---
title: "Kiln-inlet ring / \"snowman\""
description: "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."
canonical_url: "https://sylio.co/glossary/kiln-inlet-ring-snowman"
last_updated: "2026-06-28T02:29:27.311Z"
---

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](/glossary/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](/glossary/calciner) above.

## Why it forms

Snowmen are driven by the [sulphur and chloride cycles](/glossary/sulphur-cycle-chloride-cycle-alkali-cycle) — 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](/glossary/build-up-coating-accretion) on the kiln-inlet refractory and steel.

The problem intensifies sharply when plants run high [thermal substitution rates (TSR)](/glossary/thermal-substitution-rate) on [alternative fuels](/glossary/alternative-fuel) such as [RDF, SRF and TDF](/glossary/rdf-srf-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

- [Kiln inlet / riser duct](/glossary/kiln-inlet-riser-duct)
- [Rotary kiln](/glossary/rotary-kiln)
- [Build-up / coating / accretion](/glossary/build-up-coating-accretion)
- [Sonic horn](/glossary/sonic-horn)