Boilers
Heat rate
Also known as boiler heat rate, plant heat rate, heat-rate degradation.
Heat rate is the fuel energy consumed per unit of electrical energy generated, measured in BTU/kWh (US) or kJ/kWh (everywhere else). Lower heat rate equals higher thermodynamic efficiency. Heat rate is the central economic KPI of every coal-fired and gas-fired power plant — a 1% rise in heat rate at sustained load costs the operator 1% more fuel per MWh forever.
Heat rate and convective-pass fouling
Heat rate degrades from many causes. The fouling-driven contribution is normally split between:
- Economiser fouling — feedwater pre-heat falls, steam-cycle efficiency drops
- Air heater fouling — combustion-air pre-heat falls, boiler efficiency drops
- Superheater / reheater fouling — outlet temperatures fall, turbine efficiency drops
- Forced attemperation loss of margin
A typical poorly-maintained coal-fired unit carries 2–4% heat-rate penalty from cumulative fouling. Aggressive cleaning, including sonic horns on convective surfaces, can recover 1–3% of that — equivalent to USD 1–5 million annual fuel saving for a 500 MW unit.
How heat-rate recovery is monetised
Heat-rate recovery is the headline business case for sonic-horn retrofits on coal and biomass boilers. The savings flow directly through fuel cost; payback periods of 12–24 months are routinely quoted.
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.
- EconomiserAn economiser is the final tube bank in a boiler's convective pass that recovers heat from the flue gas by preheating feedwater. Ash bridging in the economiser is a routine cleaning challenge.
- Air heaterAn air heater (also air preheater, APH) recovers low-grade heat from flue gas to preheat combustion air. Cold-end fouling and corrosion are the dominant operational challenges.
- Convective pass and backpassThe convective pass is the downstream section of a boiler where heat transfer is by conduction across tube banks: superheater, reheater, economiser. The primary zone for sonic-horn cleaning.
- Sonic hornA sonic horn is a pneumatically-driven low-frequency sound emitter (typically 60–400 Hz at 140–180 dB SPL) used to dislodge particulate fouling from boilers, ESPs, baghouses and process vessels.