By Steve Fiscor, Editor-in-Chief
Mining operations, processing plants in particular, rely heavily on slurry pumps. Over the years, manufacturers have modified the designs to improve pump performance. Some of these pumps have such a long history, it seems that it would be difficult to continue to make further enhancements. The use of technology, especially simulation with computational fluid dynamics (CFD), allows todays’ engineers to view and test new designs before the first part is manufactured. This is a clear advantage over predecessors that relied on intuition and trial and error.
Last year, Weir Minerals invested in a major research and development (R&D) initiative to upgrade its line of Warman slurry pumps. In the end, the company’s engineers were able to significantly modify impeller design. The company took a bold step that is now beginning to pay dividends for its customers. It also converted a froth pump into a unit capable of handling the heavy thickener underflows, a job usually assigned to piston-type pumps. These initiatives offer the mines a chance to get a little more life and better performance from existing pumps. The program also allowed Weir Minerals to offer a new pump that can be adjusted while running.
ITT announced a similar initiative for its line of Goulds slurry pumps. The changes it has incorporated allow plant operators to adjust and even maintain the pumps while they are running. New monitoring devices provide advanced warning when operating conditions begin to deteriorate.
In the past, many mines had production bottlenecks that restrained output. Today, mines are finding that they are constrained by the permitted refuse disposal facility. Permitting new ones is extremely difficult. Producing a thickened slurry by dewatering the refuse stream increases the life and stability of the refuse disposal area. It also increases the load and wear for slurry pumps.
Weir Continues to Improve Popular Slurry Pumps
In an effort to reduce total cost of ownership, engineers at Weir Minerals initiated an extensive R&D program aimed at better understanding the wear characteristics at the inlet and outlet of centrifugal slurry pump impellers. The result was a totally new pump, the Warman WBH, and a new impeller and matching throatbush design for the Warman AH pump.
The new WBH slurry pump minimizes wear in the front liner with an adjustable throatbush to close the clearance between it and the impeller. With just a single action, the throatbush front liner can be adjusted both rotationally and axially, and at the same time. Weir Minerals refers to the new pump as a quantum leap in front liner design and said technicians can now maintain the pump’s performance and efficiency close to that of a pump in new condition, and reduce wear from a single point of adjustment. The one-point adjustment device moves the cover plate liner closer to the impeller. This will minimize the front impeller gap, reducing recirculation.
In creating the new WBH slurry pump, Weir Minerals said it looked at every aspect of maintenance ease, operating cost and safety, and this R&D work led to a list of advancements from the front liner to the drive end. As an example, there is no need to check or readjust the drive every time an adjustment is made like with the AH pump. The shaft and casing stays aligned to extend the life of mechanical seals. A robust one-piece bearing frame maintains accurate alignment.
A new impeller and volute design minimizes turbulence so that wear becomes more predictable. A unique patented design based on a vanelet in each impeller channel and a 4-vane impeller streamlines the slurry flow through the pump. The vortices between the impeller and volute will allow the pump to ramp up much more quickly, and reduce power usage, maintenance and costs.
Weir has been testing the WBH at coal mining operations in Australia with some impressive results. Coal & Allied’s Mt. Thorley operations in New South Wales installed the WBH in its southern prep plant. It reportedly only took about eight to 10 hours to swap it out. A year later, the pump is receiving high marks. According to the mine, the WBH is definitely using less power than the previous pump. Impressed by the WBH pump’s performance, they have now ordered five for the site’s north prep plant.
The Warman 8/6 AH is a very popular pump and a wealth of wear data has been collected from the field over the years. Using a novel integrated design approach, engineers compared this data with a CFD simulation to find a correlation between predicted and actual results for the standard 5-vane slurry impellers. The design team reviewed several impellers and decided a 4-vane option achieved the desired results. New impeller-throatbush inlet geometries were modeled using CFD with a focus on reducing turbulence and optimizing the balance between wear and performance. This process produced a design which would become the new Warman Wear Reduction Technology (WRT).
