Non-catalytic Reduction Of Nitric Oxide Research Articles

Quantitative evaluation of NO formation and destruction routes during methane MILD combustion using an improved calculation method

Moderate or intense low-oxygen dilution (MILD) combustion has become increasingly attractive because of its ultra-low nitric oxide (NO) emission. Although many efforts have been made to investigate the NO formation and destruction pathways of MILD combustion, their relative contribution still fails to reach an agreement when using previously-developed NO calculation methods. For this reason, these NO calculation methods are first evaluated for methane MILD combustion by the kinetic modeling of a well-stirred reactor (WSR). Then, an improved calculation method for quantifying the contribution of NO sub-routes is proposed, which involves thermal, prompt, N2O-intermediate, NNH, selective non-catalytic reduction of NO, and NO-reburning routes. Also, this improved method allows the application of a more comprehensive mechanism (Progress in Energy and Combustion Science, 2018, 67: 31–68) other than GRI-Mech 2.11. Using the improved method with the more comprehensive mechanism, the NO formation and destruction routes during methane MILD combustion are quantitatively investigated. The results show that in the WSR at 1300 K with 5% O2, the contribution of the N2O-intermediate route accounts for about 80% at an equivalent ratio (Φ) of 0.8, and it gradually decreases as Φ increases. Once Φ is >1.0, the prompt route surpasses the N2O-intermediate route to dominate the NO generation entirely. The NNH mechanism is found to be of little importance at Φ ranging from 0.5 to 1.5. Additionally, the NO-reburning reaction reduces <10% of the total NO production when Φ < 1.0, and its contribution increases abruptly at 1.0 < Φ < 1.1.

Optical analysis during reduction of nitric oxide in microwave-induced plasma promoted by activated cokes at atmospheric pressure

Emission from microwave (MW)-induced argon plasma promoted by a bed of activated coke granules was analyzed spectroscopically during non-catalytic reduction of nitric oxide (NO) at atmospheric pressure. The spectral analysis with a high resolution revealed that strong 5 peaks were recognized in a similar wavelength region to N2+ first negative band when NO molecules were included in argon plasma. The strongest peak is caused by the Ar(II) ions excited with energy corresponding to 388.033 nm in the progress of atomic transition 3s23p4(3P)4d 4D1/2 → 3s23p4(3P)4p 4D°1/2. This transition must be enhanced by an interaction with any intermediates or radical species yielded during NO reduction reactions. The plasma temperatures were determined by Boltzmann plots from intensities of any two peaks in the spectral band. The temperature was significantly different dependently on choice of two peaks, whose fact is implying non-equilibrium plasma. The maximum temperature was recognized at a high level of 40,000 K due to the activation during the reactions. The images of the plasma observed by high-speed camera showed dynamic features so that MW discharge like streamer was generated frequently in the reactor. The reaction rate could be correlated with the ratio of the area dominated by dynamic plasma to the cross section in the reactor.

A validated CFD model for prediction of selective non-catalytic reduction of nitric oxide by cyanuric acid

A CFD model for selective non-catalytic reduction of nitric oxide by cyanuric acid (rapid reduction of nitrogen oxides, RAPRENOx process) is compared against reactor experiments. The numerical simulations were carried out solving the flow field. A model for the RAPRENOx chemistry was then included in the model enabling a study of the chemistry in the reactor. The simulations showed that the proposed chemistry model is valid under certain conditions. There is an especially good agreement for high O2 concentrations while the model failed in reproducing the experimental data for 0% H2O.

A CFD-based evaluation of selective non-catalytic reduction of nitric oxide in iron ore grate-kiln plants

The overall goal of this study is to explore the function of selective non–catalytic reduction of nitric oxide (NO) in iron ore grate–kiln plants. Computational fluid dynamics is used to model the flow and the injection of urea and cyanuric acid reagents. Temperature, residence time and inlet NO content are varied, and the effects on the reduction of NO are studied. The simulations show that the use of urea results in a higher reduction of NO within the temperature window investigated as compared to cyanuric acid; however, urea cannot be used for NO reduction over the entire range of applicable temperatures. Cyanuric acid is usable within the entire temperature range for high NO content (i.e., 300 ppm) in the flue gas, but it is not effective for low NO concentration (i.e., 150 ppm). Moreover, the simulations indicate that temperature has a larger influence on the NO reduction than the residence time.

