Modeliranje turbulentnog dvofaznog toka aero-smeše sprašenog uglja u gorioničkim kanalima sa jednostepenim turbulatorima

The subject of this work is turbulent two-phase flow through air-coal channel(s) of complex geometry. The aim of this work is numerical optimization of fluid flow and coal particle distribution in reconstructed air-coal mixture channels. The single blade turbulator has been used to increase turbulence in the vertical section of an air-coal mixture channel. Standard k-ω turbulent model has been used for modeling turbulence. Lagrangian multiphase model has been used for discrete phase (coal particles) modeling. Although better particle distribution is reached using single blade turbulators, particle concentration in the evaluation section (where plasma generators will be built in) still remains anisotropic. Because uniform coal particle distribution is of great importance for the proper work of plasma generators, other solutions for achieving this goal will be the object of the future analysis.Predmet ovog rada je turbulentno dvofazno strujanje kroz gorioničke kanale aero-smeše sprašenog uglja kompleksne geometrije. Cilj ovog rada je numerička optimizacija strujnog toka i raspodele čestica sprašenog uglja u rekonstruisanim gorioničkim kanalima. Za povećanje turbulencije, u vertikalnom delu gorioničkog kanala aero smeše ugrađen je jednostepeni turbulator. Za modeliranje turbulencije korišćen je standardni k-ω turbulentni model. Lagranžeov pristup je korišćen za modeliranje sekundarne faze (čestica sprašenog uglja). Iako je upotrebom jednostepenih turbulatora postignuta bolja raspodela čestica sprašenog uglja, koncentracija čestica u prelaznom delu (u kome će biti ugrađeni plazma generatori) ostaje neravnomerna. Kako je ravnomerna raspodela čestica sprašenog uglja od esencijalnog značaja za pravilan rad plazma generatora, druga rešenja za postizanje ravnomerne raspodele čestica će biti predmet buduće analize

Turbulent Two-Phase Flow Modeling of Air-Coal Mixture Channels with Single Blade Turbulators

Abstract. Subject of this work is turbulent two-phase flow through air-coal channel(s) of complex geometry. Air flow through all eight air-coal mixture channels was simulated in first stage. Velocity and pressure field were obtained as results of this simulation. One channel was selected, based on obtained results from first case. Two-phase flow was simulated in this channel. Lagrangian multiphase model was used for discrete phase (coal particles) modeling. Two-phase flow in air-coal mixture channel without turbulator was simulated next. After that, two-phase flow in air-coal mixture channels with two different turbulator heights was simulated. Turbulators were set parallel to velocity vectors at inlet. Finally turbulators were rotated for 12 deg. around x-axis in positive mathematical direction, and simulation was repeated for both turbulator heights. The aim of this work is numerical optimization of fluid flow and coal particle distribution in reconstructed air-coal mixture channels. Single blade turbulator was used to increase turbulence in vertical section of air-coal mixture channel. Standard k-ω turbulent model was used for modeling turbulence. Lagrangian multiphase model was used for modeling coal particle distribution. More uniform coal particle distribution has been achieved using single blade turbulators. Results show that there is no significant difference in coal particle distribution between all four cases in which different turbulator geometry and position was used. Upon these conclusions, technologically simplest solution, turbulator with low height, can be suggested. Although better particle distribution is reached using single blade turbulators, particle concentration in evaluation section (where plasma generators will be built in) still remained anisotropic. Because uniform coal particle distribution is of great importance for proper work of plasma generators, other solutions for achieving this goal will be object of future analysis

Sensitivity analysis of different devolatilisation models on predicting ignition point position during pulverized coal combustion in O-2/N-2 and O-2/CO2 atmospheres

Oxy-fuel combustion is considered as a promising solution to reduce greenhouse-gases and pollutant emissions. The main advantage of oxy-fuel combustion over other technologies for pollution reduction from pulverized coal combustion is that it can be applied to the existing coal-fired power plants. However, switching from conventional to oxy-fired coal combustion brings significant challenges. One of the most important is change of pulverized coal ignition characteristics. This paper presents the results of experimental and numerical analysis of ignition phenomena under oxy-fuel conditions. The main focus of the presented paper is to evaluate the effectiveness of the mathematical devolatilisation sub-model, in predicting the ignition point of pulverized coal flames under oxy-firing conditions. Regarding this, the performance of several devolatilisation models, from simple to more complex ones, in predicting ignition point position have been investigated. Numerically determined values of the ignition point position, and ignition temperature for various O-2-N-2 and O-2-CO2 conditions were compared with experimental data from the laboratory ignition test facility. Obtained results pointed out that network devolatilisation models (CPD and FG) give more accurate results in comparison with standard devolatilisation models (single rate and two competing rates). The best performance is achieved using FG devolatilisation model. Thus, newly implemented FG model will be used for future numerical simulations of oxy-fuel pulverized coal combustion on 0.5 MW pilot plant facility. (C) 2011 Elsevier Ltd. All rights reserved.8th European conference on coal research and its applications, Sep 06-10, 2010, Leeds, Englan

