neqsim-relief-flare-network

name: neqsim-relief-flare-network version: "1.0.0" description: "Relief and flare system design — PSV sizing per API 520 (gas/liquid/two-phase, fire case), API 521 fire heat input, flare load summation, flare-tip sizing, radiation contour (API 521 §6), header back-pressure & Mach. USE WHEN: a task involves PSV sizing, relief contingency analysis, thermal relief for trapped liquid, flare network hydraulics, flare radiation/dispersion, or PSV→flare integration. Anchors on neqsim.process.util.fire.ReliefValveSizing, neqsim.process.equipment.flare.{Flare, FlareStack}, neqsim.process.equipment.valve.SafetyValve." last_verified: "2026-04-26" requires: java_packages: [neqsim.process.util.fire, neqsim.process.equipment.flare, neqsim.process.equipment.valve]

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 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 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();

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

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-dynamic-simulation — depressurization (blowdown) is separate from PSV
• neqsim-mechanical-design — PSV mechanical via SafetyValveMechanicalDesign
• neqsim-standards-lookup — API 520 / 521 / 526 / 537