---
title: "Smelt dissolving tank (SDT)"
description: "A smelt dissolving tank (SDT) receives molten smelt discharged from the recovery boiler bottom and dissolves it into weak wash water to form green liquor (the alkaline solution sent on to the recausticising plant). Internal agitators and shatter jets break the smelt stream into small droplets to control the otherwise-violent quench reaction."
canonical_url: "https://sylio.co/glossary/smelt-dissolving-tank"
last_updated: "2026-06-28T02:29:36.412Z"
---

A **smelt dissolving tank (SDT)** receives molten [smelt](/glossary/smelt) discharged from the [recovery boiler](/glossary/recovery-boiler) bottom and dissolves it into weak wash water to form *green liquor* (the alkaline solution sent on to the [recausticising](/glossary/recausticising) plant). Internal agitators and shatter jets break the smelt stream into small droplets to control the otherwise-violent quench reaction.

## SDT vent stack

The dissolution is exothermic and steamy. SDT vent gas carries sodium-rich fume that condenses on the vent stack walls as a fine sticky deposit. Over time the build-up narrows the stack and disrupts vent flow.

## Sonic-horn duty

[Sonic horns](/glossary/sonic-horn) mounted on the SDT vent stack keep the sodium-fume deposit from consolidating, preventing the periodic outages otherwise needed for vent cleaning.

## Related terms

- [Smelt](/glossary/smelt)
- [Recovery boiler](/glossary/recovery-boiler)
- [Recausticising](/glossary/recausticising)
- [Sonic horn](/glossary/sonic-horn)