scholarly journals The Effect of Variable Air–Fuel Ratio on Thermal NOx Emissions and Numerical Flow Stability in Rotary Kilns Using Non-Premixed Combustion

Processes ◽  
2021 ◽  
Vol 9 (10) ◽  
pp. 1723
Author(s):  
Mohamed el Abbassi ◽  
Domenico Lahaye ◽  
Cornelis Vuik
Keyword(s):  
Wall Temperature ◽  
Diffusion Flames ◽  
Three Dimensional ◽  
Nox Emissions ◽  
Unstable Flow ◽  
Nox Formation ◽  
Fuel Ratio ◽  
Rotary Kilns ◽  
Thermal Nox ◽  
The Impact

One of the quickest ways to influence both the wall temperature and thermal NOx emissions in rotary kilns is to change the air–fuel ratio (AFR). The normalized counterpart of the AFR, the equivalence ratio, is usually associated with premixed flames and studies of its influence on diffusion flames are inconsistent, depending on the application. In this paper, the influence of the AFR is investigated numerically for rotary kilns by conducting steady-state simulations. We first conduct three-dimensional simulations where we encounter statistically unstable flow at high inflow conditions, which may be caused by vortex stretching. As vortex stretching vanishes in two-dimensional flow, the 2D simulations no longer encounter convergence problems. The impact of this simplification is shown to be acceptable for the thermal behaviour. It is shown that both the wall temperature and thermal NOx emissions peak at the fuel-rich and fuel-lean side of the stoichiometric AFR, respectively. If the AFR continues to increase, the wall temperature decreases significantly and thermal NOx emissions drop dramatically. The NOx validation, however, shows different results and indicates that the simulation model is simplified too much, as the measured NOx formation peaks at significantly fuel-lean conditions.

Numerical Investigation of NOx Emissions Characteristics of a Natural Gas Premixed Burner Based on Chemical Reactor Network Model

2019 ◽  
Author(s):  
Bin Mu ◽  
Fulin Lei ◽  
Weiwei Shao ◽  
Xunwei Liu ◽  
Zhedian Zhang ◽  
...  
Keyword(s):  
Experimental Data ◽  
High Pressure ◽  
Chemical Reactor ◽  
Nox Emission ◽  
Recirculation Region ◽  
Nox Emissions ◽  
Nox Formation ◽  
Chemical Reactor Network ◽  
Thermal Nox ◽  
Reactor Network

Abstract Numerical optimization of nitrogen oxides (NOx) formation is an essential factor during developing low pollution combustor of gas turbine. The Computational Fluid Dynamics-Chemical Reactor Network (CFD-CRN) hybrid method has a great advantage in fast and accurate prediction of combustor NOx emissions. In this work, a hybrid CFD-CRN approach is established to predict pollutant emissions of a lean premixed model burner for gas turbine applications. Several criteria are compared for separating the combustor into chemically and physically homogeneous zones, and the crucial parameters such as residence time and flue gas recirculation ratio are calculated. The CRN model is preliminarily verified with experimental data. The effects of pressure and fuel-air unmixedness on NOx formation are subsequently investigated. In addition, the effects of changes in fuel/air flow distribution and crucial parameters of CRN model on NOx emissions are also estimated under different pressures and fuel-air unmixedness. The combustor is divided into several zones including reaction preheating region, flame front region, flame transition region, post flame region, main recirculation region and corner recirculation region based on CFD results of fuel-air mixing characteristics, velocity field, temperature field, distribution of OH mass fraction and Damkohler number. The complex CRN model has the advantage of predicting NOx emission characteristics under higher Tad conditions compared with the simple model, and its prediction of NOx emission shows good agreement with experimental data under various equivalence ratio conditions. The structure and distribution of several regions of CRN model are analogous but not significant when Reynolds number exceeds 105 under high pressure. The pathway analysis shows that the NOx emission gradually decreases through N2O and NNH mechanisms, resulted from the decreasing concentration of O radical under low Tad and high pressure. However, the pressure could significantly promote thermal NOx formation resulting form increase of temperature. The fuel-air unmixedness results in the increase of maximum flame temperature, which has significant effect on change of the CRN regions-separating. The fuel-air unmixedness causes the significant increasing of thermal NOx formation.

