Search

[Display omitted] • Review of CFD simulations that model dry reforming of methane reaction. • Various types of reactors can be optimized through CFD for efficient DRM reaction. • CFD can help identify catalytic properties needed to suppress carbon deposition. • Challenges and potential research directions on CFD simulation of DRM are presented. Computational Fluid Dynamics (CFD) is a powerful tool for modeling chemical reactors. While limited literature is available on CFD simulation of Methane Dry Reforming (DRM), this reaction presents several environmental and economic advantages. Modeling DRM using CFD can provide insights for optimizing chemical reactors, evaluating catalysts interactions with surrounding reactive flow, improving properties of catalysts that are not yet well developed and determining optimum operating conditions for high process efficiency. This review paper provides a comprehensive overview of the current state-of-the-art in CFD modeling of DRM. After a brief description of the reaction thermodynamics, the kinetic models applied in CFD simulation for DRM and their limitations are covered along with an analysis of the governing equations employed. The review also tackles various catalysts and types of reactors employed for DRM simulation. It then identifies remaining challenges and potential research directions for more efficient hydrogen and syngas production using DRM. [ABSTRACT FROM AUTHOR]

• We conducted multiple experiments involving acid injection in carbonate outcrops at various flow rates. • Our results indicate that the presence of oil saturation has a significant effect on reactive flow in carbonates. • Oil saturation typically reduces PVbt in carbonate acidizing treatments. • The impact of oil saturation is affected by the flow rate used during acid injection. • We utilized microCT to assess changes in wormhole morphology resulting from the acidizing treatments. Carbonate acidizing is a well stimulation technique used to improve oil production by acid injection into the formation, creating conductive paths through rock dissolution. Most of the acidizing laboratory experiments are conducted on water-saturated rocks, assuming no oil is present after previous drilling and completion operations. However, different saturation conditions can occur in the rock formation, affecting the acidizing process. This study aims to assess the impact of oil saturation on carbonate acidizing. Reactive flow experiments were conducted on rocks saturated with water and oil using HCl 0.5 M and HCl 15%wt. at room temperature and 45 °C at flow rates of 1 and 20 mL/min. X-ray microtomography was used to visualize the wormhole morphology and compare the pore-volume-to-breakthrough (PVBT) values for each flow condition. Oil saturation resulted in efficient propagation of the wormhole with lower acid consumption and lower PVBT values. At 45 °C, PVBT values decreased by 54% for HCl 15%wt. at 20 mL/min. Wormhole morphology showed a smaller thickness in its propagation with oil saturation than with water saturation at the lower acid concentration, but not at the higher concentration. The presented results contribute to a deeper understanding of the significance of oil saturation in reactive flow during carbonate acidizing. [ABSTRACT FROM AUTHOR]

• Sorption-enhanced glycerol steam reforming process in fluidized bed explored. • Segregation pattern of sorbent and catalyst particles is firstly reported. • HTC of catalyst particles is significantly larger than that of sorbent particles. • Reducing sorbent diameter significantly promotes C 3 H 8 O 3 conversion and H 2 yields. • Sorption-enhancement on the syngas variation is most obvious in dense phase. Sorption-enhanced glycerol steam reforming process is numerically investigated by the multiphase particle-in-cell model within the Eulerian-Lagrangian framework in the bubbling fluidized bed with the aim of exploring the particle-level fundamentals of the binary particles. After the verification, the particle-scale evaluations and gas thermal properties are comprehensively presented. The results reveal that the size- and density-induced segregation results in the preferential distribution of CaO particles in the bottom zone of the bed. The particles in the bottom, freeboard, wake vortex and bubbling regions have a comparatively large heat transfer coefficient, velocity and slip velocity. At the same volume fraction, slip velocity and time instant, the heat transfer coefficient of sorbent is lower than that of catalyst. Increasing the superficial velocity elevates the heat transfer coefficient while reduces the C 3 H 8 O 3 consumption and H 2 yield. The probed results are of profound significance to the in-depth comprehension about complex gas–solid reacting flow and the process optimization of the sorption-enhanced hydrogen production system. [ABSTRACT FROM AUTHOR]