“The WRT program was a massive initiative by Weir Minerals,” said John Otten, divisional product manager-slurry pumps, Weir Minerals. “The Warman AH range is the most sold slurry pump in the world by a long shot. It’s about 60 years old now. While we have improved it over the years, this is a significant step to improve hydraulic performance and wear life.”
In the CFD simulation, one particular 4-vane design proved outstanding in all areas. A prototype was manufactured, water tested, and an extensive field trial was conducted in an extreme application, according to Weir Minerals. Additional field trials confirmed the data. All test results were fed back into the CFD program to validate the design and prediction methodology.
This WRT design offers an efficient, streamlined entry for smooth transfer of the slurry particles from the inlet axial direction into the radial flow through the impeller. Smoother inlet flow and uniform velocities within the impeller vanes significantly lowers the net positive suction head (NPSH) characteristics, extends inlet and associated throatbush wear life, and improves overall performance.
Adding unique vanelets at the outlet of the impeller passageways maintains smooth flow from the inlet, reducing turbulence, eddies and recirculation as flow exits from the impeller into the volute casing. The key aspect of maintaining uniform velocity profiles provides for extended wear life of the surrounding pump chamber. The end result is an impeller that demonstrates improved efficiency, reduced NPSH and greatly improved wear performance reducing the total cost of ownership.
The vanelets help boost the efficiency of the 4-vane design, and Weir Minerals said it has found that sealing is also improved when using the new side-sealing vanes. The AH-WRT impellers represent a step change improvement compared to the older style 5-vane impeller design.
The AH-WRT parts are interchangeable and retrofitable into all current AH pumps. The upgrade offers performance improvements by replacing the minimum number of parts.
Converting Existing Pumps to News Uses
More mines today are considering a thickened slurry to help improve refuse disposal by reducing the expense and risk associated with pumping a lot of water into a refuse impoundment. The AHF pump from Weir Minerals was originally developed as an extension of the AH range to handle large quantities of froth or slurry with entrained air generated by the flotation process. More recently the pump has been used with a great deal of success in thickener underflow applications.
“The underflow pumping system has proven to be the limiting factor that determines the maximum underflow density at which the thickener can be operated,” Otten said. “The thickener underflow density needs to be operated within a certain density range to maintain stable operation.”
The Warman AHF flow inducer pumps have a very large inlet configuration and a unique flow inducer impeller design. The large inlet minimizes the friction associated with high yield stress materials. An open 4-vane impeller minimizes friction through the passageways. An integral flow inducer scoops in the inlet to lower the pump’s NPSH, feed the slurry into the pump, increase the shear at the inlet, and lower the apparent viscosity of the slurry. This results in more stable operation on high yield stress slurries through better head and efficiency maintenance.
“We recently installed an AHF pump on a thickener underflow application in Australia,” Otten said. “We were amazed at how well this type of design compared with positive displacement pumps. We did test work and we were pleasantly surprised with some good results.”
The AHF uses all of the common parts associated with the AH range with a few changes to the suction side. The pump relies on a special auger type impeller design. A new cover plate was designed to accommodate the larger suction arrangement that takes in a lot of the air or thicker type slurries. This is an area where mines have always had application problems, Otten explained. “A centrifugal pump does not like air, that’s one of its biggest drawbacks, the brand does not matter,” Otten said. “This is a very simple change that allows plant operators to upgrade existing pumps to handle these types of slurries. Customers are now interested in installing this design on heavy thickener applications.”
ITT’s New Slurry Pump
ITT Corp. recently launched the new Goulds XHD, an extra heavy-duty, lined slurry pump. The company bills it as a next-generation product that can handle the heaviest slurry under the toughest conditions. The new XHD pump will enable mines to move slurry with improved reliability and at lower operating cost, according to ITT.
