(480c) Development of a Thermodynamic Model and Multiphase Equilibrium Flash for Prediction of Crystallization in LNG Processes

Development of a thermodynamic model and
multiphase equilibrium flash for prediction of crystallization in LNG processes

Nevin Gerek Ince^1,*,
Freddy Garcia², Jean-Jacques Bartuel³, Seiya Hirohama¹,
David Bluck¹

text-align:center;tab-stops:.25in">¹ line-height:115%;font-family:" times new roman minor-bidi>AVEVA Software

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South, 92630 Lake Forest, California, United States}

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place Jean Millier. 92078 Paris La Défense CEDEX France}

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Allée de l’Arche}

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Paris La Défense Cedex France}

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text-align:center;tab-stops:.25in"> 115%;font-family:" times new roman color:black>*Corresponding/Presenting author: nevin.gerekince@aveva.com

Abstract normal">

layout-grid-mode:char">       Worldwide
production of natural gas is growing, mainly through the development of new
shale gas fields, using hydraulic fracturing. The distance between production
and consumption sites is increasing, making pipeline transmission of natural
gas less economically attractive than liquid phase transportation as Liquefied
Natural Gas, or LNG. In the process of liquefying natural gas, the gas feed has to be cooled to very low temperatures of around 100K or
-173°C to keep the vapor pressure low enough for safe containment. Hydrocarbons
heavier than the main constituents of natural gas, methane, ethane and propane,
even in trace amounts, can result in crystallization in the liquefaction
process. This can lead to plugging and potential damage to expensive equipment,
such as cold-box heat exchangers. Operators of LNG plants want to be able to
push operating conditions as close to the limits as possible, without risking
the formation of solids in the process as feed stream compositions change.

layout-grid-mode:char">       Simulating
LNG productions requires an accurate and robust thermodynamic framework which
can handle solid phase at the cryogenic conditions. For this goal, we gathered
the latest experimental data, and critically examined them. Thermodynamic
models were systematically investigated applying Cubic Equations of State (Soave-Redlich-Kwong in this study), tuning pure component data and binary
interaction parameters and alpha formula considering thermodynamic constraints.
We updated correlations for solid fugacity, and density models. A robust
multi-phase – V(mL)(nS)E - flash algorithm was
established for vapor-liquid-liquid-solid (VLLSE) equilibrium by applying phase
stability analysis. The revamped thermodynamic methods and data allowed us to
accurately predict the multiple phase boundaries that can be present when
cooling a typical natural gas mixture. Simulation results were also compared
against experimentally measured vapor-liquid-solid equilibrium data.