Marine Diesel Engine Exhaust Gas Emissions Control Technologies

marine diesel engine
exhaust gas EMissions
Control technologies
Mohd. Hanif Dewan, Chief Engineer and
Maritime Lecturer & Trainer, Bangladesh

Ship and Environment
 Ships have closed relation with their environment (water and air) from their
construction, through operation, until decommission and recycling.
Anti-Fouling
System,
VOC
 World fleet size of ships is increasing.
 The environment is a finite world.
 Ships need to be friendly with the environment.
Oil / Chemical
(Fuel/cargo)
Garbage, Waste
and Wash-water
Underwater
noise
Green House Gases
NOx SOx PM
Ship
Recycling
Ballast water
Maritime Lecturer & Trainer, Bangladesh.
9/23/2014 2

DIESEL ENGINE EXHAUST GAS EMISSIONS
A diesel engine is a type of internal-combustion engine in
which atomized oil fuel is sprayed into the cylinder and
ignited by the heat generated by compression. Diesel
engines are efficient with low CO2, CO and HC emissions.
However the emissions are high in NOX.
Additionally marine engines use residual bunker fuels which
contain sulphur, asphaltenes and ash. Due to these
components in the fuel, exhaust emissions contain SOX and
particulate matter which are formed during the combustion
process.
9/23/2014 3

Typical concentrations of exhaust emissions
are as follows:
- Oxygen: abt. 13% ,
- Nitrogen: abt. 76% ,,
- Hydrocarbons (HC): abt. 180 ppm
- Water vapor: abt. 5% ,
- Carbon Monoxide (CO): abt. 60 ppm
- Carbon di Oxide (CO2): abt. 5%
- Oxides of Sulphur (SOX): abt. 600 ppm
- Particulate matter (PM): abt. 120 mg/Nm3
- Oxides of Nitrogen (NOX): abt. 1500 ppm.
9/23/2014 4

EMISSIONS FROM MARINE ENGINE
EXHAUST GAS
9/23/2014 5

NOX EMISSIONS:
Fuel is injected at high pressure (through fuel injectors which
atomize the fuel) into the combustion chamber towards the end
of the compression stroke. The fuel ignites, thereby increasing
the pressure in the combustion chamber and pushes the piston
downward on the power stroke. When the fuel ignites, the flame
front travels rapidly into the combustion space and uses the
compressed air to sustain the ignition. Temperatures at the
envelope of the flame can exceed 1300 degrees C, although the
mean bulk temperatures in the combustion chamber are much
lower. At these localized high temperatures molecular nitrogen in
the combustion air is oxidized and nitrogen oxides (NOX) are
formed in the combustion chamber. Oxidation of molecular
nitrogen in the combustion air comprises of about 90% of all
NOX, the other 10% is the result of oxidation of the organic
nitrogen present in the residual fuel oil.
9/23/2014 6

The NOx-influencing components and settings depend on the
design of the particular engine, and shall be listed in the engine’s
Technical File.
The below list shows typical NOx-influencing parameters, but are
not limited to:
1. Injection timing
2. Injection system components (nozzle, injector, fuel pump)
3. Software no, checksums, or other identification of software
version
4. Hardware for fuel injection control
5. Camshaft components (fuel cam, inlet- and exhaust cam)
6. Valve timing
7. Combustion chamber (piston, cylinder head, cylinder liner)
8. Compression ratio (connecting rod, piston rod, shim, gaskets)
9/23/2014
7

9. Turbocharger type and build (internal components)
10. Charge air cooler/charge air pre-heater
11. Auxiliary blower
12. NOx reducing equipment “water injection”
13. NOx reducing equipment “emulsified fuel” (fuel/water
emulsion)
14. NOx reducing equipment “exhaust gas recirculation”
15. NOx reducing equipment “selective catalytic reduction”
The actual Technical File of an engine may include less
components and/or parameters other than the list above,
depending on the particular engine and the specific engine
design.
9/23/2014
8

