ANDRITZ water management for responsible closure of mines
Double-suction submersible motor pumps for sustainable post-closure care and maintenance in German mines.
The term “closure” in connection with mines sometimes conveys the wrong impression because the mines are far from being at a standstill just because actual mining work has come to an end. On the contrary, the operators are responsible for ensuring that the mines are cared for and maintained in the long term in a process that is, above all, sustainable. This includes socially compatible personnel adjustments, but also rehabilitation of former mining areas, repairing and rendering safe any mining damage, as well as responsible water management.
Long-term mine water concept
The latter, in particular, is one of the most crucial, eternal missions – work that will be needed long after the mine's closure. Systematic water management has so far dealt primarily with ensuring that the effects of industrial mining do not cause pit water to enter mines that are still active. This is no longer needed after a mine has been closed. When mining work stops, the main concern is to ensure that the mine water does not mix with the groundwater above it. Mine water is rainwater that seeps into the ground and solubilizes various salts and minerals from the layers of soil on its way through them. Due to this absorption of minerals, any contact with the layers containing drinking water must be avoided at all costs.
The German mining company RAG plans to let the mine water rise to a point where there is still a safety margin between the mine water and the drinking and groundwater. To do this, RAG will have to pump around 110 million cubic meters of mine water.
million cubic meters of mine water need to be pumped to keep a safety margin between the mine water and the drinking and ground water.
The solution used so far, with centrifugal pumps installed in a dry environment, requires an underground machine room and a corresponding supply of fresh air. This means also expensive maintenance and upkeep of this underground infrastructure. Submersible motor pumps are now used here instead of high-pressure pumps installed underground in a dry environment. Shrouding tubes are inserted into the shafts for this purpose so that the pumps can be brought from above ground to the level where the water is flowing and pump out the mine water. In combination with this pumping technology, the pumping depth of the mine water can be reduced, thus achieving high energy savings.
Two solutions are better than one
Implementation of this concept to resolve the problem of mine water in the long term places very high demands on the manufacturers of suitable pump technology. Pumping large volumes of liquid from great depths generates very heavy loads. Up to 30 tons of axial thrust are produced and have to be eliminated. The answer: Two solutions are better than one. A design with a double-suction submersible motor pump can fully compensate for the axial thrust.
At the moment, there are only very few manufacturers on the market who can supply this special pump technology needed by RAG, and there is only one that also has the necessary references and operating experience: ANDRITZ.
cubic meters of water per hour are conveyed by the pumps from the depths of the former mine over a head of 830 meters.
The pumps expert for mine water
International technology Group ANDRITZ produces and supplies double-suction submersible motor pumps through its subsidiary ANDRITZ Ritz GmbH, with headquarters in Schwaebisch-Gmuend, Germany. These are multi-stage, double-suction submersible motor pumps that can fully compensate for the axial thrust and have 50 percent less flow speed. The economic advantages are maximum operating reliability, minimum wear, and an extremely long lifetime of more then 20 years. Every pump with heavy-duty mining (HDM) technology is customized from standard modules for the specific application in hand. Hundreds of these pumps – including the largest submersible motor pump in the world at over 22 meters long – are operating successfully all around the world, for example in the most important mines in China or South Africa.
For the RAG project in Germany, pump specialist ANDRITZ will manufacture and deliver a total of three double-suction submersible motor pumps like those for the South Africa project based on the patented HDM (heavy duty mining) technology, which has proved its worth several times over. With a weight of 13,200 kilograms, the pumps are placed freely in the shaft underneath the shrouding tube. At a speed of 1470 revolutions per minute, these hydraulic machines achieve an efficiency of 81 percent and convey 530 cubic meters of water per hour from the depths of the former mine over a head of 830 meters. In order to achieve the necessary capacity, each of these submersible motor pumps is equipped with a special water-filled, high-voltage submersible motor. This motor provides efficiencies of 91.5 percent and a rated capacity of 1,750 kilowatts. These are four-pole motors as they are much more robust than two-pole designs. As a result of the longer lifecycle this provides and the lower wear, these motors guarantee significantly higher operating reliability – absolutely indispensable for this particular application.
Additionally, over one thousand meters of cable were laid for operation and monitoring of the pumps. While a thick, five-kilovolt cable provides a reliable supply of electricity to the motor, a manometer ensures that each pump always has the necessary counter-pressure to start up. Furthermore, the temperature of the motor is controlled by means of platinum sensors. The danger from methane gas is monitored by measuring hoses in the shrouding tubes. When the drinking water well goes into operation, one pump conveys the mine water first of all, and a second pump may be added if necessary. The third pump is available as standby. With this overall concept, the technology is excellently suited to begin reliable and sustainable operation in the long term.