Selective Catalytic Reduction Reactor Research Articles

Investigation of the complex 3D flow structure within a selective catalytic reduction (SCR) reactor of a coal-fired power plant

A selective catalytic reduction (SCR) reactor is commonly used to remove nitrogen oxides (NOx) from coal-fired boilers. Uniformity of the flow passing through the catalyst layer is important for increasing denitrification (de-NOx) efficiency. In order to examine flow uniformity, this study conducted an experimental and numerical analysis of the complex internal flow within a realistic SCR model. Magnetic resonance velocimetry (MRV) was utilized to obtain non-invasive measurements of three-dimensional three-component average velocity and validate Reynolds-averaged Navier-Stokes (RANS) numerical simulations. The computational results showed similar overall flow structure compared with the MRV results. Parameters representing flow quality such as relative standard deviation (RSD) and recirculation zone strength (RZS) were calculated by integrating the flow field. These parameters have the largest value after the straightener area and decrease towards the catalyst reactor, and are not significantly affected by Reynolds number upstream of the catalyst layer. The recirculation zone size was analyzed using spanwise uniformity and skewness indicators. As the recirculation zone induces biased flow, the non-reacted NOx concentration was more prominent in the outlet zone opposite of the recirculating area in the corresponding actual on-site SCR reactor. Based on this finding, a meaningful correlation between flow maldistribution and de-NOx reaction could be deduced.

A Model for Predicting the Erosion Rate Induced by the Use of a Selective Catalytic Reduction Denitrification Technology in Cement Kilns Flue Gas

Selective catalytic reduction (SCR) is a technology by which nitrogen oxides are converted with the aid of a catalyst into diatomic nitrogen and water. It is known that the catalyst can be easily eroded if a cement kiln with a high-dust content is considered. To understand this process, numerical simulations have been carried out considering a single catalyst channel in order to study the collision and erosion of fly ash and catalysts at meso scale. Based on a response surface methodology, the effects of five factors on the erosion rate have been studied, namely, the catalyst particle velocity, the particle size, the particle concentration, the incidence angle and the catalyst porosity. The results show that the influence of particle velocity, particle size and particle concentration is statistically significant and the particle size and incidence angle have a significant effect on the erosion rate. A quadratic polynomial prediction model for the erosion rate of honeycomb catalysts in cement kiln SCR reactors is finally proposed to support the future optimization of these systems.

Development and verification of model predictive control strategy for selective catalytic reduction with rapid prototyping

The International Maritime Organization has set forth strict regulations about the NOx emission limit of ships to address the pollution problem in the transportation sector. Selective catalytic reduction (SCR) is the most effective post-engine means to reduce emission, and the control of urea spray critically affects the SCR performance. This paper developed a predictive control strategy of the SCR system based on the state space model. Specifically, the block model of the SCR reactor was established based on the reaction mechanism of the SCR system, and the unknown model parameters were identified. Rapid prototyping of the SCR system was carried out using the dSPACE real-time simulation platform to optimize the control under steady-state conditions. The catalyst ammonia coverage was set as the control target to maximize the NOx conversion rate while maintaining the NH3 escape at the outlet less than 10 ppm. The cyclic test results showed that the control strategy can quickly respond to external disturbance and modify the control target to keep the ammonia coverage rate within the target range, to thus achieve high NOx conversion rate while maintaining the required ammonia escape.

Understanding the NH3 adsorption mechanism on a vanadium-based SCR catalyst: A data-driven modeling approach

Ammonia adsorption is a precondition for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) to take place and it influences catalyst performance under transient conditions. For a vanadium-based SCR catalyst NH3 adsorption takes place on multiple adsorption sites over the catalyst surface with different behaviours depending on temperature, gas concentration and catalyst oxidation state. In this study, a mechanistic NH3 adsorption model within the framework of Langmuir adsorption models was developed for describing the NH3 adsorption isotherms obtained with a gas flow reactor for a vanadium-based SCR. The model was created by a data-driven modeling process, which involves different steps. First, a large set of candidate models was created systematically by combining multiple feasible adsorption mechanisms. Then, a parameter estimation workflow was performed using three different objective functions with increased complexity. Finally, a model reconciliation step was executed and a quality assessment was done for creating a unified robust model with a high degree of validity. As a result of this method, an NH3 adsorption model with five adsorption sites with different mechanisms was obtained that captures the main features from the experimental data. Furthermore, the model parameters have physical significance and relate to the adsorption strength and spatial arrangement for NH3 and water molecules. The proposed model can be used in the development of transient models with increased validity over a wide experimental region.

