1 INTRODUCTION

With over 80 percent of world merchandize trade

carried by sea. Maritime transport is considered the

most attractive option for transferring commodities

[1]. Maritime transport is as essential component of

world economy is responsible for safe delivery of

grains, food, solid and energy raw materials and

consumer goods [2].

Climate change is becoming a growing global

challenge, so reducing greenhouse gas (GHG)

emissions is essential. At the same time, global energy

demand is projected to increase by 28 % between 2015

and 2040. The sea transport sector is the largest user of

fossil fuels. The fuel consumption of shipping is

dominated by three type of ships: oil tankers,

container ships and bulk carriers. Ships carry on-

board thousands of metric tons of fuel for

consumption, which is great source of strong

environmental pollutants such as CO

2, NOX, SOx,

ozone, benzene and particulate matter (PM). At the

same time, the fuel oil price is increasing and public is

becoming more concerned about the environmental

footprint of shipping. Global CO

2 emissions have

exhibited a rapid increase. According to the

International Energy Agency (IEA), CO

2 emissions

from the transportation sector represented 24 % of

global CO

2 emissions during the year 2016. Maritime

transportation is a significant source of anthropogenic

x and NOx emissions, which account for 13% of

global SO

x emissions and 15% of global NOx

emissions. [3].

The contribution of global carbon dioxide emission

from various sources is shown in Figure 1.

Alternative Fuels – Prospects for the Shipping Industry

M. Popek

Gdynia Maritime University, Gdynia, Pola

ABSTRACT: Emissions from the sea transport sector are one of the major contributors to the climate change due

to extreme dependency on fossil fuels. Environmental revolution has pushed shipping to focus significantly on

the potential application of different cleaner fuels and sustainable source of energy solutions. The global

shipping industry is considering alternative fuel options that meet economic feasibility and safety requirements.

There is a variety of alternative fuel types available for shipping, such as liquefied natural gas (LNG), methanol,

hydrogen, ethanol, ammonia and others. For many years, the advantages and disadvantages of using selected

alternative fuels have been analysed from the point of view of sea transport costs. This paper presents the basic

parameters for comparing different fuels, the characteristics needed to adopt alternative fuels in maritime

transport. In addition, it provides an overview of the main technical challenges and drivers for the adoption of

alternative marine fuels assessed through infrastructural, economic and environmental dimensions.

http://www.transnav.eu

the

International Journal

on Marine Navigat

ion

and Sa

fety of Sea Transportation

Volume 18

Number 1

March 2024

DOI: 10.12716/1001.18.01.

Figure 1. Shipping contribution to global CO2 emissions.

Source: [4]

If treated as a country, international shipping

would have been the sixth largest emitter of energy-

related CO

2, just above Germany, with total emissions

in the range of 900 million tons of CO

2 per year [5]. A

various parts of shipping industry are actively

examining a number of ways to reduce emissions,

which are primarily linked to reducing fuel

consumption. In the longer time, the ship industry is

also exploring a number of alternative fuel source. In

April 2018 Marine Environment Protection Committee

(MEPC) adopted a resolution on the IMO's Initial

Strategy for reducing greenhouse gas (GHG)

emissions from international shipping. To address

such concerns, the International Maritime

Organization has proposed measures to reduce

greenhouse gas (GHG) emissions by at least 50% by

2050 [6]. International shipping needs to reduce its

Carbon Footprint (CF) by 40 % by 2030, and by at least

70 % by 2050 compared to 2008. Reductions in carbon

intensity are to be achieved by ships by implementing

the next steps of the Energy Efficiency Design Index

(EEDI) for new ships. On June 17, 2021 the IMO

accepted amendments to MARPOL VI during MEPC

76, introducing provisions for the Energy Efficiency

Existing Vessel Index (EEXI) and a requirements to

reduce the carbon intensity of operations through the

carbon intensity indicator (CII). The vessel’s achieved

EEXI indicates its energy efficiency compared to the

baseline. The ship’s achieved EEXI index will be then

compared to the required energy efficiency index of

the existing ship based on the corresponding

reduction factor expressed as a percentage of the

baseline value of the Energy Efficiency Design Index

(EEDI. EEXI generally applies to any vessel of 400

gross tonnage and above, while CII applies to vessels

of 5000 gross tonnage and above. As of January 1

2023 all ships are required to calculate the achieved

EEXI to measure their energy efficiency and begin

collecting data for annual operational CII. This means

that the first annual reports will be completed in 2023,

and initial CII assessment will be granted in 2024. To

mitigate sulphur emissions, from January 1

2020, the

limit for sulphur in fuel oil used on-board ships

operating outside designed Emission Control Areas

(ECAs) was reduced to 0.50 percent in global seas [7].

