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Injecting hydrogen into the natural gas network to reduce CO2 emissions in the EU residential sector is considered a critical element of the zero CO2 emissions target for 2050. Burning natural gas and hydrogen mixtures has potential risks, the main one being the flame flashback phenomenon that could occur in home appliances using premixed laminar burners. In the present study, two-dimensional transient computations of laminar CH4- + air and CH4 + H-2 + air flames are performed with the open-source CFD code OpenFOAM. A finite rate chemistry based solver is used to compute reaction rates and the laminar reacting flow. Starting from a flame stabilized at the rim of a cylindrical tube burner, the inlet bulk velocity of the premixture is gradually reduced to observe flashback. The results of the present work concern the effects of wall temperature and hydrogen addition on the flashback propensity of laminar premixed methane-hydrogen-air flames. Complete sequences of flame dynamics with gradual increases of premixture velocity are investigated. At the flame flashback velocities, strong oscillations at the flame leading edge emerge, causing broken flame symmetry and finally flame flashback. The numerical results reveal that flashback tendency increase with increasing wall temperature and hydrogen addition rate. (C) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Hidrojen teknolojileri araştırmaları; hidrojenin petrol rafinerilerinde, çelik üretimi ve kimyasal üretim gibi sanayi üretiminde ve çeşitli kaynaklarla yakıt elde edilmesinde kullanılması, güç kaynağı olarak sistemi güçlendirmesi, suyun elektrolizi yoluyla elde edilmesi, enerji taşıyıcısı olarak sisteme dahil olması, depolama, taşıma ve ulaşım, havacılık ve uzay, evsel kullanım, risk ve güvenlik sorunları konularının etkileştiği bir araştırma alanıdır. Toplumsal gerçekliğe ve doğanın kendisine içkin olan bu karmaşık yapı, hidrojen teknolojileri araştırmalarının disiplinlerarası bir yaklaşımla ele alınmasını gerekli kılmaktadır. Bu nedenle çalışmanın amacı, hidrojen araştırmalarının disiplinlerarası bu yapısında toplumsal bilimler alanlarının rolünü ve katkısını belirlemektir. Bu amaçla ilgili kavramlar yardımıyla hidrojen teknolojileri araştırmaları alanında 1975-2021 yılları arasında Web of Science (WoS) Sosyal Bilimler Atıf Endeksinde dizinlenmiş 379 makale analiz edilmiştir. Çalışmanın sonuçlarına göre son 10 yılda hidrojen teknolojileri araştırmaları alanında yayın sayısı ve atıf sayısı hızla artmaktadır. Yayınların yarısından fazlasının birden fazla yazarlı olması, bu alanda yazarlar arasındaki etkileşim ve işbirliğinin yoğun olduğunu göstermektedir. Hidrojen teknolojileri alanındaki bu araştırmalar, “Teknik ve Sistemsel Bağlam”, “Enerji taşıyıcı olarak Hidrojen”, “Politik Arkaplan”, “Ulaşım ve Davranışsal Faktörler” ve “Altyapı ve Tasarım” olarak isimlendirilen beş tematik kümede toplanmıştır ve bu kümelerin birleşimini bütüncül bir toplumsal-teknik sistem olarak ele almak mümkündür. Anahtar kelime analizi, zaman geçtikçe alandaki araştırmaların toplumsal boyutlarının ve etkilerinin daha detaylı incelendiğini göstermektedir. Tematik konu haritası ise, hidrojen teknolojileri sisteminin bir bütün olarak tüm boyutlarıyla ele alındığı göstermektedir., Hydrogen technologies research is an area where various research areas interact with each other such as the use of hydrogen in oil refineries, industrial production such as steel production and chemical production and obtaining fuel from various sources, strengthening the system as a power source, obtaining water through electrolysis, inclusion in the system as an energy carrier, storage, transportation, aviation and space, risk and security issues. This complex structure, which is immanent to social reality and nature itself, requires hydrogen technologies research to be handled with an interdisciplinary approach. Therefore, the study aims to determine the role and contribution of social science fields in this interdisciplinary structure of hydrogen technologies research. For this purpose, 379 articles indexed in the Web of Science (WoS) Social Sciences Citation Index between 1975-2021 in the field of hydrogen technologies research were analyzed with the help of related keywords. According to findings, the number of publications and citations in the field of hydrogen technologies research has been increasing rapidly in the last 10 years. The fact that more than half of the publications have more than one author shows that the interaction and cooperation between the co-authors in this field are intense. Studies in the field of hydrogen technologies are gathered in five thematic clusters named as “Technical and Systemic Context”, “Hydrogen as an Energy carrier”, “Political Background”, “Transportation and Behavioral Factors” and “Infrastructure and Design”, combining these clusters into a holistic socio-technical system. Keyword analysis shows that as time passes, the social dimensions and effects of research in the field are examined in more detail. The thematic topic map, on the other hand, shows that the hydrogen technologies system as a whole is handled with all its dimensions.