Experimental and numerical investigation of flame characteristics during swirl burner operation under conventional and oxy-fuel conditions

Oxy-fuel coal combustion, together with carbon capture and storage or utilization, is a set of technologies allowing to burn coal without emitting globe warming CO2. As it is expected that oxy-fuel combustion may be used for a retrofit of existing boilers, development of a novel oxy-burners is very important step. It is expected that these burners will be able to sustain stable flame in oxy-fuel conditions, but also, for start-up and emergency reasons, in conventional, air conditions. The most cost effective way of achieving dual-mode boilers is to introduce dual-mode burners. Numerical simulations allow investigation of new designs and technologies at a relatively low cost, but for the results to be trustworthy they need to be validated This paper proposes a workflow for design, modeling, and validation of dual-mode burners by combining experimental investigation and numerical simulations. Experiments are performed with semi-industrial scale burners in 0.5 MW, test facility for flame investigation. Novel CFD model based on ANSYS FLUENT solver, with special consideration of coal combustion process, especially regarding devolatilization, ignition, gaseous and surface reactions, NOx formation, and radiation was suggested The main model feature is its ability to simulate pulverized coal combustion under different combusting atmospheres, and thus is suitable for both air and oxy-fuel combustion simulations. Using the proposed methodology two designs of pulverized coal burners have been investigated both experimentally and numerically giving consistent results. The improved burner design proved to be a more flexible device, achieving stable ignition and combustion during both combustion regimes: conventional in air and oxy-fuel in a mixture of O-2 and CO2 (representing dry recycledflue gas with high CO2 content). The proposed framework is expected to be of use for further improvement of multi-mode pulverized fuel swirl burners but can be also used for independent designs evaluation

Numerical investigation of pulverized coal jet flame characteristics under different oxy-fuel conditions

Pulverized coal combustion in mixture of oxygen and recycled flue gasses, known as oxy-fuel combustion, is considered as one of the several possible alternatives to conventional pulverized coal combustion. Switching from conventional pulverized-coal combustion to oxy-fuel combustion brings significant changes in flame properties among which the most important are ignition properties and flame stability. This paper presents the results of experimental and numerical analysis of ignition phenomena under O-2/CO2 mixtures with different oxygen content. The main focus of the presented paper is to suggest novel ignition sub-model which can describe all possible ignition mechanisms. Proposed ignition sub-model together with Large Eddy Simulation (LES) turbulence modeling enables accurate prediction of main flame characteristics: ignition point position, ignition temperature, and flame stability. (C) 2012 Elsevier Ltd. All rights reserved

Mathematical modelling of swirl oxy-fuel burner flame characteristics

Oxy-fuel combustion is the most promising carbon capture and storage technology, which eliminates carbon dioxide emissions into the atmosphere and also decreases nitrogen oxides emissions thereby lowering global warming potential. In order to implement oxy-fuel combustion technology in full scale power plants, its costs, mainly connected with the amount of pure oxygen produced, must be lowered. The main hypothesis is that it is possible to maintain similar velocity and heat transfer distribution while maintaining stable and efficient burner operation during both combustion technologies modifying burner aerodynamics. Excess oxygen is chosen as a representative parameter of burner's performance and investigation is carried out for four different oxy-fuel burner oxygen excess ratios (λ: 0.8, 0.98, 1.07, and 1.24) together with reference air combustion case. This study suggests a workflow, based on semi-industrial experimental investigations and computational fluid dynamics model composed of advanced sub-models for different combustion phases for development of real scale dual-mode coal swirl burners able for efficient operation during both combustion regimes. The results show that the temperature in near-burner zone and nitrogen oxides emissions increase, while carbon monoxide emissions decrease with the increase of burner oxygen excess ratio, and stable combustion with similar velocity and temperature distributions for both combustion modes is achieved for oxygen excess ratio of 1.07, with decrease in nitrogen oxides and carbon monoxide emissions during oxy-fuel combustion. The performed study demonstrates that it is possible to choose the appropriate burner settings regarding nitrogen oxides and carbon monoxide emissions and burner's ability to operate stably in both air and oxy-fuel combustion modes. © 2019 Elsevier Lt

