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Cannon Artes Ingegneria has contributed with two water treatment plants for the Shell project Prelude, the first FLNG vessel operating in the Australian’s coast

In the next twenty-five years, demand for energy in the world will grow even further. The increase of the demand for natural gas is supported by the liberalization of some markets, newly found reserves worldwide, the stop to nuclear decided by many countries after Fukushima, and the lower exploitation costs and price than oil. The new natural gas reserves to be exploited are mainly “unconventional” (shale gas) or in offshore fields off the coast. In the second case the use of traditional structures would be technically complex and very expensive, compared to the time of exploitation of the reservoir. The situation has prompted the major Oil&Gas companies in developing LNG plants installed on board of ships, known as Floating Liquefied Natural Gas (FLNG) – in which the extracted gas is treated and directly liquefied and transferred to ocean-going carriers, which will load the LNG as well as other liquid by-products (condensate and LPG) and deliver them to the market. The first FLNG facility in the world, owned by Shell and developed by the consortium Technip-France & Samsung Heavy Industries (Korea), will satisfy the Asian market for 25 years. It is the largest offshore facility in the world, for if its total length (top view) is compared with the height of the commonly known skyscrapers, it is as high as the Taipei Tower 101, and more than half of the Burj Khalifa in Dubai.
It represents a major engineering project of a high design complexity and very innovative application, the first of its kind to enter the operational phase. The Italian company Cannon Artes Ingegneria is extremely proud to provide its contribution: design, construction and supply of two water treatment systems to feed the steam generators. The system consists of a condensate treatment unit that removes traces of hydrocarbons present in the condensed steam to be recovered and a demineralization unit which produces ultrapure deionized water. The mechanical and process design have been influenced by the particularly severe conditions of the installation site: a floating vessel that will operate in an area subject to cyclonic events. Thus, the materials selection has to be compatible with the severe conditions of process related to the use of strong acids and bases and with the high humidity and salinity of the environment.
To reduce the assembly time of the plants inside the hull of the ship, the packages have been be supplied fully modularized. A major challenge therefore consists in the mechanical design of the structures (size: 15m x 10m x 7m) that is able to support the weight of the equipment and ensure stability both during lifting and fitting, with an estimated weight of 90 tons, and under operating conditions, with an estimated weight of 150 tons able to withstand multidirectional accelerations. The engineering of Cannon Artes Ingegneria developed specific construction solutions to be able to respect the process guarantees required by the customer even in the presence of significant wave motion that could alter the regular flows distribution inside the vessels irreparably compromising the packages performances. The condensate polishing unit produces 71 m /h of deoiled water through three granular activated carbon filters sized at 100% of capacity; two of them work in series while the other one is on stand-by, according to the “merry-go-round” scheme. A concentration of less than 0.2 mg/l of oils and residual hydrocarbons is guaranteed. The demineralization system that treats the mixture of recovered condensate and desalinated water ensures a continuous production of 235 m /h of demineralized water, thanks to the presence of three mixed-bed ion exchangers, containing strong cationic and anionic resin, each designed to treat 50% of the total flow rate. Two exchangers work in parallel, while the third one is on stand-by, ready to replace the first one that goes into regeneration. This process guarantees a specific conductivity of the demineralized water of less than 0.2 mS/cm.
The first unit of Shell FLNG will be followed in the upcoming years by other similar projects for extraction and liquefaction of natural gas in place, especially in Asia-Pacific: always off the coast of northern Western Australia, south of Papua New Guinea and Malaysia. Other projects are related to Guinea Gulf (Africa),