TEG Dehydration Modeling

Use this skill to build a complete, converging triethylene-glycol (TEG) gas dehydration plant in NeqSim. It captures a validated flowsheet topology and the non-obvious settings (CPA fluid setup, regeneration-column tolerances, recycle priorities, condenser/preheat energy coupling, makeup calculator) needed for the process to solve as a closed loop. It returns a ProcessSystem plus the key streams an agent needs for water dew point, lean-TEG purity, and still-vent emission classification.

This is a real NeqSim build, not a public correlation placeholder. For a quick "is dehydration required?" triage without building a plant, use neqsim-water-dewpoint-dehydration-screening instead.

When to Use

• When a user asks to model a TEG dehydration unit and read water dew point, lean TEG purity, or regeneration still-vent emissions.
• When an agent needs a runnable TEG flowsheet to study stripping gas, reboiler temperature, TEG circulation rate, or once-through vs recirculated stripping gas.
• When emissions (NMVOC, methane, benzene, CO2, water) from the regeneration still vent must be quantified and classified for an environmental screening.

Inputs

The build_teg_plant(...) function is fully parameterized. Key inputs:

• feed_fractions: list of mole fractions (or percentages) aligned with GAS_COMPONENTS (nitrogen, CO2, methane, ... , benzene).
• feed_flow_MSm3_day: wet/dry feed gas flow rate in MSm3/day.
• feed_temp_C, feed_pressure_bara: feed gas conditions.
• absorber_pressure_bara, absorber_temp_C: contactor conditions.
• teg_flow_kg_hr, teg_feed_temp_C, lean_teg_purity: lean TEG circulation.
• flash_drum_pressure_bara, reboiler_temp_C, stripping_gas_Sm3_hr: regeneration conditions.
• n_absorber_stages, stage_efficiency: absorber model resolution.
• water_mode: 'saturated' (water-saturate the feed) or 'specified' (set an inlet water content in mol-ppm via water_content_ppm_mol).
• saturation_temp_C, saturation_pressure_bara: optional saturation TP setter.
• recirculate_stripping_gas: True builds a true closed-loop stripping-gas recycle (split dried overhead, blower, heater) to cut still-vent emissions.

Outputs

build_teg_plant(...) returns (process, streams):

• process: a NeqSim ProcessSystem ready to run.
• streams: a dict of handles — dehydratedGas, flashGas, stillVent, leanTEGtoAbs, waterDewAnalyser, strippingGas, recircBlower.

Helper functions produce the engineering results:

• comp_mass_flows_kg_hr(stream): per-component mass flow (kg/hr).
• teg_mass_fraction(stream): TEG weight percent of a stream.
• classify_emissions(stream): dict with NMVOC, methane, CO2, water, TEG, benzene, and total mass flows (kg/hr).

Engineering Method

The flowsheet follows the standard TEG dehydration topology:

1. Fluid — SystemSrkCPAstatoil (CPA EOS) with setMixingRule(10) and setMultiPhaseCheck(False). TEG is added last so the lean-TEG composition maps to leanComp[-1] = lean_teg_purity and leanComp[-2] = 1 - lean_teg_purity.
2. Feed conditioning — optional saturation TP setter + StreamSaturatorUtil (saturated mode) or an inlet water component (specified mode), then a heater to absorber TP.
3. Absorber — SimpleTEGAbsorber with gas-in and lean-TEG solvent-in streams.
4. Rich TEG let-down and pre-heat — HP flash valve, rich preheater, lean/rich exchangers (HeatExchanger with UA values), degassing separator, fine filter, LP flash valve.
5. Regeneration — DistillationColumn (reboiler + condenser) with loosened tolerances (temperature 5e-2, mass 2e-1, enthalpy 2e-1) so the glycol/water split converges; stripping gas fed to the reboiler tray; WaterStripperColumn for deep lean-TEG purity.
6. Recycles — lean-TEG recycle (priority 200, setDownstreamProperty('flow rate')) closes the solvent loop; the internal stripping-gas recycle returns stripper overhead to the reboiler. With recirculate_stripping_gas=True, a second makeup recycle recirculates dried overhead as stripping gas. Keep both coupled stripping-gas recycles at the same controller priority (currently 100); an intermediate priority may be skipped by the current RecycleController sequence.
7. Makeup and energy coupling — a Calculator sizes TEG makeup from TEG lost in the dry gas, flash gas, still vent, and water draws; the rich preheater is driven by the condenser energy stream: richPreheat.setEnergyStream(column.getCondenser().getEnergyStream()).
8. Run — process.runAsThread() then thr.join(...) (worker thread avoids blocking and tolerates the recycle iterations). A completed worker thread or successful unit statuses do not prove closed-loop convergence: require process.solved() and inspect process.getConvergenceDiagnostics() before accepting water or TEG closure.

