Abstract
In view of the need to reduce greenhouse gas emissions from the maritime sector, this paper proposes design and operation indicators for the assessment of Floating Storage Regasification Unit (FSRU) energy efficiency and carbon footprint. Such indicators are applied to the study of five regasification systems: seawater system without recondenser (Case 0), seawater system (Case 1), open-loop propane system (Case 2), closed-loop water-glycol system (Case 3) and open-loop system with Organic Rankine Cycle (ORC) (Case 4). Of the regasification systems installed in FSRUs, Case 1 proves most energy efficient, closely followed by Case 2. If the cold energy of liquefied natural gas (LNG) were to be exploited in the regasification process, Case 4 would present an Energy Efficiency Design Index (EEDI) 41.25% lower than that of Case 1, whilst positioned at the opposite end of the scale is Case 3 with an EEDI of 347.98% higher. The Carbon Footprint Design Index (CFDI), in comparison with the EEDI, further includes emissions deriving from the methane slip from dual fuel engines and the CO2 capture ratio factor for the possible implementation of Carbon Capture and Storage (CCS) systems. In the cases analysed, the CFDI with a methane slip of 5.5 g/kWh represents an increase of 4–28% with regard to the EEDI.
Highlights
The Fourth International Maritime Organization (IMO) greenhouse gas (GHG) Study published in 2020 relates a rise in shipping GHG emissions of 9.6% between the years 2012–2018
Cases 1, 2 and 3 typify regasifi cation systems installed in Floating Storage Regasification Unit (FSRU) (Eum et al, 2011; Madsen et al, 2010; Samsung Heavy Industries, 2014), while Case 4 is a modification of Case 2 to include a system that takes advantage of the liquefied natural gas (LNG) cold energy with an architecture similar to that proposed by different researchers and Mitsui OSK Lines (MOL)
The fitting of an Organic Rankine Cycle (ORC) to exploit the LNG cold energy, as in Case 4, would reduce the Efficiency Design Index (EEDI) by 41.25% compared to Case 1
Summary
The Fourth International Maritime Organization (IMO) greenhouse gas (GHG) Study published in 2020 relates a rise in shipping GHG emissions of 9.6% between the years 2012–2018. Fulfilment of the IMO’s ambitious goals require a range of solutions such as more stringent measures related to energy efficiency in the design and operation of ships, the installation of innovative technologies that reduce emissions, and the uptake of low and zero carbon fuels. The first FSRUs were new-build or conversions of LNG vessels with steam turbine propulsion systems, today it is common to install an electric propulsion system known as dual fuel diesel electric (DFDE) (IGU, 2020) In this system, four-stroke LPDF engines generate all the power required by the ship’s auxiliary services and electric propulsion motors. Given the IMO’s ambition to reduce GHG emissions, design and operating indicators to determine the energy efficiency and carbon footprint of any vessel type are absolutely essential This es tablishes emission limits depending on the ship type, and allows assessment of the impact of new technologies related to GHG emission reduction. A total of five cases are evaluated, one of which includes an LNG cold energy exploitation system for power generation
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