A Line-Search-Based Algorithm for Multiphase Flash Calculations with CO₂-Hydrocarbon System.

Area of Science:

• Chemical Engineering
• Computational Chemistry
• Process Simulation

Background:

• Multiphase flash calculations are essential for compositional simulation.
• Existing methods can struggle with convergence in challenging scenarios.
• Robust and efficient algorithms are needed for accurate phase behavior prediction.

Purpose of the Study:

• To develop a novel line-search-based algorithm framework for stability analysis and multiphase flash calculations.
• To improve the efficiency and robustness of computational algorithms in compositional simulation.
• To address limitations of traditional iterative methods.

Main Methods:

• Utilized a modified Newton step derived from modified Cholesky factorization for guaranteed descent direction.
• Incorporated a line-search method to determine the optimal step size for convergence.
• Implemented modifications using Cholesky factorization to handle nonpositive definite Hessian matrices.

Main Results:

• The algorithm demonstrated superlinear convergence speed in phase stability analysis and multiphase flash calculations.
• Tested with classical fluids, the algorithm proved efficient and robust.
• Successfully computed the pressure-composition diagram for a CO2-hydrocarbon system with rapid convergence and no failures.

Conclusions:

• The developed line-search algorithm offers a significant advancement for multiphase flash calculations and stability analysis.
• It provides a robust and efficient computational tool for compositional and chemical process simulations.
• The algorithm's performance indicates its potential for widespread application in the field.