neqsim.process.safety.inventory.TrappedInventoryCalculator converts documented equipment and pipe volumes into a traceable trapped-inventory result. Use it when a technical-safety study needs a source term for blowdown, relief, flare-load, closed-flare, maintenance isolation, or MDMT screening.

The class is intended to sit between evidence extraction and dynamic safety calculations:

P&ID / STID / line list / datasheet evidence
  -> equipment and pipe segment volumes
  -> TrappedInventoryCalculator
  -> gas and liquid inventory with evidence references
  -> DepressurizationSimulator, flare-load screen, MDMTCalculator, or report JSON

Method

For each segment, the calculator flashes a cloned NeqSim fluid at the configured operating pressure and temperature, reads gas and liquid densities, and applies volume fill fractions.

\[m_{gas,i} = V_{gas,i}\rho_g(P,T,z)\] \[m_{liquid,i} = V_{liquid,i}\rho_l(P,T,z)\]

For pipe segments, internal volume is calculated from internal diameter and length:

\[V_{pipe} = \frac{\pi D_i^2 L}{4}\]

The aggregate result reports total gas volume, liquid volume, gas mass, liquid mass, per-segment results, evidence records, and warnings for missing evidence or fallback liquid density use.

Code Pattern

import neqsim.process.safety.barrier.DocumentEvidence;
import neqsim.process.safety.depressurization.DepressurizationSimulator;
import neqsim.process.safety.depressurization.DepressurizationSimulator.DepressurizationResult;
import neqsim.process.safety.inventory.TrappedInventoryCalculator;
import neqsim.process.safety.inventory.TrappedInventoryCalculator.InventoryResult;
import neqsim.thermo.system.SystemInterface;
import neqsim.thermo.system.SystemSrkEos;

SystemInterface gas = new SystemSrkEos(300.15, 20.0);
gas.addComponent("methane", 0.90);
gas.addComponent("ethane", 0.07);
gas.addComponent("propane", 0.03);
gas.setMixingRule("classic");

DocumentEvidence evidence = new DocumentEvidence(
    "E-INV-001",
    "P-ID-001",
    "Gas recompression P&ID",
    "A",
    "isolation boundary",
    1,
    "references/P-ID-001.pdf",
    "Pipe P-100 and compressor casing inside the isolated boundary.",
    0.90);

TrappedInventoryCalculator calculator = new TrappedInventoryCalculator()
    .setFluid(gas)
    .setOperatingConditions(20.0, "bara", 27.0, "C")
    .addPipeSegment("P-100", 0.1524, 18.0, 0.0, evidence)
    .addEquipmentVolume("K-100 casing", 0.75, 0.0, evidence);

InventoryResult inventory = calculator.calculate();
double gasMassKg = inventory.getTotalGasMassKg();
double isolatedVolumeM3 = inventory.getTotalVolumeM3();
String inventoryJson = calculator.toJson();

SystemInterface blowdownFluid = calculator.createDepressurizationFluid();
DepressurizationSimulator simulator = new DepressurizationSimulator(
    blowdownFluid,
    inventory.getTotalGasVolumeM3(),
    0.010,
    0.72,
    1.5e5);
simulator.setMaxTime(300.0);
simulator.setTimeStep(1.0);
DepressurizationResult blowdown = simulator.run();

This example is covered by TrappedInventoryCalculatorTest#documentedWorkflowCalculatesInventoryAndCreatesBlowdownFluid.

API Summary

Method Use
setFluid(SystemInterface fluid) Sets the representative fluid. Configure components and mixing rule before passing it in.
setOperatingConditions(double pressure, String pressureUnit, double temperature, String temperatureUnit) Sets pressure and temperature with unit conversion, for example bara and C.
setOperatingConditions(double pressureBara, double temperatureK) Sets pressure in bara and temperature in K.
setFallbackLiquidDensity(double densityKgPerM3) Sets fallback liquid density when a liquid fill fraction is specified but the flashed fluid has no liquid phase.
addPipeSegment(...) Adds an isolated pipe segment from internal diameter, length, liquid fill fraction, and optional evidence.
addEquipmentVolume(...) Adds a vessel, compressor casing, exchanger channel, or other documented equipment volume.
addVolumeSegment(...) Adds a generic volume segment with engineering unit conversion.
calculate() Returns an InventoryResult with totals, segment results, and warnings.
createDepressurizationFluid() Creates a lumped gas inventory fluid for DepressurizationSimulator.
toJson() Returns report-ready JSON with segment evidence included.

Evidence Handling

Pass DocumentEvidence to each segment when the volume is derived from drawings, line lists, equipment datasheets, or STID/P&ID extraction. Missing evidence is allowed, but InventoryResult.getWarnings() reports it so screening studies can distinguish documented assumptions from placeholders.

Useful evidence fields include:

Field Example use
evidenceId Stable identifier for the extracted data point.
documentId Drawing, datasheet, report, or line-list identifier.
section and page Location inside the source document.
sourceReference Local reference path or system reference.
excerpt Short quoted basis for the segment.
confidence Extraction confidence or engineering confidence from 0 to 1.

Interpreting Results

Use gas inventory for blowdown and flare source terms. Use liquid inventory for flare knockout drum screening, drain/purge planning, and carryover checks. If liquid volume is specified but the flashed representative fluid has no liquid phase, the fallback density is used and a warning is emitted.

The result is a screening basis unless all of these are current and verified:

Input Why it matters
Isolation boundary Total inventory scales nearly linearly with trapped gas volume.
Internal pipe diameter and length Nominal pipe size is not always the same as internal diameter.
Equipment hold-up volume Compressor casings, scrubbers, exchangers, and dead legs can dominate small inventories.
Initial pressure and temperature Density and blowdown stored energy depend directly on operating state.
Fluid composition Richer gas increases density and may change condensation and cooling behavior.
BDV/orifice/Cv data Controls peak mass flow and depressuring time after inventory is defined.
Material and thickness Needed before a cold-temperature result can close an MDMT assessment.

Typical Workflow

  1. Extract current isolation boundary from P&ID, STID, cause-and-effect, and operating procedure.
  2. Convert each pipe or equipment item into a segment with evidence.
  3. Flash the representative fluid at the initial operating condition.
  4. Review warnings for missing evidence or fallback density use.
  5. Use gas inventory as input to DepressurizationSimulator or a flare-load screen.
  6. Use minimum blowdown temperatures with MDMTCalculator for material verification.
  7. Save toJson() output in the task report so reviewers can trace each segment back to its source.

See Also