Page 90 - Handbook of Natural Gas Transmission and Processing Principles and Practices

FIGURE 2.12 At given temperature T 0 , the saturation pressure (i.e., bubble-point or dew-point pressure)
of a phase envelope can be interpreted as the pressure transition between 2-phase state and 1-phase
state. Open circles: (P, T) coordinates associated with vapor–liquid equilibria. Full circles: (P, T)
coordinates associated with 1-phase states.

Doing so, the PT-flash problem is thus expressed as:

(2.20)

Note that only mole-balance equations are considered because it is possible to deduce the
last one by summing the previous ones.
Eq. (2.20) contains equations and involves independent variables:

• 5 variables:
• mole fractions
• mole fractions

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