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fix(process): scale LiquidRemover mass rate by gas mass fraction #1546

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fix(process): scale LiquidRemover mass rate by gas mass fraction #1546

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aa3bf79
fix(process): scale mass rate when LiquidRemover drops out liquid phase
olelod May 5, 2026
6248fab
test(process): assert LiquidRemover scales mass rate by gas mass frac…
olelod May 7, 2026
419f661
docs: changelog entry for LiquidRemover mass-rate fix
olelod May 7, 2026
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1 change: 1 addition & 0 deletions docs/drafts/next.draft.md
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@ STP: "flare" column has been added to STP Export - for `FIXED` installations onl
## Bug Fixes

- Hardened compressor PH flash handling so invalid thermodynamic states are no longer used in compressor outlet calculations.
- `LiquidRemover` now scales the outlet mass rate by the gas mass fraction when liquid is dropped, so the removed liquid mass is no longer carried by the gas stream downstream.

## Breaking changes

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17 changes: 15 additions & 2 deletions src/libecalc/process/process_units/liquid_remover.py
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Expand Up @@ -16,7 +16,14 @@ def get_id(self) -> ProcessUnitId:

def propagate_stream(self, inlet_stream: FluidStream) -> FluidStream:
"""
Removes liquid from the fluid stream.
Removes liquid from the fluid stream. The new stream's mass rate is scaled
down by the gas mass fraction so the dropped-out liquid isn't re-injected
into the gas phase.

The removed liquid (mass = inlet.mass_rate * (1 - gas_mass_fraction),
composition = inlet - new_fluid) is currently discarded. It could later
be exposed as a separate outlet stream — e.g. routed to an oil pump,
accounted for in emissions, or reported back to the user.

Args:
inlet_stream: The fluid stream to be scrubbed.
Expand All @@ -26,6 +33,12 @@ def propagate_stream(self, inlet_stream: FluidStream) -> FluidStream:
"""
if inlet_stream.vapor_fraction_molar < ThermodynamicConstants.PURE_VAPOR_THRESHOLD:
new_fluid = self._fluid_service.remove_liquid(inlet_stream.fluid)
return inlet_stream.with_new_fluid(new_fluid)
inlet_molar_mass = inlet_stream.fluid.molar_mass
if inlet_molar_mass > 0.0:
gas_mass_fraction = inlet_stream.vapor_fraction_molar * new_fluid.molar_mass / inlet_molar_mass
else:
gas_mass_fraction = 1.0
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@kjbrak kjbrak May 8, 2026 •
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Consider failing explicitly when inlet_molar_mass <= 0.0 rather than preserving the full inlet mass rate. A non-positive molar mass is non-physical, and gas_mass_fraction = 1.0 would hide the invalid thermodynamic state while carrying all removed-liquid mass downstream again for that edge case.

If using InvalidStreamException, the matching import also needs to be added.

Suggested change
if inlet_molar_mass > 0.0:
gas_mass_fraction = inlet_stream.vapor_fraction_molar * new_fluid.molar_mass / inlet_molar_mass
else:
gas_mass_fraction = 1.0
if inlet_molar_mass <= 0.0:
raise InvalidStreamException(
f"Cannot remove liquid from stream with non-positive molar mass: {inlet_molar_mass}"
)
gas_mass_fraction = inlet_stream.vapor_fraction_molar * new_fluid.molar_mass / inlet_molar_mass

new_mass_rate = inlet_stream.mass_rate_kg_per_h * gas_mass_fraction
return inlet_stream.with_new_fluid(new_fluid).with_mass_rate(new_mass_rate)
else:
return inlet_stream
33 changes: 33 additions & 0 deletions tests/libecalc/process/process_units/test_liquid_remover.py
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Expand Up @@ -33,3 +33,36 @@ def test_liquid_remover_removes_liquid(fluid_service, liquid_remover_factory):

assert inlet_stream.vapor_fraction_molar < 1.0
assert outlet_stream.vapor_fraction_molar == 1.0

expected_gas_mass_fraction = (
inlet_stream.vapor_fraction_molar * outlet_stream.fluid.molar_mass / inlet_stream.fluid.molar_mass
)
expected_mass_rate = inlet_stream.mass_rate_kg_per_h * expected_gas_mass_fraction
assert outlet_stream.mass_rate_kg_per_h < inlet_stream.mass_rate_kg_per_h
assert outlet_stream.mass_rate_kg_per_h == expected_mass_rate


def test_liquid_remover_passthrough_when_no_liquid(fluid_service, liquid_remover_factory):
composition = FluidComposition(
nitrogen=3,
CO2=1,
methane=80,
ethane=10,
propane=6,
)
fluid_model = FluidModel(eos_model=EoSModel.SRK, composition=composition)
fluid = fluid_service.create_fluid(
fluid_model=fluid_model,
pressure_bara=STANDARD_PRESSURE_BARA,
temperature_kelvin=STANDARD_TEMPERATURE_KELVIN,
)
inlet_stream = FluidStream.from_standard_rate(
standard_rate_m3_per_day=100000,
fluid_model=fluid.fluid_model,
fluid_properties=fluid.properties,
)
remover = liquid_remover_factory()
outlet_stream = remover.propagate_stream(inlet_stream)

assert inlet_stream.vapor_fraction_molar == 1.0
assert outlet_stream.mass_rate_kg_per_h == inlet_stream.mass_rate_kg_per_h
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