Liquid stream trapped in FTPx

[dallan-keylogic]

I am using FTPx state variables in a generic property package for a Flash unit condensing water out of a hydrogen stream. I want to recycle this water stream. Since I know that flash calculations for FTPx variables are ill-posed for single-species phase equilibrium, I attempt to translate the stream into an appropriate property package (IAPWS95) using a Translator block. I create three constraints to define the new set of state variables:

def rule_flow_mol(blk,t):
    return blk.properties_in[t].flow_mol == blk.properties_out[t].flow_mol
def rule_temperature(blk,t):
    return blk.properties_in[t].temperature == blk.properties_out[t].temperature
def rule_pressure(blk,t):
    return blk.properties_in[t].pressure == blk.properties_out[t].pressure

All properties needed from blk.properties_in[t] are state variables, so no calculations in the inlet block are needed. Nevertheless, flash equations are still set up and, unsurprisingly, fail.

My options, at this point, are to either:

1. Directly write constraints at the flowsheet level, resulting in a stream that is invisible to the flowsheet visualizer and stream tables.
2. Create an imitation Translator block in which a port with appropriate variables is created but no state block for the inlet properties is created.
3. Create another FTPx property block with the same components but without phase equilibrium so I can avoid the offensive calculations in the translator block.

I think this is a user accessibility failure, and would like to give users a better way to proceed.