



Indranil Banerjee

15 September 2018





Hii guys. I am here with a new blog on thermodynamic packages, which is considered to be an important tool for chemical process simulations and flowsheet development. Right from the beginning, I was stressing on selecting thermodynamic packages and choosing them wisely. Here in this blog, I will focus more on their importance on what are they, how they are selected and some do’s and don’ts while dealing with different kinds of packages. And yes, will try to explain different processes wherein how thermodynamic packages are selected.

First of all, thermodynamic packages are a set of properties which have all the chemical and physical properties of a specific compound being incorporated into a process. These properties decide the behavior of the compound based on the inputs given to the process. They contain all the essential information starting from its state to the properties the advanced properties such as enthalpy, the heat of reactions, and many others. They have to be wisely chosen and taken up considerably.

There are many ways of selecting thermodynamic packages, to start with taking a look at the polarity of the component. The polarity of a substance ways defines the package to be used. Then keep a check at electrolytic nature of a component to use. If the substance is electrolytic go for NRTL (Non-random two liquid package) or either you can prefer Pitzer or Wilson but if you find the substance is non-electrolytic then you have to take a chance and find out the pressure of the system.

Now, when pressure comes into the picture there is a threshold depending on which you need to decide the property package. Usually, the threshold is around 10 bars and if the pressure of the system is below 10 bar you can use models such as Peng Robinson, UNIFAC, UNIQUAC or Redliech Kwong sometimes based on the interactions. Yes, Another important aspect are the interactions taking place between the phases ,either it can be liquid-liquid, gas-liquid etc, and based on the interaction parameters different packages can be used however take a call every time on the phases and the pressure properly or else pay for it, and in cases when the pressure of the system is exactly 10 bar, go for Peng Robinson model but for a convenience perform a back check with empirical values of the compound .

Now, coming to non-polar systems, there are a lot of things to take care of, firstly check whether the system is a real or pseudo-system, which means for simple systems, we consider it as a real system and for a complex system involving too many coefficients is taken as pseudo systems. If the system is real, definitely go for models such as EOS, Peng Robinson, Redliech Kwong or SRK and in case, the system tends to a pseudo-state then jump for Chao Seader or Braun k-10 Models. Thermodynamic packages also depend on phase equilibrium calculations such as Fugacity (interaction of a component coming out from a phase in equilibrium), activity coefficient etc, these situations arise during reversible reactions and should be precisely taken care of during the selection but difficult it is, isn’t it? I know.

So, I have come up with a shortcut to determine the thermodynamic packages of the complex systems. So, when systems get complicated or confusing, find out the empirical properties of the compounds used , choose Peng Robinson model follow up the simulation and then check whether the obtained values match with the empirical values of the compound, if it is true to go for the same or else calculate theoretically the properties of the compound and choose the mode according to that . Maybe feels like is a stupid stuff, but believe me, really it works.

Another important tip is for hydrocarbons, it is advisable to choose them wisely because they are characterized according to their properties. Sometimes, length of chain decides the package to be used. Usually, for long-chain hydrocarbons, PR Models and SRK models are used. Length of branching also affects the boiling point range, which is also a factor for determining the packages and yes Binary interaction parameters, they also play important role in determining which package to be used.

Sometimes people prefer to use package charts, being widely available on the internet. So, you can refer them as well for getting thermodynamics ,but my sincere advice, choose them properly and yes the most important one, choose one package at a time, don’t use different packages and make trial and error, that makes calculations vague and give wrong results, better take time and find out the best one. So, this was all about selecting thermodynamics packages in flowsheet development and how to use to them wisely. Please comment guys if you feel so that I can improve myself in my incoming blogs.



