Supervisor:
Associate Professor Kim Sørensen

Co-Supervisor:
Associate Professor Thomas Condra

Assessment Committee:
Associate Professor Samuel Simon Araya, AAU Energy (Chair)
Professor Brian Elmegaard, DTU
Professor Erik Dahlquist, Malardalen University

Moderator:
Associate Professor Samuel Simon Araya

Abstract:

The use of scrubbers in the maritime industry has seen a significant increase in the past decade due to the implementation of new environmental legislation passed by the International Maritime Organisation.
The new legislation stated that by 2020, no vessel would be allowed to emit exhaust gas produced by the combustion of fuel oil containing more than 0.5% sulphur by mass. To be able to continue the use of fuel oil containing more than 0.5% sulphur by mass, a scrubber can be installed aboard the ship capturing the sulphur contained in the exhaust gas. Marine scrubbers exists in different designs and typically operates in either open- or closed-loop. In open-loop the scrubber uses seawater to remove the SO2 from the exhaust gas, whereas in closed-loop freshwater is used where alkali substances have to be added to neutralise the acid produced in the scrubber.

Computational Fluid Dynamics (CFD) has become a popular tool for
modelling scrubbers, as it provides the basis for capturing interfacial forces,
chemistry and heat- and mass transfer. Furthermore, it can provide a possibility to examine phenomena and tendencies that occur inside industrial scale scrubbers, which is a cumbersome, if not impossible, task to achieve on installations on this size. In this work a model based on the Eulerian-Eulerian CFD framework is developed for a packed bed scrubber. The model incorporates several submodels for both the packed bed and dispersed droplets. Among these are interfacial forces in the packed bed, heat- and mass transfer in the two regimes of the scrubber, and a chemistry model that accounts for the reactions in seawater when SO2 is absorbed. Additionally custom boundary conditions for the nozzles in scrubbers have been developed, which accounts for droplet size, liquid volume fraction and liquid velocity.
The completed model was used to calibrate the coefficients for the heat
and mass transfer in the packed bed, using data gathered from an ocean
going vessel. Comparing the calibrated model results to the data, it was
found that the model was able to predict the pressure loss to within 3%,
exhaust gas and seawater temperatures to within 3% and 3.5%, respectively,
and SO2 content between -24% and 25%. Although the latter seems like a large error; due to the low concentrations of SO2 measured at the outlet of
the scrubber the absolute difference were not more than 5 ppm for five out
of the six data points.This model can be used to improve new generations of packed bed scrubbers as it allows for optimising aspects such as water consumption, pressure loss, SO2 removal efficiency, and distribution of seawater in the packed bed, to be addressed.