In 2020 IMO has compiled some new regulations, which forces the shipping companies to adapt to these legislations in order to operate at sea. The new legislation states that the sulphur content outside ECA are allowed to be 0,5% and NOx has to be controlled depending on which tier class the ship belongs to. In this page, methods to achieve the legislation is described including, scrubber, emulsifier, exhaust gas recirculation, low sulphur fuel and LNG. The page will describe and analyze some of the methods and give a suggestion on which of the systems should be applied to Britta Maersk to comply with the legislation. The analyze will consider economics briefly regarding operational costs and consider the advantages and disadvantages that belongs to the systems.
In the following page, there are certain limitations. This page focuses on the emission regarding NOx and SOx, and will not be focusing on PM.
Since information about prices on the certain system is not available for us, the choice of equipment is not depending on purchase expenses. Due to the size of this page, it is not all emission lowering systems there are going to be discussed.
With the evolving focus om emissions and fuel consumptions, it is important for the shipping companies to follow the progression in the maritime world to maintain their position on the market. More demands regarding the emissions are coming due to the fact global warming, is acknowledged as a problem, and because research has stated the emissions has fatal consequences for humans. In 2020 IMO has made some new regulations regarding NOx and SOx emission limits, the shipping companies must comply with these regulations to be allowed to operate at sea.
Statement of intent:
What are the new 2020 legislations?
What kind of solutions can be applied to Brita regarding compliance with the 2020 regulations?
Which implementation would be the best solution regarding Britta Maersk
To achieve the knowledge needed for this assignment, regarding information concerning the environmental impact of the maritime pollution, and possible ways to decrease this. We use a quantitative method for this assignment, this method is based on finding information thru given material, books, and desk research thru the internet. By using the internet, it becomes possible to acquire the newest available intel and take different problem-solutions into account when solving the problem statement. To analyze the following topics, we use equations from the current and earlier semesters.
SOx and NOx are considered as a global environmental threat, the following section will describe its origin and how it is produced in the maritime industry.
Because of the high content of Sulphur compound used in the marine fuels, a high concentration of Sulphur oxides is formed, when Sulphur is mixed with air and combusted, it oxidases and becomes SOx. Sulphur can take two forms, either Sulphur trioxide or Sulphur dioxide, it is the relation between oxygen and Sulphur that determinates the outcome:
Sulphur dioxide: S(s) + O2(g) → SO2(g)
Sulphur trioxide: 2S(s) + 3O2(g) → 2SO3(g)
When particles in the exhaust gas oxidize, and a catalyst like NO2 is presented, it will create Sulphur acid, which is a reason for acid rain. Acid rain can also be created when Sulfur dioxide reacts with water and forms sulfurous acid:
SO2(g) + H2O(l) -> H2SO3(aq)
Acid rain is not dangerous for humans when it is combined with water, but when found in the air it can turn into fine sulfate. When sulfate is inhaled it can cause heart attacks, bad lounge function and severe breathing problems for people whit asthma.
Also, fish and wildlife are affected by acid rain, most seen in aquatic environments where the acid runs through the soil, figure 1 shows the critical limit for different spices are, sulphorious acid has a PH value of 1,5 making it harmful aquatic animals.
Studies also show that SOx emissions lead to the formation of secondary inorganic aerosol gases, which are fine particles, considered very dangerous to humans.
The easiest way to decrease this problem is to use a fuel containing less sulpher, the Sulphur content in the fuel can be lowered by refining the fuel
NOx is the term for Nitrogen dioxide (NO2) and Nitrous Oxide (NO)
Nitrogen is naturally found in the atmosphere as well as in fuel, when fuel is combusted NOx can be formed in the three following ways:
When a mixture of nitrogen found in the atmosphere and oxygen, reaches a high temperature usually above 1600 °C
as a result of the reaction between nitrogen in the fuel and oxygen
as a result of the reactions with hydrocarbons and atmospheric nitrogen.
