Multiphase Multicomponent Model Research Articles

Mathematical modeling and characteristics evaluation of coke replacing with commercial biochar in iron ore sintering process

For green production of iron ore sintering, the research on replacing traditional coke with clean energy such as biochar is a new hot topic. Most of the work conducted in biomass fuel utilization in sintering is done on a laboratory or pilot-scale. Little work was reported by using mathematical models to predict the influence of biomass-based fuel replacement on sintering performance quantitatively. In this paper, a more comprehensive numerical model that incorporates most of the significant reaction processes and heat transfer modes was proposed first, especially with considerations of coke/biochardual-fuelphase heat supply and their pyrolysis, volatiles release, and combustion processes. Experimental data of the sintering pot reasonably agreed with the numerical results, which validated the model. Based on the equivalent fixed carbon method, the combustion and sintering behaviors in replacing proportions, particle size, and fuel types of commercial biochar for coke in the sintering bed were compared. With the lower replacement proportions (<20 %), both two biochars (Oak and Pine) can ensure thermal state indicators (PT, RT, MQI, CR) and combustion performance indicators (FFS and combustion efficiency), and keep the yield enough high. When the replacement proportion exceeds 50 %, the sintering index is worsened significantly. The emission of NOx can be decreased by 57.62 % when a 100 % replacement proportion of biochar is used. The results also indicate that coarsening particle size (2.4 mm was recommended for use) can further improve sintering indicators, and make Oak char 50 % replacing proportion reach the level of all coke method. The performance of pine sintering is even better than Oak sintering. The multiphase multicomponent model is used to give a mechanism explanation for the behavior and performance of biochar replacing coke in the sintering process.

Simulation-Driven Enhancement of an Alkaline CO2 Capture Electrochemical Cell

Electrochemical cells using anion exchange membranes (AEM) have been previously demonstrated to regenerate aqueous K2CO3 solutions obtained via CO2 absorption from air with aqueous KOH [1]. Preliminary results suggest this technique might significantly outperform currently employed methods in terms of specific energy expenditure (MJ/kgCO2). In order to accomplish this, we propose a computational study of an electrochemical cell designed and operated at the Paul Scherrer Institut. A multi-phase multi-component model has been developed and implemented via appropriate customization of the commercial CFD software Ansys Fluent. The model accounts for all the physical and chemical phenomena relevant to the electrochemical process, i.e. fluid flow mechanics, heat and mass transfer, electrical potential propagation and chemical and electrochemical reactions. The results of the simulations suggest two possible causes of cell overpotential. Firstly, the formation of hydrogen bubbles by the hydrogen evolution reaction in the cathode electrode, which partially cover the liquid-solid interface where the electrochemical reaction occurs. This is clearly shown by direct comparison with idealized single-phase simulations. Secondly, the flow structure of the catholyte is not optimized to favor the diffusion/migration of carbonate rather than hydroxide anions towards the membrane. This requires increasing the gap between the electrode and the membrane in order to maximize the faradaic efficiency, but it also increases the cell specific resistance. Although we show that there exists an optimal ratio of electrode-membrane gap to cell height, our simulations indicate that a topological optimization of the electrode fine structure might be beneficial to eliminate the undesired effects mentioned above. [1] Muroyama, A. P., & Gubler, L. (2022). Carbonate Regeneration Using a Membrane Electrochemical Cell for Efficient CO2 Capture. ACS Sustainable Chemistry & Engineering.

The Role of Porous Carbon Inserts on the Performance of Polymer Electrolyte Membrane Fuel Cells: A Parametric Numerical Study

Herein, for the first time, a computational fluid dynamic study is performed to investigate the effects of using porous carbon inserts (PCI) on the performance of PEMFC. A 3D multiphase multicomponent model is developed to simulate the fuel cell performance. The effects of several geometric and physical parameters of the PCI, including porosity, size, and the arrangement of PCI in the landing area, are numerically examined, which are not investigated in the literature so far. The numerical results showed that using PCI, a 23% improvement in the fuel cell performance is achieved for the optimum case with 80% PCI. In addition, increasing the PCI porosity results in performance enhancement (12.6% improvement when increasing the porosity up to 0.8). Using PCI with different rib/channel width ratios demonstrates that the use of PCI at higher ratios has a more significant effect. When using 34.1% PCI in a case with a ratio of 2:1, the performance increases about 35%. Moreover, a PCI with larger longitudinal size (4 mm compared to 2 mm) shows higher performance enhancement (5.3% compared to 3.5%).

