Soon-kyu Hwang’s research while affiliated with Daewoo Shipbuilding and Marine Engineering and other places

This study addresses the control challenges associated with loading low-pressure liquid carbon dioxide carriers (LCO2Cs), which are crucial components of the carbon capture, utilization, and storage (CCUS) chain. It explores the need for stable pressure and temperature control to prevent dry ice formation and ensure efficient cargo handling. The research employed HYSYS dynamic simulations to assess three different control strategies. The simulations assessed each strategy’s effectiveness in maintaining stable operating conditions and preventing risks, such as dry ice formation and valve blockages. The study concluded by examining the necessity of pressurization for safe and efficient LCO2 loading and by determining which control strategy is most effective and reliable based on the simulation outcomes. Among the three scenarios examined, Case A, which utilized two control valves, exhibited initial instability due to significant flow coefficient differences, resulting in temperature drops below the CO2 triple point and increasing the risk of dry ice formation. Case C, operating without pressurization, experienced severe pressure fluctuations and prolonged exposure to temperatures below the triple point, posing risks of valve blockages. In contrast, Case B, which uses a remote pressure-reducing valve and a control valve, demonstrated the most stable performance, effectively avoiding dry ice formation and pressure fluctuations, making it the most reliable method for safe LCO2 cargo loading.

The energy required for the transportation of raw materials and the production of most manufactured goods depends on crude oil. For these reasons, FPSOs (Floating, Production, Storage, and Offloading) have become the primary production units of crude oil offshore. It is leading to an increase in the number and expanding of the production and storage facilities of the FPSOs. An increase in the oil production at the topside facilities of FPSOs will contain more gases, which leads to a rise in blow-by gas. Changes to the blanket gas system may be necessary as the flow rate of the blow-by gas is expected to increase. The purpose of this paper is to suggest a novel blanket gas system with a proper control method for controlling the cargo tank pressure when the blow-by gas is occurring. Unlike the existing system, in this proposal, the purge header that supplies the inert gas is possible for a use of the vent purpose in the situation where the blow-by gas is generated. By using the vent header and purge header for the purpose of venting, the pipe size can be drastically reduced. To quickly convert the purge header for the purpose of venting, the application of an appropriate control method is essential. A simulation was carried out for confirming the efficacy of the pressure control and the processible blow-by gas quantity compared to the existing system. In addition, as the amount of blow-by gas increased, a study on the possibility of installing large pipes used in the existing system configuration and the dual pipes suggested by this proposal was investigated. As a result of the simulation, this proposal presented better results in terms of both the pressure control performance of the cargo tanks and the arrangement of the piping compared to the existing system.

Liquefied natural gas has attracted attention through an explosive increase in demands and environmental requirements. During this period, the Energy Efficiency Design Index (EEDI), which was adopted by the International Maritime Organization, expecting to significantly reduce CO2 from ships, has become an important key. It has triggered a change in use from steam turbine systems and dual fuel diesel electrics to high-efficiency main engines such as ME-GI engines to meet the EEDI requirements. However, since the ME-GI engines use 300 bar of fuel gas pressure, it is necessary to resolve problems of the pressure controllability and to prevent the reductions of the re-liquefaction amount caused by clogging of the lubricant mixed with the fuel gas during the compression. The purpose of this study is to propose a novel control strategy with a newly developed configuration for controlling the pressure so as not to trip the BOG compressors when the ME-GI engines are tripped, and for preventing a reduction on re-liquefaction amount. Unlike the typical configuration used in the current vessels, this proposal separately provides the fuel gas at 150 bar without lubricants to the re-liquefaction. In addition, three control strategies are proposed, depending upon the application of multi-controllers and the location of the pressure transmitters. A simulation was conducted to verify the efficacy of the proposed method, focusing on the controllability of the pressure and the re-liquefaction amount, in comparison with the typical configuration. As results of the simulation, the proposal showed excellent controllability without trips of the BOG compressors even in abnormal conditions and confirmed the great re-liquefaction performance.

Liquefied natural gas began to attract attention as a ship fuel to reduce environmental pollution and increase energy efficiency. During this period, highly efficient internal combustion engines emerged as the new propulsion system instead of steam turbines. However, Otto-cycle engines must use fuel that meets the methane number that was given by the engine makers. The purpose of this study was to develop a system configuration and a control method of methane number adjustment using combined cascade/feed-forward controllers for marine Otto-cycle engines to improve reference tracking and the disturbance rejection. The main principle involves controlling the downstream gas temperature of the fuel gas supply system to meet the required methane number. Three controllers are used in the combined cascade/feed-forward control for adjusting the downstream of the gas temperature: the cascade loop has two controllers and the feed-forward has one controller. The two controllers in the cascade loop are designed with proportional–integral (PI) controllers. The remaining controller is based on feed-forward control theory. A simulation was conducted to verify the efficacy of the proposed method, focusing on the disturbance rejection and set-point tracking, in comparison with a single PI controller, a single PI controller with feed-forward, and cascade control.