Glossary
Cement
Tertiary air duct
Also known as TAD, tertiary air, cement TAD.
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.
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 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
Related terms
- CalcinerA calciner is a combustion chamber in the cement preheater tower where raw meal is pre-calcined (CaCO3 → CaO) before entering the rotary kiln. Common site for AFR firing.
- Clinker coolerA clinker cooler quenches hot clinker discharged from the rotary kiln using forced ambient air. Hot air recovered is sent to the calciner via the TAD; cooler dust hoppers benefit from sonic horns.
- Preheater towerA preheater tower is a vertical stack of cyclone separators that pre-heats raw meal with kiln exhaust gas before it enters the rotary kiln. The most fouling-prone section of any cement plant.
- 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.