NOx Reduction Efficiency Research Articles

尿素SCR システムのNOx 浄化率向上に関する研究（第8報） ─NH 3 スリップ用触媒(ASC)の浄化特性─

尿素SCR システムのNOx 浄化率向上に関する研究（第8報） ─NH 3 スリップ用触媒(ASC)の浄化特性─

Investigation on the Simulation of Control Strategy for a SCR System

In this paper, the model of SCR after-treatment system is established by the software MATLAB and the control strategy for the system is studied also. Based on Eley-rideal mechanism, four major chemical reactions including the adsorption of ammonia, desorption of ammonia, selective catalytic reduction and oxidation of adsorbed ammonia are selected to study the SCR control strategy. Based on the energy conservation law, the equation calculating the temperature of the layered model is derived. Combined with the equations of chemical reaction process, a mathematical model of SCR catalytic converter is established. To achieve a high NOXreduction efficiency of SCR system, the reasonable and efficacious control strategies for the micro-element models of SCR catalytic is simulated, which including the feedback control strategy based on the feed-forward controller and the PID control strategy.

States and Function of Potassium Carbonate Species in the Polytitanate Nanobelt Supported Catalysts Used for Efficient NOx Storage and Reduction

A series of polytitanate nanobelt supported lean-burn NOx trap catalysts Pt-xK2CO3/K2Ti8O17 with different weight loading of K2CO3 (x = 0%, 5%, 15%, 20%, 25%, or 30%) were synthesized by successive impregnation. The nanobelt support K2Ti8O17 displays a specific surface area as high as 302 m2/g, and the corresponding catalysts Pt-xK2CO3/K2Ti8O17 show excellent NOx storage performance. As K2CO3 loading increases from 5% to 30%, the NOx storage capacity (NSC) exhibits a volcano-type altering tendency with the maximum appearing at 25% (2.68 mmol/g); the highest NOx reduction efficiency of 99.2% was also achieved over this catalyst in cyclic alternative lean/rich atmospheres. Further increase of K2CO3 loading induces the formation of more bulk or bulk-like K2CO3 species, decreasing the performance of the catalysts for NOx storage and reduction. HR-TEM and FT-IR results indicate that the K species exist as highly dispersed phases including K2O, K2CO3, and −OK groups, which are undetectable by X-ray diffraction (XRD) even at the K2CO3 loading of 30%. Several carbonate species with different thermal stability and reactivity are identified by FT-IR and CO2-TPD. In situ diffuse reflectance FT-IR (DRIFTS) reveals that at low K2CO3 loading (<20%) NOx is mainly stored as monodentate nitrates and monodentate nitrites, while at higher K2CO3 loading NOx is mainly stored as bidentate nitrite species, which results from the decrease of oxidation ability of the catalysts due to the potential covering of K2CO3 on Pt sites.

Numerical Simulation on Improving NO&lt;sub&gt;x&lt;/sub&gt; Reduction Efficiency of SNCR by Regulating the 3-D Temperature Field in a Furnace

The optimum temperature within the reagent injection zone is between 900 and 1150°C for the NOX reduction by SNCR (selective non-catalytic reduction) in coal-fired utility boiler furnaces. As the load and the fuel property changes, the temperature within the reagent injection zone will bias from the optimum range, which will reduces significantly the de-NOX efficiency, and consequently the applicability of SNCR technology. An idea to improve the NOX reduction efficiency of SNCR by regulating the 3-D temperature field in a furnace is proposed in this paper. In order to study the new method, Computational fluid dynamics (CFD) model of a 200 MW multi-fuel tangentially fired boiler have been developed using Fluent 6.3.26 to investigate the three-fuel combustion system of coal, blast furnace gas (BFG), and coke oven gas (COG) with an eddy-dissipation model for simulating the gas-phase combustion, and to examine the NOX reduction by SNCR using urea-water solution. The current CFD models have been validated by the experimental data obtained from the boiler for case study. The results show that, with the improved coal and air feed method, average residence time of coal particles increases 0.3s, burnout degree of pulverized coal increases 2%, the average temperature at the furnace nose decreases 61K from 1496K to 1435K, the NO emission at the exit (without SNCR) decreases 58 ppm from 528 to 470 ppm, the SNCR NO removal efficiency increases 10% from 36.1 to 46.1%. The numerical simulation results show that this combustion adjustment method based on 3-D temperature field reconstruction measuring system in a 200 MW multi-fuel tangentially fired utility boiler co-firing pulverized coal with BFG and COG is timely and effective to maintain the temperature of reagent injection zone at optimum temperature range and high NOX removal efficiency of SNCR.

