Modélisation CFD des épurateurs à gaz en milieu maritime

« Les colonnes à lit fixe à garnissage aléatoire de quatrième génération : constituent un moyen intéressant de mettre en œuvre le lavage à l'eau de mer du dioxyde de soufre (SO2) à bord de grands navires, en raison de la faible perte de charge biphasique, de la capacité élevée, et de la grande efficacité de l'élimination du SO2.L'épuration de dioxyde de soufre à l'eau de mer a été étudiée au moyen d'un modèle eulérien 3D basé sur les équations macroscopiques de continuité, de quantité de mouvement, d'énergie et d'équilibre des espèces moyennées en volume dans les phases liquide et gazeuse. Il a été constaté que les performances du processus d'absorption du dioxyde de soufre par l'eau de mer dans les réacteurs à colonnes à lit fixe avec des garnissages aléatoires de quatrième génération peuvent être améliorées par l'augmentation du débit de liquide et la diminution de la température du liquide. Par conséquent, le lavage du dioxyde de soufre à l'eau de mer à bord de grands navires s'améliore considérablement dans les océans tempérés dont la température moyenne est comprise entre 10 et 20 °C. D'autre part, l'augmentation de la pression améliore la force motrice du transfert de masse gaz-liquide et par la suite le processus d'élimination du dioxyde de soufre qui revient à des valeurs inférieures du rapport liquide-gaz. L'épuration à l'eau de mer du dioxyde de soufre à une pression plus élevée augmente le coût en capital et les besoins en énergie, mais offre des améliorations majeures telles que l'élimination totale du SO2 lors de l'utilisation du carburant à une forte teneur en soufre et la prévention de la perte de puissance du moteur en raison de la forte contre-pression à l'échappement entrant. Le fonctionnement avec une hauteur de lit garnie supplémentaire permet d'amplifier le temps de contact gaz-liquide et par conséquent les performances du processus d'absorption. Dans ce contexte s'intègre ce présent travail qui vise à atténuer l'émission de SO2 par les navires marchands utilisant des carburants à forte teneur en soufre. -- Mot(s) clé(s) en français : garnissage, quatrième génération à colonnes à lit fixe, absorption/ émission de SO2, simulation, modélisation CFD. » « Fourth-generation random packed fixed-bed columns are an attractive way to implement sulfur dioxide (SO2) seawater scrubbing on large ships because of the low two-phase pressure drop, high capacity, and high SO2 removal efficiency.Sulfur dioxide seawater scrubbing was studied using a 3-D Eulerian model based on the macroscopic equations of continuity, momentum, energy, and volume-averaged species equilibrium in the liquid and gas phases. It was found that the performance of the sulfur dioxide seawater absorption process in fixed-bed column reactors with fourth-generation random packing's, can be improved by increasing the liquid flow rate and decreasing the liquid temperature. As a result, the scrubbing of sulfur dioxide from seawater on board large ships improves significantly in temperate oceans with average temperatures between 10 and 20°C. On the other hand, the increase in pressure improves the driving force of the gas-liquid mass transfer and subsequently the sulfur dioxide removal process which becomes complete at lower values of the liquid-gas ratio. Sulfur dioxide scrubbing at higher pressure increases capital cost and energy requirements, but offers major improvements such as complete removal of SO2 at high fuel sulfur content and prevention of engine power loss due to high back pressure at the incoming exhaust. Operation with an additional packed bed height increases the gas-liquid contact time and thus the performance of the absorption process. In this context, the present work is integrated to mitigate SO2 emission from merchant ships using high sulfur fuels. -- Mot(s) clé(s) en anglais : fourth-generation fixed-bed column packing, SO2 absorption/emission, simulation, CFD modelling.

Performance Assessment of Dual-Polarized 5G Waveforms and Beyond in Directly Modulated DFB-Laser using Volterra Equalizer

International audienceWe investigate the performance of 25-Gbps dual-polarized orthogonal frequency division multiplexing (OFDM)-based modulation in a directly modulated distributed feedback (DFB)-laser over 25 km of single-mode fiber. A Volterra equalizer is used to compensate for the nonlinear effects of the optical fiber. The results show that FBMC-OQAM modulation outperforms OFDM, universal filtered multicarrier (UFMC), and generalized frequency division multiplexing (GFDM) waveforms. Indeed, a target bit error rate of similar to 3.8 x 10(-3) [forward error correction (FEC) limit] for FBMC, UFMC, OFDM, and GFDM can be achieved at -30.5, -26, -16, and -14.9 dBm, respectively. The effect of the DFB laser is also investigated for UFMC, OFDM, and GFDM, and they undergo a Q penalty of 2.44, 2.77, and 4.14 dB, respectively, at their FEC limit points. For FBMC-OQAM, the signal is perfectly recovered when excluding the DFB laser at -30.5 dBm. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE

