Emissions from Ship Machinery
Emissions
from
Ship
Machinery
Lecture notes by Ingrid Marie Vincent Andersen
Department of Mechanical Engineering
Section for Fluid Mechanics, Coastal and Maritime Engineering
Technical University of Denmark
April 16
st
2012
Table
of
Contents
Table of Contents ....................................................................................................
2
Ship Fuels ................................................................................................................
3
Fuel Oils ......................................................................................................................
3
Gaseous Fuels ............................................................................................................
7
Summary of Existing & Potential Ship Fuels ..............................................................
9
Refinery Processes for Low Sulphur Fuel Oil ...........................................................
10
Marine Engines & the Combustion Process ...........................................................
11
Main Propulsion Engines .........................................................................................
12
Auxiliary Engines ......................................................................................................
12
Power ‐ Take ‐ Off ........................................................................................................
13
Auxiliary Boilers ........................................................................................................
13
Conventional Ship Engines .......................................................................................
14
Gas and Dual ‐ Fuel Engines .......................................................................................
17
Emissions ..............................................................................................................
21
Smoke .......................................................................................................................
22
Nitrogen and Oxygen ...............................................................................................
22
Water Vapour ...........................................................................................................
23
Carbon Dioxide .........................................................................................................
23
Oxides of Sulphur .....................................................................................................
25
Oxides of Nitrogen ...................................................................................................
26
Hydrocarbons ...........................................................................................................
28
Carbon Monoxide ....................................................................................................
30
Particulate Matter ....................................................................................................
31
Ozone .......................................................................................................................
34
Green House Gasses ................................................................................................
34
Other Emissions .......................................................................................................
36
Emission Rates from Ship Machinery ......................................................................
36
Regulation of Emissions ........................................................................................
42
Emission Control Areas ............................................................................................
42
Regulation of Sulphur Content in Fuel Oil ...............................................................
44
Regulation of Nitrogen Oxides .................................................................................
46
References ............................................................................................................
50
2
Ship
Fuels
Today’s ships can be propelled by two kinds of fuel: Conventional liquid fuels that are more or less liquid at standard atmosphere and gaseous fuels that are in gas phase at atmospheric standard atmosphere.
The latter type must be stored cooled or
under pressure in the ship’s tanks, which makes liquid fuels by far the most widespread marine use because of economical and practical reasons.
Fuel Oils
All conventional fuel oils are produced from crude oil.
Lighter fuel oil products called distillates are produced by distilling crude oil.
Residual oil is what is left of the crude oil after the distillation process.
Fuel oils can consist of residual oil, distillate or a mix of both.
All fuel oil consist of mainly hydrocarbons.
The simplest hydrocarbon is methane, CH
4
, which is a gas at standard atmosphere.
For fuel oils the hydrocarbon chains can be of different length.
For light distillates they are short (between 8 ‐ 16 carbon atoms in the chain) but for heavier fuel oils, the chains are longer and can
consist of up to 70 carbon atoms as illustrated in Figure 1.
Figure 1 – Long, simple hydrocarbon chain.
Other kinds of hydrocarbon structures can be present in fuel oils.
Residual oil contains large portions of unsaturated hydrocarbon structures such as asphaltenes where the single carbon ‐ hydrogen bonds are replaced by double or triple bonds as
seen in Figure 2.
Figure 2 – The aromatic hydrocarbon structure of Pyrene, C
16
H
10
, which is a relatively simple asphaltene.
3
For distillates, which consist of short chains the hydrogen/carbon atom ratio is higher than for residual oil, which consists of longer chains as seen in Table 1.
Residual oil Distillates
Carbon [mass%] 85 – 87.2
85.8
– 87.2
Hydrogen [mass%] 10 – 12.1
12.6
– 13.5
Table 1 – Carbon and hydrogen content of residual oil and distillates.
From [1].
Bunker fuel basically fall in two categories: Distillates (also called gas oils) and residual fuels.
Gas oil can be handled under normal standard atmospheric conditions while residual fuels are so viscous they must be heated before they can be pumped.
The basic properties of the two types of fuel are listed in Table 2.
Residual oil Distillates
Viscosity [cSt] 20 ‐ 500 @ 50°C 2 ‐ 10 @ 40°C
Density [kg/m
3
] 940 – 1,010 830 – 900
Table 2 – Basic fuel oil characteristics.
From [1].
Fuel oils can contain other components than hydrocarbons of which some are of significant importance for the ship’s emissions.
Those can be sulphur, metals
(vanadium, nickel, aluminium, silicon, iron, copper, zinc, phosphor and calcium),
nitrogen, oxygen and water.
The sulphur in the oil originates from the crude oil.
The sulphur content of crude oil varies world wide with the geographical location from about 0.1% to 5% by mass.
Fuel produced from crude oil from the Caribbean and Arabian Gulf are the fuels with highest sulphur contents while fuel oil produced from crude oils from the North Sea area, North and West Africa and Alaska have lower sulphur content.
Fuel from South
America and the Far East can have sulphur content below 0.5% while some fuels from the Arabian Gulf top out at 4 ‐ 5% sulphur.
Unless desulphurization methods are used (see Refinery Processes for Low Sulphur Fuel Oil page 10) the sulphur in the crude oil will also be present after the refinery process and will be concentrated in the residual oil.
The desulphurization process is costly and the main reason that sulphur is not removed from most ship fuels.
All the mentioned contaminants become concentrated in the residual oil when the crude oil is refined.
Water can also be present in the fuel along with sediments and other contaminants, but these are normally reduced in the onboard pre ‐ combustion fuel treatment in the centrifugal separators.
Bunker fuels are classified after different standards and can have different trade names.
Most important fuel types are listed in Table 3.
4
Trade name Fuel
IFO 180 Heavy fuel oil with viscosity of 180 cSt
IFO 380
IFO LS 180
Heavy fuel oil with viscosity of 380 cSt
Composition
Mainly
residual oil
Mainly residual oil
Low sulphur heavy fuel oil with viscosity of 180 cSt Mainly residual oil
IFO LS 380
MDO
MGO
Low sulphur heavy fuel oil with viscosity of 380 cSt Mainly residual oil
Marine diesel oil Distillate/residual
Marine gas oil Distillate
Table 3 – Overview over ship fuels.
IFO is short for Intermediate Fuel Oil, which denotes that the fuel is a mix of residual fuel and some distillate oil.
Cheapest fuels listed first.
Additionally marine fuels are standardized after the ISO 8217 standard for distillate
and residual fuels respectively.
Residual Fuel Oils
The most widely used fuel on board ships world wide are residual oils or heavy fuel oil, HFO.
Because all the contaminants become concentrated in the residual oil during the refinery process HFO is inherently a very dirty product.
HFO has much higher content of e.g.
sulphur than any other fuel type and the global average for the sulphur content in HFO is about 2.7% by weight.
Heavy fuel oil is black and consists of long and very long hydrocarbon chains that are tangled into each other and causes the high viscosity.
At ambient temperatures HFO is very viscous and can sometimes be in a solid rather than liquid state.
Therefore it must be heated when stored in the ship’s fuel tanks and before being pumped through piping systems to above 60°C.
The ISO 8217 standard is used for specifying petroleum products and the corresponding ISO 8217 denomination of this fuel type is RMG 35 with the standard data listed in Table 4.
5
Parameter
Density [kg/m
3
] @ 15°C
Viscosity @ 50°C [cSt]
Viscosity @ 100°C [cSt]
Water [% by volume]
Carbon Residue [% by mass]
Sulphur [% by mass] *
Ash [% by mass]
Vanadium [mg/kg]
Flash Point [°C]
Limit
Max
Max
Max
Max
Max
Max
Max
Max
Min
991
380
35
1
18
5*
60
0.15
300
Pour point, Summer [°C]
Pour point, Winter [°C]
Max 30
Max 30
Aluminium + Silicon [mg/kg] Max 80
Total Sediment, Potential [% by mass] Max 0.10
Zinc [mg/kg] ** Max 15
Phosphorus [mg/kg] **
Calcium [mg/kg] **
Max 15
Max 30
Table 4 – ISO 8217:1996 characteristics for RMG 35 residual fuel oil (HFO).
* Sulphur content is locally regulated in sulphur ECAs.
** Fuel must not contain Used Lube Oils (ULO).
From [2].
Distillate Fuel Oils
Distillates are, as the name suggest, distilled from the crude oil, contrary to the residual oils, which are residual products from the distillation process.
ISO 8217
categorizes four types of marine distillate oil:
DMX: Pure distillate oil used in emergency equipment.
DMA: Bright and clear distillate used for general purposes.
Also called gas oil.
DMB: Distillate diesel oil used for general purposes.
May contain trace of residual oil.
DMC: Blended diesel oil used for general purposes.
Contains a significant fraction of
residual oil.
The term gas oil refers to the distillation process where the crude oil is heated; the hydrocarbons become gaseous and then condenses into the distillate (see Figure 3).
MGO is the cleanest fossil fuel oil available for ships today.
According to EU legislation the maximum allowable sulphur content of MGO is 0.1% by mass.
Without local restrictions on the sulphur content MGO can generally contain up to
1% sulphur.
6
Figure 3 – Simplified distillation process for producing petroleum products.
From www.wikimedia.org.
ISO 8217 characteristics of distillate oils are listed in Table 5.
Parameter
Density [kg/m
3
] @ 15°C, max
DMA DMB DMC
890 900 920
Viscosity @ 40°C [cSt], min
Viscosity @ 40°C [cSt], max
Flash Point [°C], min
Pour point, Summer [°C], max
Pour point, Winter [°C], max
Ash [% by mass], max
Water [% by volume], max
Sulphur [% by mass]*, max
1.5
6
60
0
11
60
6
14
60
6
‐ 6 0 0
0.01
0.01
0.05
1.5
0.3
2
0.3
2
Table 5 – ISO 8217:1996 standard for distillate oils.
*Local regulation can dictate sulphur content lower than the standard.
From [2].
Gaseous Fuels
The use of gaseous fuels is limited in ship propulsion today, except for LNG tankers, which utilize the boil ‐ off gas for propulsion.
Different gaseous types of fuels may play a larger role for ship propulsion in the future.
Gaseous fuels for ship propulsion must
be liquefied in order to be stored on board in sufficient quantities.
7
Natural Gas
While the above mentioned liquid fuels consist of many different hydrocarbon components natural gas consists mainly of one: Methane, CH
4
.
Natural gas is found in underground reservoirs or on top of crude oil reservoirs.
This gas typically consists of more than 90% methane, CH
4
.
Other components are short hydrocarbon chains such as ethane C
2
H
6
(1 ‐ 6% by volume), propane C
3
H
8
and butane.
The average composition of natural gas is 94% methane, 4.7% ethane, 0.8% propane, 0.2% butane, 0.3% nitrogen.
