Water Treatment Equipment

Documentation for produced water treatment equipment in NeqSim.

Table of Contents

Overview

Package: neqsim.process.equipment.watertreatment

Produced water treatment is critical for offshore oil and gas operations. NeqSim provides equipment models for simulating oil-in-water separation processes, helping engineers design systems that meet discharge regulations.

Key Classes

Class Description
Hydrocyclone Centrifugal oil-water separator with dP validation
GasFlotationUnit IGF/DGF multi-stage flotation
ProducedWaterTreatmentTrain Multi-stage treatment system

Hydrocyclone

Overview

Hydrocyclones use centrifugal force to separate oil droplets from water. The swirling flow creates centrifugal acceleration many times greater than gravity, causing lighter oil droplets to migrate to the center and exit through the reject stream.

Performance Characteristics

Parameter Typical Value Range
d50 cut size 10-15 μm 8-20 μm
d100 removal 20-30 μm 15-40 μm
Reject ratio 1-3% 0.5-5%
Pressure drop 1-3 bar 0.5-5 bar
Oil removal efficiency 90-98% 85-99%

Separation Efficiency Model

The grade efficiency is modeled using:

\[\eta(d) = 1 - \exp\left(-A \cdot \left(\frac{d}{d_{50}}\right)^n\right)\]

where:

Basic Usage

import neqsim.process.equipment.watertreatment.Hydrocyclone;
import neqsim.process.equipment.stream.Stream;
import neqsim.thermo.system.SystemSrkEos;

// Create produced water stream
SystemSrkEos water = new SystemSrkEos(323.15, 10.0);
water.addComponent("water", 0.995);
water.addComponent("n-heptane", 0.005);  // Oil phase
water.setMixingRule("classic");

Stream producedWater = new Stream("Produced Water", water);
producedWater.setFlowRate(500.0, "m3/hr");
producedWater.run();

// Create hydrocyclone
Hydrocyclone cyclone = new Hydrocyclone("HP Hydrocyclone", producedWater);
cyclone.setD50Microns(12.0);
cyclone.setRejectRatio(0.02);
cyclone.setPressureDrop(2.0);
cyclone.setOilRemovalEfficiency(0.95);
cyclone.run();

// Get results
System.out.println("Outlet OIW: " + cyclone.getOutletOilConcentrationMgL() + " mg/L");
System.out.println("Recovered oil: " + cyclone.getRecoveredOilM3h() + " m³/h");

Configuration Methods

// Set d50 cut size in microns
cyclone.setD50Microns(12.0);

// Set reject ratio (oil-rich stream / feed)
cyclone.setRejectRatio(0.02);

// Set pressure drop across cyclone
cyclone.setPressureDrop(2.0);

// Set target oil removal efficiency
cyclone.setOilRemovalEfficiency(0.95);

// Set inlet oil concentration
cyclone.setInletOilConcentration(1000.0);  // mg/L

Output Streams

// Treated water (underflow) - main outlet
Stream treatedWater = (Stream) cyclone.getOutletStream();

// Rejected oil-rich stream (overflow)
Stream oilReject = (Stream) cyclone.getOilOutStream();

Design Validation

The Hydrocyclone includes differential pressure and efficiency validation:

// Check if differential pressure is adequate (typically 1-3 bar)
boolean dpOk = cyclone.isDifferentialPressureAdequate();

// Calculate required inlet pressure for a target dP
double requiredInletP = cyclone.calcRequiredInletPressure(5.0);  // target outlet 5 bar

// Estimate efficiency from operating conditions
double estimatedEff = cyclone.estimateEfficiencyFromConditions(
    850.0,   // oil density kg/m3
    1025.0,  // water density kg/m3
    15.0     // droplet size microns
);

// Full validation summary
String summary = cyclone.getDesignValidationSummary();
System.out.println(summary);

Hydrocyclone Design Parameters

Parameter Default Method Description
d50 cut size 12 μm setD50Microns() 50% removal droplet size
Reject ratio 2% setRejectRatio() Oil-rich stream fraction
Pressure drop 2.0 bar setPressureDrop() Across cyclone
Min dP 1.0 bar setMinPressureDrop() Minimum acceptable dP
Max dP 3.0 bar setMaxPressureDrop() Maximum acceptable dP
Oil removal efficiency 95% setOilRemovalEfficiency() Overall efficiency

Gas Flotation Unit

Overview

The GasFlotationUnit models Induced Gas Flotation (IGF) or Dissolved Gas Flotation (DGF) for removing dispersed oil from produced water. Fine gas bubbles are injected into the water; oil droplets attach to the bubbles and rise to the surface where they are skimmed off.

