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Posted: February 28th, 2022

CO2 Emissions and Fuel Alternatives in Shipping

CO2 Emissions and Fuel Alternatives in Shipping
CO2 Emissions and Alternative Fuels in the Shipping Industry

On a dark mountainside, a bright blue glacial lake is surrounded by white ice.

CO2 Emissions and Alternative Fuels in the Shipping Industry

In the context of Alternative Fuel Options adaptation, the future of emissions is unclear.

section I: Table of Contents











Figure 1 shows an example of typical power consumption on a tanker or bulk carrier.

Figure 2: From the National Oceanic and Atmospheric Administration.

Figure 3: Schematic representation of the on-board hydrogen fuel system

Figure 4: Analysis of the cost of fuel

Eco Marine Power’s Energy Sail is depicted in Figure 5.

Figure 6: Area of LNG-fueled fleet based on AIS data from LNGi from January 1st to January 11th, 2018.

Figure 7: Engine with two fuels.

Source: TGE Marine Gas Engineering-Bjorn Munko, LNG 17 Houston. Figure 8: LNG Tank Systems.

Figure 9: The value chain for small-scale LNG production (DNV-GL 2015)

LPG Terminals in Europe (Fig. 10)


The maritime industry is comprised of businesses that are involved in the transportation of goods and people across international waters. As we all know, water makes up the majority of our planet’s surface, accounting for approximately 71 percent of its total surface area, and people have relied on the oceans and inland waterways to transport goods and themselves since the beginning of time. Although transportation is possible, it requires the use of a motor, which is the most common type of engine. The combustion engine, which is used in almost every situation today, generates the thrust that is needed to move things forward.

Figure 1 shows an example of typical power consumption on a tanker or bulk carrier.

A primary application of this technology is to generate energy, which in its proper sequence is used to drive a series of mechanical components to generate thrust. In particular, motors in the shipping industry drive propellers, which help keep the ships moving through our oceans. Despite this, we do not always obtain the much-desired production of energy as a result of this combustion. Many other biochemical constructions are released into the atmosphere as a byproduct of energy production, and these can be harmful to humans and the environment in the short term, as well as posing a long-term threat to the survival of our species and the health of the Earth’s ecosystem as a whole.

CO2, also known as carbon dioxide, is one of the most significant and harmful types of side products produced by all engines that burn fossil fuels. The greenhouse gas CO2 is well-known for its role in the regulation of the Earth’s temperature under normal circumstances, where it works in conjunction with other gases to do so. This occurs because the gases responsible for capturing the radiated heat from the sun that escapes the planet are present in the atmosphere. Because of the artificial increase in those gases caused by human activity, which occurred primarily after the Industrial Revolution of the 1700s, the atmosphere is capturing more heat than it should be in order to regulate the temperature, and as a result, we are experiencing a slow but steady increase in temperature. The acidification of the oceans is another large-scale effect of the increase in carbon dioxide emissions. This increase in acidity has had a negative impact on the life of sea organisms, and if the problem is not addressed, the acidity is expected to rise even further, causing irreversible damage to oceanic life. Climate change is having a devastating effect on the planet, and there is growing awareness among global governments that measures should be taken, and a regulatory framework should be put in place, in order to avoid those catastrophic results. Illustration of carbon dioxide

Figure 2: From the National Oceanic and Atmospheric Administration.

In the shipping industry, the most recent meeting of the International Maritime Organization (IMO) in April 2018 was held with the goal of discussing and developing a framework for reducing Green House Gases (GHG) emissions from ships by the year 2023. As previously discussed, the emissions from the global shipping industry accounted for nearly 3 percent of all anthropogenic greenhouse gas emissions. According to their research, the CO2 emissions are expected to grow at a rate ranging between 50 percent and 250 percent by the year 2050 if everything continues as it is. The International Maritime Organization (IMO) envisions taking immediate action to reduce emissions in three stages, thereby preventing climate change and harm from CO2 emissions. In accordance with the MARPOL and International Maritime Organization conventions, the guiding principles of the strategy to be implemented are non-discrimination and no preferential treatment for any group of people or organizations. One other important aspect is the differentiation of responsibilities among the various countries, as stipulated in the Kyoto Protocol as well as the Paris accord. Three stages in the course of action to be implemented have been determined and will be implemented in a straight timeline. The first is concerned with the period from 2018 to 2023, which will address short-term measures; the second is concerned with the period from 2023 to 2030, which will evaluate the short-term measures and implement what future changes should be implemented; and the third and final is concerned with the period from 2030 onwards, which will officially mark the date that the measures will come into full force and GHG emissions will begin to be reduced as a result of the measures taken into consideration. The ninth category of short-term measures, as presented in the 72nd International Maritime Organization committee, will be examined for the purposes of this project, and we will attempt to present possible solutions within this scope. “Initiate research and development activities addressing marine propulsion, alternative low-carbon and zero-carbon fuels, and innovative technologies to further enhance the energy efficiency of ships, and establish an International Maritime Research Board to coordinate and oversee those R&D efforts,” according to the text of the measures. And finally, in terms of a schedule The International Maritime Organization (IMO) began collecting data in January 2019 and expects to complete data analysis and evaluation by Autumn 2020. Phase three will begin in Spring 2022 and will culminate in a decision step that will be implemented in Spring 2023, according to the IMO.

