(1) It is hard to compute liquid density incorrectly far below the critical point, so that is not a good test of any model for liquid phase non-ideality. RE: Most appropriate fluid/thermo package for TEG/MEG/Water systems UmeshMathur (Chemical) 24 May 06 00:08 Read the Eng-Tips Site Policies at FAQ731-376 Ref 1: Matsumoto, Y Touhara, H Nakahishi, K Watanabe, N. Therefore I think I might need to include a heat of mixing into a tuned activity model to fully / accurately model this system. This is concerning as you have all indicated that PR is not to be trusted, yet there is evidence that there is an endothermic heat of mixing reaction that occurs in EG /Water systems (ref 1 - thanks to DS of AspenTech), and the activity models will NOT take this into account. In summary, both PR and UNIQUAC give quite similar results for everything other than the mixture temperature. Mixing 900kg/h Ethylene Glycol and 100kg/h Water (90%wt EG)
Mixing 100kg/h Ethylene Glycol and 900kg/h Water (10%wt EG) Mixing 1000kg/h Ethylene Glycol and 1000kg/h Water (50%wt EG) Results presented as: Mix Density (kg/m3), Mix Viscosity(cP), Mix Spec Heat(Btu/lbF), Mix Temp(C). Results, both inlet streams at 15.5C, 1 atm Well doing a sensitivity analysis revealed the following results. RE: Most appropriate fluid/thermo package for TEG/MEG/Water systems ColourfulFigsnDiags (Chemical) I would pay absolutely no attention to any simulation results for these systems using PR, as the results would be pretty close to garbage. As zoobie has noted, the "Glycol Package" may already have selected the activity coefficient model and the associated interaction parameters for you. My understanding is that Hysys does provide regressed binary interaction parameters for glycol systems (for Wilson, NRTL, or UNIQUAC). Otherwise, you would have no choice but to regress these parameters yourself. These are developed using the built-in physical properties for the pure components (most importantly, the vapor pressure), and thus you can use them directly. Modern simulators already provide regressed interaction parameters for an activity coefficient model that you select. These can be regressed against the chosen activity coefficient model to develop the required binary interaction parameters. There are many published vapor-liquid equilibrium data for glycol systems (e.g., the DECHEMA data books, available in most good chemical engineering libraries). The activity coefficients are therefore far from unity and it is obligatory to use an activity coefficient model for the liquid phase.
Such mixtures show marked deviations from ideality. PR is certainly NOT recommended for glycol systems, as these contain highly polar molecular functional groups. In such cases, the liquid phase is assumed not to exhibit strong non-ideality in the sense of Raoult's law. In general, an equation of state uses the same expression to calculate component fugacity coefficients in the vapor and liquid phases.
The PR (Peng-Robinson) option is an equation of state that is valid for hydrocarbons, light gases, and petroleum mixtures.