NOx Emission Standards
NOx emission limits are set for diesel engines depending on
the engine maximum operating speed (n, rpm), as shown in
Table 1 and presented graphically in Figure 1. Tier I and Tier
II limits are global, while the Tier III standards apply only in
NOx Emission Control Areas.
Table 1. MARPOL Annex VI NOx Emission Limits
Tier Date
NOx Limit, g/kWh
n < 130 130 ≤ n < 2000 n ≥ 2000
Tier I 2000 17.0 45 · n-0.2 9.8
Tier II 2011 14.4 44 · n-0.23 7.7
Tier III 2016† 3.4 9 · n-0.2 1.96
† In NOx Emission Control Areas (Tier II standards apply outside ECAs).
9/23/2014 9

Figure 1. MARPOL Annex VI NOx Emission Limits
Fig. 3: IMO NOx limits
9/23/2014 10

NOx emission limits – Approved Method
Ships constructed - 1 Jan 1990 to 31 Dec 1999
Required to fit an “approved method” to enable the engine to
meet Tier I limits.
IMO to be notified of approved method
The approved method to be installed at first renewal survey
12 months after IMO notified the “method” is approved
9/23/2014
11

Tier II standards are expected to be met by
combustion process optimization. The parameters
examined by engine manufacturers include fuel
injection timing, pressure, and rate (rate shaping),
fuel nozzle flow area, exhaust valve timing, and
cylinder compression volume.
Tier III standards are expected to require
dedicated NOx emission control technologies such
as various forms of water induction into the
combustion process (with fuel, scavenging air, or
in-cylinder), exhaust gas recirculation, or selective
catalytic reduction.
9/23/2014 12

SOX EMISSION CONTROL
- 19 May 2005 Annex VI to MARPOL entered into force.
- The revised Annex VI to MARPOL was adopted by IMO on
10 October 2008.
Sulfur Content of Fuel
Annex VI regulations include caps on sulfur content of fuel
oil as a measure to control SOx emissions and, indirectly,
PM emissions (there are no explicit PM emission limits).
Special fuel quality provisions exist for SOx Emission
Control Areas (SOx ECA or SECA). The sulfur limits and
implementation dates are listed in Table 2 and illustrated in
Figure 2.
9/23/2014
13

* depending on the outcome of a review, to be concluded in 2018,
as to the availability of the required fuel oil, this date could be
deferred to 1 January 2025.
Exhaust gas cleaners/Emission Abatement Technologies
Permitted World wide and in ECA under Reg.4 – Equivalents
(Equivalence option limited to Parties)
9/23/2014
14
Outside an ECA established
to limit SOx and particulate
matter emissions
Inside an ECA established to
limit SOx and particulate
matter emissions
4.50% m/m prior to 1
January 2012
1.50% m/m prior to 1 July
2010
3.50% m/m on and after 1
January 2012
July 2010
January 2020*
January 2015

Figure 2. MARPOL Annex VI Fuel Sulfur Limits
Heavy fuel oil (HFO) is allowed provided it meets the applicable
sulfur limit (i.e., there is no mandate to use distillate fuels).
Alternative measures are also allowed (in the SOx ECAs and
globally) to reduce sulfur emissions, such as through the use of
scrubbers. For example, in lieu of using the 1.5% S fuel in SOx
ECAs, ships can fit an exhaust gas cleaning system or use any
other technological method to limit SOx emissions to ≤ 6 g/kWh
(as SO2).
9/23/2014 15

