Multistage blowers unable to meet required flow turndown
Challenge
The City of Vancouver treats approximately 25 million gallons of wastewater each day between its two wastewater treatment plants. The aeration systems are required to provide oxygen for the biological processes and mixing to keep solids suspended for more effective treatment.
In 2011, the Westside Water Reclamation Facility (WWRF) had five constant-speed multistage Hoffman blowers which made up the baseline of the plant’s aeration system. Several combinations of the blowers typically operated simultaneously to satisfy varying wastewater flows because multistage blowers themselves offered very little turndown. The combination of operating Hoffman blowers consisted of two 200 HP, and three 400 HP blowers. The WWRF began evaluating different options that would help it achieve a more flexible and energy efficient blower operation. Clark Public Utilities and the Bonneville Power Administration’s Energy Smart Industrial Program worked directly with the City of Vancouver to receive an energy incentive for a high efficiency turbo blower to replace some of its existing blowers. A Custom Project proposal was completed in February 2011, with the post implementation measurement and verification monitoring initiated the following month.
Solution
As a result of the incentive program, one APG-Neuros high efficiency 300 HP turbo blower with a variable frequency drive was installed. The new blower was optimally sized to independently satisfy air requirements of the plant for most of the year. Energy Smart Industrial calculated that the new turbo blower would consume 1,123,062 kWh/year compared to the baseline energy consumption of 1,834,548 kwh/yr. The savings achieved 39% reduction in energy consumption, with an astounding final payback of 0.8 years, when combined with available incentives for the customer. Based on the results, another blower was ordered to phase-out the remaining multi stage blowers that were used at peak demand and as stand-by.