Streams - Technical Information
The streams in PRO/II can contain any number of components and can exist in mixed phases. When a unit operation module is calculated, the composition and thermal condition of the feed streams must be available for it to be solved. Similarly, the unit operation usually sets the composition and condition of its outlet streams after the calculation is finished. Some of the streams may be recycle streams, in which case the specified calculation sequence is repeated until the necessary recycle tolerances are met.
The complete specification of a stream requires defining component flowrates and the thermodynamic state of the stream. It typically is required for streams that feed into the flowsheet.
Stream Component Flowrates
There are five ways to define a stream composition and flowrate in the Stream Data Window:
1. Defined composition with defined (Library, Petroleum or User-Defined) components.
2. Assay curve supplied for stream.
2. Spiral Assay data for stream.
3. Composition referenced to another stream.
4. Solids only streams
If you give a stream composition, you must specify the flowrates of each component by supplying them explicitly or by giving the total stream flowrate and the component fractions. Assay input requires a distillation curve from which the stream is divided into pseudocomponents with various boiling point ranges. Spiral Assay stream requires selection of one or more crudes from the Assay database. The stream is then divided into various spiral components according to their boiling point ranges. This requires Spiral Assay to be installed on your computer. When a stream is referenced to another stream in the flowsheet, its composition is set to that of the reference stream. Whenever the composition of the reference stream changes, the change is immediately propagated to the referencing stream. However, the total flowrate, temperature, pressure, bubble point and dew point of the referencing stream can be different from the referenced stream. Solids only streams do not take part in equilibrium calculations.
Stream Thermal Conditions
Once the stream composition is fixed, two degrees of freedom remain to completely define its thermodynamic state. These include temperature, pressure, and phase/liquid fraction. Note that PRO/II defaults column feed stream pressures to the feed tray pressure if the pressure value is not supplied. Also, streams referenced to other streams are initially defaulted to the reference stream pressure and temperature, which can be overridden.
If you desire to study the properties of a stream over a range of temperature and pressure, you can use a Heating/Cooling Curve module.
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