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Dr. Sonal Desai
16th Sep 2021
Selecting a large pump and using a throttle is like pressing the brake and accelerator pedals simultaneously in a car, which we never do. Pumps being essential parts of industrial and commercial applications, most are selected oversized to meet variations in load as well as future load.
The major energy-saving part is associated with selecting the right pump and operating it on its best performance point.Pumping systems consume as much as 20% of the world’s total energy, and manufacturing industries use around 45% of the total electricity for pumping. Hence, they are the first targets for improving efficiency.
The Major energy-saving potential exists in impeller trimming, pump retrofits, use of correct-diameter pipes, and operation-hour optimization. Like other engineering equipment, energy-saving is possible right at the design and selection stage. However, if it is missed at the design stage, there are some other methods by which power consumption is reduced. Loss in efficiency in a pumping system is either due to oversized pumps or the use of throttle valves in most systems. The following section talks about energy saving pumps
Correct Sizing of Pumps -
Pumps are often oversized to meet a plant’s uncertainty of operation and future expansion. Uncertainty is also due to change in weather. Pumps are also oversized to meet gradual resistance build-up due to roughness and scaling.The problem with an oversized pump is that it will deliver a higher head/flow than the requirement and need constant throttling, resulting in energy waste. One or more of the following working conditions indicate oversizing of pump:
1. Excessive flow noise
2. Use of flow-throttle valve or bypass line
3. Frequent replacement of bearings, seals, and packing
The remedy of an oversized pump is to downsize the same, but it is not always possible and, hence, some other alternatives are suggested here:
1. Replace the impeller with a smaller one or trim the existing one.
2. Install an adjustable speed drive to control the flow. 3. Use an additional small pump to avoid the intermittent operation of the existing pump
Trim Impeller of an Oversized Pump-
If 10% or more flow is continuously throttled, it is advisable to trim the impeller. Some portion of the impeller is removed by machining and, thereby, energy consumption is reduced. The pump manufacturer provides the pump-performance curve for different impeller diameters and if these curves are not available, affinity laws can be applied to predict the performance after impeller trimming. Generally, oversized pumps and flow-throttled pumps are the right candidates for impeller trimming. Up to 25% of the original diameter can be trimmed to make it energy-efficient, ensuring that it is not smaller than the minimum diameter shown on the pump curve. It is to be noted that a trimmed impeller will reduce load on the motor and, hence, efficiency of the motor will change.
Keeping the Pump Clean and Well-Maintained
Dirt or other contaminations in the pump, filters, strainers, etc., reduces the efficiency of the pump and gradually increases load on the system. Timely inspection and proper maintenance will ensure pump remains working in clean conditions. Regular maintenance reduces losses and unscheduled downtime. The main cause of wear and corrosion is high concentrations of particulates and low pH values.Select Right-Size Motor for a Pump Usually, one large motor is selected to meet requirements, and this working condition never occurs. Thus, an oversized motor operates at a lower than optimum efficiency. When comparing actual power drawn and nameplate ratings, oversized motors are identified.
Dr. Sonal Desai