Comparison of Reduced and Conventional Two-Phase Flash Calculations

SPE Journal ◽  
2014 ◽  
Vol 20 (02) ◽  
pp. 294-305 ◽  
Author(s):  
S.E.. E. Gorucu ◽  
R.T.. T. Johns
Keyword(s):  
Variable Number ◽  
Binary Interaction ◽  
Binary Interaction Parameter ◽  
Computational Time ◽  
Compositional Simulation ◽  
Two Phase ◽  
Number Of Components ◽  
Speed Up ◽  
Conventional Methods ◽  
Two Parameter

Summary Phase-equilibrium calculations become computationally intensive in compositional simulation as the number of components and phases increases. Reduced methods were developed to address this problem, where the binary-interaction-parameter (BIP) matrix is approximated either by spectral decomposition (SD), as performed by Hendriks and van Bergen (1992), or with the two-parameter BIP formula of Li and Johns (2006). Several authors have recently stated that the SD method—and by reference all reduced methods—is not as fast as previously reported in the literature. In this paper we present the first study that compares all eight reduced and conventional methods published to date by use of optimized code and compilers. The results show that the SD method and its variants are not as fast as other reduced methods, and can be slower than the conventional approach when fewer than 10 components are used. These conclusions confirm the findings of recently published papers. The reason for the slow speed is the requirement that the code must allow for a variable number of eigenvalues. We show that the reduced method of Li and Johns (2006) and its variants, however, are faster because the number of reduced parameters is fixed to six, which is independent of the number of components. Speed up in flash calculations for their formula is achieved for all fluids studied when more than six components are used. For example, for 10-component fluids, a speed up of 2–3 in the computational time for Newton-Raphson (NR) iterations is obtained compared with the conventional method modeled after minimization of Gibbs energy. The reduced method modeled after the linearized approach of Nichita and Graciaa (2011), which uses the two-parameter BIP formula of Li and Johns (2006), is also demonstrated to have a significantly larger radius of convergence than other reduced and conventional methods for five fluids studied.

Rapid Flash Calculations for Compositional Simulation

2006 ◽  
Vol 9 (05) ◽  
pp. 521-529 ◽  
Author(s):  
Yinghui Li ◽  
Russell T. Johns
Keyword(s):  
Computation Time ◽  
Binary Interaction ◽  
Computational Time ◽  
Compositional Simulation ◽  
New Approach ◽  
Number Of Components ◽  
Black Oil ◽  
Reduced Parameters ◽  
Fluid Characterization ◽  
Flash Calculation

Summary The computational time for conventional flash calculations increases significantly with the number of components, making it impractical for use in many fine-grid compositional simulations and other applications. Previous research to increase flash-calculation speed has been limited to those with zero binary interaction parameters (BIPs) or approximate methods based on an eigenvalue analysis of the binary interaction matrix. Practical flash calculations, however, nearly always have some nonzero BIPs. Further, the accuracy and speed of the eigenvalue methods varies depending on the choice and number of the dominant eigenvalues. This paper presents a new and simple method for significantly increasing the speed of flash calculations for any number of nonzero BIPs. The approach requires the solution of up to six reduced parameters regardless of fluid complexity or the number of components and is based on decomposing the BIPs into two parameters using a simple quadratic expression. The new approach is exact in that the equilibrium-phase compositions for the same BIPs are identical to those with the conventional flash calculation; no eigenvalue analysis is required. Further, the new approach eliminates the Rachford-Rice procedure (1952) and is more robust than the conventional flash-calculation procedure. We demonstrate the new approach for several example fluids and show that speedup by a factor of approximately 3 to 20 is obtained over conventional flash calculations, depending on the number of components. Introduction Gas injection into oil reservoirs results in complex interactions of flow with phase behavior that often are not modeled accurately by black-oil simulation. This is especially true for miscible or nearly miscible floods in which significant mass transfer occurs between the hydrocarbon phases. Such floods are best modeled by compositional simulation. A significant disadvantage of compositional simulation, however, is that it is much more computationally intensive than black-oil simulation. The primary reason for the increased computational time is the result of solving repeated flash calculations with cubic equations of state (EOS). Research has shown that EOS flash calculations can occupy 50 to 70% of total computational time in compositional simulations (Stenby and Wang 1993; Chang 1990). This is also true for other applications, such as multiphase flow in pipelines. The use of fewer pseudocomponents can reduce the flash computation time, but fewer components results in less accuracy (Hong 1982; Liu 2001; Egwuenu et al. 2005). This is especially true in multicontact miscible displacements, in which miscibility is developed by a combined condensing/vaporizing drive process (Zick 1986; Johns et al. 1993; Egwuenu et al. 2005). Fluid characterization by pseudocomponent models can be improved by tuning to the analytical minimum miscibility enrichment or minimum miscibility pressure (Johns et al. 1994), but those models still require significant computational time, even for fewer pseudocomponents. Another way to reduce computation time is to reduce the number of gridblocks. With coarse grids, however, numerical dispersion is large, which may cloud the results (Solano et al. 2001). Ideally, fine grids should be used that better match the level of dispersion found at the field scale. More recently, methods have been examined to find reduced parameters for flash calculations. Michelsen (1982a, 1982b, 1986) significantly increased flash-calculation speed by finding three reduced parameters, regardless of the number of components. His method, however, assumes zero BIPs, which is too restrictive for real fluid characterization. Michelsen also gave a practical method for stability calculations using the tangent plane distance (TPD) (Michelsen 1982b).

