Neqsim Dry Gas Seal Screening

Dry Gas Seal Screening

Use this skill for public, educational dry gas seal screening on centrifugal compressors. It estimates the seal-gas and separation-gas supply demand from the primary seal leakage rate and flags retrograde-condensation risk by comparing the seal cavity temperature against a hydrocarbon dew point at the seal/vent reference condition.

When to Use

• When a user asks whether a compressor dry gas seal has adequate seal-gas supply margin.
• When an agent needs a quick condensation-risk triage for the primary vent / standpipe dead-leg before a detailed seal study.
• When examples must run without confidential seal vendor data, machine line lists, or project seal-gas conditioning specifications.

Inputs

• seal_leakage_rate_nl_per_min: primary seal leakage rate at standard conditions in NL/min per seal.
• seal_cavity_temperature_c: seal cavity (process-side) temperature in degrees C.
• hydrocarbon_dew_point_c: hydrocarbon dew point at the seal/vent reference condition in degrees C.
• seal_count: number of seals supplied (default 2: drive end and non-drive end).
• supply_margin: seal-gas supply margin over leakage, dimensionless, default 1.25.
• separation_gas_rate_nl_per_min: separation (secondary) gas rate per seal in NL/min, default 0.0.

Outputs

• total_seal_gas_supply_nl_per_min: screening seal-gas supply demand.
• separation_gas_supply_nl_per_min: screening separation-gas supply demand.
• seal_gas_supply_margin_ratio: the applied supply margin over leakage.
• condensation_margin_c: seal cavity temperature minus the hydrocarbon dew point.
• condensation_warning: ok, watch, or high (a small or negative margin means higher condensation risk).
• assumptions: public assumptions used by the placeholder model.

Engineering Method

The Python class DryGasSealModel uses open, public concepts only:

• seal-gas supply demand is the primary seal leakage multiplied by the seal count and a supply margin, reflecting the API 692 intent that supply must exceed leakage to keep the seal faces clean.
• separation-gas supply demand scales with the seal count.
• the condensation margin compares the seal cavity temperature against a hydrocarbon dew point at the seal/vent reference condition. A small or negative margin flags retrograde condensation risk in the primary vent piping and standpipe dead-legs, which is the failure mode that seal-gas conditioning units exist to prevent.

This is educational and screening-only logic. It is not a seal vendor method, not a seal-gas conditioning design, and not a replacement for validated dry gas seal analysis and a qualified rotating-equipment review.

Python Usage Pattern

from dry_gas_seal_screening import DryGasSealModel

model = DryGasSealModel()
result = model.evaluate(
    seal_leakage_rate_nl_per_min=280.0,
    seal_cavity_temperature_c=44.0,
    hydrocarbon_dew_point_c=40.0,
    seal_count=2,
    supply_margin=1.25,
    separation_gas_rate_nl_per_min=120.0,
)

print(result.condensation_warning)
print(result.total_seal_gas_supply_nl_per_min)
print(result.condensation_margin_c)

If the optional neqsim Python package is available, the result records that fact so an agent can recommend moving to validated NeqSim seal-gas dew-point and condensation analysis. If it is not installed, the example still runs with public placeholder logic.

Validation Checklist

• Inputs are in the documented units (NL/min, degrees C).
• Example inputs are public and synthetic.
• Tests cover ok, watch, high, and invalid-input cases.
• Results are described as educational screening indicators.
• Real seal system design is redirected to validated methods, API 692, and qualified review.

Common Mistakes

Limitations

• No seal vendor leakage curves, clearance models, or qualification data are included.
• No isenthalpic (Joule-Thomson) expansion or transient standpipe cooldown is modelled.
• No seal-gas conditioning unit (heater/separator) sizing is performed.
• Not suitable for safety-critical, design, guarantee, or standards-compliance work.

Related NeqSim Functionality

This educational screening corresponds to validated, rigorous functionality in the NeqSim Java library that a qualified engineer should use for design-grade work:

• neqsim.process.equipment.compressor.DryGasSealAnalyzer — isenthalpic seal-gap expansion, retrograde condensation mapping, dead-leg cooldown, condensate accumulation, and seal-gas conditioning unit sizing per API 692.
• neqsim.process.measurementdevice.HydrocarbonDewPointAnalyser — hydrocarbon dew-point evaluation for the seal-gas stream.
• neqsim.process.equipment.valve.ThrottlingValve — Joule-Thomson expansion modelling across the seal gap.

In Python the same classes are reachable through the neqsim package (for example from neqsim import jneqsim).

References

• NeqSim repository: https://github.com/equinor/neqsim
• NeqSim Skills Guide: https://github.com/equinor/neqsim/blob/master/docs/integration/skills_guide.md
• Public rotating-equipment references such as API 692 (Dry Gas Sealing Systems) and API 614 (Lubrication, Shaft-Sealing, and Oil-Control Systems) for general seal-gas concepts.