Python Usage Pattern

from teg_dehydration_modeling import (
    DEFAULT_FEED,
    build_teg_plant,
    classify_emissions,
    teg_mass_fraction,
)

process, streams = build_teg_plant(
    feed_fractions=DEFAULT_FEED,
    feed_flow_MSm3_day=4.65,
    feed_temp_C=25.0,
    feed_pressure_bara=70.0,
    absorber_pressure_bara=85.0,
    absorber_temp_C=35.0,
    teg_flow_kg_hr=5500.0,
    teg_feed_temp_C=48.5,
    lean_teg_purity=0.97,
    flash_drum_pressure_bara=4.8,
    reboiler_temp_C=197.5,
    stripping_gas_Sm3_hr=180.0,
    n_absorber_stages=4,
    stage_efficiency=0.7,
)

thr = process.runAsThread()
thr.join(300000)  # ~15 s once-through, ~40 s with stripping-gas recirculation

water_dew_C = float(streams["waterDewAnalyser"].getMeasuredValue("C"))
lean_teg_wt = teg_mass_fraction(streams["leanTEGtoAbs"])
still_vent = classify_emissions(streams["stillVent"])

print(water_dew_C, lean_teg_wt, still_vent["NMVOC"])

Regeneration-Pressure Sensitivity (reboiler floating on the LP flare)

Use this when the question is "does a few tens of mbar more reboiler pressure matter?" rather than a full flowsheet. A reboiler/still connected to an LP flare header has no pressure control; its pressure is the header pressure plus the pressure drop of the overhead path. Lean-TEG water content at fixed temperature and vapour composition scales with total pressure, so the effect is proportional (verified 2026-10-08, Aasta Hansteen, SRK-CPA, mixingRule 10):

• p_w(x_water, T) = y_water * P_bubble from bubblePointPressureFlash(False) on a TEG/water binary (fl.getPhase(0) is the gas); solve x_water so that p_w = y_steam * P_reboiler by bisection (y_steam = steam / (steam + stripping gas), about 0.85 to 0.92 for 76 Sm3/h stripping gas and 690 kg/h water).
• Benchmark: 98.90 wt% TEG at 204 C and 1 atm without stripping gas (textbook value about 98.7).
• 0.200 to 0.215 barg at 198 C: lean-TEG water +1.29 % relative (about -0.005 wt%-points at the design 99.6 wt%), equal to about 0.6 C of reboiler temperature, and +0.16 C on the equilibrium dry-gas dew point at 69 barg. Reaching the 0.4 barg H alarm costs about +17 % water.
• Dry-gas equilibrium: flash gas + water + TEG with 5 mol TEG solution per mol gas so the liquid composition stays fixed; dewPointTemperatureFlash() for the dew point.
• Water load: saturate the gas at the WET-GAS-SCRUBBER temperature (e.g. 22 C), not the contactor lean-TEG inlet temperature (35 C); the two differ by a factor of two in kg/h.
• In neqsim_dev_setup task scripts use ns.JClass("neqsim.thermo.system.SystemSrkCPAstatoil") and the component name TEG.

Validation Checklist

• Water dew point of the dry gas is well below 0 C at the reference pressure.
• Lean TEG purity is above 90 wt% (typically 97-99 wt% with stripping gas).
• Still-vent NMVOC and methane mass flows are finite and non-negative.
• With recirculate_stripping_gas=True, still-vent NMVOC and methane do not increase versus the once-through case.
• The process is run on a worker thread and the join timeout is large enough for the recycles to converge.
• process.solved() is true and every active recycle reports solved() == True; record priority, iterations, and residuals for any unsolved recycle.
• Water and TEG closure are interpreted only after the closed loop converges.
• Example inputs are public and synthetic.

Common Mistakes

Limitations

• Inputs and examples are public and synthetic; no proprietary plant data, vendor glycol packages, or company emission factors are included.
• Emission classification is a component-bucketing of stream mass flows (NMVOC/methane/benzene/CO2/water); it is not a regulatory emission inventory.
• The absorber uses SimpleTEGAbsorber with stage efficiency, not a rate-based contactor model; deep dew-point design needs validated review.
• Convergence depends on reasonable inputs; extreme TEG rates, stripping gas, or reboiler temperatures may require tolerance or guess-temperature tuning.

Related NeqSim Functionality

• neqsim.thermo.system.SystemSrkCPAstatoil — CPA equation of state for glycol/water/hydrocarbon systems (reached via from neqsim import jneqsim).
• neqsim.process.equipment.absorber.SimpleTEGAbsorber, neqsim.process.equipment.absorber.WaterStripperColumn — TEG contactor and stripper.
• neqsim.process.equipment.distillation.DistillationColumn — TEG regeneration column.
• neqsim.process.equipment.util.Recycle, Calculator — solvent/stripping-gas recycles and TEG makeup sizing.
• neqsim.process.measurementdevice.WaterDewPointAnalyser — dry-gas water dew point.
• For a screening-only water-content triage before building a plant, use the neqsim-water-dewpoint-dehydration-screening community skill.

References

• NeqSim repository: https://github.com/equinor/neqsim
• NeqSim TEG dehydration emissions notebook: https://github.com/equinor/neqsim/blob/master/examples/notebooks/teg_dehydration_emissions.ipynb
• NeqSim Skills Guide: https://github.com/equinor/neqsim/blob/master/docs/integration/skills_guide.md