Cement
Kiln inlet and riser duct
Also known as kiln inlet, riser duct, kiln riser.
The kiln inlet / riser duct is the connection between the upper end of the rotary kiln and the calciner / preheater tower above. Hot kiln gas rises through the inlet into the calciner, and pre-calcined meal descends from the calciner into the kiln. The geometry — narrow, hot, dust-laden — makes this the single most fouled location in any cement plant.
Why it fouls so heavily
- Temperature is in the alkali / chloride condensation window (~800 °C at the inlet)
- Gas-side velocity is high
- Sticky pre-calcined meal contacts cooler steel and refractory
- Alternative fuel firing in the calciner adds chlorine and sulphur to the gas
- The bend geometry creates dead zones where build-up accelerates
The visible result is the kiln-inlet ring or "snowman" — a massive accretion that can completely block the gas path if untreated.
Cleaning intensity
Cement plants typically run multiple sonic horns concentrated on the kiln inlet, supplemented by air cannons for periodic remediation and manual water-lancing during planned outages. The mix and intensity scale up sharply on plants running > 50% TSR.
Related terms
Related terms
- Rotary kilnA rotary kiln is a long inclined rotating cylinder where preheated raw meal is burned at 1,450 °C to form clinker. The heart of every cement plant.
- Preheater towerA preheater tower is a vertical stack of cyclone separators that pre-heats raw meal with kiln exhaust gas before it enters the rotary kiln. The most fouling-prone section of any cement plant.
- Kiln-inlet ring and snowmanA snowman is a massive accretion at the cement kiln inlet that can completely block the gas path. Driven by sulphur and chloride cycles, intensified by alternative fuels.
- CalcinerA calciner is a combustion chamber in the cement preheater tower where raw meal is pre-calcined (CaCO3 → CaO) before entering the rotary kiln. Common site for AFR firing.
- 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.