---
title: "Tubular air preheater"
description: "A tubular air preheater (TAPH) is a fixed shell-and-tube air heater in which flue gas flows inside vertical tubes and combustion air flows around the outside in cross-flow or counter-flow. The construction is mechanically simpler than the rotating Ljungström design but offers less surface area per unit volume."
canonical_url: "https://sylio.co/glossary/tubular-air-preheater"
last_updated: "2026-06-28T02:29:26.600Z"
---

A **tubular air preheater (TAPH)** is a fixed shell-and-tube [air heater](/glossary/air-heater) in which flue gas flows inside vertical tubes and combustion air flows around the outside in cross-flow or counter-flow. The construction is mechanically simpler than the rotating [Ljungström](/glossary/ljungstrom-air-preheater) design but offers less surface area per unit volume.

## Where TAPHs are used

- Smaller industrial boilers
- [Recovery boilers](/glossary/recovery-boiler) at pulp mills
- [WtE](/glossary/waste-to-energy) and [biomass](/glossary/waste-to-energy) duty where rotating-basket Ljungströms are vulnerable to sticky-ash agglomerates
- Some retrofit installations where the existing Ljungström has reached end of life

## Fouling

Tubular APH tubes plug from the inside if flue gas carries sticky ash or [ammonium bisulphate](/glossary/ammonium-bisulphate). Cleaning options:

- Steam [sootblowing](/glossary/steam-sootblower)
- [Sonic horns](/glossary/sonic-horn) mounted at the tube-bundle gas inlet
- Off-line high-pressure water washing
- Manual rodding during major outages

## Related terms

- [Air heater](/glossary/air-heater)
- [Ljungström air preheater](/glossary/ljungstrom-air-preheater)
- [Sonic horn](/glossary/sonic-horn)