Selective Catalytic Reduction DeNOx Research Articles

MnyCo3−yOx bimetallic oxide prepared by ultrasonic technology for significantly improved catalytic performance in the reduction of NOx with NH3

NOx emission is a major environmental issue. Selective catalytic reduction (SCR) is the most effective method for the conversion of NOx in flue gases to harmless N2 and H2O. In this work, a series of Mn-Co mixed metal oxides, MnyCo3−yOx, are intentionally prepared by an ultrasonic technology followed by a hydrothermal treatment, and their denitration (de-NOx) performances are evaluated by the SCR reaction in the presence of NH3. The results show that the SCR de-NOx performance of MnyCo3−yOx is significantly improved compared with single metal oxide (MnOx or CoOx). The reason can be ascribed to a strong interaction between MnOx and CoOx, which reduces the crystallinity of MnyCo3−yOx catalysts, increases the specific surface area, builds the redox cycle of Co3+ + Mn3+ ↔ Co2+ + Mn4+, improves the reducibility, enhances the surface acid sites, accelerates the reaction between the adsorbed NOx species and the coordinated NH3 bound to the Lewis acid site, resulting in a significant improvement in the SCR de-NOx performance. The work provides us with a thought to improve the de-NOx performance by building a strong interaction between catalyst components.

Sm-modified Mn-Ce oxides supported on cordierite as monolithic catalyst for the low-temperature reduction of nitrogen oxides

Nitrogen oxides (NOx) are typical atmospheric pollutants that harm the environment and human body, and selective catalytic reduction (SCR) with NH3 is one of the most effective technologies to deal with NOx emissions at present. In this work, a monolithic catalyst, Sm-modified Mn-Ce composite oxides (Sm-MnCe) supported on cordierite (CC), is prepared by impregnation for the first time, and their denitration (de-NOx) performance in NH3-SCR reaction is evaluated in detail. The results show that 0.1Sm-MnCe/CC (Sm/Mn mole ratio is 0.1) has the best de-NOx efficiency with above 80 % NOx conversion from 60° to 270°C, and the high NOx conversion can be maintained within 15 h in the presence of 100 ppm SO2. It is found that appropriate introduction of Sm increases the specific surface area and acid sites, improves the redox environment, elevates the content of Mn4+ on the catalyst surface, which are conducive to the improvement of catalytic activity. In addition, the interaction between active components (Sm, Mn and Ce) also plays a positive role for the excellent de-NOx activity. It is revealed by in-situ diffuse reflectance infrared Fourier transform spectra (DRIFTS) that the NH3-SCR reaction over the 0.1Sm-MnCe/CC catalyst follows Eley-Rideal (E-R) and Langmuir-Hinshel (L-H) mechanisms. This work provides ideas for the preparation and modification of monolithic catalysts, which is conducive to promoting the practical industrial application of low-temperature SCR de-NOx technology.

A clean and efficient solar-aided de-NOx system in solar/fuel hybrid power plants

Based on the unique characteristics of parabolic trough solar energy and selective catalytic reduction de-NOx, a novel solar/fuel hybrid power generation system is proposed. In the system, solar energy is integrated with de-NOx for keeping the NOx removal temperature at the optimal range. The additional heat brought by solar energy is sent into furnace by the following air preheating process. Thermodynamic, environmental, and economic analyses of the novel system are conducted. Based on a typical reference unit, the proposed solar/fuel hybrid power generation system increases thermal efficiency by 1.24 % with 13.8 MWe of solar generated electric power, and achieves 25.3 % of solar-to-electricity efficiency. The solar-aided de-NOx system increases 8.5 % of NOx removal efficiency and reduces 19.8 g/s of NOx emission. For the economic performance, the proposed system brings 5.38 million USD of extra annual income with 0.052 USD/kWh of cost of solar generated electricity. Overall, the results of thermodynamic, environmental, and economic analyses indicate that solar-aided de-NOx is a promising way for clean and efficient electricity generation.