IMO and Regional Ship Air Emissions Control Developments:
-- Baltic Sea – SECA from 19 May 2006 (SOX)
--North Sea/English Channel– SECA from 21 Nov 2007
- Major Revision of MARPOL Annex VI completed in Oct 2008
- Revised Annex VI effective from 1 July 2010
- European Sulphur Directive governing emissions in port
(0.1% S at berth 1 Jan 2010)
- North American area ( effect 1 August 2012) – as defined in Appendix VII of
Annex VI of MARPOL (SOx, NOx and PM); and
-- United States Caribbean Sea area (expected to enter into effect 1 January
2014) – as defined in Appendix VII of Annex VI of MARPOL (SOx, NOx and
PM).
• ISO ongoing work on Marine Fuel Oil specifications
• Discussion and development : of on-shore power supply - also called
Alternative Marine Power (AMP) or Cold-ironing
• Green House Gases (GHG) limitations
9/23/2014 16

Regulatory drivers
 SOx:
 ECA-SOx  0.1% sulphur.
 Implications:
• Marine MGO
• LNG
• SOx scrubbers
 NOx:
 ECA-NOx  Tier III ( ~80%
reduction rel. to Tier I).
 Implications:
• LNG
• SCR (Selective Catalytic
Reduction)
9/23/2014 17

Market drivers / barriers
 Fuel price differentials:
 MGO and low sulphur HFO/
MDO
 LNG and liquid fuels (MGO,
MDO and HFO).
 Additional ships’ CAPEX and
OPEX:
 Scrubber costs
 LNG engineering systems
 Technology and infrastructure
availability. MGO and HFO price trends
9/23/2014 18

Options available
 MGO or LNG for ECA beyond 1/1/2015
 LS HFO or MDO for outside ECA beyond 1/1/2020 (or 2025)
 Scrubbers for both ECA and outside ECA
 LNG for both ECA and outside ECA
 SCR for inside ECA-NOx
 Other combinations of the above
9/23/2014 19

GHG Emissions
MARPOL Annex VI, Chapter 4 introduces two mandatory mechanisms
intended to ensure an energy efficiency standard for ships:
(1) the Energy Efficiency Design Index (EEDI), for new ships, and
(2) the Ship Energy Efficiency Management Plan (SEEMP) for all
ships.
1. The EEDI is a performance-based mechanism that requires a
certain minimum energy efficiency in new ships. Ship designers and
builders are free to choose the technologies to satisfy the EEDI
requirements in a specific ship design.
2. The SEEMP establishes a mechanism for operators to improve the
energy efficiency of ships.
The regulations apply to all ships of and above 400 gross tonnage and
enter into force from 1 January 2013. Flexibilities exist in the initial
period of up to six and a half years after the entry into force, when the
IMO may waive the requirement to comply with the EEDI for certain
new ships, such as those that are already under construction.
9/23/2014 20

DIESEL ENGINE EXHAUST GAS EMISSIONS CONTROL OPTIONS
1. Using of LSFO & HSFO
2. Basic internal engine modification technique – slide valves
3. Engine Tuning or Operational mode
i. Engine Timing
ii. Operational Mode
4. Hardware design modifications and enhancements
5. Direct Water Injection (DWI)
6. Continuous Water Injection to Charge Air (CWI)
7. Fuel-Water Emulsions (FWE)
8. Humid Air Motor (HAM)
9. Scavenge Air Moisturising system (SAM)
10. Exhaust gas recirculation
11. Selective Catalytic Reduction (SCR)
12. Scrubber technology
13. Using LNG
14. ESWS for PM and SOX removal
9/23/2014 21

1. Using of LSFO & HSFO :
- Arrangements for LSFO & HSFO: 2 0r more different
types of fuels.
- Availability –Bunking strategies
- Switch-over(12 to 24 hrs) will need to be changed over
the fuel for the SECA passages.
- Handling of cylinder oils –2 qualities may be required.
- More strict follow up through sample requirements, and
control of documentation and procedure to log down.
9/23/2014
22

23
9/23/2014

2. Basic internal engine modification technique
– slide valves
The most wide-spread internal engine modification technique
involves the exchange of conventional fuel valves with low-
NOX slide valves. Slide valves can only be delivered for MAN
B&W 2-stroke engines, but the modification of the spray
pattern can be implemented on any injection nozzle. Slide
valves are designed to optimise spray distribution in the
combustion chamber, which results in somewhat lower heat
release than the conventional fuel valves, which gives a
considerable reduction of NOX emissions.
Reduction efficiency:
The slide valves will reduce the NOx emissions by 20 %. On a
longer time perspective higher reduction may be possible.
9/23/2014 24