This will significantly reduce the amount of sulphur

oxides emanating from ships and should have health

and environmental benefits for the world, particularly

for populations living close to ports and costs. There

is an even stricter limit of 0.10 percent already effect in

ECAs, which have been established by IMO. This 0.10

percent m/m limit applies in the four established

ECAs: the Baltic Sea area; the North Sea area, the

North American area (covering designated coastal

areas of the U. S. and Canada); and the Caribbean Sea

area (around Puerto Rico and the United States Virgin

Islands). Annex VI of the International Convention for

the Prevention of Pollution from Ships (MARPOL)

also establishes limits for NO

x emissions from marine

diesel engines. The IMO emissions standards are

commonly referred to as Tier I, II and III. The Tier I

standards were defined in the 1993 version of Annex

VI, while Tier II and III standards were introduced

Annex VI amendments adopted in 2008.

While the IMO has not entered into any binding

agreements on decarbonisation, the European Union

(EU) is pushing for stricter GHG reduction

regulations within its jurisdiction. For example, the

"Fit for 55" package launched in 2021 aims to

transition the EU maritime sector to decarbonisation

by reducing greenhouse gas emissions by at least 55%

by 2030 compared to 1990 levels. In 2020 The

European Parliament passed a resolution to include

shipping in the European Emissions Trading System

from 2023, with a goal of achieving a 40% reduction in

2 emissions by 2030 [1]. An alternative to reducing

shipping emissions and meeting regulations is to

switch from fossil fuels to new propulsion

technologies, such as alternative fuels. A special topic

of IMO discussion is the needs and possibilities of

countries in the process of energy transformation

towards low/zero –emission alternative fuels for

shipping. The discussion emphasizes that the

decarbonization of international shipping is a priority

for IMO. The IMO Initial Strategy on the reduction of

GHG emissions from shipping sets key ambitions. The

IMO has set two main goals. The first is to reduce

annual greenhouse gas emission from international

shipping by at least half by 2050 compared to 2008

levels, and work towards phasing out GHG emissions

from shipping entirely as soon as possible in this

century [8].The second goal includes The Initial

Strategy, which aims to reduce the carbon intensity of

international shipping (to reduce emissions per

transport work) by at least 40% on average in

international shipping by 2030, aiming to reach 70%

by 2050 compared to 2008. Policy recommendations

comprise of increasing the stringency of operational

carbon intensity standards to encourage the move to

low-carbon fuels; an evaluation of well-to-wake

emissions; the mandating of zero-emissions ships; and

an acceleration of research, design and development.

Activities are also focused on solutions to overcome

barriers to global access to low and zero-emission

marine fuels. Attention is drawn to the current

scarcity of renewable fuels such as hydrogen,

ammonia and methanol. The Initial Strategy will be

revised by 2023.

The paper presents the basic parameters for

comparing of the following alternative fuels: LNG,

hydrogen, ammonia and methanol, the characteristics

needed to adopt alternative fuels in maritime

transport. In addition, it provides an overview of the

main technical challenges and drivers for the adoption

of alternative marine fuels assessed through

infrastructural, economic and environmental

dimensions.

2 CHARACTERISTIC OF ANALYSED FUELS

Currently, the dominant fuel in international shipping

is Heavy Fuel Oil (HFO) (79% of total fuel

consumption by energy value in 2018, based on cruise

allocation). However, significant changes in the fuel

mix have been observed in recent years. It was found

that HFO consumption decreased by approximately

7% (absolute reduction of 3%), while marine diesel

(MDO) and liquid nitrogen (LNG) consumption

increased by 6 and 0.9% (absolute increase of 51 and

26 respectively %). It is estimated that methanol has

become the fourth largest fuel consumption [9].

