Fuel Gas System

Models fuel gas conditioning for process facilities including gas turbines, fired heaters, and flare pilots.

Table of Contents

• Overview
• Design Standards
• Consumer Types
• System Components
• Usage Examples
• Quality Calculations
• API Reference

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Overview

Location: neqsim.process.equipment.util.FuelGasSystem

The FuelGasSystem class models complete fuel gas conditioning systems for:

• Gas turbines - Power generation and compressor drivers
• Fired heaters - Process heating
• Flare pilots - Continuous ignition source
• Hot oil heaters - Heat transfer fluid heating
• Regeneration gas heaters - TEG/mol sieve regeneration

Key Features

• Automatic knockout drum for liquid removal
• Joule-Thomson effect calculation for pressure letdown
• Fuel gas heating for superheat above dew point
• Wobbe Index calculation for combustion control
• Multi-consumer demand management

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Design Standards

Standard	Description
API 618	Reciprocating Compressors for Petroleum Industry
NORSOK P-002	Process System Design
ISO 21789	Gas Turbine Applications

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Consumer Types

The system supports different consumer types with specific quality requirements:

Consumer	Pressure (barg)	Min Superheat (°C)	Max H₂S (ppmv)
GAS_TURBINE	30	25	20
FIRED_HEATER	3	15	100
FLARE_PILOT	1.5	10	500
HOT_OIL_HEATER	3	15	100
REGEN_HEATER	2	10	200
INCINERATOR	1	5	1000

Consumer Class Usage

import neqsim.process.equipment.util.FuelGasSystem.ConsumerType;

// Get requirements for gas turbine
ConsumerType turbine = ConsumerType.GAS_TURBINE;
double pressure = turbine.getTypicalPressureBarg();     // 30 barg
double superheat = turbine.getMinSuperheatC();          // 25°C
double maxH2S = turbine.getMaxH2Sppmv();                // 20 ppmv
String desc = turbine.getDescription();                  // "High pressure, superheated"

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System Components

A typical fuel gas system includes:

                    ┌─────────────┐
HP Gas ──────────►  │  Pressure   │
(70 barg)           │   Letdown   │
                    └──────┬──────┘
                           │ JT cooling
                           ▼
                    ┌─────────────┐
                    │  Knockout   │───► Liquids
                    │    Drum     │
                    └──────┬──────┘
                           │
                           ▼
                    ┌─────────────┐
                    │  Fuel Gas   │
                    │   Heater    │
                    └──────┬──────┘
                           │ Superheated gas
                           ▼
                    To Consumers

Component Details

Component	Purpose	Key Parameters
Pressure Letdown	Reduce pressure from source	Outlet pressure, Cv
Knockout Drum	Remove condensed liquids	Residence time, efficiency
Fuel Gas Heater	Superheat above dew point	Duty, outlet temperature

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Usage Examples

Java Example - Basic Setup

import neqsim.process.equipment.util.FuelGasSystem;
import neqsim.process.equipment.util.FuelGasSystem.ConsumerType;
import neqsim.process.equipment.stream.Stream;
import neqsim.thermo.system.SystemSrkEos;

// Create fuel gas source
SystemSrkEos gasFluid = new SystemSrkEos(273.15 + 30.0, 70.0);
gasFluid.addComponent("methane", 0.85);
gasFluid.addComponent("ethane", 0.08);
gasFluid.addComponent("propane", 0.04);
gasFluid.addComponent("CO2", 0.02);
gasFluid.addComponent("H2S", 0.00001);  // 10 ppmv
gasFluid.setMixingRule("classic");

Stream fuelGasSource = new Stream("HP Fuel Gas", gasFluid);
fuelGasSource.setFlowRate(2000.0, "kg/hr");
fuelGasSource.run();

// Create fuel gas system
FuelGasSystem fgSystem = new FuelGasSystem("Platform FG", fuelGasSource);
fgSystem.setOutletPressure(30.0);  // barg
fgSystem.setOutletTemperature(50.0);  // °C

// Add consumers
fgSystem.addConsumer("GT-101", ConsumerType.GAS_TURBINE, 800.0);  // kg/hr
fgSystem.addConsumer("H-101", ConsumerType.FIRED_HEATER, 150.0);
fgSystem.addConsumer("Pilot", ConsumerType.FLARE_PILOT, 50.0);

// Run and get results
fgSystem.run();

// Results
System.out.println("Fuel Gas System Results:");
System.out.println("  JT Cooling: " + fgSystem.getJTCooling() + " °C");
System.out.println("  Heater Duty: " + fgSystem.getHeaterDutyKW() + " kW");
System.out.println("  Dew Point: " + fgSystem.getDewPointC() + " °C");
System.out.println("  Superheat: " + fgSystem.getSuperheatC() + " °C");
System.out.println("  Wobbe Index: " + fgSystem.getWobbeIndex() + " MJ/Sm³");
System.out.println("  LHV: " + fgSystem.getLHV() + " MJ/kg");