International audience; Canada has the third-largest oil sand reserves in the world as a result of which, it generates considerable amounts of light gas oil and heavy gas oil through petroleum distillation. With the escalating energy demands, it has become essential to explore alternative fuel resources from biomass and petrochemical residues. This study explores the potential of supercritical water gasification to transform light and heavy gas oils to hydrogen-rich syngas through the optimization of process conditions such as temperature (375e675 C), feed concentration (20e35 wt%) and reaction time (30e75 min). Nickel-supported functionalized carbon nanotubes (10%Ni/FCNT) were synthesized for application in catalytic supercriticalwater gasification. The functionalization of carbon nanotubes resulted in an increase in their surface area from 108 m2/g (in pristine CNT) to 127 m2/g (in FCNT) and 122 m2/g (in 10%Ni/FCNT). The impregnation of catalytic nickel particles onto carbon nanotubes was confirmed through X-ray diffraction (XDR) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). Fouriertransform infrared (FTIR) spectroscopy of both gas oils revealed the presence of aliphatics, alkyl-aryl ethers and sulfur-containing compounds among several other aromatics. Light gas oil revealed higher hydrogen yields of 3.32 mol/kg compared to that of heavy gas oil (2.79 mol/kg) at optimal process conditions, i.e. 675 C and 75 min, 20 wt% feed concentration. However, 10%Ni/FCNT enhanced hydrogen yields (4.46 mol/kg), total gas yield (9.22 mol/kg), hydrogen selectivity (94%) and lower heating value (1685 MJ/kg) of product gases obtained from light gas oil in contrast to heavy gas oil. This study indicates a tremendous potential of gas oils for hydrogen generation via hydrothermal gasification.

International audience; Pyrolysis, combustion and gasification of solid residues from olive oil processing were investigated. The raw solid residue (RS) contains moisture (21.5%) and residual oil (6.4%). Therefore, from RS, raw samples without water (RSWW) and without oil (RSWO) were produced. Thermal analyses of samples were performed at different heating rates over a temperature range of 150–1050 °C. Pyrolysis behavior of the sample was studied in an argon atmosphere, whereas the combustion and gasification studies were conducted in oxygen and steam atmospheres, respectively. The effects of heating rate on the reaction rate and gas evolution were analyzed. Thermal degradation of RS showed that nearly 90% of the conversion occurred at below 700 °C. Gases produced in the three processes mainly consisted of hydrogen, hydrocarbons and carbon oxides. Alcohols and sulfur compounds were also detected in the temperature range of 300 to 500 °C for pyrolysis. Activation energies were determined from non-isothermal multi-heating rate thermogravimetric measurements. The variation in gas evolution was observed between the samples during gasification

International audience; Among all phenomena occurring in combustion chambers, one basic process is the interaction of a single droplet with a flamelet. Therefore, it is essential to understand the physics of individual droplet evaporation and its effects on the flame front to deal with more complex flames.The aim of this study is to investigate the ethanol droplet evaporation interacting with a premixed laminar CH4/air flame. In the experimental part of the study, the droplet was injected into the flame and visualization of the flame front and temporal monitoring of the droplet evaporation were performed using planar laser tomography (PIV, PTV, ILIDS). In the numerical part of the study, single droplet evaporation under constant temperature and stagnant environment was studied via Eulerian-Lagrangian approach with YALES2 solver. The variations of the droplet and gas properties were computed under N2 atmosphere and flame conditions. From the vaporization rate calculations, it is observed that there is a slight effect of the flame stretch on the evaporation due to the change in temperature profiles. It is also observed that the flame temperature has a leading effect on the evaporation rate rather than the burnt gas composition due to the changes in thermo-physical properties.

