QUADRATURE ALGORITHMS FOR PHASE EQUILIBRIUM OF CONTINUOUS MIXTURES

Several methods for computing the Gauss-Christoffel quadrature used for the adaptive characterization of continuous mixtures were compared as to their efficiency and robustness. Two mixtures with molar fraction distribution given by truncated gamma distributions were used. We analyzed the Product-Difference, the GolubWelsch, the Long Quotient-Modified Difference and the Chebyshev algorithms using regular and generalized moments, when applicable. The robustness and computational efficiency of changes in the distribution variable and in the orthogonal polynomial family used to calculate the generalized moments were analyzed. The methods using generalized moments proved to be more robust than those that use regular moments. Although they are computationally more expensive, this cost increase is just around 20% for the Chebyshev algorithm. The resulting adaptive characterization was employed to solve the adiabatic vapor-liquid flash of these mixtures. The results showed that eight pseudocomponents were able to well represent the properties of the equilibrium streams, showing the high accuracy of this method.