Although low greenhouse-gas fuel is an excellent idea, when one looks at the details of its implementation, all manner of potential problems arise, according to Anders Valland, research chief at SINTEF.
Valland said that the fuels with the least greenhouse gas emissions were methanol, ethanol, butane, LNG, LPG and propane. He told London’s Vessel Performance Optimisation (VPO) during a tour of his lab in Trondheim, Norway, that, unfortunately, many of these fuels had lower energy densities than heavy fuel oil and marine diesel oil. This meant that they required more space to provide the same energy. “It is more challenging for these fuels to bring the required energy for the operation of larger ships, and those that contribute the highest emissions,” he said.
So, while liquid hydrogen from renewable energy was one of the cleanest fuels, it had a very low energy density and a large storage volume. “If you have low energy density fuel, you will probably only be able to carry enough for one or maybe two legs of your journey. This means coming into port with low fuel supply,” he said.
One implication of this would be that, instead of a supplier knowing that a ship would call at the port offering the cheapest fuel, “if you change this and say that any vessel coming into port is going to have to refuel, you put him into a seller’s market rather than a buyer’s one”.
He added that there were “also consequences if ships have to refuel much more often than they do today. We already have congested harbours that will become even more congested. Fuel stations will pile up because of this.”
Meanwhile, although LNG contains no sulphur and emits very low levels of CO2, it releases unburned methane, and this had led to widespread debate as to whether LNG was a long-term sustainable fuel suited to achieving the IMO’s 2050 target, LNG is also twice the volume compared to the same energy stored in the form of heavy fuel oil.
Although hydrogen is “clean”, Valland observed that “80% of hydrogen production is from natural gas. It means there really are a lot of carbon emissions”, adding that “the overall emissions of fuels depends on how you produce it. At the moment there are no zero greenhouse gas fuels on a well to wake basis. LNG is produced in much higher quantity than what is currently used by shipping. In contrast, the production of methanol and hydrogen would need to increase to meet shipping’s energy needs.” Valland noted that, although about 70,000 of the 90,000 ships in the global fleet could adopt alternative propulsion solutions, the other 20,000 ships were the biggest emitters and are least suited to alternative fuels and propulsion systems.