Incorporation of LNG into Small Gas Networks via FSRUs

Abstract

Geopolitical risks on pipeline gas imports, increasing natural gas demand and the need to ensure continuous power supply with ever increasing fluctuating renewable power generation require diversification of gas sources to ensure supply security. With the global liquefied natural gas (LNG) trade increasing every year and natural gas prices remaining relatively low, more and more countries are interested in investing in regasification infrastructure. Establishing a floating storage and regasification unit (FSRU) and importing LNG has several advantages: lower cost compared to an onshore terminal, flexibility in relocation and the availability of short-term contracts all of which help serve small markets. FSRUs can also be operated in standby mode or used as an LNG storage facility. Operating an FSRU as a storage facility while beneficial for small networks introduces the challenges of LNG weathering and managing of the boil-off gas (BOG). To investigate these challenges on operation, a mathematical model is developed to determine the boil-off rate (BOR) over various time frames. The initial BOR is 0.129% of the initial storage volume increased to 0.143% after 10 weeks. Subsequent use of Aspen HYSYS to determine the change in LNG composition determined that Wobbe Index (WI) of the LNG varied from 51.58 to 51.616 MJ/Nm3 after 10 weeks of storage. An annual economic estimation of operating FSRU as a storage facility was carried out determining that the per unit price of gas obtained from regasified LNG is at least 42% lower than the current per unit price of gas in Ireland.