• The modified SST k - ω provide good simulation results for combustor with turbulent round jets. • The three hydrogen mechanisms with good kinetic performance well characterize the combustion characteristics of DLR combustor. • The excited species are low in content and have neglectable effect on the combustion characteristics under present condition. • Present work has reference significance for the selection of hydrogen kinetic mechanisms and turbulence models. In view of the promising application of hydrogen in scramjet combustor and the rapid development of hydrogen kinetic mechanisms, present work applies representative mechanisms with good kinetic performance to the combustion simulation of DLR scramjet combustor with a customized solver based on OpenFOAM platform. Different Reynolds-Averaged Navier Stokes (RANS) turbulence models including standard k - ε , SST k - ω and their corresponding modified versions for turbulent round jets, are utilized to simulate the non-reactive and reactive flow fields. Compared with the detailed experimental measurements of schlieren image, streamwise velocity, pressure etc., the modified k - ω SST turbulence model shows good performance and improves the simulation results near hydrogen jet. In combination with partially stirred reactor (PaSR) combustion model, three representative detailed hydrogen mechanisms (marked with Ó Conaire-2004, Varga-2015 and Konnov-2019) are adopted to evaluate their effect on combustion performance under scramjet combustion condition. And their effects on the combustion performance are quantified based on combustion efficiency, net thrust, total pressure loss, etc. All of them can well characterize the thermal combustion characteristics of hydrogen in the combustor. Among them, Ó Conaire-2004 slightly overestimates flame temperature, combustion efficiency and net thrust, and underestimates total pressure loss. Whereas Varga-2015 and Konnov-2019 provide nearly identical results on these performance parameters and give temperature profiles coinciding well with experimental data. Although the newly added excited states in Varga-2015 and Konnov-2019 deepen the understanding of hydrogen combustion processes and can served for optical combustion diagnostics, their effects on thermal combustion characteristics are negligible under present combustion condition, judging from their low content and the analysis on the performance parameters. Present work is conducive to the selection of hydrogen mechanisms for the combustion simulation of hydrogen-fueled scramjet combustor, and facilitates to obtain reliable simulation results for scramjet with turbulent round jets by employing the modified SST k - ω turbulence model. [ABSTRACT FROM AUTHOR]

An integrated approach for the three-dimensional tomographic reconstruction of multiple scalar fields in premixed gaseous non-sooting reactive flow applications is presented. Measurement of different physical quantities are combined to enable an in-depth analysis of the combustion process in premixed turbulent flames. This is achieved by utilizing a flexible and versatile evolutionary reconstruction technique, where measured chemiluminescence signals and deflections of a background-oriented schlieren tomography (BOST) setup are processed in a coupled manner for the first time. The 3D tomographic inverse problem is stated as a coupled system and is holistically solved for the chemiluminescence intensity field and the refractive index field (from BOST data) in the flow domain. The chemiluminescence field is interpreted as a pseudo flame surface density function of a progress variable field that allows the analysis of flame front curvatures. The proposed method is tested for its consistency and sensitivities on synthetically generated measurement data of different complexities. Finally, the technique is applied to experimental measurement data of turbulent stratified flames with different levels of swirl. [Display omitted] • 3D flame emission and BOS tomography performed in a coupled inverse problem. • 3D reconstructions of pseudo progress variables and flame front curvatures. • Quantification of experimentally derived 3D curvatures of turbulent swirl flames. • 3D curvatures from a DNS of a turbulent flame are compared with experimental data. [ABSTRACT FROM AUTHOR]