Different scenarios for climate targets and support for

sustainable and smart mobility strategies assume that

renewable and low-emission fuels should account for

between 6% and 9% of all fuels in international

maritime transport in 2030 and between 86% and 88%

by 2050 to contribute to the achievement of EU-wide

greenhouse gas emissions reduction targets [10].

There is a variety of alternative fuel types available for

shipping, such as gaseous fuels such as LNG, LPG,

methanol, hydrogen and ammonia, biofuels, fuel cells,

among others. The industry must choose the future

marine fuels by evaluating factors such as

environmental impact, technical performance,

availability, cost and infrastructure [11]. Among the

proposed alternative fuels for shipping, IMO has

identified LNG, hydrogen, ammonia, and methanol as

a most promising solution.

2.1 LNG

Natural gas, in the form of Liquefied Natural Gas

(LNG), is the most frequently used alternative fuel in

shipping [12]. LNG has been used to power the diesel

propulsion systems since the delivery of the Provalys

vessel in 2006.

LNG is a colourless and non-toxic liquid, that is

formed when natural gas is cooled to -162°C. During

this process, the volume of gas is reduced 600 times,

facilitating safer storage and transportation. LNG is a

cryogenic liquid that rapidly evaporates, when

exposed to normal atmospheric conditions. Such a

rapid phase transition phenomenon can lead to

critical risks, and the ignition of this flammable gas

mixture can cause catastrophic events in particular

fire and explosion [13]. LNG combustion is as

operationally efficient as HFO. LNG is considered one

of the most viable solutions, because it is the cleanest

fossil fuel used in shipping. The use of LNG as a fuel

for marine transportation will result in environmental

benefits, including a reduction of carbon dioxide

(CO

2) emissions by 25%, nitrogen oxides (NOx) by

90%, sulphur dioxide (SO

2) and fine particles by 100%

[14]. Although LNG is the cleanest fossil fuel

available, but the slippage of methane may offset its

beneficial effect on GHG reduction [15]. In addition,

the global warming potential of natural gas is an

aspect that may reduce the attractiveness of natural

gas as a fuel. The Tables 1 provides an overview of

advantages and disadvantages of LNG.

Table 1. An overview of advantages and disadvantages of

LNG as an alternative fuel

________________________________________________

Advantages Disadvantages

________________________________________________

the fastest growing gas high flammability

supply source globally methane slip- reduction of CO2

technology of gas engines is limited

is mature 40% lower volumetric energy

the cleanest fossil fuel density than diesel

available today limited infrastructure-necessary

high energy density – investment in LNG

approximately 18 % infrastructure

higher than that of HFO treated as a short-term solution,

measurable reduction of especially when the goal is

2, SOx, NOx, and zero-emission shipping

particles emissions

________________________________________________

Source: [13-16]

In marine transportation, there are currently two

different options for operating engines with LNG:

engines that run solely on natural gas, and dual-fuel

engines that either run on a mixture of diesel and

natural gas, or switch between diesel and natural gas

operation.

2.2 Hydrogen

Hydrogen (H

2) is currently an energy option in the

context of decarbonisation in various sectors of the

industry, as it has the greatest potential for zero

emissions, especially when produced from renewable

resources. The use of hydrogen as ship fuel represents

a significant opportunity for clean energy production;

however, it comes with significant implementation

challenges. With the tightening of IMO regulations to

reduce greenhouse gas emissions from ships,

liquefied hydrogen has been recognized as an

alternative to marine fuels.

Hydrogen is a colourless, odourless, tasteless,

nontoxic, relatively unreactive and flammable gas

with a wide flammability range. Hydrogen is

commonly produced by converting natural gas or coal

into hydrogen gas and CO

2. For long-term

sustainability goals, it should be generated from

renewable energy through electrolysis [17]. To obtain

liquid hydrogen, the fuel must be stored at

temperatures below -253°C, which requires a large

input of energy. Hydrogen is flammable over a wide

mixing range with air, the flammability range is from

4 to 74% by volume [18]. Hydrogen (in the gaseous

phase) is lighter than air, which means that in the

event of a leak, the gas will quickly rise and be

diluted, reducing the risk of accidental ignition and

combustion.