Three-Phase Flash in Compositional Simulation Using a Reduced Method

SPE Journal ◽  
2010 ◽  
Vol 15 (03) ◽  
pp. 689-703 ◽  
Author(s):  
R.. Okuno ◽  
R.T.. T. Johns ◽  
K.. Sepehrnoori
Keyword(s):  
Phase Equilibrium ◽  
Case Studies ◽  
Computational Time ◽  
Co2 Flooding ◽  
Compositional Simulation ◽  
Two Phase ◽  
Three Phase ◽  
Compositional Simulator ◽  
Complete Failure ◽  
Flash Calculation

Summary CO2 flooding at low temperatures often results in three or more hydrocarbon phases. Multiphase compositional simulation must simulate such gasfloods accurately. Drawbacks of modeling three hydrocarbon phases are the increased computational time and convergence problems associated with flash calculations. Use of a reduced method is a potential solution to these problems. We first demonstrate the importance of using three-phase flash calculations in compositional simulation by investigating difficulties with two-phase equilibrium approximations proposed in the literature. We then extend an algorithm for reduced two-phase flash calculations to three-phase calculations and show the efficiency and robustness of our algorithm. The reduced three-phase flash algorithm is implemented in a multiphase compositional simulator to demonstrate the speed-up and increased robustness of simulations in various case studies. Results show that use of a two-phase equilibrium approximation in reservoir simulation can result in a complete failure or erroneous simulation results. Simulation case studies show that our reduced method can decrease computational time significantly without loss of accuracy. Computational time is reduced using our reduced method because of the smaller number of equations to be solved and increased timestep sizes. We show that a failure of a flash calculation leads directly to reduced timestep sizes using the UTCOMP simulator.

scholarly journals Modelling Sorption Thermodynamics and Mass Transport of n-Hexane in a Propylene-Ethylene Elastomer

Polymers ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1157
Author(s):  
Daniele Tammaro ◽  
Lorenzo Lombardi ◽  
Giuseppe Scherillo ◽  
Ernesto Di Maio ◽  
Navanshu Ahuja ◽  
...  
Keyword(s):  
Mass Transport ◽  
Interaction Parameter ◽  
Sorption Isotherms ◽  
Binary Interaction ◽  
Binary Interaction Parameter ◽  
Theoretical Interpretation ◽  
Sorption Behavior ◽  
Solvent Mixtures ◽  
Random Lattice ◽  
Hexane Vapor

Optimization of post polymerization processes of polyolefin elastomers (POE) involving solvents is of considerable industrial interest. To this aim, experimental determination and theoretical interpretation of the thermodynamics and mass transport properties of POE-solvent mixtures is relevant. Sorption behavior of n-hexane vapor in a commercial propylene-ethylene elastomer (V8880 VistamaxxTM from ExxonMobil, Machelen, Belgium) is addressed here, determining experimentally the sorption isotherms at temperatures ranging from 115 to 140 °C and pressure values of n-hexane vapor up to 1 atm. Sorption isotherms have been interpreted using a Non Random Lattice Fluid (NRLF) Equation of State model retrieving, from data fitting, the value of the binary interaction parameter for the n-hexane/V8880 system. Both the cases of temperature-independent and of temperature-dependent binary interaction parameter have been considered. Sorption kinetics was also investigated at different pressures and has been interpreted using a Fick’s model determining values of the mutual diffusivity as a function of temperature and of n-hexane/V8880 mixture composition. From these values, n-hexane intra-diffusion coefficient has been calculated interpreting its dependence on mixture concentration and temperature by a semi-empiric model based on free volume arguments.

