Reduces annual energy costs and improves process control of the wastewater treatment for better nitrogen removal
Killingly WWTP replaced its multi-stage centrifugal and positive displacement blowers with APG-Neuros turbo blowers. The high efficiency blowers and improvements in the aeration control and modifications in the SCADA for improved DO control reduce the plant’s annual energy costs.
Project Background
In 2013, the wastewater activated sludge aeration system was consuming about 38% of the total electricity at the Killingly WWTP. After studying the energy consumption, operation flexibility and controls of the existing blowers versus various newer technology blowers, it was concluded that replacing the existing units with APG-Neuros turbo blowers would reduce the energy usage. The existing blowers operated at a constant speed and used an inlet throttling valve with some limited control functions. The blowers have been in service since 2001, so there has been some loss of efficiency compared to the original design, resulting in decreased airflow/oxygen control in the aeration basin. The entire project was undertaken by United Water (Suez Environment), originally developed by Nxegen, LLC of Middletown, CT, as a result of delays in having the project authorized initially. In addition to the blower replacement, the aeration system was upgraded as well, including piping, valves, ammonia sensing equipment and controls.
Challenge
The goal was to reduce the annual energy costs by upgrading the entire aeration system, including matching airflow to oxygen demand which would result in overall lower energy use. The plant had two constant speed multi-stage centrifugal blowers and one positive displacement blower with a VFD. One multistage blower ran 24/7, delivering a maximum of 3,800 CFM throughout the year. The positive displacement blower operated for 1,800 hours for 12 months, was manually controlled, and generally ran between 65 and 95 percent speed. The existing multistage centrifugal blowers were six stage blowers and had a maximum of 3,800 ICFM at a discharge pressure of 8.00 PSIG, consuming 167 BHP. These blowers were constant type and used an inlet throttling valve which limited operator’s ability to control the blowers and adjust the airflow to the required DO and influent wastewater quality (ammonia levels).
Solution
After an extensive study phase, the WWTP moved forward with the project in 2013. It was eligible for a substantial incentive from the Connecticut Light & Power’s Energy Opportunity Program (CL&P) of $179,872. The final implementation cost for this project was $736,000 which included engineering work, blowers, installation, SCADA, automated valves, piping, DO and ammonia sensors, diffusers, and membranes. APG-Neuros was selected as the equipment manufacturer who supplied two NX150-C060 turbo blowers for $281,000. The turbo blowers provide better load matching due to their smaller size. Their wide turndown range gives the plant operational flexibility that was not previously possible; the ability to control the blowers’ airflow in combination with the newly improved DO sensors depending on the DO levels in the aeration tanks. In addition, the blower control based on influent wastewater quality using the recently completed ammonia sensor feedback loop will result in less airflow needed to satisfy system requirements and contribute to the overall aeration system efficiency and cost savings. Thanks to the APG-Neuros blowers’ energy efficiency and a more closely matched airflow to DO demand as well as the new sensors and improved process control, the energy consumption went down by almost 400,000 kwh in 2014, reducing energy bills by over $30,000. The energy consumption savings are on track this year to exceed the previous annual savings.