3. ENGINE TUNING OR OPERATIONAL MODE
i. Engine Timing
- In the case of compression ignition (diesel) engines and on spark
ignition (gasoline) engines, timing of the fuel ignition is set a few crank
degrees before the TDC. In diesel engines this means that the
beginning of fuel injection is started before the TDC on the power
stroke.
- The advance angle before the top dead center is the pre-ignition
angle and is mainly a function of the fuel type and the speed of rotation.
Normally, Engine manufacturers optimize this pre-ignition angle for fuel
economy and reliability of the engine components.
- Retarding the injection timing can lead to lower peak temperatures in
the combustion chamber and thus lower NOX emissions. In some
engines this timing can be adjusted in service while in others this
adjustment is a major undertaking. The NOX reduction potential is
limited (about 2-3%) and the trade-off is fuel economy.
9/23/2014 25

ii. Operational Mode
With the advent of electronically controlled engines where
the fuel injector is controlled by electronic means, fuel
injection rate shaping is possible. This fuel injection
shaping rate can be optimized for fuel economy or low NOX
emissions and selecting between the two modes of
operation is a control panel function and is done in service.
9/23/2014 26

4. HARDWARE DESIGN MODIFICATIONS AND ENHANCEMENTS
O ver the last several years with the aid of advanced analytical tools such
as computational fluid dynamics, engine manufacturers have conducted
extensive research into the combustion process which led to lower
emissions:
-Optimizing engine inlet valve,
- exhaust valve and fuel injection timing,
- injection pressure,
- injection pattern,
- lowering excess air ratio,
- lowering scavenge temperature,
- modifying the combustion chamber geometry.
It is estimated that these measures will reduce NOX from the current levels
by 20%. Further decrease in NOX will require conditioning the fuel and/or
the combustion air.
9/23/2014 27

5. Direct water injection (DWI)
Direct water injection (DWI) technology can reduce NOX emissions
from marine engines by 40 to 60%, through the injection of a high-pressurized
fine water mist into the combustion chamber [2].
Reductions in PM (smoke) emissions also occur. Water injection occurs
separately from (and just prior to) fuel injection in the combustion cycle,
cooling the cylinder and reducing NOX formation.
DWI technology uses clean water injected independently into the
marine engine combustion chamber close to the injected fuel to reduce
NOX formation. The system employs a uniquely designed combined
fuel-water injection valve and nozzle mounted on each cylinder of the
engine. Each nozzle has two separate needles for fuel and water,
which are controlled separately. The water to fuel ratio usually ranges
from 40 to 70% and this can reduce NOX emissions by up to about 50
to 60%. Therefore, on mediumspeed engines using IFO or HFO, DWI
produces NOX emissions levels typically in the range of 5 to 7 g/kWh
The NOx reduction efficiency has been showed to be 50 - 60 %. MAN B&W has
achieved 20 - 30 % while there are 9/23/2014 reports on lower reductions for other systems28.

Operating Principle:
Like any other of the water-fuel technologies, DWI reduces NOX by lowering the
initial temperature of the fuel combustion. In the injection sequence, water injection
occurs before the fuel injection, resulting in a cooler combustion chamber prior to
fuel combustion. The system is designed to operate at high water injection
pressures (21 MPa to 50 MPa depending on the engine) to properly atomize the
water stream after injection. The water injection stops before the fuel injection, so
that the fuel ignition and combustion process is not compromised. The NOX
reduction effect increases in a roughly linear relationship with increasing water-fuel
ratios.
9/23/2014 29
Fig. 1. Direct Water Injection Schematic Diagram (Wartsila Technology)