Study on Expander-Auxiliary Compressor Unit Used in Refrigeration System

2011 ◽  
Vol 354-355 ◽  
pp. 811-818
Author(s):  
Tao He ◽  
Zhi Yuan Wang ◽  
Yu Qing Xue
Keyword(s):  
Energy Recovery ◽  
Rotation Speed ◽  
Cooling Capacity ◽  
Compressor Unit ◽  
Performance Parameters ◽  
Refrigeration System ◽  
Two Phase ◽  
Speed Up ◽  
Testing Condition ◽  
Auxiliary Unit

The throttling valve used in the refrigeration system always causes energy loss. In this paper, an energy recovery device in the refrigeration system which was composed of an expander-auxiliary compressor unit to replace the throttling valve was investigated. On the basis of thermodynamic analysis, two typical arrangements which the auxiliary compressor was connected to the main compressor of the refrigeration system were compared and the system performance parameters were discussed. A prototype of an expander-auxiliary unit was manufactured to observe the expander performance using R410A as refrigerant. The results showed the reliability of the unit working in the two-phase flow condition with the rotation speed up to 21020 rpm. And the maximum increases in the cooling capacity by 3.9% and COP by 3.2% could be obtained under the testing condition.

scholarly journals Parallel Algorithms for Spatial Rainfall Distribution

Jurnal INKOM ◽  
2014 ◽  
Vol 8 (1) ◽  
pp. 29 ◽  
Author(s):  
Arnida Lailatul Latifah ◽  
Adi Nurhadiyatna
Keyword(s):  
Parallel Algorithms ◽  
Computation Time ◽  
Computational Time ◽  
Rainfall Distribution ◽  
Flood Modelling ◽  
Computation Efficiency ◽  
Distance Weighting ◽  
Speed Up ◽  
Important Input ◽  
Serial Algorithms

This paper proposes parallel algorithms for precipitation of flood modelling, especially applied in spatial rainfall distribution. As an important input in flood modelling, spatial distribution of rainfall is always needed as a pre-conditioned model. In this paper two interpolation methods, Inverse distance weighting (IDW) and Ordinary kriging (OK) are discussed. Both are developed in parallel algorithms in order to reduce the computational time. To measure the computation efficiency, the performance of the parallel algorithms are compared to the serial algorithms for both methods. Findings indicate that: (1) the computation time of OK algorithm is up to 23% longer than IDW; (2) the computation time of OK and IDW algorithms is linearly increasing with the number of cells/ points; (3) the computation time of the parallel algorithms for both methods is exponentially decaying with the number of processors. The parallel algorithm of IDW gives a decay factor of 0.52, while OK gives 0.53; (4) The parallel algorithms perform near ideal speed-up.

IMPROVED FRACTAL IMAGE COMPRESSION BASED ON ROBUST FEATURE DESCRIPTORS

2011 ◽  
Vol 11 (04) ◽  
pp. 571-587 ◽  
Author(s):  
WILLIAM ROBSON SCHWARTZ ◽  
HELIO PEDRINI
Keyword(s):  
Image Compression ◽  
Computational Cost ◽  
Computational Time ◽  
Natural Scenes ◽  
Fractal Image Compression ◽  
Fractal Image ◽  
Feature Descriptors ◽  
High Compression ◽  
Speed Up ◽  
Computationally Intensive

Fractal image compression is one of the most promising techniques for image compression due to advantages such as resolution independence and fast decompression. It exploits the fact that natural scenes present self-similarity to remove redundancy and obtain high compression rates with smaller quality degradation compared to traditional compression methods. The main drawback of fractal compression is its computationally intensive encoding process, due to the need for searching regions with high similarity in the image. Several approaches have been developed to reduce the computational cost to locate similar regions. In this work, we propose a method based on robust feature descriptors to speed up the encoding time. The use of robust features provides more discriminative and representative information for regions of the image. When the regions are better represented, the search for similar parts of the image can be reduced to focus only on the most likely matching candidates, which leads to reduction on the computational time. Our experimental results show that the use of robust feature descriptors reduces the encoding time while keeping high compression rates and reconstruction quality.

