What, Why, and How of Fired Heater Efficiency
What is Efficiency?
Fired heater efficiency measures how effectively fuel energy is converted to useful process heat. Three key metrics: fuel efficiency (commercial), thermal efficiency (holistic), and combustion efficiency (burner performance).
Why It Matters
Fired heaters are the largest energy consumers in refineries. A 1% efficiency improvement on a large heater can save millions annually while reducing emissions and enhancing safety.
How to Optimize
Through precise measurement using API-560 standards, minimizing stack losses, reducing excess air, and implementing advanced control systems for real-time optimization.
API-560 in 5 Steps
Key Energy Losses
Stack Loss (60-85%)
Heat carried away by hot flue gases. Controlled by reducing stack temperature and minimizing excess air.
Setting Loss (1.5-2.5%)
Heat lost through external surfaces via radiation and convection. Indicates refractory condition.
Incomplete Combustion (~0%)
Energy lost due to unburned fuel (CO, hydrocarbons). Should be negligible in well-operated heaters.
Annex G Workflow
Interactive Efficiency Tools
Excess Air vs. Efficiency
Stack Temperature Impact
Efficiency Test Checklist
Instrumentation and Measurement
Required Input Parameters
| Parameter | Symbol | Units | Measurement Method |
|---|---|---|---|
| Ambient Air Temperature | Ta | °C / °F | Calibrated thermometer, shielded from radiation |
| Relative Humidity | RH | % | Sling psychrometer or electronic sensor |
| Flue Gas Exit Temperature | Te | °C / °F | Multi-point traverse or thermocouple grid |
| Flue Gas Oxygen | O₂ | vol % | Zirconia oxide or electrochemical analyzer |
| Fuel Composition | - | vol % / mass % | Gas chromatograph analysis |
| Lower Heating Value | LHV | kJ/kg | Calculated from composition or calorimetry |
✅ Best Practices
- • Place probes downstream of final heat transfer surface
- • Sample in central third of duct cross-section
- • Use EPA Method 1 for large duct traverses
- • Co-locate O₂ and temperature sensors
- • Calibrate instruments before each test
- • Seal all test ports during measurement
❌ Common Errors
- • Sampling upstream of air leaks (tramp air)
- • Single-point measurement in stratified flow
- • Uncalibrated or drifting instruments
- • Non-representative fuel samples
- • Ignoring humidity in air calculations
- • Operating during transient conditions
Complex Heater Configurations
Multi-Cell with Common Convection
Multiple radiant cells sharing a common convection section. Overall efficiency calculated from single stack measurement, but cell-specific monitoring required for control.
Independent Heaters, Common Stack
Independent heaters with separate process services sharing a common stack. Each heater requires individual flue gas measurement for meaningful performance monitoring.
⚠️ Measurement Strategy
For complex configurations, the "black box" API-560 approach is insufficient for diagnostics and control. Use process simulators (Aspen HYSYS) or CFD (OpenFOAM) for detailed analysis of internal behavior and optimization opportunities.
Example Calculations & Sensitivity Analysis
API-560 Combustion Worksheet (Sample)
| Component | Vol % | Mol. Wt. | Mass Fraction | LHV (kJ/kg) | LHV Contrib. | Stoich. Air |
|---|---|---|---|---|---|---|
| CH₄ | 92.5 | 16.04 | 0.8534 | 50,016 | 42,689 | 14.65 |
| C₂H₆ | 5.0 | 30.07 | 0.0863 | 47,490 | 4,098 | 1.38 |
| N₂ | 1.5 | 28.01 | 0.0241 | 0 | 0 | 0 |
| CO₂ | 1.0 | 44.01 | 0.0362 | 0 | 0 | 0 |
| Total | 100.0 | - | 1.000 | - | 46,787 | 16.03 |
Sensitivity Analysis: Stack Temperature vs. Efficiency
This chart shows how efficiency decreases with increasing stack temperature. A 50°C increase from 300°C to 350°C typically reduces efficiency by 2-3 percentage points.
Tools & Downloads
Excel Template
API-560 Annex G calculation spreadsheet with built-in formulas and validation.
DownloadPython Model
Open-source Python model for automated efficiency calculations and sensitivity analysis.
GitHub RepoWeb Calculator
Interactive web-based calculator for efficiency estimates and excess air calculations.
Open CalculatorSoftware Comparison Matrix
| Tool | Cost | Expertise | Accuracy | Best For |
|---|---|---|---|---|
| Excel Spreadsheet | Low | Medium | High | API-560 calculations, custom reporting |
| HeaterSIM | High | High | Very High | Detailed design, thermal modeling |
| Aspen HYSYS | Very High | High | High | Plant-wide simulation, integration |
| Python/MATLAB | Low | High | High | Automation, sensitivity analysis |
| Online Calculators | Free | Low | Low | Quick estimates, education |