This study presented risk-based design and economic evaluation methodologies considering quantitative assessment of equipment failures and accident risks. First, this study proposed a new methodology of combining process simulation and Monte Carlo simulation (MCS), which provided risk-based information for determination of design parameter related to operation conditions. The realistic operation scenarios of a system including equipment failure and subsequent repair obtained by MCS were used to run a process simulation, which estimated an accidental risk expressed by exceedance curve of operation conditions. The combined method was applied to determine design vapor pressure of fuel storage tanks on LNG-fueled ships, and presented the exceedance curve of the pressure to help ensure system safety effectively in the early design stage.
Second, this study proposed a methodology of exergy-based economic evaluation incorporating unavailability and safety investment cost to comparatively evaluate design alternatives while considering efficiency, economics and safety together. Exergy-based economic analysis was employed to synthetically evaluate the design factors within the same framework. The unavailability cost was estimated as the cost resulted from the equipment failure quantitatively evaluated by MCS. The safety investment cost was defined as the cost required to ensure the safety of the design by reducing accident risks to a level that is ‘as low as reasonably practicable’ (ALARP), which presents a rational approach to converting the risks associated with design alternatives into monetary values for economic analysis. Comparative studies were performed for design alternatives to manage boil-off gas (BOG) with the recovery of liquefied natural gas (LNG) cold energy in a LNG floating storage and regasification unit (FSRU).
Overall, this study dedicated to the development of the integrated methodologies to achieve system safety effectively with respect to equipment failure, and to provide a rational basis for selecting a design alternative while simultaneously considering efficiency, economics and safety together.