Amid a bewildering range of alternative fuels, methanol is emerging as a viable option for the next generation of OSVs
Projected growth in the volume of shipping over the next decades means that the OSV industry has no time to lose in the race against curbing emissions – and methanol-fuelled vessels offer the best path right now.
That is the view of Tobias Kohl, director of application engineering for marine, Rolls-Royce Power Solutions, who explored the available alternative fuel options for offshore vessels at Riviera Maritime Media’s Offshore Support Journal Asia Conference in Singapore in October. During his presentation, OSVs of the future: next generation designs for alternative fuels, Mr Kohl said: “Emissions from international shipping could grow between 50% and 250%, mainly due to the growth of the world maritime trade. If we follow this development, we will step into trouble.”
Rolls-Royce’s research shows an alarming rise in CO2 emissions, unless the industry rapidly adopts a range of measures. Under a business-as-usual scenario, emissions would take off and hit well over 2,500M tonnes by 2050. The adoption of a variety of design and technical measures (EEDI), along with different operational measures, would only slow down the rate of increase.
As the group’s predictions reveal, the zero-emission targets set by the IMO and other authorities would be missed by a considerable margin without concerted action. This “emissions gap,” said Mr Kohl, can only be filled by the use of “innovative measures, fuels and technologies.”
Govinder Singh Chopra, managing director for Singapore-based SeaTech Solutions International, agreed with Mr Kohl’s urgent call for action. In a comparison of a range of alternative fuels to VLSFO and MGO, he cited LNG’s ready availability, the relative scarcity of methanol, and the dearth of bio and other e-fuels.
SeaTech is developing with Marco Polo Marine a next-generation service operations vessels (SOV) for the offshore wind industry, whose hybrid battery-based energy storage systems (ESS) are predicted to cut emissions by 15-20% compared to a non-diesel electric-hybrid vessel.
As Mr Kohl explained, Rolls-Royce has embarked on its own decarbonisation plan. By 2023, the most important engine series are set to run on sustainable fuels and by 2025, power will also come from carbon-neutral fuel-cell systems.
Edda Passat, an 81m UT 540 WP design SOV for Østensjø’s Edda Wind, is equipped with a Kongsberg DC grid system and variable speed gensets that, suggests Mr Kohl, will be important in the future. Using this combination of technology, Edda Passat achieves a 21% fuel savings as compared with a conventional AC grid with a fixed frequency.
In another step forward for OSVs, in April 2022 Ørsted and Esvagt signed an agreement to build a SOV that will be powered by batteries and e-methanol-fuelled engines. Due for launch at the end of 2024, the SOV will be put to work on the Hornsea2 windfarm off the UK’s east coast.
“ESS can reduce fuel consumption by 20-25% and NOx emissions by 30-50%”
Looking ahead, Rolls-Royce is anticipating future requirements in next-generation OSVs. The operational profile will be built around multiple modes and extended periods in port and at sea, Mr Kohl believes. To achieve operational safety, they will have “high-propulsion redundancy, in combination with DP1 and DP2 dynamic positioning, which in turn leads to a high percentage of genset low-load operation.”
To satisfy onboard demand for energy from various power-hungry auxiliary equipment, such as cranes and pumps, the distribution and management of electrical power will be a key function. At the same time, operating costs and capital spend will have to be closely managed in a highly competitive market.
All of these functions demand a range of technologies. Diesel-electric propulsion will be teamed with high-speed diesel generator sets providing constant speed, while variable-speed gensets matched with DC grid systems will improve efficiency at times when power is in low demand. The benefits of variable speed gensets have already been seen – Ørsted’s SOV Edda Passat, designed by Rolls Royce and Østensjø Rederi and launched in 2018, has cut fuel consumption by 21%.
Battery ESS will come to the fore too, principally used for peak shaving and standby power. According to a Rolls-Royce analysis, ESS can reduce fuel consumption by 20-25% and NOx emissions by 30-50% while delivering savings on maintenance.
“Zero-emission targets [will] be missed by a considerable margin without concerted action”
In tests with mtu’s S4000 engines, renewable fuels have also proved their importance in the future energy mix. As drop-in fuels, they immediately reduce emissions, by as much as half in terms of particulate matter and NOx by 7%. And in a potentially transformative development, the internal combustion engine could be in for a new life when fuelled by methanol, provided the ship is made methanol-ready in terms of safety and other equipment.
Although shipowners face a bewildering array of options for future and current fuel types, the selection process may not be as challenging as is widely believed. According to Mr Kohl’s analysis of the various options, synthetic diesel offers several advantages because it has the highest energy density and does not require any modifications to the engine. However, synthetic diesel is in short supply and exhaust gas after-treatment systems take up valuable space.
Going through the options
Renewably produced methane is ideal where space is not a critical factor in design considerations and where the vessel’s route takes it close to the essential infrastructure.
Batteries are still considered most suitable for very short distances with low energy demand on tightly scheduled routes that are near to shore, although of course offering the highest energy efficiency and zero local emissions.
Ammonia, although a genuine zero-carbon solution, suffers from several disadvantages at present, notably high toxicity that will hamper official approval. Another zero-carbon solution, hydrogen, will be confined to short to medium routes where space is not critical.
Coming out a clear winner is methanol. Provided the production infrastructure for green and blue methanol is developed, it is highly versatile, able to be used with fuel cells and has “excellent compatibility” with internal combustion engines. “It’s a liquid and clean fuel, good for ship design,” Mr Kohl said. Also, methanol has the advantages of medium cost and energy density.
Another tick in the methanol box is that it is a proven fuel. It is being used in medium-speed engines, class societies are familiar with it, and it is a much-traded commodity that is widely used in the chemical industry. “Methanol is the best alternative in terms of volume and energy density compared to other GHG-friendly fuels,” Mr Kohl said.
In short, for OSVs, methanol is a highly viable alternative to diesel in terms of volume, weight, handling and cost. And when based on biomass or hydrogen, green methanol will play an important part in meeting those official GHG targets.