Application of the Polynomial Chaos Expansion to the simulation of chemical reactors with uncertainties

In this paper we consider the simulation of probabilistic chemical reactions in isothermal and adiabatic conditions. Models for reactions under isothermal conditions result in advection equations, adiabatic conditions yield the reactive Euler equations. In order to treat with scattering data, the equations are projected onto the polynomial chaos space. Scattering data can largely affect the estimation of quantities in the system, including variable optimization. This is demonstrated on a selective non-catalytic reduction of nitric oxide.

A lumped model for thermal decomposition of urea. Uncertainties analysis and selective non-catalytic reduction of NO

A two-step mechanism for non-catalytic thermal decomposition of urea was investigated. It involves a first order reaction for the thermolysis of urea and a pseudo-first order reaction for hydrolysis of isocyanic acid. Rate constants of these reactions were tuned on experimental measurements of NH 3 and HNCO concentrations at 423–723 K and 1083–1383 K in isothermal flow reactors made of aluminum and ceramic, respectively. A regression analysis by taking the uncertainties in the kinetic parameters into account shown that the resultant pairs of Arrhenius expressions for thermo-hydrolyzing urea were different with a 90% confidence when obtained from the different sets of experimental data. Additional results of ammonia concentration from experiments of urea solution decomposition reported in the literature revealed the reliability of the Arrhenius expressions tuned on the reaction rates obtained in the highest range of temperature in the ceramic reactor. The consistency of these equations was also verified by a comparison between calculated and experimental rates of selective non-catalytic reduction of nitric oxide with urea as reducing agent. A statistical analysis based on the identification of possible tendencies in these residuals again evidences the weakness of the Arrhenius expressions based on the experiments performed at lower temperatures, which was attributed to a non-expected catalytic effect of aluminum reactor walls on reactions rates of urea thermal decomposition.

A dynamic optimization procedure for non-catalytic nitric oxide reduction in waste incineration plants

Reduced chemical kinetic models are often used to simulate the kinetics of full-scale DeNO x systems because of the computational expense of combining a detailed description of fluid dynamics and a complete mechanism of reaction. In particular, these simplified models might be useful when complete combustion minimizes the influence of CO and hydrocarbon fuels on the kinetic mechanism of thermal DeNO x , such as that occur in large-scale systems for non-catalytic nitrogen oxides reduction installed in hazardous waste incineration plants. In this work, a lumped mechanism is involved in a dynamic optimization procedure to reach a maximum efficiency of NO abatement in such devices, by handling the inlet ratio of H 2 or CH 4 to inlet NH 3 . As a consequence, a simplified chemical kinetic model reported in the literature was modified to reproduce the influence of hydrogen and methane addition on the selective non-catalytic reduction of nitric oxide with ammonia. The consistency of the lumped mechanism, which involves only two global reactions to describe the NO / NH 3 / O 2 and H 2 or CH 4 gas phase reaction system, was verified by using a large set of experimental results obtained at stationary conditions in tubular reactors. The dynamic optimization procedure aims to compensate the effect of the main kinetic disturbances on nitrogen oxides reduction, as variation in the flue-gas temperature in NH 3 injection zones and in the flue-gas residence time, which are typically found in incinerators due to the heterogeneity of the waste composition. Calculated results of NO abatement by assuming typical fluctuations in the kinetic characteristics of exhausts in incineration plants evidence an increase of nitric oxide abatement from 5% to approximately 40–50% when involving the suggested dynamic optimization strategy.

Experimental and modeling analysis of the NO xOUT process

The selective non-catalytic reduction of nitric oxide with urea has been investigated experimentally in a temperature range from 950 to 1450 K using a laboratory reactor that approximates well stirred conditions. From the experimental results it has been possible not only to deduce some general trends of interest in the NO x OUT process, but also to validate a detailed kinetic mechanism. In particular, the experiments showed that the NO x OUT process is effective in a narrow temperature window. The effect of increasing the ratio of nitrogen in the reducing agent and in NO is to increase the efficiency of abatement, while that of increasing O 2 concentration depends on the temperature considered. Moreover, the effect of increasing the CO/NO ratio up to one is not very pronounced. The detailed kinetic mechanism developed has been validated by comparison with several experimental findings, thus providing an effective tool for process simulation in a wide range of operating conditions.

