NOx Control Technologies Research Articles

Catalytic reduction behaviors of nitrogen oxides and its use in biomass combustion

How to effectively apply NOx control technology to the biomass combustion process has become a current research hotspot. Aiming at the characteristics that the nitrogen oxides produced in biomass combustion process are mainly from the nitrogen element of biomass fuel, this paper adopts the fuel classification - zone reduction method to control NOx. Firstly, the reaction behavior, kinetic characteristics and optimal reduction parameters of NO reduction by coke were explored in a fixed-bed reactor. And then, the elemental analysis, pore analysis, scanning electron microscopy and other characterization methods combined with reduction experiments were used to study the changes of physical property parameters, reduction capacity and denitrification efficiency of coke after loading Fe based catalyst. By understanding the NO-carbon heterogeneous reduction process, the optimal conditions for enhancing reduction efficiency will be revealed, such as temperature, oxygen content in flue gas, and catalyst loading. The findings will provide a theoretical basis and technical support for implementing carbon reduction in low-nitrogen biomass combustion.

Technology development and cost analysis of multiple pollutant abatement for ultra-low emission coal-fired power plants in China

The implementation of ultra-low emission (ULE) limits (SO2: 35 mg/m3, NOx: 50 mg/m3, PM: 10 mg/m3) promoted the development of flue gas treatment technologies in China. Pollutant control technology development for Chinese coal-fired power plants was summarized and an analysis of the applicability and cost of pollutant control technologies was conducted. Detailed data were collected from 30 ultra-low emission coal-fired units across China. Based on a cost analysis model, the average unit power generation incremental costs were 0.0144 and 0.0095 CNY/(kW·hr) for SO2 and NOx control technologies, respectively. The unit power generation incremental cost of twin spray tower technology was 7.2% higher than that of dual-loop spray tower technology. The effect of key parameters on operating cost was analyzed. The unit power generation incremental cost increased because of increments in the electricity price for SO2 control technology and the price of the reductant in NOx control technology. With high sulfur content or NOx concentration, the unit power generation incremental cost caused by pollutant control increased, whereas the unit pollutant abatement cost decreased. However, the annual operating hours or load increased, thereby leading to a decline in unit power generation incremental cost and unit pollutant abatement cost.

Study on removing NO from simulated marine diesel engine exhaust gas using the novel composite system of Ozone-Na2SO3/(NH2)2CO

The pollutants from the marine exhaust gas seriously threaten air quality and human health. Wet absorption is one of the most efficient NOx control pathways. The strict emission control regulations require the wet NOx control technology to have high NOx removal efficiency and the nitrate concentration of the absorption solution to be below 60 mg/L. The novel system of ozone-Na2SO3/(NH2)2CO could not only make the NOx absorption efficiency and the amount of nitrate residue fully meet the regulations but also effectively reduce the (NH2)2CO consumption and the nitrite concentration. The final product of NO was mainly N2 instead of nitrate. The effects of O3 concentration, Na2SO3 concentration, (NH2)2CO concentration, O2 concentration, SO2 concentration, initial pH value, and temperature were thoroughly investigated. The experimental results showed that the NOx removal efficiency was mostly influenced by the O3 concentration, Na2SO3 concentration, and the initial pH value. Moreover, the nitrate concentration was mainly controlled by Na2SO3 concentration and initial pH value. While the nitrite concentration was governed by the (NH2)2CO concentration and initial pH value. The increase of O3 concentration and Na2SO3 concentration promote NOx absorption. Although the decrease of initial pH value resulted in a slight increase of nitrate, it greatly reduced the content of nitrite. Furthermore, the increase of Na2SO3 concentration helped to improve the NOx removal efficiency and inhibited the generation of nitrate. Initial pH value was the critical parameter for the NO absorption process. Ozone-Na2SO3/(NH2)2CO composite system showed great application potential in the field of marine wet NOx control technology.

Formation mechanism of NOx precursors during the pyrolysis of 2,5-diketopiperazine based on experimental and theoretical study

