Figure 1 depicts a typical pumping system. The energy efficiency of the system declines over time due to factors such as the characteristics of the fluid being pumped, cavitation and scaling. Figure 2 shows representative energy losses for various elements of the system. By some estimates, you can improve the energy efficiency of a typical system by up to 20% by taking appropriate steps.
Misalignment, imprecise balancing, hydraulics problems, inefficient bearings, and improper lubrication or sealing will lower efficiency. So, analyze your system and then take called-for corrective measures.
Check where the pump operates on its system curve. However, don't assume that running at the best efficiency point (BEP) is enough to optimize system efficiency. If a control valve always is less than 50% open or a recirculation valve never is more than 50% closed, you are wasting energy.
Look for some telltale signs of likely wasted energy:
• The pump usually doesn't operate at (or close to) its BEP during its normal duty cycle.
• The control valve constantly remains at less than 80% open.
• The recirculation line valve always is open.
• Multiple parallel (redundant) pumps in the same system all are operating continuously.
• The pump operates continuously in a batch system.
• The pump (or another component in the system) exhibits excessive noise or vibration.
You generally can improve the efficiency of a pumping system by matching capacity to actual demand. Unnecessary energy demand will occur when flow is higher than required or when a control valve or another piping component absorbs a high proportion of energy. Many pumps don't operate close to their BEP, especially when they are oversized for the job. Matching pump capacity with actual production needs can deliver significant energy savings.
To reduce energy demand to match process or production needs, take these actions:
• Switch off the system when not needed.
• Eliminate any system leaks.
• Reduce recirculation or bypass flow by trimming the pump impeller.
• Minimize head losses from the pump to the system outlet.
• Install parallel pumps for highly variable loads.
• Replace a throttling valve or recirculation loop with a VSD.
You can achieve other benefits by conducting a full system analysis. This requires a thorough understanding of the duty cycle of the pump and how flow changes with time or production patterns. Operators can contribute from the front lines by supplying information, which can augment data provided by instrumentation and chronicled in an operating log.
Ensuring that machinery is operating properly can play a vital role in improving energy efficiency (as well as system performance and reliability). This requires effective condition monitoring. It involves regularly and non-invasively measuring physical parameters, such as vibration, noise, lubricant properties and temperature, to help ascertain equipment health. Such monitoring enables detecting machine and component problems before they can result in unscheduled downtime and the high costs associated with interruptions in production.
For example, periodic monitoring of heat loss can yield significant dividends. Inspections using a thermal imaging camera can pinpoint, e.g., gaps or deterioration in insulation and poor electrical contacts.
Other condition-monitoring tools that can help identify energy efficiency opportunities include ultrasonic probes (for leak identification, steam trap inspections and flow turbulence), infrared thermometers (for motor, heat exchanger and steam trap inspections, and bearing temperatures), and strobe lights (for operating speed verification, and belt and gear inspections). There are many others, too. Indeed, you can take advantage of a wide range of portable and online condition-monitoring tools to spur energy savings (see: "Bolster Your Condition Monitoring Toolbox").
No single technology, of course, can provide all the data needed to detect all energy-improvement opportunities. So, it's best to consider which assets or processes within the plant represent logical targets for monitoring energy consumption and then to apply the appropriate technologies for the job.
In some cases, outside expertise may help in identifying and examining areas where energy-improvement opportunities may exist. The SKF Client Needs Analysis — Energy and Sustainability is an example of one such available resource. This extensive web-enabled plantwide assessment tool also can evaluate potential improvements to chemical treatments, lubrication use, and other operating processes to reduce environmental impact and promote sustainability.
ERIC HUSTON, CMRP, is San Diego-based vice president, asset and energy management, of the Service Division of SKF USA. E-mail him at Eric.Huston@skf.com.