neqsim-dry-gas-seal-screening

name	neqsim-dry-gas-seal-screening
calculation_basis	screening
version	0.1.0
description	Educational dry gas seal supply and condensation screening for centrifugal compressors. USE WHEN: a task needs a public, screening-level estimate of seal-gas and separation-gas supply demand and a seal-gas condensation-margin check (cavity temperature versus hydrocarbon dew point) before detailed dry gas seal system design per API 692.
last_verified	2026-06-19
requires	{"python_packages":[],"java_packages":[],"env":[],"network":[]}

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

Symptom	Cause	Fix
Condensation never flagged	Dew point taken at cavity pressure instead of the vent/expanded condition	Use the hydrocarbon dew point at the seal/vent reference condition
Supply demand looks low	Supply margin set to 1.0	Use a supply margin above 1.0 consistent with the seal-gas control philosophy
Wrong total supply	Seal count not matching the machine arrangement	Set seal_count to the actual number of seals supplied

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.