6. Continuous Water Injection to Charge Air (CWI)
Continuous water injection (CWI) to the charge air is a relatively
simple method of reducing NOX by up to 30% and PM emissions
by about 25%, without engine modifications.
Operating Principle:
A fine, freshwater mist is injected directly into the hot
compressed air of the turbocharger outlet. CWI achieved a 22%
reduction in NOX and an average reduction in specific fuel
consumption of 1%, which resulted in a net saving of
approximately $143 per tonne of NOX reduced. CWI is not
recommended at water-fuel ratios above 25% due to expected
fuel consumption penalties.
NOX emissions reductions follow a negative exponential pattern
with increasing water-fuel ratios. In Figure 2 the NOX reductions
are represented by the ratio of the controlled NOX formation rate
constant (K) to the uncontrolled NOX formation rate constant
(Ko).
9/23/2014 30

Fig. 4. Continuous Water Injection System Schematic Diagram
The greatest NOX reductions occur at the lowest water-fuel ratios
(slope of line is high) and reductions diminish at higher ratios (slope
is lower). At low water-fuel ratios (below about 25%), the presence
of the water acts to improve the combustion kinetics, which results
in a slight decrease in specific fuel consumption.
9/23/2014 31

Fig. 2. Theoretical NOX Reductions from Water Injection
However, above 25% water-fuel ratio, the water content starts to
interfere with the combustion process and specific fuel consumption
increases. Figure 3 shows that the optimum specific fuel consumption
is theoretically achieved at a water-fuel ratio of approximately 10%, and
that fuel penalties start occurring above 25%.
9/23/2014 32
Fig. 3. Fuel Consumption Effect of Water Injection

7. Fuel-Water Emulsions (FWE)
Fuel-water emulsion (FWE) systems c an reduce NOX formation in marine
diesel engines by 30 to 60% by intimately mixing water into the fuel oil.
The resulting dispersion of microfine water droplets in fuel is injected
normally into the engine cylinders. A significant benefit of FWE systems is
a drastic reduction of PM emissions (smoke ) and lower engine soot
deposition.
Fig. 5. Fuel-water Emulsion System Schematic Diagram 9/23/2014 33

FWE Operating Principle:
Fuel and water flow separately through a dosing control
unit and enter the homogenizer. The homogenizer unit first
creates a fine emulsion by shearing the fuel and water with
an electrically-driven mechanical mixer, the only moving
component of the system. The most common
homogenizers currently employ electronic transducers to
impart ultrasonic energy to the FWE to create microfine
emulsions, which have a high degree of stability. Ultrasonic
cavitation reduces water droplet size by almost an order of
magnitude. A water-content meter installed before the
engine injection controls the flows of water into the dosing
unit.
9/23/2014 34

8. Humid Air Motor (HAM)
The Humid Air Motor (HAM) system is a recent technology
that uses combustion air almost entirely saturated with
water vapour (humid air) in a marine diesel engine [3]. The
charge air is humidified by water vapour produced in a
humidification vessel by evaporating freshwater or
seawater directly into the charge air using the heat from the
engine or its exhaust gases.
NOX emissions reductions of 60 to 80% have been
achieved in demonstration tests.
9/23/2014 35

Operating Principle
The HAM system is based on the same general principle of the other
technologies that add water to the combustion chamber: the presence of water
reduces NOX formation in the cylinder. The key difference is that the water is
completely evaporated into the combustion air and mixed thoroughly prior to
getting to the cylinders.
After contacting with water in the humidification vessel, the relative humidity of
the combustion air is close to 100% saturation.
The presence of water vapour acts to change the thermodynamic properties of
the combustion air. The evaporation of water from liquid to vapour is an energy-consuming
process that reduces the temperature of the compressed air. The
HAM system can be used to replace the turbocharger intercooler. It is capable
of reducing typical charge air temperatures to 70°C versus 50°C for
conventional intercoolers . The saturated humid air has almost twice the heat
capacity of dry air. This allows more of the initial heat generated in the
compression cycle to be absorbed, reducing NOX formation. The presence of
water vapour also dilutes the combustion air. Since the concentration of oxygen
in the cylinder is reduced, there is lower excess oxygen and a reduced
tendency for NOX formation. Another advantage of using water vapour is that it
is mixed completely in the saturated air, producing no local “hot spots” in the
cylinder. This contributes to a uniform combustion process.
9/23/2014 36

