---
title: "Popcorn ash"
description: "Popcorn ash is a category of large-particle ash (LPA) consisting of porous, low-density particles 5–25 mm in size that resemble a kernel of popped corn. The particles form during incomplete coal combustion or low-temperature slagging, particularly on sub-bituminous coal and on units operating at reduced load. The low density means the particles are easily carried by flue gas into the SCR."
canonical_url: "https://sylio.co/glossary/popcorn-ash"
last_updated: "2026-06-28T02:29:37.882Z"
---

**Popcorn ash** is a category of [large-particle ash (LPA)](/glossary/large-particle-ash) consisting of porous, low-density particles 5–25 mm in size that resemble a kernel of popped corn. The particles form during incomplete coal combustion or low-temperature slagging, particularly on sub-bituminous coal and on units operating at reduced load. The low density means the particles are easily carried by flue gas into the [SCR](/glossary/selective-catalytic-reduction).

## Why popcorn ash matters

Once a popcorn-ash particle enters a [honeycomb catalyst](/glossary/honeycomb-catalyst) channel, the channel is essentially blocked: the particle is too soft to break up under gas flow, too large to pass through, and too irregular to dislodge with typical [sonic-horn](/glossary/sonic-horn) energy. The result is a long-lived dead channel that reduces SCR efficiency.

## Mitigation

- **Coal blending or fuel switching** to reduce popcorn-ash formation
- **Combustion-tuning** to raise furnace temperature and reduce porous-ash output
- **LPA screens** upstream of the catalyst
- **Guard layers** as first catalyst layer

## Related terms

- [Large-particle ash](/glossary/large-particle-ash)
- [Catalyst pluggage](/glossary/catalyst-pluggage)
- [Selective Catalytic Reduction (SCR)](/glossary/selective-catalytic-reduction)