To reliably guarantee dewatering in a gold mine in the US state of Montana, and to be able to ensure safe extraction of mineral resources, the operator procured a mobile back-up. Because the mine water is characterised by a low pH value and highly corrosive and abrasive properties, the operator decided on a particularly robust solution with a customer-specific design from Netzsch Pumps & Systems. Its essential component is a progressing cavity pump whose special displacement principle means it is particularly well suited to conveying water with abrasive solids. The pump is available in various materials to best suit each application, including low PH values.
For conveyance in the gold mine, Netzsch proposed the Nemo SY progressing cavity pump model, because this is particularly well suited for conveyance of the wastewater there, which may also contain abrasive solids. The special displacement principle is important here: the main parts that define the system are a rotating component, the “rotor”, and a fixed one, the “stator”, in which the rotor turns and moves radially. The precise geometrical mating means that conveying chambers are maintained between the stator and the rotor. The volume of these chambers remains constant. This ensures that the conveyed medium is transported at stable volume and pressure. The consistency and viscosity of the medium are significant in terms of product flow with this displacement technology, which means that this type of pump is particularly suitable for use with liquids containing solids, such as mine water.
With progressing cavity pumps, the delivery rate is determined by the size and speed of the aggregate and can be extremely accurately regulated in this way. This allows flexible adjustment of the pump according to the medium and the required performance. Depending on the design, pumps of this type achieve delivery rates of up to 400m³/h and pressures of up to 72 bar or higher. A flow rate of 32m³/h at a pressure of 20 bar, as was required for this project, was therefore no problem.
To prevent the service life of the pump being shortened due to corrosion, all the inner workings of the aggregate were made of stainless steel 316 and the inside of the pump housing was coated with Halar, which is a very resistant material. To prevent the stator from abrasion due to the solids contained in the water Netzsch decided on chrome plating of the stainless steel 316 rotor. In addition, a particularly reliable bevel gear motor was chosen as the drive. This not only saved space on the skid, but also further reached safety risks.
Special adaptations
Netzsch also carried out special adaptations to the 5m³ tank: it was rubber-lined to prevent corrosion due to the aggressive mine water. Deflector and separator plates were also installed, helping to filter out solids that are too large to be able to pass through the pump reliably. Easy maintenance and reliable operation are ensured by an inspection ladder installed in the tank, high and low level switches, overflow flanges and a safety cover over the container. In addition, the German manufacturer fitted a dry running protector that prevents damage to the pump in the event of a pipe work or tank blockage.
Roger Willis is with Netzsch
