---
title: "Economiser"
description: "An economiser is the tube bank in a boiler's convective pass that recovers residual heat from the flue gas by preheating boiler feedwater. It sits downstream of the reheater and upstream of the air heater; economiser performance directly affects boiler heat rate."
canonical_url: "https://sylio.co/glossary/economiser"
last_updated: "2026-06-28T02:29:25.682Z"
---

An **economiser** is the tube bank in a boiler's [convective pass](/glossary/convective-pass-backpass) that recovers residual heat from the flue gas by preheating boiler feedwater. It sits downstream of the [reheater](/glossary/reheater) and upstream of the [air heater](/glossary/air-heater); economiser performance directly affects boiler [heat rate](/glossary/heat-rate).

## Fouling

Two failure modes dominate:

- **Ash bridging** between tubes — gas can no longer pass freely; ΔP across the economiser rises
- **Large-particle ash** dropping out of the gas stream onto economiser hoppers — bridges and pluggage in the hopper itself

The first reduces gas-side heat transfer and forces gas channelling around the blocked area; the second causes hopper extraction to fail and back-pressures the gas path.

## Sonic-horn duty

[Sonic horns](/glossary/sonic-horn) mounted on the economiser shell and hopper are particularly effective because economiser deposits are dry, friable and respond well to acoustic dislodging. Plants commonly report 1–2% boiler-efficiency recovery after horn installation on heavily-fouled economisers.

## Economiser-SCR adjacency

On units with an upstream [high-dust SCR](/glossary/high-dust-low-dust-tail-end-scr), the economiser receives the same large-particle ash that the SCR is designed against. LPA screens between SCR and economiser are common; sonic horns help keep both surfaces clean.

## Related terms

- [Boiler](/glossary/boiler)
- [Convective pass / backpass](/glossary/convective-pass-backpass)
- [Superheater](/glossary/superheater)
- [Air heater](/glossary/air-heater)
- [Large-particle ash](/glossary/large-particle-ash)
- [Sonic horn](/glossary/sonic-horn)