Ejector Equipment

Documentation for ejector equipment in NeqSim process simulation.

Table of Contents

Overview

Location: neqsim.process.equipment.ejector

Classes: | Class | Description | |——-|————-| | Ejector | Steam/gas ejector for compression | | EjectorDesignResult | Design calculation results |

Ejectors use the kinetic energy of a high-pressure motive stream to entrain and compress a low-pressure suction stream. Common applications include:

Ejector Class

Basic Usage

import neqsim.process.equipment.ejector.Ejector;

// Create ejector with motive and suction streams
Ejector ejector = new Ejector("Ejector-100", motiveStream, suctionStream);
ejector.setDischargePressure(5.0);  // bara
ejector.setEfficiencyIsentropic(0.75);  // Nozzle efficiency
ejector.setDiffuserEfficiency(0.80);    // Diffuser efficiency
ejector.run();

// Get mixed stream
StreamInterface mixedStream = ejector.getMixedStream();
double dischargeT = mixedStream.getTemperature("C");
double dischargeP = mixedStream.getPressure("bara");

Stream Setup

// High-pressure motive stream (e.g., HP steam or gas)
SystemInterface motiveFluid = new SystemSrkEos(250.0, 10.0);
motiveFluid.addComponent("water", 1.0);
motiveFluid.setMixingRule("classic");

Stream motiveStream = new Stream("Motive Steam", motiveFluid);
motiveStream.setFlowRate(1000.0, "kg/hr");
motiveStream.run();

// Low-pressure suction stream
SystemInterface suctionFluid = new SystemSrkEos(300.0, 1.5);
suctionFluid.addComponent("methane", 0.95);
suctionFluid.addComponent("ethane", 0.05);
suctionFluid.setMixingRule("classic");

Stream suctionStream = new Stream("Suction Gas", suctionFluid);
suctionStream.setFlowRate(500.0, "kg/hr");
suctionStream.run();

Operating Principles

Ejector Sections

An ejector consists of four main sections:

  1. Nozzle: Converts motive stream pressure to velocity
  2. Suction Chamber: Entrains low-pressure gas
  3. Mixing Chamber: Momentum exchange between streams
  4. Diffuser: Converts velocity back to pressure

Energy Balance

The ejector performs isentropic expansion and compression:

\[\eta_{nozzle} = \frac{h_1 - h_2}{h_1 - h_{2s}}\] \[\eta_{diffuser} = \frac{h_{4s} - h_3}{h_4 - h_3}\]

Where:

Entrainment Ratio

The entrainment ratio (ER) is defined as:

\[ER = \frac{\dot{m}_{suction}}{\dot{m}_{motive}}\]

Design Parameters

Efficiency Settings

// Nozzle isentropic efficiency (typically 0.7-0.9)
ejector.setEfficiencyIsentropic(0.75);

// Diffuser efficiency (typically 0.7-0.85)
ejector.setDiffuserEfficiency(0.80);

Discharge Pressure

// Set target discharge pressure
ejector.setDischargePressure(5.0);  // bara

Design Velocities

// Optional: Override default suction and diffuser velocities
ejector.setDesignSuctionVelocity(30.0);  // m/s
ejector.setDesignDiffuserOutletVelocity(20.0);  // m/s

Connection Lengths

// Optional: Set connection pipe lengths for pressure drop
ejector.setSuctionConnectionLength(2.0);  // m
ejector.setDischargeConnectionLength(3.0);  // m

Mechanical Design

// Get mechanical design parameters
EjectorMechanicalDesign mechDesign = ejector.getMechanicalDesign();

// Calculate sizing
mechDesign.calcDesign();

// Get geometry
double throatDiameter = mechDesign.getThroatDiameter();  // m
double nozzleLength = mechDesign.getNozzleLength();  // m
double mixingLength = mechDesign.getMixingLength();  // m
double diffuserLength = mechDesign.getDiffuserLength();  // m

Usage Examples

Flare Gas Recovery

ProcessSystem process = new ProcessSystem();

// High-pressure motive gas from compressor discharge
Stream motiveGas = new Stream("HP Gas", hpGasFluid);
motiveGas.setFlowRate(2000.0, "kg/hr");
motiveGas.setTemperature(60.0, "C");
motiveGas.setPressure(40.0, "bara");
process.add(motiveGas);

// Low-pressure flare header gas
Stream flareGas = new Stream("Flare Gas", flareGasFluid);
flareGas.setFlowRate(500.0, "kg/hr");
flareGas.setTemperature(40.0, "C");
flareGas.setPressure(1.2, "bara");
process.add(flareGas);

// Ejector to recover flare gas
Ejector fgr = new Ejector("FGR Ejector", motiveGas, flareGas);
fgr.setDischargePressure(8.0);  // bara
fgr.setEfficiencyIsentropic(0.75);
fgr.setDiffuserEfficiency(0.80);
process.add(fgr);

// Run process
process.run();

// Results
double entrainmentRatio = flareGas.getFlowRate("kg/hr") / motiveGas.getFlowRate("kg/hr");
System.out.println("Entrainment ratio: " + entrainmentRatio);
System.out.println("Discharge pressure: " + fgr.getMixedStream().getPressure("bara") + " bara");

Steam Ejector Vacuum System

// HP steam as motive fluid
Stream hpSteam = new Stream("HP Steam", steamFluid);
hpSteam.setFlowRate(1500.0, "kg/hr");
hpSteam.setTemperature(200.0, "C");
hpSteam.setPressure(10.0, "bara");

// Vacuum overhead vapor
Stream vacuumVapor = new Stream("Vacuum Vapor", vaporFluid);
vacuumVapor.setFlowRate(300.0, "kg/hr");
vacuumVapor.setTemperature(50.0, "C");
vacuumVapor.setPressure(0.1, "bara");

// First stage ejector
Ejector ejector1 = new Ejector("1st Stage", hpSteam, vacuumVapor);
ejector1.setDischargePressure(0.5);  // bara
ejector1.run();

// Intercondenser
Cooler intercondenser = new Cooler("Intercondenser", ejector1.getMixedStream());
intercondenser.setOutTemperature(40.0, "C");

// Second stage ejector
Ejector ejector2 = new Ejector("2nd Stage", hpSteam2, intercondenser.getOutletStream());
ejector2.setDischargePressure(1.1);  // bara
ejector2.run();

Performance Curves

Entrainment vs Compression Ratio

For a given motive pressure and geometry, ejector performance follows characteristic curves:

// Calculate performance at different suction pressures
double[] suctionPressures = {0.5, 1.0, 1.5, 2.0};  // bara
for (double Ps : suctionPressures) {
    suctionStream.setPressure(Ps, "bara");
    suctionStream.run();
    ejector.run();
    
    double compressionRatio = ejector.getMixedStream().getPressure("bara") / Ps;
    System.out.println("Suction P: " + Ps + " bara, CR: " + compressionRatio);
}