Heating and cooling are common processes in food processing, each of which either directly or indirectly produces large quantities of heat. If not managed properly, the excess heat may damage equipment and or the product through overheating. It is, therefore, essential to have a reliable cooling system that can extract heat sufficiently with minimal maintenance.
The cooling system usually features cooling towers that house large fan blades. To power the fan, it is now possible for a high-efficiency permanent magnet direct-drive motor to be coupled directly to the fan. A variable speed drive (VSD) controls the speed of the high-torque, direct-drive motor for optimal fan operation. A major advantage of this method of speed control is its inherent adjustability. For example, in extreme cold weather conditions, tower icing can be averted by running the fan at a slower than normal speed or back-running the fan at a slow backwards speed, raising the tower and process water temperatures.
Excellent Energy Efficiency
The direct-drive design offers excellent energy efficiency. This is because the motor is run at the speed required by the fan, typically a few hundred rpm. Just a small change in the speed of a motor can result in a very significant change in the energy it uses as the energy usage varies with the cube of the speed. For example, a 20 percent reduction in fan speed results in a nearly 50 percent reduction in energy consumption. This offers the potential for large savings in energy cost with a resulting fast return on investment.
A further advantage of the VSD, as already mentioned, is that it provides precise speed control. Rather than running at full speed when it doesn’t need to, the motor is controlled to match the actual process demand.
The adjustable speed control on the drive also allows for a soft start, with a controlled ramp up to full speed. The soft start means there’s no large starting current draw, which puts less electrical and mechanical strain on the system.
Direct-drive motors are very reliable over a long service life, which is an important factor when considering the Total Cost of Ownership (TCO). Another benefit is that the motors are quick and cheap to install due to the overall simplicity of the direct drive design.
The Direct Drive Solution in Action
A typical installation has been carried out a large food production plant, where a direct-drive solution was fitted to one of the five fans of the cooling tower. This allowed the energy consumption to be monitored over five years. At the end of this period, the speed-controlled 16 kilowatt (kW) direct drive motor saved a substantial $38,855 per annum.
Direct-drive motor technology is now making it possible to achieve the ideal combination of performance, reliability and efficiency for cooling towers. The field-proven high performance of a permanent magnet direct drive motor operated by a variable speed drive (VSD) can lead to major savings. It also creates a reliable platform for continuity of production that can help drive business growth. The realization of these benefits offers an optimized TCO and improved plant reliability.
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