LNG – here to stay, but not the only solution

15 Dec 2011
A packed conference room at the top of the Inntel Rotterdam Centre Hotel heard the arguments for and against LNG as a fuel for ships

A packed conference room at the top of the Inntel Rotterdam Centre Hotel heard the arguments for and against LNG as a fuel for ships

The Motorship’s second Gas Fuelled Ships conference took place in Rotterdam on 26/27 October in Rotterdam and was judged, like its predecessor in Hamburg, a great success.

It was clear from the conference that LNG is now being taken very seriously as a ship fuel. Even last year there was a strong view that gas might be viable for certain short-sea and coastal vessels but was unlikely to catch on in a more general sense, because of the difficulties of onboard storage and setting up a supply infrastructure. Twelve months on, those problems have certainly not gone away, but are definitely being addressed in a serious manner.

The conference was chaired by John Aitken, secretary-general of cross-industry association SEAaT (shipping emissions abatement and trading) and an old friend of The Motorship, having chaired several previous conferences.

The keynote speech was given by Per A Brinchmann, technical vice-president of shipowner Wilh Wilhelmsen. Brinchmann said that his company, as an environmentally-conscious operator of large ships, recognises its environmental responsibilities, and accepts the challenges these bring. He regards the gas-fuelled ship as a major advance in marine engineering technology, somewhat akin to the introduction of the steam ship, and later the introduction of the motor ship. Then, there were different driving forces behind development – now it is the environment that is behind technological change. But shipping companies are in business to make money, and if they can increase profits while still meeting their 'green’ responsibilities, that has to be the answer. He concluded by saying that Wilhelmsen will not be the first to operate large gas-fuelled vessels, but he expects it to be the “first of the last”.

Presentations looked not only at the benefits of gas as fuel for ships, but its disadvantages too. These included potential safety concerns - though it was recognised that tank technology has been around for years without explosions occurring - and the comparative lack of infrastructure, though those giving the presentations seem sure that this can be solved.

The question of methane slip came up in several presentations and in the question and answer sessions. Some presentations continued to regard this as a minor difficulty, though others recognised that it could negate many of the benefits of LNG as a fuel. Methane is the main component of LNG, and although burning the gas as fuel undoubtedly cuts sulphur and particulate matter emissions to near-zero, and NOx to well below IMO Tier III limits, methane is a far more potent greenhouse gas than even carbon dioxide. In fact, official GHG figures put methane as around 20 times more potent than CO2. A number of speakers recognised this, but suggested that taking the overall picture, considering all greenhouse gases, the use of LNG would still cut GHG emissions by some 20%.

The mood of the conference suggested that although gas fuel is certainly attractive in terms of emissions, and depending on future prices – distillate fuel oil is expected to rise, while LNG is predicted to fall in comparison – there are likely to be cost benefits, LNG is not a universal solution. It has to be regarded as an important part of an overall re-think of the use of fossil fuels by ships.

All the usual topics came up for discussion: safety issues, onboard storage, engine technology, economics and refuelling. One interesting session dealt with the emission challenges posed by the use of LNG. Although seen as a solution to emission problems, LNG does bring its own drawbacks, and methane abatement technologies were the subject of a presentation by Ralf Jürgens of Couple Systems, better known as partners with MAN Diesel in dry SOx scrubbing technology. Jürgens concentrated first on methane slip – emission of unburned methane from the engine exhaust, usually resulting from the overlap between opening of the inlet and exhaust valves. An additional cause is incomplete combustion caused by relatively high oxygen concentrations. The other main source of methane emissions from a gas-fuelled ship is boil off gas which occurs as the gas stored in the tanks warms up, increasing the pressure in the tank. In the case of gas carriers, the boil off gas can be used as fuel or re-liquefied, but in ferries or normal cargo vessels it is not viable to do this. Boil off gas is often ignored, but it can be significant; as much as 0.15% of tank capacity per day.

Catalytic oxidisation of methane is technically possible, but the catalysts required – platinum or palladium, for example, are very costly, and very high temperatures are required. When used on dual-fuel engines, even the small amounts of sulphur emitted by the pilot fuel in gas mode can cause deterioration of the catalysts. Thermal post-combustion devices can also be used, for boil off gas as well as exhaust gas, but this to is a complex and largely untried technology.

So ways of dealing with methane emissions exist, but they are complex and demanding and, in the industrial processes where they have been used so far, are of a smaller scale than would be needed onboard ships. If LNG fuel is really to be considered part of ‘green shipping’, said Jürgens, more investigations and trials of methane abatement techniques will be necessary.

Another session looked at future gas-powered technology, and here an intriguing ‘green shipping’ concept was presented by David Surplus of B9 Shipping. B9 is developing a coastal cargo vessel concept that uses a Dyna-rig sail system in combination with spark ignition engines burning liquefied bio-methane derived from organic waste – a truly novel and renewable form of ship propulsion.

The conference concluded with a look at LNG supply, and the final session looked at the dichotomy between the large-scale LNG supply industry and the small-scale ship bunkering industry, suggesting that there need to be ways of bridging the gap between the two, and setting workable industry standards.

In conclusion, it was noted by John Aitken that gas fuelled ships is an exciting, emerging technology, which is somewhat novel in the marine industry because one never knows quite what to expect at an LNG fuel conference. So the future of the event seems assured for some years hence.

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