Denitration Efficiency Research Articles

Study on The Effect of ‘Ash Core’ on the Performance of Catalysts in the Preparation of SCR Honeycomb Denitration Catalyst

The SCR honeycomb denitration catalyst will have a “grey core” during the preparation process. In this paper, the same batch of fresh catalyst is used to prepare the “grey core” and the normal “yellow core” catalysts for comparison. Through the catalyst denitration performance evaluation test, when the denitration efficiency is 88.3%, the calculated activities of the two catalysts of “yellow core” and “grey core” are 24.9Nm/h and 25.3Nm/h, respectively; when the denitration efficiency is 85.5%, the calculated activity of the catalysts are both 24.5Nm/h. Through analysis of the physical and chemical properties of the catalyst, it is found that the alkali metal content and the alkaline earth metal content of the two catalysts are basically the same. The specific surface areas of the “yellow core” and “grey core” catalysts are 58.65m2/g and 58.24m2/g, respectively. By infrared spectroscopy, the “grey core” catalyst was produced due to the deposition of carbon, and then through the wear performance test, it is found that the “grey core” catalyst has better wear performance, but the “grey core” catalyst is more brittle, when there is external force. At the time, cracks are easily generated in both the axial direction and the radial direction, which is detrimental to the integrity of the catalyst, and also poses a safety hazard to the use of the regenerated catalyst.

Preparation of MnOx Supported LiOH Activated Soybean Oil Sludge Catalyst and Its Analysis in Denitration Mechanism of Selective Catalytic Oxidation (SCO)

Treatment with selective catalytic oxidation (SCO) is an effective technology applied recently for conversion of nitrogen oxides pollution control. In order to solve the problems of high cost and difficulties in practical application of SCO catalyst, it was put forward using the solid waste sludge from soybean oil plant as catalyst carrier to prepare denitration catalyst. The sludge was treated by alkaline activation and then MnOx-based sludge was prepared by impregnation. Finally, MnOx-based sludge was calcined in the muffle furnace. The effects of activation and calcination conditions on catalyst activity were investigated. Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the activity of the sludge based denitration catalyst, and the structure and activity of the sludge based denitration catalyst were furtherly confirmed. According to the achieved results, (1) after activated by LiOH with a mass concentration of 15% for 4 hours, the surface of the sludge catalyst has more alkali functional groups, making the denitration of sludge catalyst the best; (2) the MnOx-based catalyst calcined in the muffle furnace with calcination temperature of 450 °C for 4 hours has obvious denitration efficiency.

Influences of fine-grained NaCl particles on performance and denitration efficiency of activated carbon during sintering flue gas purification process.

Alkali metal chlorides emitted from sintering flue gas are easily adsorbed on the surface of activated carbon (AC) in the purification process. In this paper, NaCl particles adsorbing onto AC were simulated by impregnation method, and the size and morphology of NaCl particles were similar to those of NaCl-PM10 emitted from sintering flue gas. With the adsorption of NaCl particles, 2-10-μm pores of AC were filled, and the specific surface area of AC decreased. But NaCl led to the increase of acidic functional groups on the surface of AC. When 0.75 wt% NaCl was adsorbed, it was beneficial for AC catalytic denitration (de-NOx), because the chemical reaction was strengthened by acidic functional groups, so it showed a certain promotion of de-NOx efficiency. As 1.5 wt% NaCl and 3 wt% NaCl were adsorbed, NaCl had an inhibitory effect on AC de-NOx, which was because the specific surface area of AC decreased, and the prevention of physical adsorption played a major role. As a result, the de-NOx efficiency of AC adsorbed with 3 wt% NaCl decreased from 40.59 to 23.02% at 150 °C. Therefore, the absorption of NaCl fine particles on AC should not exceed 0.75 wt%.

Experimental Study on the Removal of Real Exhaust Pollutants from a Diesel Engine by Activated Carbon

So far, most of the experimental researchers studying the removal of diesel exhaust pollutants have done so with simulated exhaust gas, which cannot demonstrate the ability of catalysts accurately. Because activated carbon (AC) has low price, no secondary pollution, good adsorption performance, and certain catalytic activity, it has good application prospects in the field of marine exhaust pollutant removal. In this paper, the removal of particulate matter (PM), carbon monoxide (CO), and NOx from real exhaust gas by AC was studied. The results show that PM removal efficiency reached up to 77%, while the pressure drop increased with running time. AC may degenerate to some extent with the increase of temperature, resulting in a negative removal efficiency of CO. The denitration efficiency of AC was up to 34.5% without urea, and further increased to 44.8% after spraying urea, still a distance from industrial applications. In the future, it may be necessary to install a fan to compensate the reactor or to backwash the reactor to avoid excessive pressure drop. The thermal stability of the AC also needs to be improved. To increase the denitration performance, it may be helpful to modify the AC or impregnate other metal oxides.

