---
title: "Boiler"
description: "A boiler is a closed vessel in which fuel chemical energy is converted to steam by transferring heat into water flowing through tube banks. Industrial and utility boilers serve electricity generation, district heating, process steam, WtE, biomass and pulp-and-paper operations. All of them foul; the only variables are how much and with what."
canonical_url: "https://sylio.co/glossary/boiler"
last_updated: "2026-06-28T02:29:25.562Z"
---

A **boiler** is a closed vessel in which fuel chemical energy is converted to steam by transferring heat into water flowing through tube banks. Industrial and utility boilers serve electricity generation, district heating, process steam, [WtE](/glossary/waste-to-energy), [biomass](/glossary/waste-to-energy) and [pulp-and-paper](/glossary/recovery-boiler) operations. All of them foul; the only variables are *how much* and *with what*.

## Boiler families

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

<tbody>
  <tr>
    <td>
      <a href="/glossary/pc-boiler">
        PC boiler
      </a>
    </td>
    
    <td>
      Pulverised coal
    </td>
    
    <td>
      Dominant utility design
    </td>
  </tr>
  
  <tr>
    <td>
      <a href="/glossary/cfb-boiler">
        CFB boiler
      </a>
    </td>
    
    <td>
      Coal, biomass, RDF, lignite
    </td>
    
    <td>
      Tolerates wider fuel range; lower NOx
    </td>
  </tr>
  
  <tr>
    <td>
      <a href="/glossary/bfb-boiler">
        BFB boiler
      </a>
    </td>
    
    <td>
      Biomass, sludge, low-grade fuels
    </td>
    
    <td>
      Bubbling fluidised bed
    </td>
  </tr>
  
  <tr>
    <td>
      <a href="/glossary/recovery-boiler">
        Recovery boiler
      </a>
    </td>
    
    <td>
      Black liquor (kraft pulp mills)
    </td>
    
    <td>
      Combines chemicals recovery with steam
    </td>
  </tr>
  
  <tr>
    <td>
      <a href="/glossary/hog-fuel-boiler-bark-boiler">
        Hog-fuel boiler
      </a>
    </td>
    
    <td>
      Wood waste, bark
    </td>
    
    <td>
      Common at pulp mills as side boilers
    </td>
  </tr>
  
  <tr>
    <td>
      Gas / oil boiler
    </td>
    
    <td>
      Natural gas, fuel oil
    </td>
    
    <td>
      Lower particulate, less fouling
    </td>
  </tr>
  
  <tr>
    <td>
      HRSG
    </td>
    
    <td>
      Gas-turbine exhaust
    </td>
    
    <td>
      See <a href="/glossary/heat-recovery-steam-generator">
        heat-recovery steam generator
      </a>
    </td>
  </tr>
</tbody>
</table>

## Where sonic horns sit

[Sonic horns](/glossary/sonic-horn) installed across the convective pass — between [economiser](/glossary/economiser), [superheaters](/glossary/superheater), [reheater](/glossary/reheater) and [air heater](/glossary/air-heater) — dislodge ash and soot continuously, supplementing or partially replacing steam [sootblowers](/glossary/steam-sootblower). The benefit shows up as [heat rate](/glossary/heat-rate) recovery, deferred outages and longer intervals between water washes.

## Related terms

- [PC boiler](/glossary/pc-boiler)
- [CFB boiler](/glossary/cfb-boiler)
- [Recovery boiler](/glossary/recovery-boiler)
- [Waterwall](/glossary/waterwall)
- [Economiser](/glossary/economiser)
- [Sonic horn](/glossary/sonic-horn)