Numerical and experimental investigation on the ballast flushing system

The ballast sediments deposit not only provide the breeding ground for the survival organisms, but also affect the weight balance of the ship and even accelerate the corrosion of the ballast tank. In this work the performance of a ballast water flushing system for the 138,000 m³ LNGC (Liquefied Natural Gas Carrier) double bottom cargo ship is studied. A simulation model of the ballast tank was made to conduct the numerical analysis. Besides, a scaled experimental setup was established on basis of the similarity principle. With different injecting velocities at the flushing inlet, the sediments distribution in the ballast tank is investigated and the energy consumption of the circulating pump is studied. The results show that by flushing the ballast water on the bottom, the sediments first accumulate at the far end, with the sediments volume fraction climbs up to 10–30%, before gradually getting removed over time. Further, higher inlet velocity leads to a more rapid decrease of average sediments proportion in the ballast tank over time, but the energy consumption in circulating pump significantly increases as well. The required power for this proposed ballast water flushing system is within the common range and thus applicable in the cargo ship.