Highly-resolved Large Eddy Simulations (LES) are performed to investigate the combustion characteristics and the NO x -formation in the swirl-induced recirculation zones of the Brigham Young University (BYU) Burner Flow Reactor (BFR). The simulations are performed using the in-house LES tool PsiPhi , utilizing a flamelet/progress variable (FPV) approach to model the reactive multiphase flow. Four dimensions are used to parameterize the thermochemical quantities consisting of two mixture fractions for volatiles and char burnout, the total enthalpy and a progress variable, defined by a linear combination of key product species mass fractions. A reduced CRECK mechanism with 120 species and 1551 reactions is used, including all NO x -formation mechanisms (prompt-, fuel-, thermal-, and pathway via N 2 O). Devolatilization, char burnout and radiation effects are considered in the LES. Radial profiles of major gas species are compared with experimental data, leading to an overall good agreement. Two variants to determine NO species were investigated: (1) the direct extraction of NO from the flamelet table and (2) the solution of an additional transport equation for NO with a modified NO source term, split into a formation and a rescaled consumption part. The solution of an additional transport equation for NO is clearly superior and necessary for pulverized coal simulations, showing a much improved prediction of forward- and backward reactions of NO inside the furnace, while the direct extraction of NO from the flamelet table greatly overpredicts its formation. • FPV-LES of a swirl-stabilized pulverized coal flame are performed. • Two ways to determine NO species are investigated. • Extracting NO from the flamelet table overpredicts the experiment by a factor > 3. • An additional transport equation for NO much better predicts the experiments. • The transport equation better accounts for forward- and backward reactions of NO. [ABSTRACT FROM AUTHOR]

In this work, new test burner concepts for the non-catalytic partial oxidation of natural gas are evaluated using numerical modeling. The 3D CFD model for reactive flow calculations incorporates a detailed reaction mechanism containing 28 species and 112 reactions, and is extensively validated against data obtained in the semi-industrial test facility HP POX in Freiberg. The validation cases operate at 61 bar(a) and outlet temperatures of approximately 1688 K. The CFD models demonstrate that the optimized burner concepts result in a significantly higher natural gas conversion rate, which allows for a more compact reactor design or, alternatively, for a higher throughput in existing industrial facilities. In addition, the final burner concepts are tested experimentally. Optical measurements demonstrate that the CFD model is capable of reproducing the complex 3D flame structures and reliably predicting the overall performance of the reactor. [ABSTRACT FROM AUTHOR]

• A super-steady combustion process can be achieved by a vortex-tube combustion. • The aero-, thermo-, and flame-dynamic stability was analyzed. • Different criterion numbers is employed to quantify the stability. • The momentum flux theory is employed for the flame-dynamic stability. Aerodynamic and thermo-acoustic stability were systematically analyzed to reveal the underlying cause of the super-steady performance found in a strong rotating reactive flow, which is achieved using a stratified vortex-tube combustor (SVC) employing methanol as fuel. Results show that the SVC possesses a wide stability limit and weak pressure fluctuation with a uniform flame. The lean stability limit is always smaller than 0.2 and the amplitude of pressure fluctuation is generally within 2 kPa, indicating a super-steady combustion process. The large tangential velocity produces a large centrifugal force that suppresses the turbulent motion to promote aero-dynamic stability, yielding a small Froude number. The delay in the mixing process is the crucial reason for the generation of the stratified distribution of species and the triple-flame structure. The large transport fluxes of the species and enthalpy promote the reaction and ignition processes to intensify the combustion, which produces a large density gradient to promote thermo-acoustic stability. The large tangential velocity and density gradient result in a large Richardson number, suggesting the laminarization of the fluid. The momentum flux and its fluctuation decrease distinctly downstream of the vortex-flow because of the strong momentum exchange and transfer in the vortex flow, which weakens the pressure fluctuation in the post-flame zone. The intensified combustion can also increase the burning velocity, and promotes its matching with the flow field. The reduced momentum flux and the increased burning velocity are responsible for good thermo-acoustic stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Gas-catalyst thermochemical properties in catalytic MTO fluidized bed explored. • Non-uniform distribution of hydrodynamics and species concentrations observed. • Large catalyst HTC is located in the crucial reaction zone and freeboard zone. • Enlarging the reaction pressure significantly promotes the HTC of catalyst. The methanol-to-olefin (MTO) process enables economical production of light olefins thus decreases the reliance on petroleum resources. The reactive multiphase flow patterns and reaction behaviors inside pilot-plant MTO fluidized reactor are numerically simulated with multiphase particle-in-cell model. Based on the model validation, the thermochemical properties of catalytic particle (e.g., heat transfer coefficient (HTC), temperature) and gas phase thermal characteristics are comprehensively investigated with the discussion on several crucial operating parameters. The results reveal that large HTC of catalyst particle is located in the crucial reaction zone and freeboard zone. The HTC of catalyst material covers a range of 50 to 150 W/(m2·K). Gas-solid hydrodynamics and gas concentrations exhibit spatial non-uniform distribution. Moreover, the reactant gas flow rate is more positively sensitive to the product distributions and gas thermal properties. Enlarging the reaction pressure significantly enhances the heat transfer. The vertical dispersion coefficient of catalyst is two orders of magnitude larger than the horizontal ones. [ABSTRACT FROM AUTHOR]

