---
title: "Multi-effect evaporator"
description: "A multi-effect evaporator train concentrates kraft black liquor from ~15% solids (as it exits pulping) to 70–75% solids before it can be burned in the recovery boiler. The train consists of 5–7 evaporator effects operating at descending pressure and temperature, each one driven by the vapour from the effect upstream — a counter-flow design that minimises live-steam consumption."
canonical_url: "https://sylio.co/glossary/multi-effect-evaporator"
last_updated: "2026-06-28T02:29:36.337Z"
---

A **multi-effect evaporator** train concentrates [kraft black liquor](/glossary/black-liquor) from ~15% solids (as it exits pulping) to 70–75% solids before it can be burned in the [recovery boiler](/glossary/recovery-boiler). The train consists of 5–7 evaporator effects operating at descending pressure and temperature, each one driven by the vapour from the effect upstream — a counter-flow design that minimises live-steam consumption.

## Scaling and fouling

Black-liquor evaporators scale heavily with sodium-rich inorganic deposits, particularly in the high-solids final effects. Periodic water-washing of the evaporator tube bundles is part of routine mill maintenance.

## Sonic-horn relevance

The evaporators themselves are mostly liquid-side equipment and rarely benefit from gas-side acoustic cleaning. The downstream recovery boiler is where Sylio's products engage with the kraft chemical-recovery cycle most directly.

## Related terms

- [Black liquor](/glossary/black-liquor)
- [Recovery boiler](/glossary/recovery-boiler)