PRO/II 10.2: How to determine hydraulic power recovery potential from a high-pressure flashing liquid

I'm trying to model, in PRO/II, the potential benefits (kW recoverable) of an HPRT (hydraulic power recovery turbine) on the liquid product from a high-pressure separator in a hydroprocessing unit. This hydrocarbon liquid is at its bubble point in the separator and saturated with hydrogen and light hydrocarbon gas such as C1, C2, ... C5+.
After a flow control valve at the inlet of the HPRT the stream is two-phase, and the liquid will further flash generating more vapour as the pressure is reduced.

Colleagues of mine say the PROII Expander unit operation is only meant for 100% vapour streams (in- and outlet) 

Anyone ever considered this?