Rocky Mount's Oxygen Generation System

Innovative system design drastically cuts facility's energy bill

Winner of a 2014 Engineering Excellence Grand Award from American Council of Engineering Companies of North Carolina

The City of Rocky Mount owns and operates the 21 mgd Tar River Regional Water Reclamation Facility. It used a 50-ton-per-day cryogenic oxygen generation system for the aerobic zones of the biological nutrient removal. The cryogenic facility was nearing the end of its useful life and the operation and maintenance cost was excessive.
The plant flow averaged 10.5 mgd with an oxygen need of about 11 tons per day. Since there was no turndown capability, almost 80 percent of the pure oxygen generated was wasted at significant energy cost. We used a matrix to evaluate a number of alternative oxygen generation systems and select the optimum one.
By utilizing an innovative Vacuum Swing Adsorption system, the improvements reduced the $1,000-per-day energy bill to just $365 while significantly reducing operator time. Electricity use for oxygen generation has dropped by 65% with a system customized for today and the 20-year projected needs. And operators now control the system through a graphical display with real-time data and on/off operation with the touch of a button.
We helped the City secure and administer half a million dollars in ARRA funding from the NC Energy office and the NC DENR provided a 20-year,  $2.34 million, interest-free loan.