NOx emission characteristics of superfine pulverized anthracite coal in air-staged combustion

Superfine pulverized coal combustion is a new pulverized coal combustion technology that has better combustion stability, higher combustion efficiency, and comprehensive cost-effective operation. In this paper, the experiment of YQ anthracite coal combustion was carried out on an electrically heated drop tube furnace. Meanwhile, single air staged and multi air staged combustion were both adopted to understand NOx emission behaviors and analysis of mechanism and reaction pathways of each experimental phenomenon was proposed as well. The results indicate that the NOx reduction efficiency of superfine pulverized coal (22.5–32%) in single staged combustion is higher than that of regular particle size (10%). The NOx abatement in multi air staged combustion is greater than that in single air staged combustion. In multi air staged combustion, the NOx reduction efficiency of superfine pulverized coal is superior to that of regular size, which may be due to the reaction mechanism where further penetration and adsorption of NOx takes place in the inner pores. Particle burnout in multi staged combustion ratio was found to be irrelevant to the operating conditions. The findings of this article will provide useful data for the subsequent experiment to investigate into the mechanism of pure NO–char reduction and for the basis of W-flame furnace operation.

The effect of surface reactions on the prediction of NOX conversion efficiency in a porous burner

It is known that the presence of solid surfaces can strongly influence gas-phase reaction systems. This effect arises as a result of heterogeneous reactions between gas-phase radicals and surfaces. The rate of radical termination at a surface is strongly influenced by both the nature of the surface and the conditions, if any, under which the surface has been pre-treated. Given the large surface-to-volume ratios that are characteristic of porous burners it is imperative that these surface reactions, leading to termination of gas-phase radicals, be considered when modelling combustion, and the formation of minor species, in porous burners.The impact of surface reactions on the predicted NOX conversion within a porous burner is modelled using a short-cut approach. Limiting cases which either ignore radical termination or assume that radical termination proceeds at the mass-transfer-limited rate are considered. For intermediate cases, an effective reaction rate that includes the combined effects of mass transfer and surface reaction is assumed. The current modelling predictions are compared with our previous work on NOX conversion in a porous burner, in which the effects of surface reactions were neglected. For these data, an effective rate of radical loss at the burner surface equivalent to 8×10−4 times the mass-transfer limited rate is found to give best agreement. Comparing the assumed effective rate of H radical loss at the burner surface with the estimated surface collision rate suggests that H atoms recombine with an efficiency of 1×10−5, which is in good agreement with recent measurements on silica and Pyrex surfaces. Despite very low radical recombination efficiencies, the overall rate of surface recombination is sufficiently large to markedly influence the model predictions for this system at ϕ⩽1.3.The impact of surface reaction rate, different equivalence ratios, NO initial concentration and pathways is also investigated. It is found that under slightly fuel-rich conditions (ϕ⩽1.3), surface reaction rate has the maximum impact while for higher equivalence ratios (ϕ>1.3) the effect is minimal. It is also found that the presence of surface reactions significantly impacts on the NOX reduction efficiency for mixtures with low NO concentration. These differences are believed to be related to the NO conversion pathways under these different conditions. For conditions where the NO conversion mainly follows a pathway: NO⇒HNO⇒NH⇒N2, the presence of surface reactions has the greatest effect on NOx predictions whereas for conditions where the NO conversion follows a pathway: NO⇒HCNO⇒HNCO⇒NH2⇒NH3, the presence of surface reactions has a minimal impact on NOx predictions.