Equations of state for single-component and multi-component multiphase lattice Boltzmann method

The lattice Boltzmann method is an alternative method for conventional computational fluid dynamics. It has been used for simulating single-phase and multiphase flows and transport phenomena successfully and efficiently. In the current work, single-component and multi-component multiphase systems are studied. A methodology that differentiates between types of fluids is developed. Moreover, an approach for a multi-component multiphase system is developed in which a single distribution function is used regardless of the number of components. The value of the cohesion parameter (Gf) in the multi-component multiphase model becomes unimportant, like the cohesion parameter (Gp) in the single-component multiphase model, because their effects cancel when calculating the cohesion force. The fluids and mixtures are treated as real, so that mixing rules are used for the mixtures. Several types of fluids and mixtures are considered to investigate the capability of the proposed approach in dealing with miscible mixtures in both azeotrope and non-azeotrope situations. The layered Poiseuille flow and falling droplet on a liquid film are presented to evaluate the model developed. We conclude that this methodology can distinguish between different types of fluids when modeling single-component and multi-component multiphase systems.

LNAPL Recovery Endpoints: Lessons Learnt Through Modeling, Experiments, and Field Trials

AbstractIt is important to estimate what light nonaqueous phase liquid (LNAPL) recovery can be practicably achieved from subsurface environments. Over the last decade, research to address this included a broad field program, laboratory measurements and experimentation, and modeling approaches. Here, we consolidate key findings from the research in the context of current literature and understanding, with a focus on a well‐validated, multiphase multicomponent modeling approach to achieve estimates of reasonable endpoints for LNAPL recovery. Simple analytical models can provide approximate saturation distributions and estimates of LNAPL recoverability via transmissivity approximation, but are insufficient to predict LNAPL saturation‐ and composition‐based recovery endpoints for various recovery technologies. This is because they cannot account for multiphase, multicomponent fate and transport and key processes such as hysteresis. Recent advances to improve estimates of the fraction of recoverable LNAPL and its transmissivity are summarized. These advances include further development and application of a well‐validated model to characterize active LNAPL recovery endpoints. We present key factors that affect the determination of LNAPL recovery endpoints, and outline how recovery endpoints are affected by natural source zone depletion (NSZD—currently gaining acceptance as a LNAPL remediation option). Major factors include geo‐physical characteristics of the formation, magnitude of an LNAPL release and partitioning properties of the key LNAPL constituents of concern. Based on the capabilities of the validated model, the paper also provides a basis to optimize LNAPL recovery efforts.

Interdiffusion and diffusion paths in two-phase γ+β|γ+β diffusion couples. Comparison of experimental investigation with theoretical predictions

The first-ever experimental results concerning the interdiffusion in the two-phase, γ+β region of the ternary system are presented, together with the theoretical interpretation of the observed phenomena. In the experimental part of the study, a number of two-phase diffusion couples made from cast Ni-Cr-Al alloys was studied at 1200 °C. The application of the novel wide-line Energy-dispersive X-ray Spectroscopy (WL-EDS) allowed for previously impossible quantitative measurements of the concentration profiles within the two-phase zones. The measured profiles, together with the determined diffusion paths, were compared to the results of the simulations performed with the use of two different models: the Engstrӧm et al. model (DICTRA) and multi-component multi-phase model. The results allowed verifying the existence of a number of previously postulated features typical for the multi-phase diffusion. The comparison of the experimental and simulated results confirms that the currently used theoretical models of the interdiffusion process enable a satisfactory description of the real process. Still, some of the observed features cannot be interpreted in the light of available theory, although some of them are likely caused by the non-uniform cast microstructures. The better agreement with the experimental data obtained with the use of multi-multi model suggests that the interdiffusion should be considered simultaneously in all phases present in the system.