Causes and Countermeasures for Decrease in Denitration Efficiency and Excessive Ammonia Escape in SCR System of Coal-fired Power Plants

The good operation of the SCR flue gas denitration system in coal-fired power plants is of great significance to the environment. This paper introduces the denitrification efficiency drop and the ammonia escape exceeding standard in the operation process of a coal-fired power plant denitrification device. According to the actual situation of the plant equipment and the field investigation results, the problem is analyzed in depth, and the test measures for the optimization of ammonia injection are proposed. Through experiments, reducing the NOx concentration distribution of the outlet is to improve the denitration efficiency of the SCR system, at the same time reduce the ammonia escape rate of the denitration outlet, and ensure the safety, continuity and economical stable operation of the unit equipment.

Iron doped effects on active sites formation over activated carbon supported Mn-Ce oxide catalysts for low-temperature SCR of NO

To clarify the Fe doped effects over activated carbon (AC) supported Mn-Ce oxide catalysts and study the influence of Fe addition on the AC, several Mn/Ce/Fe mixed oxide catalysts prepared via an impregnation method supported on AC were investigated for low-temperature selective catalytic reduction (SCR) of NO with NH3. The Mn-Ce-Fe/AC catalyst with 5% (mass ratio) loading exhibited the highest catalytic activity and yielded above 90% NO conversion at 125 °C with a space velocity of 12,000 h−1. The Fe addition could obviously reduce the destruction of AC surface area. Also, the metal ions could insert into graphite crystallite structures of AC, splitting it into smaller graphene-like sheets. After doping with Fe species, the relative ratios of Mn4+/Mnn+, Ce3+/Cen+ and the surface adsorbed oxygen greatly enhanced in Mn-Ce-Fe/AC catalyst. Additionally, both weak acid and medium acid amount increased significantly after the Fe species introduced in Mn-Ce/AC, which could be attributed to the more exposed active sites of acid due to Fe species or its influence on Mn/Ce species. Relying on the obtained results, a L-H mechanism was proposed, owing to the Fe doping, the average valence state of Mn ions and surface adsorbed oxygen both increased on the Mn-Ce-Fe/AC catalyst, specially accompanying with the surface acid sites promotion, therefore remarkably promoting the denitration efficiency due to all the cumulative effect.

Discussion on the reformation plan of full-section sampling device and precision ammonia injection control technology for denitration system of a 300MW unit

Since the denitration efficiency adjustment method is extremely limited during the operation of the unit, the internal flow field of the denitration reactor is not clear, the denitration efficiency of different catalyst modules cannot be monitored, the ammonia spray is blind, and the ammonia injection amount is difficult to control. Especially under the condition of ultra-low load, in order to ensure that NOX meets the requirements of ultra-low emission, it is necessary to increase the amount of ammonia spray, resulting in large ammonia escape and high risk of air pre-blocking. For this problem, the full-section sampling device for denitration reactor and The optimization and optimization scheme of precision ammonia injection control technology is discussed.

Operation optimization of SCR system based on denitration efficiency prediction model

In this paper, models for NOx emission prediction and denitration costs are built with support vector machine. The effects of the factors such as SCR inlet NOx content, unit load, oxygen content of exhaust gas, ammonia injection rate, air distribution condition, and coal type on NOx reduction are discussed. The denitration costs under different working conditions are calculated. The ammonia injection rate is optimized with genetic algorithm. It can be shown that the actual ammonia injection rate is 1%-3.5% lower than the optimal value.

Urea solution of single droplet pyrolysis characteristics research and engineering application

The experimental bench for the pyrolysis characteristics of single droplets of urea solution was established to analyze the variation characteristics of the whole process of single droplet evaporation pyrolysis. The results show that there are a large number of bubbles in the droplets which are very favorable for pyrolysis, the pyrolysis energy and atomization degree are insufficient, leading to the formation of intermediate products, greatly reducing the efficiency of denitrification. Based on the experimental data, the urea pyrolysis system was developed and designed for the SCR denitrification project of a coal-fired boiler in a thermal power plant, and key equipment was optimized, including urea storage and supply system, denitration reactor system, spray gun device, pyrolysis furnace body, etc. The system was put into operation. After that, the NOx concentration was reduced from 250mg/Nm3 to 20 mg/Nm3, and the denitration efficiency reached over 90%. The project has strong engineering application value.

