The primary aims of a management and safety system are:

• A safe startup and shutdown of the burners

• A safe operation of all the burners in the boiler

Burner management and safety are handled by the electronics and software portions of the burners. The complexity of the logic is directly proportional to the variables of the system, such as the

• Number of burners

• Variety of fuels

• Combination of firing equipment

• Operational flexibility desired

• Local or remote-mounted BMS panel

• Extent of manual intervention

Most mishaps take place while starting and, to a lesser down the burners. NFPA, which has performed elaborate guidelines and has elaborated the procedures to be followed for single — and multi — ple-burner installations covering all the above-mentioned conditions. The guidelines refer to

1. Oil or gas burning

2. Oil and gas burning

3. Multiple-fuel combinations

4. Single or multiple burners

And are followed rigorously in the industry. As the variables increase, the logic becomes more involved.

Starting. For starting a burner, permissives and sequence are broadly indicated as follows:

• A burner can be lighted only with its own igniter.

• The igniter cannot be started unless the furnace purging is complete.

• The purging can be initiated only after a satisfactory report on the seven main boiler conditions, namely,

O Water level in the drum o Oil pressure o Oil temperature o Atomizing steam pressure o Atomizing steam temperature o FD fan

O Igniter conditions

Purge. On finding these conditions proper, it is now possible to start the FD fan. The first step is to carry out a purge of the boiler setting

• At a low airflow of —25% of normal full-load air

• For —20 min (to give five changes of volume)

• To prevent the inclusion of any traces of combustibles

Accumulation of the combustibles during operation, either at low loads or at some quies­cent pockets in the boiler, which can ignite on receiving copious amount of air under favor­able conditions, is identified as the most common cause for major and minor explosions. Carrying out a purge is the prerequisite for further steps in lighting the boiler.

Light up follows the purge.

• After the purge is completed, the igniter can provide a spark or flame. Only then the fuel can be turned on.

• Within a set time, the main flame should be visible or the whole sequence must be repeated.

In an operating boiler, all the above-mentioned conditions and flame health are to be monitored at all times. Any deviation of the main parameters beyond the limits should result in the tripping of either the burner or the boiler, depending on the cause.

A sound BMS needs (1) reliable flame monitors, (2) a good logic system, and (3) robust hardware.

Burner management and safety systems can range from simple to very elaborate for the same boiler, depending on the customer’s operating practices and the capabilities of the O&M staff (Figure 10.33).