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Finland's Deltamarin and LNG tank specialist Gaztransport & Technigaz (GTT) have developed a portfolio of cargo and passenger vessels designed to save valuable cargo space compared to classic cylindrical-type LNG tank solutions, and to enable the use of LNG bunkers for long ocean voyages. The portfolio includes a container vessel, a pure car and truck carrier (PCTC) and a cruise ship.

During development, each of the vessels was equipped with a modularised GTT membrane tank-type solution, which can be adjusted in size from 1,000 to 5,000 cubic metres, depending on the case vessel. Either one or multiple tanks can be integrated into the ship - the final fuel capacity is a trade-off between the desired cargo capacity and the interval between each bunkering operation.

Deltamarin cites the example of a container ship with a 2,500-cubic-metre (cbm) tank that can travel for 22 days or reach 10,000 nautical miles without refuelling. These figures would ensure that most intra-Asian, intra-European and intra-American trade loops could be sailed with just one bunkering operation.

Other tank sizes - such as 1,000 cbm, 1,500 cbm or 2,000 cbm - offering the same volume efficiency but less cargo space sacrificed are also available, with similar scalable solutions for the PCTC and the cruise ship concepts.

On average, calculations during development showed that only approximately 60 percent of the LNG capacity provided by membrane technology could be accommodated in the same space when using an optimised bi-lobe C-type tank solution. For large fuel capacities, therefore, the project partners say the membrane solution is the most feasible LNG fuel tank solution.

Economics

In order to evaluate whether the concept is financially viable, a scenario calculation was carried out with the following input parameters in which marine gas oil (MGO) was defined as a reference level:

- Case vessel: 8,000-CEU PCTC
- Required LNG endurance: 15,000 nautical miles
- Operation profile: 5 trips/year (Asia to Europe route)
- Other alternatives: Use of MGO, HFO + scrubber, LNG Type-C tank
- Fuel price scenario: MGO 600 $/tonne; HFO 400 $/tonne; LNG 350 $/tonne
- Price for CEU slot per voyage: 800 $

Findings: Payback period (years):

Distillates: 0
HFO + scrubber: 2.47 years
LNG membrane: 2.82 years
LNG Type C: 3.53 years

Findings: Net percent value (NPV), 10 years (i=8%)

Distillates: 0
HFO + scrubber: $5,184,989
LNG membrane: $13,031,483
LNG Type C: $9,44,044

The figures indicate that the LNG membrane tank solution would pay itself back in less than three years compared to the reference level, whereas HFO with the scrubber option offers a slightly shorter payback time.

From a net percent value (NPV) perspective, the LNG membrane solution is said to offer the highest value of all options over a ten-year period. This is due to the savings made in both LNG fuel price and the efficient use of hull volume for LNG fuel tanks.

Compared to the Type-C tank solution, a significant amount of valuable cargo space inside the hull can be saved, according to the project partners. The HFO option also has moderate fuel costs but is penalized because of the extra power and sludge handling required by the scrubber operation. With the fuel price scenario, operating with MGO is said to almost double the operating cost over 10 years compared to LNG options.

"It can thus be said that, from a financial point of view too, LNG as fuel and membrane technology as a fuel storage solution are definitely feasible for various projects. However, it must be noted that the analysis is very sensitive to fuel prices and fuel tank capacities," Deltamarin said.