Page 121 - Petroleum and Gas Field Processing

Initial phase Process and conditions
1. Higher-pressure liquids (light) Heat under pressure, then flash
adiabatically using valve
2. Low-pressure liquids (heavy) Partial vaporization by heating,
flash isothermally (no valve)
3. Gas Cool-after initial compression
4. Gas Expand through a valve or engine

Figure 30 Continuous single-stage equilibrium separation by partial condensation
of a gas feed (case similar to isothermal flash for a required T r ).

The diagram shown in Figure 30 illustrates case 3, which is a
continuous single-stage separation of a gas feed by partial condensation.
The vapor and liquid leaving the flashing drum are in intimate contact,
hence, they are in equilibrium.

3.9.2 Conditions Necessary for Flashing
For flashing to take place, the feed has to be two-phase mixture, that is, it
satisfies the following:

T BP < T f < T DP (as indicated in Fig: 31Þ
or
The sum of [z i K i ] for all components is greater than 1 and
the sum of [z i /K i ] for all components is less than 1

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