Design Requirements

Parameter Requirement
Gas supply pressure Minimum 4 bar above water pressure
Gas volume Minimum 10 Avol% of water flow
Reject flow Minimum 2% of inlet water per stage
Gas mixing dP At least 0.5 bar across mixing valve
Typical stages 3-4 in series
Oil removal 80-95% overall

Basic Usage

import neqsim.process.equipment.watertreatment.GasFlotationUnit;
import neqsim.process.equipment.stream.Stream;
import neqsim.process.processmodel.ProcessSystem;
import neqsim.thermo.system.SystemSrkEos;

// Produced water stream
SystemSrkEos pw = new SystemSrkEos(273.15 + 60.0, 5.0);
pw.addComponent("water", 0.99);
pw.addComponent("n-heptane", 0.01);
pw.setMixingRule("classic");

Stream pwStream = new Stream("Produced Water", pw);
pwStream.setFlowRate(200.0, "m3/hr");

// Gas flotation unit
GasFlotationUnit igf = new GasFlotationUnit("IGF-100", pwStream);
igf.setNumberOfStages(4);
igf.setOilRemovalEfficiency(0.90);
igf.setInletOilConcentration(200.0);  // mg/L
igf.setWaterFlowRate(200.0);          // m3/h

// Wire into process
ProcessSystem process = new ProcessSystem();
process.add(pwStream);
process.add(igf);
process.run();

// Results
System.out.println("Outlet OIW: " + igf.getOutletOilMgL() + " mg/L");

Per-Stage Efficiency

The overall efficiency is distributed across stages. Per-stage efficiency is calculated from the overall target:

\[1 - \eta_{overall} = (1 - \eta_{stage})^N\] 
igf.setNumberOfStages(4);
igf.setOilRemovalEfficiency(0.90);
double perStage = igf.calcPerStageEfficiency();  // ~0.44

Gas and Reject Flow

// Minimum gas flow (10 Avol% of water flow)
igf.setWaterFlowRate(200.0);
double minGas = igf.calcMinimumGasFlowRate();  // 20 Am3/h

// Reject flow per stage (2% of inlet water per stage)
double rejectPerStage = igf.calcRejectFlowPerStage();  // 4.0 m3/h
double totalReject = igf.getTotalRejectFlow();          // 16.0 m3/h

Nitrogen Corrosion Warning

When nitrogen is used as the flotation gas instead of fuel gas, the unit flags a corrosion risk:

igf.setFlotationGasType("nitrogen");
igf.run();

// Design summary will include corrosion warning
String summary = igf.getDesignValidationSummary();
// Contains: "nitrogen as flotation gas may cause corrosion..."

GasFlotationUnit Design Parameters

Parameter Default Method Description
Number of stages 4 setNumberOfStages() Flotation stages in series
Oil removal efficiency 90% setOilRemovalEfficiency() Overall target
Min gas overpressure 4 bar setMinGasOverpressureBar() Above water pressure
Min gas volume 10 Avol% setMinGasVolumeFractionPct() Of water flow
Min reject fraction 2%/stage setMinRejectFractionPerStage() Of inlet water
Min gas mixing dP 0.5 bar setMinGasMixingDPBar() Across mixing valve
Flotation gas type fuel_gas setFlotationGasType() fuel_gas or nitrogen

Produced Water Treatment Train

Overview

The ProducedWaterTreatmentTrain models a complete multi-stage treatment system typically used on offshore platforms. It combines multiple treatment technologies to achieve discharge compliance.

Typical Treatment Stages

Stage Equipment Target Droplets Efficiency
Primary Hydrocyclone >20 μm 90-98%
Secondary IGF/DGF >5 μm 80-95%
Polishing Skim Tank >50 μm 60-80%

Basic Usage

import neqsim.process.equipment.watertreatment.ProducedWaterTreatmentTrain;
import neqsim.process.equipment.stream.Stream;

// Create treatment train
ProducedWaterTreatmentTrain train = new ProducedWaterTreatmentTrain(
    "PW Treatment",
    producedWater
);

// Configure inlet conditions
train.setInletOilConcentration(1000.0);  // mg/L from separator
train.setWaterFlowRate(200.0);  // m³/h

// Run simulation
train.run();