Real-Time Evaluation Method of Heavy-Duty Diesel Vehicle SCR System Based on Ammonia Storage Characteristics in Real-Road Driving Emission Test

In China, where in-use heavy-duty diesel vehicles producing NOx and particulate emissions for air pollution are required to undergo emission spot inspection at check stations, it is significant to adopt a simple method to evaluate emissions due to traffic jams, especially in big cities. To realize convenient vehicle emission spot inspection, this paper investigates the effects of exhaust temperature on the Selective Catalytic Reduction (SCR) de-NOx conversion efficiency and presents a method for evaluating the SCR operation state based on ammonia storage characteristics. The paper proposes a real-road driving test procedure and verifies it by measuring NOx from a heavy-duty diesel vehicle in an on-road driving test. The results show that the SCR de-NOx efficiency experiences three operation states. In state I, SCR works and injects urea, resulting in high de-NOx efficiency (>90%); state III occurs during the cold, starting with the lowest de-NOx efficiency (<50%) due to a lack of NH3; and state II is a transition stage caused by the ammonia storage, with a certain conversion efficiency (50–90%) when SCR de-NOx efficiency linearly relates to exhaust temperature. Whether the SCR works normally can be judged based on the SCRs operation states. This method is simple and easy to implement in different SCR operation states, and it is effective and repeatable.

Emission Characteristics of Gaseous and Particulate Mercury from a Subcritical Power Plant Co-Firing Coal and Sludge

Field tests were carried out in a subcritical coal-fired power plant co-firing coal and sludge to analyze the emission characteristics of gaseous and particulate mercury. EPA30B method was applied to determine the mercury speciation in different positions of the flue gas, including the inlet and outlet of the selective catalytic reduction DeNOX system (SCR) and electrostatic precipitator (ESP); PM10 (with aerodynamic diameter ≤10 μm) was collected using a cyclone and a Dekati low-pressure impactor (DLPI). Before accessing the SCR, Hg in flue gas from both single coal combustion and co-firing mainly existed as Hg0; the higher content of Hg in sludge than coal led to the much higher Hg0 concentration for co-firing. The total Hg concentration at not only the SCR inlet and outlet but also the ESP inlet did not change obviously. However, Hgp concentration at the ESP inlet increased significantly, accompanied by a decrease in Hg0. The transformation of Hg0 to Hgp appeared to be more distinct for co-firing. The higher HCl concentration of co-firing derived from the much higher Cl content of sludge than coal, and together with the higher ash content of sludge containing more minerals capable of adsorbing Hg0, may lead to the greater transformation from Hg0 to Hg2+ and Hgp when co-firing. After the ESP disposal, nearly all Hgp was removed along with PM10, and most Hg0 was also removed. The removal efficiency of mercury after the ESP was 92.12% under coal firing and 92.83% under co-firing conditions, respectively. The slightly higher mercury removal efficiency under co-firing should be attributed to the complete removal of the higher concentration of Hgp.

Prediction and Control of the Nitrogen Oxides Emission for Environmental Protection Goal Based on Data-Driven Model in the SCR de-NOx System

In order to reduce the nitrogen oxides (NOx) emission of flue gas, a selective catalytic reduction (SCR) system must be installed. In general, the lag of the inlet NOx analyzer, the action of the NH3 injection valve and the feedforward signal are seriously delayed. Therefore, it is necessary to consider the measurement lag of inlet NOx on the NH3 injection flowrate control system. In this paper, the data-driven model of inlet NOx is proposed to improve control system, so as to avoid excessive or insufficient NH3 injection. First, the measurement lag time of inlet NOx is estimated by the blowback signal of a CEMS and the change process of the inlet O2 content. Then, an exponential model is used to predict the inlet NOx in advance, and recursive LSSVM is proposed to revise the output of the exponential model. Finally, the output of the final model is used as the feedforward signal for improved feedforward (IF) control. Based on IF control and PID control, the IF-PID control strategy for NH3 injection is proposed. The results show that the outlet NOx are close to the set value and meet the national environmental regulation. Furthermore, the average value of the NH3 injection flowrate remains unchanged. It shows that a better control effect and environmental sustainability are achieved without increasing the cost of NH3 injection.

Enhancing low‐temperature SCR deNOx MnCe catalyst based on rice husk char by KOH and H3PO4 activation