Aside from the numerous operational and other measures that can be implemented to reduce the CO2 emissions produced by the shipping industry, one of the most important is the investigation of alternative low-carbon or zero-carbon fuel inputs for ship engines, which are currently being pursued. This, on the other hand, must be approached as a long-term project rather than a short-term solution. A large number of researchers have investigated the possibilities for such alternative fuel types over the last decade, and while the implementation of such research will take time, it is considered to be a step in the right direction in terms of long-term sustainability, with the aforementioned measures coming into effect until 2030. LNG, biofuels, hydrogen, LPG, and other liquid or gaseous fuel alternatives, renewable energy, and nuclear propulsion are the alternatives to fossil fuels that have received the most attention and research. Furthermore, the regulation to reduce sulphur emissions by 2020, which will make cleaner fuel types a more economically viable solution in the future, could serve as an additional impetus for the movement toward the research and development of alternative fuel types for the shipping industry.

The ongoing concerns about alternative fuel types are not limited to concerns about the type of fuel and the reduction of emissions. There are numerous implications that must be taken into consideration in order for this to be implemented in the future, or even for this to be actively investigated in the future. The first, and arguably the most important, consideration is the ship storage on board, as well as any technical solutions that must be provided in terms of space and safety for each method of transportation. Second, economies of scale, or, more accurately, the lack of economies of scale, would be another implication. Because petroleum-based fossil fuels have been around for several decades, logistics and supply chain fundamentals have progressed to the point where they can produce significant economies of scale, thereby lowering the cost of those types of fuels by a significant margin. We would be moving toward new and unexplored alternatives, and the costs would be increasing until we reached a point where adoption and research and development reached a point where economies of scale could be achieved once more. After that, ongoing concerns must be evaluated, such as the longevity and economic and financial profitability of such alternatives in the short and long term, as well as the comparison of such alternatives, in order to potentially achieve the most desired outcome in terms of regulatory compliance.

To the best of our understanding at this point, those transitions and alternations are not to be considered in isolation or only as part of the regulatory framework and emissions reduction efforts. As in the nineteenth century, the transition from steamships to stronger fuel engines resulted in a transformation of the entire shipping industry, the transition to alternative fuel types can be viewed in the same light. Furthermore, shipping is not a sterilized organism, and it must be viewed in the context of broader changes in transportation, such as those occurring in the aviation industry and on the continent.


Historically, hydrogen was discovered and separated in the late 18th century, and ever since, scientists have attempted to capitalize on its use as a means of producing energy due to the fact that it was believed to produce significant amounts during the separation process. Many scientists have come to the conclusion that hydrogen holds the key to low-cost, zero-carbon energy production. This conclusion has been supported by extensive research. “Because of the physical and thermodynamic properties of hydrogen, hydrogen-based technologies have the potential to find many applications within a decarbonized global energy system, and it is expected that hydrogen will play a key role in the near future,” the organization believed (Winter and Nitsch, 2012; Andrews and Shabani, 2012; Barreto et. Al., 2003; Ekins, 2010). As previously stated, hydrogen is a potential alternative fuel for ship engines in the future that could be considered. While this is true, it does not rule out the possibility of research and early prototyping in the automotive, aviation, and even the shipping industries.

First and foremost, it must be stated what, if any, implications the adaptation of such a technology will have on ship design in the long run. Because of the unique and differentiated characteristics of hydrogen use as a fuel for combustion engines, the adaptation of such an alternative in the design of the ship is extremely important. More specifically, the increased gravimetric energy density of hydrogen in liquid form allows for a reduction in fuel mass when compared to the current use of fossil fuels in ships of the same size and design. This could prove to be a significant benefit for ship designers because it will reduce the amount of space required for storing the fuel used to generate propulsion, resulting in greater financial benefits for those who adopt the technology. An additional advantage could be observed in the increase in transit speed while maintaining or increasing the carrying capacity and range. Greater transport efficiency means that the ship will generate a higher profit margin when compared to the competition, which will result in a higher economic valuation of such ship designs for cargo transportation by sea.