After the gas has been processed in a production plant is
consists of almost 100% CH
4
with a very small trace of sulphur.
Natural gas in gas phase is difficult to transport unless pipelines are used, and when stored it takes up enormous amounts of space.
To solve this problem natural gas can be liquefied into Liquefied Natural Gas (LNG).
Before liquefaction the gas is cleaned for other components such as sulphur, dust and water and it then condensed into a liquid at about ‐ 163°C.
The condensation process reduces the volume of the gas down to 1/600 th
of its original volume and makes it possible to transport without the use of pipelines.
The liquefaction process requires much energy and between 5 and
10% of the energy contained in the gas is consumed during the cooling process.
Liquefied gas can not be transported in pipelines but must be transported in cryogenic tanks on trucks, trains and on board ships with specially designed and insulated tanks.
Over long distances shipping is the only way of transporting sustainable amounts of LNG across the oceans.
Methane itself is odorless, colorless, non ‐ toxic and non ‐ corrosive.
The ignition temperature of natural gas is high and explosion risk only exists for 5 ‐ 15% mixtures in air.
Contrary to many people’s impression it is therefore a very safe fuel with a
very small risk of explosion.
Some properties are listed in Table 6.
Parameter
Density
Density
Density
(liquid)
(gas,
(gas,
1
1
atm, atm,
‐ 163°C):
40°C):
430 kg/m
3
1.6
kg/m
3
0.6
kg/m
3
Boiling temperature at 1 atm: ‐ 163°C
Boiling temperature at 10 atm: ‐ 130°C
Ignition temperature: 540°C
Table 6 ‐ Properties of natural gas and LNG.
The European production of natural gas is mostly declining but other places in the
world there are large gas reserves and their distribution is illustrated in Figure 4.
8
Iran
Saudi Arabia
Qatar
United Arab
Emirates
United States
Algeria
Nigeria
Venezuela
Iraq
Rest of the World
Russia
Figure 4 – World’s largest gas reserves by country .
Source: Energy Information Agency.
Petroleum Gas
Like natural gas petroleum gas can be liquefied (LPG) and has many of the same properties such as high resistance to auto ‐ ignition.
Petroleum gas is produced as a by ‐ product from refining of natural gas and exists in two grades: One being predominantly propane and one being predominantly butane.
As ship fuel the use is theoretical since current regulations do not permit the use of LPG as fuel in ships’
engine rooms and there are no LPG fuelled ships in operation.
Summary of Existing & Potential Ship Fuels
The energy from the combustion mainly stems from oxidation of carbon and hydrogen and sulphur in a chemical reaction.
The chemical reaction for the three different components results in different amount of energy (heat) released.
Oxidation of one hydrogen atom results in the release of about four times more heat than oxidation of one carbon atom.
From this it is clear that the fuels with a high carbon/hydrogen ratio have relatively lower specific heating values than fuels with lower carbon/hydrogen ratio as seen in
Table 7.
Fuel Lower heating value [MJ/kg]
40.5
Heavy Fuel Oil (HFO)
Marine
Marine
Diesel
Gas
Oil
Oil
(MDO)
(MGO)
42.8
42.9
Liquefied Natural Gas (LNG) 50
Liquefied Petroleum Gas (LPG) 46.1
Carbon content
[mass%]
0.85
0.875
0.875
0.75
0.82
Table 7 – Lower heating values for marine fuels.
From [3].
9
Because MGO has a higher heating value than HFO less fuel is needed to create the same amount of energy in an engine.
For this study in some cases HFO is replaced with MGO and in that case only 94% of the amount of fuel is needed.
The natural nitrogen content of fuel oils varies.
For HFO it can be between 0.1
‐ 0.8
% by mass and in distillates it is lower than 0.1%.
Refinery Processes for Low Sulphur Fuel Oil
In future marine fuels the sulphur content must be lowered considerably compared to today.
Low sulphur marine fuel can be produced in different ways of which some
are more feasible than others.
Low sulphur fuel oil can be produced from naturally low sulphur crude oil or the sulphur can be removed or partially removed in during the refinery process.
The desulphurization process is costly on both energy and finances.
The removal process on land can however also be of economical benefit, since the sulphur removed during the refinery process can have many industrial applications e.g.
for production of sulphuric acid, paper production, fertilizers, and production of chemicals for insect
and fungus fighting.
The desulphurization process in the refinery is one of the last stages in the refinery process in a so ‐ called catalytic hydro ‐ refining process.
The heated product is passed through a metal ‐ salt catalyst (cobalt ‐ molybdenum ‐ aluminium) under high pressure.
Here the sulphur reacts with hydrogen to form H
2
S which can be removed from the gas by washing.
The H
2
S is burned to form solid S.
Hydrogen must be produced for this process and the production process of hydrogen is very energy demanding.
Furthermore the residual oil complicates the desulphurization process further because deposits of carbon and other substances are formed on the catalysts which subsequently must be changed more frequently.
Normally low sulphur HFO is produced from low sulphur crude oils because content of metals will contaminate and destroy the catalysts used for the desulphurization process [4].
Low sulphur fuel oil can also be produced by mixing fuels with different sulphur contents.
However the mixing of different fuel grades may result in unstable fuels.
Very low sulphur fuel oils such as fuel with 0.1% sulphur content are generally only
possible to produce through distillation.
Both distillation and desulphurization require extra energy and therefore have CO
2
emissions associated with their production.
10
Marine
Engines
&
the
Combustion
Process
Engines for marine use are generally compression ignited two ‐ and four ‐ stroke diesel engines.
From an environmental and economical point of view an important factor is the Specific Fuel Oil Consumption (SFOC, measured in g fuel oil per kWh) of the engine.
This expresses the engine’s fuel efficiency.
Other important factors are the emissions of other species such as NO
X
, SO
X
and PM.
Some factors depend on fuel oil quality and some on the combustion process in the combustion chamber.
The spray pattern and injection timing has great influence on the combustion properties and hereby the fuel consumption and emission rate and will be described here in more detail.
The fuel pattern of an arbitrary diesel engine can be seen in
Figure 5.
Figure 5 – Fuel oil injection and mixture zones.
From [1].
The fuel is injected into the cylinder at very high pressure (1,300 ‐ 1,800 bar) which results in very short injection period and atomization of the injected fuel.
The injection happens when the piston is near the top of the cylinder.
By the time of injection the air in the cylinder is compressed to high pressure (around 200 bar) and so hot that the fuel ignites when injected.
Mixing of the fuel and the air in the cylinder is essential.
Good mixing means that more fuel is exposed to the air needed for combustion.
The high injection velocity created turbulence which serves to mix the fuel and the air.
The time elapsed from the fuel is injected to it ignites is called the ignition delay.
This is because it takes time for the flame to appear and for the pressure to build up in the cylinder.
Delayed ignition can result in high peak temperatures which play an important role for NO
X
formation.
The fuel injection takes place just before the piston reaches Top Dead Center (TDC) and is stated in ° before TDC.
The timing of the fuel injection is another important engine parameter for controlling the formation of different emission species.
For complete combustion of an amount of fuel a certain amount of air is required
(two oxygen atoms for one carbon atom and one oxygen atom for two hydrogen
11
atom).
If the fuel ‐ air mixture is contains exactly the amount of oxygen required to burn all the fuel it is called stoichiometric (excess air ratio λ = 1).
If there is an excess of air the mixture is lean ( λ > 1) and if there is too little air to fully combust all the fuel the mixture is rich.
Generally there is always an excess of air in diesel engines to
ensure proper combustion of all fuel, but in the combustion chamber the mix can be locally lean or rich as seen in Figure 5.
Main Propulsion Engines
The propulsion engines(s) on the ship propel the ship.
On most cargo ships they are coupled to the propeller shaft directly or through reduction gears.
Generally low speed engines are two ‐ stroke engines and medium speed engines and high speed are four ‐ stroke engines.
The average specific fuel consumptions of the three engine
groups (and gas turbines) are listed in Table 8.
Engine Type
Low Speed
SFOC [g/kWh]
170
Medium Speed 190
High Speed
Gas turbines
200
240
Table 8 – Average specific fuel consumption (SFOC) of ship engines on test bed.
It must be kept in mind that the SFOC given by the engine manufacturer originates from the test bed where all conditions are ideal and therefore the actual SFOC in real operation may be considerably higher.
Auxiliary Engines
The auxiliary engines supply all the systems on board needed for running and operating the ship: Cooling pumps for the main engine, general service pumps, ballast pumps, bilge pumps, compressors for starting air, fuel oil treatment systems, electricity on board for lights, navigation etc, thrusters and cargo gear such as ramps and cranes.
In most ships the auxiliary engine are medium or high speed four ‐ stroke engines.
Normally each auxiliary engine is coupled to a generator which generates electricity and this couple is called a generator set or genset.
The same engine type can be a propulsion engine on smaller ships and an auxiliary engine on a larger ship.
Only difference is that it is coupled to a generator instead of a propulsion system.
On ships with diesel ‐ electric propulsion a number of gensets produce electricity for both propulsion and the auxiliary system.
12
Power ‐ Take ‐ Off
Some ships are equipped with shaft generators.
The system is also called Power ‐
Take ‐ Off (PTO) because electric power is generated off the main shaft.
PTO is generally installed on ships operation on longer trips with little speed variation [5].
The electrical efficiency of a shaft generator is typically 90 ‐ 95%.
There are several advantages of using PTO.
The power generating takes place directly off the main engine and thus one, some or all auxiliary engines can be turned off when the ship is under way.
The large main engine sometimes run on cheaper oil
than the auxiliary engines and have lower SFOC, and thus the electricity produced by
PTO will be cheaper than running the auxiliary engines.
Auxiliary Boilers
Exhaust gas boilers are used for producing heat on board for e.g.
hot water, air conditioning and heating of cargo and fuel oil.
When the ship is under way the
exhaust gas boilers are used to utilize the excess heat in the exhaust gas for heating purposes.
When the ship is at berth and the main engines are not running the heating is produced from auxiliary boilers (Figure 6) by burning various kinds of fuel oil.
The use of auxiliary boilers thus adds to the total fuel consumption of the ship.
Figure 6 – Aalborg Industries auxiliary boiler.
Please refer to Emissions from Auxiliary Boilers page 41 for further description of the
emission properties for auxiliary boilers.
13
Conventional Ship Engines
Although electronically controlled engine types have been introduced to the market the recent years many engines are of the mechanically controlled type.
Larger ships typically use two ‐ stroke engines as main propulsion, while smaller ships, e.g.
Ro ‐ Ro ships use four ‐ stroke medium speed engines.
Auxiliary engines are typically four ‐ stroke engines.
Low Speed, Two ‐ Stroke Engines
The definition of low speed is a widely used engine term but not exact.