Enhanced Low Temperature NO x Reduction Performance Over Bimetallic Pt/Rh–BaO Lean NO x Trap Catalysts

The overall NSR operation was tested over a bimetallic Pt/Rh–BaO lean NOx trap (LNT) catalyst in the range of 473–673 K with simulated diesel exhausts and compared to monometallic 1 wt% Pt/BaO/γ-Al2O3 and 0.5 wt% Rh/BaO/γ-Al2O3 samples. The results showed the beneficial effect of the simultaneous presence of 0.5 wt% Pt and 0.25 wt% Rh on the catalytic performance under lean-burn conditions at low temperatures. It was observed that both Pt/BaO/γ-Al2O3 and Rh/BaO/γ-Al2O3, which both were mildly aged, have limited NOx reduction capacity at 473 K. However, combining Pt and Rh in the NOx storage catalyst assisted the NOx reduction process to occur at lower temperatures (473 K). One possible reason could be that the combined Pt and Rh sample was more resistant to aging. In addition, the NO2-TPD data showed that the presence of Rh into the Pt/BaO/γ-Al2O3 system has a considerable effect on the spill-over process of NOx, accelerating the release of NOx at lower temperatures. These results were in a good agreement with the observed higher rate of oxygen release of the bimetallic Pt/Rh catalyst, leaving a significant number of noble metal sites available for adsorption at lower temperatures than that of the monometallic Pt sample. The superior NSR performance of the bimetallic Pt/Rh/BaO/γ-Al2O3 catalyst under lean-burn conditions suggested the existence of synergetic promotion effect between the Pt and Rh components, increasing the NOx reduction efficiency in comparison with that of the monometallic Pt and Rh–BaO LNT catalysts.

The Use of Amine Reclaimer Wastes as a NOx Reduction Agent

Amine reclaimer wastes (ARW) generated in carbon capture and sequestration (CCS) is categorized as a hazardous waste which needs proper disposal. The proposal described in this paper can bring about a multi-effective solution to the problem of CCS waste handling. Both the pilot scale and the full scale experimental trials carried out in this study using ARW and pure monoethanolamine (MEA) confirmed the possibility of utilizing ARW as a potential reagent for the selective non-catalytic reduction (SNCR) of NOx in combustion flue gases. Even though the effectiveness of ARW is lower than that of aqueous ammonia, i.e. the most common SNCR chemical reagent used in industry (above 60% NOx reduction efficiency), ARW is nonetheless shown to possess valuable SNCR qualities (at least 20% NOx reduction efficiency) considering its availability as a waste product which has to be safely disposed. A series of thermo-gravimetric analyses provided important information on vaporization characteristics of amine reclaimer bottom wastes. The proposed methodology can lead to simultaneous energy and material resource recovery while primarily solving two environmental pollution problems, i.e. toxic ARW wastes generated in CCS, and emission of NOx a class of highly active greenhouse gases.

Highly efficient NOx purification in alternating lean/rich atmospheres over non-platinic mesoporous perovskite-based catalyst K/LaCoO3

A mesoporous perovskite, LaCoO3, with a high specific surface area of 75 m2 g−1 was synthesized by a nano-casting method. Its related NOx storage/reduction catalyst K/LaCoO3, which contains no noble metals, exhibits excellent de-NOx performance under alternating lean/rich conditions, showing a high NOx reduction efficiency of 97.0% and a high NOx to N2 selectivity of 97.3%.

Sustainable Photocatalytic Asphalt Pavements for Mitigation of Nitrogen Oxide and Sulfur Dioxide Vehicle Emissions

The ability of titanium dioxide (TiO2) photocatalytic nanoparticles to trap and decompose organic and inorganic air pollutants render them a promising technology as a pavement coating to mitigate the harmful effects of vehicle emissions. This technology may revolutionize construction and production practices of hot-mix asphalt by introducing a new class of mixtures with superior environmental performance. The objective of this study was to assess the benefits of incorporating TiO2 into asphalt pavements. To achieve this objective, the photocatalytic effectiveness and durability of a water-based spray coating of TiO2 was evaluated in the laboratory. This study also presents the field performance of the country’s first air-purifying photocatalytic asphalt pavement, located on the campus of Louisiana State University. Laboratory evaluation showed that TiO2 was effective in removing NOₓ and SO2 pollutants from the air stream, with an efficiency ranging from 31–55% for NOₓ pollutants and 4–20% for SO2 pollutants. The maximum NOₓ and SO2 removal efficiencies were achieved at an application rate of 0.05 L/m². The efficiency of NOₓ reduction is affected by the flow rate of the pollutant, relative humidity, and ultraviolet (UV) light intensity. In the field, NOₓ concentrations were monitored for both the coated and uncoated sections to directly measure photocatalytic degradation. Furthermore, nitrates were collected from the coated and uncoated areas for evidence of photocatalytic NOₓ reduction. Results from both approaches show evidence of photocatalytic NOₓ reduction. Further field evaluation is needed to determine the durability of the surface coating.