Incineration of food waste leads to the release of NOx pollutants, whereas the formation mechanism of the NOx precursors (HCN, NH3, and HNCO) during the initial pyrolysis process is far from well-studied, limiting the source control on NOx release. In this work, 2,5-diketopiperazine (DKP) was selected as the N-containing model compound to study the formation mechanism of NOx precursors in food waste pyrolysis, by combining experiments and density functional theory (DFT) calculations. The C1-N2 bond broken via the N2-to-N5 H-transfer possesses the lowest energy barrier, together with the largest reaction rate constants in the range of 400–800 °C. NH3 can be easily generated with low energy barriers and high rate constants at low temperatures (below 630 °C). Whereas, the rate constants of the pathways for HCN formation will exceed those for NH3 generation in the range of 630–740 °C. In addition, the DKP pyrolysis can also lead to the formation of HNCO with a very low energy barrier, and it can convert into HCN and NH3 through further hydrogenation and decomposition. These calculation results are exactly consistent with the experimental results that NH3 was the main precursor in the range of 400–600 °C, and the yield of HCN exceeded that of NH3 when the temperature was over 600 °C. Our current work on the formation mechanism of NOx precursors during the pyrolysis of DKP can provide theoretical guidance for the development of NOx control technology in the pyrolysis/combustion process of organic waste.

Recent advances in selective catalytic reduction of NOx by carbon monoxide for flue gas cleaning process: a review

ABSTRACT It is crucial to control NOx emission into the atmosphere because it can make several harmful health and environmental effects. Many techniques are available for NOx reduction, and among them, selective catalytic reduction (SCR) is one of the most efficient techniques for NOx removal in flue gas cleaning process. The reduction of NOx by CO offers a simple and low-cost technology for reducing NOx emissions from mobile or stationary sources. In this review, NOx emission, different NOx control technologies, and the challenges for the SCR process are studied. This paper reviews various types of catalysts, including supported and unsupported metal oxide catalysts as efficient catalysts for NOx reduction by CO. The reported experimental researches are analyzed to make an overview of the NOx reduction through CO-SCR process. Moreover, catalytic performances in the presence of oxygen, water steam, and sulfur dioxide, which usually exist in exhaust gases produced in the combustion process, are discussed. Moreover, this paper reviews the possible reaction mechanisms for the CO–SCR.

Characterization of urea SCR using Taguchi technique and computational methods.

Use of biodiesel in diesel engine helps to reduce HC, CO, and smoke emissions due to their enormous oxygen content, whereas NOx emissions formed by Zeldovich mechanism shoot up. Implementation of Bharat Stage (BS) VI by April 2020 in India has created extreme pressure on automobile manufacturers to include after treatment technology in their systems. Selective catalytic reduction (SCR), a NOx control technology, is operated using aqueous urea solution as the reductant. There are several parameters that need to be monitored to enhance the NOx conversion efficiency of SCR retrofit. The uniformity index of ammonia, which determines the conversion efficiency, is greatly influenced by parameters like exhaust gas temperature, injection angle, injector position, mass flow rate, and SCR geometry. This paper considers two types of SCR design, namely SCR with and without mixer design and their impact on NOx reduction. The effect of mass flow rate on urea conversion in SCR design without mixer is 27%, but the impact is reduced greatly in SCR design with mixer with less than 2% variation. The UI resulting from different cases ranges from 0.59 to 0.83. Using Taguchi technique and CFD tool, the impact of parameters on both the SCR designs has been investigated and the optimum SCR design is reported.

Porous materials for steady-state NO conversion: Comparisons of activated carbon fiber cloths, zeolites and metal-organic frameworks

It is important to develop new materials/methods to remove NO from gas streams to protect the environment. Use of porous materials to catalytically convert NO to NO2 may improve existing NOx control technologies. In this work, three porous materials (i.e., activated carbon fiber cloths (ACFCs), zeolites, and metal-organic frameworks (MOFs)) were evaluated as NO oxidation catalysts at 25 °C. Maximum included sphere diameter (Di) between 5.5 and 11.0 Å is shown to result in higher steady-state NO conversion (23%−71.5 ± 2.5%) by providing appropriate channels/cages that accommodate and stabilize the first transition state (TS1) through van der Waals interactions. For all considered catalysts but MIL-53 (Al), steady-state NO conversion initially increases, then decreases, with increasing pore volume contributed by Di (5.5–11.0 Å). Maximum free sphere diameter (Dmax) for the selected catalysts with steady-state NO conversion between 23% and 71 ± 2.5% is between 3.7 and 9.0 Å, allowing transport of reactants and products. Extra-framework cations (H+, NH4+, and Na+) and coordinatively unsaturated sites (Cu2+, Fe3+, and Cr3+) increase steady-state NO conversion by providing TS1 stabilization through electrostatic and coordinative interactions, respectively. However, appropriate Di and Dmax values are identified as the most influential variables for steady-state NO conversion using these catalysts. For NO conversion in the presence of SO2, no impact is observed for steady-state NO conversion of a MOF sample, but decreases of 100% and 36% for ACFC and zeolite samples, respectively. These results provide direction for designing NO oxidation catalysts to improve steady-state NO conversion.

