Flash Main Window

This window is used to specify the two operating parameters required by the flash unit in order to determine the thermodynamic state of a stream.

First Specification

Select one of the following parameters

Pressure Drop : The decrease in outlet pressure over the lowest feed stream pressure. Negative values indicate a pressure rise.

Pressure : The pressure in the Flash drum.

Temperature : The temperature in the Flash drum.

Second Specification

Select the Flash Type by selecting one of the Unit Specification choices or supplying a Product Specification:

Unit Specification choices

Pressure
Pressure Drop	Isothermal flash
Temperature
Duty	Adiabatic Flash
Dew Point	General Dew Point Flash
Hydrocarbon Dew Point	Hydrocarbon Dew Point Flash (not for electrolyte models)
Water Dew Point	Water Dew Point Flash (not for electrolyte models)
Bubble Point	Bubble Point Flash
Isentropic	Isentropic Flash (not for electrolyte models)
Upper Dew Point	Upper Dew Point at specified temperature
Vapor Mole Fraction	Vapor Mole Frac Flash (FRAC)

Generalized Specification

You can specify a product stream parameter to a certain value within a Tolerance level. Click on the "Stream Parameter" text to display the Specification - Parameter Selection Window, where you can select an outlet stream and its property. Similarly, click on texts for "value" and "tolerance" to enter their desired values.

For electrolyte models, the only specifications allowed are molar product rate as a fraction of the feed or the product pH with fixed tolerances.

Temperature Estimate

Optionally, supply an estimate for the temperature value, which will be taken as the starting point of the iterative calculations to determine the actual temperature.

Pressure Estimate

Optionally, supply an estimate for the pressure value, which will be taken as the starting point of the iterative calculations to determine the actual pressure.

Pseudo Stream Flowrate

For dew point and bubble point flash types, you can designate an imaginary stream for the liquid and vapor phases respectively, to be used in calculations elsewhere in the simulation. See Flash Pseudo Stream for more details.

Product Phases button

When there are multiple product streams leaving the Flash unit this button becomes available. You must specify the product phase for each stream using the Product Phases window, which is displayed when this button is pushed.

Entrainment button

You can specify any entrainment from one phase to another through the Flash Unit Entrainment Window, which is displayed when this button is pushed.

Alternatively, instead of entering a numeric value for some of the parameters, they may be referenced using the Define system relative to any available unit operation or stream parameter calculated elsewhere in the simulation. See Flash Parameters available for Cross-Referencing for more details.

Phase Assignment

The Phase Assignment feature allows users to specify a product different than the phase assigned by Pro/II. Available choices include:

Default	PRO/II determines the product phase.
Vapor	Product returns as all vapor.
Liquid	Product returns as bulk stream liquid.
1st liquid	Product returns as the first (hydrocarbon, light) liquid sub-phase.
Water/2nd Liquid	Product returns as the second (aqueous, heavy) liquid sub-phase.

Note: The phase designation option is intended primarily for use with flashes in the super-critical region. Other usage is strongly discouraged.

Complete technical details may be found in topics under Flash Calculations in the PRO/II Reference Manual.

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