Are vapor property nonidealities of concern in chemical process simulations? This analysis shows how to reliably treat this issue in many situations.
The formulations and examples provided here form a basis for describing reliable vapor phase properties in process simulations. Figures 2 through 10 show ranges where the ideal gas (IG) and second virial (2V) equations of state can be applied to describe vapor densities, thermal properties, and vapor phases in equilibrium with liquids and solids. Table 3 summarizes some indications of when to worry about vapor phase nonideality. While the ideal gas (IG) EoS can be adequate in some situations, including nonideality is often necessary for satisfactory accuracy and reliability. In particular, the range of accurate predictions can be extended significantly by using second virial coefficients.
This article examines how the effects of vapor nonideality can be reliably estimated for typical process conditions. The focus is on vapor/gas properties used in process design and simulation for the common conditions of low to moderate pressures for substances up to their critical temperatures (Tc) and to higher pressures for supercritical components. We emphasize the virial EoS truncated at the second coefficient (2V), since it rigorously gives the initial departure from IG (1–3).