Until the IMO made its announcement in 2018, the biggest driving factor in marine fuel choice was meeting NOx and SOx targets with the result that LNG was being heavily promoted and for the longer term, fuel cells were seen to be the answer. Today both of these options are still on the table and LNG is finally beginning to become accepted, albeit several years later than initially thought.
As for fuel cells, R&D work is still ongoing but there is a discernible surge of support for retaining internal combustion engines as the propulsion system of choice but running on fuels not previously used to any great extent in marine circles.
Alongside truly carbon-free fuels such as ammonia and hydrogen, bio and synthetic variants of LNG and oil fuels also have their supporters and – more importantly – investors. These fuels are seen by engine makers and the industry as a whole as presenting a simple fix for meeting emission targets because by and large, biofuels are a simple drop in replacement or complement for current fossil fuels.
Biofuels are, as the name suggests, fuels derived from biological sources. These can be both animal and vegetable in origin and except for vegetable oils such as rapeseed and palm oil for example are usually produced from waste or by products of processing. Waste can also include used culinary oils.
The price of coming clean
Although experience of using biofuels in ships is limited, its use ashore is not at all uncommon and several power stations using engines very similar to those in ships have been burning a variety of biofuels for decades. Kai Juoperi, Chief Expert Engine Fluids at Wärtsilä highlights that the company has a long history with biofuels going back to testing rapeseed-based fuels in the 1990s.
There are currently several projects running in Europe producing and providing biofuels for ships but these are only on a small scale and certainly not an immediate option to ending fossil fuel use other than for a handful of vessels. Scaling up production could be the biggest hurdle to making biofuels a perfect choice to help shipping meet the IMO’s reductions.
Although there are bio versions of heavy fuel oil, most biofuel produced is the equivalent of distillate fuels and is in heavy demand for road, rail and other shore uses. That does mean that competition for product is likely to put shipping at a disadvantage as automotive fuels tend to have a higher price than marine fuels of similar grade. Conceivable the cost could be between two and three times that of a fossil fuel equivalent.
If biofuels are to become a large part of the marine fuel mix it is likely to be as part of a blended product with fossil fuels making up the majority. Mikael Wideskog, Director Sustainable Fuels and Decarbonisation at Wärtsilä, explains that EU rules already allow as much as 7% biofuel in a blended fuel but there is nothing to stop parties agreeing to even higher ratios.
Counting carbon not straight forward
From the environmental impact perspective, the exhaust of a ship burning a biofuel equivalent of an oil fuel will be almost identical in chemical content to conventional oil fuel. The decarbonisation potential attributed to biofuels comes as a result of the idea that emissions will be absorbed by new crops used to make the next batch of fuel.
However, others will argue that this is too simplistic, and a fairer comparison would take into account all of the raw material, production process and cultivation footprint of the fuel and compare to the well to wake figure for fossil fuels.
Although biofuels are considered to be carbon-neutral either entirely or partially by some nation states and regional bodies, they are not yet recognised as such when it comes to assigning an EEDI rating to ships. This is because, unlike pure gas burning vessels, it cannot be known if the operator will run the ship on biofuels, fossil fuels or a combination. The potential for confusion is even more present in vessels with a dual-fuel engine that might burn LNG, ammonia or hydrogen at some point in its life.
Early biodiesels were not without problems especially those of animal origin and although issues of combustibility have largely been overcome some issues remain and some care is needed. Of most importance is managing fuel use so that storage time is kept as short as possible.
This is necessary to avoid contamination with water and also because some biofuels suffer from accelerated oxidation leading to increased acidity. This is less of a problem with hydrotreated biofuels.
When it comes to biogas which is an alternative to LNG, the problems are actually less than with LNG from a fossil source. This is because biogas is methane derived from decaying organic material including food waste and even sewage and the production process ensures that the resulting fuel is purified to a greater degree than fossil-based gas fuels.
Unlike some of the biodiesels which can cause blockage of fuel lines and injectors, biogas is considered a much cleaner fuel and engines run particularly well on it. The same is true of synthetic natural gas which is methane formed by a chemical process. It is also possible to further react synthetic natural gas to LPG which may be a better choice for marine fuels because it does not require such extreme low temperature for storage.