As the shipping industry hunts for ways to slash greenhouse gas emissions, companies are experimenting with cleaner fuels made from cashew shells and other types of biomass to power their vessels. But it is unlikely there will be enough of such biofuels to make much difference for an industry that consumes hundreds of millions of tonnes of fossil fuels each year.
鈥淭he shipping industry has been on this walk through the desert just trying to find stuff that works in their existing infrastructure,鈥� says at MASH Makes, a company in Denmark that has developed a process to turn agricultural waste into fuel.
One option being trialled is a fuel made from the energy-dense liquid in cashew shells, an acid similar to alcohol. at Veritas Petroleum Services, a marine fuel testing firm in the Netherlands, says he knows of at least three shipping operators now testing this biofuel in their ships.
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Up to 30 per cent of the nut shell waste left over from cashew processing is composed of this liquid by weight, and it is already used to produce a variety of chemicals, including ingredients in paint and mortar. As a fuel, it can be blended with higher quality fuel and used in existing diesel engines, although tests have seen it cause corrosion and gum up components, says Bee.
It is crucial for the shipping industry find fuel alternatives. As a whole, shipping is responsible for about 3 per cent of global carbon dioxide emissions, and the UN agency that regulates international shipping has pledged the industry will reach net-zero emissions by the middle of the century. But shipping is moving slowly 鈥� according to the from the Global Maritime Forum, shipping emissions in 2023 were 17 per cent higher than what is needed to stay on track for net zero targets.
Despite experiments with onboard carbon capture or ways to improve fuel efficiency, there are limited options to decarbonise the tens of thousands of large ships on the ocean, which together use more than 300 million tonnes of fuel each year.
Swapping fossil fuels with lower-emissions alternatives is one approach, but not all replacements are equal. Fuels made from green hydrogen, such as ammonia or e-methanol, are promising because they could eventually be produced at large scales, says at University College London. However, they would also require ships to install new engines, and the supply of clean hydrogen is still small.
In the near term, fuels made from plants or other biological sources that can be used in existing engines present a cheaper option. Such biofuels still emit CO2 when burned. But if produced sustainably using waste biomass, their net emissions can be than fossil fuels. 鈥淚n the transition, it makes some sense,鈥� says Smith.
Most biofuels tested in ships so far have been made from animal fat or vegetable oils, says Bee. But he says the shipping industry has had trouble competing with industries like aviation, which can pay higher prices and is in its own search for sources of 鈥渟ustainable aviation fuel鈥�.
This has led shipping companies to experiment with fuels made of other types of waste, such as old car tyres 鈥揳nd now cashew shells, says Bee. 鈥淧eople are really looking at many different biosources to see what can be used.鈥�
At its plant in India, MASH Makes is taking the cashew shells further still, using waste left over from producing the nut shell liquid to create even more fuel by heating it in the absence of oxygen. The resulting bio-oil reduces emissions by 90 per cent compared with conventional fossil fuels, and will be tested in ships operated by the Danish shipping firm Norden later this year, says Andersen.
Another byproduct of this process is biochar, which can be used to enrich soil and sequester carbon. That could help farmers grow more crops on infertile land, in turn generating more waste biomass to use as fuel, says Andersen.
But even with that approach, Smith says he doubts there will ever be enough sustainably produced biomass to fuel more than a small fraction of ships, especially with competition from industries like aviation and carbon dioxide removal. 鈥淭he [shipping] sector is grasping at gimmicks,鈥� he says.
