Fire and blowdown calculation enhancements

This note summarizes how to extend NeqSim blowdown calculations with rigorous fire exposure models.

Heat transfer modelling (wetted vs. unwetted)

• Use the FireHeatTransferCalculator utility to compute inner/outer wall temperatures with separate film coefficients for wetted and unwetted regions. The calculator solves a 1-D thermal resistance network so that external fire temperatures and internal boiling/convective coefficients can be applied consistently. Wetted and dry areas can be pulled directly from a Separator via getWettedArea() / getUnwettedArea(), so dynamic level changes during blowdown feed into the fire heat flux sizing automatically.
• Representative coefficients:
  • Wetted zones: high internal film coefficients (nucleate boiling/forced convection)
  • Unwetted zones: lower internal coefficients to reflect vapor-side natural convection
• The SurfaceTemperatureResult object reports heat flux and both metal surface temperatures so material-strength checks can be driven by actual wall metal temperature.

Fire heat loads

• Legacy API 521 pool fire: FireHeatLoadCalculator.api521PoolFireHeatLoad(wettedArea, F) gives the classic correlation in Watts using the 6.19e6·F·A^0.82 metric form.
• Generalized Stefan–Boltzmann: FireHeatLoadCalculator.generalizedStefanBoltzmannHeatFlux(...) provides radiative heat flux using emissivity and view/configuration factors. Combine with convective terms for jet fires or shielding adjustments.
• Live flare radiation: SeparatorFireExposure.evaluate(config, flare, distanceM) can fold in the actual flare heat duty and radiant fraction (via Flare.estimateRadiationHeatFlux) at a specified horizontal distance so you can compare environmental fire sizing vs. radiation from the burning gas itself.

Vessel rupture assessment (Scandpower guideline)

• Use VesselRuptureCalculator.vonMisesStress(P, r, t) to derive von Mises stress from hoop and axial components for thin-walled vessels.
• Compare against material allowable tensile strength via ruptureMargin or isRuptureLikely to flag impending rupture. Feeding these checks with the metal temperatures from the heat-transfer calculator allows temperature-dependent strength curves to be implemented later.

These utilities are designed to plug into existing blowdown scenarios and flare models so that transient depressurization can be tracked alongside external fire loads and structural integrity. The helper SeparatorFireExposure.evaluate(...) (or separator.evaluateFireExposure(...)) wraps area lookup, heat-load estimation, wall temperatures, and rupture checks into a single call so the fire calculations can be dropped into a process simulation loop without hand-wiring each piece. If you want the separator inventory to warm up from the calculated fire load, set the duty on the separator (separator.setDuty(fireResult.totalFireHeat())) and call separator.runTransient(...) so the energy balance absorbs that heat during the timestep.

Separator fire blowdown worked example

The runnable SeparatorFireDepressurizationExample (src/main/java/neqsim/process/util/example/SeparatorFireDepressurizationExample.java) illustrates how to couple a separator depressurization to the flare with the fire utilities:

• Dynamic separator blowdown via BlowdownValve + Orifice feeding a Flare
• API 521 pool-fire loads plus generalized Stefan–Boltzmann radiative flux
• Wetted vs. unwetted wall temperatures from FireHeatTransferCalculator
• Von Mises rupture margin from VesselRuptureCalculator
• Optional separator temperature rise using separator.setDuty(fireResult.totalFireHeat())

To run the illustration:

mvn -pl . -Dexec.mainClass="neqsim.process.util.example.SeparatorFireDepressurizationExample" exec:java

The output prints separator pressure, flow to flare, wall temperatures, rupture margin, and fire heat metrics at each timestep so the fire impact on depressurization can be reviewed end-to-end.