headsUP: HRSGs

HRSG inspection and maintenance planning

Bill Kitterman, Bremco Inc

Kitterman talked about the problems some operators are experiencing from wear and tear on transition ducts. After heat-recovery steam generators operate for 10 years or so under today’s demanding service conditions—such as daily cycling and fast ramping—you can expect damage to the liner that allows insulation to be sucked downstream, he said.

Fouling of CO catalyst is one possible problem when insulation goes airborne. Insulation exposed to high heat over a long period deteriorates and the resulting powder is carried along with the exhaust gas stream, limiting catalyst effectiveness. In some severe cases, it might not be possible to meet the permitted CO emissions limit at full load and vacuuming of the catalyst face will be necessary.

Fouling of the SCR catalyst is another possibility. This can compromise NOx destruction and possibly cause over-feeding of ammonia. The latter could increase ammonia slip beyond permitted limits. Reducing power output might be a short-term fix, but eventually the catalyst will have to be cleaned.

Finally, any foreign material in the exhaust gas stream that gets by the catalyst beds is likely to contribute to plugging of the finned heat-transfer sections in the back end of the unit, thereby reducing efficiency.

To minimize the possibility of catalyst and finned-tube fouling, Kitterman suggested regular walk-downs of your HRSGs with a thermal imaging gun to identify hotspots. Followup internal inspections of the liner area should be conducted to determine the extent of damage and to plan the necessary maintenance.

One example of a liner repair effort is profiled in an article on Orlando Cogen, which is still current two years after it was written.

Posted in WTUI |

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