Resumo

GAMMIERO, Alexis. Evaluation of several successive substitution algorithm for gas-liquid equilibrium with equations of state. Rev. Fac. Ing. UCV [online]. 2013, vol.28, n.2, pp.101-116. ISSN 0798-4065.

The calculations of vapor-liquid equilibrium with equations of state are widely used in the oil industry, and they consume a lot time in numerical simulations. Therefore, in this paper several flash calculation models based on successive substitutions and the different parts that defines these algorithms are studied. Basically, the evaluations are performed with different methods to determine the fraction of vapor, correlations to estimate the equilibrium constants and the various proposals for upgrading equilibrium ratios in the iterative process. The results of the evaluation show that the method of Leibovici-Neoschil with Newton-Raphson routine is the most efficient way to determine the fraction of vapor since it requires fewer iterations and time. Sensitivity analyses are performed considering the correlation used to estimate initial equilibrium relationships. It has been found that Wilson’s proposal is the most effective since the convergence has been achieved in a greater number of cases. The analysis of the accelerated methods of Risnes-Jessen, Mehra et al. and Crowe Nishio of updating the equilibrium relationships could conclude that the type I algorithm of Mehra is the fastest of all the options, without having to converge in any case to the trivial solution. Finally, a new algorithm which combines the methods from Crowe Nishio, Mehra type I and Leibovici has been proposed. With this model the convergence is achieved in 100% of the cases. Additionally, the computation time is lower than any of the other methods under study.

Palavras-chave : Flash calculation; Liquid-Vapor equilibrium; Successive Substitution; Leibovici; Rachford-Rice; Equilibrium constant; Equation of state.

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