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Decarbonization options for bulk carriers
The challenge of maritime decarbonization
Although shipping is one of the most efficient modes of transport, with a relatively low carbon footprint per tonne mile, the expectation persists that it should further reduce its carbon emissions. Given that fuel costs already constitute a significant portion of overall operating expenses (OPEX), the adoption of more expensive and less available alternative fuels like LNG, methanol, or ammonia has been particularly sluggish in the bulk carrier segment. While over 50% of vessels across all segments are being ordered with alternative fuel options, orders have been notably lower in the bulk carrier segment. As stated in DNV’s latest Maritime Forecast to 2050 report, while the transition to low- or zero-carbon fuels is necessary for shipping to fully decarbonize, this is unlikely to happen in the short to medium term, so other decarbonization options need to be explored, that will assist in the accelerated adoption of fuels as well. This is particularly true for the bulk carrier segment due to high retrofitting costs, space and operational limitations, crew training issues and bunkering difficulties for vessels in tramp trade.
Rising fuel and decarbonization costs
A tightening regulatory environment means that the cost of conventional fuels is also increasing. DNV estimates that under the European Union’s emissions trading system (ETS), a typical 180,000 dwt Capesize bulk carrier consuming around 11,000 tonnes of conventional fuel and emitting 35,700 tonnes of CO2 annually may face annual additional costs of 3.2 million euros by 2026 at a rate of 90 euros per tonne of CO2. Decarbonization is no longer a choice, and it is crucial that operators across the bulk carrier segment examine all available emissions reduction solutions.
Promising fuel options: Biofuels
Biofuels offer a promising decarbonization option for the bulker segment. They are compatible with existing engines and bunkering infrastructure, requiring minimal adjustments. Biofuels can be used as blends with conventional fuels or as drop-in fuels, helping ships stay IMO-compliant. DNV’s 2023 white paper on biofuels estimates that by 2050, up to 1,300 million tonnes of oil equivalent (Mtoe) of sustainable biofuels could be available annually, with 250 Mtoe needed for full decarbonization. However, current production is low, and shipping will need to compete with other sectors for supply.
Promising fuel options: LNG
LNG is another option for bulk carriers. LNG-ready dual-fuel engines could be viable for the bigger-sized bulk carrier newbuilds, like Capesize, Newcastlemax and VLOC. LNG technology is mature, bunkering is widely available, and the CO2 output is about 20 per cent below that of conventional fuel oil. In addition, synthetic or bio-LNG may be substituted in the future, potentially leading to even more emissions reductions. Methanol has also gained some traction for bulk carriers, especially for vessels that plan to trade in China. As China ramps up the production of green methanol, the availability challenge may be easier.
Going carbon-neutral with reduced energy demand
In DNV’s Maritime Forecast to 2050 report, our prediction is that until 2040, reducing energy consumption is very important to reduce emissions, sustain increased energy costs, and enable the adoption of new fuels. This may be especially valid for the existing bulk carrier fleet, which is typically in tramp trade and therefore has less predictability of where to bunker.
Efficiency and cost advantages through energy efficiency
While fuels like biofuels and LNG can help to reduce the emissions of some vessels in the bulker fleet, energy efficiency is the quickest route to emissions reduction today. About 60 per cent of the existing bulk carrier fleet is less than 10 years old. Unless tightening regulations severely increase the cost penalty of operating older vessels, this means that 7,000 to 8,000 bulk carriers on the water today may still be operating in 2040, the year in which IMO intends to have achieved a 70 per cent reduction in greenhouse gas emissions. For most of these vessels, implementing energy efficiency measures will reduce both emissions and operating costs, while also reducing the dependency on expensive carbon-neutral fuels, many of which also have their own emissions and environmental impacts from production and transport.
Maximizing efficiency – general optimization options
A number of fleet management and navigational measures can be taken to reduce energy consumption and carbon emissions immediately: + Plan voyages to avoid waiting time, power variations and excessive speed. Whether this can be done depends on the charter arrangements + Optimize fleet utilization, always using the right ship for the job + Minimize time spent in port to maximize the time spent with transport work + Use weather routing to optimize fuel usage
Essential, low-investment optimization measures suitable for most bulkers in operation
Low-investment measures for bulk carriers, with payback times ranging between 3 and 4 years, include: + Frequent propeller polishing to protect the surface and maximize efficiency + Frequent hull cleaning to reduce resistance using an active cleaning system; benefit from fleet-wide experience + Better hull coating (low-friction paint) + Auxiliary system optimization to ensure operation at optimum loads: ballast water, hydraulics, steam, low-pressure air etc. This requires crew training to raise awareness. DNV can provide support by visualizing and calculating the best operational modes + Main engine tuning to optimize the combustion of the bunkered fuel, as well as turbocharging tuned towards actual operational loads + Autopilot optimization to avoid wasted energy due to large-angle movements
Machinery and equipment-related retrofitting measures
Each of the listed measures above may yield improvements in the range of 1 to 5 per cent, and payback times of 1–4 years (except waste heat recovery, which may have a slightly longer payback time). When combined, the overall efficiency benefit may amount to as much as 10 to 23 per cent. Waste heat recovery alone could reduce fuel consumption and emissions by as much as 5 to 12 per cent; a shaft generator (power take-off) allows crews to switch off the auxiliary engines entirely when sailing, saving 2–5 per cent of fuel. Electronic auto-tuning and auxiliary engine economizers can each save 0.5-2 per cent of fuel costs and emissions, variable frequency drives 1 to 2 per cent and LED lighting up to 1 per cent.
