133 research outputs found
Thermodynamic Properties of 1:1 Salt Aqueous Solutions with the Electrolattice Equation of State Propriétés thermophysiques des solutions aqueuses de sels 1:1 avec l’équation d’état de réseau pour électrolytes
No full textThe electrolattice Equation of State (EOS) is a model that extends the MattediTavares-Castier EOS (MTC EOS) to systems with electrolytes. This model considers the effect of three terms. The first one is based on a lattice-hole model that considers local composition effects derived in the context of the generalized Van der Waals theory: the MTC EOS was chosen for this term. The second and the third terms are the Born and the MSA contributions, which take into account ion charging and discharging and long-range ionic interactions, respectively. Depending only on two energy interaction parameters, the model represents satisfactorily the vapor pressure and the mean ionic activity coefficient data of single aqueous solutions containing LiCI, LiBr, LiI, NaCl, NaBr, NaI, KCl, KBr, KI, CsCl, CsBr, CsI, or RbCI. Two methods are presented and contrasted: the salt-specific and the ion-specific approaches. Therefore, the aim of this work is to calculate thermodynamic properties that are extensively used to design, operate and optimize many industrial processes, including water desalination. L’équation d’état, dite électrolattice, est un modèle qui étend l’équation d’état de Mattedi-Tavares-Castier à des systèmes avec électrolytes. Ce modèle prend en compte l’effet de trois termes. Le premier terme est basé sur les trous dans le réseau en considérant les effets de la composition locale, étude effectuée dans le cadre de la théorie généralisée de Van der Waals : l’équation d’état de Mattedi-Tavares-Castier a été choisie pour ce premier terme. Les deuxième et troisième termes sont les contributions de Born et du MSA. Ils tiennent compte du chargement et du déchargement des ions, et des interactions ioniques à longue distance, respectivement. Le modèle n’ayant besoin que de deux paramètres d’interaction énergétique, il modélise de manière satisfaisante la pression de vapeur et le coefficient d’activité ionique moyenne pour des solutions aqueuses simples contenant du LiC1, LiBr, LiI, NaC1, NaBr, NaI, KC1, KBr, KI, CsCl, CsBr, CsI, ou du RbC1. Deux méthodes pour obtenir les paramètres du modèle sont présentées et mises en contraste : une méthode spécifique pour le sel en question et une autre basée sur les ions. Par conséquent, l’objectif de ce travail est de calculer les propriétés thermophysiques qui sont largement utilisées pour la conception, l���exploitation et l’optimisation de nombreux procédés industriels, parmi eux le dessalement de l’eau
Techno-Economic Analysis of Full-Scale Pressure Retarded Osmosis Plants
No full textPressure retarded osmosis (PRO) is a power generation process that harnesses the salinity gradient between two bodies of water. In literature, the most dominant example of this type of energy is from the mixing of sea water and river water. However, as the first pilot plant of this type proved, this pair is not sufficient to generate enough energy to offset the cost of generation and is unfeasible economically.
This work aims to assess the techno-economic feasibility of both single stage and multistage PRO design configurations using hypersaline solution (as Draw) and Seawater (as feed). The hypersaline draw of focus is produced water which is obtained from oil and gas reservoirs. For this work, a PRO simulator is used, which was developed at Texas A&M University at Qatar. It uses the Q-electrolattice Equation of State (EoS) and a mass transfer model to determine equipment parameters, pump and turbine powers as well as stream properties of interest. This work extends the capabilities of the simulator to handle economic calculations as well as the decision-making criteria that points to profitability or lack thereof. Its capabilities were also extended to interface with DAKOTA ��� a tool to aid in sensitivity analysis and mathematical optimization.