尿素SCR システムのNOx 浄化率向上に関する研究（第6報）

尿素SCR システムのNOx 浄化率向上に関する研究（第6報）

Selective catalytic reduction of NOx by diesel fuel: Plasma-assisted HC/SCR system

A new NOx reduction system has been developed which can reduce NOx emissions in diesel engine exhaust using oxygenated hydrocarbons (OHCs) generated from diesel fuel reforming as the primary reductants. The system consists of a sidestream hyperplasma reactor, a diesel fuel reformer and a dual-bed catalytic reactor. A unique feature of this system is a diesel fuel reformer that can produce highly reactive OHCs for NOx reduction. Steady-state performance as well as simulated FTP performance of this system for NOx reduction was evaluated in a sidestream connected to the main exhaust stream of a 4.9L, 6-cylinder Isuzu diesel engine dynamometer system. A dual-bed (BaY+CuY) catalyst yielded a mode-average FTP NOx conversion of 61% when the catalyst volume was 3.6 times the engine displacement. NOx reduction efficiency of the reformed diesel fuel was compared with that of an ethanol–dodecane mixture, E-diesel and NH3 in laboratory microreactor experiments and engine dynamometer tests.

Modeling Species Inhibition and Competitive Adsorption in Urea-SCR Catalysts

Although the urea-SCR technology exhibits high NOx reduction efficiency over a wide range of temperatures among the lean NOx reduction technologies, further improvement in low-temperature performance is required to meet the future emission standards and to lower the system cost. In order to improve the catalyst technologies and optimize the system performance, it is critical to understand the reaction mechanisms and catalyst behaviors with respect to operating conditions. Urea-SCR catalysts exhibit poor NOx reduction performance at low temperature operating conditions (T < 150 C). We postulate that the poor performance is either due to NH3 storage inhibition by species like hydrocarbons or due to competitive adsorption between NH3 and other adsorbates such as H2O and hydrocarbons in the exhaust stream. In this paper we attempt to develop one-dimensional models to characterize inhibition and competitive adsorption in Fe-zeolite based urea-SCR catalysts based on bench reactor experiments. We further use the competitive adsorption (CA) model to develop a standard SCR model based on previously identified kinetics. Simulation results indicate that the CA model predicts catalyst outlet NO and NH3 concentrations with minimal root mean square error.

Adaptive and Efficient Ammonia Storage Distribution Control for a Two-Catalyst Selective Catalytic Reduction System

This paper presents an adaptive urea-SCR dosing control design for a two-catalyst SCR system. A novel SCR ammonia storage distribution control (ASDC) approach aiming to simultaneously increase the SCR NOx conversion efficiency and reduce the tailpipe ammonia slip was proposed and experimentally validated. Based on the insight into SCR operational principles, a high ammonia storage level at the upstream part of the catalyst can generally yield a higher NOx reduction efficiency while a low ammonia storage level at the downstream part of the catalyst can reduce the undesired tailpipe ammonia slip. To achieve such an ammonia storage distribution control, a two-catalyst (in series) SCR system with NOx and NH3 sensors was devised. Grounded in a newly developed SCR control-oriented model, an adaptive (with respect to the SCR ammonia storage capacity) controller was designed to control the urea injection rate for achieving different ammonia storages in the two catalysts. Experimental data from a US06 test cycle conducted on a medium-duty Diesel engine system showed that, with the similar total engine-out NOx emissions and NH3 (AdBlue) consumptions, the proposed ASDC strategy simultaneously reduced the tailpipe NOx emissions by 57% and the ammonia slip by 74% in comparison to those from a conventional controller.