Generally engines operating with a speed lower than 200 revolutions per minute are designated low speed engines.
Low speed type today always incorporate two ‐ stroke
operation and crosshead type design which makes the engine narrow and rather tall.
A typical tall two ‐ stroke engine with crosshead can be seen in Figure 7.
Crosshead
Figure 7 – MAN Diesel L60MC ‐ C engine layout.
This is a low speed, two ‐ stroke, long stroke crosshead engine.
This engine can be compared to the two four ‐ stroke MAN Diesel engines in
Figure 10 which do not have a crosshead and therefore are considerably lower.
As the name suggests the working cycle of a two ‐ stroke engine consists of two ‐ strokes i.e.
one power stroke for every two piston strokes (or per one revolution).
The downward piston stroke is the expansion stroke and produces the power.
At the bottom of the stroke the exhaust gasses are forces out of the cylinder and replaced by fresh charge air by the scavenge process.
The injection takes place around 10 ‐ 20° before TDC and the combustion lasts 30 ‐ 50°.
At 110 ‐ 120° after TDC the exhaust valves open or the exhaust ports are uncovered by the piston.
The inlet ports are opened about 20 ‐ 30° later.
The inlet ports will be
14
closed as many degrees after BDC as they opened before it and the compression of the air in the cylinder begins again.
The upward stroke is the compression stroke which compresses the air in the cylinder prior to the ignition.
The cycle of a two ‐ stroke engine is illustrated in Figure
8 where the timing of the fuel injection and the opening and closing of intake ‐ and exhaust valves are also illustrated.
Figure 8 – Cycle of two ‐ stroke engine.
Illustration from [6].
Low speed two ‐ stroke engines are the most energy efficient engines on the market and the dominating engine type on large vessel types such as tankers, bulk carriers and container ships.
Some two ‐ stroke engines are very large and can deliver up to 85
MW.
At the same time the low speed two ‐ stroke design is one of the simplest and most reliable engine designs.
For very large bore engines the SFOC can be as low as
154 g/kWh [6] and have an overall thermal efficiency of up to 55%.
If no other data is available the SFOC of low speed engines is estimated to 170 g/kWh.
Two ‐ stroke engines are typically insensitive to fuel oil quality and are normally operated on cheap residual oils.
The engine is coupled directly to the propeller without the use of a gearbox and thus the propeller turns with the same number of revolutions as the main engine.
If the ship is to move in reverse the main engine
must be stopped and started again turning in the opposite direction.
Medium Speed, Four ‐ Stroke Engines
Medium speed engines are primarily used for propulsion of smaller vessels, but also in some ship types such as large cruise ships and Ro ‐ Ro ships.
Marine applications range from one ‐ engine/one ‐ propeller configurations to multiple engines/two propellers mechanical or diesel/electric transmission systems.
The speed range is from 200 – 1,000 rpm.
Four ‐ stroke engines are found in in ‐ line and V ‐ configurations.
One advantage of medium speed four ‐ stroke engines is the lower weight ‐ to ‐ power ratio compared to low speed two ‐ stroke engines and the compactness.
15
Fuel injection takes place about 10 ‐ 20° before TDC and the actual combustion is initiated around 2 ‐ 7° BTDC depending on engine type.
The fuel burns over 30 ‐ 50° during the expansion stroke.
The exhaust valve(s) opens around 120 ‐ 150°.
On the rising stroke after BDC the piston expels the rest of the exhaust gasses.
About 70 ‐ 80°
BTDC the inlet valve(s) opens and the scavenge air blows through the cylinder supplying fresh air.
For turbocharged engines the exhaust valve(s) closes around 50 ‐
60° after TDC to allow for a good throughflow of fresh air.
After BDC the intake valve(s) is closed and then the charge is compressed by the rising piston.
The cycle of
a four ‐ stroke diesel engine is illustrated in Figure 9.
Figure 9 – Cycle of four ‐ stroke engine.
Illustration from [6].
Engine output for four ‐ strokes can be up to 20,000 kW and the engine type is found in configurations varying from 4 in ‐ line cylinders to V20 ‐ configurations.
Four ‐ stroke engines are normally coupled to the propeller via reduction gears and more than one
engine can be coupled to one propeller shaft.
NO
X
emissions are generally lower for four ‐ stroke engines than for two ‐ strokes and thus four ‐ strokes meet IMO NO
X
regulations more easily.
Depending on the engine they can run on HFO or distillates.
If no other data is available the SFOC of medium
speed engines can be estimated to 190 g/kWh.
16
Figure 10 – MAN Diesel medium speed engines L58/64 and L48/60.
The L58/64 engine is the largest four ‐ stroke engine produced by MAN Diesel.
High Speed, Four ‐ Stroke Engines
High speed engines run at a speed of 1,000 rpm or more.
On larger ships high speed engines are only used as auxiliary engines.
All high speed engines are four ‐ stroke engines and most run on distillates.
High speed engines are normally small (< 7,000
kW).
If no other data is available a SFOC of 200 g/kWh can be estimated.
Gas and Dual ‐ Fuel Engines
Three types of engines are capable of burning gaseous fuels.
These engines can be either running purely on gas or they can be dual ‐ fuel capable of running on both diesel fuel and gas.
Here it is implicit that gas is natural gas stored on board as LNG.
The thermal efficiencies of different gas ‐ and gas ‐ diesel engines can be seen in Figure
11.
As seen gas engines are generally not as efficient as diesel engines, which can reach thermal efficiencies about 50%, and they thus have higher SFOC than diesel engines.
17
Figure 11 – Thermal efficiency of dual ‐ fuel (gas ‐ diesel), lean burning spark ignition engines and gas turbines as function of engine load.
Illustration from [6] (originally from Wärtsilä).
Gas Turbines
Gas turbines were first used in naval ships but have now found increasing use in faster crafts such as ferries.
They are very lightweight with a very high power ‐ to ‐ weight ratio and thus size ‐ to ‐ power ratio.
Gas turbines do not necessarily – contrary to what the name suggests – burn gas and most gas turbines run on diesel type fuels.
As seen from Figure 11 the efficiency of gas turbines is smaller than for other marine engine types and gas turbine burn about 25% more fuel per kWh than diesel engines
(SFOC about 240 g/kWh) even though more energy efficient turbine configurations incorporating waste heat recovery have been developed.
The combustion process is more complete and generally cleaner than for conventional engines.
This is due to a high excess air ratio of three times more air than needed to combust the fuel and thus the exhaust contains a lot of fresh air.
The combustion process is controlled more efficiently because it takes place continuously and not momentarily like in a piston engine.
Emissions of NO
X
are lower due to lower peak temperatures and can be as low 1 g/kWh when the gas turbine is operated on natural gas and about 4 g/kWh when running on distillate fuels [1].
PM emissions are low as well – partially due to cleaner fuels.
The working principle of a gas turbine can
be seen in Figure 12.
Figure 12 – Principle of gas turbine.
From [6].
18
Lean Burning Spark Ignition Gas Engines
This engine type is derived from marine four ‐ stroke engines.
The term lean burning refers to the gas ‐ air mixture in the combustion chamber: More air than needed for complete combustion of the gas is available.
The lean burning principle reduces peak temperatures and thus NO
X
production during combustion.
The air/fuel ratio λ of the engine type is about 2.2
and the mixture is ignited by a spark plug like in a gasoline engine.
Bergen Rolls ‐ Royce has manufactured lean burning spark ignition engines for land operation and has now introduced a series of marine engines.
A gas fuelled engine from Bergen Rolls ‐ Royce is illustrated in Figure 13.
Knocking is normally a problem for gas ‐ fuelled engines but be avoided with lean gas ‐ air mixtures.
Compared to a conventional diesel engine meeting IMO Tier II NO
X
limits this engine type is claimed to emit 92% less NO
X
already meeting IMO Tier III
requirements (see page 46).
Today Rolls ‐ Royce deliver lean burning gas engines with output up to 7,000 kW.
Figure 13 – Bergen Rolls Royce spark ignited lean burn gas four ‐ stroke engine type B35:40 with a power range of 2,400 to 8,800 kW and a mechanical efficiency of 49%.
From Rolls ‐ Royce Marine.
Dual ‐ Fuel Engines
Gas ‐ diesel engines are also called dual ‐ fuel engines and are capable of burning both gas and oil.
They are typically used on LNG carriers where the boil off gas from the tanks is used for propulsion and can be run in gas ‐ or oil mode.
When working in oil mode the operation is much like a conventional marine diesel engine with compression ignition.
When working in gas mode the lean, premixed air ‐ gas mixture is ignited by a small pilot injection of fuel instead of a spark plug as seen in Figure 14.
Because dual ‐ fuel engines are compression ignition engines they operate at higher combustion temperatures then spark ignition engines and thus are likely to produce more NO
X
than the lean burning spark ignited engine and gas turbines.
To avoid high peak
temperature and NO
X
production the pilot injection must be very small.
19
Figure 14 – Wärtsilä lean burn dual ‐ fuel engine operation system.
Illustration [6].
For Wärtsilä dual ‐ fuel engines the pilot diesel injection is less than 1% of that on a diesel engine and NO
X
emissions are about 10% of a conventional diesel engine [6].
Knocking (premature self ignition of the gas ‐ air mixture in the combustion chamber during compression) can be a problem for dual ‐ fuel engines.
To solve this pilot diesel injection and the gas ‐ air mixture can be electronically controlled.
Dual ‐ fuel engines are more efficient than gas turbines and lean burning spark ignition engines but not as fuel efficient as mono ‐ fuel engines.
20
Emissions
When fossil fuel is burned in a normal combustion engine a number of different emissions will be present in the exhaust gas.
Depending on the combustion conditions, the engine load, and the type of fossil fuel some or all of the following
emission types will exist:
Free Nitrogen, N
2
Free Oxygen, O
2
Water Vapour – H
Carbon Dioxide –
2
O
CO
2
Oxides of Nitrogen – NO
X
Oxides of Sulphur – SO
X
Hydrocarbons ‐ HC
Carbon Monoxide – CO
Particulate Matter – PM
Traces of other gasses such as argon and micro ‐ pollutants in trace quantities
such as polycyclic aromatic hydrocarbons (PAHs) and dioxins.
The composition of normal exhaust from a ship engine is illustrated in Figure 15.
Figure 15 – Marine Diesel Exhaust Emission Composition.
From [7].
While CO
2
and SO
X
and partly PM are proportional to the amount of fuel burned and the sulphur content respectively the remaining emissions HC, CO and NO
X
vary largely with engine load.
21
Smoke
When talking about emissions from engines one often thinks about the smoke intensity.
Smoke from ships is often visible and can be different in appearance but can also be invisible.
Exhaust plumes from large engines are more visible than from small engines due to the greater diameter of the plume.
