Account for phase changes in adiabatic reactions

[BenPortner]

Dear @yoelcortes,

It seems that thermosteam does currently not or incorrectly account for phase changes during adiabatic reactions. Using electrolysis of steam as an example:

import thermosteam as tmo

tmo.settings.set_thermo(["H2O", "O2", "H2"])
electrolysis = tmo.Reaction(
    'H2O -> O2 + H2', # Reaction
    correct_atomic_balance=True,
    reactant='H2O',
    X=0.13,
)
feed = tmo.Stream(H2O=1, T=900+273.15, P=1e5, units='kg/s', phase='g') # H2O is gaseous here
electrolysis.adiabatic_reaction(feed)
feed.show() # H2O should be liquid here

"""
Stream: s2
 phase: 'g', T: 79.243 degC, P: 1 bar
 flow (kg/s): H2O  0.87
              O2   0.115
              H2   0.0145
"""

Expected behavior

Water is liquid at 79°C and 1 bar. After the reaction, feed should be a MultiStream with water in the liquid phase and oxygen and hydrogen in the gas phase.

Current behavior

Water remains in gaseous state.

Similar issues

The issue is loosely related to #29 and #62.

[yoelcortes]

Hi Ben,

Thanks for posting this issue! Thermosteam reaction objects do not perform phase equilibrium (yet). You can perform phase equilibrium with just adding one line:

import thermosteam as tmo

tmo.settings.set_thermo(["H2O", "O2", "H2"])
electrolysis = tmo.Reaction(
    'H2O -> O2 + H2', 
    correct_atomic_balance=True,
    reactant='H2O',
    X=0.13,
)
feed = tmo.Stream(H2O=1, T=900+273.15, P=1e5, units='kg/s', phase='g')
electrolysis.adiabatic_reaction(feed)
feed.vle(H=feed.H, P=feed.P) # ADD THIS LINE!
feed.show()

Output:

MultiStream: s2
 phases: ('g', 'l'), T: 367.13 K, P: 100000 Pa
 flow (kmol/hr): (g) H2O  171
                     O2   13
                     H2   26
                 (l) H2O  2.53
                     O2   1.34e-05
                     H2   3.58e-08

I'd be happy to add a note/warning on this in the documentation. It may be a good idea to add a phase equilibrium feature as an optional argument just like Stream objects, but it may take me a while due to:

• Reaction objects would need to handle when phases are given (ignore given phases and perform vlle or raise error).
• It cannot be used if solids are present.
• Reaction objects are designed to work with arrays too (not just stream objects).
• Require optional P argument.
• VLLE is still clunky with supercritical mixtures.
• Additional documentation required.

I'll leave this issue open so that I can remember to get to it,
Thanks!