---
title: "Calciner"
description: "A calciner is the combustion chamber in a modern cement preheater tower where raw meal is pre-calcined — the endothermic CaCO₃ → CaO + CO₂ reaction is driven to ~90% completion — before the meal enters the rotary kiln. Calciners can be inline (placed in the kiln-riser gas path) or separate (a dedicated combustion chamber receiving tertiary air through a dedicated tertiary air duct)."
canonical_url: "https://sylio.co/glossary/calciner"
last_updated: "2026-06-28T02:29:27.188Z"
---

A **calciner** is the combustion chamber in a modern cement preheater tower where raw meal is pre-calcined — the endothermic CaCO₃ → CaO + CO₂ reaction is driven to ~90% completion — before the meal enters the [rotary kiln](/glossary/rotary-kiln). Calciners can be **inline** (placed in the kiln-riser gas path) or **separate** (a dedicated combustion chamber receiving tertiary air through a dedicated [tertiary air duct](/glossary/tertiary-air-duct)).

## AFR firing

Calciners are the dominant firing location for [alternative fuels](/glossary/alternative-fuel) ([RDF, SRF, TDF](/glossary/rdf-srf-tdf), sewage sludge). They tolerate variable-quality waste fuels better than the main kiln burner because residence time is longer and temperatures are lower. Cement plants targeting high [thermal substitution rates (TSR)](/glossary/thermal-substitution-rate) concentrate their AFR firing in the calciner.

## Fouling

AFR firing in the calciner raises the chlorine and sulphur loading of the gas reaching the [preheater cyclones](/glossary/preheater-cyclone) above. This intensifies the [build-up](/glossary/build-up-coating-accretion) problem in the lower preheater stages and the [kiln riser](/glossary/kiln-inlet-riser-duct), driving the need for [chloride bypass](/glossary/chloride-bypass) and active [sonic-horn](/glossary/sonic-horn) cleaning.

## Cleaning

Sonic horns are mounted on calciner walls and on the calciner outlet to the preheater stage 5 cyclone, keeping the gas path free of the alkali coatings that accumulate at high AFR rates.

## Related terms

- [Preheater tower](/glossary/preheater-tower)
- [Preheater cyclone](/glossary/preheater-cyclone)
- [Rotary kiln](/glossary/rotary-kiln)
- [Alternative fuel (AFR)](/glossary/alternative-fuel)
- [Sonic horn](/glossary/sonic-horn)