Research progress on catalytic denitrification technology in chemical industry

In recent years, due to the rising emission of NOx annually, attention has been aroused widely by people on more and more severe environmental problems. This paper first discusses applying NOx removal and control technologies and relating chemical principles. Of many technologies, selective reduction reaction (SCR) is the most widely used. Catalysts, the concentration of NOx at the entrance of SCR catalytic reactor, reaction temperature, NH3/NOx mole ratio and NH3 slip rate analyzed later contributes to the removal efficiency of NOx. Finally, the processing and configuration of SCR de-NOx system are briefly introduced.

In-Use Emissions from 2010-Technology Heavy-Duty Trucks: Impact on Air Quality Planning in California

Introduction of a selective catalytic reduction system for heavy-duty diesel trucks (HDDTs) has substantially reduced emissions of oxides of nitrogen (NOx). However, it was found that in-use NOx emissions measured from three 2010-technology HDDTs were higher than the certification standard and higher than the levels measured during engine certification. In-use NOx emissions from three HDDTs tested over chassis dynamometer cycles were 1.7 to 9 times higher than the NOx certification standard of 0.20 grams per brake horsepower-hour, and the emissions measured with a portable emissions measurement system over highway test routes were up to five times higher than the certification standard. Such high in-use NOx emissions occurred primarily during low-speed operations (25 mph or less). This is a concern in California because more than 50% of running-exhaust NOx emissions from HDDTs will occur during low-speed operations that constitute only 11% of total vehicle miles traveled by 2025. This substantial contribution of NOx emissions during low-speed operations should be addressed carefully in the process of developing regulations and strategies to improve air quality in California. For better understanding and control of high in-use NOx emissions, there is a strong need for investigation of NOx control technologies effective at low-speed operation, differences between engine testing and whole vehicle testing procedures, and the roles of both engine certification requirements and in-use compliance requirements in reducing real-world NOx emissions.

Vehicular Emissions in Review

The review paper summarizes major developments in vehicular emissions regulations and technologies in 2013. First, the paper covers the key regulatory developments in the field, including proposed light-duty (LD) criteria pollutant tightening in the US; and in Europe, the continuing developments towards real-world driving emissions (RDE) standards. Significant shifts are occurring in China and India in addressing their severe air quality problems. The paper then gives a brief, high-level overview of key developments in fuels. Projections are that we are in the early stages of oil supply stability, which could stabilize fuel prices. LD and HD (heavy-duty) engine technology continues showing marked improvements in engine efficiency. Key developments are summarized for gasoline and diesel engines to meet both the emerging NOx and GHG regulations. HD engines are or will soon be demonstrating 50% brake thermal efficiency using common approaches. NOx control technologies are then summarized, including SCR (selective catalytic reduction) systems and SCR filter developments. Emphasis is on low-temperature deNOx and integration of components and control. Diesel PM (particulate matter) reduction technologies are evolving around the behavior of ash deposits and SCR integration. Filters for direct injection gasoline applications are developing very rapidly, and in some cases the back pressure, light-off characteristics, and emissions reductions are very similar to standard three way catalysts (TWCs). Oxidation catalysts mainly involve developments towards stubborn problems, like low-temperature performance with exhaust with high hydrocarbon and CO, and methane oxidation. Finally, the paper discusses some key developments in gasoline gaseous emission control, focusing on matching engine calibration with emissions system characteristics; and on lean burn gasoline emissions control. CITATION: Johnson, T., Vehicular Emissions in Review, SAE Int. J. Engines 7(3):2014, doi:10.4271/2014-01-1491. 2014-01-1491 Published 04/01/2014 Copyright © 2014 SAE International doi:10.4271/2014-01-1491 saeeng.saejournals.org 1207 This paper is posted on this website with permission from SAE International. It may not be shared, downloaded, duplicated, or transmitted in any manner without prior written permission from SAE.

CFD analysis on the catalyst layer breakage failure of an SCR-DeNOx system for a 350 MW coal-fired power plant

Selective catalytic reduction as one of the secondary NOx control technologies is widely used in industrial sources including coal-fired power plants and large boilers. The performance of an SCR-DeNOx system is sensitive to the installment of its components such as turning vanes and hybrid grids. In this work, three-dimensional CFD simulations are carried out to analyze the breakage failure of an SCR-DeNOx system for a certain 350MW coal-fired power plant. Research results are consistent with the phenomena that occur in the industrial application. It reveals that the breakage failure in the industrial application is likely to be caused by the inappropriate installation of the turning vane 3 locating closest to the catalyst, especially the angle of the turning vane 3. The analysis further shows that the lifetime or the breakage of the catalyst layers depends highly on the gas velocity, the fly ash distribution and its particle velocity.