Effect of Catalyst Inlet Flow Field Distribution Characteristics on Outlet NO Concentration Distribution in SCR Denitration Reactor Based on Monte Carlo Method

Selective catalytic reduction (SCR) technology plays a crucial role in flue gas denitration. The nonuniform distribution of catalyst inlet parameters causes the nonuniform distribution of NO concentration at the outlet, thus affecting accuracy of ammonia injection. Regarding this issue, this paper describes the impacts of nonuniform velocity and temperature on both the confidence of NO concentration measured at a single measuring point at the outlet and the denitration efficiency, which can provide a basis for structural optimization of SCR denitration reactor and decrease in ammonia slip. The random distribution form of velocity and temperature above the catalyst layer are derived from the actual gas volume and the actual SCR reactor model, and then the catalyst inlet boundary conditions were generated with different relative standard deviation of velocity and temperature accordingly. The confidence of outlet NO concentration measurement results can be counted by means of Monte Carlo simulation. Finally, the relation model can be obtained to calculate the confidence of outlet NO concentration measurement results at different working conditions. The results show that within the gas volume range of this work, in order to ensure the confidence of the NO concentration measurement results, the relative standard deviation of temperature before the catalyst inlet must be within 0.005 and the relative standard deviation of velocity before the catalyst inlet must be within 0.1. With the increase in relative standard difference in temperature, there is a slight decrease in the efficiency of denitration. With the different mean value of temperature, the variation range of denitration efficiency is similar to that of temperature-relative standard difference. With the different mean value of velocity, the deviation range of corresponding efficiency is similar to that of the temperature-relative standard difference. When the relative standard difference in velocity increases, the denitration efficiency decreases slightly. The greater velocity value, the decreasing range of denitration efficiency is larger than the variation range of relative standard difference in velocity.

Modeling and simulation of marine SCR system based on Modelica

With the increasing awareness of global marine environmental protection, the emission of ship exhaust pollutants is strictly restricted. Selective catalytic reduction (SCR) technology is the mainstream technology to reduce ship NOx emission and make it meet IMO tier III regulations. A SCR reaction kinetic model based on Modelica language was established by Dymola software to predict the denitration efficiency, ammonia slip rate, and other parameters of SCR system. According to the functional structure of marine SCR system, the SCR system model is divided into urea injection module, mixer module, and SCR reactor module. The model was verified by SCR system bench test of WD10 diesel engine, which proved that the model can preferably reflect the actual situation. Using the established model, the effects of temperature, flow rate, NH3/NOx Stoichiometric Ratio (NSR), and cell density on the denitration performance of SCR system were analyzed. The results showed that the exhaust gas temperature and NSR have a great influence on the denitration efficiency. The injection amount of urea solution in marine SCR system should be based on the exhaust gas temperature and exhaust flow rate.

Parameter Identification and Model Predictive Control of Selective Catalytic Reduction Reactor

Parameter Identification and Model Predictive Control of Selective Catalytic Reduction Reactor

Investigation of after treatment technique to mitigate emission in IC Engine

Environmental pollution is a wide-reaching problem and it is likely to influence the health of the living population to a great extent. We need to mitigate the effects of harmful emissions before it is ungovernable. This project will concentrate on the reduction of NOx using ceria alumina catalyst, on a diesel engine as 5.2 kW water-cooled single-cylinder diesel engine. Solution and catalyst will play an important role in this process. Usually, the material is of high cost, here we have to choose low-cost material and solution. This leads to reduced nitrogen oxide (NOx) after treatment. Selective catalytic reduction (SCR) based on a solution like aqueous urea. This paper discusses the development of a static mixer and SCR reactor compatible with CI engine.