Fig. 6. Humid Air Motor System Schematic Diagram
9/23/2014 37

9. scavenge air moisturising system (SAM)
The SAM system has a seawater injection stage, where a
surplus of seawater is injected for saturation and cooling of the
hot air from the compressor. The sea water stage will provide a
near 100% humidification of the scavenge air and supply all of
the water for humidification.
The SAM system from Man B&W and the WetPac from Wärtsiä
are in principle the same techniques as HAM. The SAM system
reduces NOx emissions by spraying sea and fresh water into the
hot scavenging air for cooling and humification of it. The water
injection takes place in three stages. First sea water is used for
humification and cooling and then two fresh water stages for
removal of any salt from the scavenging.
The scavenging air will be fully saturated. From each of the
stages, surplus water will be drained back into three different
tanks.
9/23/2014 38

Fig. 10: SAM part on the engine
9/23/2014 39

The reduction efficiency of HAM is reported to be 70 – 85
%. The latest measurements on Mariellas four engines
have shown emissions on the main engines to be reduced
from 17 to between 2.2 and 2.6 g/kWh. For the Wetpac
method the reduction efficiency is reported to be equal to
50 % below the present IMO NOx curve, equal to 7
g/kWh. For SAM 30-40 % reduction is expected, but since
it is still under testing, these levels may be somewhat
uncertain.
9/23/2014 40

10. Exhaust gas recirculation
When a small percentage of e xhaust gas is introduced into
the combustion air, the oxygen purity of the combustion air
is reduced leading to lower NOX emissions. This system is
widely employed on smaller car and truck engines
Fig: The newly developed EGR scrubber applied to the test engine
9/23/2014 41

Various arrangements have been tested for recirculation, including
internal recirculation in 2-stroke engines by timing adjustment, hot and
cold exhaust recirculation from the high and low pressure side of
exhaust gas turbocharger. This system is an effective means of NOX
reduction. With a 20% EGR NOX reduction is in the order of 50% with
very little fuel consumption penalty.
Operating Procedure:
In an EGR system, exhaust gases from the engine pass through the
turbocharger, releasing energy to compress the incoming combustion
air. The temperature and pressure of the gases are reduced
considerably. A portion of the exhaust gases is recirculated back and is
added to the compressed air before the cylinder. Particulate filters are
used to remove entrained solids prior to mixture with the combustion
air. The exhaust slipstream flow is carefully controlled to adjust for
engine load changes. The lower temperature of the exhaust gases
contributes to a cooler combustion. The increased mass flow increases
the combustion pressure and dilutes the oxygen content. All these
effects contribute to lower NOX formation.
9/23/2014 42

11. Selective Catalytic Reduction (SCR)
An SCR (Selective Catalytic Reduction) unit is an effective
means of conditioning the exhaust gas after the combustion
process for reducing NOX already formed in the combustion
process.
The process essentially involves injecting ammonia in the
exhaust stream and in the presence of a catalyst the NOX reacts
with the ammonia and forms water vapor and nitrogen. Due to
the hazardous properties of ammonia, urea solution is generally
used to provide the required ammonia.
Selective catalytic reduction (SCR) is the only technology that
controls NOX emissions in the exhaust gas after they have been
generated. SCR is capable of reducing NOX emissions by up to
99% by reacting NOX with ammonia (from a urea solution) over
a catalyst in the hot exhaust gases of marine engines. Inert
nitrogen and water are produced in the reaction. HC and CO are
also reduced significantly, but PM and SOX are uncontrolled.
9/23/2014 43

