---
title: "Hog-fuel boiler / bark boiler"
description: "A hog-fuel boiler (or bark boiler, sometimes generically power boiler) is a biomass-fired auxiliary boiler installed at most pulp and paper mills to burn wood waste, bark, sawdust and screened biomass residues, supplying additional steam and electricity alongside the kraft recovery boiler."
canonical_url: "https://sylio.co/glossary/hog-fuel-boiler-bark-boiler"
last_updated: "2026-06-28T02:29:25.966Z"
---

A **hog-fuel boiler** (or **bark boiler**, sometimes generically *power boiler*) is a biomass-fired auxiliary boiler installed at most pulp and paper mills to burn wood waste, bark, sawdust and screened biomass residues, supplying additional steam and electricity alongside the [kraft recovery boiler](/glossary/recovery-boiler).

## Combustion types

<table>
<thead>
  <tr>
    <th>
      Type
    </th>
    
    <th>
      Fuel handling
    </th>
  </tr>
</thead>

<tbody>
  <tr>
    <td>
      Grate-fired
    </td>
    
    <td>
      Older designs, simple, tolerates wet fuel
    </td>
  </tr>
  
  <tr>
    <td>
      <a href="/glossary/bfb-boiler">
        BFB
      </a>
    </td>
    
    <td>
      Common modern design for variable biomass
    </td>
  </tr>
  
  <tr>
    <td>
      <a href="/glossary/cfb-boiler">
        CFB
      </a>
    </td>
    
    <td>
      Larger capacity, broader fuel flexibility
    </td>
  </tr>
</tbody>
</table>

## Fouling characteristics

- Alkali- and chloride-rich ash from bark and forest residues
- High variability in fuel moisture and composition
- Slagging on first-pass tubes; bonded ash on [superheaters](/glossary/superheater)
- Cold-end build-up on the [economiser](/glossary/economiser) and [air heater](/glossary/air-heater)

## Sonic-horn fit

[Sonic horns](/glossary/sonic-horn) are well established on hog-fuel-boiler convective passes; the OEM aftermarket teams that serve recovery boilers also typically include hog-fuel cleaning in the same service contract.

## Related terms

- [Boiler](/glossary/boiler)
- [BFB boiler](/glossary/bfb-boiler)
- [CFB boiler](/glossary/cfb-boiler)
- [Recovery boiler](/glossary/recovery-boiler)
- [Superheater](/glossary/superheater)