Energy efficiency and environmental measures for Floating Storage Regasification Units

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.