Glossary
SCR and SNCR
Catalyst pluggage
Also known as catalyst plugging, catalyst channelling, SCR catalyst pluggage.
Catalyst pluggage is the physical blockage of SCR catalyst channels by particulate material. Unlike catalyst masking (a thin surface blanket), pluggage fills the catalyst channels themselves, stopping gas flow through affected cells. The result is ΔP rise across the SCR, gas-flow maldistribution into the remaining open cells, and channelling effects that reduce overall NOx reduction.
Sources of pluggage material
- Large-particle ash (LPA) — slag fragments and agglomerated ash carried over from the boiler
- Popcorn ash — porous low-density ash particles that wedge into honeycomb cells
- Ammonium-salt deposits — ammonium bisulphate on tail-end SCRs at lower temperatures
- Refractory debris — fragments from upstream furnace or duct repairs
Prevention
- LPA screens — coarse mesh screens upstream of the catalyst trap large particles
- Guard layers — sacrificial top catalyst layer with larger pitch absorbs the initial particulate
- Larger pitch on the top layer — wider cell openings on the first catalyst layer pass LPA through to a removable screen below
- Periodic sonic-horn cleaning — dislodges accumulating ash before it cements
- Steam sootblowing — for harder deposits
Related terms
Related terms
- Selective Catalytic ReductionSCR is the dominant NOx-control technology on industrial combustion plant. Ammonia is injected upstream of a catalyst that converts NOx to nitrogen and water.
- Large-particle ashLPA is fly ash larger than typical (>1 mm), produced by slag fragmentation and agglomeration in the boiler. It is the leading cause of SCR catalyst channel pluggage.
- Popcorn ashPopcorn ash is porous low-density fly-ash particles, typically 5–25 mm, formed during incomplete coal combustion. They wedge into SCR catalyst channels and resist cleaning.
- Catalyst maskingCatalyst masking is the deposition of a thin ash layer on the SCR catalyst face that blocks ammonia and NOx from reaching the active sites. Distinct from pluggage and poisoning.
- Honeycomb catalystA honeycomb catalyst is an extruded ceramic block with parallel square channels, the most common SCR catalyst form. High surface area but susceptible to channel pluggage.
- Sonic hornA sonic horn is a pneumatically-driven low-frequency sound emitter (typically 60–400 Hz at 140–180 dB SPL) used to dislodge particulate fouling from boilers, ESPs, baghouses and process vessels.