Process simulation is to use a digital model to describe a chemical process composed of many unit processes, and to obtain the required results by changing various effective conditions on the computer, such as operating conditions.
The ASPEN PLUS chemical simulation system is a large-scale chemical simulation software developed by the Massachusetts Institute of Technology in the United States after 1970. This software system has complete functions and large scale. It can be used in many industrial fields such as petrochemical industry, waste oil distillation plant, gas processing, coal, medicine, metallurgy, environmental protection, power, energy saving, food processing, etc., and it has been widely used in many industrial fields all over the world.
The modules related to distillation in ASPEN PLUS are:
(1) Simple method model: including DSTWU (shortcut method distillation design model), Distl (shortcut method distillation calculation model), SCFrac (shortcut method multi-column distillation model).
(2) Strict grid method model: MuhiFrac (strict grid method multi-tower rectification model), PetroFrac (strict grid method fractionation tower), RateFrac (rectification calculation and design model), Extract (strict extraction tower model).
Among them, RateFrac is a non-equilibrium model based on flow rate. It is used to simulate various types of multi-stage gas-liquid distillation operations. It can be used for general distillation, absorption, reboil absorption, steam stripping, reboil stripping, and extraction. And azeotropic distillation. It is suitable for two-phase systems, narrow boiling range and wide boiling range systems, and liquid phase systems with a strong non-ideal degree. Its composition includes any group input, any group side line, any group heater (or heat flow) and any group decanter.
For the distillation simulation, the following conditions must be determined:
(1) Feeding properties (including feed composition, temperature, pressure, feed volume, phase number, etc.) and feed location.
(2) Discharge properties (including phase number, etc.) and discharge position.
(3) The properties of the tower, such as the number of trays, the pressure distribution of the tower, the reflux ratio, the ratio of gas phase products to the total top product, or the top discharge, bottom discharge, backflow, etc.
Others such as side discharge, heat load of heater and reboiler, initial value of steam composition, tray efficiency, reflux temperature, filling quality or tray quality, etc. can be set by the simulator according to the requirements.
For a simulation process, the accurate selection of physical properties is the key to a good simulation result. ASPEN PLUS provides thermodynamic properties and transfer properties for unit operation calculations, in a typical AS. In PEN PLUS simulation, the commonly used physical parameters are fugacity coefficient, enthalpy, density, entropy and free energy.