• A nexus exists among dissolution, precipitation and wettability. • Dissolution, precipitation and relative permeability are interlinked. • Capillary pressure is affected by dissolution and precipitation. Numerous studies have attempted to assess the possible changes in the petrophysical parameters of sandstone reservoirs for the geological storage of CO 2. However, the results have been highly variable and hardly conclusive, highlighting mineral alteration, precipitation, dissolution, and fine migration as the main drivers of changes in porosity, permeability, and surface wettability. In this paper, a series of systematic experimental studies were carried out on the Berea sandstone samples to carefully analyse the changes in porosity, relative permeability, capillary pressure, and surface wettability after CO 2 treatment. The results obtained indicated that porosity increased in the samples due to dissolution of minerals (calcite and clay) and there was no sign of pore throat closure due to mineral precipitation. It was found that the surface wettability can be shifted towards a CO 2 wet system, probably because of calcite precipitation and clay dissolution or reduction in the hydrophilicity of quartz, leading to a decrease in capillary entry pressure. It appears that the mineral and capillary trapping in sandstone make it a suitable storage site for CO 2 , but that require further research to fully understand the changes posed by mineral dissolution in the long term. [ABSTRACT FROM AUTHOR]

• Generated proppants inside shale fractures by injecting chemicals with fracturing fluid. • Demonstrated increase in microfracture conductivity due to in situ proppants. • Determined proppant size and number as a function of chemical mix. • Showed that the micro-proppants formed in calcite-rich regions of the shale. A large fraction of the fractured surface created during hudraulic fracturing is not propped. Injected proppants often settle near-wellbore in low viscosity fracturing fluids like slick water and do not reach the end of fractures. Many microfractures are too narrow to accommodate injected proppants and close during production. Poor placement of proppant leads to a loss of fracture conductivity and undermines the productivity of shale wells. In this study, reactive chemicals are injected to generate hydroxyapatite crystals on calcite-rich shale surfaces to act as in-situ proppants to improve microfracture conductivity. Batch experiments were conducted with reservoir shale samples in both low salinity frac water and high salinity brine. Crystals were generated in both low and high salinity brines. The crystals grew to several hundred microns and tended to form on calcite-rich shale surfaces. The hardness data showed that properly designed formulations could avoid the shale softening and even increase the hardness of the fracture surface (from 230 to 280 MPa). Reactive flow experiments were performed to evaluate fracture conductivity change after the chemical treatment. Micro-CT and scanning electron microscopy were used to visualize in situ proppants. A 3–10 times increase in post fracture conductivity was observed for both reservoir and outcrop shale samples. The propping of the microfractures can decrease the production decline during hydrocarbon production in shale reservoirs. [ABSTRACT FROM AUTHOR]