Fluid-Rock Interactions in Carbonates: Applications to CO2 Storage

It is well established that more than half of the world’s hydrocarbon reserves are contained in carbonate reservoirs. In a global context, which is characterized by an increasing demand in energy, population growth and overall economic development, it is very important to unlock potential carbonate resources while mitigating the effects of climate change. Moreover, significant volumes of carbon dioxide – the major greenhouse gas contributor to global warming – can be stored in carbonate subsurface formations such as carbonate depleted reservoirs and deep saline aquifers. Therefore, better understanding of carbonate porous media has a wide range of major industrial and environmental applications. However, because of complex pore structures, including the presence of micro-porosity, heterogeneities at different scales, combined with high chemical reactivity, it remains very challenging to describe flow and transport in carbonates. In this thesis, we focus on carbonate porous media and aim to better describe flow, transport and reaction in them. The main application of this work is related to carbon storage in deep saline carbonate aquifers. More particularly, we address fluid-rock interactions e.g. wettability alterations and reactive transport, that occur in carbonate formations. First, we investigate the impact of wettability alteration on multi-phase flow properties. We use pore-network modelling to analyze the impact of wettability alteration by modelling water-flood relative permeability for six different carbonate samples with different connectivity. Pore-scale multi-phase flow physics is described in detail and the efficiency of water-flooding in mixed-wet carbonates is related to the wettability and pore connectivity. We study six carbonate samples. Four quarry samples – Indiana, Portland, Guiting and Mount Gambier – and two subsurface samples obtained from a deep saline Middle Eastern aquifer. The pore space is imaged in three dimensions using X-ray micro-tomography at a resolution of a few microns. The images are segmented into pore and void and a topologically representative network of pores and throats is extracted from these images. We then simulate quasi-static displacement in the networks. We represent mixed-wet behaviour by varying the oil-wet fraction of the pore space. The relative permeability is strongly dependent on both the wettability and the average coordination number of the network. We show that traditional measures of wettability based on the point where the relative permeability curves cross are not reliable. Good agreement is found between our calculations and measurements of relative permeability on carbonates in the literature. The work helps establish a library of benchmark samples for multi-phase flow and transport computations. The implications of the results for field-scale displacement mechanisms are discussed, and the efficiency of waterflooding as an oil recovery process in carbonate reservoirs is assessed depending on the wettability and pore space connectivity. Secondly, we investigate at the laboratory column scale (50 cm), fluid-rock interactions that occur through the injection of an acidic solution into carbonate porous media. Laboratory columns are packed with crushed and sieved porous Guiting carbonate grains. Therefore a homogenous porous medium at the Darcy scale is created and the effect of micro-heterogeneities on transport and reactive transport properties is highlighted. We first conduct a series of passive tracer experiments. Salinity is used as a non-reactive tracer as brine is injected at a constant flow rate into columns pre-saturated with equilibrated deionised water. Solute breakthrough curves are experimentally obtained by measuring the conductivity of collected effluent samples. Subsequently, by solving the advection-dispersion equations using PHREEQC geochemical software, we compare the experimental measurements with numerical predictions of breakthrough curves. A good match is obtained for a dual porosity model and a dispersion coefficient is estimated. We then investigate reactive transport by injecting at constant flow rate acidic brine (hydrochloric acid diluted in saline brine with an overall pH of 3) into columns pre-saturated with equilibrated brine. We measure the effluent concentrations using ICP-AES (inductively coupled plasma atomic emission spectroscopy) Moreover; scanning electron microscopy (SEM) is used to determine single grain-scale changes. We assess the impact of flow rate on the resident time distribution of solutes and reaction profiles along the columns. We discuss challenges encountered regarding the reproducibility of the results and we highlight the implications of such phenomenological studies on carbon storage in carbonates. Finally, we experimentally examine fluid-rock interactions that are induced by the injection of supercritical CO2 (sc-CO2) in carbonate formations at the pore scale. I designed and built a novel experimental apparatus that allows the injection of brine enriched with sc-CO2 at typical CO2 storage conditions. In our experiments the temperature is 500C and the injecting pressure is 9MPa. A novel methodology that combines pore-scale imaging, core flooding and pore-scale modelling is applied in the context of CO2-carbonate-brine interactions. We experimentally use a high pressure and temperature mixing vessel to generate brines enriched with sc-CO2.The mixture is then injected using high precision piston pumps at a constant flow rate (Q=0.1 ml/min) into carbonate micro samples (5 mm diameter and 20 mm length) saturated with pre-equilibrated high salinity brine. We measure the permeability changes in real time during the injection of reactive fluids, In addition, dry high-resolution micro-computed tomography scans are obtained prior to and after the experiments and the pore structure, connectivity and computed flow fields are compared using image analysis and pore-scale modelling techniques. We perform direct simulations of transport properties and velocity fields on the three-dimensional scans and we extract representative pore-throat networks to compute average coordination number and assess changes in pore and throat size distributions. Moreover, we assess the impact of reaction rate on reactive transport. We alter the reaction rate and hence the Damkӧhler number by under saturating the sc-CO2/brine mixture with crushed and sieved carbonate grains. Two regimes of dissolution are experimentally observed: dominant wormholing and a more uniform dissolution regime. High resolution 3D scans of the dissolution patterns confirm these observations. Permeability increases over several order of magnitude with wormholing whereas for the uniform dissolution, the increase in permeability is less pronounced. Overall, fewer pore and throats are present after dissolution while the average coordination number does not change significantly. Flow becomes concentrated in the wormhole regions after reactions although a very wide range of velocities is still observed. We then compare the observed results for single phase flow (wormholing induced by the injection of single phase brine saturated with sc-CO2) to two-phase flow reactive flow experiments (co injection of sc-CO2 and brine). Results show that wormholing is also seen in the two-phase experiments. Directions for future research in the area of fluid-rock interactions are then discussed.Open Acces

