Bringing Bytes to Your Boilers

Do your boiler plant controls need an IQ injection? New electronic control systems can help you stay on the information highway.

Modern electronic controls offer the central plant more power than ever before to control the big job steam boilers found in a campus central plant. These boilers, typically in the 40,000 lb/hr to 100,000 lb/hr range, are critical to the mission of the enterprise. Unfortunately, many of these big boilers are suffering from a lack of reliability due to the obsolescence of old pneumatic or electric controls. The time has come to learn how to bring modern electronics to bear on the reliability issue, and reduce energy bills at the same time.

Today's boiler plant is equipped with electronic (digital or analog) controls for each boiler to control flame monitoring, fuel and air valves, and startup and shutdown sequences. Further, the plant is equipped with a separate microprocessor, the plant master, which coordinates all boilers and equipment while recording data and providing a communications link. The modern plant master controller may be a proprietary combination of hardware and software specially designed for boilers or it may be a general-purpose industrial controller programmed for the needs of the plant.
Individual boilers have always had safety circuits to monitor the presence of the combustion flame and ensure that the fuel supply is completely shut off in the event of a flame failure. Redundant automatic valves in the gas supply piping or fuel train (Figure 1) shut off the fuel supply in the event of a boiler trip. Without such a system, the boiler could fill with combustible fuel and present the danger of explosion when the burner is restarted. Most boiler safety controls use a photoelectric sensor to confirm the presence of a stable, efficiently burning flame. If this flame is lost or becomes unstable for any reason, the fuel is shut off and an alarm is sounded.