Cement
Kiln-inlet ring and snowman
Also known as snowman, kiln inlet ring, ring formation, inlet ring.
The kiln-inlet ring (also commonly called a "snowman" for its characteristic shape) is a massive accretion of alkali-sulphate and chloride-bearing material that forms at the kiln inlet / riser duct of a cement plant. A fully-developed snowman can be metres across, weigh several tonnes, and completely block the gas path between the kiln and the calciner above.
Why it forms
Snowmen are driven by the sulphur and chloride cycles — volatile species evaporate from the kiln burning zone, are carried upward in the gas, condense in the cooler kiln-inlet region, and accumulate as a sticky build-up on the kiln-inlet refractory and steel.
The problem intensifies sharply when plants run high thermal substitution rates (TSR) on alternative fuels such as RDF, SRF and TDF, all of which carry more chlorine and sulphur than fossil-fuel coal or coke.
Consequences
- Kiln stop when the snowman blocks the gas path
- Manual cleaning by hammer and lance during the outage — slow, hazardous, intensive
- Refractory damage from the cleaning operation itself
- Lost clinker output — 24–72 hours per snowman event
Prevention
- Sonic horns on the kiln inlet — continuous prevention of the early build-up
- Chloride bypass — extracting a slipstream of gas to remove chloride from the cycle
- Operating discipline on raw-meal alkali / chloride / sulphur ratios
- Limiting AFR rate below the plant's calibrated threshold
Related terms
Related terms
- Kiln inlet and riser ductThe kiln inlet / riser duct is the connection between the rotary kiln and the calciner / preheater. It is the most-fouled location in any cement plant, the focal point for sonic-horn cleaning.
- 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.
- Build-up, coating and accretionBuild-up, coating and accretion are interchangeable terms for accumulated deposits on cement-plant gas-path surfaces. The leading cause of kiln stops in cement manufacture.
- 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.