Absorbers and Strippers

Documentation for mass transfer columns in NeqSim.

Table of Contents

Overview

Location: neqsim.process.equipment.absorber

Classes: | Class | Description | | ———————– | —————————————————– | | Absorber | General absorption column | | SimpleAbsorber | Simplified absorber model (base class) | | SimpleTEGAbsorber | TEG dehydration with Fs-factor sizing | | SimpleAmineAbsorber | Amine gas sweetening (MDEA, DEA, MEA) | | WaterStripperColumn | Water stripping column |

Absorbers transfer components from gas to liquid phase, while strippers transfer from liquid to gas.

Absorber

Basic Usage

import neqsim.process.equipment.absorber.Absorber;

Absorber absorber = new Absorber("Amine Absorber");
absorber.addGasInStream(gasStream);
absorber.addSolventInStream(amineSolution);
absorber.setNumberOfTheoreticalStages(10);
absorber.run();

Stream sweetGas = absorber.getGasOutStream();
Stream richAmine = absorber.getLiquidOutStream();

Absorption Efficiency

// Component removal efficiency
absorber.setRemovalEfficiency("CO2", 0.95);  // 95% CO2 removal
absorber.setRemovalEfficiency("H2S", 0.99);  // 99% H2S removal

Stage Configuration

absorber.setNumberOfTheoreticalStages(20);
absorber.setStageEfficiency(0.7);  // Murphree efficiency

Stripper

Basic Usage

import neqsim.process.equipment.absorber.WaterStripperColumn;

WaterStripperColumn stripper = new WaterStripperColumn("Regenerator");
stripper.setLiquidInStream(richAmine);
stripper.setNumberOfStages(15);
stripper.setReboilerTemperature(120.0, "C");
stripper.run();

Stream leanAmine = stripper.getLiquidOutStream();
Stream acidGas = stripper.getGasOutStream();

Simple Absorber

Simplified mass transfer model.

Usage

import neqsim.process.equipment.absorber.SimpleAbsorber;

SimpleAbsorber absorber = new SimpleAbsorber("CO2 Absorber");
absorber.addGasInStream(feedGas);
absorber.addSolventInStream(solvent);
absorber.setAbsorptionEfficiency(0.90);
absorber.run();

Fs-Factor and Wetting Rate

The base SimpleAbsorber class provides Fs-factor and wetting rate calculations used by all absorber subclasses:

\[F_s = v_s \cdot \sqrt{\rho_g}\]

where $v_s$ is the superficial gas velocity (m/s) and $\rho_g$ is gas density (kg/m3).

The wetting rate is the liquid volume flowing per unit packing area:

\[WR = \frac{Q_L}{\pi / 4 \cdot D^2}\]

Simple TEG Absorber

SimpleTEGAbsorber extends the base absorber with TEG-specific sizing via the Kremser equation and Fs-factor capacity checking.

Fs-Factor Sizing

The Fs-factor determines whether the contactor diameter is adequate for the gas load. Industry practice limits Fs to approximately 2.5-3.5 (Pa)^0.5 for structured packing:

import neqsim.process.equipment.absorber.SimpleTEGAbsorber;

SimpleTEGAbsorber tegAbsorber = new SimpleTEGAbsorber("TEG Contactor");
tegAbsorber.addGasInStream(wetGasStream);
tegAbsorber.addSolventInStream(leanTEGStream);
tegAbsorber.run();

// Fs-factor capacity check
double fs = tegAbsorber.getFsFactor();
double maxFs = tegAbsorber.getMaxAllowableFsFactor();  // default 3.0
boolean withinLimit = tegAbsorber.isFsFactorWithinDesignLimit();
double utilization = tegAbsorber.getFsFactorUtilization();  // fs / maxFs

// Minimum diameter needed
double minDiameter = tegAbsorber.getMinimumDiameterForFsLimit();

// Full validation report
String report = tegAbsorber.validateContactorDesign();
System.out.println(report);

TEG Quality and Water Dew Point

// Check equilibrium water dew point from TEG purity
double dewPointC = tegAbsorber.getLeanTEGEquilibriumWaterDewPoint(99.5);
System.out.println("Water dew point at 99.5 wt% TEG: " + dewPointC + " °C");

// Check if TEG quality margin is adequate
boolean adequate = tegAbsorber.hasAdequateTEGQualityMargin(99.5, -18.0);

Key Methods

Method Description
getFsFactor() Current Fs-factor from gas outlet stream
getMaxAllowableFsFactor() Design limit (default 3.0)
setMaxAllowableFsFactor(double) Override design limit
isFsFactorWithinDesignLimit() Check if Fs is below limit
getFsFactorUtilization() Fraction of capacity used (0-1)
getMinimumDiameterForFsLimit() Minimum diameter at current gas load
getLeanTEGEquilibriumWaterDewPoint(double) Water dew point for a TEG purity
hasAdequateTEGQualityMargin(double, double) TEG purity vs target dew point
validateContactorDesign() Full text validation report

Simple Amine Absorber

SimpleAmineAbsorber models amine-based gas sweetening for CO2 and H2S removal. It calculates acid gas removal by applying user-specified removal efficiencies, and includes design calculations for column sizing, loading, and validation.

