Page 120 - Gas Purification 5E

acid gas systems (as discussed in a previous section), and to predict mass transfer rates
with chemical reaction based on an enhancement factor to include the reaction effects (see
Chapter 1). These have been used by several investigators to develop rate-based, nonequi-
librium stage computer mod& for amine process absorbers and strippers. An example of
such a model is described in detail by Sardar and Weiland (1985). An alternative
approach, proposed by Tomcej et al. (1987), uses a sophisticated nonequilibriurn stage
model to determine tray efficiency values for C02 and H2S absorption in alkanolamine
solutions. Rate-based, nonequilibrium stage models have been used in commercial com-
puter programs.

Computer Programs

Several computer programs have been developed for designing and simulating amine
plants. Development of the Dow Chemical amine plant simulator is described by Katti and
Langfitt (1986A and B). The absorber simulator includes models to predict vapor-liquid
equilibria, reaction kinetics, hydrodynamics, and the effect of reactions on mass transfer.
Thermal parameters included in the model are the heats of reactions, heat transfer between
phases, and latent heats of evaporation andor condensation. According to Katti and Langfitt
(1986B), the Dow simulator on average solves a set of 200 coupled nonlinear equations per
pass through the column.
Computer programs which have been reported to be commercially available for use in
designing amine plants are

Program Licensor Reference

AMSIM D. B. Robinson & Associates, Ltd. Tomcej et al. (1987)
Alberta, Canada Zhang et al. (1 993)
APM Oklahoma State University, Vaz et al. (1981)
Stillwater, OK
Gas Plant Taylor, Weiland & Associates Vickery et al. (1988)
TSWEET Bryan Research & Engineering Bullin and Polasek (1982);
Bryan, TX King et al. (1985);
Polasek et al. (1992)

These programs were included in a list published by Manning and Thompson (1991).
Some may no longer be available. Also, most of the commercial process plant simulation
programs (PROLI, Hysim, Aspen Plus) have amine plant simulation capability. Of all the
commercial amine plant simulators, TSWEET is probably the most popular.
A common problem with many of the commercially available programs is their inability to
make an accurate prediction of the lean amine solution composition and therefore the product
gas purity. As a result, it is good practice to check stripper performance predicted by a comput-
er program with correlations derived from actual plant experience when available. For applica-
tions where little or no plant data are available, such as selective absorption systems. the com-
puter models are the only practical design tools. Furthermore, the models are continually being
upgraded, so deficiencies noted in previous versions may be resolved in more recent editions.