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July 2014 www.coalage.com 49 p i t d e w a t e r i n g c o n t i n u e d How Have New Materials Helped in This Process? The toughest application for centrifugal slurry pumps is in mill circuits, Weir Minerals said, pointing out that one material does not suit all applications. Typically, for Weir Minerals' lined pump concept, the preference is for using rub- ber liners with a metal impeller/suction throatbush combination. There have been great strides in devel- oping rubber formulations over the past two decades, Weir added. In the develop- ment process, some of the improved vari- ables include determining the best performance raw materials and recipes. There has been a move from traditional physical properties to viscoelastic proper- ties when designing rubber formulations, and there are better ways to define and understand the wear mechanisms in each component of the pump. This has helped in the development of new compound formulations for each wear mechanism, and in identifying the possible use of "dual" compounds in the slurry pump. Weir noted that its road map for white cast-iron metals has headed in the direc- tion of basic high-chrome irons with a matrix consisting of 25% (by volume) chromium carbides in 75% ferrous, with a principle hardness in the range of 600–650 Brinnell. Hyperchrome develop- ment is already at a matrix consisting of 60% chromium carbides in 40% ferrous, with a principle hardness of 750–800 Brinell. Either way, the company said, these materials clearly last longer, giving lifespan improvements of 20%–30%. Xylem said advances in recent years have been more a result of technological developments than new materials. Hard iron and stainless steel, both used widely in pump manufacturing, have been around for a long time. Improvements in dewatering pumps have resulted primari- ly from good hydraulic design and smart technologies that increase a pump's wear-resistance and efficiency. How Have You Been Able to Make Your Pumps More Energy Efficient? With energy usage and efficiency becom- ing increasingly important in the mining industry, both companies were asked for their views. Weir: Computational fluid dynamics (CFD) is helping to streamline the design of impellers to fit suitable casing configu- rations, which enhances pump efficiency. This is sized up with the actual field per- formance of components to match the fit- ting of pump components to suit. Large mill-circuit pumps are already in the 85% best efficiency range for continuous per- formance. Xylem: We have made significant strides in enhancing the energy efficiency of our pumps. For example, our Flygt 2600 drainage series features a closed impeller (not very widely used in drainage pumps), which is more efficient and wear resis- tant. An efficient hydraulic design, which uses less energy to move the water, is another fundamental aspect of our dewa- tering pumps like the new Flygt BIBO and the 2600 drainage series. Both of those pumps feature Xylem's DuraSpin hydraulic technology, which combines a closed impeller with a hard suction cover that sweeps abrasive parti- cles away from the impeller neck, protect- ing it from wear and tear. Wear resistance means that a pump delivers a high rate of efficiency on a consistent basis, and that the performance does not drop as rapidly as for non-wear-resistant pumps. "We find that we have been most effective in lowering mining customers' dewatering costs when we are able to par- ticipate in the design of piping and pump controls," Xylem said. "By consulting with a knowledgeable pump company, cus- tomers are able to get the ideal dewater- ing system for their projects, which will meet their needs much more efficiently without under- or over-estimating their requirements." What Can Operators do to Make Their Pumps More Energy-efficient? Weir: Undertaking a suitable care and maintenance program. In addition, im- peller-to-suction throatbush combina- tions should be regularly adjusted. If this is carried out, up to 15% more life is possi- ble for pump components while energy usage is enhanced by 5%–7% in this time period. Xylem: First and foremost, mine oper- ators should ensure that they are using the correct pump for the job. Is the pump of the right size, capacity and power for the specific application? The size of the pipe should also be carefully considered as it will also impact energy consumption. Pump snoring — where a pump is sucking air and emitting a "snoring" sound — is a common problem. This can wear out a pump very quickly, as well as result in a smaller volume of water being moved. Level sensors and snore controls can help to prevent this problem and keep the dewatering system operating at an optimum level. In addition, operators can employ automatic variable RPM con- trol for both diesel- and electric-driven operations. Regular maintenance is important to ensure that there are no glitches in the system and that energy consumption is being kept to a minimum. Our mine audits, which indicate how much can be saved in energy costs by changing to a dif- ferent pump, can be a real eye-opener for customers. What do Pump Operators do Wrong? Looking at operating practice, the compa- nies were asked if are there any specific problems they come across time and time again. According to Xylem, a key mistake made by some mine operators is not get- ting expert advice on board from the out- set. Mine operators are not dewatering experts, the company pointed out, and sometimes they use whatever pump they have on hand, which may be too large or too small, leading to unnecessary cost. Bringing an expert on board at the begin- ning of the project will ensure that the right system is put in place, and that it operates at an optimum level throughout the lifetime of the dewatering task. Inadequate solids handling is another common problem that can lead to snor- ing. Pumps can fill up with solids if the "active volume" in the sump is very low, and as a result the pump begins to snore. The active volume is the actual volume of Recent pump designs have helped to make mainte- nance easier and more cost-effective.