The world largely depends on oil supplies from potentially politically unstable regions, which can have an adverse effect on fuel security. For some countries, this is a major driver for developing technology for exploitation of local unconventional resources, such as shale oil and gas in USA, and for investing in the development of biofuels, such as ethanol in Brazil and in USA, and biodiesel in Europe.
Finding capital to fund proven fuel saving technologies can be a challenge – even for technologies that pay for themselves in a matter of years. When introducing a new fuel, existing ships may have to be retrofitted because of incompatible machinery. This makes changes a long term investment. For pioneers – owners who take the risk to invest in new technology solutions – unforeseen technical issues often result in significant delays, requiring additional capital. At the same time, bunker costs for certain shipping segments are paid for by the charterer, removing incentives for owners to explore alternative fuels or even fuel efficiency measures.
Patch work regulations, enforced by different government bodies, and lack of standards, have also slowed coordinated actions. Lack of appropriate infrastructure, such as bunkering facilities and supply chains, and uncertainty regarding long-term availability of fuel are additional barriers for the introduction of any new fuel.
Owners will not start using new fuels if an infrastructure is not available, and energy providers will not finance expensive infrastructure without first securing customers. Breaking this deadlock will require a coordinated, industry-wide effort and the political will to invest in the development of new infrastructure. Overview of potential alternatives Over the next four decades, it is likely that the energy mix will be characterised by a high degree of diversification.
LNG has the potential to become the fuel of choice for all shipping segments, provided the infrastructure is in place, while liquid biofuels could gradually also replace oil-based fuels. Electricity from the grid will most likely be used more and more to charge batteries for ship operations in ports, but also for propulsion of relatively small vessels. Renewable electricity could also be used to produce hydrogen, which in turn can be used to power fuel cells, providing auxiliary or propulsion power. If a drastic reduction of GHG emissions is required and appropriate alternative fuels are not readily available, carbon capture systems could provide a radical solution for substantial reduction of CO2.
While renewable energy (solar, wind) may have some potential to mitigate carbon emissions, this is not seen as a viable alternative for commercial shipping. Certainly, vessels equipped with sails, wind kites or solar panels may be able to supplement existing power generating systems, but the relative unreliability of these energy sources make them appropriate only for special cases where favourable weather conditions prevail. Liquefied Natural Gas – LNG as fuel offers clear environmental benefits: elimination of SOX emissions, significant reduction of NOX and particulate matter, and a small reduction in greenhouse gas (GHG) emissions.
LNG as fuel is now a proven and available solution, with gas engines covering a broad range of power outputs. Engine concepts include gas-only engines, dual-fuel four-stroke and two-stroke. Methane slip (contributing to GHG) during combustion has been practically eliminated in modern two-stroke engines, and further reductions should be expected from four-stroke engines. On the production side, the recent boom in non-traditional gas (shale) has had a dramatic effect on the market for gas, particularly in North America. Exploitation of shale gas in other parts of the world could also prove to be significant for LNG.
However, the extraction process (hydraulic fracturing or “fracking”) remains a controversial technology, due to growing public concerns on its impact on public health and the environment, regarding both air and water quality. There are currently around 50 LNG-fuelled ships (excluding LNG carriers) in operation worldwide, while another 69 orders are now confirmed. The relatively high capital cost of the system installation can be a barrier in some cases. LNG uptake is expected to grow fast in the next five to 10 years, first on relatively small ships operating in areas with developed gas bunkering infrastructure, where LNG prices are competitive to HFO prices.
Ship electrification and renewables
Recent developments in ship electrification hold significant promise for more efficient use of energy. Renewable power production can be exploited to produce electricity in order to power ships at berth (cold ironing) and to charge batteries for fully electric and hybrid ships. Enhancing the role of electricity on ships will contribute towards improved energy management and fuel efficiency on larger vessels.
For example, shifting from AC to on board DC grids would allow engines to operate at variable speeds, helping to reduce energy losses. Additional benefits include power redundancy and noise and vibration reduction, which is particularly significant for passenger ferries. Energy storage devices are critical for the use of electricity for ship propulsion, while they are also important for optimization of the use of energy on board in hybrid ships. There are several energy storage technologies currently available.
Battery powered propulsion systems are the most popular ones, and they are already being engineered for smaller ships. For larger vessels, engine manufacturers are focussing on hybrid battery solutions. Challenges related to safety, availability of materials used and lifetime must be addressed to ensure that battery-driven vessels are competitive with conventional ones, but the pace of technology is advancing rapidly.
Other energy storage technologies that could find application in shipping in the future include flywheels, supercapacitors, and thermal energy storage devices. Electrification has generated strong interest, particularly for ship types with frequent load variations. Significant growth in hybrid ships, such as harbour tugs, offshore service vessels, and passenger ferries should be expected in the next few years.
Biofuels
Biofuels can be derived from three primary sources: (a) edible crops, (b) non-edible crops (waste, or crops harvested on marginal land) and (c) algae, which can grow on water and does not compete with food production. In addition to having the potential to contribute to a substantial reduction in overall greenhouse gas emissions, biofuels also biodegrade rapidly, posing far less of a risk to the marine environment in the event of a spill. Biofuels are also flexible: they can be mixed with conventional fossil fuels to power conventional internal combustion engines, while biogas produced from waste can replace LNG. Biofuels derived from waste have many benefits, but securing the necessary production volume can be a challenge.