Using Multi-Dimensional Combustion Simulations of a Natural Gas/Diesel Dual Fuel Engine to Investigate NOx Trends With Air-Fuel Ratio

2017 ◽  
Author(s):  
Andrew Hockett ◽  
Michael Flory ◽  
Joel Hiltner ◽  
Scott Fiveland
Keyword(s):  
Natural Gas ◽  
Oil And Gas ◽  
Operating Conditions ◽  
Dual Fuel ◽  
Nox Emissions ◽  
Nox Formation ◽  
Jet Flame ◽  
Gas Drilling ◽  
Fuel Ratio ◽  
Wide Range

Natural gas/diesel dual fuel engines used in oil and gas drilling operations must be able to meet NOx emissions limits across a wide range of substitution percentage, which affects the air to natural gas ratio or gas lambda. In a dual fuel engine operating at high substitution, premixed, propagating natural gas flames occur and the NOx formed in such premixed flames is known to be a strong function of gas lambda. Consequently there is interest in understanding how NOx formation in a dual fuel engine is affected by gas lambda. However, NOx formation in a dual fuel engine is complicated by the interaction with the non-premixed diesel jet flame. As a result, previous studies have shown that enriching the air-fuel ratio can either increase or decrease NOx emissions depending on the operating conditions investigated. This study presents multi-dimensional combustion simulations of an air-fuel ratio sweep from gas lambda 2.0 to 1.5 at 80% substitution, which exhibited a minimum in NOx emissions at a natural gas lambda of 1.75. Images from the simulations are used to provide detailed explanations of the physical processes responsible for the minimum NOx trend with natural gas lambda.

scholarly journals Effect of Steam Addition on the Flow Field and NOx Emissions for Jet-A in an Aircraft Combustor

2016 ◽  
Vol 33 (4) ◽  
Author(s):  
Rui Xue ◽  
Chunbo Hu ◽  
Theoklis Nikolaidis ◽  
Pericle Pilidis
Keyword(s):  
Nox Reduction ◽  
Chemical Reactor ◽  
Steam Injection ◽  
Nox Emissions ◽  
Nox Formation ◽  
Steam Content ◽  
Injection Technology ◽  
Integrated Performance ◽  
Processing Techniques ◽  
The Impact

AbstractThe steam injection technology for aircraft engines is gaining rising importance because of the strong limitations imposed by the legislation for NOx reduction in airports. In order to investigate the impact of steam addition on combustion and NOx emissions, an integrated performance-CFD-chemical reactor network (CRN) methodology was developed. The CFD results showed steam addition reduced the high temperature size and the radical pool moved downstream. Then different post-processing techniques are employed and CRN is generated to predict NOx emissions. This network consists of 14 chemical reactor elements and the results were in close agreement with the ICAO databank. The established CRN model was then used for steam addition study and the results showed under air/steam mixture atmosphere, high steam content could push the NOx formation region to the post-flame zone and a large amount of the NOx emission could be reduced when the steam mass fraction is quite high.

CFD Analysis of NOx Formation in Waste-to-Energy Systems Using Detailed Chemical Kinetic Modeling

2012 ◽  
Author(s):  
Alex Frank ◽  
Marco J. Castaldi
Keyword(s):  
Three Dimensional ◽  
Chemical Kinetic ◽  
Waste To Energy ◽  
Combustion Model ◽  
Nox Emissions ◽  
Nox Formation ◽  
Chemical Kinetic Model ◽  
Small Impact ◽  
Detailed Chemical ◽  
No Emissions

This study was undertaken to better understand the governing processes and reaction conditions under which NOx is produced in Waste to Energy (WtE) boilers. A three dimensional CFD model was created and calculated using the GRI 3.0, 50 species, 309 step detailed chemical kinetic model (DCKM) for methane/ethane combustion. Model results for primary NOx emissions and other pollutants agree well with collected data, proving the fidelity of the model. NO was the primary pollutant accounting for approximately 99% of the total NOx emissions. Fuel bound nitrogen was found to be the main source of NO produced in the boiler with thermal and prompt mechanisms having lesser impacts. Three principal intermediates were identified in the formation of NO; NH, HNO, and NCO. The assumption of fuel nitrogen conversion to either NH3 or HCN is an unknown parameter that was shown to have a small impact on NO emissions, indicating that this is an area that should not be explored further in this continuing study. Furthermore, varying the boiler pressure had a small impact on final NO emissions, indicating that this is not a condition that should be considered for plant operation. The next phase of this research will include the development of a reduced DCKM in order to expedite the running of new scenarios for future studies as well as optimization of boiler geometry and combustion mixing to achieve the lowest possible NOx emissions.

