Glossary
HRSG and gas path
Stack and breeching
Also known as stack, breeching, flue, chimney.
The stack (chimney) is the vertical structure that releases flue gas to atmosphere at sufficient height to comply with dispersion-modelling regulations and prevent ground-level concentrations of pollutants. The breeching is the horizontal duct that connects the ID fan discharge (or boiler outlet on natural-draught units) to the stack inlet.
Stack-related issues
- Stack liner corrosion from condensed sulphuric acid below the acid dew point
- Visible plume caused by sulphate aerosol from SO₂/SO₃ conversion or low-load operation
- Opacity exceedances from upstream particulate control failure
- Breeching deposition during low-load operation, occasionally falling as chunks during transients
Sonic horns on breeching
Where breeching deposition is significant, sonic horns on the breeching wall prevent the accumulation that would otherwise risk falling debris during load changes.
Related terms
Related terms
- ID, FD and PA fansBoilers use three fans: ID (induced draft) pulls flue gas through the convective pass, FD (forced draft) pushes combustion air, PA (primary air) conveys pulverised coal to the burners.
- Opacity (stack)Opacity is the percentage of light obscured by particulate in stack flue gas. The headline visual KPI for ESP performance; continuously monitored and permit-limited.
- 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.