Another important consideration that must be considered is the ship design modifications that will be required in order to store the LH2 that will be used in the combustion. When it comes to ship modifications, there are significant hydrodynamic considerations that must be researched and taken into account, despite the fact that we do not want to get too technical for the purposes of this paper. The large fuel volumes required for LH2 storage have been demonstrated in other sectors, but in shipping, this has not been demonstrated, despite the fact that it should be carefully considered in the future. The on-board design of a hydrogen-based fuel system for a prototype catamaran is depicted in the following figure as a point of reference. In general, new ship designs would necessitate significant increases in above-water constructions in order to accommodate those storage units, making it difficult to retrofit hydrogen fuel systems into existing vessels.

Figure 3: Schematic representation of the on-board hydrogen fuel system

Another significant distinction between conventional fuel types and hydrogen fuel systems is the ability to store hydrogen at extremely low temperatures, as well as the manufacturing process. Another important difference between carbon-based fuels and hydrogen-based fuels is the temperature at which the fuel is introduced into the engine, whether it is an internal combustion engine or a gas turbine. The viscosity of conventional HFO fuel must be reduced to allow it to pass through the injectors, which necessitates a temperature increase of approximately 120 degrees Celsius. Although in the case of LH2, that is a cryogenic fluid, stored in temperatures of below 20k, additional heating is required to ensure the vaporization and then pass into the combustion engine. Another less obvious but important difference is the fuel path of LH2 in comparison with HFO’s. The high concentration of different materials in the conventional fuels means that during the heating process more purification procedures are needed in comparison with LH2 that in general is a more pure and easy to manipulate type of fuel.

From the shore production of LH2 until the usage in the ship engine the liquified gas will pass many systems. Such systems consist of cryogenic storage tanks, liquid pumps and gas compressors, heat exchangers and long pipes specifically created for the transport of cryogenic gases. At this point in time the main input for an onshore production plant of LH2 is Natural Gas (NG). Although in the future other ways such as electrolysis might emerge for the production of LH2. For the use of NG to produce LH2 the production of CO2 from the plant is almost three times the mass of LH2 produced. Although this side effect of GHG produced is important on onshore production bases there is the technology and the space without the need to retrofit to capture the harmful GHG and reduce the negative effects for climate change.

As discussed above the hydrogen marine fuel systems for ships are very much capable of completely eliminating the emissions of CO2 and SO2 in the atmosphere from ships. Although the problem of those emissions is transferred to the onshore production. This can be controlled by CO2 capture filters but needs further investment and procedures to take place to achieve optimal results. The LH2 as a marine propulsion fuel itself needs large amounts of investment if it is to be adopted by the industry. Another important thing to be stated is that the burn of LH2 as a fuel produces a large amount of fresh water that can be used for the on board needs during the voyage of a ship. Safety issues and measures have to be taken into consideration and regulatory framework has to be discussed and adopted in order for such a transition to be successful.


From what known at this point, power storage and generation predominantly comes from the breakage of the chemical bonds between atoms. On the other hand, nuclear power comes from the fission of large nuclei into smaller products under controlled chain reactions. With this procedure a large amount of heat is produced that in its respective order is moved to a coolant to produce power through basic thermodynamic procedures. Therefore, nuclear energy produced represents a potentially high reward alternative for marine propulsion in terms of CO2 and generally GHG emissions.

When talking about nuclear power generation, there are multiple types of fission, coolants for the reactors and types of fuels to be used in the shipping industry. Although the most common one is the Uranium pressurized water reactor. Uranium in its natural form is compromised by three different elements: U239 at 99.3%, U235 at 0.7% and U234 at 0.005%. The basic component for the production of nuclear energy is the U235 when neutrons are emitted in the process and cooled down by the coolant, in this case water, and in continuation causing further fissions in U235 atoms. The actual power is produced when the energy from the coolant is moved to another steam cycle that then generates electricity or direct shaft power. Although the percentage of U235 is almost 5% it can be enriched to be more productive, although worldwide international regulations do not allow more than 20% enrichment to avoid miss use in nuclear weaponization.

When nuclear reactors started emerging in the end of the previous century those reactors had a small MW production, although moving in the future economies of scale, specialization has payed merits and the production has been increased by much. For the use in shipping though, those reactors are far too large to be accommodated on board and by the increased demand small modular reactors are emerging. Those types of nuclear reactors are not just smaller in terms of MW production but also in size and this could mean potential use in smaller spaces such as a ship. The following graph presents small modular nuclear reactors and their power output compared with the potential needs in MW of vessel types and sizes. In the US currently, the Energy Department in co-sponsoring a program to evaluate the efficiency and financial and economic viability of such projects.