CFD analysis of influencing factors on SCR denitration efficiency of sintering flue gas based on response surface methodology

Selective catalytic reduction（SCR） technology is the key technology of flue gas denitration. SCR reactors are the systems contributing to pollution-free emission if they function properly. In order to study SCR denitration chemical reaction simulation and optimize the denitration effect, the CFD analysis of SCR reactor was carried out. The realizable k-ϵ turbulence model, component transport model and chemical reaction model were used to simulate the SCR denitration reactor. Based on the response surface methodology (RSM), the effects of three factors on the denitration efficiency were studied, including catalyst inlet gas velocity, reaction temperature and NH3/NO molar ratio. The quadratic multinomial regression model of three factors affecting the denitration efficiency was established. In addition, the structure of hot air duct and guiding plate were optimized based on the non-uniform inlet temperature. The results showed that: three factors had a significant impact on the denitration efficiency, and the interaction of catalyst inlet gas velocity and reaction temperature is the most significant; the structure optimization of hot air duct and guiding plate can improve the denitration efficiency and reduce outlet NO concentration relative standard deviation, and avoid catalyst abrasion. In this paper, a suitable numerical simulation model is proposed for SCR denitration reaction, and the consideration of non-uniform inlet temperature and the proposition about taking relative standard deviation of NO concentration at the outlet as an optimization index contribute to a more practical and more reasonable structure optimization.

Low-medium temperature application of selective catalytic reduction denitration in cement flue gas through a pilot plant

Low-medium temperature application of selective catalytic reduction (SCR) denitration in cement flue gas was established and investigated in this study. The 2000 h continuous operation shows the concentration of NOx at the outlet can be maintained at 24 mg/Nm3 on average, while due to the increase of SO2 in flue gas, the NOx concentration increased to 57.5 mg/Nm3 after long time operation. The sulfur deposition is the main reason for catalyst deactivation, and SO2 is still a big obstacle for low-medium temperature SCR application in cement flue gas. The denitration efficiency was tested as fluctuated from 73.5% to 86.2%, and ammonia concentration after SCR was as still as high as 22.5–60.0 mg/Nm3 due to the excessive ammonia injection from selective non-catalytic reduction (SNCR), shows serious ammonia escape problem for SNCR, and the potential application of hybrid SNCR-SCR technology. In order to maintain the denitration efficiency above 85.0%, the gaseous hourly space velocity (GHSV) should not be exceeded 2800 h−1, the electrostatic precipitators (ESP) setting at 60 kV was relatively appropriate, the temperature of the flue gas should be kept at above 200 °C. The concentrations and toxic equivalent quantities (TEQs) of the PCDD/Fs congeners in the flue gas raised greatly after SCR reactor, indicating the PCDD/Fs concentration should be concerned during the application of low-medium temperature SCR, especially for the waste co-disposal processes.

Nanometric Iridium Overlayer Catalysts for High-Turnover NH3 Oxidation with Suppressed N2O Formation

In the present study, we prepared a 12 nm thick Ir overlayer via pulsed cathodic arc plasma deposition on a 50 μm thick Fe–Cr–Al metal (SUS) foil. Using this thin-film catalyst made NH3–O2 reactions more environmentally benign due to a much lower selectivity for undesirable N2O (<5%) than that of a Pt overlayer (∼70%) at 225 °C. Despite its small surface area, Ir/SUS exhibited promising activity as an ammonia slip catalyst according to a turnover frequency (TOF) >70-fold greater than that observed with conventional Ir nanoparticle catalysts supported on γ-Al2O3. We found that the high-TOF NH3 oxidation was associated with the stability of the metallic Ir surface against oxidation by excess O2 present in simulated diesel exhaust. Additionally, we found that the Ir overlayer structure was thermally unstable at reaction temperatures ≥400 °C and at which point the Ir surface coverage dropped significantly; however, thermal deterioration was substantially mitigated by inserting a 250 nm thick Zr buffer layer between the Ir overlayer and the SUS foil substrate (Ir/Zr/SUS). Although N2O formation was suppressed by NH3 oxidation over Ir/Zr/SUS, other undesired byproducts (i.e., NO and NO2) were readily converted to N2 by coupling with a V2O5–WO3/TiO2 catalyst in a second reactor for selective catalytic reduction by NH3. These results demonstrated that this tandem reactor configuration converted NH3 to N2 with nearly complete selectivity at a range of 200–600 °C in the presence of excess O2 (8%) and H2O (10%).

