Vertical turbine pumps provide reclaimed water to mines in South America’s deserts.
Water is vital to the mining industry, especially in South America where many mining companies are located in areas where the resource is highly scarce and environmentally sensitive. One of these locations is the Atacama’s Desert—the driest in the world. However, mining companies require steady and reliable delivery of water to their processes to operate and accomplish production goals. Reclaim water pumping systems represent an opportunity to reuse an abundant water source by recycling the water from the process and returning it to the mine. This minimizes the demand for fresh water by approximately 20 percent.
A defining parameter in selecting the type of pump is the method of suction from the reservoir. Among all the centrifugal pump types, horizontal pumps are the most popular and most commonly used in many applications.
Though this is the simplest arrangement for a pump station, generally this solution is not technically viable in most reclaim water pumping systems used in the mining industry. In a reclaim water system, it is usually not possible to control the level of the water in the suction reservoir. This makes the vertical turbine pump (see Figure 1) the best choice.
In these types of stations, the length of the vertical turbine pump is designed according to the minimum water suction level and pump submergence requirement. This guarantees its high efficiency performance and avoids specific hydraulic phenomena that can adversely affect its performance, such as vortices, excessive pre-swirl and cavitation.
Although vertical turbine pumps, due to their vertical and multistage nature, seem suitable for this application, some other parameters should be considered to specify the right equipment that guarantees high efficiency and long-lasting performance in a reclaim water pumping system.
The type and quality of liquid to be pumped is a major parameter in selecting the type of pump and its technical specifications. The presence of solid particles in the water and its corrosive properties, as well as the maximum allowable particle size that can pass through the pump, will determine the material of the pump components.
Reclaim water pumping systems are characterized by handling abrasive and chemically aggressive fluids due to the nature of the mining process. While reliability and efficiency are the key requirements for a non-stop process such as the mining industry, corrosion and erosion damage that can be caused by the aggressive properties of the reclaim water can reduce the life and performance of the pumps.
The life of pumping equipment is related primarily to the design of the pump and the resistance of the material used for cavitation, corrosion and erosion under operating conditions. Therefore, the exact properties of the water to be pumped in each project must be known to select the best material. The chosen material must be adequately resistant to the fluid characteristics and the velocity effects in the different areas of the pump. Special materials—such as Duplex steels—are widely used in modern reclaim water pumping systems for all the main pump parts (see Figure 2).
This material is popular because of its strength and abrasion and cavitation resistance. New advanced engineering thermoplastic materials have also been developed to be used in pump bearings and wear rings with outstanding performance in the roughest conditions. These alloys and engineered materials guarantee a high efficiency performance and an improved pump life. Although this type of material may represent a higher purchase cost, it is commonly accepted in the industry that approximately 90 percent of the total cost of ownership is maintenance, operation and installation, leaving only 10 percent as the initial pump purchase cost.
Figure 1. Reclaim water pumping system – 13,800 total installed horsepower in a copper mine in Chile
Figure 2. Vertical turbine pump—All wetted parts made of Duplex 2205 designed to handle large amounts of solids
High Head Pumps
Generally in the mining industry, the required head is so large that pumping must be done in multiple pump stations, installed in series, with several discharge reservoirs constructed at different levels and altitudes. This increases the construction costs, as well as the required maintenance of the pumping systems. Sometimes, even this alternative may not be feasible, as in cases in which geographical conditions do not allow the installation of several pump stations. One solution for this is the design of engineered vertical turbine pumps within a limited range of specific speeds —ns—(1549 < ns < 2585 ), for high heads per stage (see Figure 3) with total dynamic heads (TDH) up to 500 meters or 1,640 feet.