Fouling
Derate
Also known as capacity derate, load derate, generation derate.
A derate is reduced operating capacity below the equipment's nameplate, imposed because a limiting condition has been reached. Unlike a forced outage (full shutdown), a derate keeps the unit running at lower throughput while the limit persists.
Fouling-driven derates
- ID fan capacity limit — high baghouse ΔP demands more fan power than available, forcing load reduction
- Boiler tube-metal temperature limit — fouling reduces heat absorption, raising tube-metal temperature; protective derate engaged
- Stack opacity limit — ESP efficiency loss forces load reduction to meet emission limits
- HRSG approach-temperature limit — fouling on gas-side surfaces reduces heat recovery; gas-turbine output drops
Economic impact
Derates are usually less costly per hour than outages but can persist much longer. A 5% derate sustained for a month on a 500 MW unit loses ~9,000 MWh — comparable to a multi-day forced outage but easier to overlook in the maintenance ledger.
Sonic horns and derate avoidance
Sonic horns preserve heat-transfer effectiveness, ESP collection efficiency, baghouse ΔP and hopper discharge. Each of these directly defends against the most common fouling-driven derate triggers.
Related terms
Related terms
- Forced outageA forced outage is an unplanned shutdown of an industrial unit, typically triggered by equipment failure or pressure-vessel safety conditions. The dominant economic cost of poor cleaning practice.
- 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.
- Fouling (general)Fouling is the accumulation of unwanted deposits on process-equipment surfaces. The general umbrella term covering slagging, scaling, coking, sintering and many other specific mechanisms.
- Differential pressure (baghouse)Differential pressure (ΔP) across a baghouse is the pressure drop between dirty and clean plenums. It is the headline operational KPI: too low signals broken bags, too high signals fouling.