TL;DR
Fouled superheater tubes raise flue-gas exit temperature and reduce steam output. Confirm by comparing exit temperature trend to baseline, then schedule sootblowing or offline cleaning.
What you might see
- rising flue-gas exit temperature
- reduced steam temperature at turbine inlet
- increased fuel consumption for same load
- sootblower frequency increased with diminishing returns
Likely causes
Carryover of sodium and potassium salts from the furnace depositing on tube surfaces
Insufficient sootblowing frequency during high-solids firing periods
Reduced steam-side velocity from low-load operation allowing deposits to accumulate
Plugged sootblower nozzle reducing effectiveness of cleaning cycles
Required tools
- DCS historian access
- Sootblowing sequence log
- Pressure gauge for sootblower steam header
- Camera for deposit documentation
Safety first
- Sootblower steam lines are at high pressure and temperature. Verify steam traps are functioning before starting a sootblowing sequence.
- Offline water washing requires full boiler isolation and lockout before personnel enter the superheater gas path.
Procedure
- 1
Pull the last 30 days of flue-gas exit temperature trends from the DCS historian and confirm a rising baseline.
- 2
Check the sootblowing log. Count the number of sootblowing cycles per day and compare to the baseline frequency for this load level.[1]
- 3
Inspect the sootblower steam supply pressure at the header. Low supply pressure reduces cleaning reach.
- 4
Run a full sootblowing sequence and log the change in exit temperature before and after. A drop of less than 3 deg C suggests heavy fouling beyond sootblowing capacity.
- 5
If sootblowing is ineffective, schedule an offline water-wash cleaning at the next planned outage.
- 6
During the outage, open the superheater access ports and inspect tube surfaces for hard deposits or tube distortion.[1]
- 7
Document deposit thickness and appearance for the root-cause record before washing.
Sources
ANDRITZ ANDRITZ HERB Recovery Boiler general technical documentation, ANDRITZ
Recovery boiler superheater fouling and sootblowing guidelines, general industry practice (general)
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