A Comprehensive Modeling as a Tool for Developing New Mini Blast Furnace Technologies Based on Biomass and Hydrogen Operation

The mini blast furnace based on biomass operation is a viable technology that neutralizes fossil carbon emissions in the production route of green hot metal. In this study, we analyze the actual mini blast furnace operation and propose new operational practices using the multiphase multicomponent modeling approach. We newly introduced additional chemical species and rate equations to account for the proposed new simulated scenarios. The model results for actual operation are favorably compared with the industrial data. Thus, new promising operational techniques based on high rates of pulverized charcoal and hot hydrogen injections are proposed and analyzed from the point of view of the process efficiency and carbon intensity. It is demonstrated that the combined operational conditions of higher pulverized charcoal and hot hydrogen injection furnish the best performance for cleaner hot metal production with the lowest carbon intensity.

Multicomponent multiphase modeling of dissimilar laser cladding process with high-speed steel on medium carbon steel

During a laser cladding process, the transport phenomena in the molten pool, including rapid solidification, strong fluid convection, and species diffusion are complex, and determine the microstructure and composition of the cladding layer. In this study, a three-dimensional transient multicomponent multiphase model was proposed to simulate the dissimilar laser cladding process with T15 powder and T15/CeO2 mixed powder on 42CrMo substrate. The position and expression of the source terms on energy and mass were clearly defined. The model was validated by comparing the morphology of the cross section with single-track cladding experiments. The simulation results indicate that the molten pool is dominated by a strong Marangoni flow that results in a fully mixed cladding layer and a narrow transition zone at the bottom. The molten pool exhibits an inward flow pattern with pure T15 powder and an outward flow pattern with T15-CeO2 mixed powder. The content of the elements and the microstructure of the cladding layer were investigated by using an electron probe micro-analyzer and a scanning electron microscope. The microstructure evolves from planar to cellular, and to equiaxed dendrites from the substrate–clad interface to the top surface. The transition zone comprised of planar and cellular grains. The solidification characteristics calculated from the numerical model were associated to the grain morphology.

Lattice Boltzmann modeling and experimental study of water droplet spreading on wedge-shaped pattern surface

Water droplet on wedge-shaped pattern surface with hydrophilic and hydrophobic regions can spread spontaneously in a specific direction. In this study, we investigated the mechanism of the surface tension-driven spontaneous drop spreading behaviors by the lattice Boltzmann modeling and experimental validation. Based on the Shan-Chen (SC) type multicomponent multiphase model with an algorithm for relatively accurate contact angle measuring, we simulated four cases with various vertex angles (ψ = 15°, 20°, 28°, 35°) of wedge-shaped pattern. After then, such surfaces were fabricated and corresponding experiments were conducted. The time dependence of the droplet move distance was characterized in both the simulations and experiments with average deviation within 6.11%. Related force contour and vector analyses were presented to discuss the driving mechanism. This study is expected to shed light on the physical exploration and provide insightful hints to better tune and control the directional spreading of the surface tension-driven droplet.

A multiphase multicomponent modeling approach of underground salt cavern storage

In the current energy transition context, large-scale underground facilities, such as salt caverns, able to deliver high flow rates, represent the most promising viable massive energy storage system that can respond efficiently to the flexibility needs of the renewable energy.In order to predict the performances of these facilities, while ensuring a high safety level over long time periods, the reservoir behavior must be studied by higher accuracy approaches. Based on a multiphase multicomponent approach, a cavern thermodynamic model, that can be used in field applications, is derived for this purpose. Particular attention is given to salt caverns where the stored fluid can be in contact with the brine. All the balance equations that govern the well that connects the cavern to the ground surface and the surrounding formation are presented. An illustrative example, showing the necessity of taking into account the thermo-mechanical aspects when considering the cavern thermodynamic behavior under cyclic loading conditions, is also discussed.

Three-Dimensional Simulation of Macrosegregation in a 36-Ton Steel Ingot Using a Multicomponent Multiphase Model

A multicomponent multiphase solidification model has been developed to predict macrosegregation of steel ingots in three dimensions. The interpenetrating continua of liquid melt and solid grains is coupled with air for the mass, momentum, concentration, and heat transfer. Interfacial solute constraint relationships are derived to close the model by solving the solidification paths of multicomponent alloy. The upward unidirectional solidification case of a ternary Al-6.0 wt.%Cu-1.0 wt.%Si alloy is taken as a basic validation. Predictions have well captured the inverse segregation profiles induced by shrinkage during solidification. Then, the model is applied to a 36-ton steel ingot, which was experimentally investigated by temperature recording and concentration analysis. Predictions have reproduced the macrosegregation patterns in the measurements. Confidence levels of current predictions compared to the concentration measurements have been presented. General good agreements are exhibited in quantitative comparisons between measurements and predictions of carbon and sulfur variations along selected positions.

