Customized Pumping System Brings New Efficiencies to Mineral Processing

Energy-efficient pumps, intelligent pump-control logic and variable-frequency drives help the company process more minerals and cut energy use.

In 1862, while prospecting for what was thought to be a vast deposit of silver and gold, John Searles made a serendipitous discovery in this unforgiving and isolated area southwest of Death Valley: Borax and other minerals so plentiful, that the engineer complained they would interfere with refining the long sought, but never unearthed, metal ore.

Within a decade, a borax mining business was formed at what is now known as Searles Dry Lake, a depository rich with useful chemicals and minerals that serve a variety of industrial and agricultural needs. Brine from these salt layers is today’s source of sodium, potassium, borate, carbonate and sulfate, which are processed in facilities that trace their lineage back to John Searles’ San Bernardino Borax Mining Company.

From a modest production of a few tons of borax per month in 1873, Searles Valley Minerals (SVM) today ships more than 1.7 million tons annually, as well as hundreds of thousands of tons of high-grade mineral products to major manufacturers in 52 countries. These products are used to make everything from automobile windshields and laundry detergents to flat screen televisions, fire retardants and fiberglass insulation.

Mining solutions 

Unlike other mining techniques such as open pit and underground mining, SVM uses a unique, ecologically friendly process called Warm Solution Mining (WSM), wherein a leaching solution, in this case brine, is pumped into the mineral deposit field where it dissolves ore content, which is pumped to the surface and processed. The extraction process is made possible in part through a custom-designed, industrial-grade pumping station from Grundfos that accommodates the aggressive and continuously changing brine solution chemistry, not to mention the extreme temperatures that can reach 130 F.

“The company’s mining processes are subject to some of the harshest conditions, including extreme desert temperatures and caustic solutions. Therefore, the pumping systems that support these systems need to be highly reliable and efficient,” says Milt Bachman, President of Delta Pump Systems, a California-based industrial distributor specializing in pump design and specifications. “Variable-speed pumping combinations had failed the operating conditions in the past, and Searles management was looking for a more dependable, engineered solution.”

The extraction process begins at Searles Dry Lake, a 125-square-mile mineral field with nearly 200 vertical wells that are fueled by thousands of submersible and vertical turbine pumps that range from 3 to 50 HP and generate nearly 14,000 gpm. The pumps carry thousands of gallons of brine solution from one reservoir or lake bed to another, and the eventual transfer of the mineral-rich brine into holding tanks. The application’s challenges—both in terms of extreme operating conditions, as well as the required variable pumping volumes—led Searles’ Operations Engineer, David Hakim, to search for a more efficient and cost-efficient solution.

An integrated approach 

In spring 2012, Hakim asked Delta Pump Systems’ Bachman and the Grundfos Engineered Systems (GES) group to help him brainstorm a new, integrated pumping process. The GES team works with clients to develop one-of-a-kind, custom-engineered pumping systems that integrate engineering, intelligent controls and the most efficient pump types and technologies available for a specific application.

In the case of SVM, Hakim deployed the Grundfos CU 352 controller to manage the energy-efficient PACO horizontal split case pumps, intelligent pump control logic, and Danfoss variable-frequency drives (VFD). This new pumping station design allowed for the ability to monitor real-time flows, pressures and temperatures in one location.

“The integrated GES systems approach that SVM envisioned was critical in developing a pumping system that helped increase production reliability, boost mineral yield and reduce energy costs,” says Wil Wilkes, a Regional Sales Manager for Denmark-based Grundfos. “Likely the single most important aspect of the new system is the ability to embed the operation’s existing pump curve data to maximize pumping performance and energy use by operating solely at the equipment’s best efficiency point.”

Because the Grundfos controller “knows” the application’s required flow, as well as the equipment’s optional performance level, the system can make real-time efficiency decisions that can significantly impact energy consumption. For example, the software and integrated monitoring features can instantly determine if it would be more efficient to run two pumps at 50% capacity, one pump at top speed or any combination thereof. According to Wilkes, this advantage allows Grundfos to match pump output with actual demand—without additional external sensors, flow meters and voltage monitors—that for the SVM application was integral in creating an intuitive pumping solution.

The Grundfos design team drew from multiple pumping technologies to deliver a solution that would meet SVM’s varying production demands and application conditions.

The pump station ensures the pressure and flow remains constant on a 24/7 basis, operating at 13,800 GPM at 45 PSIG discharge pressure with an inlet pressure of 20 PSIG. The pumping media consists of brine heated to 130F with a 10-12% NaCl concentration, a formula which requires pump seals to be mechanically flushed regularly with 160-180 F solution to eliminate brine crystallization (the media will congeal below 90 F).

The main pump skid consists of four 100 HP PACO-brand KP horizontal double-suction, split-case pumps (each weighing more than a half ton) that provide 85 percent design efficiency. The split-case design offers better efficiency and operating performance compared with other designs, as well as easy access to pump components (bearings, wear rings, impeller, and shaft seal) without disturbing the motor or pipe work. The inboard and outboard mechanical seals remain serviceable without having to remove the top casing. This key design element—the ability to service units without interrupting production—was pivotal in the team’s selection of this pump series.

The overall feedback regarding the GES system has been overwhelmingly positive thus far. According to Hakim, the current savings compared with the previous constant-speed pump station is $3500/month with a two-year payback. He calls the new system “a precedent for all future pump stations.” MT

This article was prepared with information provided by the Grundfos (grundfos.com) Engineered Systems (GES) team.