Neqsim Relief Flare Network

NeqSim Relief & Flare Network Skill

End-to-end relief design — from individual PSV sizing through plant-wide load summation, flare-tip selection, and radiation/dispersion checks per API 520, API 521, API 537.

When to Use

• Sizing a single PSV (gas / liquid / two-phase / fire case)
• Checking whether a blocked-in liquid segment needs thermal relief or source-term handoff after rupture screening
• API 521 fire heat input on wetted area
• Aggregating simultaneous relief loads to a flare header
• Flare tip diameter and stack height (radiation)
• Header hydraulics: back-pressure on PSVs, Mach < 0.7
• Sour-gas dispersion check (toxic clouds)

Standards: API 520 Part I/II, API 521 (relief contingencies + radiation), API 537 (flare equipment), NFPA 30, EN ISO 23251.

Pattern 1 — Gas-phase PSV (API 520)

import neqsim.process.util.fire.ReliefValveSizing;
import neqsim.process.util.fire.ReliefValveSizing.PSVSizingResult;

PSVSizingResult psv = ReliefValveSizing.calculateRequiredArea(
    massFlowRate_kgs,
    setPressure_barg,
    backPressure_barg,
    T_K,
    MW,
    k_cpcv,            // ratio of specific heats
    Z_compressibility,
    overpressure_frac, // 0.10 process, 0.21 fire
    Kd                 // discharge coeff (0.975 typical)
);

double area_m2  = psv.getRequiredArea();
String orifice  = psv.getRecommendedOrifice();        // API 526 letter
String issues   = ReliefValveSizing.validateSizing(psv, /*fire*/ false);

Pattern 2 — Fire Case (API 521)

double Q_fire_W = ReliefValveSizing.calculateAPI521FireHeatInput(
    wettedAreaM2,
    /*hasDrainage*/ true,
    /*hasFireProofInsulation*/ false
);

// Mass flow = Q_fire / latent heat at relieving conditions
double mdot = Q_fire_W / latentHeat_J_per_kg;

PSVSizingResult psv = ReliefValveSizing.calculateRequiredArea(
    mdot, setP, backP, T_relief, MW, k, Z,
    /*overpressure_frac*/ 0.21,   // fire allows 21%
    Kd
);

API 521 fire equation: Q = C × F × A_wet^0.82 with credit factors for drainage / insulation.

Pattern 3 — Liquid PSV (API 520 Part I §5.8)

import neqsim.process.util.fire.ReliefValveSizing.LiquidPSVSizingResult;

LiquidPSVSizingResult lpsv = ReliefValveSizing.calculateLiquidReliefArea(
    volumeFlowRate_m3s,
    setPressure_barg,
    backPressure_barg,
    rho_kg_m3,
    viscosity_cP,
    Kd
);

Pattern 4 — Two-Phase (Omega Method)

double area = ReliefValveSizing.calculateTwoPhaseReliefArea(
    massFlow_kgs, setP_barg, backP_barg, omega, rho_relief, Kd
);

Pattern 4b — Integrated Overpressure Study (TR3001 / API 521)

For a full overpressure-protection study on one protected item — enumerate credible relief contingencies, pick the governing case, size the PSV, and check acceptance — use neqsim.process.safety.overpressure. Each cause calculator is fluent and returns an immutable ReliefScenario; the engine selects the maximum-rate credible scenario and sizes accordingly (vapour via ReliefValveSizing API 520; liquid via the API 520 liquid method; two-phase via the omega method).

import neqsim.process.safety.overpressure.*;

// 1. Cause scenarios (fluent → ReliefScenario)
ReliefScenario blocked = new BlockedOutletRelief().setName("Blocked gas outlet")
    .setInflowRateKgPerHr(36000.0).setReliefPressureBara(50.0)
    .setReliefTemperatureC(20.0).setFluid(gas).calculate();
ReliefScenario fire = new FireCaseRelief().setName("Pool fire")
    .setVesselDiameterM(2.0).setWettedHeightM(3.0)   // or setWettedAreaM2(..)
    .setHasDrainage(true).setHasFireFighting(true)
    .setLatentHeatJPerKg(350000.0).setReliefPressureBara(60.0)
    .setReliefTemperatureC(120.0).setFluid(gas).calculate();