Carbon deposition enhanced selective catalytic reduction of nitric oxide by a new catalytic process as well as increasing reducibility of catalyst

Carbon deposition usually hinders catalytic activity in one catalysis. In this work, carbon-deposition influence was investigated on selective catalytic reduction (SCR) of nitric oxide (NO) by a theoretical−experimental method. Density-functional-theory calculations showed that carbon deposition increased adsorption energy of NO on oxide. For example, adsorption energy on Fe2O3 increased from 1.70 to 5.27 eV. Carbon deposition increased activity by following processes: NO adsorption, NO dissociation, oxygen transmittance, CO-group formation, and N2/CO2 evolutions. Among these stages, CO-group formation was a key step. Based on these computational predictions, an experimental SCR was carried out for the verification. As a result, a carbon-deposited catalyst had a better SCR activity (20% higher) than the corresponding oxide catalyst. Characterizations showed that carbon deposition increased the amounts of medium/strong acidic sites as well as the reducibility of the catalytic center. The main result of this article helps to understand the interface behavior of carbon on a catalyst during SCR. Above results are also in favor of designing a more effective SCR reactor to ensure a more stable running.

Removal of PCDD/Fs and CBzs by Different Air Pollution Control Devices in MSWIs

ABSTRACT This study investigated the removal efficiencies of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and chlorobenzenes (CBzs) by different air pollution control devices (APCDs) in three municipal solid waste incinerators (MSWIs). These devices were the semi-dry flue gas desulfurization (SDFGD) system, activated carbon (AC) injector, bag filters (BF), selective catalytic reduction (SCR) reactor, and wet scrubber. The SDFGD system, AC injector, and BF exhibited similar removal efficiencies for all of the pollutants. Overall, the removal efficiency of CBzs was also considerably lower than the PCDD/Fs. The less chlorinated CBzs were also less likely to be adsorbed by AC and BF and more likely to be decomposed by the SCR reactor. Additionally, the “memory effect” in the wet scrubbers elevated the concentrations of the PCDD/Fs and even the CBzs in the flue gas, with the highest increases observed for penta- to hepta-chlorinated PCDD/Fs and TrCBzs. Given the different effects of these various devices, especially the wet scrubber, the correlation between PCDD/F and CBz removal should be individually assessed for each APCD unit. More accurate indicators of PCDD/F removal are also examined.

Compact research for maritime selective catalytic reduction reactor based on response surface methodology

Selective Catalytic Reduction (SCR) system provides an effective approach to removing NOx emission, in order to meet stringent emission legislation of NOx generated by internal combustion engine. However, the oversize SCR system would increase its operation costs and occupy more space, which restricts its widespread application to a certain extent. Therefore, the compact structure design of SCR system is worthy of research considering the limited installation space. In the present study, one-dimensional SCR model is established, and the effect of structural parameters on the SCR performance has been investigated by AVL BOOST. Then, based on the Response Surface Methodology (RSM), the coupling relationship among these structural parameters is explored. The optimal structural parameter values of SCR are calculated through the coupling relationship function. The SCR volume of the optimal structural parameters is reduced by 23.82% and the pressure drop generated by SCR reactor is reduced by 10.38%, which not only lead to the reduction of fuel consumption and also save the space and energy on ship. Meanwhile, and the NOx conversion is decreased slightly to 0.51%.

Selective Catalytic Reduction of NOx over V2O5-WO3-TiO2 SCR Catalysts—A Study at Elevated Pressure for Maritime Pre-turbine SCR Configuration

The selective catalytic reduction (SCR) of NOx using NH3 was studied at pressures up to 5 bar over a vanadium-based SCR catalyst (~1 wt% V2O5 and 10 wt% WO3/TiO2), relevant for the installation of SCR reactors upstream of the turbocharger at marine engines. Experiments were performed using both granulated catalyst in a lab-scale fixed-bed reactor and a monolith catalyst in a bench-scale setup. The residence time across the catalytic bed was kept constant, by increasing the (normalized (0 °C, 1 atm)) volumetric flow rate proportionally to the pressure. The results show that for the granulated catalyst, the NOx conversion was independent of the pressure, indicating that the SCR kinetics are not affected by the increased pressure up to 5 bar. NH3 temperature-programmed desorption experiments showed that the catalyst NH3 adsorption increased with more than 30% when the pressure was increased from 1 bar to 4.5 bar. On the other hand, when the adsorption temperature was increased from 150 to 300 °C, the adsorption capacity decreased by approximately 60% independent on the pressure. The SCR reaction was unaffected by the increased NH3 uptake caused by the increased pressure, because only a certain fraction of the sites ( $$ {\theta}_{N{H}_3}^{\ast } $$ = 0.14) was found to be active in the SCR reaction, and these are filled up at lower NH3 partial pressure than the total number of sites. Experiments using a monolithic catalyst showed that at temperatures above 250 °C, the NOx conversion was lower at an increased pressure (3.1 bar) when the residence time was held constant. This decrease was ascribed to increased internal and external diffusion limitations at the elevated pressure.