Operating Principle
SCR is based on a reaction between urea - decomposed to ammonia
(NH3) - and NOx in the flue gas over a catalyst. NOx is then reduced to
nitrogen (N2). Urea solution is injected into the hot flue gas after the
combustion. SCR can be installed in or after any type of motor, as long as
the flue gas temperature is in the specified temperature interval, from 270
oC up to 500 oC, usually around 320 oC. The urea injection is automatically
tuned to power changes in the engine.
Once the urea solution is vapourized in the hot exhaust gases, it
immediately decays to ammonia and CO2 and the following two reduction
reactions convert the NOX to nitrogen and water:
4NO + 4NH3 + O2 ----------> 4N2 + 6H2O
6NO2 + 8NH3 ----------> 7N2 + 12H2O
The catalyst is made from titanium oxide and vanadium oxide and consists
of small exchangeable units (monolites of extruded ceramics).
9/23/2014 44

Fig: Selective Catalytic Reduction Schematic Diagram
Reduction efficiency for NOx :
Technically it is possible to reach 95 % or even higher reduction.
However, the NOx reduction efficiency of the SCR is often
operated to reach around 90 %. The efficiency is dependent on
the urea flow. To achieve 90 % NOx reduction approximately 15 g
urea is needed per kWh energy from the engine. The engine may
be fuel-optimised, so that the fuel consumption is minimised to
the cost of somewhat higher NOx emission. In this way lower
fuel consumption can be combined with low NOx emissions.
9/23/2014 45

SCR for ships
 Effective method for reducing NOx.
 Installed on many ships.
 High initial costs.
 High running costs (cost of urea
and maintenance).
 NOx regulatory limits from 2016
will lead to wider use of this
technology.
 Not compatible with use of
SOx scrubbers.
Ref: Wartsilla
9/23/2014 46

12. Scrubber technology
Source: Force Technology, 2012 9/23/2014 47

Types of SOx scrubbers
 Wet scrubbers:
 More conventional ones as used in land-based power
stations.
 Small ones are routinely used on oil tankers for IG scrubbing.
 Two types:
• Sea water (open loop) scrubber
• Fresh water (closed loop)
• Hybrid of the above
 Needs water treatment plant and other auxiliaries
 Dry scrubbers:
 They rely on dry material such as Caustic Soda (NaOH) to
absorb SOx:
• NaOH + SO2 → Na2SO3 + H2O
• NaOH + SO2 + O2 → Na2SO4 + H2O
 Needs supply of these materials to ships.
.
9/23/2014 48

Open Loop Scrubber System
salt water scrubbing is a open system. It is considered to be a cost-effective
readily available technique. The main principle is that warm
exhaust gases are mixed in a cascade of salt water and the SO2 in the
exhaust is caught in the slightly alkaline salt water. The water is re-circulated
and particles are separated in a settling tank. The sludge is
later disposed. Filtered and used sea water is brought back to the sea.
However, there are discussions of the quality of the used water and
how it should be treated. Due to formation of sulphuric acid in the
scrubber, corrosion problems may arise.
Closed Loop Scrubber System
The system operates in a closed loop, i.e. the wash water is being
circulated within the scrubber. Exhaust gas enters the scrubber and is
sprayed with fresh water that has been mixed with caustic soda
(NaOH). The SOX in the exhaust react with this mixture and are
thereby neutralised.
9/23/2014 49

From the closed loop, a small bleed-off is extracted and
treated to fulfill requirements stipulated by the IMO.
Cleaned effluents can be safely discharged overboard with
no harm to the environment.
Using a fuel with 2.5 % sulphur, a reduction of the SO2
emissions from around 70 to over 90 % is possible. The
efficiency depends on contact time between sea water and
exhaust gases, but also the salt concentration and the
temperature may influence the reduction.
9/23/2014 50

