Roger Willis describes how progressing cavity pumps dose a wide variety of auxiliary substances in extractive metallurgy
Many complex industrial processes now require a wide range of different catalysts, reagents and other auxiliary substances that have to be delivered in precise quantities. In most cases this leads to a whole fleet of different pump systems being set up depending on the medium requirements, with correspondingly high expenditure in terms of maintenance and spares inventory.
For a single project, a South African producer of platinum metals was therefore looking for both peristaltic pumps to dose flocculants and progressing cavity pumps for anti-foaming agent, as well as vertical centrifugal pumps to supply water to several stuffing boxes - three quite different conveying technologies each with different operating conditions and know-how requirements for the operators.
As a more cost-effective and above all simpler alternative to this, the German company, Netzsch, instead came up with a solution that only used progressing cavity pumps, enabling a considerably less complicated design of the operation and availability of a central contact in the event of any questions. This simplification is made possible by the special conveying principle: the rotation of a helix rotor in a stator that is geometrically adapted to it forms closed conveying chambers. In these, the medium is conveyed smoothly - that is without any strong shear forces or pulsation - from the inlet to the discharge side, irrespective of its consistency or viscosity. In addition, the uniform volumes of the chambers allow accurate, continuous dosing of the delivery volumes using the speed. This enables an accuracy of between 5% and 3% to be achieved; small dispensers even achieve 1%.
In the end, these advantages led the metal producer to order a total of 18 progressing cavity pumps of the Nemo BY type for all three areas of application. Two versions were fitted, involving the larger one providing around 4 m³/h of water at 10 bar for the stuffing boxes, while the smaller one feeds flocculants and anti-foaming agents into the appropriate sections of the process. Both models are equipped with robust stators made of chemical-resistant elastomer Nemolast S45 and have a dry running protection system and a pressure relief valve to increase operational reliability. Sealing is achieved using elastomer bellow seals with silicon carbide sliding rings. This configuration, which is specially designed for a long service life, has enabled the pumps to operate without any problems and to meter the different auxiliary substances with the required accuracy since they were commissioned in the spring of 2013.
Roger Willis is business field manager Chemical, Pulp and Paper with Netzsch.