Glossary
Pulp and paper
Recausticising
Also known as recausticizing, causticising, causticizing, causticising plant.
Recausticising (also recausticizing in US spelling) is the chemical step that regenerates kraft cooking liquor by reacting green liquor (sodium carbonate from the smelt dissolving tank) with burnt lime (CaO from the lime kiln) to produce white liquor (sodium hydroxide + sodium sulphide) and lime mud (CaCO₃). The white liquor is returned to the digester for pulping; the lime mud goes back to the lime kiln for re-calcination.
The closed chemical cycle
Kraft recovery is a closed loop:
- Pulping consumes white liquor; produces black liquor
- Black liquor concentrated in evaporators, burned in the recovery boiler
- Recovery boiler produces smelt, which dissolves into green liquor in the SDT
- Recausticising converts green liquor + burnt lime → white liquor + lime mud
- Lime kiln calcines lime mud → burnt lime
- Burnt lime returns to recausticising
Sonic horns appear at several points around this loop, principally on the recovery boiler, SDT vent stack, lime-kiln preheater and lime-kiln ESP hopper.
Related terms
Related terms
- Black liquorBlack liquor is the concentrated spent cooking liquor from kraft pulping. It is burned in the recovery boiler to generate steam, power and to recover the pulping chemicals.
- Smelt (recovery boiler)Smelt is the molten sodium carbonate and sulphide mixture that accumulates in the bottom of a kraft recovery boiler. It is dissolved into green liquor and recausticised to pulping reagent.
- Smelt dissolving tankAn SDT receives molten smelt from the recovery boiler and dissolves it into weak wash to form green liquor. The vent stack accumulates sodium fume; sonic horns prevent stack-line plugging.
- Lime kilnA lime kiln calcines spent lime mud back to burnt lime (CaO) for re-use in the kraft pulping chemical recovery cycle. Preheater chain section fouling is a recurring operational issue.