Pulp and paper
Lime kiln
Also known as kraft lime kiln, rotary lime kiln, lime recovery kiln.
A lime kiln at a kraft pulp mill calcines spent lime mud (CaCO₃) back to burnt lime (CaO) at ~1,200 °C for re-use in the recausticising chemical-recovery cycle. The kiln is a long inclined rotating cylinder, similar in form to a cement rotary kiln but smaller and lower-temperature.
Preheater and chain section
Most modern lime kilns have a preheater (often a chain section inside the kiln itself or an external preheater) where incoming damp lime mud is pre-dried by exhaust gas. The chain section accumulates lime-mud build-up — mud rings — that progressively narrow the gas path and reduce kiln throughput.
Lime-kiln ESP
The flue gas exiting the kiln carries entrained lime dust, captured in a downstream ESP before the stack. The ESP hopper handles fine lime, which bridges easily.
Cleaning
Sonic horns are installed at three points on a typical lime-kiln gas-cleaning train:
- Lime-kiln preheater / chain section — prevent mud-ring formation
- Lime-kiln ESP hopper — prevent fine-lime bridging
- Stack adjacency — if vent fouling becomes problematic
Related terms
Related terms
- RecausticisingRecausticising converts green liquor (sodium carbonate) and burnt lime back into white liquor (sodium hydroxide and sulphide) for re-use in kraft pulping.
- Recovery boilerA recovery boiler burns kraft black liquor to generate steam, electrical power and recovered pulping chemicals. Iconic application for sonic horns on superheater cleaning.
- Rotary kilnA rotary kiln is a long inclined rotating cylinder where preheated raw meal is burned at 1,450 °C to form clinker. The heart of every 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.