Hydrothermal carbonization (HTC) of Agave Salmiana bagasse was investigated to assess the potential of hydrochar as an energy resource. The effect of operating conditions on the mass yield and the energy quality of hydrochar was examined by varying the temperature and the holding time over the ranges of 180–250 ℃ (T) and 0–60 min (t), respectively. These parameters were screened using the response surface methodology through a Doehlert design. Performances of HTC were assessed on the basis of the hydrochar mass yield higher heating value ultimate and proximate analyses. In the studied domain, the modeling results indicated that the hydrochar mass yield varies between 45% and 86% and higher heating valuesfrom18 to 23 MJ.kg-1, which is similar to that of peat. In addition, the volatile matter and fixed carbon fractions of hydrochars ranged from 54 to 80% and between 12 and 36%, respectively. Energy yield modeling indicated that the mass yield is the most influent parameter. The maximal energy yield value was obtained at 180 ℃ with time equal to 0 min. Globally, the evolution of H/C ratio is amplified for temperatures greater than 215 ℃ by increasing the holding time from 30 to 60 min. For O/C ratio the maximal variation is below these conditions. It is concluded that increased hydrothermal carbonization conditions favor dehydration reactions, while decarboxylation reactions are favored in mild HTC conditions. The combustion characteristics such as ignition peak and burnout temperatures were significantly modified for hydrochars. The model results indicated that lowest ignition and peak temperature values are obtained at both low-temperature and low-holding time, and high-temperature and high-holding time zones. An increase in the burnout temperature was correlated with the increase of the fixed carbon content in hydrochars.

Computational Fluid Dynamics simulation was used to study hydrothermal carbonization of avocado stone (AS) in a batch stirred reactor, using an open-loop controller system. The corresponding simulations were carried out in COMSOL Multiphysics 5.2. The different biomass-to-water ratio was investigated. The hydrodynamic study shows that the ideal stirring speed to obtain a homogeneous mixture inside the reactor is 550 rpm, due to the high density of AS particles (1547.64 ± 27.33 kg/m3). However, a stagnant zone was observed just below the impeller. To validate the CFD simulations temperature profiles with experimental data, the heat transfer coefficient of the insulator was determined (11.66 W/m2.K), this value was used to set the heat loss in the CFD simulation. According to the model, the difference between the thermal properties of biomass and water under hydrothermal carbonization conditions is negligible. However, experimentally, an increase in temperature was observed with increasing biomass to-water-ratio; this is due to the global hydrothermal carbonization of AS is exothermic reaction. The heat released during 8 h, including heat-up time, was −7.25 ± 0.32 MJ/kg of feedstock. Finally, a kinetic model was proposed taking into account the influence of temperature, heat-up time, reactor volume, and biomass concentration.

International audience; The purpose of this study is to develop an experimental data-based char particle gasification model in order to assess the effects of particle size, gasification temperature and char generation heating rate on global gasification parameters. Also, the effect of initial porosity is observed by performing parametrical numerical simulations. A continuum-based model is used to solve the gasification inside a char particle and within the external boundary layer. The intrinsic rate of CO2 gasification reaction is computed according to Langmuir-Hinshelwood (LH) mechanism. External mass transfer is modeled by Stefan-Maxwell relations, and Cylindrical Pore Interpolation Model (CPIM) is used for intra-particle molecular diffusion. In the model, all the effects due to particle internal structure changes are represented by a global conversion function, f(X) which is computed from local reaction rate values. In this study, f(X) is deduced from experimental results instead of phenomenological models almost impossible to validate. The best reproduction of the experimental gasification results is obtained for the function f(X) postulated as a summation of two Gaussian functions which represent the char particle random pore structures and their dynamics during gasification. Comparative simulation results show that the Gaussian for low conversion interval is shifted to even lower conversion values for higher gasification temperature and higher initial porosity. Thereby, the Gaussian function for low conversion rates (large particle sizes) is interpreted as representative of the diffusion-limited gasification regime in conjunction with the network of macropores and molecular diffusion rates. The modification of the pore structure due to char generation heating rates causes a shift of the second Gaussian towards higher conversion rates. It is therefore postulated that the second Gaussian function corresponds to the boundary layer diffusion-controlled regime related to available outer surface area of the particle.

International audience; Model-free and model-fitting kinetic approaches were used to investigate the hydrothermal carbonization (HTC) of avocado stone. The total solid mass yield was used to estimate the kinetic parameters and reaction mechanism. The results obtained show that the HTC process for avocado stones could be divided into four temperature zones. Up to 160 °C, the initial induction period where the reaction rate is relatively slow. The second zone (160 to 200 °C) corresponds to the maximum decomposition rate. The third zone between 200 and 220 °C corresponds to the stabilization zone; in this zone, the total solids yield is practically constant, and finally, the polymerization zone, between 220 and 250 °C, where an increase in total solid yield was observed. The kinetic parameters and reaction mechanism were determined in two temperature zones, from 150 to 210 °C and 210 to 250 °C. In the first zone, the decomposition of avocado stone during the HTC process followed a random nucleation reaction mechanism (Avrami-Erofeev-1) with the activation energy of 87.84 ± 3.28 kJ/mol. In contrast, in the second zone, it followed a first-order reaction model, and the activation energy was 230.96 ± 28.84 kJ/mol. Analysis of PAHs with gas chromatography-mass spectrometry showed that the number of PAHs in the hydrochar increases with an increase in temperature from 190 to 250 °C. The 3–4 rings PAHs were dominant in the hydrochars prepared at temperatures between 230 and 250 °C, while two rings were largely prevalent in the hydrochar obtained at low temperatures.