NOx is created in the early stage of combustion at high temperatures, and later in the combustion after a longer period in the combustion chamber. This means that in order to create the formation of NOx both high temperatures and exposure time is required
Although nonroad NOx emissions only consist of 7% figure 2(EU 2011) the number is high taken the ratio between cars and ships into account
Figur 2 Emissions devided into categories
So in regards to health and environmental impacts its clear why MARPOL Annex VI Regulation 13 sets limits in regards to NOx.
NOx causes respiratory conditions, and long-term exposure can decrease lung function, NOx also increase the formation of fine particles (PM) and a rise of ozone at ground level, which both are leading to severe health effects
Therefore, several solutions have been made to minimize the production of NOx, mentioned later in this page
Air pollution regulations:
In order to achieve a better air quality, the extent of regulations continues to increase, and the emissions limits get stricter. Shown below is the demands for Annex VI of the MARPOL Convention. This Convention affects all ships trading internationally.
MARPOL Annex VI primary goal is to reduce NOx and Sox emissions, other pollutants like carbon monoxide and particulate matter, have not yet gained any standards for emissions limits
SOx emission regulations:
MARPOL Annex VI Regulation 14
Regulation 14 seeks to lower the Sulphur and PM content in the fuel, in order to decrease SOx and PM, the regulation works in several steps and has increased demands inside ECA
As shown on figure 3 The ECAs established areas are:
Baltic Sea area – as defined in Annex I of MARPOL (SOx only);
North Sea area – as defined in Annex V of MARPOL (SOx only);
North American area (entered into effect 1 August 2012) – as defined in Appendix VII of Annex VI of MARPOL (SOx, NOx, and PM);
The United States Caribbean Sea area (entered into effect 1 January 2014) – as defined in Appendix VII of Annex VI of MARPOL (SOx, NOx, and PM).
As seen in figure 4 , where the fuel oil Sulphur limit is set to 0,50% by 2020, the reason why there is another deadline. Is that this may not be possible to for fill. In 2018 there will be performed a fuel oil availability test where it will be decided, whether it should be in 2020 or 2025 the legislation enters into force
Figur 4 Guidance for shipowne
rs and operators, Lloyd’s register PDF
MARPOL Annex VI Regulation 4:
This regulation allows flag administrations to approve ships to sail on fuel that has a higher sulphur content than stated in regulation 14, but only if the following guidelines are taken into advance:
The SOx emissions isn’t higher than if the ship sailed on fuel that complied whit regulation 14.
This can be accomplished by fitting a scrubber, but if this method Is used it must be approved by flag administration, and notified to IMO.
NOx emission regulations:
MARPOL Annex VI Regulation 13
On figure 5 is the limits stated by Regulation 13 shown, the limits are divided into 3 tiers. How these tiers apply depends on:
The ships construction date, or if the ships has fitted an additional, or nonidentical replacement engine
Engine speed (rpm)
The limits on the three tiers are as mentioned below:
Tier l: apply to engines installed on ships built on or after 1 January, 2000.
Tier ll: apply to engines installed on ships built on or after 1 January , 2011.
Tier llI: apply to ships built on or after 1 January, 2016, if operating within the North American and US Caribbean ECA-NOx
Figur 5 Tier categories
Its main purpose is to reduce nitrogen oxide (NOx) this is done by recirculating a small amount of cooled exhaust gas back into the combustion chamber, this creates a mixture that dilutes the original oxygen mixture, incoming from the inlet manifold. By adding this inert gas to the incoming air, it becomes possible to slow the combustion and reduce combustion temperature, which will result in a decrease in NOx.
EGR valves are considered highly effective at reducing NOx, studies show that a decrease in 90% NOx production is possible, making this method capable of reaching tier lll whithout any after treatment.
A disadvantaged by using an EGR valve is the increased particulate emissions, in the future it could be necessary to have a system for after treatment of the particulate emissions.
Fuel water Emulsion technology (FEW):
The NOx emissions increases with the combustion temperature, a way to reduce the pollution of NOx is therefore to bring down the combustion temperature.
