160

Source: Ref. 10.

If the fouling is on the water side because of scale buildup, accumulation of mud or slime, or for some other reason, heat transfer will be impeded as described above, and increased stack temperature will result. The effect of this scaling is seen in Table 14.13. The detrimental effect can be severe.

As with excess oxygen, it is advisable to monitor stack temperature on an hourly basis and to record the readings. By graphing the readings, it is possible to determine how much variation is caused by shifting load, when given temperature indicates that something unusual has happened, and when a gradual temperature rise indicates that it is time to clean the water side or the fire side of the boiler. If soot blowers are being used, the stack temperature should drop immediately after the tubes are cleaned. If the temperature does not drop, the soot blowers may not be working or the thermometer may have become fouled—in any case, something is wrong.

Smoking or Excess CO

Excess CO, in the case of natural gas, or smoking for coal or oil fuels, gives an indication that something has changed. Changes in the fuel composition or wear in some component of the burner can cause these problems, or there may be a change in the air supply. In any case, the problem should be corrected immediately. A stack-gas analyzer can be used to monitor the percentage of CO on a continuous basis.

Flame Appearance

The appearance of the flame can give some valuable information. If the pattern is unusual, there may have been changes in the burner tips or in other parts of the burner, or there may be a malfunction in a related part of the boiler. Also, examining the flame pattern can show if part of the boiler is getting overheated. At the same time the flame is being examined, the inside of the boiler can be examined as far as possible to see that everything is in order—the stoker (if it is a coal-fired boiler), the refractory, the burners, and so on. The flame check is quick and should not replace the other inspections noted above, but it can provide additional information. Such a check should be performed every hour.

Record Keeping

The Environmental Protection Agency guidelines recommend that a log be kept on each boiler with the information shown in Table 14.14.9 In addition to recording this information, plotting it on a graph can give early indications of unusual trends or cycles in the data; these patterns can then be incorporated into the general system used to indicate when something is about to go wrong.

Maintenance Actions and Frequencies

Table 14.15 gives a list of the most common boiler maintenance actions that need to be performed annually. Table 14.16 gives a checklist of other routine maintenance items. If your staff is trained in boiler operation and maintenance this table can be used to help define a pattern of boiler maintenance. If you decide to hire boiler maintenance done by an outside firm, the table can help you to determine what they should do and to determine whether you would gain more from doing this work with your own personnel.

Ultimately, your own maintenance personnel will do much of the routine maintenance. To be sure they know what to expect and how to perform these tasks, have a boiler service representative or contractor train each person in the more routine kinds of boiler operation, such as reading a sight glass, inspecting the flame, and blowing down the boiler. In particular, they should learn enough about the boiler that they know how to operate it safely. Keep in mind that many maintenance people are undertrained as well as underpaid and that they are not familiar with procedures for handling live steam. Without proper training, they may also let sight glasses go dry, and they may miss such facts as that the low-water cutoff valve is not working. These maintenance people can be the most expensive ones you hire—if their lack of training causes you to lose a boiler.

Another note—the given maintenance intervals are averages. If your boiler uses a great deal of makeup water, more sludge can develop, and this will have to be removed by blowing down more often than indicated. If your boiler is a closed system with very few leaks, it is possible that water quality will not be a problem. In that case, the blowdowns can be much less frequent. You must adapt the procedures to your own boiler, preferably with the help of a local professional and the vendor.

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