Application of Volume Translation to Process Calculations

Equation of state models PVT relationship of pure compounds and their mixtures. Vapor-Liquid equilibrium is very common in industrial processes such as petroleum refining, bulk gases etc. Therefore a single equation of state applicable to liquid as well as gaseous phase is the most relevant equation for industrial use. Cubic equations of state (CEOS) are the most successful models for representing PVT data; therefore, CEOS are widely used in process calculations. Accuracy of CEOS property estimates is of critical importance because, in process calculations, CEOS are used to calculate thermodynamic properties of all the process streams.
It is observed that CEOS accurately model VLE data but fail to provide reasonably accurate estimates of volumetric properties [1] [2]. This limitation can be addressed by either using new equations of state with better volumetric property estimates or correcting volumetric property estimates of the CEOS. Volume translation is an approach for correcting volumetric property estimates while preserving vapor- liquid equilibrium of the compounds [3] [4]. CEOS have many advantages compared to other thermodynamic models therefore, volume translation approaches are preferred for process calculations.
Many volume translation functions are proposed in literature. Volume translation functions can be broadly categorized into two categories i.e. Constant volume translation and temperature dependent volume translation. Temperature dependent volume translation, in general, provides better average percent absolute deviation results for volumetric property estimates. But it is reported in [5] and [6] that temperature dependent volume translation can lead to discontinuity in the thermodynamic property estimation and unrealistic PVT behavior. Therefore volume translation functions need to be evaluated on multiple aspects before incorporating them in process calculations.
Five volume translation functions are evaluated and four volume translation approaches are presented in this work. Volume translation approaches are evaluated in the context of process calculations and discussion on advantages and disadvantages of the proposed volume translation approaches is presented.

References

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