NNH mechanism in low-NOx hydrogen combustion: Experimental and numerical analysis of formation pathways

Purohit, Anmol L.; Nalbandyan, Armen; Malte, Philip C.; Novosselov, Igor

doi:10.1016/j.fuel.2021.120186

Cited by 25 publications

(7 citation statements)

References 52 publications

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“…Hydrogen-enriched flames in low-NOx combustion have been widely studied for NOx concentration (Liu et al, 2022;Rahman et al, 2022). It should be mentioned that besides thermal NOx, the hydrogen addition also promotes the generation of the NNH route (Purohit et al, 2021) and the fact that the NNH route dominating the NOx formation has been reported recently. The changes in NOx formation pathways suggest that a hydrogen-enriched flame promotes thermal NOx and the NNH route among the four main NOx formation pathways in gas combustion, while thermal NOx and prompt NOx are the dominant mechanisms in methane combustion.…”

Section: Effects Of Hydrogen Addition On No X Formation In a Nonpremi...mentioning

confidence: 99%

“…Prompt NOx is the dominant pathway in low-NOx methane combustion, while thermal NOx and the NNH route quickly dominate the NOx generation in hydrogen-enriched flames. As a latest discovered NOx pathway, the NNH route has been studied in hydrogen flames (Bozzelli et al, 1995;Purohit et al, 2021). The NNH route becomes the second dominant pathway in hydrogen-added flames.…”

Section: Nox Concentrations and Relative Weights Of The Main Formatio...mentioning

confidence: 99%

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Effects of hydrogen addition on NOx formation in a non-premixed methane low-NOx combustor

CHENG,

ZHU,

DENG

2024

Mechanical Engineering Journal

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Hydrogen is a promising carbon-free fuel, but nitric oxides (NO x ) emissions are significantly increased with higher temperature in hydrogen combustion. Internal flue gas recirculation (IFGR) is one of the most effective NO x reduction techniques in boilers. Previous research has widely reported NO x generation with hydrogen enrichments from a chemical kinetic perspective, however, the NO x formation principles in non-premixed methane/air combustion using IFGR with hydrogen addition are still unclear. This work aims to investigate the effects of hydrogen addition on NO x formation in a non-premixed methane low-NO x combustor using IFGR. The Reynolds-averaged Navier-Stokes (RANS) simulations were conducted on a 5 kW non-premixed combustor with IFGR rate of 17.7%, which generated 11.3 mg/m 3 of total NO x generation in methane combustion. A series of three-dimensional computational fluid dynamics (CFD) simulations with detailed mechanisms was tested on four hydrogen power fractions. The reaction intensities of the main NO x formation pathways were analyzed on reaction rates. The results show that 70% hydrogen power fractions lead to significantly greater NO x concentration to 677.8 mg/m 3 , as high as 60 times of the original concentration. With no additional techniques, the original methane low-NO x combustor is only allowed for hydrogen addition of less than 20% power fraction. The NNH route becomes the second dominant pathway in hydrogen-added flames. Influenced by the growing hydrogen contents, the generation of the NNH route is largely generated from 2 mg/m 3 to 65 mg/m 3 . This work connects the hydrogen addition and the NO x formation pathways in non-premixed methane combustion, and highlights the importance of eliminating thermal NO x and the NNH route to achieve low-NO x combustion rather than sole NO x suppression method, which can provide a reference for designing low-NO x techniques.

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Section: Effects Of Hydrogen Addition On No X Formation In a Nonpremi...mentioning

confidence: 99%

Section: Nox Concentrations and Relative Weights Of The Main Formatio...mentioning

confidence: 99%

Effects of hydrogen addition on NOx formation in a non-premixed methane low-NOx combustor

CHENG,

ZHU,

DENG

2024

Mechanical Engineering Journal

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“…Despite the extensive coverage of chemical reactions, the influence of the distribution of hydrogen and air before combustion is not given in the process. This issue is covered in the study [13], which shows the design of a hydrogen jet burner for a wide range of air excess ratios. However, for mixing flows in jet burners, a relatively long device length is required.…”

