Pulsation free hydraulically driven piston pump

Abstract

The mining industry has recognised the advantages of high density tailings (also referred to as paste), as demonstrated by the continuously increasing number of modern high density tailings operations world-wide. Because of the higher solids content, high density tailings have a different rheology, i.e. a higher viscosity, and this requires a specific pumping technology. Positive displacement pumps are generally required to pump viscous tailings to their final destination. Two-cylinder hydraulically driven piston pumps (also referred to as paste pumps) have been shown to be the appropriate pump type for medium to high viscous pastes. Typically, positive displacement pumps generate a discontinuous discharge flow due to the nature of the displacement of discrete slurry or paste. In the case of a two-cylinder hydraulically driven piston pump (or paste pump), the reciprocating action of the piston produces a discontinuous flow, which gives rise to a discontinuous pressure characteristic known as pressure pulsations. Pressure pulsations are the result of any change in flow speed. Every start and stop of the slurry that is being moved in the discharge pipeline will cause pulsations in the pressure pattern. Pressure pulsations are undesired in pumping installations for a number of reasons, such as damage to the pumping system including piping and supports, disturbing noise levels, and safety risks for operators and maintenance personnel. Pressure pulsations require a higher design pressure rating of the pumping equipment and attached discharge piping. As a means to somewhat reduce these pulsations, external dampeners can be mounted in the pipeline but there are drawbacks to using such a device, and the results are marginal and still lead to a considerable level of pressure pulsations. For its paste pumps, GEHO has developed a sophisticated system (named VZ Pulsation Free System) that delivers a continuous flow to the pipeline system and will reduce the pressure pulsations to virtually zero. The theory behind the system is to create an independently controlled piston speed pattern and drive the two pistons individually in such a manner that the pulsations generated by one cylinder are compensated by the pulsations generated by the other cylinder. This is made possible thanks to some minor hardware and a smart control algorithm, which enables control of each of the two slurry pistons independently and specifically. The pulsation reduction system is unique in design thanks to the fact that it requires no additional hydraulic control valve block manifold and no additional hoses and connections. Besides eliminating the pressure pulsations, one of the additional benefits is that the GEHO VZ Pulsation Free System allows the pump to be sized to the nominal design pressure instead of the higher pulsation peak pressure. In practice, this will often result in a smaller size pump and pipeline and thus reduced capital costs. This paper describes the design concept of the GEHO VZ Pulsation Free System, presents the results obtained, and shows the additional benefits of the system in practical paste pumping operation.