// 2. Engine: governing case + sizing + acceptance
ProtectedItem item = new ProtectedItem("V-100", 100.0)   // tag, MAWP [bara]
    .setReliefSetPressureBara(100.0).setBackPressureBara(1.5);
OverpressureStudyResult result = new OverpressureProtectionStudy(item)
    .addScenario(blocked).addScenario(fire).evaluate();

result.getGoverningScenario().getName();   // worst credible case
result.getRequiredAreaIn2();               // API 526 required orifice area
result.getRecommendedOrifice();            // orifice letter
result.isCapacityAdequate();               // area-based adequacy
result.getAcceptance().getAccumulationFraction();  // vs 1.10 / 1.16 / 1.21

// 3. TR3001 compliance findings (PASS/FAIL/NEEDS_REVIEW)
List<ComplianceFinding> findings = new TR3001ComplianceChecker().check(result);
boolean compliant = new TR3001ComplianceChecker().isCompliant(findings);

// 4. Roll relief loads up to a disposal header (API 521 §5.3)
ReliefDisposalResult disposal = new ReliefDisposalNetwork("Fire zone 1")
    .addRelief(resultA, true).addRelief(resultB, true).calculate();
disposal.getTotalSimultaneousKgPerS();   // simultaneous header load
disposal.getPeakSingleKgPerS();          // largest single contributor
disposal.getGoverningContributor();

• Cause calculators: BlockedOutletRelief, CheckValveLeakRelief, ControlValveFailureRelief, TubeRuptureRelief, FireCaseRelief.
• Set ReliefScenario phase to LIQUID (with densityKgPerM3/viscosityPaS) or TWO_PHASE (with gasMassFraction, gasDensityKgPerM3, liquidDensityKgPerM3, latentHeatJPerKg, liquidHeatCapacityJPerKgK) to trigger the matching sizing path; missing two-phase inputs are reported as warnings.
• Accumulation limits: 1.10 single non-fire, 1.16 multiple, 1.21 fire (ASME VIII Div 1).
• Verified by OverpressureProtectionStudyTest + OverpressureExtensionsTest.

Adequacy is judged by AREA, not by re-plugging the selected area into the nozzle equation: calculateRequiredArea (API 520 empirical) and the nozzle capacity formula use different coefficient bases and are not inverses.

Pattern 5 — Flare Tip & Stack (API 537 + 521 §6)

import neqsim.process.equipment.flare.Flare;

Flare flare = new Flare("MainFlare");
flare.setInletStream(reliefStream);
flare.setRadiantFraction(0.30);                // typical 0.20–0.40
flare.setTipDiameter(0.5);                     // m
flare.setDesignHeatDutyCapacity(150.0, "MW");
flare.run(UUID.randomUUID());

// Radiation at ground distance
double q_Wm2 = flare.estimateRadiationHeatFlux(75.0);   // 75 m
double dSafe = flare.radiationDistanceForFlux(4730.0);  // K = 1.5 kW/m² × 4 hr exposure

API 521 §6.4 radiation criteria:

Pattern 5b — Detailed Flare Flame & Sterile-Zone (API 537)

For sterile-zone radii, wind-tilted flame geometry, and flare noise, use Api537FlareFlameModel (Kent 1968 flame length + tilt + iso-flux solver):

import neqsim.process.safety.fire.Api537FlareFlameModel;