Fuel

In this study, we investigate the feasibility of foam enhanced oil recovery (EOR) for a dual porosity and heterogeneous carbonate reservoir in the Middle East with medium temperature (55 °C) and high formation salinity (16% TDS). An Alkyl Poly-Glycoside (APG) surfactant was firstly selected based on the solubility tests and bulk foam tests. Afterwards, a series of core flooding experiments both in the absence and in the presence of crude oil were performed on Estaillades limestone, a dual-porosity and heterogeneous carbonate presenting reasonable similarities with the actual formation. In these foam tests, the influence of surfactant concentration, foam quality, injection velocity, brine composition, injection mode and permeability on foam strength and incremental oil recovery were systematically investigated. The optimal foam quality is found to be around 60–70% from foam quality scan tests in the absence of crude oil. Moreover, foam can still be generated in Estaillades under strongly oil-wet conditions, and the foam strength in the high-quality regime is largely dependent on surfactant concentration. More than 10% original oil in place (OOIP) of the water flooded residual oil was recovered after co-injecting 2.0 total pore volume (TPV) of nitrogen and 0.5 wt% APG surfactant (in synthetic seawater brine) at 65% foam quality and 4 ft./d. Interestingly, it was observed that the presence of lauryl betaine (LB) can significantly enhance the stability of APG foam in the presence of crude oil, though LB surfactant itself is not a good foamer. At last, the three phase co-injection tests proved the presence of foam at approximately 70% oil saturation. The results of this study may provide insights into the foam transport behavior in a dual porosity and heterogeneous porous media under strongly oil-wet condition

Pore-scale imaging and modelling

Pore-scale imaging and modelling – digital core analysis – is becoming a routine service in the oil and gas industry, and has potential applications in contaminant transport and carbon dioxide storage. This paper briefly describes the underlying technology, namely imaging of the pore space of rocks from the nanometre scale upwards, coupled with a suite of different numerical techniques for simulating single and multiphase flow and transport through these images. Three example applications are then described, illustrating the range of scientific problems that can be tackled: dispersion in different rock samples that predicts the anomalous transport behaviour characteristic of highly heterogeneous carbonates; imaging of super-critical carbon dioxide in sandstone to demonstrate the possibility of capillary trapping in geological carbon storage; and the computation of relative permeability for mixed-wet carbonates and implications for oilfield waterflood recovery. The paper concludes by discussing limitations and challenges, including finding representative samples, imaging and simulating flow and transport in pore spaces over many orders of magnitude in size, the determination of wettability, and upscaling to the field scale. We conclude that pore-scale modelling is likely to become more widely applied in the oil industry including assessment of unconventional oil and gas resources. It has the potential to transform our understanding of multiphase flow processes, facilitating more efficient oil and gas recovery, effective contaminant removal and safe carbon dioxide storage

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P < 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)