Section: This Work Presents the First Stage Of Research Into The Oper...mentioning

confidence: 99%

The determination of the features of the process of mixture formation of hydrogen burner

Romanova,

Mitchenko

2024

EEJET

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The use of hydrogen fuel as an alternative source of individual heat supply is a rather promising direction in the development of thermal energy. However, due to the physical properties of hydrogen and the peculiarities of its combustion, several problems arise for the practical use of hydrogen heat generators. Such problems include ensuring flare stability and large emissions of thermal nitrogen oxides (NOX). For stable operation of the hydrogen burner, safe operation, and reduction of nitrogen oxide emissions when burning hydrogen, first, it is necessary to ensure high-quality pre-mixing with air. This work presents the first stage of research into the operation of a hydrogen burner for heat production in the Flow Simulation module of the SolidWorks software environment. For volume flow rates of air and hydrogen corresponding to capacities of 1, 1.5 and 2 kW and air excess coefficient α=1.6. The given design makes it possible to ensure uniform mixture formation (the volume fraction of hydrogen is approximately 18.5 % at the outlet cross-section of the burner and the speed at the outlet of the burner is 5.4, 8.1, and 10.8 m/s, respectively. The burner is a nozzle with a short premixing chamber First, hydrogen is supplied for mixing into the air flow through symmetrically located holes. After that, a vortex is created, which ensures high-quality mixing of gases with a short length of the burner, as well as a uniform distribution of velocity at the exit. The obtained results allow to proceed to the next stage – the study of hydrogen combustion processes in the combustion chamber of the contact heat generator, which would ensure the formation of a stable flame and low NOX emissions. In addition, this design can be used in the development of hydrogen burners for heating boilers to meet the needs of private homes and small businesses

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“…The uniform temperature profile allows us to predictably calculate the exposure to temperature and the oxidative species required to destroy the recalcitrant compounds. The ability to operate in a distributed regime opens the possibility to model the process using relatively simple chemical reactor networks (CRN), i.e., a mix of perfectly stirred reactor (PSR) and plug-flow reactor (PFR) elements. − This reduced-order fluid modeling allows the incorporation of large chemical kinetic mechanisms with low computational costs.…”

Section: Model Predictions Vs Experimental Datamentioning

confidence: 99%

Design of a Small-Scale Supercritical Water Oxidation Reactor. Part II: Numerical Modeling

Purohit

Misquith

Pinkard

et al. 2021

Ind. Eng. Chem. Res.

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Experimental data from a bench-scale reactor was used to validate the computation fluid dynamics (CFD) methodology for modeling the supercritical water oxidation (SCWO) process. The reactor was operated on ethanol as pilot fuel and H2O2 as an oxidizer. Fluid properties were modeled using polynomial fit approximations validated against NIST data over a range of subcritical and supercritical temperatures at 25 MPa. The model predicts the fluid temperature in the reactor within 30 °C of measured values over a range of inlet fuel concentrations. The ethanol decomposition of ∼99% occurs within 20% of the reactor length at T ∼ 600 °C. The nondimensional analysis shows that the reactor operates in a distributed reaction regime due to the enhanced stability of the inverted gravity reactor configuration. The modeling approach can inform the designs of practical SCWO reactors, increase operational safety related to material limits, and optimize operating conditions required to destroy toxic wastes.

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NNH mechanism in low-NOx hydrogen combustion: Experimental and numerical analysis of formation pathways

Cited by 25 publications

References 52 publications

Effects of hydrogen addition on NO<i><sub>x</sub></i> formation in a non-premixed methane low-NO<i><sub>x</sub></i> combustor

Effects of hydrogen addition on NO<i><sub>x</sub></i> formation in a non-premixed methane low-NO<i><sub>x</sub></i> combustor

The determination of the features of the process of mixture formation of hydrogen burner

Design of a Small-Scale Supercritical Water Oxidation Reactor. Part II: Numerical Modeling

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