Using Levelized Cost of Electricity (LCOE) as the techno-economic parameter of interest, this work shows that energetic and economic optimum occur at different system conditions, quantifies the effect of membrane nonidealities on LCOE, shows the optimal plant dimensions and system conditions to operate a PRO plant using both ideal and real membranes and compares PRO to other renewable energy technologies. It also shows results of the energetic and economic performance of multistage systems
ANALYSIS AND VALIDATION OF INTEGRAL POOL SPREADING MODELS OF LNG SPILLS ON CONCRETE
No full textWhen a loss of primary containment of liquefied natural gas (LNG) occurs on the ground, a pool, that simultaneously spreads and vaporizes, is formed posing cryogenic, asphyxiating, and flammable hazards to its surrounding. Determining the pool size and vapor generation upon release play key roles in the accuracy of dispersion and consequence models. This work focuses on expanding the available data to be used for LNG source term model validation through the evaluation of an existing model.
A field-scale experimental setup was designed to study the pool temperature, pool spreading and heat flux under the concrete, after a release. In this work, liquid nitrogen (LNv2) was used as a safer analogue to LNG as it is a non-toxic non-flammable cryogen. The experiments were carried out inside a 6��5��1.2 m pit. A vaporizing pool spreading model based on Gas Accumulation over a Spreading Pool (GASP) was then implemented and used to predict the vaporization and pool spreading rates of the spill. Finally, the model predictions were compared to the experimental data.
The results of this work gave insight to the validity of two existing source term models, the coupling of a pool spreading model with Fourier���s one-dimensional conduction heat transfer model. While the first model assumes that heat flux is uniform across the pool, the second model takes into account higher heat transfer due to exposure time difference between the outer rings of the pool to the center of the pool during pool spreading. Both models assume that the pool boils until it completely vaporizes. Experimental results indicate that the pool does boil until it completely vaporizes, and that the temperature at the center of the substrate was cooler than its outer parts. It was found that the model which accounts for higher heat transfer in the pool outer rings tends to underestimate pool size. Both models, however, overestimate the pool size at the early stages of the spill. As both models incorporate a solution of Fourier���s one-dimensional conduction equation, a comparison was also done between the predicted and experimental temperature
An Investigation of Using Isochoric Data Points in the Development of Natural Gas Equation of State
No full textAccess to energy is essential for the survival of humans, and the need for energy rises continuously because of population increase and economic progress. Fossil fuels continue to play the major role in satisfying energy demand. Among the fossil fuels, natural gas is the cleanest, most available, and most useful of the energy sources. It finds extensive use in residential, commercial, electric power generation and industrial applications. Moreover, the international energy outlook report released in 2011 indicates that yearly world natural gas consumption should increase from 111 trillion cubic feet in 2008 to 169 trillion cubic feet in 2035. Recently, new natural gas reservoirs have been discovered in many places throughout the world. In 2012, the total world supplies of proved natural gas reserves were estimated to be 6,746.8 trillion cubic feet. Thus, studies on natural gas are significant to advance the technique of natural gas processing, transportation and storage. In these three sectors, an accurate knowledge of the thermodynamic properties of natural gas is essential for engineering and technical processes. Developing accurate equations of state is important, and can provide us with accurate thermodynamic properties for natural gas. In addition, developing new techniques to produce mathematical models is important to create more accurate results and to enrich this field with new ideas, which might provide progress in the future. The aim of this thesis is to demonstrate a new approach for developing an equation of state.
This technique relies upon isochoric data of carbon dioxide pure component to develop mathematical models. This thesis contains nine models based upon experimental and generated data. The generated data come from REFPROP, which also provides an accurate means to adjust experimental data to true isochores. Within this thesis, a regression analysis was performed - using Polymath 6.1 - to provide mathematical structure of the equation for carbon dioxide. Results indicate that models covering vapor phase has less deviation than models covering liquid or both phases, and models developed by the generated data has less deviation than models developed by the experimental data. The deviation obtained by most of the models was less than the random error imposed upon the data. In this study, we conclude that modeling an equation of state from isochores appears to provide sufficient advantages to encourage additional studies on pure fluids and multi-component mixtures
AVALIAÇÃO DA EdE MATTEDI-TAVARES-CASTIER (MTC) PARA A DESCRIÇÃO DE DENSIDADE, PRESSÃO DE VAPOR E VELOCIDADE DO SOM DE HIDROCARBONETOS
No full textPrediction of the Three-Phase Coexistence Conditions of Pure Methane and Carbon Dioxide Hydrates Using Molecular Dynamics Simulations
No full textClathrate hydrates are solid crystals that consist of three-dimensional networks of hydrogen-bonded water molecules forming well-defined cages within which small ���guest��� molecules are needed in order to stabilize the structures. More than 130 different molecules can form hydrates when mixed with water at relatively low temperatures and high pressures, including methane, ethane, propane, iso-butane, carbon dioxide, nitrogen and hydrogen. The accurate prediction of thermodynamic properties of clathrate hydrates has gained much attention due to the relevance of clathrate hydrates to many industrial applications. For example, hydrates play a major role in the problem of flow assurance in the oil and gas industry. They are also being considered for use in gas transport and separation applications. In addition, the existence of methane hydrates in large quantities in nature makes them a potential energy source.