A numerical model for the fractional condensation of pyrolysis vapours

Experimentation on the fast pyrolysis process has been primarily focused on the pyrolysis reactor itself, with less emphasis given to the liquid collection system (LCS). More importantly, the physics behind the vapour condensation process in LCSs has not been thoroughly researched mainly due to the complexity of the phenomena involved. The present work focusses on providing detailed information of the condensation process within the LCS, which consists of a water cooled indirect contact condenser. In an effort to understand the mass transfer phenomena within the LCS, a numerical simulation was performed using the Eulerian approach. A multiphase multi-component model, with the condensable vapours and non-condensable gases as the gaseous phase and the condensed bio-oil as the liquid phase, has been created. Species transport modelling has been used to capture the detailed physical phenomena of 11 major compounds present in the pyrolysis vapours. The development of the condensation model relies on the saturation pressures of the individual compounds based on the corresponding states correlations and assuming that the pyrolysis vapours form an ideal mixture. After the numerical analysis, results showed that different species condense at different times and at different rates. In this simulation, acidic components like acetic acid and formic acids were not condensed as it was also evident in experimental works, were the pH value of the condensed oil is higher than subsequent stages. In the future, the current computational model can provide significant aid in the design and optimization of different types of LCSs.

Analysis by multiphase multicomponent model of iron ore sintering based on alternative steelworks gaseous fuels

This paper presents the numerical simulation of the technology of gaseous fuel utilisation for iron ore sintering. The proposed methodology is to partially replace the solid fuel by steelworks gases. A multiphase mathematical model based on transport equations of momentum, energy and chemical species coupled with chemical reaction and phase transformations was proposed to analyse temperature distributions of the process. A base case of actual industrial operation of a large sintering machine was monitored with thermocouples inserted into the sinter bed to validate the model. The model was used to predict four cases of fuel gas utilisation: feeding from N01 to N15 wind boxes with blast furnace gas (BFG); natural gas (NG); coke oven gas (COG); and a 50–50 mixture of BFG and COG. The model predictions indicated that for all cases the sintering zone is enlarged and the solid fuel consumption could be decreased.

Phase-field model with finite interface dissipation: Extension to multi-component multi-phase alloys

A previously developed phase-field model with finite interface dissipation for binary dual-phase alloys out of chemical equilibrium is generalized to a multi-component multi-phase model in the framework of the multi-phase-field formalism, allowing the description of multiple junctions with an arbitrary number of phases and components. In multiple junctions, each phase concentration is assigned to a dynamic equation to account for finite interface dissipation, and its formulation is proposed in two different models. The overall mass conservation between the phases of a multiple junction is used in model I, whereas the concentrations of each pair of phases have to be conserved during the transformations for model II. Both models demonstrate the decomposition of the nonlinear interactions between different phases into pairwise interaction of phases in multiple junctions. They converge to the same equilibrium state while in non-equilibrium states different predictions are given.

A modified pseudopotential for a lattice Boltzmann simulation of bubbly flow

The pseudopotential in Shan and Chen-type multiphase models was investigated and modified based on a virial equation of state with newly proposed parameters. This modified pseudopotential was used in a lattice Boltzmann model and shown to be suitable for simulating sufficiently large gas–liquid density ratios with good numerical stability and only small spurious velocities. The spurious velocity was reduced by reducing the pseudo-sound speed by the use of suitable parameters. The multicomponent multiphase model based on this modified pseudopotential can be used in bubbly flow simulations. Bubble rise behavior was simulated using a 3D multicomponent and multiphase model with a high density ratio. The predicted terminal velocity and drag coefficient of a single bubble agreed well with those calculated from empirical correlations. The drag coefficient of bubbles in the homogenous regime decreased with increased gas holdup. A new relationship between the bubble drag coefficient and gas holdup in the homogenous regime was proposed.