The more properties of biodiesel one wishes to represent, the more complex the surrogate mixture becomes. Often the aim is to represent the H/C and O/C ratios and molecular weight using a small number of pure components. In this article, a turbulent jet diffusion flame of a biodiesel surrogate, composed of 50% Methyl Decanoate, 40% n-heptane, 9% methyl crotonate and 1% ethanol is modeled and simulated. The strategy used is to apply the Directed Relation Graph technique for a first reduction, and Layerless Neural Network to define the main chain and obtain a skeletal mechanism. The results obtained for temperature and mass fractions of CO 2 , CO and H 2 O agree reasonably with literature data for a mechanism of 147 reactions and 45 species. The small number of species facilitates the simulation of the coupling between turbulence and chemical kinetics, a desirable feature of reduced mechanisms. • A skeletal mechanism is obtained for a biodiesel surrogate. • The cost to resolve reactive flow is reduced by two orders of magnitude. • The skeletal mechanism is defined using Layerless Neural Networks. • AI provides the reactions of the ester group to the biodiesel surrogate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Acid pre-flushing before pH-sensitive microgel flooding is investigated in carbonates. • Acetic acid was selected from static & dynamic tests to lower carbonate rock pH. • The developed geochemical model could predict pH variation and Ca concentration. • Salinity influence on pH & distribution of ions during acid pre-flush were analyzed. • Field-scale reservoir model showed recovery increment after pH-sensitive treatment. pH-sensitive microgel flooding is a deep conformance control technique in which the microgel viscosity depends on formation pH. Lowering the formation pH by an acid pre-flushing treatment guarantees easy injection of these microgels. The applications of these microgels were mainly dedicated to sandstones in the literature. However, this study provides an integrated laboratory and numerical modeling approach to find a proper pre-flushing acid in carbonates. The performance of various acids (strong and weak) is evaluated via batch experiments (static tests). The dynamic of acid pre-flushing (dynamic test) and pH-sensitive microgel injection are investigated by flooding experiments. A compositional reactive flow model (advection-diffusion-reaction), developed in Python, is also used to analyze the behavior of the flooding experiments. To evaluate the flooding performance, a 3-D field-scale reservoir simulation model with high-permeability contrast is then implemented. The batch and dynamic tests show that acetic acid can maintain a low-pH environment across the medium, which provides a favorable condition for pH-sensitive microgel transports. The geochemical model can accurately predict the measured equilibrium pH and calcium concentration of effluents at different injection rates and salinities. After the establishment of a near-equilibrium condition, the remaining unionized acids in the flooding experiments result in deep conformance control of pH-sensitive microgels. The pH-sensitive microgel flooding at the field-scale reveals an excellent performance in permeability modification of high-conductive zones. Plugging the first 30% of a high-permeable channel can guarantee the recovery factor increase of this deep conformance control technique. [ABSTRACT FROM AUTHOR]

A high-fidelity numerical solver, RYrhoCentralFoam, is developed based on OpenFOAM® to simulate turbulent compressible reactive flows. It is designed for accurately simulating combustion with detailed chemistry, turbulence, shock wave and their interactions. The features that we develop in this work include: (1) multi-species transport, (2) detailed fuel chemistry, and (3) turbulent combustion models in Large Eddy Simulations (LES). Two hydrogen flames with detailed measurements are studied, including turbulent auto-igniting flame in hot co-flowing jet and supersonic combustion in a supersonic burner. For the first flame, the lift-off height, overall flow and flame behaviors, as well as the statistics of the velocity and reactive scalar are computed accurately. For the second flame, the RYrhoCentralFoam is also shown to have the ability for modelling supersonic combustion in model combustors, in terms of the velocity and temperature fields as well as unsteady flame lift-off dynamics in a recirculating zone. The accuracies of LES with RYrhoCentralFOAM in both flames are comparable to those with other well-validated compressible flow solvers. [ABSTRACT FROM AUTHOR]