AbstractBACKGROUNDIt is of great significance industrially to find cheap materials as low‐temperature selective catalytic reduction (SCR) catalyst support. Pyrolyzed rice husk char (RC) is not only cheap, but also has the characteristics of high porosity, large SSA and good adsorption. Therefore, there is emerging interest in RC as an SCR support. The present contribution is a comparative study of low‐temperature SCR manganese–cerium (MnCe) catalysts based on RC activated by potassium hydroxide (KOH) and phosphoric acid (H3PO4), revealing the different mechanisms of improvement in catalytic performance.RESULTSMn‐Ce/RCK (catalyst of MnCe loaded on KOH activated RC) has a wider activity temperature window in the range 120–260 °C, while Mn‐Ce/RCP (catalyst of MnCe loaded on H3PO4 activated RC) can reach the highest NO conversion of 97% at 240 °C.CONCLUSIONSN2 adsorption–desorption, Fourier transform infrared (FTIR), X‐ray diffraction (XRD), NH3‐temperature programmed desorption (TPD) and X‐ray photoelectron spectroscopy (XPS) were used to characterize and analyze their catalytic performance. The N2 adsorption–desorption and NH3‐TPD showed that Mn‐Ce/RCK has a larger SSA and more acid sites than those of Mn‐Ce/RC and Mn‐Ce/RCP. XRD indicated that Mn‐Ce/RCP has a better dispersion than that of Mn‐Ce/RCK. FTIR showed that Mn‐Ce/RCP had more oxygen (O)‐containing functional groups. The XPS revealed that Mn‐Ce/RCP has higher ratios of Mn4+, Ce3+ and Oβ. © 2021 Society of Chemical Industry (SCI).

Low-Temperature Selective Catalytic Reduction DeNOX and Regeneration of Mn-Cu Catalyst Supported by Activated Coke.

The activated coke is a promising support for catalysts, and it is important to study the performance of the activated coke catalyst on the removal of NOx. In the current research, a series of the activated coke-supported Mn–Cu catalysts are prepared by the incipient wetness impregnation method. The effects of the molar ration of Mn/Cu, the content of Mn–Cu, the calcination temperature, and reaction space velocity on NO conversion are investigated, and it was found that the 8 wt.% Mn0.7Cu0.3/AC had the best catalytic activity when the calcination temperature was 200 °C. The existence of SO2 caused the catalyst to deactivate, but the activity of the poisoning catalyst could be recovered by different regeneration methods. To uncover the underlying mechanism, BET, XPS, XRD, SEM and FTIR characterizations were performed. These results suggested that the specific surface area and total pore volume of the poisoning catalyst are recovered and the sulfite and sulfate on the surface of the poisoning catalysts are removed after water washing regeneration. More importantly, the water washing regeneration returns the value of Mn3+/Mn4+, Cu2+/Cu+, and Oα/Oβ, related to the activity, basically back to the level of the fresh catalyst. Thus, the effect of water washing regeneration is better than thermal regeneration. These results could provide some helpful information for the design and development of the SCR catalysts.

A CFD Study on Flow Control of Ammonia Injection for Denitrification Processes of SCR Systems in Coal-Fired Power Plants

The selective catalytic reduction method is a useful method for the denitrification process of exhaust gas emitted from industrial facilities. The distribution of the ammonia–nitrogen oxide mixing ratio at the inlet of the catalyst layers is important in the denitrification process. In this study, a computational analysis technique was used to improve the uniformity of the NH3/NO molar ratio by controlling the flow rate of the ammonia injection nozzle according to the flow distribution of nitrogen oxides in the inlet exhaust gas of the denitrification facility. The application model was simplified to the two-dimensional array adopted from the existing selective catalytic reduction (SCR) process in the large-scaled coal-fired power plant. As the inlet conditions, four (4) types of flow pattern were simulated, i.e., parabolic, upper-skewed, lower-skewed, and random. The flow rate of the eight (8) nozzles installed in the ammonia injection grid was controlled by Design Xplorer as the optimization tool. In order to solve the two-dimensional steady, incompressible, and viscous flow fields, the commercial software named ANSYS Fluent was used with the κ-ε turbulence model. The root mean square of NH3/NO molar ratio at the inlet of the catalyst layer has been improved from 84.6% to 90.1% by controlling the flow rate of the ammonia injection nozzles. From the present numerical simulation, the operation guide could be drawn for the ammonia injection nozzles in SCR DeNOx facilities.

Improvement of ammonia mixing in an industrial scale selective catalytic reduction De-NOx system of a coal-fired power plant: A numerical analysis

In this study, several methods are proposed to improve the denitrification (De-NOx) performance of the selective catalytic reduction (SCR) system. To illustrate how the proposed methods can be applied, the numerical analysis for the SCR system of an industrial-scale thermal power plant is conducted. There are two important indices affecting the performance of SCR system: one is the degree of mixing of the injected NH3 and the other is the uniformity of flow velocity before entering the catalyst layer. To improve the NH3 mixing, a static mixer in a location downstream of the ammonia injection grid (AIG) is generally installed. However, the uniformity of flow velocity distribution is severely aggravated as the mixer induces vortex. Therefore, it is suggested to place the mixer away from the catalyst layer to enhance the NH3 mixing and the uniformity of flow velocity together. The effect of the number of injection nozzles of the AIG on the SCR performance is also investigated. The number of nozzles of the ammonia injection grid can be reduced without affecting the uniformity in flow velocity. However, too much reducing the number of nozzles would result in improper ammonia mixing. Therefore, it is recommended to reduce the number of nozzles within a tolerable range of the NH3 mixing.

