Faster connection times boost crew safety by minimising exposure and enabling operations to be completed more quickly
Bangladesh’s Moheshkhali floating LNG vessel (MLNG) plays a critical role in meeting the country’s growing energy needs.
Commissioned in August 2018, MLNG has a baseload capacity of 500M ft3 per day (MMscf/d) and enables state-owned Petrobangla to procure gas from international markets.
Operated by Excelerate Energy, MLNG needs to be able to operate safely and efficiently in the challenging weather conditions encountered during both the hot and humid summer season and the extremely wet monsoon season.
To maximise efficiency and increase crew safety, the facility incorporates a fast-connection element in its 10-inch hose transfer system that delivers reduced operator time for LNG transfer.
Signum Technology subsidiary KLAW LNG, a specialist in ship-to-ship and ship-to-shore LNG transfer systems, reports that the CryoFC system can deliver an up to 75% reduction in connection times when compared with traditional nut-and-bolt methods.
The CryoFC system uses a 10-inch American National Standards Institute Class 150 flange joint and takes approximately four minutes to connect and three minutes to disconnect. On a transfer system using multiple lines, this can equate to significant time savings, says KLAW LNG technical director Tony Webber.
In practical terms, the CryoFC differs from nut-and-bolt connections in that it uses a sealing gasket automatically held in the correct position ready for connection. There is a self-aligning mechanism, and no loose parts requiring assembly for the connection process.
“The presentation of the hose end for connection to the manifold can be executed efficiently with control from cranage. This means far less reliance on manipulation from the crew on the manifold and is far simpler in terms of alignment,” says Mr Webber.
This benefits safety in that it reduces the risk of trapped fingers and hands, and removes the need for fitting of gaskets or bolts and studs through flange holes. Furthermore, the faster connection and disconnection times reduce exposure for crew on deck, which can be particularly acute in extremely hot or cold operating conditions.
Another key aspect in the development of the system was the use of standard cryogenic flange gaskets and avoiding reliance on special or bespoke sealing. KLAW LNG carried out analysis of traditional methods and flange camlock couplers. This highlighted the aforementioned issues with the nut-and-bolt method, but also showed that camlock-type products could not provide the necessary clamping capability for true cryogenic applications. A new approach was needed.
KLAW LNG worked with an undisclosed customer to trial the technology on a vessel and obtain operational feedback. The same customer is currently using the technology on two FSRUs, and the system is being adopted on other projects, Mr Webber says.
Critics are questioning whether the conventional method of evaluating LNG cargo value during loading and offloading is the best option available.
Established as a standard method in the natural gas industry, gas chromatography (GC) is commonly used as a component in assessing the quality and composition of LNG in order to determine density and gross calorific value, and thereby determine the amount of energy transferred.
This involves at regular intervals taking a sample of the LNG in its liquid state and vaporising it in order to carry out analysis.
But while this method is well established and versatile, a new method based on inferential devices may be faster and cheaper while maintaining accuracy, a paper titled “A Rethink of the Evaluation of LNG Cargo Value during Loading and Offloading” argues.
Authored by Orbital Gas Systems’ team leader for steam systems and gas analysis Dr Jürgen Zipprian, head of R&D for global product sales Tony Wimpenny, and international business development lead Harry Jones, the paper argues that GC assumes that each sample analysed is a perfect representation of the entire sample stream between the point at which that sample is taken and the next point. “The vaporised LNG composition and related properties will never be perfectly consistent, and do not vary linearly or predictably,” the paper says, going on to argue that in the case of an LNG tanker discharging even with a GC operating without any malfunctions, the magnitude of error could run to the tens of thousands of dollars.
As an alternative, the paper posits using a more “real-time” technique such as inferential devices. These can continuously track changes in LNG quality, providing a more detailed and accurate representation of the entire LNG cargo. The paper adds: “The real-time nature of the measurement also eliminates the risk of temporary excursions going completely unnoticed and maximises the monetary value.”
The paper’s authors also argue that benefits include reduced capital and operational expenditure, less required infrastructure and a smaller footprint.