Kamal Al-Malah , is professor of chemical engineering at Higher Colleges of Technology, United Arab Emirates and former chairman of the chemical engineering department at the University of Hail in Saudi Arabia. He holds B.S., M.S., and Ph.D. degrees in chemical/biochemical engineering. Dr. Al-Malah graduated from Oregon State University in 1993 and his area of specialty deals with mathematical modeling, optimization, simulation, and computer-aided design. Professor Al-Malah is Windows-based software developer and MATLAB® book author
INTRODUCING ASPEN PLUS
1.1 WHAT DOES ASPEN STAND FOR?
ASPEN is an acronym of A dvanced S ystem for P rocess EN gineering. It is based on a flowsheet simulation. Notice that Aspen was replaced by Aspen Plus® in latest versions. A flowsheet simulation is a computer software that is used to quantitatively model a chemical processing plant, which, in addition to the core reactor unit, also includes pre- and post-treatment steps. Thus, simulation of an entire chemical process, starting from the raw material to the final finished product, is symbolically represented by different icons where each icon stands for a unit operation, chemical process, input/output material stream, input/output energy stream, or input/output electric/pneumatic signal. In terms of Aspen Plus flowsheet notation, there will be a block icon and stream icon. The iconic flowsheet simulator, such as Aspen Plus, allows us to predict the behavior of a process using basic engineering relationships. As taught in process modeling and simulation course that we describe a given physical (i.e., real) process by a set of linearly independent algebraic/differential equations such that the number of written equations will be equal to the number of variables (or unknown quantities) and the physical process as such is said to be specified or described by an equivalent mathematical portray. In general, writing such equations stems from
balance equations of extensive thermodynamic properties, such as mass, mole, and energy;
thermodynamic relationships for reacting and non-reacting medium, such as phase and chemical equilibrium;
rate correlations for momentum, heat, and mass transfer;
reaction stoichiometry and kinetic data;
physical constraints imposed on the process.
Given reliable thermodynamic data, sensible operating conditions, and rigorous equipment models, Aspen Plus can simulate actual plant behavior. Aspen Plus flowsheet simulation enables us to run many tasks, such as
conduct "what if" tests;
design specification (plant configuration) checks;
carry out "de-bottlenecking of constricting parts of a process" studies;
perform sensitivity analyses;
run optimization investigations.
With Aspen Plus process simulator, we can design better plants and increase profitability in existing plants. Aspen Plus flowsheet simulation is useful throughout the entire lifecycle of a process, starting from a rough R&D concept/idea and zooming to a refined projected idea with a different level of details, including conceptual engineering, basic engineering, detailed engineering, and finally plant operations and revamps.
1.2 WHAT IS ASPEN PLUS PROCESS SIMULATION MODEL?
In general, a chemical process consists of chemical components, or different species, that are subject to physical or chemical treatment, or both. The goal of applying such treatment steps is basically to add a value or convert the raw, cheap material(s) into valuable, final finished products (gold). The physical treatment steps may include mixing, separation (de-mixing), such as absorption, distillation, and extraction, and heating/cooling with or without a phase change. On the other hand, the chemical treatment step involves a single or set of parallel, series, or mixed reactions, which results in a change of chemical identity of each of reacting species. Such treatment steps are visualized in the flowsheet simulator as components being transported from a unit (or block) to another through process streams.
We can translate a process into an Aspen Plus process simulation model by performing the following skeletal necessary steps:
Specify the chemical components in the process. We can fetch these components from Aspen Plus databanks, or we ca