Collaborative optimization of energy conversion and NOx removal in boiler cold-end of coal-fired power plants based on waste heat recovery of flue gas and sensible heat utilization of extraction steam

Abstract Based on the close relationship among the feed water heating process, Selective catalytic reduction (SCR) de-NOx and air preheating process, collaborative optimization of energy conversion and NOx removal in the boiler cold-end of coal-fired power plants is proposed in this paper. In the proposed system, recovery of flue gas waste heat and sensible heat efficient utilization of extraction steam provide engineering support for the collaborative optimization concept. The proposed system achieves optimal performance by increasing SCR de-NOx temperature and energy for air preheating. The results reveal that, based on 50% load of a typical 1000 MW coal-fired power plant, the proposed system could increase 5.4 MWe of additional output power with a 0.47% increase of thermal efficiency. The increase of SCR de-NOx temperature brings 6.5% of NOx removal efficiency increase and 28.4 mg/Nm3 of NOx emission decrease. Besides, the proposed system gains 2.27 million USD of extra annual income. In general, the proposed system achieves great energy savings, NOx removal, and economic performances.

The insight into the role of Al2O3 in promoting the SO2 tolerance of MnOx for low-temperature selective catalytic reduction of NOx with NH3

This research aims to enhance the SO2 tolerance of manganese oxide (MnOx) catalysts for low-temperature selective catalytic reduction (SCR) de-NOx. Based on the deactivation mechanism of MnOx, we target at the promotion of the byproduct (NH4HSO4) decomposition and the inhibition of the byproduct (MnSO4) formation. To achieve this target, thermogravimetric (TG) and temperature programmed desorption of SO2 (SO2-TPD) are performed upon as many as 21 kinds of single metal oxides to explore the potentially effective chemical composition as the additive of MnOx catalysts. The TG result indicates that Al2O3 can remarkably decrease the thermal stability of NH4HSO4. In addition, the SO2-TPD analysis reveals that the formed species after SO2 adsorption are weakly adsorbed on Al2O3. Thus, Al2O3 is selected to mix with MnOx to optimize its SO2 tolerance. Further experimental results demonstrate that the proper introduction of Al2O3 can effectively enhance the low-temperature SCR de-NOx activity and the SO2 tolerance of MnOx. It is revealed that the introduction of Al2O3 into MnOx can not only facilitate the decomposition of NH4HSO4 but also lead to reduced thermal stability of the adsorbed SO2 species to some extent. As compared to the pristine MnOx, the slight introduction of Al2O3 as the additive is beneficial to the low-temperature SCR de-NOx activity and SO2 tolerance of MnOx.

Tailored Alkali Resistance of DeNOx Catalysts by Improving Redox Properties and Activating Adsorbed Reactive Species

SummaryIt is still challenging to develop strongly alkali-resistant catalysts for selective catalytic reduction of NOx with NH3. It is generally believed that the maintenance of acidity is the most important factor because of neutral effects of alkali. This work discovers that the redox properties rather than acidity play decisive roles in improving alkali resistance of some specific catalyst systems. K-poisoned Fe-decorated SO42−-modified CeZr oxide (Fe/SO42−/CeZr) catalysts show decreased acidity but reserve the high redox properties. The higher reactivity of NHx species induced by K poisoning compensates for the decreased amount of adsorbed NHx, leading to a desired reaction efficiency between adsorbed NHx and nitrate species. This study provides a unique perspective in designing an alkali-resistant deNOx catalyst via improving redox properties and activating the reactivities of NHx species rather than routinely increasing acidic sites for NHx adsorption, which is of significance for academic interests and practical applications.