Pilot scale study on medium/low temperature SCR denitration technology for industrial flue gas

Based on laboratory research, the titanium-based honeycomb molding catalysts with MnOx/CeO2/V2O5 as the main active material were prepared, and a pilot scale study on medium/low temperature SCR denitration technology for ceramic kiln flue gas was carried out on a 5000 m3/h pilot scale equipment. The influences of flue gas flow, ammonia-nitrogen molar ratio and ammonia concentration on denitration efficiency were investigated. The result showed that the medium-low temperature SCR denitration technology had an excellent NOx removal efficiency. Under the conditions of the flue gas flow was 3000 m3/h, the ammonia-nitrogen molar ratio was 1.2:1, and the ammonia concentration was 25%, the NOx removal efficiency coulld reach 86%, and NOx emission concentration and ammonia escape amount were less than 40 mg/m3 and 1 mg/m3 in the flue gas, respectively. The technology can achieve deep reduction of NOx in ceramic kiln flue gas, and has a good application prospect.

Quantum Chemical Study on the Reaction Mechanism of Fast SCR Catalyzed by ZSM-5 Doped with Mn/Co–Al/Ce

Fast selective catalytic reduction (SCR) is regarded as a good choice to improve the SCR denitrification efficiency and reduce the using of catalyst. For a good understanding and further improvement, the investigation on the mechanism of SCR and fast SCR is essential. A four-step catalytic mechanism for SCR and fast SCR catalyzed by ZSM5 doped with Mn/Co–Al/Ce is proposed in this paper, and the catalytic mechanism is studied in detail by using the method of quantum chemistry. Results show that, by using ZSM5–Mn/Co catalyst, the activation energy of fast SCR (83.35/87.55 kJ/mol) is much lower than that of SCR (154.98/219.70 kJ/mol). This indicates that fast SCR has a better catalytic effect and higher denitration efficiency. Moreover, when Al/Ce is added into ZSM5–Mn/Co, the active center Si is replaced by Al/Ce, and the activation energy of fast SCR is further decreased to about 40–60 kJ/mol. This shows that the catalysts for SCR and fast SCR not only relate to the supported transition metal such as Co and Mn, but also highly relate to the activity center such as Al and Ce.

Simultaneous Removal of SO2 and NOX by a Combination of Red Mud and Coal Mine Drainage

Simultaneous removal of sulfur dioxide (SO2) and nitrogen oxides (NOX) is an important research field in air pollution control. The combination application of red mud (RM) with coal mine drainage as absorbent in simultaneous desulfurization and denitrification is an innovative attempt. In this study, a series of bubbling and spray tower tests were conducted to improve desulfurization and denitration abilities. Effects of RM concentration, gas flow, liquid–gas ratio, and SO2 concentration were investigated in the test. Our results indicated that SO2 removal efficiency depends primarily on RM concentration, gas flow, and the liquid–gas ratio. In the denitration test, the denitration characteristics of the absorbent were not consistent with industrial requirements, but denitration ability could be improved by the addition of an oxidant. In addition, influence of interactions between SO2 and NOX was observed, and low concentrations of SO2 could enhance NOX absorption, whereas high SO2 concentrations inhibit NOX absorption. Meanwhile, NOX concentration has a negligible effect on SO2 removal. Under optimized conditions, such as with RM concentration of 12%, gas flow of 40 L/min, liquid–gas ratio of 20 L/m3, absorbent renewal rate of 15%, and a sodium chlorite concentration of 1.9%, desulfurization efficiency is >99.0%, and denitration efficiency ranges from 45.0% to 47.0%. RM and mine water slurry show strong potential as a novel absorbent for the simultaneous removal of SO2 and NOX. This study provides a potential feasible technology for reusing RM and coal mine drainage with low cost instead of conventional method.

Enhanced low‐temperature Selective Catalytic Reduction (SCR) of NOx by CuO‐CeO2‐MnOx/γ‐Al2O3 mixed oxide catalysts