At high loads most modern engines give very little smoke, but during low or transient loads, particularly during start ‐ up and maneuvering the turbochargers deliver less air than is necessary for complete combustion and smoke is created.
Smoke is highly undesirable – especially on passenger ‐ and cruise ships.
The colour of the smoke can vary depending on its content of different kinds of emissions such as PM, NO
2
and water vapour.
Black smoke is primarily caused by soot (carbon particles) and there is a clear dependency between the type of fuel used and the smoke formation as heavy fuel oil generates more particles and soot and thus more smoke than distillate fuels.
Blue smoke is a sign of the presence of incompletely burned droplets of fuel ‐ or lubrication oil.
The smoke gets a brownish hue from NO
2
and white smoke is simply a sign of condensed water vapour present in the exhaust smoke.
The white appearance is more pronounced in cold weather
where condensation is greater.
An overview of smoke appearances is found in Table
9.
Smoke colour Source
Black Soot (carbon particles)
Blue
White
Brown
Combustion
Water
NO
2
of vapour
lubrication or cylinder oil
Table 9 – Smoke appearance overview.
Smoke that looks clean or invisible is not necessarily clean.
Light HC components and very small PM are invisible to the eye and therefore even smoke that appears to be clean can contain relatively high rates of HC and PM.
Furthermore the unpleasant looking smoke can be “wet” with oil.
When the gas cools, in or outside the exhaust system, the oily particles condense on colder surfaces.
If this depositing of oily substances happens inside the exhaust system on the ship it can cause a potential fire hazard and increased back pressure.
If it
happens in the atmospheric air the deposits can damage structures and plants.
In the following the nature of the emissions will be describe along with ways to calculate or estimate the content of emission types in the exhaust gas.
Nitrogen and Oxygen
Since free nitrogen (N
2
) and free oxygen (O
2
) are both major components of atmospheric air they are naturally preset in the exhaust gas and are not regarded as
22
air pollutants.
The content of the two gasses in the atmospheric air is about 78.1% nitrogen and 20.95% oxygen (by volume).
Most nitrogen that passes through the engine does not react with oxygen during the combustion process.
A minor portion does however become oxidized to nitrogen oxides which will be described in the following.
A portion of the oxygen in the intake air is consumed during the combustion process
depending on the excess air ratio λ .
Water Vapour
Some water vapour is already present in the intake air, but most of the water vapour in the exhaust is formed during the combustion process of any kind of hydrocarbon when oxygen reacts with the hydrogen in the fuel.
The formation of water vapour, together with CO
2
, during the combustion is illustrated using combustion of the simplest hydrocarbon: methane, CH
4
.
For ideal complete combustion:
CH
4
+ 2O
2
→ CO
2
+ 2H
2
O
The amount of water vapour is thus proportional to the amount of fuel burned.
Water vapour is, in principle, a green house gas (see Green House Gasses page 34) but is not considered as such since the concentration of water vapour in the
atmosphere is normally considered to be constant due to rainfall.
Carbon Dioxide
Carbon dioxide is a product of any combustion process of fossil fuels and is formed during the combustion process as can be seen from the reaction above.
The amount of CO2 from a combustion process depends on the fuel and its carbon content as
described in Emission Rates from Ship Machinery from CO
2
page 36.
The last century the CO
2
concentration (Figure 16) and the average temperature on
Earth have been rising constantly and CO
2 is regarded the major contributor to the global warming.
23
Figure 16 – CO
2
content in the atmosphere measured in ppm from year 1860 to year 2000.
Source:
National Oceanic and Atmospheric Administration (NOAA).
It is an ongoing discussion if the increasing CO
2
content in the atmosphere is mostly natural or caused by human activity.
It is however widely agreed that deforestation and burning of fossil fuels has increased the CO
2
content in the atmosphere the last decade.
The worldwide CO
2
emission is estimated to 770 ∙ 10
9
tons with about 26 ∙ 10
9
tons being man ‐ made [8].
The annual growth rate is estimated to 1.9% which gives a 2008 figure of 8.30
∙ 10
11
tons per year.
Apart from man ‐ made CO
2
natural sources are unusual sun activity, volcanic eruptions and El Niño and other ocean ‐ atmosphere
related phenomena.
Figure 17 illustrates the distribution of the world’s CO
2
emissions in 2007.
Figure 17 – Global CO
2
emissions by country in 2007.
Source: www.wikimedia.org.
The shipping industry is estimated to have emitted 1,054 million tons of CO
2
in 2007, which corresponds to 3.3% of the global emissions.
International shipping (domestic transport excluded) is estimated to emit 847 million tons of CO
2
which corresponds to 2.7% of the global CO
2
emissions in 2007 [9].
24
Apart from its adverse effect as a green house gas CO
2
is generally non ‐ toxic and is not considered an air pollutant.
The gas itself is colourless and odorless.
Oxides of Sulphur
The sulphur content in the fuel determines the content of SO
X
in the exhaust gas.
In the combustion chamber the sulphur present in the fuel is being oxidized into primarily SO
2
.
A much smaller portion, some 3 ‐ 5% is further oxidized into SO
3
.
Together SO
2
and SO
3
are called SO
X
.
The cylinder lubrication oil contains substances that serve to neutralize the sulphur and thus prevent damage from sulphuric acid in the engine.
Only a very small portion of the SO
X
is thus neutralized into calcium sulphate and is considered insignificant.
Generally the sulphur content in fuels for land ‐ based transportation vehicles is very low and modern power plants are becoming natural gas fuelled or they the exhaust by adding calcium carbonate CaCO
3
and hereby form gypsum for the building industry.
This makes shipping a big contributor to the global SO
X
emissions together with oil refineries and older coal ‐ and oil fired power plants.
The SO
X
contribution from shipping in 1997 is illustrated in Figure 18.
Figure 18 – Global SO
X
emissions from shipping in 1997.
The shipping routes are clearly seen as areas with high SO
X
concentration.
Source: College of Marine and Earth Studies, Delaware.
In 2001 12% of the European sulphur emissions came from shipping and the total could rise to as much as 18% in 2010 [6] and continue to increase as sulphur regulations on land tighten.
SO
X
in mainly known to cause acidic rainfall that damages buildings, lakes and forest areas.
In areas with natural low alkalinity, such as parts of Northern Scandinavia, the damage is more pronounced and large areas of forest land have been destroyed along with other adverse effects such as acidification of ground water and damage to aquatic life in fresh water lakes.
Limestone buildings are endangered by the acidic rain as they are literally dissolved.
In the atmosphere sulphur oxides are washed out rather quickly and have an average lifetime of just two days.
25
SO
2
can be carried with the wind over vast distances and be converted to sulphuric acid, H
2
SO
4
, by the humidity in the atmosphere and fall down as rainfall, snow or fog when it encounters the right meteorological conditions.
Normal rain has a pH value of about 5 because of a natural content of carbonic acid, but sulphuric acidic rain can have pH values of below 3 – corresponding to vinegar and Coca Cola.
Furthermore SO
X
is harmful to humans when inhaled by harming the lung functionality and increases the frequency of respiratory infections.
In concentrations higher than 500 ppb it can be fatal to weak individuals such as old people.
At lower concentrations SO
2
can cause chest pain, respiratory problems, eye irritation and increased risk for heart and lung illnesses.
SO
2
is harmless to healthy people in concentrations below 20 ppb and normal background concentration is about 10 ppb.
CONCAWE (Conservation of Clean Air and Water in Europe), which is the oil companies’ European Association for environment, health and safety in refining and distribution has made a study about sulphur emissions [10].
The study suggest that
SO
X
in the atmosphere have a “global cooling” effect as it is known from volcanic eruptions.
The sulphur aerosols in the atmosphere have both direct and indirect negative forcing and thus contribute to counteract the global warming.
The direct forcing come from reflection effects of the SO
X
in the atmosphere and the indirect forcing is due to extra condensation of water vapor around the SO
X
particles which bring along increased cloud cover.
Clouds have negative radiation forcing i.e.
they reflect incoming radiation from the sun.
Aerosols such as SO
X
have a short lifetime in the atmosphere and are therefore washed out quickly.
CO
2
and CH
4
are long lifetime agents and are slowly removed.
The study suggests that the negative forcing from SO
X
aerosols roughly balances the positive (warming) fording from CO
2
from global shipping and if the indirect cooling effect of increased cloud cover is taken into account the SO
X
emissions from shipping actually leads to a net cooling effect.
The study suggests that benefits of the global sulphur emission reduction are counterbalanced by the negative effects the sulphur reduction will have on global warming.
However the conclusions in [10] must be considered relative to SO
X
’s adverse effects on human health and the environment.
Oxides of Nitrogen
Although free nitrogen N
2
is normally considered an inert gas it is not the case when
N
2
is exposed to elevated temperatures.
Even though most N
2
passes through the engine unaffected a minor portion reacts with O
2
present in the air to form oxides of nitrogen.
While only a small part of the N
2
present in the ambient air reacts with oxygen the same happens for almost all the nitrogen present in the fuel oil, which reacts to either N
2
or NO [1].
In heavy fuel oil some organic nitrogen is present which can contribute to the formation of NO
X
.
When organic nitrogen is present in the fuel it is expected that the majority of this nitrogen is oxidized during the combustion process.
Particularly HFO can contain significant amounts of organic nitrogen and thus contribute to the formation of NO
X
during the combustion.
26
Oxides of nitrogen are often referred to as NO
X
to express that these oxides can constitute different combinations of nitrogen and oxygen, most commonly nitric oxide, NO, or nitrogen dioxide, NO
2
.
Other oxides of nitrogen may be present in more minor concentrations such as nitrous oxide, N
2
O.
At ambient temperatures the free oxygen and nitrogen in the air does not react, but in the combustion chamber the temperature is high enough for a reaction to take
place.
The formation of NO starts at about 1,200°C and accelerates as a function of temperature as illustrated in Figure 19.
Figure 19 – NO formation as function of temperature.
Source [1].
Because of the higher temperatures and larger excess air ratios in compression ignition diesel engines compared with spark ignited gasoline engines, NO
X
formation is more pronounced in diesel engines than spark ignition and gas turbines, but also parameters such as engine load, design and settings and nitrogen content in the fuel play a role.
Also the humidity of the charge air plays a role since the water vapor in
the air lowers the peak temperature during combustion and thus NO
X
‐ production.
When an excess of oxygen is present NO is oxidized to NO
2
during the time span illustrated below in Table 10.
NO [ppm] Half ‐ life for NO
20,000
→ NO
2
[min]
0.175
10,000
1,000
100
10
1
0.35
3.5
35
350
3,500
Table 10 – Half ‐ life for NO.
The time is takes for half the existing NO amount to be oxidized into
NO
2
.
In the exhaust stream NO will account for 90 ‐ 95% of the total NO
X
and only in the
last part of the exhaust system of after expelling of the gas from the exhaust system the formation of NO
2
will take place.