The logistics of collecting and transporting biomass to a processing facility contribute significantly to cost. Algae-based biofuels seem to be very promising, but more work needs to be done to identify processes that would be suitable for efficient large scale production. Experimentation with various types of biofuels has already started on ships, and the first results are encouraging. Concerns related to long-term storage stability of biofuels on board, and issues with corrosion need to be addressed, but the main obstacle to be overcome is related to fuel availability.
Advances in the development of biofuels derived from waste or algae will depend on the price of oil and gas. It is expected that by 2030 biofuels are set to play a larger role, provided that significant quantities can be produced sustainably, and at an attractive price. The world ship fuel consumption today is approx. 400 mio. tonnes per annum. The development of world bio fuel production indicates the challenge for biofuel as a major ship fuel.
Methanol, LPG and other liquid or gaseous fuel options
A number of other liquid fuels can be used in dual-fuel engines. In these engines a small quantity of marine fuel oil is typically used as pilot fuel, to initiate the ignition process, followed by combustion of the selected alternative fuel. Some of the fuels that can be used are Liquefied Petroleum Gas (LPG – a mixture of propane and butane), Methanol, Ethanol, and Di-Methyl Ether (DME). Most of these fuels offer significant reductions of NOX and Particulate Matter emissions, while they are sulphur free and can be used for compliance with ECAs regulations.
Marine engine manufacturers offer dual-fuel engines that can be operated with the fuel options mentioned above. Depending on the type of fuel, special designs for fuel tanks and piping are required. However, these fuels do not require cryogenic temperatures for storage (as opposed to LNG); hence, the fuel tanks and related equipment are simpler and less expensive. In July 2013, DNV released rules for using low flashpoint liquid (LFL) fuels, such as methanol, as bunker fuel. Interest in methanol as fuel for passenger ferries is growing in Sweden in response to the need to reduce NOX and SOX emissions.
Methanol has a relatively low flashpoint, is toxic when it comes into contact with the skin or when inhaled or ingested and its vapour is denser than air. As a result of these properties, additional safety barriers are required by DNV GL. The new mandatory notation LFL FUELLED covers aspects such as materials, arrangement, fire safety, electrical systems, control and monitoring, machinery components and some ship segment specific considerations. Due to the relatively limited availability of all these fuels (compared to oil and gas), it is not expected that they will penetrate deep sea shipping sectors in the near to medium term future. However, they can become important parts of the fuel mix in local markets or specialized segments, such as local ferries or chemical tankers.
Hydrogen
Renewable electricity can be employed to produce hydrogen, which can be utilized to power fuel cells on board ships. However, hydrogen as fuel can be difficult and costly to produce, transport, and store. Compressed hydrogen has a very low energy density by volume requiring six to seven times more space than HFO. Liquid hydrogen on the other hand, requires cryogenic storage at very low temperatures, associated with large energy losses, and very well insulated fuel tanks. Fuel cells are the most commonly used devices to convert the chemical energy of hydrogen into electricity.
When a fuel reformer is available, other fuels, such as natural gas or methanol can also be used to power a fuel cell. Although operational experience has shown that fuel cell technology can perform well in a maritime environment, further work is necessary before fuel cells can compete with existing technologies powering ships. Challenges include high investment costs, the volume and weight of fuel cell installations, and their expected lifetime. Special consideration has to be given to storage of hydrogen on board ships, to ensure safe operations.
The way forward
The introduction of any alternative energy source will take place at a very slow pace initially as technologies mature and the necessary infrastructure becomes available. In addition, introduction of any new fuel will most likely take place first in regions where the fuel supply will be secure in the long-term. Due to uncertainty related to the development of appropriate infrastructure, the new energy carriers will first be utilised in smaller short sea vessels, and small ferries are expected to be some of the first movers. As technologies mature and the infrastructure starts to develop, each new fuel can be used in larger vessels.
At present, LNG represents the first and most likely alternative fuel to be seen as a genuine replacement for HFO for ships. The adoption of LNG will be driven by fuel price developments, technology, regulation, increased availability of gas and the development of the appropriate infrastructure.
The introduction of batteries in ships for assisting propulsion and auxiliary power demands is also a promising low carbon energy source. Ship types involved in frequent transient operations (such as frequent manoeuvring, dynamic positioning, etc.) can benefit most from the introduction of batteries through a hybrid configuration. Moreover, energy storage devices can be used in combination with waste heat recovery systems to optimise the use of energy on board. Cold ironing could become a standard procedure in many ports around the world.
The pace of development for other alternative fuels, particularly biofuels produced from locally available waste biomass, will accelerate, and may soon compliment LNG and oil-based fuels. Indeed, it is likely that a number of different biofuels could become available in different parts of the world between 2020 and 2030. Maritime applications for renewable energy (solar, wind) will certainly continue to be developed, but it is unclear if these will have a significant impact on carbon emissions. It is very likely that in the future there will be a more diverse fuel mix where LNG, biofuels, renewable electricity and maybe hydrogen all play important roles.
Alexandros Chiotopoulos
PULL QUOTE: Recent developments in ship electrification hold significant promise for more efficient use of energy
PULL QUOTE: LNG as fuel is now a proven and available solution, with gas engines covering a broad range of power outputs