Hydrodynamic retrofitting measures
+ New propeller optimized for slower speeds + Propeller boss cap fins + Pre-swirl or wake-equalizing ducts + Ultrasonic propeller antifouling system + Full spade rudder; Each of these measures can generate savings in the range of 1 to 5 per cent, for a potential combined benefit between 7.5 and 15 per cent.
Wind-assisted propulsion systems
Wind-assisted propulsion is an attractive option for bulk carriers because of the available open deck surface. As such, bulk carriers are early adopters of wind propulsion technologies, accounting for a majority of the existing installations. All three leading system types – rotor sails, hard wing sails and suction-type systems – are currently being tested and used on bulkers. DNV has issued rules and guidelines, offers verification, and has worked with all major WAPS system manufacturers. To avoid interference with loading and discharging operations, many sail systems can be tilted and retracted. Depending on the sail type, arrangement and vessel size, fuel and CO2 savings between 5 and 15 per cent are achievable. Recently, DNV developed a Recommended Practice on assessing WAPS systems. It is currently in public hearing.
Gearless vessels: Minimizing time spent in port to maximize profitable time and reduce emissions
High-capacity ballast water pumps and ballasting/deballasting operations synchronized with cargo loading and discharging operations enable bulk carriers to load one complete cargo hold at a time without having to shift their position, which is a time-consuming process that is customarily applied to avoid overstressing the hull structure. With synchronized deballasting, loading can proceed faster while protecting the hull structure. DNV’s Easy Loading class notation confirms that the whole structure is robust enough for this continuous loading process, and that the ship’s ballast pumps are capable of transferring the ballast water at high speed.
Geared vessels: Power plant optimization and improved cargo intake
On geared bulk carriers, which discharge their cargo themselves in ports lacking appropriate infrastructure, an optimized power plant will reduce fuel consumption and emissions significantly. Using batteries for “peak shaving” – covering the extra power need during cargo operations – reduces the load on generator sets and their emissions. A shaft generator can charge the batteries efficiently when sailing. Shore power could also be a useful option, although this is not yet readily available in most ports attended by bulk carriers. DNV is contributing to ongoing efforts to establish a standard for high- and low-voltage shore connections and cable management suitable for bulk carriers. Gains can also be attained through optimizing cargo intake. This is good economy while also reducing the carbon footprint per tonne mile. DNV’s Steel Load Planner is a software that enables optimized loading of steel coils on bulk carriers, often resulting in an additional 10–15 per cent coils being loaded compared to conventional methods for load planning.
On-board carbon capture and storage
Several players in shipping, including within the bulk carrier segment, are increasingly viewing on-board carbon capture and storage (OCCS) as a potential decarbonization solution. While this has already been proven to be technically feasible for some vessel types, there is still a lot of road to travel before the required land-based value chain including receiving, storage and processing infrastructure is sufficiently established. Once available, OCCS may present an attractive measure for the existing fleet to reduce its carbon footprint, potentially in combination with the use of biofuels. In addition, the techno-economic feasibility of an OCC system needs to be investigated for each ship type, taking into account machinery space requirements, tank size, route change options, cost of deposit and additional fuel consumption.
Newbuilds – general measures to consider
Optimizing a ship and installing energy-saving technology is much more economical at the newbuilding stage than on an existing vessel. DNV believes that between 2024 and 2035 the most likely course of action for the bulk carrier segment will be energy-efficiency-enhancing design measures such as highly optimized hull lines, propulsion efficiency and engine optimization, energy-saving devices, low-friction paint, wind-assisted propulsion, power take-off and battery power. Designers should account for lower cruising speeds, which today typically range between 9 and 12.5 knots. This should be reflected in the hull shape, engine and propeller design. For a longer-term perspective, dual-fuel engines enabling bulk carriers to operate on low- or zero-carbon fuels like LNG, methanol and ammonia are viable options for newbuilds, initially mainly for bigger vessels in a fixed trade, and eventually also for smaller, geared vessels.
Making energy efficiency a topic of charter negotiations
While cargo owners seek to negotiate the lowest-cost charter contracts, shipowners naturally want to ensure a viable profit. In their negotiations with charterers, bulk carrier owners should stress the importance of ensuring the long-term operability of their vessels. In 2023, DNV introduced the Vessel Technical Index (VTI), which reflects a ship’s technical performance relative to its initial state, thereby eliminating the influence of external operational factors. When used to measure, evaluate and verify the technical performance of operating ships, it allows the industry to determine the efficiency gains from all enhancement measures taken. The VTI is also meant to be used as a facilitator for the adaptation of charter contracts and negotiations so that energy efficiency measures pay off better for shipowners, and charterers can rest assured that efficient vessels are being operated.