Two types of hydrogen are currently being studied

as fuel options: compressed hydrogen and liquefied

hydrogen. These options have the advantage of an

uncomplicated fuel production process, as only one

additional step (liquefaction or compression) is

needed to produce the final fuel. However, the energy

density of these fuels is lower than alternative fuels.

The low energy density makes the use of hydrogen

make the most sense for short shipping application,

where the amount of fuel that needs to be stored on

board is the smallest. The advantage of hydrogen

options is that none of them require reforming or

cleaning on board before use. Some applications of

hydrogen are currently being considered, such as gas

turbines, fuel cells or internal combustion engines in

stand-alone operations [19]. The Tables 2 provides an

overview of advantages and disadvantages of

hydrogen.

Table 2. An overview of advantages and disadvantages of

hydrogen as an alternative fuel

________________________________________________

Advantages Disadvantages

________________________________________________

carbon and sulphur low volumetric energy

free-reduction of emission density – efficient storage

electrolysis process is mature of fuel is high

and available low temperatures below -

very high gravimetric energy 253°C to liquefy

density a flammable gas with very

suitable for relatively short low activation and

distance ignition energy

lack of marine transport

experience

permeability – material

challenges

high fuel cost

high cost of bunkering

infrastructure

lack of safety regulation for

bunkering

a lack of standardised design

and fuelling procedures

________________________________________________

Source:[17-19]

With properly advanced technology, there are not

principal limitations to production capacity that could

restrict the amount of available hydrogen to the

shipping industry.

2.3 Ammonia

In the Full Report of the Fourth IMO GHG Study

2020, it was assessed that ammonia is one of the

promising alternative fuels. Ammonia is an important

option for zero-carbon fuel, because it can be used

either directly as a fuel in internal combustion engines

or as a chemical carrier for hydrogen to be used in

fuel cells [20]. Around 80% of the world’s production

of ammonia is as a widely used chemical and its

production amounts to approximately 200 million

tons yearly and is used as feedstock for the

production of fertilizers [21]. Unfortunately, currently

most of the hydrogen used to produce ammonia is

produced using fossil fuels such as natural gas and

coal, and only a small portion is produced from other

sources such as electrolysis. Although large quantities

of anhydrous ammonia are now being sold and

handled around the world it is not considered one of

the most toxic cargoes handled in shipping. The risk

of fire and explosion is lower than with other fuels

due to its low flammability limit and strict ignition

conditions. Nonetheless, with the right conditions

there exists a potential for ammonia to ignite. Thus, in

principle ammonia is required to be isolated from any

ignition source on-board vessel, when used as a

marine fuel. Small fires involving ammonia can be

extinguished with dry chemicals or CO

2 and large

ammonia fires can be extinguished through water

spray, fog, or foam emissions [22]. The main risks

associated with ammonia are due to its toxic and

corrosive nature. Thus, liquid ammonia allows storing

more energy per cubic meter than liquid hydrogen,

and moreover, without the need for cryogenic

temperature storage - as is the case with liquid

hydrogen. Storing ammonia at -33.4°C is

technologically easier and cheaper than storing

hydrogen at -252.9°C [23]. There is therefore no need

for a cryogenic system to store ammonia. In principle,

therefore, ammonia storage is much less complicated

than hydrogen and LNG. Ammonia can be stored at

ambient temperature (20°C) at a pressure of just 10

bar. Liquid ammonia has a higher energy density

(12.7 GJ/m3) than both liquid and compressed

hydrogen, which benefits fuel storage [24]. Ammonia

can be decomposed to produce hydrogen, and can

also be burned directly [25]. Ammonia offers the

possibility of storing more hydrogen in liquid form

without the need for cryogenic storage (-33.4°C for

ammonia versus -252.9°C for hydrogen), thus NH3 is

a suitable hydrogen carrier [26]. This is an important

consideration because hydrogen is much more

expensive to store than ammonia, despite the fact that

the two fuels have similar energy densities. They have

already begun work on ammonia-powered marine

engines; the first ammonia-powered marine engine is

expected to enter service around 2024 [25]. The Tables

3 provides an overview of advantages and

disadvantages of ammonia.

