An expander is used to obtain energy from a pressure drop of gaseous fluids. An expander has one inlet and one outlet.
As for pump, either pressure drop or an absolute outlet pressure is specified. Furthermore, either an isentropic efficiency or the actual work that is generated has to be specified. The inlet for the expander correspond to the cone for the compressor. However, the efficiency and work generated, W, are related to the work needed for an isentropic (adiabatic) pressure change, WΔS=0, by:
If efficiency is specified, we therefore obtain use a pS equilibrium calculation to determine the conditions at ΔS=0, enthalpy for the outlet. Work can also be specified directly, or via an energy inlet stream.
The remaining outlet conditions of the expander are determined by an enthalpy flash.
If work is not specified via an energy inlet stream, an energy outlet stream can be connected that will receive a value for the work produced by the expander.
For a liquid flow, use a turbine unit operation.