International audience; The main aim of this study is to investigate the usability of the process water obtained from the hydrothermal carbonization (HTC) of two different types of biomass waste for microalgae production. In this context, the process waters released as a result of hydrothermal carbonization of olive and orange pomace were diluted in different proportions (50×, 100×, 200×, and 400×) and used in the cultivation of Chlorella minutissima and Botryococcus braunii microalgae. It was observed that the growth rates were higher and the doubling times were shorter at low dilution rates for both microalgae species. The highest growth rate and the shortest doubling time values were found as 0.130 g/L/day and 5.33 day, respectively, for Chlorella minutissima microalgae cultivated in the HTC process water of olive pomace. It was also observed that the process water dilution rate had no specific effect on microalgae biochemical characteristics. It can be concluded that the aqueous phases from HTC of orange and olive pomaces can be a good source of nutrients for different types of microalgae, opening a sustainable, cost effective and environmentally friendly approach for microalgae cultivation and, at the same time, for the cleaning of the otherwise biochemically toxic HTC process waters.

This article represents the parallel multigrid component analysis of Robust Multigrid Technique (RMT). The RMT has been developed for black-box solution of a large class of (non)linear boundary value problems in computational continuum mechanics. Parallel RMT can be constructed by combination of the algebraic and geometric approaches to parallelization. The geometric smoother-independent approach based on a decomposition of the given problem into \(3^\kappa _{}\) (\(\kappa =1,2,\ldots \)) subproblems without an overlap should be used to overcome the problems of large communication overhead and idling processors on coarser levels. The algebraic grid-independent approach based on a decomposition of the given problem into \(C 3^\kappa _{}\) (\(\kappa =1,2,\ldots \)) subproblems with an overlap (multicoloured Vanka-type smoother) should be used for parallel smoothing on finer levels. Standard programming model for shared memory parallel programming OpenMP has been used for parallel implementation of RMT on personal computer and computer cluster. This paper represents parallel multigrid cycle, algebraic and geometric approaches to parallelization, estimation of the parallel RMT efficiency and parallel multigrid component analysis.

International audience; Five coal samples from different origins are characterized for their pyrolysis and combustion features using coupled thermogravimetry - mass spectrometry (TG-MS). The samples are heated at temperatures ranging from 25 to 900 degrees C in air atmosphere under heating rates of 10, 20, and 30 degrees C/min. The characteristic temperatures (initial, peak, burn out), reaction intervals, mass loss rate, ash residues, ignition and combustion performances, an ignition-combustion index and the reactivities of the coal samples are calculated and the associated heating rate effects are estimated. The less reactive coal exhibits higher peak temperature in conversion and low value of ignition index and reactivity. The reactivity of the coal samples varied in between 2.31 and 7.84 x10(2) (1/min). The main volatile and combustion products (H-2, CH4, H2O, CO, CO2, C6H6, COS, SO2) release for the corresponding TG and temperatures are estimated using online 3D measurements of MS based on their relative intensities and relevancy. Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS) type model free kinetic methods are applied to determine the activation energies of the coals which are exhibited in-between 44.6 - 75.1 kJ/mol and 50.5-96.6 kJ/mol using OFW and KAS methods respectively. The estimated kinetic constants are compared and found consistent with combustion performance parameters.

This paper presents experimental results of the effects of CO2 and H2O dilution on CH4-air flames enriched by oxygen. The study focuses on pollutant emissions, flame stability through the determina...

This study evaluates and compares the responses of two kinds of lignocellulosic biomass (pine and acacia) and sewage sludge to their hydrothermal carbonization treatment. All materials were subjected to HTC processes in an aqueous environment at 200 °C for 4 h with a 1:8 biomass to water ratio, using a Zipperclave Stirred Reactor. The physical, chemical analyses and, additionally, fibre, mercury porosimetry analyses and optical microscope images applied to both raw materials and to hydrochars, proved that HTC enhances the energy related properties of lignocellulosic biomass. Whereas, for sewage sludge, the HTC effect is negligible, because most of the carbon is transferred to the HTC liquid phase, confirmed by high COD and high ash content in the sewage sludge hydrochar. Subsequently, the thermo-chemical conversion kinetics of the raw and HTC materials were examined in the TGA analyser through nonisothermal runs. Finally, kinetics analyses were performed by two methods based on the TGA results. The estimated apparent activation energy values obtained by the Coats & Redfern method were higher than those given by the Arrhenius method, which also gave almost similar values for all samples, shedding doubt on the accuracy of this method for the current experiments. The Coats & Redfern analysis gave activation energy values which were lower by one half for sewage sludge hydrochars compared to lignocellulosic hydrochars. This indicates the potential of the HTC process for generating sewage sludge hydrochars suitable for co-combustion or co-gasification with other biomass solid fuels.