Internal Flow Analysis of SCR-Exhaust Aftertreatment System

Selective Catalytic Reduction system (SCR) has made great contributions to diesel engine NOx control technology. The gas flow condition in exhaust pipe has a great effect on catalytic reduction reaction of SCR, especially the airflow through carriers. In this paper, CFD technology was used to simulate the internal flow field, and analyze the gas flow uniformity, which would give us reasonable suggestions to optimize the structure of SCR-Exhaust aftertreatment system.

The Discharge Status and Technical Analysis of NO<sub>X</sub> of Thermal Power Plant Boiler

NOXis one of the pollutants which will be key governanced by Government in Twelfth Five, and thermal power plant boiler is the main source of NOXin the atmospheric. Overview of the discharge status of NOXand the state-controlled status of the power plant NOXdischarge regulations with the latest standards, analysis of the current two thermal power plant NOXcontrol technology: low-NOx combustion technology and flue gas denitrification technology. Low NOx combustion technology introduces low excess air combustion technology, air staged combustion technology, flue gas recirculation technology, flue gas denitrification technology introduced four methods which is selective catalytic reduction, selective non-catalytic reduction, hybrid SNCR-SCR catalyst reduction combined metgod and wet NOXabsorption system, principle of denitration and their advantages and disadvantages of different methods are discussed. Finally a brief introduction of the difficulties of governance NOXand some necessary issues when select zhe control methods.

Biological NOx removal by denitrification process in a jet-loop bioreactor: system performance and model development

Nitrogen monoxide (NO) and nitrogen dioxide referred as NOx are one of the most important air pollutants in the atmosphere. Biological NOx removal technologies have been developing to reach a cost-effective control method for upcoming stringent NOx emission standards. The BioDeNOx system was seen as a promising biological NOx control technology which is composed of two reactors, one for absorbing of NO in an aqueous Fe(II)EDTA2− solution and the other for subsequent reduction to N2 gas in a biological reactor by the denitrification process. In this study, instead of two discrete reactors, only one jet-loop bioreactor (JLBR) was utilized as both absorption and denitrification unit and no chelate-forming chemicals were added. In other words, the advantage of better mass transfer conditions of jet bioreactor was used instead of Fe(II)EDTA2−. The process was named as Jet-BioDeNOx. The JLBR was operated for the removal of NOx from air streams containing 500–3000 ppm NOx and the results showed that the removal efficiency was between 81% and 94%. The air to liquid flow ratio (QG/QRAS) varied in the range of 0.07–0.12. Mathematical modelling of the system demonstrated that the removal efficiency strongly depends on this ratio. The high mass transfer conditions prevailed in the reactor provided a competitive advantage on removing NO gas without any requirement of chelating chemicals.

Towards ideal NOx control technology for bio-oils and a gas multi-fuel boiler system using a plasma-chemical hybrid process

A super-clean boiler system comprising a multi-fuel boiler and a reactor for plasma-chemical hybrid NOx aftertreatment is developed, and its industrial applications are examined. The purpose of this research is to optimally reduce NOx emission and utilize waste bio-oil as a renewable energy source. First, NO oxidation using indirect plasma at elevated flue gas temperatures is investigated. It is clarified that more than 98% of NO is oxidized when the temperature of the flue gas is less than 130°C. Three types of waste bio-oils (waste vegetable oil, rice bran oil, and fish oil) are burned in the boiler as fuels with a rotary-type burner for CO2 reduction considering carbon neutrality. NOx in the flue gases of these bio-oils is effectively reduced by the indirect plasma-chemical hybrid treatment. Ultralow NOx emission less than 2ppm is achieved for 450min in the firing of city natural gas fuel. The boiler system can be successfully operated automatically according to unsteady steam demand and using an empirical equation for Na2SO3 supply rate, and can be used in industries as an ideal NOx control technology.

Numerical Simulation of NSP Cement NOx Formation and Control Technology

In this paper, in considering the influence of interaction and material decomposition, the generation of NOx inside the rotary kiln and precalciner, which are the main NOx emission equipments in cement production process, are simulated by CFD technology, and the results is tally with the actual situation. This shows that numerical simulation can be a very good guidance on NOx emission reduction technology and staged-combustion precalciner structure design, and we can design and optimize the NOx emission reduction scheme based on numerical simulation to achieve the purpose of reducing NOx pollution in cement production.