Table 3. An overview of advantages and disadvantages of

ammonia as an alternative fuel

________________________________________________

Advantages Disadvantages

________________________________________________

carbon free fuel toxic properties-the need for

stored as a liquid at ambient a safety equipment

temperature NO

x and N2O are generated

low flammability-low risk of when burned

ignition slow flame propagation

commonly shipped around speed

the world corrosive nature-

available port loading incompatible with various

infrastructures-commonly industrial materials

traded commodity larger storage tanks

storage is easier and less lack of regulations issues of

expensive than H

2 toxicity, safety, and

experience in handling – storage

established safe handling production reliant on natural

procedures gas

________________________________________________

Source:[20-26]

LNG, liquefied ammonia and liquefied hydrogen

have different physical properties. Analysis has

shown that liquefied ammonia and liquefied

hydrogen were disadvantageous as far as maritime

transportation cost is concerned due to calorific value

and density per unit. However, price competitiveness

of ammonia and liquefied hydrogen may vary in the

future based on policy support for carbon trading

schemes or subsidies [27]. On an equal volume basis,

LNG transports 22.88 MMBTU/m3 of energy, 14.53

MMBTU/m3 of liquefied ammonia, and 9.51

MMBTU/m3 of liquefied hydrogen. In order to

transport the same amount of energy, assuming that

the cargo hold size for LNG is 1.00, a cargo hold about

1.57 times larger and about 2.41 times larger is

required for liquefied ammonia and liquefied

hydrogen, respectively (Fig.2.).

*Volume: Require volume for transporting the same energy

Figure 2. Physical properties of gas fuels. Source: [27].

2.4 Methanol

Methanol (MeOH) is a substance commonly used in

the chemical industry to make consumer and

industrial products, but is also used as an alternative

marine fuel. Methanol is also well known as a fuel for

cars and similar engine applications. Every year over

70 million tons of methanol are produced globally.

Methanol is produced mainly via catalytic

conversion of synthesis gas (CO and H

2) from natural

gas reforming, coal gasification or synthesis from

biomass. Currently, many research and production

initiatives are being undertaken that treat solid and

liquid forms of forest biomass (such as pyrolysis

liquid, forest residues, black liquor, etc.) as raw

materials for methanol production [28]. Methanol can

also be produced by catalytic synthesis of carbon

dioxide (CO

2) and hydrogen obtained via electrolysis.

Methanol was classified, as per European

classification (modified 67/548/CEE and 1999/45/CE

directives), as an easily flammable fluid. Following

the European Classification (modified 1272/2008

Regulation), methanol is classified as a toxic substance

of category 3, and as a hazardous substance for health

of category 1.

There are also fewer challenges in adopting

methanol as a marine fuel compared to LNG or

hydrogen. Investigations shows that the handling and

installation of a liquid like methanol had clear

advantages over gas or cryogenic fuels regarding fuel

storage and bunkering. Because methanol is a liquid,

it is very similar to marine fuels such as heavy fuel oil

(HFO). This means that existing storage, distribution

and bunkering infrastructure could be used for

handling of methanol. Only minor modifications of

infrastructure are required [29]. From an

environmental perspective, methanol is readily

biodegradable in both aerobic and aquatic

environments.

Methanol requires larger storage volumes or more

frequent bunkering as compared to conventional fuel

oils. As with other fuels, methanol's future will be

determined not only by the upscaling of its

production, but also by its availability at various ports

and the future cost of the fuel. The Tables 4 provides

an overview of advantages and disadvantages of

methanol.

Table 4. An overview of advantages and disadvantages of

methanol as an alternative fuel

________________________________________________

Advantages Disadvantages

________________________________________________

liquid at ambient temperature lower volumetric energy

potential of widespread density than diesel

availability central nervous system toxic

retrofitting ships is not fuel

expensive highly flammable – low flash

the same bunkering and safety point, require more

standards as conventional extensive monitoring

marine fuels

easier to store and handle than

hydrogen and ammonia

low investments and

bunkering infrastructure

________________________________________________

Source:[28-29]

3 POTENTIAL AND LIMITING FACTORS

Alternative fuels have great advantages as well as

their own problems. An important aspect of the use of

alternative fuels is the identification of barriers that

hinder their use in maritime transport. The possibility

of using alternative fuels in the maritime sector

strongly depends on the type of fleet, technical

parameters of ships, ship operation, investment costs,

environmental impact and geographical location,

which determines the availability of alternative fuels.

