by John Kozel, Sims Pump Company
December 17, 2011

 

Composites significantly reduce energy consumption, maintenance costs and repair costs.

Today, tremendous effort is made to reduce energy consumption. The Department of Energy (DOE) and the Hydraulic Institute (HI) work together to reduce the energy consumption of pumps, motors and pump systems. This is where composites can be of great benefit. They can significantly reduce energy consumption—in some cases by 20 percent or more. 

Figure 1. A corroded impeller on the left and a composite impeller on the right

Corrosion, Cavitation & Erosion Resistant 

Corrosion, erosion, cavitation, rotor imbalance and leakage between the wear rings, casing rings and inter-stage bushings are major contributors to the loss of pump efficiency. Damage from corrosion, erosion, and cavitation quickly destroys the metallic pump and pump parts, which makes the pump inefficient and increases energy consumption.

As seen in Figure 2, energy costs dwarf any other expenses. Here, the acquisition cost is only 9 percent of the total life cycle cost of one pump. 

This is why the DOE, Europump, and the HI have focused on pump life cycle costs. 

Composite Wear Components and Surface Finish 

Wear between the rings and bushings create large clearances, which result in substantial decreases in pump efficiency as well as huge increases in the energy consumed to operate the pump.

Historically, most pump companies and repair facilities have used metallic parts for wear rings, casing rings, sleeves, bushings, and guide bearings. These metallic parts have the potential to gall and seize and, therefore, require larger clearances between the parts. Compounding the issue is that these metallic parts do not have self-lubricating qualities as many composites do. Also, metallic parts are subject to corrosion, which further increases clearances and energy consumption.

Thermoplastic and thermoset engineered composites have been used successfully to replace these metallic parts. In a structural composite the fibers are not chopped, cut or macerated. Thermoset structural composites have the mechanical strength of metal and have self-lubricating qualities embedded in the composite eliminating the risk for seizing and galling. Furthermore, these engineered composites have extremely smooth surfaces with an excellent surface finish and a low coefficient of friction on all surfaces. This low coefficient of friction increases efficiency and reduces energy consumption. Because they will not seize or gall like metallic rings, they run with tighter clearances, which adds to the increased efficiency and decreased energy consumption. 

Low Coefficient of Friction

As shown in Figure 3, most composites have a lower coefficient of friction than metallic materials—such as bronze or stainless steel—that have been traditionally used in pumps. Structural graphite composites and engineered composites have the lowest coefficient of friction, lubricated or non-lubricated. The low coefficient of friction reduces the friction losses of the liquid being pumped, which allows for an increase in efficiency and a reduction in energy consumption.

Composite coatings have been used to coat pump casings, which not only protects the casings against corrosion and erosion but also smooths the rough surfaces, reducing friction and increasing efficiency. Some studies have shown that efficiency can be improved by as much as 2 to 3 percent by using composite rings, guide bearings and coatings. 

Savings Potential

Since many composites are impervious to different corrosive environments, they will not corrode, or erode. Although composite wear components will reduce energy consumption for all pumps, including all fresh water services, the greatest savings occur in corrosive environments such as salt water, wastewater, chlorinated water and chemical processing because the composites, in many cases, will not corrode at all.

When metallic pump parts begin to wear from corrosion, pump efficiency drops drastically. The life cycle of the pump is often reduced to months instead of years.

Life Cycle Costs

According to the DOE, many centrifugal pumps may be less than 50 percent efficient but have the potential to improve by 20 to 30 percent through upgrades and system changes. Pump upgrades can improve performance, maintenance and repair issues and improve efficiency, pump life and reliability. Pump upgrades prevent expensive products from deteriorating. They can prevent pump leaks that can result in costly cleanups and fines from regulatory agencies. In most cases, reduced downtime outweighs all other benefits.

In difficult times, allocating the funds for the upgrades may be hard, but the payback is quick. The resulting savings frees up funds that otherwise would have been wasted on energy, and more expensive repairs at a later date. The incremental costs of upgrades are minimal when compared to the expense of downtime and repairs.

Plant outages, ship overhauls, building new vessels, building new manufacturing plants, plant expansions and new system installations are good opportunities to specify pumps with upgraded efficiency and reliability features such as structural graphite composite pump components (impellers, casing rings, sleeves, bushings, bearings and mechanical seals). 

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