---
title: "Kiln inlet / riser duct"
description: "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."
canonical_url: "https://sylio.co/glossary/kiln-inlet-riser-duct"
last_updated: "2026-06-28T02:29:27.262Z"
---

The **kiln inlet / riser duct** is the connection between the upper end of the [rotary kiln](/glossary/rotary-kiln) and the [calciner](/glossary/calciner) / [preheater tower](/glossary/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](/glossary/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"](/glossary/kiln-inlet-ring-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](/glossary/air-cannon-air-blaster) for periodic remediation and manual water-lancing during planned outages. The mix and intensity scale up sharply on plants running > 50% [TSR](/glossary/thermal-substitution-rate).

## Related terms

- [Rotary kiln](/glossary/rotary-kiln)
- [Preheater tower](/glossary/preheater-tower)
- [Kiln-inlet ring / snowman](/glossary/kiln-inlet-ring-snowman)
- [Calciner](/glossary/calciner)
- [Sonic horn](/glossary/sonic-horn)