Boilers
Complete encyclopaedia entry for industrial boilers — what they are, how they work, common failures, maintenance, lifespan, and selection criteria.
What Is It?
A boiler is a pressure vessel that converts water into steam by transferring heat from combustion gases or an electric element. Steam is used for process heating, power generation, sterilisation, and space heating. Boilers range from small domestic units producing a few hundred kg/hr of steam to large power station boilers producing thousands of tonnes per hour.
How Does It Work?
In a fire-tube boiler, hot combustion gases pass through tubes surrounded by water in a large pressure vessel. In a water-tube boiler, water passes through tubes arranged in the combustion chamber, absorbing heat directly. In both cases, the heat converts water to steam, which is drawn off at the top of the boiler. The steam pressure is controlled by the burner firing rate and the steam demand.
Common Failures
- Tube rupture: Overheating from scale buildup, low water level, or corrosion causes tubes to rupture.
- Scaling: Hardness deposits on tube surfaces reduce heat transfer and cause overheating.
- Oxygen pitting: Dissolved oxygen causes deep pitting corrosion on the water side.
- Low-water damage: If water drops below tubes, they overheat and can rupture within minutes.
- Refractory failure: Cracks and spalling in the refractory lining expose the casing to furnace heat.
Maintenance
- Daily water tests: Test TDS, pH, hardness, and oxygen. Adjust chemical dosing accordingly.
- Daily blowdown: Bottom blowdown to remove sludge; surface blowdown to control TDS.
- Daily low-water cutoff test: Blow down the float column and verify the burner shuts down.
- Annual inspection: Open the boiler, inspect tubes and refractory, hydrotest if required, and service the burner.
- Combustion tuning: Analyse flue gas (O₂, CO, temperature) at all firing rates and adjust the burner.
Typical Lifespan
A well-maintained industrial boiler can last 25–40 years. Fire-tube boilers in heating service often last 30+ years. Water-tube boilers in heavy process service may need retubing after 15–20 years. The pressure vessel itself can outlast the plant, but tubes, refractory, and controls need periodic replacement.
Selection Criteria
- Steam pressure: Below 20 bar → fire-tube. Above 20 bar → water-tube.
- Steam capacity: Below 25 t/hr → fire-tube. Above 30 t/hr → water-tube.
- Fuel type: Gas, oil, biomass, or electric. Match burner to available fuel.
- Efficiency: Look for 85%+ thermal efficiency with economiser. Condensing economisers can reach 95%.
- Controls: Modulating burner control, fully automatic start-up, and remote monitoring.
- Compliance: Must meet local boiler codes (AS 2593, ASME Section I, etc.).
How CHI can help
Ask CHI about boilers — how it works, common failures, and maintenance requirements. The CHI assistant can explain how the equipment works, recommend maintenance tasks, help with selection criteria, and troubleshoot common failures based on the symptoms you describe.