Valve Unit Operation - Technical Information
The valve regulates the flow of fluid through a pipe. Normally there is a pressure drop when the fluid flows through a valve, which can be accompanied by phase changes. If the valve has multiple product streams, you must designate a phase condition for each stream.
Calculation Method
The valve provides two options for specifying its operating pressure: pressure drop or outlet pressure. PRO/II performs an enthalpy balance to determine the combined product stream enthalpy. An adiabatic flash calculation is used to determine the product phases and the outlet temperature at the specified pressure condition. The product stream is then split according to your stream phase specifications.
The valve unit supports both VLE (two phase) and VLLE (three phase) calculations to determine the individual phase compositions. See the VLE Model and the VLLE Model for more details.
Feed and Product Streams
The valve unit can have an unlimited number of feed streams. The inlet thermal condition is determined by an adiabatic flash calculation at the lowest feed stream pressure.
The valve unit can have up to four product streams, with different phases in each stream. The possible product phases are vapor, liquid, decanted water / second liquid phase, a mixture of vapor and liquid, and solids. If there are multiple product streams leaving the valve unit, the phase condition for each stream must be specified using the Product Phases Window.
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