One of the most important considerations when we are considering nuclear power production is the ship design alternations and the regulatory framework that has to be very stringent. The whole procedure of the ship design and build would have to be driven entirely by safety measures in terms of operation, maintenance and decommission of the vessel. Not only the mechanical aspect of the shipbuilding would have to comply with nuclear regulations but also the electro-technical aspects and the naval architecture plans have to comply with extreme safety measure in mind. Those types of safety measure and procedures have to bring to the table all the involved parties in the process such as the builder, the flag states that vessels fly and are willing to undertake such projects, classification societies, insurance makers, the shipowner and international nuclear administration bodies. Furthermore the shipowner has to demonstrate in an independent regulator the ability to operate the ship in a safe manner and report to the International Atomic Energy Agency (IAEA) specifically adapted for marine use. The IMO and IAEA have to work together in the process to create an efficient and strict enough regulatory framework for such nuclear powered ships and assign critical control points in all the involved parties such as the ports and counties themselves. Although this would prove to be challenging because each nation has each own nuclear regulations it is absolutely crucial to be a centralized framework in order to avoid unpredictable scenarios.

The cost of nuclear driver energy and conventional fuel types has also to be examined to provide accurate comparisons between the feasibility of such projects. Nuclear propulsion ships would require a much higher initial capital outlay for all the reasons mentioned previously the operating fuel costs show a much more competitive positioning over conventional oil type fuels as show in the graph below.

Figure 4: Fuel Cost analysis

As it is to be expected because of the high oil price differentiations through the life cycle of a ship the gradient of line that present the conventional fuel costs is higher and more unpredictable than nuclear fuel costs. A move to nuclear powered ships would mean that shipowners become price takers since there would be close to zero control over the cost rates of such equipment and expertise. There are many other costs that have also to be taken into consideration, such as the port dues, through life fuel costs, pilotage costs, insurance and survey costs and most importantly maintenance.

Nuclear propulsion provides clear benefits in terms of CO2 and GHG emissions and the adaptation of naval ships and submarines has shows that also the technology is present and it is practical. Although as stated before there multiple limitations if this technology is to be applies in merchant ships. Crew and staff in general training has to take place, naval architecture of the next generation has to accumulate expertise, regulation formation has to take place and of course disposal measures have to be of extreme importance. For all those reasons this type of transition to nuclear powered merchant ships is somewhat a venture with a medium to long term horizon that needs expertise, regulations and public perception to be formed before any major changes are to adopted.


It’s a common fact that biofuels in the maritime industry are rarely used, although the global biofuel consumption is steadily increasing. However, since biofuels can replace or blend with petroleum diesel with little or no engine modifications, they are a viable alternative, leading many engine manufacturers to develop new technologies to accommodate their adoption in shipping. Indeed, according to experts, biofuels, have a large potential to combat climate change and reduce emissions over their life cycle.

Currently, a variety of ship compatible biofuels are manufactured globally, but the most widely used types of biofuel are bioethanol and biodiesel. Plant oil is another form of first generation biofuels that is mainly used for engines running on heavier diesel oil. Worth mentioning are the second generation biofuels, also called BTL process (Biomass-To-Liquid), which are produced from wastes, residues or novel feedstocks such as algae. The latter are “greener” than the first generation biofuels since they are made from sustainable feedstock. As a result, their impact on GHG emissions is much lower than that of the first generation. However, due to their underdevelopment they are not widely available for use. Another promising type of biofuel are the drop-in biofuels and they definitely show a strong potential to replace part of the fuel mix. These are liquid bio-hydrocarbons which are functionally equivalent to petroleum-derived fuels and fully compatible with existing petroleum structure. Furthermore, experts predict that in the future some sorts of wood-based products, such as pyrolysis oil and synthetic biodiesel will also be used.

MAN B&W Diesel along with Wärtislä, are the engine manufacturers with the biggest experience on biofuels and play an important role in the development of this alternative option in shipping. When using biofuels in vessels, all ship installations such as fuel storage, fuel treatment system, piping, centrifuges need to be evaluated for possible modifications. Once these modifications have taken place, a switch to biofuels is deemed rather uncomplicated (MAN B&W Diesel Press Release, 2007).

