Next Generation Cryo-Powered Regas System For Fsru

In recent years, environmental awareness has been on the rise, and liquefied natural gas (LNG) has been attracting attention worldwide, as a clean energy source. Demand for it is expected to increase in the future. However, construction of onshore LNG receiving facilities requires huge amounts of initial investment and a long construction period. Therefore, Floating Storage and Regasification Unit (FSRU) is attracting attention, especially in countries new to importing LNG. FSRU is a facility that not only receives LNG, but also stores and regasifies LNG, as its name suggests. This article gives an introduction to the technical specifications of MOL FSRU CHALLENGER (Fig.1) – the world’s largest FSRU owned and operated by MOL- and the Cryo-Powered Regas System – a new generation FSRU system that MOL has newly developed in collaboration with Daewoo Shipbuilding & Marine Engineering (DSME) which will reduce fuel usage and environmental impact of FSRU operations.

Fig.1 MOL FSRU CHALLENGER

MOL FSRU CHALLENGER

The main specifications of the Vessel are as follows.

  • It is the world’s largest FSRU with 5 Cargo tanks and a volume of 263,000 m3.
  • Nominal send out rate of high pressure natural gas (NG) is 540 MMSCFD (540 million ft3/day).
  • For low send out demand, the system’s high pressure compressor can boost the boil-off gas (BOG) in the tank for sending out to the onshore receiving facility.
  • The vessel’s power generation and propulsion system is powered by dual-fuel diesel power generation + electric propulsion system (DFDE, Dual Fuel Diesel Electric Propulsion).

BASIC OUTLINE OF REGASIFICATION FACILITIES

One of the FSRU’s main aspects is the regasification facility, a plant for regasification of LNG. This section describes the overall flow of the regasification facility. Fig. 2 shows the layout of regasification equipment on the Vessel, and Fig. 3 shows the regasification flow.

Fig.2 Arrangement of regasification related equipment
  • (1) Submerged pumps in cargo tank

FSRU has three types of pumps in each cargo tank. The cargo pump is used for the transfer of LNG between tanks. The stripping/spray pumps are used for tank cooling and dredging of liquid remaining in tanks. The medium-capacity regas feed pump, is used to deliver LNG to the regasification facility.

  • (2) Recondenser/Suction Drum

The Recondenser/Suction Drum is located between the cargo tank and the High Pressure/Small High Pressure pump in the LNG supply flow and serves as a buffer tank for safe operation of the pump. It also serves to re-liquefy part of the BOG generated in the tank.

Fig.3.Regasification Flow

  • (3) High Pressure (HP)/Small High Pressure (SHP) pump

The HP/SHP pump increases the pressure of LNG from 4 bar to about 120 bar to meet the pressure required by the onshore NG receiving facility.

  • (4) HP vaporiser

The HP vaporiser plays a role in regasification of LNG to NG and is the most important equipment for regasification. MOL FSRU CHALLENGER uses a Shell and Tube type heat exchanger as shown in Fig. 4. Sea water is sent to the Shell Side as a heating medium, and the LNG passing through the Tube is heated and regasified to NG. The seawater used in this system is cooled when the LNG is regasified and discharged into the sea (Open Loop Mode).

Fig.4 Shell and Tube Type Heat Exchanger Schematic
  • (5) Low Duty (LD) compressor

The LD compressor supplies BOG from the cargo tank to the DFDE and boiler as fuel. It also supplies BOG to the Recondenser.

  • (6) High Pressure (HP) compressor

The HP compressor increases the pressure of the BOG generated in the cargo tank and sends it out to the land as high-pressure NG. This operation is performed during demand off-season when a minimum amount of NG is required from the receiving facility. By sending out BOG, the accumulated pressure in the tank can be adjusted.

  • (7) Metering unit

The metering unit measures the gas flow with an ultrasonic flow meter and samples the gas components using gas chromatography.

  • (8) Trim water

The trim heater is responsible for heating the NG to the specified temperature, which can be heated by steam if the temperature of the NG is lower than that required by the project.

NON-DRYDOCK FOR 20 YEARS

In the design stage of this vessel, MOL worked hard to achieve 20 years of non-docking and specifications to achieve an annual availability over 98.5%. While regular vessels are regularly docked in the shipyard for repair work, the vessel is designed so that maintenance can be carried out at site. Some of these are introduced here.

  • The equipment and cargo pipe system are separated so that the regasification operation and maintenance of a specific cargo tank can be performed simultaneously.
  • Because the vessel is basically designed to be moored at all times without sailing, the bottom paint for preventing growth of marine organisms is kept to a minimum. On the other hand, extra rust preventive paint is applied since the vessel will not be entering dry-dock for repainting.

CRYO – POWERED REGAS SYSTEM

As mentioned in Section 3.1, MOL FSRU CHALLENGER adopts a direct seawater regasification system (Fig. 5) in which LNG is regasified from LNG to NG by direct heat exchange with seawater. In this system the cold heat of LNG is not utilised.

The new technology Cryo-Powered Regas System (Fig. 6), co-developed by DSME and MOL, recovers the cold heat of LNG to generate power by incorporating an Organic Rankin Cycle (ORC) into the conventional regasification process. Since power is generated during the regasification process, the fuel consumption amount and the CO2 emissions of an operating FSRU can be reduced by up to 55%.

Fig.6 Schematic of Cryo-Powered Reags System

This technology has secured the official approval of the classification society (Fig. 7) and the Cryo-Powered Regas System is ready to be introduced to the market with confidence.

Fig.7 “Approval in Principle (AIP)” certificate acquisition from classification society

In the ORC, by using an organic heat medium with a low evaporation temperature as the working heat medium, it is possible to generate power efficiently through the regasification process.

As shown in Fig. 6, the organic heat medium vaporised by the ORC Vaporiser is used in turbine generators as a working fluid to drive turbines. The higher the temperature of the seawater, the more, turbine inlet pressure can be increased. This improves the efficiency of the ORC and enables the system to obtain greater power. Thus, this technology is best fit for projects in tropical and subtropical regions where the temperature of the seawater is high.

The Cryo-Powered Regas System is believed to be a promising technology, in regions where demand for LNG-to-power projects and environmental awareness are increasing.

SUMMARY

This article gives an outline and description of the FSRU, and its future technology based on knowledge attained through the operation of MOL FSRU CHALLENGER.

The key takeaways are as follows:

  • The regasification process for an FSRU.
  • MOL FSRU CHALLENGER is designed so that 20 years non-dry docking is possible.
  • MOL has developed the Cryo-Powered Regas System for regasification. It has a higher energy efficiency and less environmental impact, forming a basis for market leading, next generation FSRU specification. MOL intends to contribute to the preservation of global environment through eco-friendly technologies.

This article is an editorial contribution by Yuta Morimoto in FSRU Project Team, Offshore Technical Division and Kyohei Oka and Junko Baba in FSRU Team(A), Offshore Gas Project Division, MITSUI O.S.K LINES, LTD. with the cooperation of Daewoo Shipbuilding & Marine Engineering Co., Ltd. Petromin Fuels & Power wishes to express its sincere thanks to its authors.

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