Pump Up Energy Savings

Motors and pumping systems often offer ample opportunities

By Eric Huston, SKF

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Cutting energy use has never been more important for chemical companies. Reducing consumption not only helps cope with ever-increasing energy costs but also generally decreases carbon dioxide emissions and thus lowers environmental impact and improves sustainability of processes.

A comprehensive energy-reduction program should recognize that virtually every business decision has possible energy implications, and should involve measuring, managing and sustaining energy savings. Achieving maximum success demands an organized and dedicated program that incorporates five key principles:

1. commitment to a specific and quantifiable target;
2. full assessment of energy management status, tools and technology;
3. appointment and empowerment of "energy champions" with well-defined responsibility and accountability;
4. visible program execution across the organization; and
5. monitoring and tracking of results. (You can't manage what you don't measure.)

At the plant level, you usually can discover many potential energy savings. Motors and pumping systems, which represent major energy consumers at most sites, often present significant opportunities, as we'll discuss.

Pumping systems, fans, compressors and a wide range of other assets at plants rely on motors. Electricity accounts for as much as 98% of the cost of an electric motor over a 10-year service life. An analysis focused on a motor's cost per kWh to operate, driven load requirements, scheduled hours of use, and environmental factors influencing performance, coupled with process knowledge, can help uncover areas of potential energy savings.

Savings can come from steps as straightforward as turning off or putting a motor into standby mode when possible. Simply put, the motor using the least amount of energy is the one that is turned off. Sometimes a motor is operating needlessly, not providing work. For instance, agitators on empty vessels and pumps on full recirculation offer opportunities to idle motors without negatively impacting operations.

You can gain energy savings by reducing the driven load through operational and maintenance procedures. Misapplication and poor maintenance practices can rob motors of efficiency.

A common cause of lost efficiency is running a motor in an overloaded condition. The extra load results in increased motor temperature, which degrades the motor and lowers efficiency. Conversely, motors also will run at very low efficiencies if very lightly loaded. So, you should survey motor loads — actual versus full-rated — to confirm efficiency potential and expectations.

If you send failed motors to an outside shop for repair, carefully vet the shop and become familiar with procedures and practices that ultimately impact the efficiency of a repaired motor and the system in which it operates. If "best practices" aren't followed during the repair, the motor likely won't provide "as new" efficiency. Whether beneficial, consider buying a new motor, because many now boast higher efficiencies than few-years-old models.

Consider integrating a variable speed drive (VSD). It often can optimize energy efficiency by enabling you to match motor speed to the demands of the system. Look for opportunities, for example, to replace throttle valves or dampers used to restrict flow. However, a VSD may not make sense if the load on the motor is relatively small and constant — because speed changes will occur infrequently and any benefits from varying the speed will be negligible. So, thoroughly assess the system load profile to determine the scale and frequency of required speed changes before deciding about installing a VSD.

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