As far as the engine types are concerned, there are two main categories which can accommodate the use of biofuel. The low speed two-stroke engine and the medium speed four-stroke engine, both used as main and auxiliary engines. Low speed engines generally drive the propeller shaft directly while medium speed engines may drive the shaft via a generator/electrical motor (diesel-electric propulsion). Various investigations have proven that diesel engines which run on heavy fuel oil can also operate on vegetable oil without any malfunction, whereas engines designed for diesel or gas oil may show problems due to the higher density of the vegetable oil (MAN Diesel, 2006).

On the environmental aspect, use of biofuels not only reduces ship emissions on air quality, due to their zero sulphur content, but also it is a strong option to realize lower carbon intensity in the propulsion of ships. Although the combustion of carbon-based material will always lead to some level of emissions, biofuels can be considered as a renewable energy since the amount of CO2 that is released from their combustion has previously been taken up from the atmosphere as the plant grows, and as a result does not lead to any net increase in the concentration of CO2 in the atmosphere. Greenhouse gas emissions produced by biofuel feedstock are much lower than those produced by conventional type of fuels. However, it should be noted that some fossil-fuel energy is used when producing the raw material for biofuels. Furthermore, biofuels in 100% blends can even lead to an improved HSQE (Health, Safety, Quality, Environmental) result, in the case of spills to the marine environment due to their biodegradable nature, compared to the conventional fossil marine fuels.

On the other hand, it should be noted that biofuels face some significant obstacles as a maritime fuel replacement. Specifically, compared to petroleum-based fuels, their price is higher. First generation biofuels such as vegetable oil-based biodiesel or bioethanol from corn or sugarcane can typically compete with fossil fuels at oil prices around 60 USD/barrel. Second generation biofuels have higher production costs as they are newer and less optimized technologies. On the other hand, the taxation of fossil fuels like MDO and HFO is expected to be increased, fact which could balance out the cost gap.

Furthermore, their insufficient logistic support at ports is another issue which will likely limit them to niche applications involving smaller vessels operating in environmentally sensitive areas. In the above, we should also add the limited expertise in the handling of some biofuels, including long-term stability within the shipping sector. Shipping industry should be encouraged by outstanding examples of biofuel use, such as Maersk Group, who strive to achieve their corporate goal of reducing CO2 emissions by 60% from 2007 levels.

What is more, since most biofuels are extracted from plants and crops they will create in a way shortage of food supply and this situation will lead to a rise in food prices. A possible solution to the above could be the use of waste material from plants as a raw material. In addition, significant land areas need to be devoted to first generation biofuel production if they had to supply the whole marine market. In other words, in order to power the current worldwide fleet of merchant ships, it is estimated that it would require a land area equivalent to that of about twice the size the United Kingdom (MacKay, 2011).

The regulatory framework will also play an important role in the adoption of biofuels since the international maritime sector is currently not covered by any regulatory mandate on GHG emissions. Of course, the latest IMO convention will play a crucial role, but other measures should also assist For example, ship operators could be forced to comply with regulatory mandates and use cleaner fuels around densely populated areas. Ports of Rotterdam and Amsterdam are good examples of this effort as well as the cruise ships in Sydney harbour. Also, in countries such as the Netherlands, biofuels for both road and marine transport are considered as a part of national climate targets.

According to surveys, there is an agreement that biofuels have the potential to replace approximately 10-30% of the fossil fuels currently used. Estimates for the global biofuel production by 2020 are around 115 million tons oil equivalents. In addition, the formation of a global ECA as well as financial incentives in ports for ships that produce fewer emissions would increase the biofuel demand even further. To combat the problem of price competitiveness, biofuel production facilities should be located near major ports or bunker stations. Lastly, the key element for the successful implementation of this alternative, is the availability of marine biofuel in the long term.


More than ever before, shipping companies are exploring mitigation measures to reduce GHG footprints through renewable energy. The motivating factor for that is the abundance of energy sources such as wind, sun, ocean waves and tides, river currents, as well as salinity and seawater temperature gradients. Renewable options can be used in ships of all sizes to provide primary, hybrid and auxiliary propulsion, as well as on-board and on-shore energy use. Renewable power production can also be exploited to produce electricity to power vessels at berth and to charge batteries for fully electric and hybrid ships and in that way contributes towards an improved energy management and fuel efficiency across the shipping sector. A wide range of innovative technologies are being developed for the marine renewable energy generation, with wind, solar and in-stream tidal energy generation facilities, being the most promising.

Several concepts and technologies have been constructed by innovative shipping companies which are expected to produce favourable environmental results using renewable resources. An outstanding example is a “Wind-Solar” ship constructed by Eco Marine (illustrated bellow), which offers both reduced GHG emissions and lower consumption levels. Also, NYK with their “Eco-Ship 2030” is planning to design a futuristic vessel which will produce zero emissions.


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