Knud E. Hansen has designed a series of innovative medium-capacity liquified gas/gas bunkering tankers as part of the X-gas project. The flagship design of the project is a 126.5 metre vessel with a cargo capacity of 9000 m3, split between two Type C tanks. Batteries can provide all of the power required during cargo transfer, allowing bunkering to take place emission-free.

The platform is highly customisable and can be tailored to accommodate a range of tank capacities, as well as various containment systems including membrane tanks.

Forward deck house and autodocking

Special feature of the X-gas platform is a low-profile, forward deck house. This enables the vessel to safely approach and pull alongside cruise ships with low-hanging lifeboats. This also minimises the need for ballast during cargo transfer, thereby lowering operational costs. Lastly, the forward deck house allows for larger cargo tanks without impeding bridge visibility.

For improved manoeuvring and safety, the design features two propulsion thrusters aft and two bow thrusters, as well as an autodocking system for alongside mooring.

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Batteries and boil-off gas

The design features a novel and extremely fuel-efficient diesel electric power and propulsion plant consisting of one of the most fuel efficient dual-fuel four-stroke engines available. Integrated with the propulsion plant is an Energy Storage System (ESS) with a lithium-ion battery bank that allows for engine load optimisation with reduced methane slip. The batteries also provide all of the power required during cargo transfer, resulting in no emissions or exhaust in way of the ship being bunkered, an especially important feature for passenger vessels.

Boil-off gas from the cargo tanks is captured and consumed in the dual-fuel engines and the energy surplus generated can be stored in the batteries. Waste heat from the engine cooling water is converted to electric and thermal power through a number of ORC (Organic Rankine Cycle) waste heat units.

As a novel approach, wasted energy captured during operation can be stored in accumulators and released as required to drive absorption chiller and reduce the electrical load onboard. This approach boosts energy efficiency to a very high level.

Energy bay

Another feature of the design is an aft “energy bay” that allows the vessel to provide containers loaded with fuel or stored electrical power to a receiving vessel. It also allows the vessel to provide fully charged battery banks to remote locations ashore, where current infrastructure does not allow sufficient power to be provided.

The principal particulars of the baseline vessel are as follows:

  • Length (overall): 126.5 metres
  • Breadth (moulded): 20.5 metres
  • Design draught: 5.25 metres
  • Service speed: 13 knots
  • Ice class: 1A
  • Deadweight: 4775 tonnes
  • LNG capacity: 9000 cubic metres
  • Crew capacity: up to 16

Knud E. Hansen is already expanding the X-gas platform to accommodate zero-emission fuels such as liquid and compressed hydrogen to meet the growing demand in this sector.