Chemical Reaction Modeling with ThermoFluid/MF and MultiFlash

The free Modelica library ThermoFluid was developed for simulation ofthermo-hydraulic applications, both for single-species applicationslike the water-steam cycle in a thermal power plant and formulti-species applications with gas mixtures. It has demonstratedits flexibility for modeling thermodynamic and process applicationsin a variety of industrial and academic projects. This articledescribes how support forchemical reactions and membrane diffusion has been added to ThermoFluid,thus expanding the area of possible applications to include reactingflows, chemical batch reactors, catalytic converters, etc. Anothercrucial part of the modeling work has to be spent on gettingphysical property data of sufficient accuracy and with acceptablecomputational complexity for engineering purposes into the model.This has been adressed in the development of a commercial interfaceto the industry-standard physical property package MultiFlash. Thenew Modelica library ThermoFluidMF provides the modeler with two toolboxes.Firstly, a low-level Modelica function interface to MultiFlash.MultiFlash consists of a core of physical property calculationroutines and a basic database of the most comman chemical componentsand a number of add-on property databases. The interface givesaccess to multi-component, multi-phase property calculationsincluding gas, several liquid and condensed phases, wax formationsand hydrates. Secondly, a high-level Modelica model library which isfully integrated with the tf library and implements robust andefficient dynamical models for the most common process engineeringequipment. In addition, reliable crossing functions for detectingphase boundaries in multi-phase, multi-component mixtures have beenimplemented for the first time in a high-level modelinglanguage. The crossing functions make it possible to simulateprocesses correctly even at off-design operating points and understart-up conditions. A flash volume may in such cases be filled withonly liquid or only gas. Crossing functions for phase transitionsensure high performance simulation even in these cases