An analysis of SCR reactor deactivation impact on NOx emissions from a compression ignition engine

Catalytic exhaust gas aftertreatment devices fitted to combustion engines are susceptible to partial deactivation as their operating time progresses. This includes selective catalytic reduction (SCR) reactors meant for NOx emission control. There are several known deactivation mechanisms of SCR reactors already analyzed in detail in the literature. This paper, however, approaches the analysis of reactor deactivation by comparison of exhaust gas characteristics over repeatable cycle for fresh and aged samples of a SCR reactor for non-road mobile machinery. The research aims to outline which parameters describing the SCR reactor’s performance are most affected by its ageing. In order to do that, fresh and aged samples of the reactor were tested under the Non Road Steady Cycle. The acquired emission results, including concentration traces of particular compounds were analyzed. The specific NOx emission of the aged reactor was significantly higher than that of the fresh one. The NOx conversion efficiency of both reactors was found similar at periods of steady engine operation. It was recognized that during transient conditions the NOx conversion efficiency of the aged reactor was decreased. It was found that the main factor contributing to that phenomenon is the drop in the ammonia storage capacity of the aged SCR sample.

An investigation on the catalytic characteristic of NO reduction in SCR systems

Abstract The Selective catalytic reduction (SCR) technology is an effective and economical method for reducing NOx emissions from the heavy duty diesel engine. To ensure a reasonable design of the SCR system, it is critical to understand the effects of space velocity (GHSV), NO2/NOx ratio, NH3/NOx ratio and structural parameters of the SCR reactor on the NOx conversion efficiency. Using the experimental method to conduct all the investigations though the entire development cycle of SCR system is expensive and would cost a long time. Numerical method as a complementary tool to bench tests can help to optimize the design and shorten the development cycle of SCR system. In this paper, a mathematical model is developed to predict the NOx conversion efficiency over a Cu catalyst. The model is calculated in the MATLAB environment. The simulation results agree well with the experimental data, which indicates that the mathematical model is reliable and can effectively predict the performance of the SCR catalytic system. Then the effects of the parameters, such as space velocity, NO2/NOx ratio, NH3/NOx ratio, length, diameter and number of channels per square inch (CPSI) of the SCR reactor on the NOx conversion efficiency were studied.

Structure Optimization for SCR Reactor Based on RSM Method

Selective Catalytic Reduction (SCR) system provides an effective approach to removing NOx emission, to meet stringent emission legislation of NOx generated by internal combustion engine. However, the oversized SCR system would increase its operation costs and occupy more space, which restricts its widespread application to a certain extent. Therefore, the compact structure design of SCR system is worthy of research considering the limited installation space. In the present study, one-dimensional SCR model is established, and the effect of structural parameters on the SCR performance has been investigated. Then, based on the Response Surface Methodology (RSM), the coupling relationship among these structural parameters is explored. The optimal structural parameter values of SCR are calculated through the multi-objective optimization function. The SCR volume of the optimal structural parameters is reduced by 23.82% and the pressure drop generated by SCR reactor is reduced by 10.38%. Meanwhile, the decrease of NOx conversion efficiency could be negligible under the same condition.

Economic Operation Analysis of Environmental Protection Facilities in Coal-fired Power Plants under the New Environmental Protection Policy

With the transformation of ultra-low emissions and the increasingly stringent emission standards for environmental pollutants, power plants have to seek the best economic operation mode to meet the requirements of the policy. In this paper, taking a power plant in North China as an example, the economic operation mode of denitration and desulphurization under the new local policy is considered. When the emission concentration of NOX at the outlet of selective catalytic reduction reactor is controlled in 20 mg/Nm3 and 15 mg/Nm3, the power plant has a significant economic effect. However, the desulfurization system is inappropriate if reduces the SO2 emission concentration.

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.