SCR Catalyst and Ammonia Injection Grid Cleaning with Dry Ice
Plugged catalyst faces and fouled AIG nozzles drive up backpressure, ammonia slip, and NOx. Dry ice blasting restores flow area without damaging catalyst substrate.
SCR performance depends on two things staying clean: an open catalyst face and an evenly distributed ammonia injection grid. When ash, ammonium bisulfate, and rust scale bridge the catalyst channels, backpressure rises, NOx removal falls, and ammonia slip climbs — often forcing load restrictions well before the catalyst has reached end of chemical life.
What fouls and why it matters
- Ash bridging across the catalyst inlet face — direct loss of active area
- Ammonium bisulfate deposition in the cooler layers — sticky and self-accumulating
- Popcorn ash carried past screens after upstream cleaning
- Corrosion scale from the duct walls settling on the face
- Plugged and eroded AIG nozzles causing maldistribution
Why dry ice for catalyst work
The catalyst substrate is a brittle ceramic honeycomb. Water washing risks channeling and chemical carryover. Grit blasting can fracture channel walls and, worse, leave media inside the channels to be carried downstream. Dry ice removes the bridging deposit and sublimates — nothing is left in the channels.
- Blast at controlled pressure parallel to channel axis
- Work face-by-face with vacuum capture at the layer below
- Follow with a Δp check across the layer to confirm restored flow area
- Clean AIG nozzles and lances in place; verify spray pattern where accessible
Measuring the result
Do not accept a visual-only close-out on SCR work. Record pressure drop across each layer before and after, and track NOx removal and ammonia slip after restart. On a plugged layer, restored Δp and reduced slip are the numbers that justify the outage hours.
Frequently Asked Questions
Will dry ice damage the catalyst?+
Not at controlled pressure with the stream aligned to the channels. Uncontrolled high-pressure blasting perpendicular to the face can chip channel walls, which is why parameter control matters.
Does it restore chemical activity?+
No. It restores flow area and mechanical access. Chemical deactivation from poisoning or sintering requires regeneration or replacement.
Can this be done during a short outage?+
Yes — catalyst face and AIG cleaning are common short-outage scopes because there is no drying or media recovery step.
Planning an outage? See our HRSG cleaning services and get on the schedule early.
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