Large Eddy Simulation (LES) has become an attractive option for the modelling of turbulent combustion, and a significant effort has been put into the development of suitable models for combustion at the subgrid-scale (SGS). Comparatively, little attention has been paid to the impact of SGS stress models in the simulation of complex reactive flows. In the present work, a partially-premixed case from the Sydney swirl-stabilised flames series has been investigated using LES and the Flamelet Generated Manifold (FGM) approach, employing four different SGS stress models on three numerical grids with different levels of refinement, quantified with an a priori mesh quality criterion. It was found that the use of advanced SGS models can improve the accuracy of the results significantly in both the highly turbulent region close to the burner and in the low-turbulence region further downstream. Also, a physically sound formulation for SGS stresses was found to reduce the sensitivity of the results to mesh refinement, giving acceptable results on relatively coarse grids. This can be a significant advantage in the modelling of complex geometries where there is a need to find a compromise between mesh refinement and computational costs. [ABSTRACT FROM AUTHOR]

The present study addresses the autoignition and detonation characteristics of n -heptane/air mixture with water droplets in a confined one-dimensional reactor. A Eulerian-Eulerian formulation for gas and liquid phases is employed to simulate multi-component, fully compressible and reactive multi-phase flows. The parametric investigations covering a range of droplet diameters and number densities are conducted to understand the reaction front development in gas phase and droplet evaporation characteristics under different gaseous combustion conditions. Four modes of autoignition behaviours in the reactor are identified and they are found to greatly depend on both droplet diameter and number density. At a relatively small droplet diameter and/or number density, detonation is initiated by hot spot but no autoignition occurs at the right boundary. When both or either of them increase, autoignition occurs at the right boundary and the reaction front may further evolve into detonative or deflagrative waves. This is because the temperature inhomogeneity in that region is considerably enhanced. Furthermore, droplet diameter and number density are used to quantify the different modes of autoignition and detonation development. For the droplet evaporation dynamics during the reactive front development process, various mechanisms are observed, related to the different effects dominated by the velocity difference between two phases (characterized by the droplet Reynolds number), high local gas pressure and also the droplet temperature. This results in non-monotonic spatial distributions of droplet evaporation rate in the reactor, e.g. M -shaped in the detonated or shocked regions. [ABSTRACT FROM AUTHOR]

• Dilute spray flames in a model supersonic combustor fueled with hydrogen are studied. • Liquid droplet evaporation, reactant mixing and supersonic flame lift-off dynamics are discussed. • Strong inhomogeneity is observed in the mixing field of the H 2 / n -C 7 H 16 /air mixtures. • Stratified combustion occurs due to inhomogeneous mixing and distributed droplet evaporation. • Novel blow-off behaviors are found in the recirculating dual-fuel two-phase flames. Combustion characteristics of n -heptane dilute sprays in a model supersonic combustor fueled by hydrogen are numerically investigated. The two-phase compressible reactive flows are solved by a Eulerian-Lagrangian framework. Supersonic air enters the combustor at Mach 2.0, whereas hydrogen is injected sonically at the strut base. Monodispersed liquid n -heptane droplets are carried by hydrogen jet at different Spray Equivalence Ratios (SERs), which range from 0 to 0.096. The results show that the varied SERs negligibly influence the time-averaged length of the recirculation zone (about 50 mm off the rear of the strut). However, the low-speed regions in the combustor is increased with SER. High droplet evaporation rates are observable in the downstream of the recirculation zone, and meanwhile continuous evaporation also occurs downstream beyond that due to the local high temperature. The mixing field of the dual-fuel system shows strong inhomogeneity with various compositions of hydrogen/ n -heptane/air mixtures in both mixture fraction space and physical space. Moreover, the fraction of heat release rate from hydrogen decreases from 100% to 43.3% due to the increased SERs from 0 to 0.096, and the averaged heat release from hydrogen before blow-off are close, whereas that from n -heptane increases stably. With increased SER, the hydrogen flame base moves upstream towards the strut base, whereas that of n -heptane is lifted off the strut gradually. When SER exceeds some critical value, e.g. 0.096 for the current combustor, the flame blows off, with the two separate reaction zones (upstream hydrogen and downstream n -heptane) fully quenched. [ABSTRACT FROM AUTHOR]