Influence of Equation-of-States on Supercritical CO2 Combustion

2020 ◽  
Author(s):  
K. R. V. (Raghu) Manikantachari ◽  
Scott M. Martin ◽  
Ramees K. Rahman ◽  
Carlos Velez ◽  
Subith S. Vasu
Keyword(s):  
Supercritical Co2 ◽  
Carbon Capture ◽  
Flame Structure ◽  
Compressibility Factor ◽  
Operating Conditions ◽  
Binary Interaction ◽  
Binary Interaction Parameter ◽  
Combustion Modeling ◽  
Equation Of States ◽  
Supercritical Combustion

Abstract Fossil fuel based direct-fired supercritical CO2 (sCO2) cycles are gaining the attention of industry, academia and government due to their remarkable efficiency and carbon capture at high-source temperatures. Modeling plays an important role in the development of sCO2 combustors because experiments are very expensive at the designed operating conditions of these direct-fired cycles. Inaccurate density estimates are detrimental to the simulation output. Hence, this work focuses on comprehensive evaluation of the influence and applicability various equation-of-states (EOS) which are being used in the supercritical combustion modeling literature. A state-of-the-art supercritical combustion modeling methodology is used to simulate counter-flow supercritical CO2 flames by using various equation-of-states. The results show that, using the corresponding state principle to evaluate compressibility factor is not accurate. Also, van der Waal type EOSs predictions can be as accurate as complex Benedict-Webb-Rubin EOSs; hence van der Waal EOSs are more suitable to simulate sCO2 combustor simulations. Non-ideal effects are significant under the operating conditions considered in this work. The choice of EOS significantly influences the flame structure and heat release rate. Also, assuming the binary interaction parameter as zero is reasonable in sCO2 combustion simulations.

Phase Behavior and Physical Properties of Dimethyl Ether/Water/Heavy-Oil Systems Under Reservoir Conditions

SPE Journal ◽  
2021 ◽  
pp. 1-17
Author(s):  
Desheng Huang ◽  
Ruixue Li ◽  
Daoyong Yang
Keyword(s):  
Physical Properties ◽  
Phase Behavior ◽  
Dimethyl Ether ◽  
Heavy Oil ◽  
Partition Coefficients ◽  
Binary Interaction ◽  
Binary Interaction Parameter ◽  
Translation Strategy ◽  
Wide Range ◽  
Oil Mixtures

Summary Phase behavior and physical properties including saturation pressures, swelling factors (SFs), phase volumes, dimethyl ether (DME) partition coefficients, and DME solubility for heavy-oil mixtures containing polar substances have been experimentally and theoretically determined. Experimentally, novel phase behavior experiments of DME/water/heavy-oil mixtures spanning a wide range of pressures and temperatures have been conducted. More specifically, a total of five pressure/volume/temperature (PVT) experiments consisting of two tests of DME/heavy-oil mixtures and three tests of DME/water/heavy-oil mixtures have been performed to measure saturation pressures, phase volumes, and SFs. Theoretically, the modified Peng-Robinson equation of state (EOS) (PR EOS) together with the Huron-Vidal mixing rule, as well as the Péneloux et al. (1982)volume-translation strategy, is adopted to perform phase-equilibrium calculations. The binary-interaction parameter (BIP) between the DME/heavy-oil pair, which is obtained by matching the measured saturation pressures of DME/heavy-oil mixtures, works well for DME/heavy-oil mixtures in the presence and absence of water. The new model developed in this work is capable of accurately reproducing the experimentally measured multiphase boundaries, phase volumes, and SFs for the aforementioned mixtures with the root-mean-squared relative error (RMSRE) of 3.92, 9.40, and 0.92%, respectively, while it can also be used to determine DME partition coefficients and DME solubility for DME/water/heavy-oil systems.

scholarly journals Illustrative Case Study on the Performance and Optimization of Proton Exchange Membrane Fuel Cell

2019 ◽  
Vol 3 (1) ◽  
pp. 23 ◽  
Author(s):  
Yuan Yuan ◽  
Zhiguo Qu ◽  
Wenkai Wang ◽  
Guofu Ren ◽  
Baobao Hu
Keyword(s):  
Proton Exchange Membrane ◽  
Proton Exchange ◽  
Cell Performance ◽  
Computational Time ◽  
Oxygen Stoichiometry ◽  
Illustrative Case ◽  
Membrane Thickness ◽  
Two Phase ◽  
Process Gas ◽  
Exchange Membrane

Modeling is a powerful tool for the design and development of proton exchange membrane fuel cells (PEMFCs). This study presents a one-dimensional, two-phase mathematical model of PEMFC to investigate the two-phase transport process, gas species transport flow and water crossover fluxes. The model reduces the computational time for PEMFC design with guaranteed accuracy. Analysis results show that the concentration and activation overpotentials of the cell decrease with the increase of operation pressure, which result in enhanced cell performance. Proper oxygen stoichiometry ratio in the cathode decreases the cell activation overpotential and is favorable for performance improvement. The cell ohmic resistance correspondingly increases with the increase of catalyst layer thickness, which leads to a deteriorated cell performance. The improvement on cell performance could be facilitated by decreasing the membrane thickness. Predicted results show that the present model is a useful tool for the design optimization of practical PEMFCs.

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