Cement
Chloride bypass
Also known as cement chloride bypass, bypass system (cement), Cl bypass.
A chloride bypass is a flue-gas slipstream system that extracts a fraction (typically 3–15%) of the kiln gas before it enters the preheater tower, cooling it and removing the chlorine-rich dust to prevent chlorine accumulation in the chloride cycle.
Why bypasses are increasingly needed
Conventional cement raw materials and fossil fuels carry modest chlorine and sulphur. Alternative fuels — especially RDF, SRF and TDF and sewage sludge — carry much more. Above a TSR threshold (typically 30–50% depending on raw materials), the chloride cycle saturates and starts to drive heavy kiln-inlet build-up that ultimately causes kiln stops. The bypass extracts chlorine fast enough to stabilise the cycle and let the plant operate at high TSR.
Bypass-specific fouling
The bypass duct itself, the quenching tower, and the bypass dust hopper all foul aggressively:
- Hot kiln gas containing high concentrations of chlorides condenses on the cooler bypass-duct walls
- Quench water dropout creates sticky chloride-rich slurry
- Bypass dust hopper bridges with fine sticky chloride material
Sonic horns on the bypass duct and dust hopper are the standard cleaning fit.
Related terms
Related terms
- Kiln inlet and riser ductThe kiln inlet / riser duct is the connection between the rotary kiln and the calciner / preheater. It is the most-fouled location in any cement plant, the focal point for sonic-horn cleaning.
- Sulphur, chloride and alkali cyclesSulphur, chloride and alkali cycles describe how volatile species evaporate from the kiln burning zone, condense in the cooler preheater, and recirculate. Their build-up drives kiln-stop fouling.
- Alternative fuelAlternative fuels (AFR) replace fossil fuel in cement kilns. They cut CO2 emissions and waste-disposal cost but increase chlorine, sulphur and alkali loading in the kiln gas.
- 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.