Engineering & Mining Journal

DEC 2015

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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DECEMBER 2015 • E&MJ; 73 www.e-mj.com P U M P I N G S Y S T E M S it's treated further to remove the cyanide and other contaminants. It is then discharged according to effluent permit standards ore reused for another gold-recovery process. Line shaft turbine pumps are char- acterized by high hydraulic efficiency, relative to many other pump types. They can be ideally suited for heap- leach applications where the pregnant solution is collected in sumps and the solution must be pumped signifi- cant distances or to higher elevation. Pump Selection The distance liquid must travel is just one of the factors to consider in select- ing pumps for mining, according to Maguire. "Before evaluating specific products, the first step is to define the objectives from both application and equipment efficiency perspec- tives," Maguire said. "Once those goals have been established, the process of choosing the most durable and efficient pumps for a mining application can begin." For a dewatering application, it is important to select a pump made of material that is compatible with the solids being pumped, Maguire ex- plained. Some pumps are specifically designed to handle slurries because they are constructed with a hardened shaft, hardened steel impellers, and certain types of stainless steel to pump mixtures with high slurry content. Engineers often take water samples and test them in a lab to determine the makeup of the water. They check to determine how abrasive the contents of the water may be by measuring the amount of solids suspended in it. Then, they can identify the chemical compat- ibility using a material compatibility guide to understand the water makeup. There are natural chemicals and miner- als in the water, and the chemicals will react to the material that make up a pump as well. The turbine pumps used at the Colorado gold mine are made of 316 stainless steel, Maguire said, so the pump will not corrode during repeated contact with cyanide. Turbines are designed to operate continuously, which makes them ideal for gold recov- ery where pumps are working 24:7. "Pumps are constructed with cer- tain materials to suit multiple mining applications. The ability to produce all- iron, all-stainless, duplex and super- duplex units is important for mining because these materials protect the pump from corrosion when it comes into contact with chemicals and miner- als," said Sarah Boynton, product line manager at Xylem. Engineers also use a number of cal- culations to determine pump selection. First, they must identify the flow rate, or volume of water that passes through the pump per unit in time, based on the duty point—the spot on the pump curve where the pump will be operating at maximum efficiency. The flow rate can be fixed or variable. Identifying the flow rate will measure the amount of solids suspended in the water, and how abra- sive they may be. Then they determine the static head and friction loss of the pumping sys- tem. The static head is the height of a column of water that would be pro- duced at a given pressure. Calculating the static head identifies the internal energy of a fluid due to the pressure exerted on it from the pump. Friction loss is the reduction of static head that occurs in the pump due to viscous effects generated by the size and sur- face of the pump. Friction loss occurs throughout the entire pump; narrow corners and valves that impede flow create high friction loss. Many pump manufacturers offer online selection software to calculate the Best Efficiency Point (BEP) and find the flow curves to ensure that the pump will operate at the duty point. Online software can also help deter- mine the Net Positive Suction Head (NPSH), or the suction head valve at a specific flow point that is required to keep the pump out of cavitation. (All pumps require a certain level of pres- sure coming into them to operate effectively.) Once all the calculations are con- ducted, engineers might find there are a number of different pumps that meet the criteria. Then they must take into account other factors that influence pump selection, such as efficiency and application. It is important to consider the environmental conditions in which Figure 1—Turbines feature a sleek hydronic design that contains four basic subassemblies. Multistage bowl assembly is used to submerge the pump into the liquid and control the hydraulic performance. A column, or riser, moves the liquid to the surface.

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