In this work, Molecular Dynamics (MD) simulations have been used in order to determine the Hydrate ��� Liquid water ��� Guest coexistence line for methane and carbon dioxide hydrates. The direct phase coexistence method was used where slabs of the three constituent phases were separately equilibrated and then brought in contact at the conditions under investigation. In order to account for the stochastic nature of the hydrate growth and dissociation processes, many long, independent simulations at different conditions of temperature and pressure were conducted while avoiding bubble formation phenomena. This allowed for performing a statistical averaging of the results to identify the three-phase coexistence temperature at different pressures. Also, the erroneous use of dispersion tail corrections was investigated.
For methane hydrates, where the Lorentz-Berthelot combining rules for the two force fields used gave accurate predictions for the solubility of methane in the aqueous phase, this approach yielded predictions that are in good agreement with experimental data. A correction to the Lorentz-Berthelot cross-interaction energy parameter was applied in the case of carbon dioxide hydrates to obtain accurate predictions of the solubility of carbon dioxide in the aqueous phase, which in turn resulted in equally accurate and consistent predictions of the three-phase coexistence temperature. Therefore, it was shown that both the water-water and water-guest interactions play an important role in the application of this methodology to the study of clathrate hydrate systems. For systems where the water-guest interactions can accurately predict guest solubility in water, the predictions of the three-phase coexistence are as accurate as the water force field used to predict the melting of ice.
It was also shown that the methodology cannot be directly applied to low pressures for carbon dioxide hydrates, where a liquid-like layer of carbon dioxide is adsorbed at the water surface. Several possible causes for this deficiency are suggested, including the possible effect of box anisotropy and box size fluctuations at low pressures
Development of a Thermodynamic Model for Fluids Confined in Spherical Pores
No full textThe thermodynamic properties of a fluid confined in extremely small pores can be substantially different from those observed of the same bulk fluid. These differences in behavior could have technical applications in adsorption-based separations; may pose a challenge with regards to the extraction of oil entrapped in the small cavities of reservoir rocks; or could even be utilized in complex heterogeneous catalytic systems such as those used in gas-to liquid fuel conversions.
