Optimize Centrifugal Pump System Efficiency

Take steps to reduce energy consumption, lower maintenance costs and improve process control

By Robert Lax, ITT PRO Services, and Mike Pemberton, ITT Goulds Pumps/Plant Performance Services

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Most chemical plants are working to become more energy efficient. Companies are implementing energy management software, installing occupancy sensors throughout plants to help lower electricity bills, and even changing times of operation to use less power at peak load to avoid the associated higher rates. One of the best ways to save energy is to focus on motor-driven pumps.

Pumps consume more energy in chemical plants than any other category or type of rotating equipment. The average annual spending on pump maintenance and operations is approximately 50% greater than that of any other rotating machine, according to a recent study by the FiveTwelve Group. Companies that operate large numbers of pumps usually recognize the high energy costs as well as the impact pumps have on reliability and process control. However, too many organizations focus on these factors separately when, in fact, they are closely linked.

A recent report on the use of motor efficiency technologies by the U.S. Department of Energy’s Industrial Technologies Program (ITP) contained an in-depth analysis of energy use and savings potential by market segment and industry. The report identified centrifugal pumps as the largest consumers of motor energy (Figure 1). Also, among all rotating assets in the plant, process pumps had the highest overall potential for electrical energy savings.

A separate Finnish Research Center study of centrifugal pump performance found that the average pumping efficiency was less than 40% for the 1,690 pumps reviewed in 20 different plants across all market segments. That study also revealed that 10% of the pumps were operating at less than 10% hydraulic efficiency. Considering this sizable efficiency loss, you can expect that from 10% to 20% of the pumps in any continuous process plant are candidates for optimization. More than likely, the real number is much higher.

In the largest continuously operating process plants, opportunities for cost reduction—when all aspects of the system are considered —can easily represent millions of dollars and, thus, significantly impact the bottom line.

Efforts to improve reliability and achieve optimization of pumping systems invariably involve addressing what is called the “energy and reliability nexus.” In general, mechanical energy in excess of that required for moving process fluid through the pipes is manifested as vibration, heat and noise. This excess energy becomes a destructive force that undermines pump and process reliability.

As a result, pump systems routinely have the highest overall maintenance cost compared to other motor systems, including control valves, instrumentation and other types of process control equipment. In addition, pumps and valves are the primary process leak paths for fugitive emissions.

Today, companies increasingly are relying on lifecycle costing (LCC) for selecting an optimal solution to create economic and environmental value over the life of a system. Using a lifecycle-cost perspective during initial system design will minimize operating costs and maximize reliability. For pump systems, using LCC makes particular sense because the initial purchase price typically represents only about 10% of long-term costs (Figure 2).

A LCC analysis assesses the cost of purchasing, installing, operating, maintaining and disposing all the system’s components. Determining the LCC of a system involves using a methodology to identify and quantify all the components of the LCC equation. For instance, the equation provided in the Hydraulic Institute’s “Pump Life Cycle Costs: A Guide to LCC Analysis for Pumping Systems” includes terms for initial cost or purchase price (e.g., the pump, pipe, auxiliary equipment); installation and commissioning costs (including training); energy costs (predicted for entire system, including controls); operating costs (labor man-hours for normal system supervision); maintenance costs (e.g., parts, tools, labor man-hours); downtime costs (loss of production); environmental costs (leakage losses and permit violations); and decommissioning costs (disassembly and disposal).

Energy consumption is a major element in pump lifecycle costs. Because excess energy consumption leads to higher maintenance costs, these two elements combined typically dominate total lifecycle cost. Thus, it’s important to determine the current cost of energy and the expected annual escalation in energy prices over the system’s projected life, along with labor and material costs for maintenance.

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