The XHD is designed to be maintained even while running, and to require less downtime for service procedures—with parts that are more accessible and adjustable than in other slurry pumps. The pump’s short bearing housing is adaptable to existing foundation, so operators can retrofit existing pumps. The pump’s features include:
- An adjustable suction seal ring, which enables adjustment even while the pump is running, compensates for wear and maintains optimum impeller clearance for peak performance;
- A split stuffing box that improves accessibility for easier and faster packing maintenance;
- Dual impeller adjustment that provides quick, easy access for operators to perform impeller corrections;
- A replaceable wet end cartridge that allows operators to change parts more quickly and efficiently with the help of a unique, tapered impeller shaft; and
- i-Alert condition monitor, ITT’s proprietary technology measures vibration and temperature, and signals users with a blinking red LED when it detects a potential problem.
“The mining industry has seen dramatic improvements in extracting and crushing methods, and now this new pump provides that same leap in productivity for moving slurry,” said John Manna, vice president of global marketing. “We’ve designed the XHD pump based on detailed customer input and testing. Our field results indicate the XHD pump will set new industry standards for reliable performance, quick maintenance and efficiency savings.”
The XHD pump is designed to work optimally on both Service Class III (heavy) and Class IV (very heavy) slurries as defined by the Hydraulic Institute. The pump is available in six discharge sizes ranging from 80 mm (3 inches) to 300 mm (12 inches), and in four power frames. Its flow range extends to 2,950 m3/hr (13,000 gpm), and discharge pressures to 85 m (280 feet).
Engineered for Harsh Demands
The Goulds Pumps XHD has excelled in two measures of performance related to moving heavy slurries: high reliability, with design features in every critical area, which reduce wear and extend equipment life while pumping abrasive minerals; and easy serviceability, with a unique suction seal ring that can be adjusted while the pump is running to maintain optimal impeller clearance and a split stuffing box for packing maintenance.
The XHD also includes several other features that make parts more accessible to perform required maintenance more quickly, according to ITT. It is also relatively easy to install, without changing piping configurations or process design. A low center-line height and the wet-end design allow the XHD pump to be adapted to the foundations of currently installed slurry pumps from ITT Goulds Pumps or other manufacturers.
“The XHD pump is designed to withstand the wear caused by pumping heavy-duty slurries, and to help operators get back in operation quickly when service is required,” Manna said. “We are confident the XHD pump will offer higher uptime and lower cost of ownership than any other slurry pump available today.”
Built with double-wall construction, the XHD pump features a full metric design and a large-diameter closed impeller, which extends wear life by enabling lower RPM operation. Using the CFD technology, ITT Goulds Pumps engineers designed the XHD pump for optimal hydraulic operation—resulting in higher efficiency, longer wear and lower power consumption. Early XHD users have reported drops in electrical consumption of 10% to 15% over previously installed pumps.
A number of innovative operational features combine to make the XHD pump easy and cost-effective to operate and maintain. The adjustable suction seal ring maintains proper clearance and users get longer wear life—not just for the impeller, but for the entire liquid end of the pump. In fact, the wet end of the XHD pump is designed as a replaceable cartridge, which allows operators to change parts more quickly and efficiently. To help the process, the XHD pump is built with a unique, tapered impeller shaft thread to aid removal, and for faster replacement of the impeller, with assurance that the shaft and bearing cartridge are properly aligned when the pump is reassembled.
The XHD pump’s open seal chamber uses a removable split stuffing box and gland for easier packing maintenance. Operators can choose their packing arrangement with dedicated seal water ports, and the stuffing box is designed to accommodate most mechanical seals by simply removing the split stuffing box.
The i-Alert conditional monitoring system identifies problems early. It measures vibration and temperature (a standard feature on all process pumps from ITT Goulds Pumps). When an i-Alert monitor detects that pre-set limits have been exceeded, it signals users with a blinking red LED.
A heavy duty bearing cartridge is mounted on fully protected machined rails that provide positive alignment and are easy to re-establish fit should wear occur, unlike saddle mounted bearing cartridges. The shaft on the XHD pump is manufactured for low deflection and longer seal life. Pump wear also is improved through heavy-duty bearings, standard oil lubrication (a grease option is available) and Inpro Seal bearing isolators.
ITT Goulds Pumps is taking orders for the XHD pump. Shipping is expected to begin in the first quarter of 2012. Added features expected in 2012 include expellers and rubber liners. The company also plans to offer additional pump sizes and higher pressure capabilities.