---
title: "High-dust / low-dust / tail-end SCR"
description: "High-dust, low-dust and tail-end describe where an SCR catalyst sits in the flue-gas path relative to upstream particulate-control equipment."
canonical_url: "https://sylio.co/glossary/high-dust-low-dust-tail-end-scr"
last_updated: "2026-06-28T02:29:37.231Z"
---

**High-dust**, **low-dust** and **tail-end** describe where an [SCR catalyst](/glossary/selective-catalytic-reduction) sits in the flue-gas path relative to upstream particulate-control equipment.

<table>
<thead>
  <tr>
    <th>
      Configuration
    </th>
    
    <th>
      Position
    </th>
    
    <th>
      Gas temperature
    </th>
    
    <th>
      Trade-off
    </th>
  </tr>
</thead>

<tbody>
  <tr>
    <td>
      <strong>
        High-dust (HD-SCR)
      </strong>
    </td>
    
    <td>
      Upstream of <a href="/glossary/electrostatic-precipitator">
        ESP
      </a>
      
       / baghouse
    </td>
    
    <td>
      300–400 °C
    </td>
    
    <td>
      Natural operating temperature; high catalyst pluggage and erosion
    </td>
  </tr>
  
  <tr>
    <td>
      <strong>
        Low-dust (LD-SCR)
      </strong>
    </td>
    
    <td>
      Between hot-side ESP and air heater
    </td>
    
    <td>
      300–400 °C
    </td>
    
    <td>
      Cleaner gas; needs hot-side ESP upstream
    </td>
  </tr>
  
  <tr>
    <td>
      <strong>
        Tail-end (TE-SCR)
      </strong>
    </td>
    
    <td>
      Downstream of all particulate control
    </td>
    
    <td>
      130–200 °C
    </td>
    
    <td>
      Cleanest gas; requires gas reheating; ABS risk
    </td>
  </tr>
</tbody>
</table>

## Why high-dust dominates

Most coal-fired utility SCRs are high-dust because no flue-gas reheating is required and SCR slots cleanly between the [economiser](/glossary/economiser) outlet and the [air heater](/glossary/air-heater) inlet at the natural process temperature. The penalty is high fly-ash loading at the catalyst inlet — hence the need for [LPA screens](/glossary/large-particle-ash), guard layers and active cleaning ([sonic horns](/glossary/sonic-horn) plus [sootblowers](/glossary/sonic-sootblower)).

## Tail-end SCR niche

Tail-end SCRs are favoured where dust loading would otherwise destroy the catalyst (some [WtE](/glossary/waste-to-energy) plants), where retrofitting onto an existing layout leaves no upstream space, or where catalyst poisons (arsenic, alkali) must be filtered out first. The reheating energy penalty is significant.

## Related terms

- [Selective Catalytic Reduction (SCR)](/glossary/selective-catalytic-reduction)
- [Catalyst pluggage](/glossary/catalyst-pluggage)
- [Ammonium bisulphate](/glossary/ammonium-bisulphate)
- [Electrostatic precipitator](/glossary/electrostatic-precipitator)