Api537FlareFlameModel flame = new Api537FlareFlameModel(
        50.0,      // relief mass flow [kg/s]
        50.0e6,    // heat of combustion [J/kg]
        0.20,      // radiant fraction
        200.0)     // tip exit velocity [m/s]
    .setStackHeightM(40.0)
    .setWindSpeedMPerS(10.0);

double lFlame = flame.flameLengthM();
double tilt   = flame.flameTiltRad();
double r158   = flame.sterileZoneRadiusM(Api537FlareFlameModel.FLUX_1_58_KW); // ~personnel continuous
double r473   = flame.sterileZoneRadiusM(Api537FlareFlameModel.FLUX_4_73_KW); // property line
double r946   = flame.sterileZoneRadiusM(Api537FlareFlameModel.FLUX_9_46_KW); // emergency-only
double q75    = flame.heatFluxAtGroundDistance(75.0);  // W/m²
double pwl    = flame.soundPowerLevelDb();
double spl    = flame.soundPressureLevelDb(100.0);

Verified by Api537FlareFlameModelTest. Radii are nested (lower flux reaches further); flame tilts downwind and the tip moves horizontally with wind speed.

Pattern 6 — Plant Load Summation

For each contingency (general power failure, total reflux failure, fire zone):

1. List PSVs that lift simultaneously
2. Sum mass flows at each PSV at its relieving conditions
3. Pick the governing contingency (highest header load)
4. Size the flare for that load

double totalReliefLoad = psvs.stream()
    .filter(p -> isActiveDuring(p, contingency))
    .mapToDouble(p -> p.getMassFlowCapacity())
    .sum();

For simultaneous blowdown contingencies (multiple BDVs into one header), use MultiVesselBlowdownStudy (see neqsim-depressurization-mdmt) — it superimposes the transient blowdown curves on a common time grid and reports the peak combined header mass flow and the header Mach at that instant, which is the load that actually sizes the header.

Pattern 7 — Header Back-Pressure & Mach

For balanced-bellows / pilot-operated PSVs, verify:

• Built-up back-pressure ≤ 50% set (conventional 10%)
• Header Mach < 0.7 at any location (avoid critical flow choking design)

import neqsim.process.equipment.valve.SafetyValve;
SafetyValve sv = new SafetyValve("PSV-101", inletStream);
sv.setSetPressure(120.0, "barg");
sv.setBackPressure(15.0, "barg");
sv.run();
double KbCorrection = sv.getBackPressureCorrectionFactor();  // > 0.6 for balanced PSV

Pattern 8 — Dispersion of Unignited Release

FlareDispersionSurrogateDTO disp = flare.getDispersionSurrogate();
// Use to bound H2S / SO2 ground concentration vs. IDLH/ERPG-2

For a governed production-readiness record, use neqsim.process.engineering.safety.FlareConsequenceCalculation. It combines explicit point-source radiation, neutral Gaussian centerline dispersion, spherical noise spreading, and tip-Mach constraints in one typed result with uncertainty and provenance. Set productionQualification=true only with standards/evidence references and consequenceMethodApplicability=approved. This is a screening interface, not a substitute for validated complex-terrain, stability-class, toxic, combustion, or detailed acoustic modeling.

Common Mistakes

Validation Checklist

• Each contingency has a documented worst-case mass flow
• Wetted-area calculation shows boundary up to 7.6 m
• Drainage / insulation credits supported by P&ID review
• Header sized so Mach < 0.7 at peak load
• Built-up back-pressure ≤ 10% (conventional) or ≤ 50% (balanced) of set
• Inlet line ΔP < 3% of set pressure
• Flare radiation ≤ 4.73 kW/m² at property line (incl. solar)
• Dispersion check at flame-out (toxic species)
• Results saved to results.json under relief_system with PSV table + flare load summary

Related Skills

• neqsim-process-safety — when PSV is the IPL of last resort in LOPA
• neqsim-trapped-liquid-fire-rupture — blocked-in liquid fire rupture screening before thermal relief/PFP decisions
• neqsim-depressurization-mdmt — blowdown transients + MultiVesselBlowdownStudy for coupled header loads
• neqsim-consequence-analysis — Api537FlareFlameModel radiation/noise and hazardous-area zoning
• neqsim-dynamic-simulation — depressurization (blowdown) is separate from PSV
• neqsim-mechanical-design — PSV mechanical via SafetyValveMechanicalDesign
• neqsim-standards-lookup — API 520 / 521 / 526 / 537