Proof Positive

A side-by-side test documents energy savingsfrom a hybrid rotary lobe compressor at a treatment plant in New York
Proof Positive

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An upgrade in 2008 reduced the nitrogen discharge of the Town of Huntington (N.Y.) Wastewater Treatment Plant by 90 percent and met state-mandated 2014 water-quality standards, but plant personnel were troubled by the energy consumed by three 125 hp blowers powering aerators with variable-frequency drives in the two 1.5-million-gallon sequencing batch reactors.

The plant found a solution in hybrid rotary lobe compressors, which proved its energy-saving potential in a side-by-side test with one of the older blowers.

 

Checking alternatives

When the original blowers went online, the plant’s electric bill rose from $205,000 per year to $500,000, an increase not anticipated by town officials. Under the direction of town supervisor Frank Petrone, John Pavlik, plant supervisor, looked at various blower manufacturer proposals.

Aerzen USA suggested a pilot project that would make Huntington the country’s first facility to install a Delta Hybrid rotary lobe compressor, made in Germany by Aerzener Maschinenfabrik GmbH.

Side-by-side comparison testing revealed that the hybrid blower used far less energy than the original blowers. Based on the test, the projected annual savings, including maintenance and labor, was $79,320 with a two-year payback. Huntington officials were encouraged enough by the results to seek funding to install Delta Hybrid units on the two batch reactors.

 

Baseline establishment

Pavlik designed the comparison test and served as the technical field consultant. For two months before the compressor arrived, Huntington operators collected data to establish a baseline. They installed E-Mon D-Mon Class 5000 Advanced series demand meters on two of the original blowers and took readings four times per day. “My staff did an excellent job monitoring the systems,” says Pavlik.

Once the hybrid came online last November, operators disconnected the meter from an existing blower and connected it to the hybrid for comparison with the meter on another existing blower. After equal flow rates between the blower and the hybrid were verified, the trial began.

Four times per day, staff took readings and checked blower temperatures and pressures. “For the first few days, we questioned if we were monitoring the meters correctly because the numbers shocked us,” says Pavlik. “They showed a 28 to 29 percent kW reduction, a 30 percent peak demand reduction, and a 45-degree temperature difference between the two units.” The trend continued throughout the trial, and performance improvement increased at higher ambient temperatures.

“Replacing the three original blowers will save us $56,000 to $58,000 in electricity per year, not including labor and materials,” Pavlik says.

 

How they work

The belt-driven Delta Hybrid unit combines the packaging principles of Aerzen rotary lobe blowers with screw compressor technologies for volume flows of 400 to 2,000 cfm. The model at Huntington uses the internal compression of a screw compressor to increase compression efficiency.

Low-pressure (3 to 5 psi) units use a 3+3 twisted rotor (supercharger) profile, while a 3+4 compressor rotor profile is used for higher pressures (up to 22 psi). The compressor is matched to the required pressure range for optimum efficiency.

“Every 1 percent excess in volume flow corresponds to a 1 percent increase in energy consumption,” says Pavlik.

Maintenance, including the setting of belt tension, is minimal. “The hybrid unit has a pivoting mount that allows some of the motor’s weight to actuate the tensioning device and set it automatically,” says Pavlik.

The hybrid unit needs few adjustments, but when they are necessary, the case has ample space for technician access. “And while every other piece of equipment in the plant requires an oil change at 400 hours or less, the hybrid is good for two years,” says Pavlik. “That reduces the cost factor dramatically.”

 

Sensitivity training

Simultaneously, Aerzen engineers tested iAir Remote, a standalone remote monitoring system that does not need integration with SCADA systems. The unit on the hybrid monitored blower output, inlet and discharge temperature and pressure, vibration, speed, and oil temperature in real time. It downloaded the data every 30 seconds via cell phone uplink, and will eventually send emails should maintenance or other interventions be necessary.

Personnel from sister plants and other sewerage districts, engineering firms, and county regulators with their engineers have visited Huntington. “Everyone has been impressed with the data,” says Pavlik. “Very rarely can a plant run equipment in a comparison test and prove how it works. It was an honor to have this opportunity.”



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