Benefits of VFD in water & waste-water treatment process
Variable frequency drives (frequency inverters, VFDs) are widely applied in water & waste-water treatment process.
Single speed drives start motors abruptly, subjecting the motor to high torque and current surges up to 10 times the full-load current. In contrast, variable frequency drives (frequency inverters, VFDs) offer a "soft start" capability, gradually ramping up a motor to operating speed. This lessens mechanical and electrical stress on the motor system. It can reduce maintenance and repair costs, will extend motor life.
Variable frequency drives (frequency inverters, VFDs, variable speed drives) allow more precise control of processes, such as water distribution, aeration and chemical feed. Pressure in water distribution systems can be maintained to closer tolerances. Waste-water treatment plants can consistently maintain desired dissolved oxygen concentrations over a wide range of flow and biological loading conditions by using automated controls to link dissolved oxygen sensors to variable frequency drives (frequency inverters, VFDs, variable speed drives) on the aeration blowers.
Energy savings from variable speed drives can be significant. Affinity laws for centrifugal pumps suggest that even a small reduction in motor speed will highly leverage the energy savings.
Variable speed drives (frequency inverters, VSDs, VFDs, variable frequency drives) can reduce a pump's energy consumption by as much as 50%. A variable frequency drive controlling a pump motor that usually runs less than full speed can substantially reduce energy consumption over a motor, which is running at constant speed for the same period.
For example, for a 25 horsepower (hp) motor running 23 hours per day (2 hours at 100% speed; 8 hours at 75%; 8 hours at 67%; and 5 hours at 50%), a variable speed drives can reduce energy use by 45%. At $0.15 per kilowatt hour, this saves $8,061 annually. Because this exact benefit varies depending on system variables, such as pump size, load profile, amount of static head, and friction, it is important to calculate benefits for each application before specifying a VFD.
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