Effective utilization of equations of state for thermodynamic properties in process simulation

Abstract

Thermodynamic property computations using equations of state first require computation of the density root. Since higher level calculations such as single-stage flash, distillation and data regression are usually performed iteratively, properties are often demanded at conditions where the appropriate density root does not exist. A strategy of returning suitable pseudoproperties under such conditions is proposed. It has been successfully used in ASPEN (Advanced System for Process Engineering), a general process simulator developed at the Massachusetts Institute of Technology.

Experimental vapor-liquid equilibria data for binary mixtures of xylene isomers

“…Although, the Peng-Robinson EOS predicts a deviation in the normal boiling point less than 0.08%, this is not satisfactory for xylene isomers and the EOS is not able to satisfactorily describe Txy plots for these systems. If an equation of state is preferred, these systems are more accurately described by the Soave-Redlich-Kwong EOS (modified by Mathias et al (1984)), since pure normal boiling points are better predicted. …”

“…Binary interaction parameters were reported for the NRTL, UNIQUAC and Wilson models, as well for the classic mixing rules for the Peng-Robinson and the Soave-Redlich-Kwong (modified by Mathias et al (1984)) cubic equations of state. Deviations are quite small for all of these models.…”

“…In order to improve these predictions, another cubic equation of state was used; the Soave-RedlichKwong EOS (Soave, 1972) modified by Mathias et al (1984) was chosen, since this EOS normally represents pure vapor pressures very accurately and is available in the Aspen Plus®10.1 software.…”

“…The compositions of liquid and vapor phases were analyzed by gas chromatography (GC). Experimental data were regressed with Aspen Plus ® 10.1 and binary interaction parameters were reported for the most frequently used activity coefficient models and for classic mixing rules of two cubic equations of state (Peng and Robinson (1976) and Soave-Redlich-Kwong (Soave, 1972) modified by Mathias et al (1984)). …”

Performance analysis of a Kalina cycle for a central receiver solar thermal power plant with direct steam generation

“…The KC and the SRC were modelled using Aspen Plus (v7.2) [19]. The thermophysical properties of the working fluids for both the cycles were evaluated using the Peng-Robinson equation of state with BostonMathias extension (PR-BM) [20]. All the models were steady-state models.…”