Analysis of the thermal DeNO x process at high partial pressure of reactants

The selective non-catalytic reduction of nitric oxide with ammonia has been investigated experimentally using a perfectly stirred reactor. In a temperature range from 1000 to 1450 K, a set of experimental runs has been performed to investigate the influence of increasing the partial pressure of all the reactants simultaneously. No kinetic limitation to the efficiency of the process due to the high partial pressures of the reactants has been found. This can provide interesting information about the effect of an overall pressure increase on all the reactions involved apart from the three-body ones. Comparison with several detailed kinetic models previously presented in the literature evidenced that these models are not able to represent correctly the process behavior in the conditions investigated. One of these has been properly modified in order to reproduce the experimental data so as to provide an effective tool for process simulation in a wide range of operating conditions.

Balance of NH 3 and behavior of polychlorinated dioxins and furans in the course of the selective non-catalytic reduction of nitric oxide at the TAMARA waste incineration plant

Investigations were performed on the selective non-catalytic reduction (SNCR) of nitric oxide (NO) at TAMARA, the pilot-scale waste incineration plant of the Karlsruhe Research Center. Aqueous ammonia (NH 3) was injected into the combustion chamber as reductant. The influence of NH 3 on various inorganic and organic compounds in the flue gas was investigated. The concentrations of NO were reduced by up to about 90% by NH 3 injection. The concentrations of most of the other inorganic and organic compounds, including in particular PCDD and PCDF, did not change significantly.

A kinetic model for the reduction of nitric oxide by hydrazine

A chemical kinetic model is developed for the non-catalytic reduction of nitric oxide (NO) by hydrazine (N2H4). Since the reduction of NO was observed in an experimental reaction with N2H4, the hydrazine has been suggested as a new reductant of NO in addition to the conventional ammonia, urea and isocyanic acid. In the proposed kinetic model, a set of fifty one chemical reactions that includes the various branching reactions of N2H4 to NH2 and the wellknown reaction NO+NH2→N2+H2O is simultaneously considered with the usual partial equilibrium assumptions. The NO reduction is estimated to occur at a temperature range between 700K and 1400 K, which is wider and lower than in the conventional Thermal DeNOx process. The maximum amount of the reduced NO is slightly less than that in the Thermal DeNOx. The effects of the other input parameter on the NO reduction rate also discussed.

Influence of additives on selective noncatalytic reduction of nitric oxide with ammonia in circulating fluidized bed boilers

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInfluence of additives on selective noncatalytic reduction of nitric oxide with ammonia in circulating fluidized bed boilersBo Leckner, Maria Karlsson, Kim Dam-Johansen, Claus Erik Weinell, Pia Kilpinen, and Mikko HupaCite this: Ind. Eng. Chem. Res. 1991, 30, 11, 2396–2404Publication Date (Print):November 1, 1991Publication History Published online1 May 2002Published inissue 1 November 1991https://doi.org/10.1021/ie00059a006RIGHTS & PERMISSIONSArticle Views302Altmetric-Citations34LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Pilot-scale experiments with ammonia and urea as reductants in selective non-catalytic reduction of nitric oxide

Comparative studies of ammonia and urea as reductants of nitric oxide have been carried out in a pilot-scale reactor, in the injection temperature range from 1023 K to 1373 K. The reactor has a temperature gradient of about 200 K/s. The efficiency of the two reductants and the emissions of CO, N 2 O, HCN and NH 3 have een measured. The optimum temperature was found to be 1223 K with ammonia, 1273 K with urea. No significant difference in reducing capacity was found. At a molar ratio NH i /NO of 1.3, 70% reduction was achieved with either reductant at their optimum temperatures. The emissions of nitrous oxide (N 2 O) and carbon monoxide turned out to be the major problem with the use of urea, especially at lower temperatures. At a temperature of 1223 K, a maximum of 85 ppm of N 2 O was found. With ammonia, no more than 18 ppm was measured at any temperature. With urea, the emission of carbon monoxide rose to 95 ppm at 1223 K. With ammonia, a maximum of 55 ppm was found at 1123 K. An explanation for the observations, based on NCO as an intermediate in the decomposition of urea, is discussed. With methylamine as an exception, hydrocarbons, amines, and alcohols as additives to ammonia generally shift the active temperature window as well as the maximum degree of reduction toward lower values. The emission of HCN was nearly zero with no additive to the reductant, less than 8 ppm with most additives, but in special cases over 200 ppm with dimethylamine.