Numerical Simulation of Flow Characteristics in an Inclining Rotating Kiln with Continuous Feeding

2019 ◽  
Vol 17 (10) ◽  
Author(s):  
Xin Zheng ◽  
Baosheng Jin ◽  
Yong Zhang ◽  
Youwei Zhang ◽  
Chunlei Zhou
Keyword(s):  
Velocity Distribution ◽  
Influencing Factor ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Multiphase Model ◽  
Rotating Speed ◽  
Inclination Angles ◽  
Continuous Feeding ◽  
Rotary Kilns ◽  
The Impact

Abstract The granular behaviors in rotating kilns have been investigated using a three-dimensional CFD model based on Euler-Euler multiphase model and the kinetic theory of granular flow. The model is validated by comparing with published experiment data and existing theory. The continuous feeding progress and inclination angles are both taken into account in this work for thorough discussion. Typical regimes of solid motions and velocity distributions are shown in the simulation results. The results show that the impact caused by feeding process has an obvious influence on the velocity distribution of z axis, especially at the charging end of the kiln. A small inclination angle has a slight influence on the velocity distribution of z axis, and causes the thickness of the active region increasing with the increasing of axil distance. The rotating speed is the biggest influencing factor for the velocity distribution in the transverse plane. The result can help the development of three-dimensional models for rotary kilns and the improvement of kiln design and performance.

A Diffusion Limited Model That Accurately Predicts the NOx Emissions From Gas Turbine Combustors Including the Use of Nitrogen Containing Fuels

1976 ◽  
Vol 98 (3) ◽  
pp. 320-326 ◽  
Author(s):  
W. S. Y. Hung
Keyword(s):  
Gas Turbine ◽  
Water Injection ◽  
Combustion Process ◽  
Nox Emissions ◽  
Nox Formation ◽  
Gas Turbine Combustors ◽  
Injection Process ◽  
Hydrocarbon Combustion ◽  
Diffusion Limited ◽  
Thermal Nox

A diffusion limited model has been described previously to simulate accurately the thermal NOx emission processes in various gas turbine combustors for fuels containing negligible amounts of fuel bound nitrogen. The application of this model to simulate accurately the water injection process has also been demonstrated. It is currently proposed that any bound nitrogen in fuel is completely reacted to form nitric oxide during the hydrocarbon combustion process; the ultimate net conversion is determined subsequently based on the Zeldovich mechanisms. With this additional assumption, this model has been generalized to include the use of fuels containing significant amounts of bound nitrogen, such as crude or residual oils. The predicted NOx emissions from these nitrogen containing fuels are in excellent agreement with laboratory and field data including the effect of water injection. Comprehensive understanding of the NOx formation processes has been gained from the current analytical study.

Analyzing the Impact of X-Ray Tomography on the Reliability of Integrated Circuits

2015 ◽  
Author(s):  
Halit Dogan ◽  
Md Mahbub Alam ◽  
Navid Asadizanjani ◽  
Sina Shahbazmohamadi ◽  
Domenic Forte ◽  
...  
Keyword(s):  
Integrated Circuits ◽  
Integrated Circuit ◽  
3D Imaging ◽  
Three Dimensional ◽  
Serial Sectioning ◽  
Promising Technique ◽  
Flash Memories ◽  
X Ray ◽  
3D Information ◽  
The Impact