This study focused on the analysis of the pyrolytic behavior of four lignocellulosic biomasses: avocado stone (AS), Agave salmiana bagasse (AB), cocoa shell (CS), and α-cellulose (CEL). According to the triplet kinetics analysis, the order of pyrolytic decomposition was AS AB CEL CS. The AS was dominated by a second-order reaction, while AB followed a 2D diffusion-Valensi model. On the other hand, the pyrolysis of CS starts with an nth-order reaction and ends random nucleation model, and CEL was dominated by one-dimensional diffusion and first-order reaction. Thermodynamic studies reveal that the difference between the activation energy versus enthalpy change was6.5 kJ/mol for all biomasses, thus showing the ease of pyrolysis reaction of these biomasses. Furthermore, the AS and AB showed that the reactions are close to thermodynamic equilibrium and stability, whereas CS and CEL indicated high reactivity.

Pinecone is a lignocellulosic forest residue with value-added industrial importance in terms of energy and materials production. Although promising, pinecone has received inadequate attention as a biofuel feedstock for thermochemical conversion. Water above its critical temperature (T C ≥ 374 °C) and critical pressure (P C ≥ 22.1 MPa), termed as supercritical water, has high kinetic energy and densities similar to that of gases and liquids, respectively. When employed in gasification, supercritical water has an ability to completely dissolve organics and gases. Therefore, this study identifies the candidacy of pinecone as a precursor for conversion to hydrogen through hydrothermal gasification. Pinecone was gasified in subcritical water (300 and 350 °C; 21 MPa), near-critical water (370 °C; 22 MPa) and supercritical water (450 and 550 °C; 23 MPa) to investigate the impacts of temperature (300–550 °C), feed concentration (10–25 wt%) and residence time (15–60 min). The impacts of alkali catalysts (e.g., Na 2 CO 3 , NaOH and KOH) at a loading of 30 wt% were examined to maximize hydrogen yields. The hydrochar generated from gasification in subcritical water, near-critical water and supercritical water were physico-chemically characterized through proximate and ultimate analysis (carbon-hydrogen-nitrogen-sulfur-oxygen), thermogravimetric analysis, X-ray diffraction, Fourier transform infra-red spectroscopy, Raman spectroscopy, Scanning electron microscopy and Nuclear magnetic resonance spectroscopy. In the non-catalytic gasification of pinecone, highest hydrogen (1.42 mmol/g) and total gas yields (6.6 mmol/g) with lower heating value (488 kJ/Nm 3 ) of the gas products were obtained in supercritical water at 550 °C with 10 wt% feed concentration for 60 min. Moreover, at 30 wt% catalyst loading, highest hydrogen yield was obtained from KOH (3.26 mmol/g) followed by NaOH (2.71 mmol/g) and Na 2 CO 3 (1.96 mmol/g). Hydrochars generated in supercritical water at 550 °C had a greater content of aromatic carbon and were thermally stable. The findings reveal, for the first time, the potential of pinecone for hydrogen production through subcritical, near-critical and supercritical water gasification, as well as the prospective of its hydrochar for environmental and material applications.

Combustion takes place within turbulent environments and under pressurized conditions in most industrial applications, for instance, gas turbines and internal combustion engines. The mixing of fuel and oxidizer is enhanced by turbulence, so that combustion will be more efficient. In addition, during combustion, heat is released; therefore, it causes flow instability as a result of gas expansion and high gradients of temperature. The interaction of turbulence and combustion under pressurized conditions may lead to modifications and even disruption of the flame. There are still ongoing studies on the prediction of flame and flow statistics, which are crucial for the stable operation of high-pressure combustion systems. In the present study, the aim is to investigate the influence of elevated pressures on the structure of turbulent premixed methane–air flames, within the range from atmospheric to 0.9 MPa, by numerical modeling and experimental validation. The computations are performed initially for the cold...

Hydrothermal carbonization (HTC) of dried olive pomace (DOP) was performed in subcritical water under HTC conditions (180–250 °C) to assess the potential of the generated hydrochar to produce energy. The effects of process parameters (holding time, temperature and DOP/water weight ratio) on the yield and the quality of the hydrochar were examined. The mass yield of hydrochar was between 56% and 71% and its HHV increased by more than 23% compared to the HHV of DOP giving a hydrochar similar to a lignite-type coal. The results reveal that a 30 min treatment at 215 °C with a DOP/water weight ratio of 1/6 maximizes the energy yield (83%) of the HTC process. Both the DOP and the hydrochar were characterized by ultimate, proximate and thermogravimetric analyses. The ultimate and thermogravimetric analyses showed that the hydrochar is more carbonaceous and more thermally stable than untreated DOP. The HTC conversion of raw DOP was carried out by dehydration reactions. The proximate analysis showed that hydrochars contained lower ash and volatile matter compared to the raw DOP.

