Log-on – Gas fuel, the unanswered questions
The overwhelming message from our recent Gas Fuelled Ships conference in Rotterdam was that LNG fuel is a viable option for ships under IMO Tier III and other strict emissions controls, but there are plenty of problems left to solve.
The biggest of these is the supply and infrastructure, which although not part of the ships and their machinery has a great impact on their operation. Although cost of LNG fuel is expected to come down as that of MDO rises the economics are making more sense, though these are based on forecasts rather than certainties. On-board storage and safety has seen some progress, but as there have been no major accidents to ships carrying LNG, proof has yet to be established.
On the other hand, although the conference gave the message that the uncertainty over gas availability and cost, combined with the traditional conservatism of the industry, meant that dual-fuel engines were the prime movers of choice, not everybody agrees. The week after the event, The Motorship visited Rolls-Royce Marine in Norway, where we heard from Oddbjorn Eliassen, Rolls-Royce Marine president, merchant, that the gas-only engine would always be a better engineering solution than dual-fuel engines.
A gas-only engine can be significantly more efficient, with the Bergen lean-burn option recording figures of 50.3% efficiency, compared with a figure of 45% to 46% for diesels, less for dual-fuel versions which always have to be a compromise between two different technologies.
The single-fuel option also obviates the need for two fuel storage and handling systems, which add to capital cost and complexity, and reduce potential cargo volume. And methane slip – methane being a powerful greenhouse gas – is inevitably greater with a dual fuel engine.
Another consideration, of which we were previously unaware, is the apparent poor transient load performance of dual fuel engines. When a dual fuel engine is operating in gas mode, we were told, it can take some two minutes to respond to changes of speed. If this is the case, it makes the dual-fuel option unsuitable for use in harbours and other close-quarter manoeuvring, because it is in port, rather than on the open sea, when the low NOx, SOx and PM emissions associated with gas fuels are most needed.
So, gas has much in its favour, but, as our conference underlined, we cannot let enthusiasm for new fuels run away with us.