Le Grand écho du Nord de la France

10 avril 19021902/04/10 (A84,N100).Appartient à l’ensemble documentaire : NordPdeC

Health-status outcomes with invasive or conservative care in coronary disease

BACKGROUND In the ISCHEMIA trial, an invasive strategy with angiographic assessment and revascularization did not reduce clinical events among patients with stable ischemic heart disease and moderate or severe ischemia. A secondary objective of the trial was to assess angina-related health status among these patients. METHODS We assessed angina-related symptoms, function, and quality of life with the Seattle Angina Questionnaire (SAQ) at randomization, at months 1.5, 3, and 6, and every 6 months thereafter in participants who had been randomly assigned to an invasive treatment strategy (2295 participants) or a conservative strategy (2322). Mixed-effects cumulative probability models within a Bayesian framework were used to estimate differences between the treatment groups. The primary outcome of this health-status analysis was the SAQ summary score (scores range from 0 to 100, with higher scores indicating better health status). All analyses were performed in the overall population and according to baseline angina frequency. RESULTS At baseline, 35% of patients reported having no angina in the previous month. SAQ summary scores increased in both treatment groups, with increases at 3, 12, and 36 months that were 4.1 points (95% credible interval, 3.2 to 5.0), 4.2 points (95% credible interval, 3.3 to 5.1), and 2.9 points (95% credible interval, 2.2 to 3.7) higher with the invasive strategy than with the conservative strategy. Differences were larger among participants who had more frequent angina at baseline (8.5 vs. 0.1 points at 3 months and 5.3 vs. 1.2 points at 36 months among participants with daily or weekly angina as compared with no angina). CONCLUSIONS In the overall trial population with moderate or severe ischemia, which included 35% of participants without angina at baseline, patients randomly assigned to the invasive strategy had greater improvement in angina-related health status than those assigned to the conservative strategy. The modest mean differences favoring the invasive strategy in the overall group reflected minimal differences among asymptomatic patients and larger differences among patients who had had angina at baseline

Initial invasive or conservative strategy for stable coronary disease

BACKGROUND Among patients with stable coronary disease and moderate or severe ischemia, whether clinical outcomes are better in those who receive an invasive intervention plus medical therapy than in those who receive medical therapy alone is uncertain. METHODS We randomly assigned 5179 patients with moderate or severe ischemia to an initial invasive strategy (angiography and revascularization when feasible) and medical therapy or to an initial conservative strategy of medical therapy alone and angiography if medical therapy failed. The primary outcome was a composite of death from cardiovascular causes, myocardial infarction, or hospitalization for unstable angina, heart failure, or resuscitated cardiac arrest. A key secondary outcome was death from cardiovascular causes or myocardial infarction. RESULTS Over a median of 3.2 years, 318 primary outcome events occurred in the invasive-strategy group and 352 occurred in the conservative-strategy group. At 6 months, the cumulative event rate was 5.3% in the invasive-strategy group and 3.4% in the conservative-strategy group (difference, 1.9 percentage points; 95% confidence interval [CI], 0.8 to 3.0); at 5 years, the cumulative event rate was 16.4% and 18.2%, respectively (difference, 121.8 percentage points; 95% CI, 124.7 to 1.0). Results were similar with respect to the key secondary outcome. The incidence of the primary outcome was sensitive to the definition of myocardial infarction; a secondary analysis yielded more procedural myocardial infarctions of uncertain clinical importance. There were 145 deaths in the invasive-strategy group and 144 deaths in the conservative-strategy group (hazard ratio, 1.05; 95% CI, 0.83 to 1.32). CONCLUSIONS Among patients with stable coronary disease and moderate or severe ischemia, we did not find evidence that an initial invasive strategy, as compared with an initial conservative strategy, reduced the risk of ischemic cardiovascular events or death from any cause over a median of 3.2 years. The trial findings were sensitive to the definition of myocardial infarction that was used