This thesis describes the use of the generalized van der Waals theory to extend cubic equations of state, such as Peng-Robinson, that are widely applied in the oil and gas industry to model the behavior of pure fluids as well as mixtures confined in spherical pores. Empirical expressions were developed for the coordination number in spherical pores as a function of the molecule to pore size ratio, for the distribution of molecules along the pore radius as function of temperature, and of the interaction potential between the molecules and the pore wall. Despite their relative simplicity, the expressions capture the limiting behaviors expected at high and low temperatures. The model parameters were then fitted to experimental data for the adsorption of light hydrocarbons and gases in common adsorbents. Finally, the calculated results were compared to the experimental results in order to assess the performance of the model, through adsorption equilibrium calculations
Modeling Fischer-Tropsch Product Distribution of a Cobalt Based Catalyst in Different Reaction Media
No full textThis work discusses the modeling of hydrocarbon product distribution up to carbon number 15 of a cobalt-based catalyst under Fischer-Tropsch (FT) synthesis conditions. The proposed kinetics of the reaction has been adapted from Todic et al. In the first part of the study, a Genetic Algorithm code in MATLAB�� was developed to generate parameters of the 19-parameter kinetic model. In the next part of the work, an experimental campaign was conducted in a high pressure FT reactor unit to verify the model predictability of the cobalt catalyst product profile in gas phase. The results in terms of conversion and hydrocarbon product formations were reported. Less than 12% CO conversion was maintained in all 7 runs in order to ensure that the reaction was occurring in the kinetic regime. After the peak identification and analysis, the experimental data was input into the developed MATLAB�� code to estimate model parameters. This model estimates the FT product distribution in the gas phase media with a mean absolute relative residual (MARR) of 48.44%. This is higher than that obtained by Todic et al. The higher error is attributed to the fewer number of experimental runs carried out and due to some assumptions made in product characterization. This work lays the foundation for future work towards investigations of FT product distribution in the presence of a supercritical solvent to bring the reaction media to near critical and supercritical phase conditions
Multiphase Equilibrium of Fluids Confined in Fisher-Tropsch Catalytic Systems
No full textEnergy supply and security imposes a significant challenge in our modern world stemming from our dependence on depleting resources such as petroleum and oil. Fischer-Tropsch synthesis (FTS) is considered as a great energy alternative which can significantly reduce our dependence on oil, improve rural economics, reduce greenhouse emissions, and promise energy security. It is a key technology for converting syngas, produced from coal, biomass or natural gas, into a variety of hydrocarbon products. Although this technology was discovered in 1923, commercialization and scale up are limited to the use of few reactor configurations (e.g. multi-tubular fixed-bed reactor, Slurry-bubble column reactor, and fluidized bed reactors).
In order to improve the limitations in both reactor configurations, on lab scale near critical media was utilized, since it offers a great combination of the advantages of both the gas-phase reaction (multi-tubular fixed-bed reactor) and the liquid-phase reaction (slurry-bubble column reactor), while simultaneously overcoming their limitations. This work focuses on modeling the phase behavior of the FTS mixture in fixed bed reactor in the bulk phase inside the reactor bed or inter-particle and then zoom into the catalyst (confined phases within the catalyst pores or intra-particle). This is done by using an extended Peng-Robinson (PR) equation of state (EOS) that is capable of accounting for the fluid behavior inside confined pores as well as in the bulk phases.
The PR Equation of state model extended to confined fluid (PR-C) has been utilized in multiphase equilibrium algorithm using FORTRAN. The simulation results provide the composition and the condition of each bulk phase and pore phase for a given initial mixture. Two different scenarios were studied for fixed bed reactor: the first one is the conventional gas phase FTS and the second one is for the supercritical phase FTS (SCF-FTS). In each case, the phase behavior of the mixture of the reactants and products was investigated at different conversions along the bed length. The simultaneous assessment of both gas phase FTS and SCF-FTS phase behavior and reaction performance open the door for optimizing the design FTS reactor and enhance the efficiency of the process.
Preferential adsorption of hydrogen has been observed and this could be due to the small size of the hydrogen molecules compared to those of the other components. Our studies suggested that the supercritical phase provides superior heat dissipation due to the existence of denser phase in the bulk and the confined regions than the conventional gas phase. On the other hand in the gas phase and for limited carbon number (up to C8) the pore phase is found to be in a vapor state which should provide higher diffusivity of the reactant than that in the supercritical phase. Our study will continue by integrating the developed phase behavior studies in the reactor design model
Targeting Power Generation from Waste Heat Streams
No full textThe paper proposes two procedures to target thermodynamic power generation limits from a set of heat source streams. The first procedure takes the form of an algebraic targeting approach commonly applied in process heat integration. This procedure is based on fundamental thermodynamics laws and the Carnot cycle. The procedure allows the designer to quickly determine the maximum amount of power that can theoretically be generated from the available heat in thermodynamic cycles. The second procedure uses the Rankine cycle to determine the amount of power that can be generated using a real power generating cycle. The paper describes both procedures and their applicability in the context of common data availability for heat source streams in the form of Composite Curves or Total Site Profiles (hot composites) commonly developed in heat integration. The application of both procedures is illustrated with examples
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