Centrifugal Pump Saves Sand Mine More than $1.5 Million

For more than 100 years, Wisconsin sand has been prized for industrial applications—including metal casting, construction and consumer products such as iPods. Now, the sand has found new applications in hydraulic fracturing, or fracking. During fracking, pumps open up deep rock formations using a high-pressure mixture of solutions such as sand and water. The sand opens the rock, releasing oil and gas deposits for extraction. White Wisconsin sand works well in hydraulic fracturing applications. The large grains and round shape better open fissures, allowing more successful extraction of fossil fuels.

In 2015, energy companies will use more than 2.6 million tons of sand in exploration & production (E&P) activities. Demand for sand has increased more than 40 percent since 2011.

Challenges

A remote Wisconsin sand mine experienced pump deterioration from the abrasive sand. Because of the harsh Midwest winters, the mine only operates from April 1 to Thanksgiving. During operating season, the plant is scheduled to run 24 hours per day to maximize production. Initially, the plant used vertical turbines on the wet side of the process, where the sand was washed, scrubbed of impurities and sized. The wash removes metals and small particles of silica. Afterward, the sand moves to the dry side, where it dehydrates in specific storage areas based on its composition. The sand is inspected and tested after drying. Rail cars transport the sand to frac sites for mixing and injection. The process water is recycled, reducing the plant's costs and water needs. While the process removes the large particles for sale, the fine particles remain suspended in the recycled water. Over time, this microscopic slurry attacks the bronze-fitted vertical turbine. Particle accumulation around the seal leads to failures, and the residue eventually reduces pump flow. The grit forces openings in the rubber bushings, allowing water to escape. Eventually, the turbine shuts down, ceasing all operations. Because of constant operation, the turbines failed frequently as fine particles accumulated quickly. The sand mine incurred major expenses from repairs and lost productivity.

Patented Solutions

A pump distributor working with the plant operator offered a centrifugal pump with a specialized mechanical sealing system, slurry-resistant construction material and superior solids-handling capability. Unlike the seals in the vertical turbine, the pump's mechanical sealing system uses vanes cast into the impeller to wash away fine particles behind the impeller. Specially angled deflector vanes on the dished backplate create a cyclonic action, which pulls in the particles. The mechanical seal system provides greater reliability without the need for flush water or additional gauging systems. The pump has 10-inch suction and 8-inch discharge and features a cast-iron impeller and volute. More resilient than the bronze fittings on the turbine, the cast iron helps the pump better withstand the silica slurry. The pumps also include a 416 stainless shaft and sleeve as well as deep groove bearings rated for at least 50,000 hours. The unit can handle heads up to 360 feet, flow rates up to 8,000 gallons per minute and solids up to 3.38 inches in diameter.

Additional Features

The pump also features a dry-priming system with a vacuum assist. If the pump loses prime, the system engages the assisting vacuum pump to draw sand into the volute. When normal operation resumes, the system disengages. Unlike a venturi system, this dry-priming method does not materially affect efficiency. An oil reservoir can lubricate the pump's seal faces if it loses prime. With the dry-priming vacuum, the system protects the seal faces from heat and cracking that could occur without pumpage to lubricate it. When the system reprimes, the gland disengages. The system is self-contained and does not spill over into the pump stream. The pump can run dry for hours without damaging the seal faces. The new centrifugal pump was more efficient than the vertical turbine—hitting the same design and flow specifications while requiring less energy and saving operation costs. The motor for the centrifugal pump is readily available in nearby Milwaukee or Minneapolis, while the motor for the turbine required a significantly longer lead time to order.

Millions Saved

Since installation in March 2014, the plant has run continuously. With the previous turbines, the plant would have experienced at least 60 hours of downtime. Processing more than 600 tons an hour meant the plant would have lost the opportunity to process more than 36,000 additional tons of sand in a year. With high-quality hydraulic fracturing sand selling at more than $50 a ton, the new pump helped save more than a $1.5 million dollars of downtime losses in a year. The plant operator plans to open several more locations in 2015, and because of the success of this system, each facility will be installed with 8- or 10-inch versions of the new pump.