The oxidation of NO to NO
2
in the atmosphere is partly a reversible reaction with a state of equilibrium of NO vs.
NO
2
depending on atmospheric factors.
27
Nitrogen oxide, NO, is colourless and only moderately toxic.
However it is, as seen in
Table 10 relatively quickly oxidized into nitrogen dioxide, NO
2
, which is a much more harmful gas.
NO
2
is a toxic brownish gas, which has a stinging smell.
NO
2
bonds with blood hemoglobin and thus deprives to body of oxygen.
NO
X
in concentrations about
100 ppb can cause respiratory illness (normal rural concentration is typically below about 20 ppb).
Concentration of NO
2
above 150 ppm is fatal to humans [1].
NO
X
can react with HC and other organic materials present in the lower atmosphere in the presence of sunlight and form photochemical oxidants (ozone, O
3
, being the dominant – Ozone page 34).
Smog is created when NO
X
reacts with water vapour and particulate matter in urban areas in photochemical reactions which occur when warm layers of air exposed to sunlight become trapped under cooler layers of air.
This particularly happens in cities located in lower areas surrounded by more elevated areas.
In the city the air is still and production of ozone takes place in the sunlight.
NO and NO
2
react with organic substances in photochemical reactions to produce more ozone which results in reduced visibility.
The colour of the smog is often brownish and depends on the sulphur and nitrate content.
Children and people with respiratory diseases such as asthma and bronchitis who are exposed to smog can experience adverse effects like damage to lung tissue, reduction in lung function and increased risk of infection.
Another concern about NO
X
emissions is the contribution to acidic rain.
Acidic rain is formed when NO
2
reacts with the moisture in the air.
2NO
2
+ H
2
O → HNO
2
+ HNO
3
The acidic rain harms vegetation and structures and contributes to eutrophication of
lakes and e.g.
the Baltic Sea.
N
2
O is also called “laughing gas” and is used by dentists and at births.
It is an anaesthetic and a strong green house gas.
Considered over a 100 year period, it has
310 times more impact per unit weight than CO
2
.
Even though N
2
O is only emitted in small amounts it is the 4 th
largest contributor to the green house effect after CO
2
,
H
2
O and CH
4
.
Human activity is thought to account for 30% of the global N
2
O emissions.
N
2
O also plays a role in the decomposition of the ozone layer since it reacts with ozone.
NO
X
emissions can cause problems hundreds of kilometers from where they were emitted.
The NO
X
itself can easily be carried over vast distances and when exposed to sunlight they will cause problems in the new location.
Shipping is thought to contribute with 7% of global NO
X
emissions [6].
Hydrocarbons
A small fraction of the fuel oil, which consists of hydrocarbons, will pass through the engine unburned and other hydrocarbons are formed during the combustion process.
The hydrocarbons are thus mainly particles of unburned and partly burned original fuel.
Lubrication oil also contributes to the emission of hydrocarbons.
28
Hydrocarbon emissions can be a variety of different configurations with different contents of for example H, C, N, S and O and in different sizes from methane (CH
4
) to longer hydrocarbon chains.
Gaseous and non ‐ gaseous hydrocarbons are distinguished by the following: Gaseous hydrocarbons are those that exist in gas phase at a temperature of 190°C.
At lower temperatures some hydrocarbons condense into liquid or solid states [1].
Some large hydrocarbons with high molecular weight are the so ‐ called complex aromatic structures.
Included in the group of aromatic structures are the Polycyclic
Aromatic Hydrocarbons (PAHs).
Emissions of HC are normally largest at low loads and idling, where combustion can be incomplete, and become more or less constant at loads above 50% of MCR as can be seen in Figure 20.
At low loads over ‐ lean fuel ‐ air mixtures exist [1] and here the fuel does not ignite during the fuel injection.
Over ‐ fuelling is another source of hydrocarbon emissions.
Where zones of over ‐ rich fuel ‐ air mixtures exist combustion will also be incomplete.
Later in the combustion process when the hot gasses are mixed some of the initially unburned fuel may burn completely or partly.
HC emissions are thus greatly influenced by the condition of the engine and a badly maintained engine with worn valves and injectors; bad engine timing, fouled air filters etc.
can increase HC emissions drastically.
Within shipping particularly oil tankers pose problems with hydrocarbon emissions through their pressure relief valves on the cargo tanks.
These hydrocarbons are
normally described as Volatile Organic Compounds (VOC).
Figure 20 – Hydrocarbon emission rates as function of engine load for diesel engines.
From [1].
Hydrocarbons take so many different shapes and appear randomly in liquid, solid and vapour phases which makes them difficult to quantify.
The same is true to their impact of human health, which depends on the actual composition of the hydrocarbon.
Some hydrocarbons can also be categorized as particulate matter (see page 31).
Methane constitutes a large part of all HC emissions and currently the concentration in the atmosphere in increasing.
Since the Global Warming Potential (GWP) of CH
4
is much higher than for CO
2
, it has been suggested that within 50 years methane may overtake CO
2
and be the principal GHG [1].
29
In general HCs are accused of causing a broad range of adverse health effect like drowsiness, eye irritation to more severe cases they can be mutagenic (increasing the frequency of mutation in an organism) and carcinogenic (causing cancer).
Benzene (C
6
H
6
) is known as a carcinogen, and the larger and more complex polycyclic aromatic hydrocarbons are also known as being carcinogenic even when present in very small quantities.
Other hydrocarbons again might not be as harmful, but can still cause eye irritation and respiratory problems.
Non ‐ methane HC (the VOCs) can also be involved in photochemical reactions leading to formation of ground level ozone
and smog (see page 34) when exposed to sunlight by reacting with NO
X
.
Carbon Monoxide
Like CO
2
carbon monoxide emissions arise from the combustion of fossil fuel.
CO
2
comes from complete oxidation of the carbon in the fuel and CO results from incomplete combustion of the fuel due to local areas with shortage of air supply.
In a normal compression ignition engine the excess air ratio λ is larger than 1 and thus the CO emission is generally low.
Theoretically, if λ > 1 combustion will be complete and no CO will be formed.
In practice this is not the case, and there is always CO present in the exhaust gas because there will be local areas with insufficient air supply to facilitate complete combustion.
The CO emissions vary with engine load
and for higher loads they are more or less constant as show in Figure 21.
Figure 21 – Emission rates for CO from diesel engines as function of engine load.
From [1].
Even though CO emissions from compression ignition engines are normally low they can be significantly higher at low loads or when idling.
Here the fuel ‐ air mixture is often over ‐ rich and the temperature is relatively low which results in incomplete combustion.
Accidental after ‐ injection of fuel or nozzle drip can also cause CO formation.
CO is toxic and can be very harmful to humans.
It is colorless and odorless, tasteless and has caused many deaths both intended and unintended.
CO is naturally present in the atmosphere in concentrations of around 0.2
ppm and harmless in such low concentrations.
CO is only harmful close to the emission source because only here are concentrations large enough to cause problems to humans.
30
In elevated concentrations the gas causes dizziness and headache and at higher concentrations possibly death.
CO bonds very effectively with the body’s hemoglobin
Hemoglobin’s affinity for CO is 200 time greater than for O
2
, and thus the blood’s capacity to transport the necessary vital oxygen is dramatically reduced even at low
concentrations.
At concentrations above 750 ppm CO is lethal.
The environmental effects of CO are not quantified although CO is suspected to play a minor role in global climate change.
The CO formed during combustion does not
oxidize significantly further into CO
2
.
Instead CO can react with radicals in the air and in some circumstances react to form ground level ozone.
Particulate Matter
Particulate matter is a designation for a large variety of extremely small particles of organic and inorganic origin.
They can contain carbon, metals, ash, soot (almost purely elemental carbon), acids such as sulphates and nitrates and carbonates.
Some
PM consist of partly combusted or non ‐ combusted hydrocarbon material (fuel and lubrication oil) and there is an overlap between the designations of PM and HC.
Ash from fuel and lube oil is only a minor component of the emitted PM and come mainly from metals (vanadium and nickel) present in those oils.
In air quality terms also pollen, spores, viruses, debris, ocean salt spray and dust are categorized as particulates, but here particulate matter is a result of combustion of fuel oil.
Volcanoes and forest fires are other sources of PM, but particle emission caused by human activity by burning fossil fuels is a major contributor.
To formation of PM takes place in steps of growth which is illustrated in Figure 22.
The first stage consists of extremely small particles of mainly soot (carbon) formed in the fuel ‐ rich zones in the combustion chamber.
Afterwards other substances adhere to the soot particles and the particles start to grow.
They collide with each other and the number of particles is reduced, but the particle size increases.
Some of the formed PM will be combusted during the combustion process.
In the exhaust system where the exhaust gas is cooled the less volatile substances condensate.
SO
X
can react with water, condense and form sulphuric acid which adheres to the particles as
a liquid film (Figure 22).
31
Figure 22 – PM formation process during and after the combustion process.
From [1] .
Particulates are a result of incomplete combustion, dirty fuel oil and imperfect lubrication of the cylinders.
At low and transient loads soot can be a high contributor to the total PM emissions while at higher loads the fraction is much smaller.
Because
the PM emission depends on the load, the fuel oil composition, and the lubrication oil type and dosage it is difficult to establish general emission rates for PM.
The sulphur content on the fuel has a large influence on the PM emissions as illustrated in Figure 23.
Figure 23 – PM emission as function of sulphur content in the fuel oil.
From MAN Diesel.
32
Particulate matter is categorized by the size of the particles:
Fraction Size range
PM
10
PM
2.5
PM
1
<
<
<
10
2.5
1 μ
μ
μ m m
m
Ultra Fine Particles (UFP) < 0.1
μ m
Table 11 – Particle size (aerodynamic diameter) for particulate matter.
Particles from marine fuel oils are normally in the small end of the size range, while deposits from the combustion chamber and exhaust system are much larger.
Generally the size of the particles from burning heavy fuel is larger (PM
10
) than from burning distillates (PM
2.5
– PM
1
).
The size of the particles determines how dangerous they are to humans.
The particles that are smaller than 10 μ m in diameter can be inhaled by humans and the smaller the size the further the particle can penetrate into the lungs.
Some may even get into the bloodstream and can cause serious health problems.
Smaller particles can furthermore be carried with the wind over larger areas.
Increasing concern exists with regards to PM being the cause of lung cancer and other respiratory ‐ and circulatory diseases.
Studies suggest that there are many consequences of PM ‐ pollution including the following
1
:
Increased respiratory symptoms, such as irritation of the airways, coughing and difficulty breathing
Decreased lung function
Aggravated asthma
Development of chronic bronchitis
Irregular heartbeat
Nonfatal heart attacks
Premature death in people with heart or lung diseases
Mutagenic and carcinogenic effects
The PM containing large heavy aromatic HCs (PAHs and PAH ‐ nitrogen combinations) pose a greater risk to human health, because they are carcinogenic.
