HRSG Cleaning Explained: Tube Bundles, SCR Catalysts, and AIG
HRSG fouling steals megawatts and raises emissions. Here is what fouls, why it matters, and how dry ice blasting helps restore performance during outages.
Heat recovery steam generators (HRSGs) are the backbone of combined-cycle power generation. They capture turbine exhaust heat and convert it into steam for a downstream Rankine cycle, lifting plant efficiency from the high 30s into the 60% range. Every percentage point of HRSG performance shows up in the daily MW report — and every layer of fouling steals it back.
What actually fouls inside an HRSG
- External tube bundle fouling — ammonium bisulfate, iron oxide, insulation fibers, and combustion deposits caking onto finned tubes.
- SCR catalyst fouling — masking and pore plugging that reduces NOx conversion.
- CO catalyst fouling — surface deposits that reduce CO oxidation efficiency.
- Ammonia injection grid (AIG) nozzle fouling — uneven ammonia distribution that drives slip and ABS formation downstream.
- Duct burner and transition duct deposits.
- Turbine inlet hardware deposits affecting compressor performance.
Why HRSG cleaning matters
- Restored heat transfer — more steam, more MW, the same fuel.
- Lower stack temperatures and lower backpressure on the gas turbine.
- Improved emissions compliance (NOx, CO, and ammonia slip).
- Extended catalyst life — replacement is six and seven figures per layer.
- Reduced ABS formation in the cold end of the HRSG.
- Lower risk of forced outages between scheduled inspections.
Why dry ice blasting is the right tool
HRSG internals do not tolerate water well. Wet cleaning drives corrosion in carbon steel finned tubes, damages catalyst substrates, and extends outage windows because everything has to dry before restart. Grit blasting is even worse — media gets trapped in bundles and fins and ends up downstream.
Dry ice blasting cleans HRSG tube bundles externally, SCR and CO catalyst faces, AIG nozzles, transition ducts, and turbine inlet hardware without water and without secondary waste. The CO₂ pellet sublimates on impact — nothing stays behind to migrate into the cold end or get baked onto a catalyst on restart.
A typical outage scope
- Pre-outage walkdown and scope confirmation with the outage manager
- Tube bundle external cleaning, bay by bay, with documented before/after
- SCR catalyst face cleaning, layer by layer, with vacuum recovery
- CO catalyst cleaning where present
- AIG nozzle cleaning and flow verification support
- Duct burner and transition duct cleaning as scoped
- Daily turnover reports to the outage manager
Schedule reality
Inside an outage window every hour counts. Dry ice blasting crews work shifts (typically 12-hour rotations) and stage equipment to keep blasting continuous. We bring our own diesel compressors so we do not compete with the plant for utility air, and we mobilize with enough CO₂ and operator depth to keep the job moving even if a unit goes back online mid-window.
Outage planning
Most plants book HRSG cleaning 60–180 days in advance for major outages. We also support forced outages on short notice when capacity allows. Call (866) 648-0030 to lock a date or request a quote and include unit configuration, last cleaning date, and target outage window.
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