An Efficient Method to Calculate Three-Phase Free-Water Flash for Water−Hydrocarbon Systems

and, Yiping Tang; Saha, Sanjoy Kumar

doi:10.1021/ie010785x

Cited by 20 publications

(21 citation statements)

References 18 publications

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“…In the free‐water assumption, we assume that water component can be present in all phases, while the non‐water components can be only dissolved in the non‐water‐rich phases. In other words, the water‐rich phase is assumed as pure water.…”

Section: Mathematical Formulationsmentioning

confidence: 93%

“…Equation refers to the “effective” equilibrium constants as defined by Tang and Saha . Combining Equations and gives the mole fractions of non‐water components in the non‐reference phases except the water‐rich phase:

y_{i j} = \frac{K_{i j} z_{i}}{1 + \sum_{j = 2}^{N_{p} - 1} (K_{i j} - 1 + \frac{y_{1 j} - x_{1}}{1 - x_{1}}) β_{j} + \frac{x_{1} - z_{1}}{1 - x_{1}}} = \frac{K_{i j} z_{i}}{\sum_{j = 2}^{N_{p} - 1} (K_{i j} - K_{w j}^{*}) β_{j} + K_{w z}^{*}}, i \neq 1, j \neq 1

…”

Section: Mathematical Formulationsmentioning

confidence: 93%

“…where K represents the equilibrium ratio; f represents the fugacity coefficient; x and y are the mole fractions in the reference phase and the non-reference phase, respectively. In the free-water assumption, [15] we assume that water component can be present in all phases, while the non-water components can be only dissolved in the non-water-rich phases. In other words, the water-rich phase is assumed as pure water.…”

Section: Mathematical Formulationsmentioning

confidence: 99%

“…Therefore, only conducting a two‐phase vapour‐liquid phase equilibrium calculations cannot yield an accurate description of the real phase behaviour where a three‐phase vapour‐liquid‐aqueous equilibrium exists. Hence, in order to simultaneously consider the effect of water and enhance the calculation speed, Lapene et al proposed a three‐phase free‐water flash method using a newly modified Rachford‐Rice equation based on the free‐water assumption which considers the water‐rich phase as a pure phase . The fraction of the water‐rich phase can be calculated based on the vapour‐phase fraction in the modified Rachford‐Rice equation.…”

Section: Introductionmentioning

confidence: 99%

“…Hence, in order to simultaneously consider the effect of water and enhance the calculation speed, Lapene et al [14] proposed a three-phase free-water flash method using a newly modified Rachford-Rice equation [8] based on the free-water assumption which considers the water-rich phase as a pure phase. [15] The fraction of the water-rich phase can be calculated based on the vapour-phase fraction in the modified Rachford-Rice equation. This algorithm replaces the three-phase flash by a pseudo-two-phase flash, leading to a significant improvement in the calculation speed.…”

Section: Introductionmentioning

confidence: 99%

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New two‐phase and three‐phase Rachford‐Rice algorithms based on free‐water assumption

2017

Can J Chem Eng

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Based on the free-water assumption that the water-rich liquid phase contains only pure water, we develop two simple free-water Rachford-Rice methods: 1) a two-phase free-water Rachford-Rice method where the phase fractions can be analytically solved; and 2) a three-phase free-water Rachford-Rice method where there is only one unknown in the objective function (i.e. the vapour-phase fraction) that is used for solving the phase fractions. Combining these two Rachford-Rice methods, a new free-water flash algorithm is developed to perform multiphase flash calculations where single-phase equilibria, two-phase equilibria, and three-phase vapour-liquid-aqueous equilibria can be considered. In this free-water flash algorithm, we first test if the mixture is stable; if the mixture is found to be unstable, we directly initiate the three-phase free-water flash. A set of criteria is developed for one to properly switch from a three-phase free-water flash to either a two-phase free-water flash or a conventional two-phase flash, depending on whether a water-rich phase is present in the two-phase equilibrium. We also develop efficient and robust methods for initializing the equilibrium ratios for the two-phase flashes. The negative flash is allowed in the flash calculation algorithms. A number of example calculations are carried out to demonstrate the robustness of the newly developed algorithm. A good agreement can be achieved between the flash results obtained by the new flash algorithm and those obtained by the conventional full three-phase flash algorithm.

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Section: Mathematical Formulationsmentioning

confidence: 93%