The small particles can be transported by air and the effects of PM pollution can show up far away from the source of the pollution.
The lifetime of PM in the atmosphere is long compared to e.g.
SO
X
.
Background concentration of PM is about 20 ‐ 30 μ g/m
3
but can be much larger in
trafficked areas during peak periods.
From a climate point of view emissions of PM are of concern in polar areas because the black carbon particles enhance the absorption of infrared radiation and thus contribute to the accelerated melting of ice at the poles.
1
U.S.
Environmental Protection Agency www.epa.gov.
33
Ozone
Ozone, O
3
, is not emitted from engines but is a by ‐ product from some ship emissions.
Ozone is found naturally in both the stratosphere and in the troposphere.
The stratosphere is the 2 nd
layer of the atmosphere seen from ground level.
It is above the troposphere and just below the mesosphere and situated between approximately 10 km and 50 km and a bit lower at the poles.
The troposphere is the lowest part of the atmosphere and contains about 75% of the atmosphere’s total mass and 99% of all water vapour (clouds) in the atmosphere.
The average thickness of the troposphere is about 20 km at the Equator, 17 km at the middle latitudes and 7 km at the poles.
The stratosphere is where most of the atmospheric ozone is found (about 90%).
This is the so ‐ called ozone layer where the ultraviolet ‐ B radiation is partially filtered out of the amount of sunlight that reaches the surface of the Earth.
The B ‐ rays are the most severe sunrays resulting in sunburns, skin cancer and eye damage.
The ozone layer is very important to life on Earth.
The ozone layer is all the time being destroyed and rebuilt by different chemical processes.
The ozone in the stratospheric ozone layer is destroyed by the ozone depleting substances such as chlorine ‐ containing halogenated refrigerants, fire ‐ retardants, some propellant gasses and N
2
O.
In the troposphere ozone is also found though in much smaller concentrations than in the stratosphere.
The tropospheric ozone is formed through photochemical reactions between NO
X
and organic substances present in the lower atmosphere.
The reaction takes place in the presence of sunlight and ozone is the major product of the photochemical process.
The ozone formed this way is also called ground level ozone and for obvious reasons has much more adverse impact on human health than stratospheric ozone in the ozone layer.
The ground level ozone has an adverse effect on human health and irritates the mucous membranes.
It furthermore harms vegetation and certain materials such as elastomers, paints and textiles.
Ground level ozone is a strong GHG with a GWP of
2,000.
Ozone furthermore contributes to the formation of smog.
Green House Gasses
Many of the above mentioned emission types also act as Green House Gasses
(GHGs) i.e.
gasses with a global warming potential.
CO
2
is the most important green house gas and one of the main reasons that life can exist on Earth in the form we know.
As the name green house gas suggests CO
2
acts like the glass in a greenhouse.
Without it Earth would be a very cold and hostile place with an average surface
temperature of about ‐ 20°C.
When the energy (mostly visible light) from the sun hits the atmosphere about 50% is immediately reflected.
The other half is absorbed by the earth’s atmosphere and surface which becomes heated.
Heated bodies radiate energy in the infrared range, so infrared heating is emitted from the earth’s surface and atmosphere.
The GHGs
34
trap the infrared radiation and radiate it on to other gasses in the atmosphere and back to the earth’s surface, and thus both atmosphere and earth is warmed as
illustrated in Figure 24.
Figure 24 – Green house effect.
Illustration from www.myclimatechange.net.
Other green house gasses are refrigerants, fire protecting agents and propellants for spray cans.
Classic refrigerants such as chlorofluorocarbon products (CFC ‐ products) with the trade name Freon have now been replaced by products without GHG effect.
The Global Warming Potential (GWP) is given in relation to CO
2
in a given time span.
In a 100 year time span the GWP for Freon is 4,000 ‐ 8,500.
The GWP of some GHGs
are listed in Table 12.
There are many natural sources of the GHG CH
4
such as wetlands and termites, but human activities such as oil refinery, farming and rubbish dumps are dominating.
These sources are larger sources than actual combustion of fossil fuels.
GHG
H
2
O
CO
2
CH
4
N
2
O
HC
SF
6
Freon 11 (CFC ‐ 11)
Freon 12 (CFC ‐ 12)
O
3
(tropospheric)
100 year GWP
0
1
23
310
Up to 30
24,900
4,000
8,500
2,000
Table 12 – Global Warming Potential (GWP) for certain GHGs.
35
Other Emissions
Generally the concentration of other emission types is very small, but some compounds can still have severe adverse effect on human health.
Other emissions can for example be heavy metals known to the harmful to human health.
Numerous other organic compounds such as benzene are found in the category and are highly toxic.
The heavy metal group comprises cadmium, chromium, copper, mercury, nickel and zinc and generally reflects the heavy metal content of the fuel oils being burned.
Heavy metals can cause damage to the marine fauna and cause cancer in
humans.
Emission Rates from Ship Machinery
Ship emission rates can be stated brake specific (g/kWh) or fuel specific (g/kg fuel oil) depending on convenience for the species of emission.
The emission rates stated here are only for primary emissions – the emissions coming from the ship – and not
the secondary formed ones like ozone.
CO
2
It is straightforward to calculate the amount of CO
2
emitted from an engine running on any kind of fuel.
The amount emitted depends on the number of carbon atoms in the chains of hydrocarbons that constitute the fuel.
The CO
2
emission is generally independent of engine power and only varies with the amount of fuel burned.
The calculations are based on the molecular weight of carbon, oxygen and CO
2
.
The molecular weights are for the three reactants respectively: 12.01, 16.00, and 44.01.
The conversion factor can be found from the carbon content and the basic reaction:
C + O
2
→ CO
2
If e.g.
the carbon content of the fuel oil is 86% by mass the conversion factor C
F
can be found from the following:
86% ∙ (44.01/12.01) = 3.15
36
The conversion factors have been found for different ship fuels and are stated in
Table 13.
Fuel
Heavy Fuel Oil (HFO)
CO
2
emission (C
F
)
[ton CO
2
/ton fuel]
3.1144
CO
2
emission
[kg/MJ fuel]
0.078
Marine Gas Oil (MGO) 3.206
Liquefied Natural Gas (LNG) 2.75
Liquefied Petroleum Gas (LPG) 3.00
‐ 3.03
2
0.074
0.055
‐
Table 13 – CO
2
conversion factors C
F
for different kinds of marine fuels.
Data from [1] and [3].
For heavier fuel oils the carbon/hydrogen ratio is much larger than for e.g.
LNG.
A
methane molecule CH
4
has a ratio of one carbon atom to four hydrogen atoms whereas diesel oil with the average composition of e.g.
16 carbon atoms to 34 hydrogen atoms has a much smaller ratio.
Therefore CO
2
emission per weight unit fuel oil burned will be higher than for gaseous fuels.
SO
X
The SO
X
emission is independent of sulphur content in the fuel burned 3 the engine power and mainly depends on the
.
There is a linear relationship between fuel
sulphur content and SO
2
emissions from medium and low speed engines proved in
[7] and illustrated in Figure 25.
Since the vast majority (95 ‐ 97%) of all SO
X
is SO
2
the SO
X
emission from the ship can be estimation as follows:
S + O
2
→ SO
2
Since the molecular weights of S and SO
2
are 32.07
and 64.07
respectively the SO
2
emission in tons can be calculated as follows [11]:
Fuel burned [ton] ∙ (sulphur content [mass%] / 100) ∙ (64.07/32.07) [1]
Where 64.07
is the molecular weight of one SO
2
atom and 32.07
is the molecular weight of one sulphur atom.
Another way of calculating fuel specific and brake
specific SO
2
emissions is by using the simpler formula from [7]:
20 ∙ S kg SO
2
per ton fuel oil or
4.2
∙ S g/kWh
where S is the sulphur content in the fuel in mass%.
2
Average value depending on the propane/butane ratio of petroleum gas.
3
Except from a negligible amount of sulphur being neutralized by the cylinder lubrication oil.
37
Figure 25 – Relationship between fuel oil sulphur content and SO
2
emissions for different engine types.
From [7].
NO
X
NO
X
emissions depend on engine type.
Low speed two ‐ stroke engines generally have higher brake specific NO
X
emissions than medium and high speed engines.
All ships built on or after January 1 st 2000 must comply with MARPOL NO
X
emission regulations and thus the specific NO
X
emission from younger ships are in accordance with MARPOL Annex VI, which is described in Regulation of Emissions page 42.
For engines older than year 2000 the NO
X
emission varies depending on engine type and load from about 8.3
‐ 21.8
g/kWh for medium speed engines and 11.5
‐ 23.6
g/kWh for low speed engines.
Due to the lack of precise emission rates the general numbers stated below in Table 14 for the emission factors are given from reference [7].
Even though NO
X
vary depending on the nitrogen content of the fuel the variation is often neglected.
Engine → Low speed 2 ‐ stroke
NO
X
[g/kWh]
4
17
NO
X
[kg/ton oil] 87
Medium and high speed 4 ‐ stroke
12
57
Gas turbines*
4
17
Table 14 – Emission factors for calculation of NO
X
at 50 ‐ 85% MCR.
Data from [1] and [7].
*NO
X
emissions from gas turbines running on distillates.
For lean burning spark ignition gas burning engines Rolls ‐ Royce informs that a typical emission rate for NO
X
is 1.2
g/kWh.
The same emission rate is assumed to be valid for LNG burning gas turbines.
With assumed SFOC for the two engine types of 185 g/kWh and 240 g/kWh respectively the brake and fuel specific NO
X
emissions for LNG operation are listed in Table 15.
4
Average values.
Values are generally declining and can be lower for more modern engines.
38
Engine →
NO
X
[g/kWh]
NO
X
[kg/ton oil]
Spark ignition engines
1.2
6.5
Gas turbines
1.2
5.0
Table 15 – Emission factors for NO
X
for engines running on natural gas.
HC
For hydrocarbons the emission factors are stated in Table 16:
Engine →
HC [g/kWh]
Low speed
2 ‐ stroke
0.5
Medium and high speed 4 ‐ stroke
0.5
Gas turbines*
0.35
HC [kg/ton oil] 2.94
2.6
1.46
Table 16 ‐ Emission factors for calculation of HC from [1].and
[7].
*HC emissions from gas turbines running on distillates.
Only data for gas turbines running on distillates is available.
For gas turbines running on LNG the emission rates are assumed to be similar even through they are likely to be smaller.
Lean burning spark ignition engines running on LNG have a fuel slip of
1.35%, which is converted into the emission rate of HC for this engine type.
CO
The CO emissions vary with engine load and for higher loads they are more or less constant as show in Figure 21.