In this research, thermogravimetric and mass-spectrometric (TG-MS) analysis and kinetics of different sized (60 μm, 800 μm, and 3 mm) Saray (Turkish origin) coal is examined at various combustion temperature ranges. Experiments are performed at the heating rate of 40 °C/min in an argon atmosphere up to combustion/gasification temperatures (850–1150 °C), which is close to the conditions of fluidized bed systems for high ash coal applications. The combustion tests are performed at isothermal conditions under air and oxygen ambience. The reaction regions, peak and burn-out temperatures, mass loss, maximum mass loss rate, and ash content of the different sized coal samples are evaluated. Reactivity index is also calculated to compare the reactivity of various sized coal samples. This research also focused on the main volatile products (H 2 , O 2 , CO, CH 4 , CO 2 ) of different sized coal samples on the basis of both their relative intensities and on their relevancy. Activation energy and Arrhenius constant of the coal samples are calculated using volumetric, grain and the random pore models and the results are discussed. The volumetric model showed higher activation energy values as both in the case of air and oxygen gasification.

International audience; Massive amounts of waste tires are generated globally posing disposal and recycling challenges. Waste tires were gasified in subcritical and supercritical water to study their degradation behavior during syngas production. The process parameters including temperature (325 degrees C to 625 degrees C), reaction time (15 min to 60 min) and feed concentration (5 wt% to 20 wt%) were optimized to maximize gas yields from waste tires. The highest total gas yields (34 mmol/g), hydrogen yields (14.4 mmol/g) and carbon gasification efficiency (42.6%) were achieved at optimal temperature (625 degrees C), reaction time (60 min) and feed concentration (5 wt%). The application of homogeneous and heterogeneous catalysts improved hydrogen yields from waste tires in the order: Ni/SiO2-Al2O3 (19.7 mmol/g) > Ru/Al2O3 (17.9 mmol/g) > Ba(OH)(2) (16.9 mmol/g) > Ca(OH)(2) (16.7 mmol/g) > Mg(OH)(2) (15.4 mmol/g). The results suggest waste tires as a potential resource for recovery of hydrogen-rich fuel gas through hydrothermal gasification. (C) 2019 Elsevier B.V. All rights reserved.

International audience; Mathematical modeling of devolatilization plays a significant role in the prediction of flame development in solid fuel combustion simulations. Commonly implemented devolatilization models available in the literature to simulate pulverized coal combustion are reviewed and evaluated. The effect of the particle heating rate on the onset of devolatilization and on final volatile yield is discussed. Selected devolatilization models are investigated with respect to their implementation in Computational Fluid dynamics (CFD) simulations of methane-assisted pulverized coal jet flame experiments. Differences in volatile release region, particle temperature and species concentration are presented and discussed with comparisons to the experimental data.

In this research, combustion properties and kinetics of different biomass samples known as poplar wood, hazelnut shell and wheat bran were studied using thermogravimetry–mass spectrometer. Experiments were performed at three different heating rates (10, 20 and 30 °C min−1) under air atmosphere. The reaction regions, peak and burnout temperatures, mass loss, maximum mass loss rate and residue of the biomass samples were determined. It was observed that all the biomass samples studied show similar combustion characteristics. This study was also focused on the main volatile products (H2, O, CO and CO2, etc.) of biomass combustion on the basis of their relative intensities across the temperature range 150–750 °C and on their relevancy, respectively. Activation energy and Arrhenius constant of the biomass samples were calculated using two different iso-conversional methods, known as Ozawa–Flynn–Wall and Kissinger–Akahira–Sunose. It was observed that the activation energy values were in the range of 66.80–68.56 kJ mol−1 for poplar wood, 83.73–93.25 kJ mol−1 for hazelnut shell and 162.17–167.4 kJ mol−1 for wheat bran, respectively. The biomass reactivity is directly related to the light volatile content, whereas combustion of fixed carbon affected the energy release.

