---
title: "Tertiary air duct (TAD)"
description: "The tertiary air duct (TAD) routes hot combustion air from the clinker cooler to the calciner firing zone, bypassing the rotary kiln. The TAD is essential to separate-calciner designs because it provides the oxygen needed to burn calciner fuel without diverting kiln air."
canonical_url: "https://sylio.co/glossary/tertiary-air-duct"
last_updated: "2026-06-28T02:29:28.165Z"
---

The **tertiary air duct (TAD)** routes hot combustion air from the [clinker cooler](/glossary/clinker-cooler) to the [calciner](/glossary/calciner) firing zone, bypassing the [rotary kiln](/glossary/rotary-kiln). The TAD is essential to separate-calciner designs because it provides the oxygen needed to burn calciner fuel without diverting kiln air.

## Operational issues

- **Dust dropout** — fine clinker dust carried over from the cooler settles along the TAD bottom and accumulates
- **Localised build-up** at bends and restrictions in the duct path
- **Pluggage** at the TAD-calciner inlet
- **Refractory wear** from impingement at duct bends

## Cleaning

[Sonic horns](/glossary/sonic-horn) installed along the TAD prevent dust settlement and keep the air flow free of restrictions. Periodic pneumatic-gate discharge of accumulated dust from purpose-built TAD hoppers complements acoustic cleaning.

## Related terms

- [Calciner](/glossary/calciner)
- [Clinker cooler](/glossary/clinker-cooler)
- [Preheater tower](/glossary/preheater-tower)
- [Sonic horn](/glossary/sonic-horn)