The insight into the role of CeO2 in improving low-temperature catalytic performance and SO2 tolerance of MnCoCeOx microflowers for the NH3-SCR of NOx

A new MnCoCeOx microflower is rationally designed by a series of elaborate steps for the selective catalytic reduction (SCR) of NOx with NH3. The MnCoOx microflower is firstly synthesized by the self-assembly of Mn-Co mixed oxide nanosheets, and then CeO2 nanoparticles are in-situ grown on the surface of Mn-Co mixed oxide nanosheets by dipping MnCoOx microflower in Ce(NO3)3 solution followed by a heat-treatment. The resultant MnCoCeOx microflower presents significantly enhanced low-temperature catalytic performance and SO2 tolerance. It is revealed that the attached CeO2 plays several important roles in the improvement of low-temperature de-NOx performance, such as decreasing the apparent activation energy, increasing the ratios of Ce3+/Cen+, Mn4+/Mnn+ and Oα/(Oα + Oβ), enhancing the oxidation ability of MnCoOx at low temperatures. Moreover, by preventing MnCoOx from being vulcanized into metal sulfate species, CeO2 plays an important role in enhancing the resistance to SO2 poisoning. The in-situ DRIFTS results disclose that the NH3 coordinated on Lewis acid sites, NH4+ bound to Brønsted acid sites, the NO2 and bidentate nitrates linked on metal oxides are the major reactive species on MnCoCeOx catalyst, which occur SCR de-NOx reaction following both Eley-Rideal and Langmuir-Hinshelwood mechanisms.

Investigation of low-temperature selective catalytic reduction of NOx with ammonia over Cr-promoted Fe/AC catalysts.

Fe/activated coke (AC) and Cr-Fe/AC catalysts with AC as a supporter and Cr and Fe as active components were prepared by an impregnation method for low-temperature selective catalytic reduction (SCR) of NO with NH3. The effects of Cr addition and its concentrations on the deNOx performance of Fe/AC catalysts were studied at low temperature. The Cr addition promotes the low-temperature SCR activity of the 8Fe/AC catalyst and the 8Fe6Cr/AC catalyst has the best low-temperature SCR deNOx performance, which the NOx conversions are greater than 90% at 160-240 °C. The 8Fe6Cr/AC catalyst has good water resistance. However, when 100 ppm SO2 was introduced into the reaction gas, its deNOx efficiency drops to 45% at 180 °C. To clarify the specific effects of Cr addition on the NOx conversions and sulfur poisoning, the Cr-Fe/AC catalysts were characterized by X-ray diffraction, BET, H2 temperature-programmed reduction, NH3 temperature-programmed desorption, X-ray photoelectron spectroscopy, and Fourier infrared spectroscopy. The addition of Cr into Fe/AC catalysts greatly increases the BET surface area and the number of weak and medium-strong acid sites on the catalyst surface and improves the ratio of Fe3+/Fe2+. These factors enhance the NOx conversion of 8Fe/AC catalyst. The formed sulfates and hydrogen sulfates cover the active sites on the catalyst surface, which lead to the sulfur poisoning of the 8Fe6Cr/AC catalyst. Graphical abstract.

CFD modeling of unsteady SCR deNOx coupled with regenerative heat transfer in honeycomb regenerators partly coated by Vanadium catalysts

The unsteady selective catalytic reduction (SCR) of NOx with honeycomb regenerators coated by Vanadium catalysts, under the condition of hot gas and cool air blowing alternately in the opposite direction, should be simulated coupled with regenerative heat transfer, because catalyst activity depends on temperature greatly. In the current work, the SCR deNOx model based on the porous medium and volumetric reaction assumptions is developed for the catalyst layer and integrated into our existing three-dimensional (3D) CFD heat transfer model of honeycomb regenerators. Steady SCR deNOx experiments with monolith catalysts are simulated for model validation and the contour is presented to study the NOx concentration polarization. With the novel model, unsteady SCR deNOx in honeycomb regenerators partly coated by a film of V2O5-WO3/TiO2 is simulated, and the effects of structural and operational parameters on the NOx conversion and thermal-hydraulic performances are studied. Besides, the temporal variation curves of fluid temperatures and NO concentration are presented for discussions. Numerical results demonstrate that current CFD model could predict the performances of partly-coated honeycomb regenerators with a reasonable precision and the regenerator with square openings of 6mm×6mm could work with a good overall performance at the gas inlet velocity of 4m/s.

