Oil & Gas

LNG re-gasification facilities

Re-gasification of LNG is to convert the LNG back to its gas state by heating it to ambient temperature.

The re-gasification process

The LNG is transported from the LNG liquefaction facilities to the re-gasification terminal by LNG carriers. The LNG is temporary stored fully refrigerated in LNG storage tanks at shore.

The LNG is pumped from the LNG storage tanks to the vaporizers where it is re-gasified. The pressure of the LNG stream is increased by the booster pumps upstream the vaporizers to meet the pipeline export pressure.

Ramboll has been involved in feasibility studies, concept evaluation and selection, FEED studies, detailed design and operational support on LNG projects

The LNG is in equilibrium with vapour at approximately ambient pressure in the LNG storage tanks. The sub-cooled LNG stream from the LNG storage tanks is used to condense the boil-off vapours from the LNG storage tanks in the re-condenser before the LNG is routed to the vaporizers.

Different technologies for vaporising the gas

The technology used to vaporise the LNG differs based on the application:

Water is typically used as heating medium where warm water is available in sufficient amounts throughout the year and at locations where cold water may be discharged and power is cheap.
Direct fired heaters are typically used for onshore locations with expensive power or in cold climates with cold sea water temperatures during some periods of the year.
Shell and tube vaporizers are typically used on floating facilities where the sea water or direct fired heaters cannot be used to vaporise the gas or in locations where synergy with other industries is possible.

Exporting the gas from the gas terminal

The export gas is typically routed from the vaporisers via export custody flow metering facilities to the gas transmission net.

Temperature and pressure probes, gas sampling equipment and export custody flow metering facilities are fitted at the gas export stream to verify that the export specification is met at all times and the actual export rates are monitored and logged before the gas is exported from the gas terminal.

The export gas can be odorized if it is exported to the gas distribution system, whereas gas exported to transmission systems is typically not odorized.

Modifying the heating value to fit demands

Usually natural gas markets can be divided in three markets depending on the heating value of the gas required: Asia (Japan, Korea, Taiwan) where gas distributed is rich, UK and US markets, where the distributed gas is lean and Continental Europe, where the acceptable heating value range is wider.

Different heating values

There are some methods to adjust the heating value of the gas to the desired level. For the purpose of increasing the heating value, propane and butane can be injected. For the purpose of decreasing heating value, nitrogen injection or extracting butane and propane are proved solutions. Blending with gas or LNG of different specification can also be used to adjust the heating value of the export gas.

Re-gasification facilities onshore or offshore

LNG re-gasification facilities have previously been located onshore but there has been a move towards floating re-gasification facilities in the form of FSRU’s (Floating Storage and Re-gasification Units) and SRV’s (Shuttle Re-gasification Vessels). There are several advantages to locating the re-gasification facilities offshore, such as, reduced environmental impact on shore line, shorter planning and permitting process and re-location flexibility.

Strategic storage of LNG leads to long term storage of the liquefied natural gas

Some technologies used for the vaporisers are motion-sensitive and thus not suitable for offshore applications. Other challenges to be solved for offshore re-gasification terminals include sloshing in the tanks and safety issues.

Heat efficiency issues

The heat efficiency of the re-gasification process is an issue of increased focus. Again, the selection of technology for the vaporisers is of significant importance for the overall performance and operating costs of the re-gasification facilities as the heat efficiency varies from less than 70% to more than 95%, depending on the selected technology.