Large boilers, for sizable buildings in northern latitudes, require a much more extensive level of maintenance than small utility boilers that almost every facility has, be it in a warm or cold climate. A few of the chief maintenance items are delineated here.
1. Scale is the operating boilers’ nemesis. It reduces the efficiency of the system and can even lead to overheating of the furnace, embrittlement, and cracking of tubes and flashing of the fluid within, and many other problems. The rear of the boiler is most susceptible to the formation of scale, so it should be inspected often.
2. The fireside of the furnace has its own problems. The tubes should be inspected for soot deposits, ash, and slag. These carbon-based deposits reduce the heat-transfer properties of the metal tubes by forming an insulating layer; this lowers the overall efficiency of the system. A thermometer installed in the vent outlet will give external evidence of these buildups and signal when a visual inspection of the tubes and refractory is needed.
3. Replace door gaskets if they’re not sealing well. A daily log of pressure, temperature, and all other data from installed instrumentation will signal when it’s time to clean tubes or nozzles and adjust linkages and pressure seals. Problems on oil-fired units that can be diagnosed from the instrumentation readings include a plugged strainer, a faulty regulating valve, or an air leak in the suction line.
4. Note the firing rate at the time the log entries are made. Keep in mind that when the load on the boiler changes, there can result in stack-temperature changes of up to 100°F. So a jump in stack temperature does not always mean poor combustion.
5. Stacks should be free of haze, which is an indication that the burners need adjustment.
6. Linkages should be tight and should not be jerky or have any slippage.
7. The fire should shut down as soon as the unit stops; a faulty solenoid valve could be the problem if this does not occur.
8. Inspect and clean the nozzles regularly.
9. The burner firing period is modulated by the controls. Flawed controls can cause improper firing times.
10. The stack temperature should not be more than 150°F above the steam or water temperature.
11. Dirty tubes and an out-of-adjustment fuel burner are the likely culprits.
12. Perform a flue-gas analysis regularly, to be sure the oxygen, carbon dioxide, and carbon monoxide are within acceptable limits.
13. This, in turn, will cause soot and carbon buildup on the tubes, and diminished heat-transfer capability. If too much air is delivered to the burners, then excess air is heated and discharged up the stack. This is wasted heat energy and reduces the overall efficiency of the system.
14. Look for hot spots in the boiler insulation, refractory, brickwork, and boiler casing. These give evidence of unnecessary thermal losses.
15. Clean mineral and corrosion buildup off the gas burners.
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Excerpt from Energy Conservation Projects.