Investigation of liquefied natural gas ageing and boil-off gas management at Klaipeda LNG reloading station

Abstract

Today the world energy market is in great transition and the demand for clean energy such as liquefied natural gas (LNG) is increasing rapidly. LNG is the main transfer form of long-range for water transportation and short range for land transportation. For socioeconomic aspects, using LNG for road transport could reduce oil demand, contribute energy security in nations with scarce energy resources and could change the quality of life for people because LNGpowered transport produces a low amount of noise and air pollutants. For the environmental aspects, LNG supplies as fuel for marine vessels or road trucks, toxic engine emissions are lower than traditional fuels: up to 80% for carbon monoxide, 70% for nitrogen oxides and 45% for non-methane volatile organic compounds, because of reduction of sulphur oxides and particulate matter are larger than 97%. The main objective of this research work was to evaluate the impact of technological operations and composition of LNG on LNG ageing and management of boil-off gas during its storage in Klaipeda LNG Reloading Station. This terminal is used as intermediate storage of LNG before loading LNG trucks, LNG bunkering ships and operation of process heat production plant. When LNG is stored for a long time, the volatile components (nitrogen and methane) start evaporating and this causes changes in composition and quality, which is called ageing process. This investigation could be useful in case of LNG market oversupply or with existing demand to storage LNG as a reserve. It was found that the nitrogen and methane concentrations of LNG remained practically unchanged during the analysis of the loading in the Klaipeda LNG Reloading Station cycles, and the corresponding calorific values only fluctuated within the error range. So, the LNG does not chemically age concerning to its market value. However, there is technical ageing that affects the management of the distribution system. The LNG as well as the percentage of vaporized gas in the storage tanks were mainly influenced by technical parameters such as the time of complete unloading from the storage tank into the LNG trucks, a number of LNG loading to the LNG trucks and the transfers between storage tanks. The transfers between the tanks are in turn influenced by the heat exchange in the processing pipeline with the environment, which leads to an increase in LNG temperature. The analysis also showed that discharging a tank over a longer period of time causes rapid heating of the LNG. This leads to an increase in the BOG. It is recommended to avoid these transfers between tanks until the planned technical improvements have been implemented.