13. ESWS for PM and SOX removal
Electrostatic seawater scrubber for PM removal
Employs electrostatic forces for enhance removal efficiency via:
• electrically charging of spray droplets,
• electrically charging of particles oppositely to droplets,
• electrostatic deposition of the particles onto droplets.
It combines advantages of other methods like conventional or Venturi
scrubbers and dry or wet electrostatic precipitators.
Electrostatic seawater scrubber for SOX removal
Electrostatic interactions between charged droplets and dipole
moleclues (e.g. SO2) increases the absorption rate.
It allows reducing scrubber height
9/23/2014 51

Physical background
10-1 100
101
dp, m
1.0
0.8
0.6

0.4
0.2
0.0
SO2
q/qR = 0.3
q/qR = 0.1
q/qR = 0. 05
q
q/qR = 0
/qR = 0. 01
9/23/2014 52

ESWS design
Exhaust
gases
PM,
soluble
gases
 400 ppm SOx (2% sulfur),
5.0E+11
4.0E+11
3.0E+11
2.0E+11
1.0E+11
0.0E+00
Particle diameter, nm
Particle concentration,
#/m3
9/23/2014 53

ESWS design - details
Wet electrostatic scrubber for PM removal
9/23/2014 54

14. Using of LNG
 LNG: Liquefied Natural Gas.
 Natural gas (NG) is mainly methane (~95%) with some ethane and
propane (together about 2-3%) plus small amounts of other gases:
 N2
 CO2
 H2S
 NG under atmospheric pressure is liquefied at -162 0C.
 LNG tanks remain at this temperature via vaporization of gas in
proportion to heat input (BOG: Boil Off Gas).
 BOG is then either re-liquefied or burned.
9/23/2014 55

LNG as compare to liquid fuels
 Volumetric energy density of LNG is less than FO
 LNG (22 TJ/m3) and FO (39 TJ/m3)
 Mass energy density of LNG is higher than FO
 LNG (55 MJ/kg and MDO (42.8 MJ/kg)
 Almost no sulphur
 Very low flash point of NG at ~ -149 0C (gas oil is ~74 0C).
 Vey high auto-ignition temperature of 540 (Gas Oil is ~315 0C)
9/23/2014 56

Dual fuel engines: Basic principles
 They work according to diesel
principle (Compression Ignition).
 Liquid fuel is used as pilot injection
to initiate combustion.
 NG is mixed with air prior to pilot
injection.
 The design could facilitate a varied
ratio between liquid fuel and LNG.
Source: Wartsilla
9/23/2014 57

Dual fuel (DF) engines
 Ability to operate on a wide range of fuels
(LNG, HFO, LSFO, MDO).
 Flexibility to operate across ECA zones.
 Mature technology.
 Technology is mainly for 4-stroke engines.
 MAN Electronic–Gas Injection (ME-GI)
2 stroke dual fuel
High pressure gas direct injection
Simultaneous burning of HFO and NG
With EGR meets Tier III NOx limits
MAN ME-GI
9/23/2014 58

Dual fuel engines: Types
 Conventional DF engines are low pressure gas supply into intake system.
 MAN ME-GI is high pressure dual fuel with fuel directly injected inside
cylinder.
9/23/2014 59
Source: MAN B&W

Pure natural gas engines
 Works with 100% gas.
 Single fuel natural gas
engines
 Low pressure gas.
 Spark plugs initiate combustion:
 Works according to Otto
cycle
 Less efficient than the diesel
options.
Source: Rolls Royse (Bergen K-GE)
9/23/2014 60

9/23/2014
61

For more information please see:
www.imo.org
Reference:
1. www.imo.org
2. www.dieselnet.com
3. IMO MEPC Air pollution prevention and energy efficiency working group
4. Marine Environment Division, IMO.
5. www.mandieselturbo.com
9/23/2014 62

ANY QUESTION?
THANK YOU!
9/23/2014
63

Marine Diesel Engine Exhaust Gas Emissions Control Technologies

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