Worldwide energy demands are growing rapidly, and liquefied natural gas (LNG) is fast becoming a hot commodity. Rising prices and lower costs are creating a boom, but the rapid conversion of existing technology to fit this complicated product is neither straightforward nor risk free. Competency and practical experience from a range of engineering fields is necessary to make the transition safe.
Natural gas was long considered an unwanted by-product of oil exploration, symbolised by the flares that once illuminated oil platforms and terminals. Now the energy industry has a different view. Encouraged by lower production and transportation costs, demand for environmentally friendly power, to say nothing of regulations prohibiting burn-off, natural gas is in demand.
LNG
Much of the world's resources of natural gas are typically located far from the major energy markets, such as the United States of America, Japan and Europe. In order to transport the gas effectively, it's cooled to approximately minus 160* Celsius until it takes the form of a liquid, reducing the gas' volume by about 600 times in the process. This liquefied natural gas (LNG) is then shipped to the customers. Before it can be used, however, it must be offloaded from the ships and returned to gas form for pipeline transmission at a receiving terminal, also called a re-gasification terminal.
Offshore and out of sight
To cope with increased demand for imported LNG, around 40 new terminals or expansions to existing LNG receiving terminals are planned in North America alone. Many of these new terminals will be located offshore.
"There are many reasons for having the installations offshore, not least the public concern for safety and the dislike of large industrial structures in their vicinity," says Pal Jahre Nilsen, global gas manager for DNV Technology Services. "Another reason is the lack of favourable sites and the difficult and time-consuming approval process to get a facility up and running. The process of approval is typically easier for offshore installations. But while the approval is easier, other things become more difficult when taking this technology offshore."
New and existing technology
Taking a land based technology offshore presents a whole new set of issues that must be addressed before a safe and regulatory compliant installation can be built and operated. A major challenge is combining existing and novel technology safely.
"When moving land based storage solutions and gas processing plants offshore, the design must take into account the marine environment and be
made more compact due to the restricted space," says Conn Fagan, senior principal engineer in DNV Technology Services. "Operating in an exposed offshore environment creates relative movement between gas carriers and the offshore terminal, whether these are fixed or floating, and that puts a strain on the existing transfer technology. In some cases new technology may need to be qualified. At the same time, technology used in maritime transport of LNG is being adapted to offshore terminal design. This includes both floating hull design and design of the LNG containment systems. It is crucial to identify and address the gap between these existing technologies and the novel application of them to offshore terminals."
Not straightforward
DNV has a great deal of experience within all the relevant areas of these existing technologies, from use of concrete offshore to design of LNG containment systems.
"The new LNG production process combines technology and competency from three areas; traditional land based LNG terminals, maritime transport of LNG, and offshore oil/gas structures. This is not easy to do. There are key interface issues that must be resolved, and the industry must take into account all the novel operational challenges," says Nilsen.
Staying ahead
As part of efforts to remain in the forefront of new technology and new applications, DNV engages in both internal and external research into these areas. Current work includes evaluation of sloshing in containment tanks, venting and relief from LNG storage, lifecycle assessment of containment systems, and qualification of novel LNG transfer systems.
"Our engagement with all the major offshore concrete structures in the North Sea, our experience with the development of the various containment system designs in use today, together with our access to in-house competence in key areas such as risk assessment and technology qualification, give us an advantage when approaching offshore gas terminals. We are also in contact with regulatory authorities and closely follow their work in developing a regulatory framework for these new concepts," says Fagan.
Offshore Technical Guidance from DNV
In May 2004 DNV issued the Offshore Technical Guidance "Verification, Certification and Classifi-cation of Gas Export and Receiving Terminals." It describes various approaches to the Verification of gas development projects, including the services of Classification, Certification and Qualification of Novel Technology.
"By combining DNV's breadth of competency and experience with existing technology, our research and knowledge on new technology qualification, DNV is in a unique position to assist clients in identifying the novel challenges and reaching their economic and safety goals," says Nilsen.