A series of CuO‐MnOx‐CeO2/γ‐Al2O3 catalysts in different ratios were synthesized by a sol‐gel method with the purpose of improving the low‐temperature denitration performance (loading a transition mental oxide (MnOx, CeO2) on a CuO/γ‐Al2O3 copper‐based catalyst). The denitration performance of a low‐temperature SCR under the condition of simulated flue gas was measured using the programmed heating method in the catalytic reaction efficiency evaluation system. The denitration efficiency of the 6 % CuO‐5 % MnOx‐10 % CeO2/γ‐Al2O3 catalytic particles was maintained at over 80 % within a temperature range of 100–200 °C. The catalysts were characterized by surface area analysis (BET), x‐ray diffraction (XRD), and scanning electron microscopy (SEM). The best surface structure characteristics include the 5 % MnOx + 10 % CeO2 loading capacity of the catalyst, which was indicated by a BET analysis. The catalyst surface structure characteristics were effectively promoted by the amount of CeO2 and MnO2 loading proved by the SEM analysis. The possible mechanisms involved in SCR denitration at a low temperature were also discussed. The experimental results revealed that the catalyst granule with perfect surface characteristics and pore features was successfully synthesized by the sol‐gel method. The denitration performances were restrained by 10 % of H2O and 800 mg · m−3 of SO2, indicating that SO2 and H2O have an inhibiting effect on NOx conversion.

A superior liquid phase catalyst for enhanced absorption of NO2 together with SO2 after low temperature ozone oxidation for flue gas treatment

NOx and SO2 are the main air pollutants emitted from the coal-fired combustors. Since the typical combination of selective catalytic reduction (SCR) and wet flue gas desulfurization (WFGD) is not suitable for some of industrial flue gas treatment due to their unsuitable temperature window and limited retrofitting space, new technologies must be developed. This paper proposes an effective wet method for simultaneous removal of NOx and SO2. The insoluble NO was first oxidized into NO2 by ozone, and then NO2 together with SO2 were both absorbed in one wet wash tower. To further improve NO2 removal efficiency, a new kind of additive was proposed and tested. Effects of various influence factors, such as additive concentration, residence time in the wash tower, liquid/gas ratios, initial NO/SO2/O2 concentration and slurry pH value, were carefully evaluated in a home-designed experimental platform. Results indicated that the NOx removal efficiency was positively correlated with the increasing the additive concentration, while the maximum denitration and desulfurization efficiency were more than 95% and 86%. The NOx removal efficiency was enhanced with the increasing residence time and liquid/gas ratios. The alkaline environment was verified to be beneficial for the simultaneous absorption process. The exiting O2 in flue gas would not consume additives, and the denitration and desulfurization efficiency were insensitive to the initial NO and SO2 concentration as well. Only 2% decrease of the denitration efficiency was observed after 300 mins stability test, while the desulfurization efficiency kept >98%. With the characterizations of Ion Chromatograph (IC), NO2−, NO3− and SO42− were detected as the main absorption by-products anions, whereas NO2− accumulation would inhibit the overall NOx removal. Finally, the mechanism of simultaneous removal of SO2 and NO using the novel liquid phase catalyst was proposed and discussed.

Improvement of SO2 Resistance of Low-Temperature Mn-Based Denitration Catalysts by Fe Doping.

The influence of vapor and SO2 in coal firing flue gas on the selective catalytic reduction activity of Mn/γ-Al2O3 and Mn–Fe/γ-Al2O3 catalysts was investigated at 150–275 °C. Denitration experiments and detailed characterization of catalysts were conducted. Vapor had no chemical effects on denitration, and the mechanism of SO2 deactivating the Mn/γ-Al2O3 catalysts was investigated in detail. This is due to the reaction between MnO2 and SO2 and the ammonium sulfate deposits forming on the surface. Sulfation of the Mn-active component was significantly reduced by doping the Mn/γ-Al2O3 catalyst with Fe. Iron doping also lowered the stability of the ammonium sulfate surface deposits, forcing them to rapidly decompose. Thus, iron doping significantly improved SO2 resistance and the denitration efficiency of Mn–Fe/γ-Al2O3 catalysts was not clearly decreased.

The Effect of K Salts on SO2–SO3 Conversion and Denitration Behavior over V2O5–WO3/TiO2 Catalysts

A series of V2O5–WO3/TiO2 catalysts treated by KCl or K2SO4 were prepared using the equal volume impregnation method. The effects of adding these K salts on SO2–SO3 conversion and on denitration behavior over the catalyst were studied, using reactor trials and various characterization methods, including NH3-TPD, H2-TPR, ICP, BET, XRD, SEM, FT-IR and XPS. The results of catalytic activity evaluation tests show that adding K salts decreases the denitration efficiency, while SO2 enhances the activity of the KCl-poisoned catalyst to an extent. The presence of K salts also improves the SO3 formation rate, such that the SO3 formation rate for the K2SO4-poisoned catalyst is as high as 1.53% at 410 °C (compared with 0.60% for the fresh catalyst). The characterization data indicate that K salts aggregate on the catalyst surface, blocking the pores of the catalyst. The reduction ability of the catalyst is decreased slightly and new weakly acidic sites appear. In addition, the concentration of strongly acidic sites declines. SO2 can increase the surface acidity of the catalyst. K salts increase the number of V5+=O bonds and weakly acidic sites, but consume oxygen atoms along with V and W species. Importantly, the strength of the V5+=O bonds, the concentration of surface chemically adsorbed oxygen and the V4+/V5+ ratio all played vital roles in improving the conversion of SO2–SO3 and in enhancing the NO reduction.