For higher loads (above 50% MCR) the carbon monoxide emission factors are stated in Table 17.
Engine → Low speed Medium and high Gas
CO [g/kWh]
2 ‐ stroke
1.6
CO [kg/ton oil] 9.41
speed 4 ‐ stroke
1.6
8.4
turbines*
0.1
0.42
Table 17 ‐ Emission factors for calculation of CO.
*CO emissions from gas turbines running on distillates.
Only data for gas turbines running on distillates is available.
For gas turbines and
spark ignition engines running on LNG the emission rates are assumed to be similar.
PM
Particulate emissions are mainly affected by the sulphur content in the fuel and the general fuel oil quality.
Lower grade fuels result in higher PM emissions i.e.
engines
39
running on HFO will have higher emission rates than engines running on distillates.
There is no significant difference in PM emissions between two ‐ and four ‐ stroke engines running on the same fuel.
Simple estimates of fuel specific PM emission rates are found in Table 18.
PM [g/kWh]
PM [kg/ton oil]
HFO MGO Gas turbines*
1.5
0.2
7.6
1.2
0.1
0.4
Table 18 – Particulate matter emission rates for engines running at 50 ‐ 85% MCR.
[1] and [7].
*Data for gas turbines running on distillates.
The residual oil used for the measurements in [7] had a sulphur content of 3% and the MGO had sulphur content of 0.17%.
The dependency of PM emissions on sulphur content in the fuel was measured in [7] and illustrated in Figure 26.
Figure 26 – PM emissions vs.
sulphur content of fuel oil.
From [7].
The PM emission in kg per ton fuel oil burned can be calculated as follows:
0.1014
∙ S 5 – 0.6056
∙ S 4 + 1.3819
∙ S 3 – 0.7883
∙ S 2 + 0.4023
∙ S + 1.1
[2]
where S is the sulphur content in the fuel oil in mass percent.
The formula is derived from [7] by Hans Otto Kristensen in [12].
The reason the relationship between sulphur content and PM emissions is not linear could be that fuel with higher sulphur content often is residual oil that also contains other substances that contribute to particulate emissions other than sulphur whereas lower sulphur fuels are often distillates and thus more “clean” resulting in less PM.
Equation [2] is used for calculating PM in this report except for LNG where the sulphur content is close to zero.
Equation [2] is not valid for sulphur contents close to zero, and since it is assumed that the sulphur content of LNG is negligible the same is assumed with PM emissions.
There will be PM emissions arising from the lubrication oil, but since these emissions can not be quantified here, PM emissions from engines running on LNG are assumed zero.
Naturally the composition and particle size of the PM would be of interest when quantifying the emissions and particularly their threats to health.
Composition and size of PM emissions are hard to predict and calculate even through some people
40
claim that PM from distillates are smaller than PM from HFO and therefore more dangerous to human health.
Emissions from Auxiliary Boilers
The emissions of CO
2
and SO
X
from oil fired auxiliary boilers are straight forward to calculate because they only depend on the amount and type of fuel burned in the boiler.
Exhaust emissions from boilers are yet unregulated and there are no rules regarding e.g.
NO
X
.
According to Aalborg Industries the NO
X
emissions from auxiliary boilers vary greatly for different manufactures depending on their working principles and the burner unit installed.
According to Aalborg Industries there is also a large difference in NO
X
emissions from auxiliary boilers depending on the fuel type.
According to Aalborg Industries a marine boiler normally produces about 500 mg
NO
X
per about
200 m
3
exhaust gas at standard operation conditions when burning HFO and mg/m
3
when burning MDO and MGO.
The density of the intake and the exhaust is assumed to be the same (1.2
kg/m
3
).
If
3% (by volume) oxygen is left in the exhaust gas the excess air ratio λ is about 1.14.
For stoichiometric combustion of 1 kg fuel oil (86 mass% C, 15 mass% H)
5
14.68
kg of
air is required [13].
With λ = 1.14
the air/fuel ratio is 16.78
kg air/kg fuel.
Then
(16.78/1.2) ∙ 500 mg NO
X
~ 6,990 mg NO
X
/kg fuel for HFO and
(16.78/1.2) ∙ 200 mg NO
X
~ 2,796 mg NO
X
/kg fuel for MDO/MGO
The approximate emission rates for boilers used in the further calculations are stated in Table 19.
Note that this is a simple estimate.
Actual NO
X
emissions from boilers could be higher or lower.
When compared to main and auxiliary engines the emission rates from boilers are small because the burning process in a boiler is a continuous
process, so the high peak temperatures that normally generate NO
X
in combustion engines are avoided.
HFO Distillates
NO
X
[mg/m
3
]
6
500
NO
X
[g/kg oil] 6.99
200
2.80
Table 19 – Estimated NO
X
emission rates for auxiliary boilers.
5
This approximation is used here for HFO, MDO and MGO.
6
NO
X
content per m
3
exhaust gas.
Standard test condition for boilers with 3% oxygen left in the exhaust gas.
This corresponds to normal operating conditions for boilers according to Aalborg
Industries.
41
Regulation
of
Emissions
Ship emissions are regulated world wide.
The principle of all regulations is that they shall apply to all ships regardless of flag state.
Two main authorities establish the emission regulations in Europe: The International Maritime Organization (IMO) and the European Union (EU).
Some countries have additionally enforced national regulations for different kinds of emissions.
One country is Norway, which has introduced a NO
X
‐ tax for ships operating between Norwegian ports.
The International Maritime Organization is a specialized organization within the
United Nations (UN).
168 countries are member states and three are Associate
Members (Hong Kong & Macao (China) and the Faroe Islands (Denmark)).
IMO works to facilitate cooperation among shipping countries, governments and the shipping industry working on improving safety and security at sea and to prevent pollution of
oceans, coasts and the atmosphere.
IMO MARPOL 73/78 is the International Convention for the Prevention of Pollution from Ships.
It was first laid down in 1973 and subsequently modified in 1978.
The
MARPOL 73/78 is one of the most important environmental conventions for the shipowners to adhere to.
The convention was agreed to control pollution of the oceans including emissions to the atmosphere from exhaust gasses from ship engines.
MARPOL Annex VI is the part of the MARPOL convention concerned with air pollution.
All ships over 400 GT must comply with the IMO regulations after the IMO principle about “no more favourable treatment”.
Normally the regulations adopted in IMO also become part of the EU legislations.
Independent EU regulations for ship emissions include demands to the quality of marine fuel oil, regulations on ship fuel used in inland waterways and ports in the EU
and special regulations for passenger ships.
Emission Control Areas
The concept of Emission Control Areas (ECAs) is that they are areas where stricter mandatory regulations apply to all ships operating in the area regardless of flag state in order to prevent and reduce air pollution from emissions from ships.
The idea is that reductions are enforced in areas where the emissions are most harmful to humans and the environment i.e.
in densely populated areas and in areas with low alkalinity where acidic rain can damage crops and fresh water basins instead of reducing emission in the more open ocean where they affect relatively few people.
As an example a unit of SO
X
emitted in the North Sea ECA has much larger
environmental and health impact than a unit of SO
X
emitted in the Mediterranean
[10] as illustrated in Figure 27.
42
Figure 27 ‐ Impact of particulate matter derived from SO
X
emissions on the EU population per unit
SO
X
emissions relative to the North Sea, the Baltic Sea, the Mediterranean and the Atlantic Ocean.
From [10].
The Baltic Sea is one of the world’s largest seas of brackish water.
Over 85 million people live in the countries around the Baltic Sea.
Due to geographical, climatological, and oceanographic characteristics it is a highly sensitive ecosystem.
The Baltic is almost closed off by the Danish Sound and the Belt Sea and water exchange between the Baltic and the open sea is very limited.
The Baltic is very shallow with an average depth of only 53 m.
Currently two ECAs have entered into force.
One is the Baltic Sea and the other is the
North Sea including the English Channel area as can be seen on Figure 28.
The two
ECAs include coastal areas of heavy population where a unit of air emission has a much bigger impact than a unit emitted on the open ocean or in a less densely populated area.
The Baltic Sea ECA went into operation on May 19 2006 and the
North Sea ECA went into operation on November 22 nd
2007.
Initially the existing ECAs were proposed as SECAs (Sulphur Emission Control Areas)
due to the concern sulphur emissions were causing in Northern Europe.
So far the two ECAs have only been regulated with respect to sulphur emissions, but NO
X
is likely to be added with time.
43
Figure 28 – The two existing ECAs in the North Sea and Baltic Sea.
From www.ecmeurope.net.
The United States and Canada has proposed for designation of an Emission Control
Area for certain portions of the United States and Canadian coastal waters, for the control of both NO
X
and SO
X
after the MARPOL Annex VI principle of ECAs.
The proposal was approved in July 2009 and will enter into force in 2012.
The ECA is going to include waters adjacent to the Pacific coast of USA to the
Mexican border and Canada, the Atlantic (USA and Canada), the US Gulf coast and the Hawaiian Islands (USA).
The Atlantic/Gulf portion of the ECA is bounded in the
West by the border between Texas with Mexico and continues around the peninsula
of Florida and north up the Atlantic coasts of the United States and Canada.
The ECA will extend 200 nautical miles from the coast as illustrated in Figure 29.
Figure 29 – Future USA/Canadian NO
X
and SO
X
Emission Control Area.
From [14].
Regulation of Sulphur Content in Fuel Oil
The MARPOL Annex VI regulation 14 about SO
X
and PM applies to all ships with engine power output of more than 130 kW and SO
X
is regulated through limits on the sulphur content in marine fuels.
The global sulphur cap for any marine fuel oil used on board ships set forth by IMO is currently 3.5%.
The world average sulphur
44
3
2.5
2
1.5
1
0.5
0 content for fuel oil is currently about 2.7%.
The global cap applies everywhere.
In the two ECAs the current sulphur limit is 1.0%.
Both globally and locally Annex VI includes drastic, gradual reductions in the allowable sulphur content of marine fuel oils.
The reductions for the global sulphur
limit are stated from MARPOL Annex VI [15] :
The sulphur content of any fuel oil used on board ships must not exceed the following limits:
4.50% m/m prior to January 1 st
2012;
3.50% m/m on and after January 1 st
2012; and
0.50% m/m on and after January 1 st
2020.
In 2018 a review of fuel availability is carried out and if supply of low sulphur fuel oil is found insufficient the enforcement of the global 0.5% sulphur limit can be postponed to year 2025.
For ships operating within the Emission Control Areas the
limits for the sulphur content of the fuel oil are considerably lower and follow the same stepwise reduction as the global level:
1.50%
1.00%
m/m m/m
prior on
to and
July after
1 st
2010;
July 1 st
2010; and
0.10% m/m on and after January 1 st
2015.
The reductions are illustrated in Figure 30.