Controlling Mercury Emission for China's Coal Fired Electricity Plants: an Economic Analysis

Abstract This study aims to identify the least-cost strategy for controlling the emission of mercury from coal-fired electricity generation plants in China, which helps to provide technical guidance to firms and decision making basis for designing mercury control strategy and policy for the government. Based on the analysis and evaluation of technical and economic features of the available technologies/alternatives, this study develops a Cost -Effectiveness Oriented Model (CEOM) at enterprises level. A least cost solution for each type of plants is estimated. Further, sector-level mercury abatement cost is estimated by grouping the plants by size and existing technologies, giving concern of the possible policy scenarios which based on proportional allocation of the emission control targets and based on the marginal abatement cost allocation, as well as the existing SO2 control policies. It concludes that by combining the pretreatment technology, particulates removing technology, and SO2 control technology, as well as the NOx control technologies, China can control over 90% of emission. At least 12% of the mercury can be removed by strictly enforcing the Two Control Zone's policy, and the co-benefit is significant by introducing multiple pollutants control. A sets of policy recommendation is concluded, that China should enforce SO2 control policy more effectively, the multiple pollution control strategy should be developed, and a emission trading scheme can provide plant flexibility to compliance and can generate cost saving.

Comprehensive process design study for layered‐NOX‐control in a tangentially coal fired boiler

AbstractAs emissions regulations for coal‐fired power plants become stricter worldwide, layering combustion modification and post‐combustion NOX control technologies can be an attractive option for efficient and cost‐effective NOX control in comparison to selective catalytic reduction (SCR) technology. The layered control technology approach designed in this article consists of separate overfire air (SOFA), reburn, and selective noncatalytic reduction (SNCR). The combined system can achieve up to 75% NOX reduction. The work presented in this article successfully applied this technology to NRG Somerset Unit 6, a 120‐MW tangential coal‐fired utility boiler, to reduce NOX emissions to 0.11 lb/MMBtu (130 mg/Nm3), well under the US EPA SIP Call target of 0.15 lb/MMBtu. The article reviews an integrated design study for the layered system at Somerset and evaluates the performance of different layered‐NOX‐control scenarios including standalone SNCR (baseline), separated overfire air (SOFA) with SNCR, and gas reburn with SNCR. Isothermal physical flow modeling and computational fluid dynamics simulation (CFD) were applied to understand the boiler flow patterns, the combustible distributions and the impact of combustion modifications on boiler operation and SNCR performance. The modeling results were compared with field data for model validation and verification. The study demonstrates that a comprehensive process design using advanced engineering tools is beneficial to the success of a layered low NOX system. © 2009 American Institute of Chemical Engineers AIChE J, 2010

Exploring Links Between Innovation and Diffusion: Adoption of NOX Control Technologies at US Coal-fired Power Plants

While many studies have looked at innovation and adoption of technologies separately, the two processes are linked. Advances (and expected advances) in a single technology should affect both its adoption rate and the adoption of alternative technologies. This paper combines plant-level data on US coal-fired electric power plants with patent data pertaining to NOX pollution control techniques to study this link. As in other studies of environmental technologies, the effect of other explanatory variables is dominated by the effect of environmental regulations, demonstrating that the mere presence of environmental technologies is not enough to encourage its usage. Nonetheless, I do find that technological advances are important for the adoption of existing combustion modification technologies. However, these advances are less important for the adoption of newer post-combustion control techniques, which are adopted only when needed to comply with the strictest emission limits.

Controlling NOx emission from industrial sources

AbstractA number of regulatory actions focused on reducing NOx emissions from stationary combustion sources have been taken in the United States in the last decade. These actions include the Acid Rain NOx regulations, the Ozone Transport Commission's NOx Budget Program, and the NOx SIP Call rulemakings. In addition to these regulations, the recent Interstate Air Quality Rulemaking proposal and other bills in the Congress are focusing on additional reductions of NOx. Industrial combustion sources accounted for about 18% of NOx emissions in the United States in 2000 and constituted the second largest emitting source category within stationary sources, only behind electric utility sources. Based on these data, reduction of NOx emissions from industrial combustion sources is an important consideration in efforts undertaken to address the environmental concerns associated with NOx. This paper discusses primary and secondary NOx control technologies applicable to various major categories of industrial sources. The sources considered in this paper include large boilers, furnaces and fired heaters, combustion turbines, large IC engines, and cement kilns. For each source category considered in this paper, primary NOx controls are discussed first, followed by a discussion of secondary NOx controls. © 2005 American Institute of Chemical Engineers Environ Prog, 2005