// Check compliance
System.out.println("Outlet OIW: " + train.getOutletOilConcentration() + " mg/L");
System.out.println("Compliant: " + train.isCompliant());
System.out.println("Overall efficiency: " + (train.getOverallEfficiency() * 100) + "%");

Stage Types

import neqsim.process.equipment.watertreatment.ProducedWaterTreatmentTrain.StageType;

// Available stage types
StageType.HYDROCYCLONE    // Centrifugal separation
StageType.FLOTATION       // IGF/DGF units
StageType.SKIM_TANK       // Gravity separation
StageType.FILTER          // Filtration
StageType.MEMBRANE        // Membrane separation

Custom Stage Configuration

// Clear default stages
train.clearStages();

// Add custom stages
train.addStage("Primary Cyclone", StageType.HYDROCYCLONE, 0.95);
train.addStage("Compact Floatation", StageType.FLOTATION, 0.92);
train.addStage("Final Polish", StageType.SKIM_TANK, 0.75);

// Run with custom configuration
train.run();

Detailed Results

// Get stage-by-stage results
for (WaterTreatmentStage stage : train.getStages()) {
    System.out.println(stage.getName() + ":");
    System.out.println("  Inlet OIW: " + stage.getInletOilMgL() + " mg/L");
    System.out.println("  Outlet OIW: " + stage.getOutletOilMgL() + " mg/L");
    System.out.println("  Efficiency: " + (stage.getEfficiency() * 100) + "%");
}

// Get treated water and oil streams
Stream treatedWater = train.getTreatedWaterStream();
Stream recoveredOil = train.getRecoveredOilStream();

Design Considerations

Droplet Size Distribution

The performance of water treatment equipment depends heavily on the oil droplet size distribution in the feed:

Source Typical d50 Comments
HP Separator 100-300 μm Large droplets, easy separation
LP Separator 30-100 μm Moderate separation
Degasser 10-30 μm Fine droplets, challenging
Direct discharge <10 μm Very fine, requires flotation

Sizing Guidelines

// Hydrocyclone sizing (typical)
double feedFlowM3h = 200.0;
int numberOfLiners = (int) Math.ceil(feedFlowM3h / 35.0);  // ~35 m³/h per liner
double cycloneDP = 1.5 + 0.02 * feedFlowM3h / numberOfLiners;

// Flotation unit sizing
double retentionTime = 3.0;  // minutes
double flotationVolume = feedFlowM3h * retentionTime / 60.0;

Temperature Effects

Oil-water separation efficiency varies with temperature:

Regulatory Compliance

Norwegian Continental Shelf (NCS)

Requirement Limit Monitoring
Monthly average OIW 30 mg/L Weighted average
Dispersed oil Monitored Daily sampling
Zero discharge target Best available technology Continuous improvement

OSPAR Convention

Region OIW Limit Notes
North Sea 30 mg/L Monthly average
Atlantic 30 mg/L Monthly average

Compliance Checking

// Check against NCS requirements
boolean ncsCompliant = train.getOutletOilConcentration()
    <= ProducedWaterTreatmentTrain.NCS_OIW_LIMIT_MGL;

// Check against OSPAR
boolean osparCompliant = train.getOutletOilConcentration()
    <= ProducedWaterTreatmentTrain.OSPAR_OIW_LIMIT_MGL;

// Get compliance report
String report = train.getComplianceReport();
System.out.println(report);

Integration with Process Systems

Complete Process Example

import neqsim.process.processmodel.ProcessSystem;
import neqsim.process.equipment.separator.ThreePhaseSeparator;
import neqsim.process.equipment.watertreatment.ProducedWaterTreatmentTrain;

// Create process system
ProcessSystem process = new ProcessSystem();

// Add production separator
ThreePhaseSeparator prodSep = new ThreePhaseSeparator("Production Separator", wellStream);
process.add(prodSep);

// Add water treatment train
ProducedWaterTreatmentTrain pwTrain = new ProducedWaterTreatmentTrain(
    "PW Treatment",
    prodSep.getWaterOutStream()
);
pwTrain.setInletOilConcentration(800.0);
process.add(pwTrain);

// Run process
process.run();

// Check results
System.out.println("Water cut: " + (prodSep.getWaterCut() * 100) + "%");
System.out.println("OIW to discharge: " + pwTrain.getOutletOilConcentration() + " mg/L");
System.out.println("Compliant: " + pwTrain.isCompliant());

See Also