Shape Optimization of Marine Exhaust Gas Scrubber with Silencer

Abstract

The International Maritime Organization (IMO) is strengthening regulations on reducing emissions of sulfur oxides. Therefore various technologies and researches have been investigated. There are many methods to reduce sulfur oxides emissions, such as using low sulfur oil, LNG fuel, and installing the post-processing devices. If low-sulfur oil and LNG fuel are used, engine modifications and replacements are required to apply for the existing vessels. However, engine modification and replacements are costly. Among them, studies on scrubbers that reduce pollutant particles and sulfur oxides in exhaust gas by spraying droplets are actively being conducted. Wet scrubbers are being considered as post-processing devices because of their various advantages such as high reduction efficiency and economic benefits. A diesel engine is a device that converts the thermodynamic energy of diesel fuel into mechanical energy, which generates vibration noise by fuel explosions, piston up and down motion, and crankshaft rotational motion. This is a main source of noise for ships. Due to environmental noise problems of ships, noise transmitted to crew members, and operation in special environments, he need of reducing exhaust noise has been increasing. However researches and developments on a silencer optimized for exhaust noise of ships to reducing pressure drop and noise are insufficient. In this study, acoustic and flow characteristics were analyzed by changing the shape of a composite scrubber combined with a marine wet scrubber with a silencer. Among the existing silencer shapes are used in various fields, the acoustic and flow characteristics were analyzed when a suitable shape was selected and combined with the top of the scrubber for a ship. Based on these results, we devised a combination silencer for higher performance and studied the variables that affect on the performance. Among the shapes of existing silencers, Vane and Resonate type were selected as suitable shapes for ships. The vane is installed outside or inside the silencer, the inclined direction of the vane is in the forward or reverse direction of the fluid flow direction, and the effects of the length of the vane were analyzed. Moreover, the effects of change in the number of hole lines in the direction of height and the outside or inside position of the silencer was also analyzed. For transmission loss and pressure drop, the outer vane reverse type which showed optimum performance in the vane shape, and the inner resonate type which showed high performance in the resonate type, are combined. A guide vane was additionally installed on the hole of the combined silencer, and the effect of changing the length of the outer vane and guide vane was analyzed. In addition, the effect of changing the number of outer vanes, the diameter of the hole in the resonator, and the number of hole lines in the height direction was analyzed. The low-frequency and entire-frequency average transmission loss of combination silencer optimal shape was 23.9 dB and 14.4 dB higher compared to conventional silencer optimal shape