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Ind. Eng. Chem. Res. 1991,30,2363
Response to Comments on “Asymptotic Effects Using Semicontinuous vis-&-vis Discrete Descriptions in Phase Equilibrium Computations” Sir: Lira-Galeana et al.’s criticisms of our paper essentially are semantic. They make two primary points: 1. The more mathematically complicated a distribution function is, the better the job it can do in describing a continuous portion of a semicontinuous description (or the entire description, if so chosen). 2. A quadrature treatment of a continuous portion is an effective way to deal with describing the continuous portion. We have no quarrel with these two points. Our point about conservation of species (mass) in a continuous description is more fundamental than those raised by LiraGaleana et al.; the conservation-of-mass problem is the central point of our paper, and they fail to address it formally in their comments. First let us clarify the terminology. We do not label a description *continuous” after quadrature has been applied. Our comparison is between (I) a continuous description (a priori quadrature) and (11) a discrete description arising from that continuous description (a posteriori quadrature). This distinction has apparently led to semantic confusion on the part of Lira-Galeana et al., who classify both problems I and I1 in their comments as *continuous*. Our paper shows that the asymptotic quadrature result I1 does not agree with result I in the case of a saturation calculation, which is a limiting flash calculation, due to the conservation-of-mass failure characteristic of all continuous (not quadrature) flash calculations. For some time, there has been a prevailing misconception that saturation calculations, by their very na-
ture of having one infinitesmal phase, cannot suffer from the conservation-of-mass difficulties that occur with flash calculations in general (i.e., those with finite equilibrium phases). Our paper hopefully elucidates that a saturation calculation does experience a conservation-of-massproblem when a continuous (not quadrature) description is used. Use of quadrature circumvents the conservation-of-mass problem and is therefore implicitly recommended by our paper as the treatment of choice. The results of our paper are meant to be of formal significance. Our paper is not directed toward how serious the conservation-of-mass problem is in saturation calculations for continuous mixtures. We are simply pointing out that it is there. Additionally, we are not addressing how to reduce the resulting discrepancies, quantitatively speaking. This latter topic appears to be the primary focal point of Lira-Galeana et ala’s comments. Their exercise is not related to our paper in any formal way. Kraemer D. Luks*
College of Engineering University of Tulsa 600 South College Tulsa, Oklahoma 74014-3189 Edward A. Turek, Tor K. Kragas
Amoco Production Company Box 3385, Tulsa, Oklahoma 74102
0888-5885/91/2630-2363$02.50/00 1991 American Chemical Society