Several important criteria have been identified, which

are used in the selection of alternative fuels (Fig. 3.).

Figure 3. Main aspects important for evaluation of

alternative fuel solutions for shipping

It is recognized that the cost of fuel is the main

criterion for evaluating alternative marine fuels and

that significant increases in fuel costs will be borne by

ship owners, ship operators, shippers and,

consequently, end consumers. The total cost for a fuel

includes the production cost, transportation, storage

cost and possible regulatory costs in the future (such

as carbon tax). Compared to hydrogen and ammonia,

LNG currently has a lower cost, as among alternative

shipping fuels, it is widely available shipping fuel

today [30]. Alternative fuels not only vary in price

among themselves, but also independently vary

considerably from port to port around the world.

Therefore, fleet operators are making decisions not

only about what to bunker with, but also where to

bunker. Available data indicate that estimated prices

for fuels derived from natural gas, such as LNG and

methanol, trough 2030 are associated with less

uncertainty than fuels derived from renewable

sources, including hydrogen and ammonia [31].

Each type of alternative fuel requires specialized

infrastructure for its production, storage, delivery and

combustion at port, terminals and ships. Building and

testing alternative-fuel ships involves large capital

expenditures [32]. The development of alternative fuel

infrastructure is hampered by economic

consideration, as fleet operators choose not to make

the necessary retrofits to ship engines and fuelling

systems and build new vessels, fearing the high cost

of both upgrades and alternative fuel. They are also

concerned about the low availability of alternative

fuels in ports [33]. An important aspect of fuel

infrastructure construction, in addition to capital

investment, is the availability of standards for fuel

quality and production. To ensure the safe operation

of fuels, it is necessary to standardize them.

Parameters such as energy density and storage

volume are important in the selection of alternative

fuels for marine sector, because they affect the

endurance range of ship and the frequency of

bunkering. Alternative fuels with lower volumetric

energy density than HFO require a larger fuel volume

to provide the same cargo work, This either reduces

the volume of space available for cargo transport or

will reduce the vessel’s range between bunkering [34].

Increasing vessel fuel storage capacity is therefore

costly and reduces the amount of space available for

cargo transportation. Different solutions are currently

available or under development to carry out the

fuelling of LNG ships. These differ mainly due to the

availability of LNG supply infrastructures and the

ship type. The LNG bunkering methods currently in

use are truck-to-ship (TTS), ship-to-ship (STS) and

pipeline-to-ship (PTS) [12]. The most widely accepted

LNG bunkering method is to use pipelines to transfer

the fuel from an LNG depot to a receiving point on

ships, known as pipeline-to-ship (PTS). Unfortunately,

there is a lack of infrastructure in the terminals for this

type of bunkering and therefore alternative methods

are used. Hydrogen storage is one of the main

obstacles for its wider application in the marine

sector. It is estimated that new infrastructure would

cost over several billion dollars in the coming decade.

Ammonia is already a widely traded commodity with

established supply chains and availability at most

ports around the world. Compared to hydrogen, there

is an extensive ammonia distribution network, and

port infrastructure is available. At the same time,

possible accessibility problems are pointed out,

particularly in terms of geographic locations for

ammonia bunkering. Methanol as an alternative fuel

solution is a readily available fuel solution as there is

a global production infrastructure and the potential as

a fully renewable fuel of the future. Since methanol is

a well-known and widely used substance, distribution

infrastructure already exists, as well as experience in

handling it. Bunkering infrastructure is also available,

but may not be sufficient given the use of methanol as

a marine fuel.