A mathematical optimization technique for managing selective catalytic reduction for coal-fired power plants

Selective catalytic reduction (SCR) is an emissions control technique that primarily reduces harmful emissions of oxides of nitrogen (NOx). To maintain SCR performance, catalyst layers maybe added, removed, or replaced to improve NOx reduction efficiency. To make these changes, power plants must be temporarily shut down, and SCR maintenance during scheduled power plant outages can be very expensive. Consequently, developing a fleet-wide SCR management plans that are both efficient at reducing NOx and limiting operating costs would be extremely desirable. We propose an SCR management framework that finds an optimal SCR management plan that minimizes NOx emissions using integer programming. The SCR management tool consists of two main modules—the SCR schedule generation module and the SCR optimization module. Furthermore, the SCR management framework addresses decision making from the fleet-wide perspective as well as a single plant as opposed to only a single plant, which is currently commercially available. We demonstrate the effectiveness of the tool and provide a tradeoff between NOx reduction and operating cost using Pareto optimal efficient frontiers.

A Study on the Improvement of NOx Reduction Efficiency for a Urea SCR System (Fifth Report)

A Study on the Improvement of NOx Reduction Efficiency for a Urea SCR System (Fifth Report)

尿素SCRシステムのNOｘ浄化率向上に関する研究（第2報） -NO2/NOｘ比がNOｘ浄化特性に与える影響-

尿素SCRシステムのNOｘ浄化率向上に関する研究（第2報） -NO2/NOｘ比がNOｘ浄化特性に与える影響-

尿素SCRシステムのNOx浄化率向上に関する研究(第3報):-低温過渡時における高効率NOx浄化メカニズム -

尿素SCRシステムのNOx浄化率向上に関する研究(第3報):-低温過渡時における高効率NOx浄化メカニズム -

Design and Test of a Selective Noncatalytic Reduction (SNCR) System for Full-Scale Refinery CO Boilers To Achieve High NOxRemoval

Selective noncatalytic reduction technology (SNCR) is an effective and economical method of reducing NOx emissions from a wide range of industrial combustion systems. It is widely known that the SNCR process is primarily effective in a narrow temperature window, around 900−1000 °C, and that high CO concentrations can both shift the temperature window and limit its effectiveness. While the application of SNCR on a utility boiler is challenging because of a number of factors that can have negative impacts on SNCR NOx reduction performance, the implementation of SNCR technology on an industrial or refinery boiler has unique challenges intrinsic to these boiler designs and fuels fired. This paper describes the design and test of SNCR technology on two refinery CO boilers. The work presented consisted of (1) baseline testing, (2) process analysis, (3) computational fluid dynamics (CFD) simulations, and (4) optimization testing. A three-dimensional full-scale CFD model was constructed for the boiler and was calibrated using baseline test data to simulate the flow characteristics, temperature profile, and oxygen/combustibles distribution of the boiler. The CFD model was also used to design and optimize a reagent injection system that resulted in fast and effective distribution of the reagent in the flue gas of the boiler. The CFD model, which incorporates a reduced SNCR chemistry model, was further applied to predict NOx reduction efficiency and ammonia slip. After installation and commissioning of the SNCR system, a series of parametric optimization tests were performed on both units. The final performance tests showed that the application of SNCR technology could reduce NOx emissions by at least 50%, with less than 5 ppm of ammonia slip, at a nitrogen stichiometric ratio (NSR) of 1.5. The test results are shown in the paper for a comparison to the model predictions made during the design phase.

석탄 화력 보일러의 공기 다단공급방식을 통한 연소 및 배기 배출물 특성 최적화에 관한 수치해석 연구

Air-staged combustion is known to be one of the techniques of NOx reduction. The objective of this study is to determine the optimal ratio of air flow distributed for CCOFA and SOFA; at this optimal ratio, the combustion and exhaust emission characteristics of a pulverized coal-fired boiler are maintained at a satisfactory level. A numerical investigation was performed at various airflow ratios of 16.7/83.3%, 25/75%, 50/50%, 75/25%, and 83.3/16.7%. An inert gas was considered as a substitute for air to isolate the effects of the cooling process and chemical reaction on NOx reduction; during NOx reduction in air-staged combustion, both the effects typically occur simultaneously. The results of our study show that the optimum condition, under which the maximum NOx reduction and highest boiler efficiency can be obtained, corresponds to the equal splitting of the over-fire air between CCOFA and SOFA.