Basic Usage

import neqsim.process.equipment.absorber.SimpleAmineAbsorber;
import neqsim.process.equipment.stream.Stream;
import neqsim.process.processmodel.ProcessSystem;
import neqsim.thermo.system.SystemSrkEos;

// Create sour gas
SystemSrkEos sourGas = new SystemSrkEos(273.15 + 40.0, 70.0);
sourGas.addComponent("methane", 0.85);
sourGas.addComponent("CO2", 0.10);
sourGas.addComponent("H2S", 0.005);
sourGas.addComponent("ethane", 0.045);
sourGas.setMixingRule("classic");

Stream sourGasStream = new Stream("Sour Gas", sourGas);
sourGasStream.setFlowRate(50000.0, "kg/hr");

// Create amine absorber
SimpleAmineAbsorber absorber = new SimpleAmineAbsorber("MDEA Absorber", sourGasStream);
absorber.setAmineType("MDEA");
absorber.setAmineConcentrationWtPct(50.0);
absorber.setCO2RemovalEfficiency(0.95);
absorber.setH2SRemovalEfficiency(0.99);

// Wire into process
ProcessSystem process = new ProcessSystem();
process.add(sourGasStream);
process.add(absorber);
process.run();

// Get treated gas
Stream sweetGas = (Stream) absorber.getSweetGasOutStream();

With Lean Amine Stream

When a lean amine stream is provided, the absorber also calculates the rich amine outlet (acid gas picked up by the solvent):

// Lean amine
SystemSrkEos amineFluid = new SystemSrkEos(273.15 + 42.0, 70.0);
amineFluid.addComponent("MDEA", 0.50);
amineFluid.addComponent("water", 0.50);
amineFluid.setMixingRule("classic");

Stream leanAmine = new Stream("Lean Amine", amineFluid);
leanAmine.setFlowRate(30000.0, "kg/hr");

absorber.setLeanAmineInStream(leanAmine);
process.add(leanAmine);
process.run();

// Rich amine with absorbed acid gas
Stream richAmine = (Stream) absorber.getRichAmineOutStream();

Design Calculations

// Acid gas loading
absorber.setLeanAmineLoading(0.01);
absorber.setApproachToEquilibrium(0.70);
double richLoading = absorber.calcRichAmineLoading(0.50);
// richLoading = 0.01 + (0.50 - 0.01) * 0.70 = 0.353 mol/mol

// Amine circulation rate
double rate = absorber.calcRequiredCirculationRate(
    10.0,     // mol/s acid gas to remove
    1050.0,   // kg/m3 amine density
    0.119     // kg/mol MDEA molar mass
);

// Packing height with redistribution sections
absorber.setMaxPackingHeightPerSection(5.5);
absorber.calcPackingHeight(1.0, 12.0);  // HTU=1.0m, NTU=12
int sections = absorber.getNumberOfPackingSections();  // 3

// Demister K-factor
double kFactor = absorber.calcDemisterKFactor(2.0, 50.0, 1050.0);
boolean withinLimit = absorber.isDemisterWithinLimit();  // K <= 0.08

// Temperature margin check
boolean tempOk = absorber.checkAmineTemperatureMargin(30.0, 37.0);  // need 6°C margin

// Foaming derating
double effectiveFlow = absorber.getEffectiveGasCapacityWithFoamingMargin(100.0);  // 120.0

Design Validation

// Run all design checks at once
Map<String, SimpleAmineAbsorber.DesignCheck> checks = absorber.validateDesign();
for (Map.Entry<String, SimpleAmineAbsorber.DesignCheck> entry : checks.entrySet()) {
    System.out.println(entry.getKey() + ": " +
        (entry.getValue().isPassed() ? "PASS" : "FAIL") +
        " - " + entry.getValue().getDetail());
}

// Get full design summary
System.out.println(absorber.getDesignSummary());

