This paper describes a new formulation of the vapor−liquid equilibrium problem. The proposed model reveals a great mathematical similarity between the stability test problem and the isothermal flash problem, particularly in regions of interest in reservoir engineering near phase boundaries and in the vicinity of critical points. This similarity is mathematically studied and then explored to find a means of minimizing the Gibbs free energy in a more efficient way. The Peng−Robinson cubic equation of state was used to represent the phase behavior of multicomponent mixtures. The simulated annealing (SA) algorithm was used to carry out isothermal flash calculations and phase stability tests. The SA algorithm is essentially an iterative random search procedure whose moves are adapted by some suitable mechanism. It is robust and easy to implement. The algorithm was tested for several hydrocarbon mixtures. The few experimental data available in the literature were compared with theoretical predictions. The proposed methodology produced high-quality solutions.

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SUMMARYThis paper presents a simulation study of an ethanol}water distillation column with vapour recompression. The compression of the overhead vapour from the distillation column and the use of condensing vapours to reboil the bottom products were modelled. Predicted results were compared with those from a simulation model for an ethanol}water distillation column assisted by an external heat pump, as previously developed by the authors.

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SUMMARYThis paper presents a simulation of an ethanol-water distillation column assisted by a vapour-compression heat pump. The heat pump is of the external type, i.e., it uses a working fluid (refrigerant) different from that of the column. A simulation model was developed and four different working fluids were studied: R-11 and R-114 and, as substitutes, the column own fluids, water and ethanol. Results from the simulation model have shown that considerable reduction in energy consumption can be achieved with the installation of a heat pump.