International audience; The presence of liquid fuel droplets in a flammable mixture causes cellular instabilities on the flame surface, which significantly enhances the flame speed when compared to the fully vaporized case. The prediction of the mechanisms responsible for the onset of cellularity for two-phase mixtures is essential to better understand spray combustion. The present study considers an innovative experimental strategy to isolate and investigate any potential mechanisms. The fuel droplets were replaced by inert water droplets in order to amplify the thermal sink effect, characterized by the absorption of part of the heat released by the flame, and to suppress the local enrichment of fuel formed around droplets. Spherical expandingflames with narrow-size distribution droplets were used and qualitative comparisons of the flame structure were performed with a shadowgraph system. The results have shown that the heat sink has no significant effect, whereas the local enrichment of fuel appears as a key phenomenon, which suggests that in the case of fuel droplet aerosols the onset of cellularities is triggered in the inhomogeneous part of the gaseous phase.

This article presents the effect of inlet swirl motion on the flow behavior and combustion dynamics of pulverized olive cake (OC) in a 3D vertical furnace. The spherical OC particles are injected p...

Periodicity in evolution of premixed methane–air V-shaped flames in the space domain is investigated experimentally. The experiments were performed using the Mie scattering and Particle Image Velocimetry techniques. Three Reynolds numbers of 510, 790, and 1057 along with two fuel–air equivalence ratios of 0.6 and 0.7 were tested in the experiments. The analyses were performed using the Proper Orthogonal Decomposition (POD) technique for the flame front position as well as the velocity data pertaining to non-reacting flow condition. The POD analysis shows that the spectral characteristics of the mode shapes associated with the velocity and the flame front position data feature similarities; however, the corresponding temporal coefficients are significantly different. Specifically, the POD mode shapes pertaining to both velocity and flame front position data feature dominant instabilities. It was shown that the normalized wave number pertaining to these instabilities are similar and equal to the Strouhal number corresponding to non-reacting flow over a circular cylinder. Comparison of the normalized temporal coefficients show that, for the flame front position data, the normalized first and second coefficients are mainly centered close to the origin; however, those associated with the velocity data are positioned around a unity radius circle. This was argued to be linked to the ratio of the corresponding first and second eigenvalues. Specifically, it was shown that, as this ratio approached to unity, the signal energy becomes distributed between the first and the second POD modes. As a result, the normalized temporal coefficients follow a circular pattern.

This is the post-print version of the following article: "An analysis of the droplet support fiber effect on the evaporation process", which has been published in final form at https://www.sciencedirect.com/science/article/abs/pii/S001793101833196X?via%3Dihub; International audience; This paper presents an analysis of the effect of the droplet support fiber on the droplet evaporation process. This effect is evaluated for a droplet evaporating in a hot environment at atmospheric pressure using the experimental results of the present study and those in the literature. Selected published results are acquired using similar test conditions and experimental setups as the present data. The only main difference between these studies is the droplet support fiber diameter which varies between 14 µm and 225 µm. The ambient temperature explored in these studies ranges from room temperature up to 973K. n-heptane is selected because it is the most common fuel used in these studies. The main findings are that the cross-fiber technique, which uses 14 µm fiber diameters, induces no noticeable heat transfer into the droplet and consequently does not interfere with the evaporation process. In contrast, the classical fiber technique, which uses relatively larger fibers, greatly enhances the droplet evaporation rate as a consequence of increased conduction heat transfer through the fiber. A correlation is proposed to quantify the level of this increase as a function of ambient temperature and the fiber cross-sectional area, 2 .

International audience; A techno-economic feasibility analysis for a 5 MWe scrap tire granulés gasification facility is presented. Electricity generation is based on gas engines with the option of waste heat recovery. Based on our previous work, it is demonstrated that the best thermochemical option for waste tire disposal and energetic valorization is gasification using a mixture of preheated air and steam as the gasification agent. Also based on our previous work, the best gasification technology is shown to be the circulating fluidized bed technology. The study shows that under the regulatory and financial conditions prevalent in Turkey, the project is both technically and economically feasible .

International audience; In this study, the eulerian probability density function approach (EPDF) has been applied to simulate turbulent diffusion flame in a Vitiated Coflow. EPDF is the eulerian method to solve the PDF transport equations with a direct-quadrature-method-of-moments (DQMOM) closure. The PDF transport equation represented by a set of governing equations for the probability of occurrence in any environmental condition and the probability weighted species mass fractions, which are solved in an eulerian solution [1]; it is considered a product of the delta function, in order to model the turbulence–chemistry interaction. Among these advantages are the prediction and the kinetic control of the species such as CO and NOX. Even though the EPDF approach has been improved in recent years, most improvements have been achieved with parametric study in order to investigate the impact of the model accuracy. The main objective of this investigation is the numerical evaluation of the PDF approach accuracy, using different mixing models and turbulence models, to predict the lift-off height, the extinction and ignition of the flame. Another study comparative of eulerian (EPDF) and lagrangian monte-carlo (LPDF) was applied by equivalent physical models and numerical parameters for evaluating the performances of each approach such as precision and computational specification. The chosen mixture model is the IEM (Interaction by Exchange with the Mean) for micro-mixing closure. The number of environment in the eulerian approach EPDF is (2.0). Through the use of a dynamic model for the mixing time-scale, by computing the individual time-scales for the reactive scalars dynamically in each cell during the course of the simulation using the ANSYS-Fluent/MM-INTAS CFD codes and the chemical reaction mechanism injected is GRI mech 2.1. The results such as mixture fraction, temperature, species mass fraction is validated with experimental data and discussed.

