Cities of Greenville and Bushnell
The City of Greenville is a rural community in Bond County with approximately 7,000 residents. It operates a water treatment plant north of the city on Governor Bond Lake and a waste treatment facility south of the city.
The City of Bushnell is a small community in McDonough County with approximately 3,200 residents. It operates a water treatment plant within the city, which draws from the St. Peters aquifer, and two wastewater treatment lagoons.
Illinois Electric Works (IEW) of Granite City agreed to partner with Illinois Sustainable Technology Center (ISTC) to provide technical assistance in identifying energy-saving opportunities at the participating municipalities treatment facilities. IEWs core competencies are blower, pump and motor efficiency, with specialization in motor controls, variable frequency drives, and load balancers.
Water treatment facilities incorporate a variety of techniques when processing drinking water. No matter what individual techniques they use, all processes involve a series of pumps and motors to move water from a source (lake, stream, aquifer), through the treatment facility, into storage vessels to the public distribution system. Wastewater treatment facilities also use motors, pumps and fans to move the wastewater from the community to the facility, and to process and treat the wastewater once it enters the facility. These pumps, blowers, and motors require substantial amounts of energy, which makes them expensive to operate.
A Variable Frequency Drive (VFD), also known as an Adjustable Speed Drive (ASD), is a system that controls the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor. VFDs enhance process control and provide energy savings by matching motor speed with load requirements. Pump, fan and blower applications at water and wastewater facilities are excellent candidates for retrofits because VFDs match motor speeds to fluctuating loads at these facilities, which is more economical than running motors at a constant speed.
Load balancers are controls that take advantage of a VFDs ability to control motor torque. Instead of only controlling speed, the load balancer forces the pumps or blowers to spin at the speed that produces the proper load. When tied into a common header, the pumps work evenly share the work. This operating efficiency also optimizes energy use and saves money. Load balancers are a sensible complement to VFDs because they offer up to 30% energy savings if the pumps are in good working order. The energy savings is even greater if the pumps are worm or operating at less than peak efficiency.
In the city of Greenville, the greatest opportunity for energy savings involved the installation of a VFD on a 60 HP lake recirculation pump that runs 24/7 at the water treatment plant. This installation will save approximately $9800 per year, with a projected payback to be 0.9 years. The wastewater treatment facility treats wastewater with activated sludge and 280HP disc aeration running at either idle or full speed. By retrofitting the aeration disc motors with VFDs coupled with a load balancer, facilities can save energy through efficient load sharing and matching aerator motor speed to the systems dynamic dissolved oxygen load requirements. This retrofit is projected to have annual savings of $28,375 with a payback period of about 1.5 years.
In the city of Bushnell, similar solutions were suggested to provide significant energy savings. The water treatment facility draws its water from three deep wells and is processed by reverse osmosis (RO). The well pumps range from 20HP to 65HP, running either independently or in pairs for 16 hours each day. Two high service pumps (25HP each) transport water to the water tower and run individually 10 hours each day. Installation of VFDs on the high service water pumps is projected to save $2400 annually, with a payback period of 3.8 years, while the installation of the VFD and a load balancer on the well pumps would produce an annual savings of $8300 with a payback period of 2.5 years. Another solution that the water treatment facility could employ would be to upgrade the Reverse Osmosis System Motor, which would save about $256 per year with a payback period of 2 years. At the wastewater facility, aeration is provided to the two lagoons by three 15HP (east) and three 20HP (west) positive displacement compressors, with one or more running continuously 24/7 regardless of dissolved oxygen levels. Adding simple timers to the aeration blowers would reduce the run time by about 20%, saving $3000 each year, with a payback period of 0.3 years.
Details of Reductions
Additional Information :
Water treatment facility applications:
" Well pumps, intake pumps, high service pumps and booster pumps
Wastewater treatment facility applications:" Lift station pumps, influent station pumps, aeration blowers, sludge return pumps and effluent pumps
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