// Get JSON report
String report = fgSystem.toJson();

Python Example

from neqsim import jneqsim

# Create fuel gas system
FuelGasSystem = jneqsim.process.equipment.util.FuelGasSystem
ConsumerType = jneqsim.process.equipment.util.FuelGasSystem.ConsumerType

# Create fluid and stream
SystemSrkEos = jneqsim.thermo.system.SystemSrkEos
Stream = jneqsim.process.equipment.stream.Stream

gas = SystemSrkEos(273.15 + 30.0, 70.0)
gas.addComponent("methane", 0.85)
gas.addComponent("ethane", 0.08)
gas.addComponent("propane", 0.04)
gas.addComponent("CO2", 0.02)
gas.addComponent("H2S", 0.00001)
gas.setMixingRule("classic")

source = Stream("HP Fuel Gas", gas)
source.setFlowRate(2000.0, "kg/hr")
source.run()

# Create fuel gas system
fg_system = FuelGasSystem("Platform FG", source)
fg_system.setOutletPressure(30.0)
fg_system.setOutletTemperature(50.0)

# Add consumers
fg_system.addConsumer("GT-101", ConsumerType.GAS_TURBINE, 800.0)
fg_system.addConsumer("H-101", ConsumerType.FIRED_HEATER, 150.0)

fg_system.run()

print(f"Heater duty: {fg_system.getHeaterDutyKW():.1f} kW")
print(f"Wobbe Index: {fg_system.getWobbeIndex():.1f} MJ/Sm³")
print(f"Superheat: {fg_system.getSuperheatC():.1f} °C above dew point")

Calculating Gas Quality

// Calculate heating values and combustion indices
fgSystem.run();

// Lower Heating Value
double LHV = fgSystem.getLHV();  // MJ/kg
double LHV_vol = fgSystem.getLHV("MJ/Sm3");  // MJ/Sm³

// Wobbe Index (combustion interchangeability)
double WI = fgSystem.getWobbeIndex();  // MJ/Sm³

// Check if within turbine limits (typically ±5%)
double designWI = 50.0;  // MJ/Sm³
double deviation = Math.abs((WI - designWI) / designWI * 100);
if (deviation > 5.0) {
    System.out.println("WARNING: Wobbe Index outside turbine limits!");
}

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Quality Calculations

Wobbe Index

The Wobbe Index indicates fuel gas interchangeability:

\[WI = \frac{HHV}{\sqrt{SG}}\]

Where:

• $HHV$ = Higher Heating Value (MJ/Sm³)
• $SG$ = Specific Gravity relative to air

Dew Point and Superheat

The system calculates:

1. Cricondentherm - Maximum dew point temperature at any pressure
2. Dew point at delivery pressure - Actual condensation temperature
3. Superheat - Temperature margin above dew point

// Get dew point at delivery pressure
double dewPoint = fgSystem.getDewPointAtDeliveryPressure();  // °C

// Get actual superheat
double superheat = fgSystem.getSuperheatC();  // °C

// Check gas turbine requirement (>25°C superheat)
if (superheat < 25.0) {
    System.out.println("Increase heater duty for gas turbine!");
}

JT Cooling Effect

Pressure letdown causes Joule-Thomson cooling:

// Get JT cooling across letdown valve
double jtCooling = fgSystem.getJTCooling();  // °C (negative = cooling)

System.out.println("JT cooling: " + jtCooling + " °C");
// Typical: -5 to -15°C depending on composition and pressure drop

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API Reference

Constructors

Constructor	Description
FuelGasSystem(String name)	Create system with name
FuelGasSystem(String name, StreamInterface inlet)	Create with inlet stream

Configuration Methods

Method	Description
setInletStream(StreamInterface)	Set fuel gas source
setOutletPressure(double)	Set delivery pressure (barg)
setOutletTemperature(double)	Set delivery temperature (°C)
addConsumer(String, ConsumerType, double)	Add consumer (name, type, flow kg/hr)
setTotalDemand(double)	Set total fuel gas demand (kg/hr)

Results Methods

Method	Description
getJTCooling()	Get JT temperature drop (°C)
getHeaterDutyKW()	Get required heater duty (kW)
getDewPointC()	Get dew point at delivery (°C)
getSuperheatC()	Get superheat above dew point (°C)
getWobbeIndex()	Get Wobbe Index (MJ/Sm³)
getLHV()	Get Lower Heating Value (MJ/kg)
getLHV(String unit)	Get LHV in specified unit
getOutletStream()	Get conditioned fuel gas stream
toJson()	Get full results as JSON

Consumer Management

Method	Description
addConsumer(String, ConsumerType, double)	Add fuel gas consumer
getConsumers()	Get list of consumers
getTotalDemand()	Get total demand (kg/hr)
getConsumerDemand(String)	Get specific consumer demand

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Related Documentation

• Flare Systems - Flare and relief systems
• Gas Turbines - Power generation equipment
• Measurement Devices - CombustionEmissionsCalculator
• Emissions Reporting - Emission calculations