Definition
Smelt dissolving tank
A smelt dissolving tank receives molten recovery-boiler smelt and dissolves it in weak wash to make green liquor. Vent deposits and safety controls are important.
- Subject
- Pulp and paper
- Also known as
- SDT, smelt dissolving tanks, dissolving tank
A smelt dissolving tank (SDT) receives molten smelt from a kraft recovery boiler and dissolves it in weak wash to form green liquor. The tank sits below the recovery boiler smelt spouts and is a critical link between combustion in the boiler and chemical recovery in the recausticising plant.
Molten smelt contains mainly sodium carbonate and sodium sulphide. When it enters the tank, it reacts violently with water and releases heat, steam, and reduced sulphur gases. Agitation, dilution flow, shatter jets, venting, and level control are designed to dissolve the smelt while controlling noise, fumes, and splashing.
Operating and safety context
The SDT handles hot caustic liquor, molten chemical, steam, and odorous gases. Safety concerns include smelt-water reaction, spout plugging, green liquor overflow, vent restrictions, toxic and odorous gas exposure, and maintenance access around spouts. The tank and spout area require disciplined procedures because conditions can change quickly when a spout flow changes or a plug clears.
Green liquor quality matters downstream. Poor dissolving, dregs carryover, density swings, or weak-wash problems can disturb clarification and recausticising.
Deposit problems
SDT vent lines and stacks can accumulate sodium salt fume and entrained droplets. Deposits can narrow the vent path, increase draft problems, and create messy or hazardous maintenance work. Spout hoods, demisters, duct elbows, and fan inlets are common problem points.
Acoustic cleaning context
Sonic horns are relevant mainly on the SDT vent and associated ducting, not inside the liquid tank. Their role is to keep dry or semi-dry sodium deposits from plugging vent lines and stack sections. They should be applied with careful attention to corrosion, washdown, access, and noise. Wet sticky deposits or chemical scaling may need washing or process changes rather than acoustic cleaning.
Operating and safety context
The smelt dissolving tank receives molten smelt from a recovery boiler and dissolves it in weak wash to form green liquor. Stable operation depends on smelt spout flow, shattering steam or jets, tank level, agitator performance, venting, green-liquor density, and control of violent local reactions. The area is noisy, hot, chemically aggressive, and exposed to splash hazards.
Maintenance checks include spout cooling, shatter-jet alignment, agitator seals, vent deposits, tank lining, weak-wash supply, density instruments, and access guarding. Safety reviews focus on molten smelt, caustic liquor, steam, pressure relief, total reduced sulphur gases, and emergency response. Acoustic cleaning is generally not applied to the wet tank contents. Its relevance is limited to dry vent, duct, or dust-handling deposits around the dissolving system where the deposit is accessible and cleaning will not disturb smelt handling.
Related terms
Explore the subject
Related terms
4 terms
- Smelt (recovery boiler)Smelt is the molten sodium salt mixture formed in a kraft recovery boiler. It drains to the dissolving tank and becomes green liquor.
- Recovery boilerA recovery boiler burns black liquor to generate steam and recover pulping chemicals. Ash deposition, smelt safety and tube cleanliness are central operating concerns.
- RecausticisingRecausticising converts green liquor and lime into white liquor for kraft pulping. It links the recovery boiler, smelt dissolving tank and lime kiln.
- Sonic hornA sonic horn is a pneumatic low-frequency sound emitter used to dislodge particulate fouling from boilers, ESPs, baghouses, ducts and silos while the plant stays online.
References