The shipping industry faces the challenge of

choosing alternative fuels to decarbonize its

operations, while renewable fuels and related

infrastructure remain under development. Shipping

companies choose multiple fuels to diversify. The

most common scenario envisioned by 2050 is ships

simultaneously fuelled by variants of diesel/biodiesel,

methane, methanol and ammonia. This represents a

significant increase in complexity compared to today's

fleet, where simultaneous management of the

consumption of more than one fuel type within a fleet

is rare. Compliance with regulations and practical

needs affect the technological potential of alternative

fuel. Most metals corrode over time when in contact

with fuel. Uncertainty about current and future

marine fleet that may be susceptible to high levels of

corrosion when using alternatives fuels shrouds the

potential for adoption.

Developing a legal framework for the introduction

of alternatives fuels is a challenge and requires both

scientific knowledge and practical information. It is

essential for a systematic and consistent evaluation in

the selection of marine fuels. The ideal marine fuel

will the one with the best properties that coincide

with the concept of sustainable development (in terms

of economic, environmental and social aspects), that

contribute to the goals of decarbonisation of the

maritime transport, while recognizing the pace of

technological development. In addition, there is a

need for international harmonization of safety

standards, as well as national regulations, for both the

production of fuels and their operation on-board ship.

From the environmental perspective, the amount

of emissions generated by the use of a particular fuel

indicates environmental friendliness. The emissions

greenhouse gases and other emitted substances from

fuel production and use have a direct impact on

climate and thus are very important when comparing

the environmental impact of different fuels. However,

the emission associated with any fuel are not limited

to those generated in the process of consuming it. The

production of fuels contributes significantly to the

total gasses emissions and should be considered

together with fuel combustion. A significant portion

of the emissions generated along the entire value

chain of a given fuel is generated during the

transportation phase. Therefore, Life Cycle

Assessment (LCA), which considers environmental

aspects and potential environmental aspects

throughout their life cycle can be used to support

analysis for the whole life benefit of the fuels. There

are two primary factors that make LNG appear to be

an attractive alternative for meeting Annex VI fuel

sulphur content requirements. LNG enables ships to

meet MARPOL Annex VI requirements in global

trade, because LNG's sulphur content is significantly

lower than Annex VI requirements for ECAs areas, as

its sulphur content is significantly lower than Annex

VI requirements for ECAs. In addition, LNG reduces

x emissions to a level that will meet MARPOL

Annex VI requirements. In some markets, natural gas

and LNG are cheaper than high-sulphur marine fuel

oils, based on heating value. Currently, ammonia

faces several barriers before it can be used as an

energy carrier on a global scale. As a result,

ammonia as a fuel still requires further research and

analysis that takes into account all the effects in both

the production and use of ammonia produced by

different methods. First, ammonia should be

produced cheaply. Current methods still rely on

hydrogen production contributes significantly to

climate change. Globally, about 420 million tons of

2 are emitted into the atmosphere during ammonia

synthesis, and it is estimated that ammonia

production accounts for more than 1 % of total

energy-related CO

2 emissions [35. A significant

contribution of the marine sector is only possible with

ammonia produced by electrolysis from renewable

source. All changes in ammonia production and

operation technology must be cost-effective. Burning

ammonia leads to elevated levels of emissions of

nitrogen oxides, which are environmental pollutants,

and nitrous oxide, which is a greenhouse gas. As a

result, ammonia cannot be considered a “greenhouse

gas-free” or environmentally friendly energy source

unless steps are taken to reduce emissions. Ammonia

is also labelled as highly toxic to aquatic organisms

with long-lasting effects. Most liquid ammonia spilled

directly into water, dissolves forming a balance of

mostly ammonium hydroxide and a little ammonia

depending on the pH and temperature of the water.

Dissolved ammonia poses a serious threat to aquatic

organisms, killing most of them in close proximity, as

lethal concentrations can be easily exceeded. The

long-term effects of an ammonia spill are related to

the time required to restore the original state through

the nitrogen cycle [36]. Leaks or incomplete

combustion can contribute to ammonia emissions into

the atmosphere and, consequently, would contribute

to acid deposition and eutrophication, which could

harm soil and water quality. However, with careful

operation and control of the combustion system, these

emissions can be prevented. Currently, hydrogen

produced mainly by steam reforming of natural gas,

which is a fossil fuel. A by-product of this process is

CO2, which is a greenhouse gas. It is estimated that

hydrogen produced from fossil fuels contributes to

global warming at a similar rate to the direct burning

of fossil fuels. In contrast, hydrogen derived from

renewable energy, such as solar power, is

environmentally clean both in its generation and

combustion. The actual CO

2 emissions from burning

methanol result from the carbon content of the fuel as

well as depending on the purity of the fuel. CO

2 from

burning bio-methanol is considered climate neutral

and therefore not considered a GHG gas. CO

2 emitted

from biomass-based fuels is assumed to be removed

from the atmosphere when new biomass is grown to

replace the biomass used to produce the fuel.