Mechanism and Performance of the SCR of NO with NH3 over Sulfated Sintered Ore Catalyst

A sulfated sintered ore catalyst (SSOC) was prepared to improve the denitration performance of the sintered ore catalyst (SOC). The catalysts were characterized by X-ray Fluorescence Spectrometry (XRF), Brunauer–Emmett–Teller (BET) analyzer, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared spectroscopy (DRIFTS) to understand the NH3-selective catalytic reduction (SCR) reaction mechanism. Moreover, the denitration performance and stability of SSOC were also investigated. The experimental results indicated that there were more Brønsted acid sites at the surface of SSOC after the treatment by sulfuric acid, which lead to the enhancement of the adsorption capacity of NH3 and NO. Meanwhile, Lewis acid sites were also observed at the SSOC surface. The reaction between −NH2, NH 4 + and NO (E-R mechanism) and the reaction of the coordinated ammonia with the adsorbed NO2 (L-H mechanism) were attributed to NOx reduction. The maximum denitration efficiency over the SSOC, which was about 92%, occurred at 300 °C, with a 1.0 NH3/NO ratio, and 5000 h−1 gas hourly space velocity (GHSV).

Experimental research on performance test after SCR denitration system ultra-low emission retrofit in a 600 MW coal-fired unit

A systematic performance test was carried out for the ultra-low emission modification project of the Selective Catalytic Reduction (SCR) denitration system of a 600 MW coal-fired unit in a thermal power plant. Terms of the performance tests include denitration efficiency, ammonia escape rate, and SO2/SO3 conversion rate. The distribution of gas velocity and NOx concentration in flue gas of SCR inlet and outlet were summarized. The effect of unit load and gas velocity to denitration efficiency, ammonia escape rate and SO2/SO3 conversion rate were discussed after the test. The result favours design and retrofit of the ultra-low emissions coal-fired power unit in China. Through technical trials, a set of practical test methods suitable for the actual situation was concluded.

Effect of the Cement Raw Meal Rate Value on SNCR deNOx Efficiency with NH<sub>3</sub> as Reducing Agent

Many complex factors can affect the process of SNCR in cement calciner, and the cement raw meal rate value is a relatively important one. In the present study the influence of the cement raw meal rate value on the SNCR denitration efficiency was investigated in a tubular reactor with a space velocity of 27000 ml/h in the temperature range of 700-1100 °C, and the oxygen concentration was 5% and both the inlet concentration of NO and NH3 was designed as 1000ppm. The results showed that the denitrification rate of SNCR decreased with the increase of the lime saturation factor (KH) of cement raw meal and increased with the increase of aluminum rate (IM) of cement raw meal at 700~900 °Crecommended that the cement raw meal with low KH, medium silica acid rate (SM) and high IM should be used. In the temperature range of 900~1100 °C the denitrification efficiency of SNCR increased with the KH and decreased with the increase of IM. Based on the experimenyal results it is suggested that the cement raw meal with high KH, high SM and low IM should be adopted.

Large eddy simulation of transient turbulent flow and mixing process in an SCR denitration system

Selective catalytic reduction (SCR) with ammonia is a key technology to reduce the NOx emissions from the coal-fired power stations. The denitration efficiency of SCR system depends on whether the flue gas and ammonia can get a good mixing in the reactor. Combined with the species transport model and porous medium model, the large eddy simulation (LES) is carried out to simulate the transient multi-species flow in an SCR system at a 310MW coal-fired station. Predicted transient total pressure drop histories for various loads are compared against the measurements, and close agreements are achieved for the mean values. The instantaneous velocity field is composed of various small recirculation zones and multiple vortices, and their positions and intensity are ever-changing. For the SCR reactor without any gate leaves, a big secondary recirculation flow is found around the straightener, and several dead zones of ammonia mass fraction distributions are found at the corners of the catalyst layers. The mixing quality is improved significantly by incorporating a series of gate leaves. Predicted transient turbulence information by LES may be important for the optimization of the SCR reactor structure.