Analysis of Energy Consumption of Novel Re-Liquefaction System Integrated with Fuel Supply System (FSS) for LPG-Fuelled LPG Carrier to Conventional Systems

Abstract

This study analysed a novel re-liquefaction system integrated with a fuel supply system (FSS) for an LPG carrier to conventional systems. The re-liquefaction system and FSS were installed independently in a conventional LPG carrier, while those systems were combined in the novel system. The condensed LPG in the re-liquefaction system was directly transferred to the FSS without the cooling and expansion process in the novel system. 84,000 m3 LPG carrier equipped with a 10 MW engine at normal continuous rating (NCR) was selected as a target ship. Aspen HYSYS ver.12.1 was employed for process simulation. The results showed that the energy consumption for the novel system was reduced by 38%. The energy for re-liquefaction was decreased because the flow rate recirculated was decreased, and the energy for FSS was reduced as the temperature of the stream supplied to the FSS was relatively high in the novel system. A sensitivity analysis was conducted to investigate the effect of the parameters on the results. The investigated parameters were LPG compositions, seawater temperature, compressor efficiency, and pump efficiency. The energy consumption for the system was significantly different depending on the LPG composition, and the energy consumption was changed by 2.5% for conventional systems and 0.9% for the novel systems with the variation of 4 °C seawater temperature. The energy for the novel system was reduced by 2.8% for conventional systems and 2.3% for the novel systems with the 5% increment of compressor efficiency, whereas pump efficiency had little effect on the results.