Variable-frequency drives (VFDs) have been used for decades to control multistage centrifugal blowers. The increasingly popular turbo blowers also use VFDs for flow control and energy optimization.VFDs have not been applied to geared, single-stage centrifugal blowers — economic rather than technical obstacles have limited such applications to smaller blowers. Recently, however, the staff at the Lemay Wastewater Treatment Plant in St. Louis has shown that changing economics can enable a cost-effective, energy-efficient application of VFDs to large blowers.BackgroundTwo types of single-stage centrifugal blowers are commonly used in wastewater aeration. They include large blowers that use a conventional AC motor and