A multi-objective optimization framework for surfactant-enhanced remediation of DNAPL contaminations

The occurrence of Dense Non-Aqueous Phase Liquid (DNAPL) contaminations in the subsurface is a threat for drinkwater resources in the western world. Surfactant-Enhanced Aquifer Remediation (SEAR) is widely considered as one of the most promising techniques to remediate DNAPL contaminations in-situ, be it with considerable additional costs compared to classical pump-and-treat remediations. A cost-effective design of the remediation set-up is therefore essential. In this work, a pilot SEAR test is executed at a DNAPL contaminated site in Belgium in order to collect data for the calibration of a multi-phase multi-component model. The calibrated model is used to assess a series of scenario-analyses for the full-scale remediation of the site. The remediation variables that were varied were the injection and extraction rate, the injection and extraction duration, and the surfactant injection concentrations. A constrained multi-objective optimization of the model was applied to obtain a Pareto set of optimal remediation strategies with different weights for the two objectives of the remediation: (i) the maximal removal of DNAPL and (ii) a total minimal cost. These Pareto curves can help decision makers to select an optimal remediation strategy in terms of cost and remediation efficiency. The Pareto front shows a considerable trade-off between the total remediation cost and the removed DNAPL mass.

A Fuzzy-Set Approach for Addressing Uncertainties in Risk Assessment of Hydrocarbon-Contaminated Site

This study presented an integrated approach for evaluating environmental risks associated with hydrocarbon-contaminated sites through incorporation of a multiphase multi-component modeling system within a general risk assessment framework. The uncertainties associated with risk evaluation criteria were emphasized and effectively addressed through the development of a fuzzy-set approach. This development was based on (a) simulation of the fate of the contaminant in the subsurface to calculate contaminant concentrations in groundwater; (b) examination of the excess lifetime cancer risk (ELCR) distributions; (c) quantification of uncertainties in ELCR evaluation criteria using fuzzy membership functions; (d) categorization of the related risk levels into low, low-to-medium, medium, medium-to-high, and high, and (e) assessment of risk levels based on ELCR distribution and fuzzy evaluation criteria. The developed fuzzy risk assessment approach (FRA) was applied to a hydrocarbon-contaminated site in western Canada. Three remediation scenarios with different efficiencies (0, 60, and 90%) and planning periods (10, 20, 40, and 60 years later) were considered, and the spatial and temporal variations of risk values were examined. The temporal variation of membership values for different risk levels at locations of interest was also identified. The FRA is useful for the decision maker to gain insight into the environmental risks by considering uncertainties and to make more realistic remediation decisions.

Simulation-based risk assessment of contaminated sites under remediation scenarios, planning periods, and land-use patterns—a Canadian case study

Risk assessment of contaminated sites is crucial for quantifying adverse impacts on human health and the environment. It also provides effective decision support for remediation and management of such sites. This study presents an integrated approach for environmental and health risk assessment of subsurface contamination through the incorporation of a multiphase multicomponent modeling system within a general risk assessment framework. The method is applied to a petroleum-contaminated site in western Canada. Three remediation scenarios with different efficiencies (0, 60, and 90%) and planning periods (10, 20, 40, 60, and 80 years later) are examined for each of the five potential land-use plans of the study site. Then three risky zones with different temporal and spatial distributions are identified based on the local environmental guidelines and the excess lifetime cancer risk criteria. The obtained results are useful for assessing potential human health effects when the groundwater is used for drinking water supply. They are also critical for evaluating environmental impacts when the groundwater is used for irrigation, stockbreeding, fish culture, or when the site remains the status quo. Moreover, the results indicate that the proposed method can effectively identify risky zones with different risk levels under various remediation actions, planning periods, and land-use patterns.

AN INTEGRATED DECISION SUPPORT SYSTEM FOR THE MANAGEMENT OF PETROLEUM-CONTAMINATED SITES

In this study, a decision-support system was developed for providing environmental managers with an integrated way for concisely analyzing and visualizing the subsurface contamination problem as well as a means for evaluating alternative remediation technologies. It integrated contaminant-transport modeling, risk assessment, and remediation-system design within a general framework. The developed system was applied to a site in western Canada that is contaminated by petroleum products. A three-dimensional multiphase multicomponent model was established, which provided a basis for further risk assessment. Several approaches based on different environmental guidelines were used to analyze risks due to the site contamination. The results suggested the urgency of taking remediation actions. Six remedial alternatives for cleaning up the site were recommended. Decisions could then be made based on a series of analyses and comparisons among the given alternatives.