Study on the NO2 production pathways and the role of NO2 in fast selective catalytic reduction DeNOx at low-temperature over MnOx/TiO2 catalyst

Selective catalytic reduction of NO by NH3 (SCR) at low temperature usually considered to be the combination of NO oxidation and “Fast SCR” process. However, the NO oxidation mechanism and the role of NO2 over “Fast SCR” process are controversial. Focusing on these problems, the in-deep studies were performed over the typical MnOx/TiO2 catalysts. Combining in-situ DRIFT, TPD-MS and DFT calculation results, an integrated NO oxidation mechanism was proposed based on an “Nitro-assisted oxygen activation” concept where the activation and transformation of O2 is linked with the transformation of nitro species. The OO bond of O2 can be weakened by generating a variation of bidentate nitrates, which can promote the break of OO bond and the formation of NO2. The formation of the variation of bidentate nitrates was the rate-determining step over NO oxidation. Additionally, we further reveal that the crucial role of NO2 over “Fast SCR” process lies in participating the hydrogen abstraction from coordinated NH3 and promoting the production of NH2 active species which can direct react with NO to generate N2 and H2O. The removability of NO2 can coupling the MnO2 (NO oxidation active component) and TiO2 support (“Fast SCR” active component) together. Our findings provide insight into the design and improvement of catalysts or reaction pathways over the low-temperature SCR process.

Durability of V2O5-WO3/TiO2 selective catalytic reduction catalysts for heavy-duty diesel engines using B20 blend fuel

The durability of V2O5-WO3/TiO2 selective catalytic reduction (SCR) catalysts for heavy-duty diesel engines was evaluated based on 500 h SCR durability tests conducted using B20 fuel (20% v/v biodiesel + 80% v/v petroleum diesel). The fresh and deteriorated SCR catalysts were characterized by X-ray fluorescence, X-ray diffraction, and Brunauer-Emmett-Teller surface area measurements to investigate the deterioration mechanism of the catalysts. The results show that the SCR de-NOx performance is degraded after SCR durability testing, particularly at high engine speeds. The NOx conversion efficiency of the deteriorated SCR catalysts decreases at temperatures above 400 °C but remains high at temperatures between 250 and 400 °C. The catalyst characterization results reveal that the deterioration in the de-NOx performance is not owing to anatase-to-rutile transformation of TiO2, but because of a decrease in the specific surface area and the loss of the catalyst components, which are greater in the front cross section of the SCR than in the rear cross section. For a given catalyst cross section, the decrease in the specific surface area exhibits a positive correlation with the flow rate of the exhaust gas.

Analysis of the spray wall impingement of urea-water solution for automotive SCR De-NOx systems

Selective catalytic reduction (SCR) is the most popular automotive exhaust after-treatment solution for nitrogen oxides (NOx) emission reduction. The mitigation of solid deposit formation is a big challenge for SCR system operation. Urea-water spray impingement is an important parameter which effects on solid deposit formation, should be investigated duly. This study presents an experimental investigation of urea-water spray impingement on the heated wall of automotive SCR systems for diesel engine exhaust gases. The investigation focused on the impingement conditions and distribution of the spray droplets, which are important parameters for system performance. This work was conducted with a commercial pressure driven SCR injector into an optically accessible test chamber at different wall temperatures and injection height. The spray impingement phenomena captured by means of Z-type shadowgraph high-speed Imaging technique. The injection quantity of the injector was measured to determine the injection rate. The high-speed imaging reveals in detail spray distributions, liquid film formation and urea crystallization. Relevant dimensions of spray distribution after the impingement have been estimated with digital image processing. The investigation reveals that high wall temperature produces swirl and bouncing that entrain rebounded droplets of the impinging spray on the wall, which leads to improved mixing. High temperature also causes longer spray front projection length which is an important factor for the mitigation of urea deposits.

Effects of insulation on exhaust temperature and subsequent SCR efficiency of a heavy-duty diesel engine

Ammonia/urea selective catalytic reduction (SCR) is an efficient technology to control NOx emission from diesel engines. One of the critical challenges of SCR systems is its lack of catalytic activities in low temperature conditions such as cold start or warm-up periods. In this study, the effect of pipe insulation on the reduction of exhaust temperature drop was experimentally investigated based on dynamometer tests with a heavy-duty non-road diesel engine. The temperature drop of exhaust gas was measured with and without applying pipe insulation. Measurement results revealed that the effect of insulation on the mitigation of temperature loss becomes significant as engine brake power decreases. Thus, it is expected that the need for pipe insulation would be increased to keep SCR deNOx efficiency high, especially at low temperature conditions. Also, this study carried out numerical simulations to quantify the impact of pipe insulation on NOx conversion efficiency of a commercial SCR catalyst over a scheduled non-road transient cycle (NRTC) mode. Under the current heavy-duty non-road engine and SCR conditions, the application of pipe insulation would reduce 19.5 % of total cumulative tail-out NOx emission over NRTC hot mode. These results led to the cycle-averaged SCR efficiency of 98.2 % for ‘with insulation’, while it was predicted to be lowered to 97.6 % for ‘without insulation’.