Glossary
Boilers
Subcritical, supercritical and ultrasupercritical boilers
Also known as subcritical boiler, supercritical boiler, ultrasupercritical boiler, USC boiler.
Subcritical, supercritical and ultrasupercritical (USC) describe steam-condition classes for utility boilers. The classification refers to whether the working fluid is operated below or above the critical point of water (22.064 MPa, 373.95 °C).
| Class | Steam pressure | Steam temperature | Plant efficiency (LHV) |
|---|---|---|---|
| Subcritical | < 22.1 MPa | 540–565 °C | 36–39% |
| Supercritical | 22.1–25 MPa | 560–600 °C | 41–43% |
| Ultrasupercritical (USC) | 25–28 MPa | 600–620 °C | 44–47% |
| Advanced USC (A-USC, developmental) | 30+ MPa | 700 °C+ | 50%+ target |
Fouling implications
Higher steam conditions concentrate value in every operating hour: a 1 percentage-point efficiency loss from convective-pass fouling on a USC plant costs measurably more in fuel than on a subcritical one. The economic case for sonic-horn installation on economisers, air heaters and reheaters rises with steam-condition class.
Related terms
Related terms
- BoilerA boiler is a vessel that converts fuel chemical energy into steam by heating water. Coal-fired, biomass, oil, gas and recovery boilers all foul; sonic horns clean heat-transfer surfaces.
- Pulverised-coal boilerA pulverised-coal boiler grinds coal to fine powder and injects it through burners into a furnace. The dominant utility-scale boiler design worldwide.
- Heat rateHeat rate is the fuel energy required to produce one unit of electrical output, measured in BTU/kWh or kJ/kWh. Fouling on convective surfaces directly degrades heat rate.
- SuperheaterA superheater is a tube bank that raises steam temperature beyond the saturation point using flue-gas heat. Sticky alkali ash and slag deposits are the dominant fouling concerns.