Abstract X-ray tomography is a promising technique that can provide micron level, internal structure, and three dimensional (3D) information of an integrated circuit (IC) component without the need for serial sectioning or decapsulation. This is especially useful for counterfeit IC detection as demonstrated by recent work. Although the components remain physically intact during tomography, the effect of radiation on the electrical functionality is not yet fully investigated. In this paper we analyze the impact of X-ray tomography on the reliability of ICs with different fabrication technologies. We perform a 3D imaging using an advanced X-ray machine on Intel flash memories, Macronix flash memories, Xilinx Spartan 3 and Spartan 6 FPGAs. Electrical functionalities are then tested in a systematic procedure after each round of tomography to estimate the impact of X-ray on Flash erase time, read margin, and program operation, and the frequencies of ring oscillators in the FPGAs. A major finding is that erase times for flash memories of older technology are significantly degraded when exposed to tomography, eventually resulting in failure. However, the flash and Xilinx FPGAs of newer technologies seem less sensitive to tomography, as only minor degradations are observed. Further, we did not identify permanent failures for any chips in the time needed to perform tomography for counterfeit detection (approximately 2 hours).

scholarly journals Numerical simulation of the impact of an integrated renovation project on the Maowei Sea hydrodynamic environment

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Cui Wang ◽  
Ling Cai ◽  
Yaojian Wu ◽  
Yurong Ouyang
Keyword(s):  
Water Exchange ◽  
Land Reclamation ◽  
Three Dimensional ◽  
Exchange Capacity ◽  
Reclamation Project ◽  
Hydrodynamic Environment ◽  
Sea Area ◽  
Water Quality Models ◽  
The Impact ◽  
Main Factor

AbstractIntegrated renovation projects are important for marine ecological environment protection. Three-dimensional hydrodynamics and water quality models are developed for the Maowei Sea to assess the hydrodynamic environment base on the MIKE3 software with high resolution meshes. The results showed that the flow velocity changed minimally after the project, decreasing by approximately 0.12 m/s in the east of the Maowei Sea area and increasing by approximately 0.01 m/s in the northeast of the Shajing Port. The decrease in tidal prism (~ 2.66 × 106 m3) was attributed to land reclamation, and accounted for just 0.86% of the pre-project level. The water exchange half-life increased by approximately 1 day, implying a slightly reduced water exchange capacity. Siltation occurred mainly in the reclamation and dredging areas, amounting to back-silting of approximately 2 cm/year. Reclamation project is the main factor causing the decrease of tidal volume and weakening the hydrodynamics in Maowei Sea. Adaptive management is necessary for such a comprehensive regulation project. According to the result, we suggest that reclamation works should strictly prohibit and dredging schemes should optimize in the subsequent regulation works.

scholarly journals Mechanical Behavior of Hydroxyapatite-Chitosan Composite: Effect of Processing Parameters

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 213
Author(s):  
Hamid Ait Said ◽  
Hassan Noukrati ◽  
Hicham Ben Youcef ◽  
Ayoub Bayoussef ◽  
Hassane Oudadesse ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Compressive Strength ◽  
Mechanical Strength ◽  
Bone Repair ◽  
Mechanical Stability ◽  
Three Dimensional ◽  
Processing Parameters ◽  
Composite Effect ◽  
Solid Liquid ◽  
The Impact

Three-dimensional hydroxyapatite-chitosan (HA-CS) composites were formulated via solid-liquid technic and freeze-drying. The prepared composites had an apatitic nature, which was demonstrated by X-ray diffraction and Infrared spectroscopy analyses. The impact of the solid/liquid (S/L) ratio and the content and the molecular weight of the polymer on the composite mechanical strength was investigated. An increase in the S/L ratio from 0.5 to 1 resulted in an increase in the compressive strength for HA-CSL (CS low molecular weight: CSL) from 0.08 ± 0.02 to 1.95 ± 0.39 MPa and from 0.3 ± 0.06 to 2.40 ± 0.51 MPa for the HA-CSM (CS medium molecular weight: CSM). Moreover, the increase in the amount (1 to 5 wt%) and the molecular weight of the polymer increased the mechanical strength of the composite. The highest compressive strength value (up to 2.40 ± 0.51 MPa) was obtained for HA-CSM (5 wt% of CS) formulated at an S/L of 1. The dissolution tests of the HA-CS composites confirmed their cohesion and mechanical stability in an aqueous solution. Both polymer and apatite are assumed to work together, giving the synergism needed to make effective cylindrical composites, and could serve as a promising candidate for bone repair in the orthopedic field.

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