Pumps for Water Extraction
“Water extraction” refers to the process of drawing water from a natural or man-made source. It is usually a first step before water is sent to a treatment facility and/or a distribution system. Water sources include reservoirs, wells, lakes and rivers, or even oceans. The destination of the water could be a municipal water supply, an irrigation system, industrial processes or the cooling system for a power plant or refinery. Different water extraction application will have very different pumping requirements and there are a number of different types of pumps available to help the designer to achieve the best solution.
Axial Flow Pumps
When a water extraction process requires large volumes of water to be raised relatively small distances (10 – 40 metres), large axial flow pumps can be a highly effective solution. These pumps are normally mounted in a vertical orientation. Water enters from below and is propelled upwards through the annular space between the impeller/shaft/motor enclosure and the outer casing. KSB offers two main types of axial flow pumps. The AMACAN family is a submersible design: the entire pump is installed in an open-bottomed well so that water is drawn from below and then pumped up into the well and around the pump. Meanwhile, the PNW and SNW designs are vertical tubular casing pumps. As the name suggests, these pumps are housed in a long tube, with an axial-flow impeller mounted near the bottom end and the motor mounted above the tubular casing, where it is kept dry and easily accessible for maintenance. Water is drawn in at the bottom end of the tube and discharged from an opening near the top, an arrangement that lends itself to very straightforward plant layouts.
Axial flow pumps offer high efficiency and excellent reliability. Made from the appropriate materials (such as duplex stainless steel) they can be used pump seawater or water with abrasive suspended solids.
KSB offers axial flow pumps in a wide range of sizes, with capacities ranging from approximately 500 m3/hour to over 10,000 m3/hour. Reliability and longevity are guaranteed by the use of highly reliable bearings and special corrosion and wear-resistant materials. These pumps are especially well suited to serving as the ‘front end’ to water supply facilities or cooling systems for power plants or refineries.
Submersible Borehole Pumps
© KSB Aktiengesellschaft When water is to be extracted from deep wells drilled into rock or shale formations, special borehole pumps can be the answer. These pumps are specially designed to fit into a narrow hole and have all of their elements – intake, impeller, motor and discharge pipe – arranged in a compact cylindrical package. Since boreholes are typically small, these pumps have lower capacities than the axial flow pumps described above. However, bored wells are often very deep, so this class of pumps is available with efficient multi-stage centrifugal impellers that provide maximum heads of 400 metres or more. Where brackish or corrosive water is encountered, corrosion-resistant stainless steel materials are advised.
In addition to well-water extraction applications, KSB’s UPA-series borehole pumps have been successfully used to de-water mines.
Between the high volume/low head axial flow pumps and the specialized borehole pumps we find conventional centrifugal pumps. These are available in a variety of configurations – submersible or dry-well, single- or multi-stage, vertical or horizontal mounted – and in a wide range of sizes and capacities. They are the reliable workhorses of water extraction and transport.
In Canada, we are fortunate to have access to generous quantities of fresh water from our lakes, rivers and wells. However, in many parts of the world, fresh water is in very short supply and it has become increasingly essential to extract clean water from saltwater sources. Reverse osmosis (RO) desalination processes have emerged as the most effective and economical way of achieving this.
In the RO process, water is pumped through a filter membrane that allows water molecules to pass, but holds back molecules of salt and other dissolved solids. The pressure required to accomplish this is very high – over 900 metres head – so that specialized multi-stage pumps such as KSB’s HGM models are required. Moreover, because of the high concentration of chloride ions in seawater, special corrosion-resistant alloys are required to ensure long-term reliability.
Reverse-osmosis systems have been used successfully in water-starved regions such as the Middle East and on the Mediterranean islands. They are also used for cruise liners and other large seagoing vessels.