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CHAPTER ONE
INTRODUCTION TO ASPEN PLUS
Aspen Plus is based on techniques for solving flowsheets that were employed by
chemical engineers many years ago. Computer programs were just beginning to be
used, were of the stand-alone variety, and were typically used for designing single
units. The solution of even the simplest flowsheet without recycle required an engineer
to design each unit one at a time and, manually, introduce the solution values of a
previously designed unit into the input of the next unit in the flowsheet. When it
became necessary to deal with a recycle, the calculations began with a guess of the
recycle values, and calculations ended when the values produced by the last unit in
the loop matched the guesses. This involved much repetitive work and convergence
was not guaranteed. This procedure evolved through the construction of rating models
of units, as opposed to design models, which could be tied together by software in a
way that emulated the procedure above and employed robust mathematical methods
to converge the recycle elements of the process. This type of system is termed a
sequential modular simulator . An excellent example of such software was Monsanto
Corporation's Flowtran (1974), which eventually became the kernel upon which Aspen
Plus was built.
Subsequently, Aspen Plus, although still basically a sequential modular simulator,
has grown considerably and has many advanced functionalities, such as links to a
variety of specialized software, such as detailed heat exchanger design, dynamic sim-
ulation, batch process modeling, and many additional functions. It also has a facility
for using an equation-based approach in some of its models, which permits convenient
use of design specifications in process modeling.
The Aspen Engineering Suite, which incorporates Aspen Plus, can be installed
in a variety of ways using network servers or on a stand-alone personal computer.
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