Solving a Pipeline Pulsation Problem

A recently published white paper by two employees of Weir Minerals Netherlands describes an innovative engineering solution to a pumping problem at a large South American iron ore mine. According to authors Ralph van Rijswick and Erik Vlot, Anglo American operates 18 GEHO piston diaphragm pumps in two pump stations along the 529-km-long Minas Rio iron ore concentrate pipeline. The pipeline is designed to transport 26.5 million metric tons per year of concentrate to the export terminal at the coast.

During the commissioning of the pipeline, high-pressure pulsation levels were experienced with peak-to-peak levels as high as 20 bar. Based on pressure readings, it was concluded that hydraulic resonances were present in the system and were excited by the third and sixth harmonic of the flow pulsation generated by the pumps.

The authors determined that crankshaft- driven positive displacement pumps generate a fluctuating volumetric flow rate, which, depending on the hydraulic response of the connected system, generates pressure pulsations. This may cause unbalanced loads in the piping system, especially when hydraulic resonances are present. When several pumps are connected in parallel, the likelihood for excitation of hydraulic resonances increases. The resulting pressure pulsation is, among other factors, dependent on the phase shift between the crankshafts of the individual pumps.

Based on this observation, Weir Minerals Netherlands recommended installing a phase shift controller, which controls the phase shift between the crankshafts of the individual pumps, minimizing the effect of the hydraulic resonances. An important element of the solution was the implementation of a “virtual master pump.” The authors stated that use of a virtual master pump significantly increases the reliability and simplicity of the complete pump system and its operation. When using a real master pump, a trip of the master pump could cause tripping of all pumps in the pump station. It requires a continuous reassignment of a new master pump when taking the master pump offline for maintenance. In addition, unstable speed behavior of the master pump, for example with a hanging or severely leaking valve, will cause unstable speed behavior of all the pumps in the pump station. The reduction in reliability and the complex master-slave scheduling is completely eliminated by using a virtual master pump. The virtual master pump can be started and stopped and ramped up and down similarly to a real master pump but does not have to be taken offline for maintenance and has an availability close to 100%.