Design Parameters

Parameter Default Description
Amine type MDEA Amine solvent (MDEA, DEA, MEA)
Concentration 50 wt% Amine weight percent in lean solvent
CO2 removal 90% Overall CO2 removal efficiency
H2S removal 99% Overall H2S removal efficiency
Foaming margin 20% Capacity derating for foaming
Max packing height 5.5 m Maximum per section before redistribution
Amine temperature margin 6 °C Lean amine T above gas feed T
Gas carry-under 0.03 Am3 gas per Am3 amine
Demister K-factor limit 0.08 m/s Wire mesh at gas outlet
Approach to equilibrium 70% Fraction of thermodynamic equilibrium loading

Examples

Example 1: Amine Gas Treating

import neqsim.thermo.system.SystemSrkCPAstatoil;
import neqsim.process.equipment.stream.Stream;
import neqsim.process.equipment.absorber.Absorber;

// Sour gas
SystemSrkCPAstatoil sourGas = new SystemSrkCPAstatoil(313.15, 70.0);
sourGas.addComponent("methane", 0.85);
sourGas.addComponent("CO2", 0.10);
sourGas.addComponent("H2S", 0.01);
sourGas.addComponent("water", 0.04);
sourGas.setMixingRule("classic");

Stream gasIn = new Stream("Sour Gas", sourGas);
gasIn.setFlowRate(100000.0, "Sm3/hr");
gasIn.run();

// Lean amine (MDEA solution)
SystemSrkCPAstatoil amine = new SystemSrkCPAstatoil(313.15, 70.0);
amine.addComponent("water", 0.50);
amine.addComponent("MDEA", 0.50);
amine.setMixingRule("classic");

Stream leanAmine = new Stream("Lean Amine", amine);
leanAmine.setFlowRate(50000.0, "kg/hr");
leanAmine.run();

// Absorber
Absorber absorber = new Absorber("Amine Contactor");
absorber.addGasInStream(gasIn);
absorber.addSolventInStream(leanAmine);
absorber.setNumberOfTheoreticalStages(15);
absorber.run();

// Results
Stream sweetGas = absorber.getGasOutStream();
double co2Out = sweetGas.getFluid().getMoleFraction("CO2") * 1e6;  // ppm
System.out.println("Sweet gas CO2: " + co2Out + " ppm");

Example 2: TEG Dehydration

// Wet natural gas
SystemSrkEos wetGas = new SystemSrkEos(303.15, 70.0);
wetGas.addComponent("methane", 0.90);
wetGas.addComponent("ethane", 0.05);
wetGas.addComponent("propane", 0.03);
wetGas.addComponent("water", 0.02);
wetGas.setMixingRule("classic");

Stream gasIn = new Stream("Wet Gas", wetGas);
gasIn.setFlowRate(5000000.0, "Sm3/day");
gasIn.run();

// Lean TEG
SystemSrkEos teg = new SystemSrkEos(313.15, 70.0);
teg.addComponent("TEG", 0.99);
teg.addComponent("water", 0.01);
teg.setMixingRule("classic");

Stream leanTEG = new Stream("Lean TEG", teg);
leanTEG.setFlowRate(1000.0, "kg/hr");
leanTEG.run();

// Contactor
Absorber contactor = new Absorber("TEG Contactor");
contactor.addGasInStream(gasIn);
contactor.addSolventInStream(leanTEG);
contactor.setNumberOfTheoreticalStages(3);
contactor.run();

Stream dryGas = contactor.getGasOutStream();
double waterContent = dryGas.getFluid().getMoleFraction("water") * 1e6;
System.out.println("Dry gas water content: " + waterContent + " ppm");

Example 3: Water Wash Column

// Gas with methanol
SystemSrkEos gas = new SystemSrkEos(280.0, 50.0);
gas.addComponent("methane", 0.95);
gas.addComponent("methanol", 0.03);
gas.addComponent("water", 0.02);
gas.setMixingRule("classic");

Stream gasIn = new Stream("Gas", gas);
gasIn.setFlowRate(10000.0, "kg/hr");
gasIn.run();

// Wash water
SystemSrkEos water = new SystemSrkEos(290.0, 50.0);
water.addComponent("water", 1.0);
water.setMixingRule("classic");

Stream washWater = new Stream("Wash Water", water);
washWater.setFlowRate(500.0, "kg/hr");
washWater.run();

// Absorber
SimpleAbsorber waterWash = new SimpleAbsorber("Water Wash");
waterWash.addGasInStream(gasIn);
waterWash.addSolventInStream(washWater);
waterWash.setAbsorptionEfficiency(0.85);
waterWash.run();

Stream cleanGas = waterWash.getGasOutStream();
double meohRemaining = cleanGas.getFluid().getMoleFraction("methanol") * 100;
System.out.println("Methanol in clean gas: " + meohRemaining + " mol%");