Membrane Separation Equipment
Documentation for membrane separation equipment in NeqSim process simulation.
Table of Contents
Overview
Location: neqsim.process.equipment.membrane
Classes:
| Class | Description |
|——-|————-|
| MembraneSeparator | Generic membrane separation unit |
Membrane separators provide selective separation based on component permeabilities through a membrane material. Applications include:
- CO₂ removal from natural gas
- Hydrogen recovery
- Nitrogen generation
- Dehydration
- Vapor/gas separation
MembraneSeparator Class
Basic Usage
import neqsim.process.equipment.membrane.MembraneSeparator;
// Create membrane separator
MembraneSeparator membrane = new MembraneSeparator("CO2 Membrane", feedStream);
// Set permeate fractions for each component
membrane.setPermeateFraction("CO2", 0.95); // 95% of CO2 permeates
membrane.setPermeateFraction("methane", 0.05); // 5% of methane permeates
membrane.setPermeateFraction("ethane", 0.03); // 3% of ethane permeates
membrane.run();
// Get output streams
StreamInterface permeate = membrane.getPermeateStream();
StreamInterface retentate = membrane.getRetentateStream();
Constructor Options
// With name only
MembraneSeparator membrane = new MembraneSeparator("MEM-100");
membrane.setInletStream(feedStream);
// With name and inlet stream
MembraneSeparator membrane = new MembraneSeparator("MEM-100", feedStream);
Permeation Models
Permeate Fraction Method
The simplest approach specifies what fraction of each component permeates:
// Set permeate fraction (0.0 to 1.0)
membrane.setPermeateFraction("CO2", 0.90);
membrane.setPermeateFraction("H2S", 0.85);
membrane.setPermeateFraction("methane", 0.02);
membrane.setPermeateFraction("ethane", 0.01);
membrane.setPermeateFraction("propane", 0.005);
// Set default for unlisted components
membrane.setDefaultPermeateFraction(0.01);
Permeability Method
For more rigorous calculations using permeability coefficients:
// Set membrane area
membrane.setMembraneArea(100.0); // m²
// Set permeability for each component (mol/(m²·s·Pa))
membrane.setPermeability("CO2", 1.0e-9);
membrane.setPermeability("methane", 2.0e-11);
membrane.setPermeability("nitrogen", 5.0e-12);
Selectivity
The selectivity of component A over B is:
\[\alpha_{A/B} = \frac{P_A}{P_B}\]Where $P_A$ and $P_B$ are the permeabilities of components A and B.
Typical selectivities for polymeric membranes: | Separation | Selectivity | |————|————-| | CO₂/CH₄ | 15-50 | | H₂/CH₄ | 30-100 | | O₂/N₂ | 4-8 | | H₂O/CH₄ | >100 |
Configuration
Operating Conditions
// Inlet stream conditions affect separation
feedStream.setPressure(50.0, "bara"); // High feed pressure
feedStream.setTemperature(40.0, "C");
// Permeate side typically at lower pressure
// (Pressure difference drives permeation)
Stage Cut
The stage cut (θ) is the fraction of feed that permeates:
\[\theta = \frac{\dot{n}_{permeate}}{\dot{n}_{feed}}\]membrane.run();
double feedFlow = feedStream.getFlowRate("kmol/hr");
double permeateFlow = membrane.getPermeateStream().getFlowRate("kmol/hr");
double stageCut = permeateFlow / feedFlow;
System.out.println("Stage cut: " + (stageCut * 100) + " %");
Output Streams
Permeate Stream
The permeate contains components that pass through the membrane:
StreamInterface permeate = membrane.getPermeateStream();
// Get permeate composition
double co2InPermeate = permeate.getFluid().getMoleFraction("CO2");
double permeateFlow = permeate.getFlowRate("kmol/hr");
System.out.println("Permeate CO2: " + (co2InPermeate * 100) + " mol%");
Retentate Stream
The retentate contains components that do not permeate:
StreamInterface retentate = membrane.getRetentateStream();
// Get retentate (product gas) composition
double co2InRetentate = retentate.getFluid().getMoleFraction("CO2");
double ch4InRetentate = retentate.getFluid().getMoleFraction("methane");
System.out.println("Retentate CO2: " + (co2InRetentate * 100) + " mol%");
System.out.println("Retentate CH4: " + (ch4InRetentate * 100) + " mol%");
Usage Examples
CO₂ Removal from Natural Gas
ProcessSystem process = new ProcessSystem();
