- The key challenge of using LNG as marine fuel is a relatively big space required for cryogenic tanks. When compared with oil fuel, the amount of LNG with equal power content will require 1.9 times as much space. Taking into consideration thermo insulation of the tank this space will be 2.3 times as much as needed for oil fuel. If LNG tanks are installed inside the hull, the required space can be 4-fold larger.
Tankers (as well as railway ferries which have a cargo-free upper deck or have holds without cargo) let solve the problem of gas fuel storage through placing cryogenic tanks on the cargo deck (or in a hold of a ferry) while dry cargo carriers and auxiliary vessels can only offer this space if the volume of cargo tanks or useful underdeck space is decreased. It is a real problem indeed since the endurance of gas-powered ships (not gas carriers which are fuelled by the cargo they transport) does not exceed 10 days amid the deficit of available space.
Possible fuel storage variants include special cryogenic tanks of containerized cryogenic tanks within a standard 40-foot container.
Possible variants of filling the tanks include fuelling from gas carrying tank truck carriers, from a bunkering ship or from a port based bunkering station. For example, new Baltic railway ferry of Project CNF19M with about 1,500 cbm of tanks capacity is supposed to be bunkered from either tank trucks (simultaneously from four trucks, about 200 cbm per hour) or from a bunkering ship (up to 1,000 cbm per hour).
When using containerized cryogenic tanks LNG can be delivered to ships by railway or road transport without conventional bunkering operations. That will only require the replacement of tanks. To take a decision on using containerized tanks it should be taken into consideration that relatively small useful space of containerized cryogenic tanks will mean the necessity for their larger number; that will also require fixing of evaporator units and gas heaters with pipes and fittings for pressure control of gas supplied to gas valve units; replacement of containers at ports will require special lifting facilities.
The global practice offers all solutions for gas fuelling but its application for tankers of mixed sea/river navigation and rescue ships is hindered by absence of bunkering infrastructure.
Absence of infrastructure on the rivers did not let ship owners determine the price of LNG as a marine fuel. For example, 3-4 ago LNG/diesel fuel price ratio was estimated at about 0.50 while today it is estimated at 0.70. It is clear that if the unit price of heavy fuel oil is about 0.60 (let’s suppose it will be 0.80 for low sulphur HFO in the future) and construction cost of gas-powered ships is 10-15% higher as compared with ships driven by heavy fuel, it is not economically reasonable to build, let’s say, gas powered tankers of mixed sea/river navigation. So, it is necessary to debottleneck LNG bunkering infrastructure at inland water ways, otherwise sea and river going ships will continue operating on heavy fuel oil and diesel fuel.
Written at the conference on design of ship structures.
This and other issues will be discussed at the Second Conference “LNG fleet ad LNG Bunkering in Russia” in October 2018.