---
title: "Fume (recovery boiler)"
description: "Fume in recovery-boiler vocabulary refers to the very fine sub-micron sodium-sulphate particulate that forms by vapour-phase condensation in the upper furnace as gas cools from the combustion zone. Distinct from larger carry-over particles, fume is too fine to settle by gravity and remains entrained until captured by the downstream ESP."
canonical_url: "https://sylio.co/glossary/fume"
last_updated: "2026-06-28T02:29:35.929Z"
---

**Fume** in recovery-boiler vocabulary refers to the very fine sub-micron sodium-sulphate particulate that forms by vapour-phase condensation in the upper furnace as gas cools from the combustion zone. Distinct from larger [carry-over](/glossary/carry-over) particles, fume is too fine to settle by gravity and remains entrained until captured by the downstream [ESP](/glossary/electrostatic-precipitator).

## Where fume deposits

Fume's small particle size means it follows gas streamlines closely but still deposits where flow eddies allow contact with cooler surfaces:

- [Superheater](/glossary/superheater) and [generating-bank](/glossary/generating-bank) tubes — alongside larger carry-over particles
- [Economiser](/glossary/economiser) tubes — fume-rich bottoming deposits
- ESP collecting plates — fine cake build-up

## Cleaning

[Sonic horns](/glossary/sonic-horn) on the recovery-boiler convective pass and ESP address both fume and coarser carry-over deposits in the same firing pattern.

## Related terms

- [Recovery boiler](/glossary/recovery-boiler)
- [Carry-over](/glossary/carry-over)
- [Superheater](/glossary/superheater)
- [Electrostatic precipitator](/glossary/electrostatic-precipitator)