// Feed gas with CO2
SystemInterface feedFluid = new SystemSrkEos(310.0, 60.0);
feedFluid.addComponent("methane", 0.85);
feedFluid.addComponent("ethane", 0.05);
feedFluid.addComponent("propane", 0.02);
feedFluid.addComponent("CO2", 0.08);
feedFluid.setMixingRule("classic");
Stream feedGas = new Stream("Feed Gas", feedFluid);
feedGas.setFlowRate(100000.0, "Sm3/day");
process.add(feedGas);
// Membrane unit
MembraneSeparator membrane = new MembraneSeparator("CO2 Membrane", feedGas);
membrane.setPermeateFraction("CO2", 0.90);
membrane.setPermeateFraction("methane", 0.03);
membrane.setPermeateFraction("ethane", 0.02);
membrane.setPermeateFraction("propane", 0.01);
process.add(membrane);
// Run
process.run();
// Check CO2 spec
double productCO2 = membrane.getRetentateStream().getFluid().getMoleFraction("CO2");
System.out.println("Product gas CO2: " + (productCO2 * 100) + " mol%");
// Methane recovery
double feedCH4 = feedGas.getFlowRate("Sm3/day") * 0.85;
double productCH4 = membrane.getRetentateStream().getFlowRate("Sm3/day") *
membrane.getRetentateStream().getFluid().getMoleFraction("methane");
double recovery = productCH4 / feedCH4 * 100;
System.out.println("Methane recovery: " + recovery + " %");
Multi-Stage Membrane System
For deep CO₂ removal, multiple stages may be required:
// First stage membrane
MembraneSeparator stage1 = new MembraneSeparator("Stage 1", feedGas);
stage1.setPermeateFraction("CO2", 0.80);
stage1.setPermeateFraction("methane", 0.05);
process.add(stage1);
// Second stage on retentate
MembraneSeparator stage2 = new MembraneSeparator("Stage 2", stage1.getRetentateStream());
stage2.setPermeateFraction("CO2", 0.80);
stage2.setPermeateFraction("methane", 0.05);
process.add(stage2);
// Recycle permeate from stage 2 to stage 1 feed
Mixer mixer = new Mixer("Feed Mixer");
mixer.addStream(feedGas);
mixer.addStream(stage2.getPermeateStream());
process.add(mixer);
// Connect mixer to stage 1
stage1.setInletStream(mixer.getOutletStream());
// Add recycle
Recycle recycle = new Recycle("Membrane Recycle");
recycle.addStream(stage2.getPermeateStream());
recycle.setOutletStream(mixer);
process.add(recycle);
process.run();
Hydrogen Recovery
// Refinery off-gas
SystemInterface offgas = new SystemSrkEos(320.0, 30.0);
offgas.addComponent("hydrogen", 0.40);
offgas.addComponent("methane", 0.35);
offgas.addComponent("ethane", 0.15);
offgas.addComponent("propane", 0.10);
offgas.setMixingRule("classic");
Stream feed = new Stream("Off-gas", offgas);
feed.setFlowRate(5000.0, "Sm3/hr");
// H2 selective membrane
MembraneSeparator h2Membrane = new MembraneSeparator("H2 Membrane", feed);
h2Membrane.setPermeateFraction("hydrogen", 0.95);
h2Membrane.setPermeateFraction("methane", 0.08);
h2Membrane.setPermeateFraction("ethane", 0.02);
h2Membrane.setPermeateFraction("propane", 0.01);
h2Membrane.run();
// H2 purity in permeate
double h2Purity = h2Membrane.getPermeateStream().getFluid().getMoleFraction("hydrogen");
System.out.println("H2 purity: " + (h2Purity * 100) + " mol%");
Process Integration
With Compression
// Compress permeate for recycle or further processing
Compressor permeateComp = new Compressor("Permeate Comp", membrane.getPermeateStream());
permeateComp.setOutletPressure(feedPressure, "bara");
permeateComp.setIsentropicEfficiency(0.75);
With Cooling
// Cool membrane feed to improve selectivity
Cooler feedCooler = new Cooler("Membrane Feed Cooler", feedGas);
feedCooler.setOutTemperature(30.0, "C");
membrane.setInletStream(feedCooler.getOutletStream());
Design Considerations
Operating Conditions
- Higher feed pressure → higher driving force → more permeation
- Lower temperature → higher selectivity (for most membranes)
- Higher stage cut → lower product purity
Membrane Selection
| Type | Applications | Selectivity | |——|————–|————-| | Cellulose acetate | CO₂/CH₄ | 15-25 | | Polyimide | CO₂/CH₄, H₂ | 20-50 | | Polysulfone | O₂/N₂ | 5-6 | | PDMS | VOC removal | varies |
Related Documentation
- Absorbers - Alternative for gas treating
- Separators - Phase separation
- Streams - Stream handling