Hexagonal reciprocating pump: advantages and weaknesses

Abstract

This paper reports the 1-D fluid transient simulation results of the discharge flow conditions in a 6-cylinder reciprocating slurry pump. Two discharge manifold configurations are studied comparatively; a case with a hexagon shaped discharge manifold where each cylinder discharges at a single vertex, and a case where all the cylinders discharges are lumped together into a tank shaped manifold. In addition, the study examines the effect of two pulsation mitigation measures in the case of hexagonal manifold; a single inline orifice in one of the hexagon sides and a volumetric dampener at the manifold outlet. The study establishes the pressure and flow fluctuation characteristics of each configuration and decouples the pulsation characteristics of the pump and the discharge manifold. 1. Summary Reciprocating pumps produce flow variations in their discharge end that may excite severe pressure pulsation in their discharge manifolds and piping systems. Therefore, developing of new designs of such pumps or introduction of novel configurations of discharge manifold warn an investigation of their flow dynamic characteristics and their susceptibility to acoustic and mechanical resonance. Numerical transient flow simulation is an effective front-end engineering measure to assess the susceptibility to detrimental pulsation flow acoustic performance. This paper reports the simulation results of the discharge flow conditions in a 6-cylinder hexagon shaped reciprocating slurry pump (Hexagonal pump). Two discharge manifold configurations of the same pump are studied comparatively; a case with a hexagon shaped discharge manifold where each cylinder discharges at a single vertex, and a case where all the cylinders discharges are lumped together into a tank shaped manifold. The study establishes the discharge pressure fluctuation characteristics of each configuration, quantifies the flow and pressure pulsation, and decouples the pulsation characteristics of the pump and the discharge manifold. In addition, the study examines the effect of two pulsation mitigation measures in the case of hexagonal pump with hexagonal manifold; a single inline orifice in one of the hexagon sides and a volumetric dampener at the manifold outlet. Finally, it compares the discharge pulsation characteristics of a reciprocating hexagonal pump with those of similar capacity triplex pumps conventionally used in oil wells drilling and in the mining industry. A one-dimensional transient flow simulator is used to investigate the pumping hydrodynamic of a slightly-compressible homogeneous slurry flow. The Hexagonal pump analyzed is based on an emerging industrial product design where the vertical reciprocating motion of the pistons is driven by a rotating cam, and where the kinematic of the piston motion is carefully configured, by the cam profile, to smooth the compound pump discharge flow/pressure. The simulation results of the common discharge tank case show that, under realistic conditions of delays in valves actions, severe discharge pulsation occurs. This pressure pulsation is in the same level of severity as in the crankshaft driven triplex pump used conventionally in drilling oil and gas wells. Furthermore, the simulations of the hexagonal manifold revealed that a complex alternating flow condition prevails in the six sides of the hexagons in response to the six reciprocating pistons actions. Simulation results suggest that the Hexagonal manifold provides certain level of damping when compared with the case of discharging to a common tank manifold. However, it generates multiple high energy frequency spikes over a wide frequency range, some of them at the high frequency range, with tendencies to excite the piping system and the mechanical frame of the pump.