Re ECF Project: 2011-30

Project Title: Demonstration of an efficient air pollutants scrubbing device for marine applications

Applicant: Prof. Dennis YC Leung, Department of Mechanical Engineering, The University of Hong Kong

Total Approved Grant: $1,998,200

Duration: 1/12/ 2012 to 30/6/2014

Project Status/Remarks: Completed

The project seeks to demonstrate a low cost and efficient technology that can remove major air pollutants emitted from marine fleets. This technology is expected to reduce several air pollutants including particulate matters (dark smoke), sulphur dioxide, hydrocarbon, as well as NOx in the tailpipe exhaust emissions from marine engines. The capability of removing NOx from the exhaust gas will be highlighted in this demonstration project.

Summary of the Findings/Outcomes:
A De-NOx system was installed in one of the seawater scrubber of the Star Ferry “Day Star” and sea run demonstration test for the system was successfully carried out. The original scrubber system installed was found to be effective in reducing several important pollutants such as dark smoke, SO2 and hydrocarbon but has very little effect on NOx. With the installation of an ozone dosing system, the NOx in the exhaust gas can also be reduced with a maximum reduction of ~70% and 65% respectively for NO and NOx at low speed operation mode and ~38% and 35% respectively for NO and NOx at high speed operation mode. The results were in line with those obtained from the laboratory set-up. A very strong linear relationship between scrubber inlet O3/NO ratio and NO / NOx removal efficiency is found. Hence the NO / NOx reduction can be increased further by higher O3 injection. The performance of the scrubber can also be further improved by better design of the mixing chamber and reheater of the scrubber. This can be done through computational fluid dynamics analysis to enhance the reaction between ozone and inlet NO from the engine exhaust to form NO2 and the mixing between the formed NO2 and scrubbing seawater in the scrubber. The effluent discharge due to the scrubbing was also found to be acceptable to local discharge standards.