Variable Speed Drives

A VSD fitted  to the forced draught (FD) motor on a burner will compliment the digital combustion control system and produce further savings. Depending on the modulating characteristics of a burner there are considerable power savings to be made. These savings are maximised on lower fire settings and deteriorate as the burner modulates to a high fire. As the burner modulates past half fire, the savings gradually disappear. A typical 'old technology' burner will have a fixed speed FD motor with the modulating air flow controlled by mechanical dampers.

When a VSD is fitted to the FD motor, the dampers are removed with the fan speed controlling the amount of air required for the combustion setting. More savings are possible because the digital combustion control system combined with a VSD enables the turndown of the burner to increase from typically 4-1 for a mechanical system to 8-1 with an electronically controlled system including VSD. This means that the burner will continue to fire on extremely low fire settings and reduce the need for the burner to keep constantly stopping and starting during periods of low steam consumption, which will consume more energy as well as cool the boiler down through periods of pre and post purge during the start up cycle.

Power savings can be 50% resulting from a 20% turndown from VSD to FD fan motor. Further savings of 6% can be made on fuel.