Methanol has a much lower environmental impact

in the event of a spill or leak than conventional

hydrocarbon fuels. Methanol in case of spills into the

aquatic environment is fully soluble in water,

biodegradable and non-bioaccumulative. Only very

high concentrations in the environment pose a lethal

threat or affect local marine life. This means that a

methanol spill would cause limited damage to the

environment.

The impact of the use of alternative marine fuels

on human health and occupational safety is

important, as potential problems associated with

alternative marine fuels (e.g., toxicity, flammability,

explosiveness) can lead to occupational health risks

for ship crews and shore personnel. The hazards

posed by the properties of ammonia mean that safety

principles used in the ammonia industry should be

implemented on ships and the crew on board must be

equipped with appropriate chemical-resistant

protective clothing and breathing apparatuses.

There are a number of significant barriers that

need to be overcome before ammonia can be more

widely used in the shipping industry. Ammonia as a

fuel can compete with fertilizers in food production,

which can have serious socio-economic consequences.

The question remains to be resolved: Will ammonia

production be sufficient to meet the demands of

agriculture and the maritime economy? Globally,

ships in operation consume about 300 million tons of

fuel annually. In order for ammonia to completely

replace diesel fuel

its production would have to be

twice as large, or about 550 million tons. This is

because the energy density of ammonia is half that of

diesel fuel. Another important socio-economic issue in

the future may be the need to support the economic

transition after the reduction of coal mining and

exports in the some regions of the world.

4 CONCLUSIONS

Protection of environment and sustainable growth of

international sea transportation is the unquestioned

goal and a common understanding for the countries

as well as various stakeholders of shipping industry.

To achieve the ambitious emission reduction targets

set by IMO and the EU, alternative fuels within the

maritime industry are receiving attention over the

years from state administration, shipping company,

industrial partners and academic researchers. A

successful transition from fossil fuels to renewable

fuels in the maritime sector requires simultaneous

attention to regulation, production, distribution and

ships.

In the search cleaner fuels in shipping, several

solutions to find new alternative fuels that could

replace fossil fuels are currently being explored.

Alternative fuels such as ammonia, methanol and

especially hydrogen are currently being explored by

the maritime sector. Currently, the lack of

infrastructure for alternative fuels is the main obstacle

to the development of alternative fuel-powered

maritime transportation.

The use of LNG provides a readily available

transition fuel for the maritime industry. Of the

alternative fuels analysed, natural gas has the least

potential as a long-term solution. This is due to its

characteristics, as it is susceptible to constraints and

changing prices. It can be concluded that while LNG

allows for air pollution reduction, it is certainly not an

option for decarbonizing shipping.

Hydrogen is the most promising zero-emission

fuel of the future. However, there are still some

barriers and limitations that need to be addressed

before its global deployment. Among others, the need

to develop a production base and distribution

infrastructure, as well as to further improve hydrogen

storage technologies, remain among the key obstacles

at present. Hydrogen is being considered as part of an

intensive energy transition effort, which will only

become profitable when production and demand

increase significantly as costs fall. Methanol and

ammonia are fuels that are cheaper to produce and

easier to store then hydrogen and can be considered

as potential substitutes for it. Both hydrogen and

ammonia have promising potential to replace

conventional fuels, because only hydrogen and

ammonia have the potential for zero carbon

emissions. Moreover, of the alternative fuels,

methanol, hydrogen and ammonia can be produced

using renewable electricity. This is expected to

happen in the future due to increasing global energy

demand and the time required to develop supply

chain and the infrastructure for these alternative fuels.

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