contained two valence state (Cu2+ and Cu+), and Cu2+ was dominant. (3) As the preparation time of the catalyst increased, the denitration also increased. When the preparation time was 30 h, the denitration rate reached the highest at 270 °C, which was as high as 90.36%.

Establishment of NOx Concentration Model at the Outlet of SCR Denitrification System for Alkali Recovery Furnace Flue Gas Based on Improved LSSVM

In the case of alkali recovery, it is difficult to measure with precision the NOx concentration at the output of the denitrification system. In order to solve this problem,variable adjustment experiments was carried out on the work site. According to the obtained modeling data, the least squares support vector machine (LSSVM) optimized by adaptive inertia weight particle swarm optimization (AIWPSO) was used to establish the NOx concentration model at the outlet of the SCR flue gas denitrification system in the alkali recovery section. Finally, comparing the model with the traditional mechanism model, the verification results show that the outlet NOx concentration model based on AIWPSO optimized LSSVM had the better fitting ability and error precision.

Shear Stress on the Structure Control of a Supported Fly Ash‐Based Catalyst and Its Application in SCR* Denitration

AbstractNitrogen oxides (NOx) are one of the air pollutants, mainly from coal‐fired power plants, industrial furnaces, etc. In order to control NOx, reduce the preparation cost of denitration catalyst. Selective catalytic reduction is currently the most effective and mature technology for removing NOx. In this paper, solid waste fly ash was used as catalyst carrier, shear reactor was used to prepare Mn−Ce/FA catalyst, and successfully applied to SCR denitration. The catalyst was characterized by SEM, XRD, FTIR, XPS. The results showed that the catalyst prepared by shearing had more dispersed active components. When the power was 80 W, time was 20 min, rotation speed was 120 r/min, and the molar ratio of Mn−Ce was 1 : 1, the optimal catalyst was prepared. Under these conditions, the catalyst had the best activity and strong stability, the denitration performance was the best, up to 82.6 % within 30 min. The introduction of SO2 still showed high catalytic activity and stability, and the removal rate reduced to 73.21 %. After SO2 was stopped, the removal rate rebounded to 77.89 %. Also, Mn−Ce/FA catalyst had good cyclability and stability in the denitration process.

Enhancement of Hg0 oxidation removal in chloride-free flue gas over FeOCl-modified commercial selective catalytic reduction catalyst

SCR denitration catalysts have been considered for the synergistic catalytic oxidation of gaseous elemental mercury (Hg0) depending on HCl in flue gas. In this study, FeOCl was used for the enhancement of Hg0 removal in chloride-free flue gas over a commercial SCR catalyst. The results indicated that loading 10% FeOCl can significantly improve the Hg0 removal efficiency of SCR catalyst to 97% at 250 °C in chloride-free flue gas. O2 exerted an important positive effect on the conversion of Hg0 to HgO. The FeOCl/SCR catalyst exhibited satisfactory SO2 and H2O resistance. The examination of the mechanism of action indicated that Hg0 reacts with •Cl released from FeOCl/SCR to form HgCl2. A spot of Hg0 can directly react with adsorbed surface oxygen to generate HgO fixed on the active site of FeO on the FeOCl/SCR catalyst via chemisorption.