International audience; High turbulent swirling reacting flow is investigated in a swirled premixed burner using hybrid RANS-LES method. The hybrid method is the Detached Eddy Simulation (DES) and it is combined with the Finite-Rate/Eddy Dissipation (FR/EDM) combustion model to treat turbulence-chemistry interaction. The instantaneous flow fields are well captured by DES and the premixed flame is well reproduced by FR/EDM. It is shown that DES is capable to reproduce the experimental profiles of the mean axial velocity and temperature. Phase-angle analysis of the instantaneous flow field shows the presence of large-scale coherent structures. Q-criterion is used to visualize the 3D behaviour of the structures; it is found that the unsteady flow contains a Precessing Vortex Core (PVC) and Secondary Outer Vortex (SOV).

International audience; Ignition and combustion characteristics of a low-vulnerability propellant based on RDX are studied experimentally. Ignition is obtained using a laser diode. Experiments are performed in a cylindrical closed-volume reactor for different initial pressures and initial propellant masses under nitrogen and argon surrounding atmospheres. Ignition delays, maximal overpressures, and propagation rates are obtained for different initial pressures and laser powers. Thermodynamic predictions of overpressures are also compared with experimental ones. Finally, ignition probabilities for different laser powers and gaseous atmospheres are investigated using a revised Langlie method.

Ulva ( Ulva armoricana and Ulva rotundata ) are macro algae which are responsible of environmental damages and are a cause of an eutrophication of the water in the French coast (Mediterranean sea, Brittany). In this study, Ulva were gasified in supercritical water in a batch reactor and in Hydrothermal Diamond Anvil Cell apparatus. Experimental conditions evolve between 400 and 550 °C at around 250 bar. Results show that a short time (7 min) in supercritical condition is sufficient to obtain a significant conversion rate. H 2 and CH 4 concentrations exceed 15 mol.% at high temperature (550 °C) and high algae concentrations are not favorable for H 2 production. The solid residue represents between 7 and 20 wt.% of the initial dry material and is mainly constituted of carbon (20 wt.%) and inorganic compounds: salts (KCl, NaCl), CaSO 4 , SiO 2 and CaCO 3 . The very low dissolved organic carbon (DOC) values of the liquid residue (

Biomass co-firing within the existing infrastructure of pulverized coal utility boilers is viewed as a practical near-term means of encouraging renewable energy while minimizing capital requirements and maintaining the high efficiency of pulverized coal boilers. Coal/biomass co-firing is a complex problem that involves gas and particle phases, along with the effect of turbulence on chemical reactions. Computation Fluid Dynamic (CFD) simulations can provide insight to design and operational issues, such as co-firing percentage, load swings, injection location, excess air and air/fuel staging, and predictions related to heat release, unburned carbon, and NOx emissions. The CFD based co-firing tools consist of models for turbulent flow, gas phase combustion, particles dispersion by turbulent flow, coal/biomass particles devolatilization, heterogeneous char reaction and radiation. Additional models related to slagging and fouling can also be found. This paper presents a review on CFD based modeling approaches used to predict the combustion characteristics of co-firing biomass with pulverized coal under air and oxy-fuel conditions.

Char particles of high ash Indian coal with different sizes are produced using thermogravimetric method at different heating rates. Particle diameter and porosity changes during devolatilization significantly affect char gasification rates. The effect of coal particle size on char production under various heating rates is reviewed. Char gasification is affected by operating conditions such as reaction temperature, char production method, and particle size in addition to chemical composition and physical structure of char. The measurements of the steam and CO2 gasification rate of the produced chars are performed by an isothermal thermo-gravimetric analysis at the temperatures of 900, 950, and 1000 °C under ambient pressure conditions. It is found that the reactivity of char gasification is increased along with heating rate of char. Three kinetic models are applied to describe the varying conversion rate: volumetric model, grain model, and random pore model. The activation energy of the gasification is varied based on the char generation method and particle sizes. The activation energy is varying from 122 to 177 kJ mol−1 for steam gasification and 130 to 214 kJ mol−1 for CO2 gasification to different sized char particles. The effect of char heating rate on gasification is more pronounced in the activation energies of smaller sized particles.