By Michelle Jackson, Marketi ng Manager, Castle Pumps Ltd.
- Avoid oversizing Oversizing the pump during specification is common to cater for any uncertainties in the design process. However, as achieving higher performance, in terms of flow and pressure, requires the motor to run at a higher power, an oversized pump uses more energy than necessary. For that reason, a pump should be selected that can be run as close to its Best Efficiency Point (BEP) as possible.
- Impeller trimming If a pump has been oversized, then sometimes a throttling valve is used to achieve the lower duty requirements. This process is not the best course of action however, as it is not as energy efficient as trimming the impeller. Trimming the impeller is a relatively cost-effective way of reducing the pressure and _ ow that is produced. As the casing clearance becomes larger when the impeller is shaved, impeller trimming is also not the most energy efficient solution. For that reason, variable frequency drives (VFDs) are often selected for peak efficiency.
- VFDs The purpose of a variable frequency drive is to vary the speed of a motor to achieve the actual performance requirements of the application, as opposed to the maximum that the pump can provide. This provides operators with the chance to reduce energy waste caused by the pump in two ways. Firstly, it can slow down the motor on an oversized pump and secondly, it can control a pump in situations where there are differing duty requirements at different times; i.e. sometimes the pump is required to operate at full speed and others it is not. An example of this is a cooling pump, where the temperature of the component that needs to be cooled may vary considerably.
4.Parallel pumping systems Another energy efficient solution for a pump installation that has varying performance requirements is the use of parallel pumping systems. When the occasional duty requirements of a system are significantly higher than the standard operating conditions, a single pump could be forced to operate way off from its BEP. By installing a second, smaller pump with lower power to meet the average system requirements, the larger, higher energy consuming pump would only need to be used when the system warrants it.
5. Limit pipework pressure loss To determine the required power of a pump, the pressure loss in the system needs to be taken into account. As the length, diameter, layout, and internals of pipework all affect the pressure loss in a system, consideration should be given to the piping system layout. To increase the efficiency of a piping system, bends and changes in the size of the pipework should be kept to a minimum, and the diameter should be carefully selected, as smaller pipework results in more friction. Corrosion and rust can also increase resistance resulting in pressure loss, which means cleaning and maintenance of pipework is important too.
6. Prevent unnecessary use It might surprise you how often pumps are in operation when they are not actually doing anything, due to lack of control. Control systems can be implemented to control and shut down pumps not in use. Using pressure switches, the number of pumps in service can be automatically adjusted as duty requirements vary.
7.Maintenance Like any equipment, wear on a pump can reduce its efficiency. A pump’s energy efficiency can degrade as much as 10-25% before it is replaced, which is why routine maintenance is vital. It is important to replace wearing parts such as wear rings, as leakages mean that the power requirements to produce the same f low is increased.
Closing Remarks
If an operator is concerned about a plant’s energy efficiency and is looking for ways to reduce it, a good place to start is with the facility’s pumps. These seven tips can help reduce unnecessary energy consumption. It is important to note that despite consistent maintenance and diligent monitoring, eventually the most energy efficient option will be to replace the pump!
About the Author
Michelle Jackson has worked within the fluid handling industry for the last decade, with almost 8 years specifically in pumps. As Marketing Manager as Castle Pumps Ltd, she works to the premise that whilst many pumps can do the job, it takes the right pump to truly deliver a process.