Phase Envelope - Technical Information
This module generates phase envelopes for multi-component streams. The algorithm can easily generate points in the retrograde condensation region. The calculations are limited to the Equation of State methods and work best for the mixtures of non-polar hydrocarbons.
PRO/II allows a maximum of five curves to be specified in each phase envelope module. This module is always executed after the flowsheet calculations have solved and therefore does not affect flowsheet convergence.
Output Options
Phase envelope tables are printed in the standard PRO/II output format for all the streams selected in a module. You can select the plot options to obtain plots for all or selected streams. After the calculations are completed, select the Output \ Generate Plot menu option to generate plots and/or to export the phase envelope data to a file that can be used with external spreadsheet application software.
In SimSci plot, to distinguish one type of curve from another, Bubble point curves are colored green, Dew point curves are colored pink, and Water dew point curves are colored blue.
The plots may be printed individually or can be combined to produce a comparison plot. See Phase Envelope Plot Options for more details.
Calculation Method
The Michelsen method is used to compute the true critical point, cricondentherm, cricondenbar, and other points on the envelope. Water is always treated as a regular component by the calculations, regardless of the declared state of water immiscibility. Note that systems containing more than one mole percent hydrogen usually are not totally condensable, so bubble points may not be possible. Among others, helium and nitrogen often show the same behavior. Results of bubble point calculations for streams containing high percentages of these components should be reviewed carefully.
In addition to the phase envelope, which consists of the bubble and dew point lines for the mixture, lines of constant liquid fraction may also be computed.
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