NeqSim provides two related process-equipment models in neqsim.process.equipment.tank:

Class Maintained purpose
Tank A thermodynamic vessel with gas and liquid outlet streams, steady-state execution, optional lumped transient execution, auto-sizing, capacity constraints, and mechanical-design access.
LNGTank A Tank extension that adds a steady heat-ingress and boil-off-gas (BOG) calculation for an LNG inventory.

These models do not have the same contract. Use Tank for the generic vessel state and outlet APIs. Use LNGTank when the required result is the simplified steady LNG heat-leak/BOG screen described below.

API and unit map

Tank accepts an inlet StreamInterface in its constructor or through setInletStream/addStream. Its maintained outlets are getGasOutStream() and getLiquidOutStream().

LNGTank adds the following explicit inputs and outputs:

Method Quantity and unit
setAmbientTemperature(value, "C" or "K") Ambient temperature
setTankSurfaceArea(value) External area in m²
setOverallHeatTransferCoefficient(value) Overall coefficient in W/m²/K
setLNGInventory(value) LNG inventory in kg
setStoragePressure(value) Storage pressure in bara
getHeatIngress() Heat ingress in W
getBOGMassFlowRate() BOG mass flow in kg/hr
getBoilOffRatePctPerDay() Percent of inventory per day
getBOGStream() BOG outlet stream
getLNGProductStream() LNG liquid outlet stream when created

getBoilOffRatePctPerDay() already returns percent/day; do not multiply it by 100 again.

Model equations

The steady screen calculates heat ingress as

\[\dot{Q}_{\mathrm{in}} = U A (T_{\mathrm{ambient}} - T_{\mathrm{LNG}})\]

and BOG mass flow as

\[\dot{m}_{\mathrm{BOG}} = \frac{\dot{Q}_{\mathrm{in}}}{\Delta h_{\mathrm{vap}}}.\]

Here, U is in W/m²/K, A is in m², both temperatures use the same absolute scale, and the latent heat is in J/kg. NeqSim attempts to obtain the latent heat from the flashed inlet fluid at the storage pressure. If that calculation cannot supply a usable two-phase value, the implementation retains its documented default latent heat. The resulting mass rate is converted from kg/s to kg/hr.

Executable LNG boil-off example

The following is one complete Java 8 program. It uses Log4j2, runs the actual LNGTank implementation, and checks heat-ingress closure plus bounded, positive BOG results.

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import neqsim.process.equipment.stream.Stream;
import neqsim.process.equipment.tank.LNGTank;
import neqsim.process.processmodel.ProcessSystem;
import neqsim.thermo.system.SystemInterface;
import neqsim.thermo.system.SystemSrkEos;

public final class LNGTankGuideExample {
  private static final Logger logger = LogManager.getLogger(LNGTankGuideExample.class);

  private LNGTankGuideExample() {}

  public static void main(String[] args) {
    double lngTemperatureC = -162.0;
    double ambientTemperatureC = 25.0;
    double storagePressureBara = 1.1;
    double overallHeatTransferCoefficientWm2K = 0.04;
    double surfaceAreaM2 = 12000.0;
    double inventoryKg = 60000000.0;

    SystemInterface lng = new SystemSrkEos(273.15 + lngTemperatureC, storagePressureBara);
    lng.addComponent("methane", 0.92);
    lng.addComponent("ethane", 0.05);
    lng.addComponent("propane", 0.02);
    lng.addComponent("nitrogen", 0.01);
    lng.setMixingRule("classic");

    Stream feed = new Stream("LNG feed", lng);
    feed.setFlowRate(100000.0, "kg/hr");
    feed.setTemperature(lngTemperatureC, "C");
    feed.setPressure(storagePressureBara, "bara");

    LNGTank tank = new LNGTank("LNG storage", feed);
    tank.setInsulationType(LNGTank.InsulationType.MEMBRANE);
    tank.setAmbientTemperature(ambientTemperatureC, "C");
    tank.setTankSurfaceArea(surfaceAreaM2);
    tank.setOverallHeatTransferCoefficient(overallHeatTransferCoefficientWm2K);
    tank.setLNGInventory(inventoryKg);
    tank.setStoragePressure(storagePressureBara);

    ProcessSystem process = new ProcessSystem();
    process.add(feed);
    process.add(tank);
    process.run();

    double expectedHeatIngressW = overallHeatTransferCoefficientWm2K * surfaceAreaM2
        * (ambientTemperatureC - lngTemperatureC);
    double bogMassFlowKgPerHr = tank.getBOGMassFlowRate();
    double boilOffRatePctPerDay = tank.getBoilOffRatePctPerDay();

    assert Math.abs(tank.getHeatIngress() - expectedHeatIngressW) < 1.0e-6;
    assert bogMassFlowKgPerHr > 0.0;
    assert boilOffRatePctPerDay > 0.0 && boilOffRatePctPerDay < 1.0;
    assert tank.getBOGStream() != null;
    assert Math.abs(tank.getBOGStream().getFlowRate("kg/hr") - bogMassFlowKgPerHr) < 1.0e-6;

    logger.info("Heat ingress: {} W", tank.getHeatIngress());
    logger.info("BOG rate: {} kg/hr ({} %/day)", bogMassFlowKgPerHr, boilOffRatePctPerDay);
  }
}

Run documentation examples with assertions enabled (java -ea) so the engineering checks are not skipped.

Engineering boundaries

This model is an engineering screen, not a detailed storage-tank design or operations simulator. It does not resolve stratification, rollover, weather transients, filling and withdrawal schedules, pressure-relief sizing, vent hydraulics, sloshing, structural loads, or a dynamic vapor-space pressure balance. It also does not replace a vendor thermal design, an API/NFPA/EN code assessment, or an independent process-safety review.

Before using the result, confirm:

  1. the inlet composition and storage state represent the design case;
  2. U, area, ambient temperature, inventory, and storage pressure use the units listed above;
  3. the calculated latent heat is appropriate for the fluid and pressure;
  4. BOG handling, pressure control, relief, and disposal capacity are assessed in their dedicated models.

For API 650/620 mechanical screening, see Mechanical design. For API 2000 vent-demand and rated-capacity screening, see API 2000 tank venting.