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SCR Catalyst Cleaning and Maintenance: Keeping the Layer Healthy

Part of the SCR DeNOx: The Complete Guide — this article is one of the detailed pages in the guide.

Direct answer: In-service SCR catalyst maintenance is built around three routines: sootblowing or acoustic cleaning to control ash deposits, pressure-drop monitoring to catch plugging early, and periodic inspection/activity testing to time regeneration or replacement. A maintained layer keeps both conversion and pressure drop stable; a neglected layer loses activity to plugging before chemical deactivation ever shows up.

Cleaning systems

  • Steam sootblowers — the traditional answer; effective on loose ash, but condensation risk if steam quality is poor.
  • Acoustic horns — low-frequency sound dislodges ash before it cakes; increasingly standard on high-dust applications.
  • Combined systems — sootblowers for deep deposits, acoustic horns for continuous prevention.

Cleaning frequency is set by fuel and ash type — high-alkali fuels demand more aggressive schedules.

Pressure drop as a diagnostic

Differential pressure across the catalyst layer is the cheapest, most reliable health signal:

  • Gradual rise — normal ash accumulation; clean on schedule.
  • Step change — plugging event, channel collapse or water carryover; investigate immediately.
  • No rise at all — either unusually clean gas or bypass around the catalyst; verify sealing.

Inspection routine

Annual or outage-based inspection covers:

  • Visual face inspection for erosion, plugging and mechanical damage.
  • Sample core removal for laboratory activity testing (K value).
  • Hardness/compressive strength spot checks on aging modules.
  • Seal and frame inspection for bypass.

When cleaning is not enough

Cleaning restores gas paths but not catalytic activity. If inspection shows:

  • Activity below the end-of-life threshold → plan regeneration or replacement.
  • Localized erosion or collapse → replace the affected modules, not the whole layer.
  • Persistent plugging from unusual fuel → revisit the cleaning system and the catalyst pitch.

Manufacturer perspective

Maintenance starts with design: the catalyst geometry, cleaning system and monitoring points are specified together. We provide inspection checklists and activity-testing support so the plant always knows the true remaining life of its layer.

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