4.5
ECA
4
Global
3.5
Year
Figure 30 – Current and future IMO sulphur limits of marine fuel oil for ships operating globally and in ECAs.
As seen the reduction in the ECAs over the next relatively few years is quite considerable (about 93%).
The European Union has also set forth sulphur regulations on shipping in EU waters and ports.
The limit of sulphur content in fuel of 1.5% set forth in the MARPOL Annex
VI is also included in the EU regulations.
45
EU is concerned with the marine fuel burned in inland waterways and ports and about the sulphur content of marine fuels available in the EU.
All current and future
sulphur regulations valid for EU territories are listed in Table 20 [16].
Area/fuel Authority Year Limit
[S% m/m]
Until 2010 4.5%
Until 2010 1.5%
Current 0.1%
Current 0.1%
Current
Current
Current
2015
2020
0.1%
3.5%
1.0%
0.1%
0.5%
Global
Fuel burned in ECAs
Marine Gas Oils used in EU
Marine fuels used in EU inland waterways and ports
7
Marine Gas Oil sold in the EU
Global
Fuel burned in ECAs (excl.
MGO)
Fuel burned in ECAs
Global*
IMO
IMO
EU
EU
EU
IMO
IMO
IMO
IMO
Table 20 – Sulphur regulation overview with current future regulations on fuel oil quality in EU and globally.
* Depending on the availability of low sulphur fuel oil on the global market.
To be analyzed and reviewed in 2018 and if necessary the enforcement will be postponed to 2025.
Two significant changes are the reduction from the current allowable use of fuel oil with a sulphur content of 1.5% while in port which drops to 0.1% from January 1 st
2010 [16] and the 0.1% sulphur cap on fuels used in ECAs from January 1 st
2015.
With the MARPOL regulation of sulphur content in the fuel oil IMO targets SO
X
and
PM emissions simultaneously.
Regulation of Nitrogen Oxides
Since the amount of NO
X
emissions does not depend exactly on the amount of fuel
burned the NO
X
regulations are, contrary to the SO
X
regulations, brake specific i.e.
expressed in g/kWh.
The NO
X
regulation is limited to apply only to ships where the keel was laid after January 1 st
2000.
IMO Tiers
IMO has decided a gradual reduction in the limits for NO
X
emissions from ships.
The reduction has three steps; Tier I, II and III.
The limits are the same for two ‐ and four ‐
stroke engines in steady state operation.
They are depending on engine speed and apply to engines with an output of more than 130 kW.
The following regulations are partially quoted from MARPOL Annex VI regulation 13.
Revised MARPOL Annex VI
[15].
7
This regulation does not apply whenever, according to published timetables, ships are due to be at berth for less than two hours; in Greece until 1 January 2012 or if ships use shore power while at berth.
46
Tier I
The operation of a marine diesel engine which is installed on a ship constructed on or after January 1 st 2000 and prior to January 1 st 2011 is prohibited, except when the emission of nitrogen oxides (calculated as the total weighted emission of NO
2
) from the engine is within the following limits, where n = rated engine speed (crankshaft
revolutions per minute).
17.0
g/kWh when n is less than 130 rpm;
45 ∙ n
( ‐ 0.2)
g/kWh when n is 130 rpm or more but less than 2,000 rpm;
9.8
g/kWh when n is 2,000 rpm or more.
Tier II
For an engine installed on a ship constructed on or after January 1 st
2011 the
emission of nitrogen oxides from the engine must be within the following limits:
14.4
g/kWh when n is less than 130 rpm;
44 ∙ n
( ‐ 0.23)
g/kWh when n is 130 rpm or more but less than 2,000 rpm;
7.7
g/kWh when n is 2,000 rpm or more.
Tier III
For an engine installed on a ship constructed on or after January 1 st
2016 the
emission of nitrogen oxides from the engine must be within the following limits:
3.4
g/kWh when n is less than 130 rpm;
9 ∙ n ( ‐ 0.2) g/kWh when n is 130 rpm or more but less than 2,000 rpm;
2.0
g/kWh when n is 2,000 rpm or more.
The three tiers are illustrated in Figure 31.
Tier III will enter into force on January 1 st
2016 and reduces the NO
X
limits drastically (about 80%) compared to Tier II.
Tier III will only apply in NO
X
Emission Control Areas (also at times called NECAs).
Currently there are no ECAs for NO
X
, but the Helsinki Commission (HELCOM) is determined to designate the Baltic Sea an ECA for NO
X
.
HELCOM is working to protect the marine environment in the Baltic Sea area and is an intergovernmental cooperation
between Denmark, Estonia, the European Community, Finland, Germany, Latvia,
Lithuania, Poland, Russia and Sweden.
47
18
16
14
12
10
8
Tier I Tier II Tier III
6
4
2
0
0 400 800 1,200 1,600 2,000 2,400
Rated Engine Speed [rpm]
Figure 31 – Brake specific NO
X
emission limits for Tier I, Tier II and Tier III.
An overview of current and future NO
X
emission limits and their enforcement times is shown in Table 21.
Year
Ships constructed on or after January 1 st
2000 and prior to 1 January 2011
Ships constructed on or after January 1 st
2011
Ships constructed on or after January 1 st
2016
Regulation Area Authority
Tier I
Tier II
Tier III
Global IMO
Global IMO
ECA * IMO
Table 21 – Overview of future NO
X in existence.
regulations.
* There are currently no NO
X
Emission Control Areas
In order to show compliance with the NO
X
regulations engines are delivered with a letter of compliance that shows certification according to the NO
X
technical code.
The certification includes NO
X
measurements of the engine type.
Engines installed on a ship constructed after January 1 st
1990 but before January 1 st
2000 and with a power output of more than 5,000 kW and a displacement per cylinder of or above 90 litres shall comply with the Tier I emission limits, provided that a certified “Approved Method” for that engine is available.
The regulation means that if there is an upgrade available from the engine
manufacturer the shipowner must buy it and install it on the ships in the fleet constructed before January 1 st
2000.
Since the IMO NO
X
regulation only applies to new ships it will take a long time before reductions are visible.
With this in mind there could be a possibility that NO
X
is the next emission species for authorities to regulate for existing ships, but this is yet
doubtful.
48
National NO
X
Regulations
On January 1 st
2007 Norway introduced a tax on NO
X
emissions.
The tax applies to ships with propulsion machinery of more than 750 kW operating between two or more succeeding Norwegian harbours.
A Norwegian oil rig is also considered a
Norwegian harbour.
The tax is as follows [17]:
15 NOK (€ 1.7) per kg emitted NO
X
or
Enter into an agreement with the Norwegian government about installation of NO
X
abatements on board.
In this case the NO
X
tax is reduced to 5 NOK (€
0.6) per kg emitted NO
X
.
Local NO
X
regulations are enforced e.g.
in Sweden and in the harbour of Hamburg,
Germany through harbour fees.
49
References
[1] A.A.
Wright: Exhaust Emissions from Combustion Machinery .
MEP Series, Volume
3, Part 20, Institute of Marine Engineers, 2000.
ISBN 1 ‐ 902536 ‐ 17 ‐ 7
[2] Bunkers.
An Analysis of the Practical, Technical and Legal Issues.
Christopher
Fisher & Jonathan Lux, Third Edition, Petrospot Limited, 2004.
ISBN: 0 ‐ 9548097 ‐ 0 ‐ X.
[3] IMO MEPC.1/Circ.681.
17 August 2009.
Interim Guidelines on the Method of
Calculation of the Energy Efficiency Design Index for New Ships.
[4] Sulphur Content in Ship Bunker Fuel in 2015.
A Study on the Impacts of the New
IMO Regulations on Transportation Costs.
Ministry of Transport and Communications
Finland, April 2009.
ISBN 978 ‐ 952 ‐ 243 ‐ 074 ‐ 8
[5] Allan M.
Friis, Poul Andersen & Jørgen Juncher Jensen: Ship Design .
Department of Mechanical Engineering, Section of Costal, Maritime and Structural Engineering,
Technical University of Denmark, 2002.
ISBN 87 ‐ 89502 ‐ 56 ‐ 6
[6] Doug Woodyard: Pounder’s Marine Diesel Engines and Gas Turbines .
8 th
edition,
Elsevier, 2004.
ISBN 0 ‐ 7506 ‐ 5846 ‐ 0
[7] Marine Exhaust Emissions Research Programme.
Lloyds Register of Shipping,
1995.
[8] J.
Isensee & V.
Bertram: Quantifying External Costs of Emissions due to Ship
Operation .
Proceedings of the Institution of Mechanical Engineers, Part M: Journal of Engineering for the Maritime Environment, 2004
[9] Study of Greenhouse Gas Emissions from Ships .
Prepared for the International
Maritime Organization by MARINTEK, Norway; CD Delft, The Netherlands; Dalian
Maritime Institute, India; Deutsches Zentrum für Luft ‐ und Raumfart e.V., Germany;
DNV, Norway; Energy and Environmental Research Associates, USA; Lloyds Register ‐
Fairplay Research, Sweden; Manchester Metropolitan University, UK; Mokpo
National Maritime University, Korea; National Maritime Research Institute, Japan &
Ocean Policy Research Foundation, Japan.
Draft February 2009.
[10] Reducing the Sulphur Content of Marine Fuels.
CONCAWE review Volume 17,
Number 2, autumn 2008
[11] IMO BLG 12/INF.10.
28 December 2007.
Revision of MARPOL Annex VI and the
NO
X
Technical Code.
[12] Hans Otto Kristensen: Preliminary ship design of container ships, bulk carriers, tankers and Ro ‐ Ro ships.
Assessment of environmental impact from sea ‐ borne transport compared with land based transport.
Department of Mechanical
50
Engineering, Section of Costal, Maritime and Structural Engineering, Technical
University of Denmark, 2009.
[13] Spencer C.
Sorenson: Engine Principles and Vehicles.
Department of Mechanical
Engineering, Technical University of Denmark, 2007.
[14] IMO MEPC 59/6/5.
2 April 2009.
Interpretations of, and Amendments to,
MARPOL and related instruments.
Proposal to Designate an Emission Control Area for Nitrogen Oxides, Sulphur Oxides and Particulate Matter.
Submitted by United
States and Canada.
[15] Revised MARPOL Annex VI.
Regulations for the Prevention of Air Pollution from
Ships and NO
X
Technical Code 2008.
2009 Edition.
International Maritime
Organization, 2009.
ISBN 978 ‐ 92 ‐ 801 ‐ 4243 ‐ 3
[16] Council Directive 1999/32/EC of 26 April 1999 relating to a reduction in the
sulphur content of certain liquid fuels and amending Directive 93/12/EEC.
[17] Danish Shipowners’ Association: Technical Circular no.
14/2007.
NO
X
duty in
Norway.
51
