Turbulent mixing analysis of discharge streams for open-loop exhaust gas cleaning system
11th International Workshop on Ship and Marine Hydrodynamics (IWSH2019), Paper 28
Contribution to Conference
Due to IMO regulations on sulphur oxides (SOx) emissions after 2020, exhaust gas cleaning systems (EGCS) or equivalent measures are commonly being adopted on ships. For open-loop type SOx scrubbers, one of the requirements is that, during commissioning of the EGC unit, the pH-value of the discharged wash water plume shall be no less than 6.5, measured 4 meters externally from the ship at rest, verified either by means of direct measurement or by using CFD method. A uniform jet inlet from a circular hole into stationary water was built up using Star-CCM+, to conform with a cited experimental setup. The grids were carefully adjusted to resolve the core region of turbulent mixing at the jet nozzle. The axial velocity profiles at several positions were in good agreement with the experiment results. Also the universal dispersion angle of the jet envelope cone, where the axial velocity is zero, was correctly demonstrated to be about 12 degrees. The volume fraction of wash water and seawater was traced via the passive scalar method, which was then converted to pH-value by using the standard titration curve of seawater. The iso-contour of pH-value equal to 6.5 was captured so as to determine its distance from the discharge point. The test case also included a configuration with an inducer and diffuser mounted at the end of the discharge pipe, which showed considerable effects on the mixing performance and the length of streams.