Fuel water emulsion technology (FEW or WIF) is a technique where water is continuously added to the fuel in a homogeneous way through an emulsifier, ensuring the fuel and water are not separating. An emulsifier is used to reduce the size of the droplets since larger droplets have a stronger tendency for sedimentation
When the mixture is injected additional heat is required to heat up the water to the boiling point, the evaporation and super heating, is requiring energy and thereby reducing the combustion temperature. A rule of thumb is that the NOx emission is reduced 1% per 1% presented water added to the mixture .
On figure 6 is showed a stable emulsion, and the difficulties faced using an emulsifier. it is important, that each droplet is surrounded by fuel, and not beginning sedimentation or flocculation, where the droplets react with each other.
By adding water into the fuel, tests have shown some advantages and disadvantages:
– Disadvantages: Due to the fact, that energy is required to heat up the injected water, the SFOC will increase.
– Advantages: NOx level decreases, The CO emission decrease rapidly, SOx emission decrease rapidly, Particulate emissions decreases,
Figur 6 Dificulities and stable emulsions
In order to comply with the legislation stated by MARPOl Annex VI, which requires the SOx and NOx emissions reduced, is one of the possibilities too for fill those requirements the use of a scrubber. The scrubber is defined as “An alternative means of compliance” and therefore needs an approval by or on behalf of the flag state and needs to be notified to the IMO The approval is needed to ensure the equipment meets with the required performance criteria and classification society approval to show that the equipment does not present an unacceptable risk to the ship and its crew . By using a scrubber redundancy is required, since you are not allowed not fore fill the legislation at any time stated by MARPOL Annex VI.
Types of Scrubbers:
The principals of a scrubber system are to wash out the Sulphur particles in the exhaust gas. This is done by a chemical reaction between the Sulphur and alkanity in the water used in the scrubber. The reaction creates sulfuric acid and it is there for important the water used can absorb this sulfuric acid to avoid corrosion .
There are two main types of SOx scrubber:
Wet scrubbers – Wet scrubbers use water (seawater or freshwater) as the scrubbing medium.
Dry scrubbers – Using a dry chemical as a medium for scrubbing.
Dry scrubber: Dry scrubbers are mainly used on shore, and will not be described in the page.
Wet scrubbing is the most common technique used onboard vessels, it is a simple, effective and robust way to lower SOx level in the exhaust gas.
The wet scrubber can be divided up into three different types:
Open Looped – which uses seawater for washing.
Closed Lopped – Which uses seawater combined with the alkaline chemical.
Hybrid Looped – Which can be either of the above.
Open looped System:
The open looped system uses seawater to washout the Sulphur in the exhaust gas, the system utilizes the natural alkalinity in the seawater and can be used in most seas around the world where alkalinity levels are sufficient.
Figur 7 Open looped scrubber
In the open looped method, the seawater is pumped in directly from the sea or the seawater chest, into the scrubber, where it is sprayed into the exhaust gas. The alkanity will react with the Sulphur in the gas and creates sulfate. The wash water is afterwards led into a water treatment system, to separate the particles from the water, which are separated into the sludge tank.
The seawater is monitored for its PH value both at inlet and outlet in order to show compliance with regulations stated in MEPC washwater discharge criteria 10.1.2.1 before discharged overboard. The open loop system may in the future meet some restrictions due to the acidity of washwater discharged. There have also been concerns about contaminants which are not monitored, an example could be heavy metals and the potential that those heavy metals would accumulate in the sediments, in shores or other areas with limited water exchange
In a closed loop scrubber, treated water in this case with sodium hydroxide(NaOH) is circulated through the scrubber to keep the process independent from the seawater. In the closed loop scrubber, the amount of water discharged is minimized or none if a holding tank is available to store, which makes it suitable for special areas, where discharging is not allowed. The chemical processes to remove SOx emissions are similar to the open looped system, the main difference is that the closed looped system does not discharge the wash water immediately, but circulates through the process tank where it is being processed and then recirculated through a cooler and into the scrubber to perform a new cycle. Before entering the cooler, the water is dosed with caustic soda to restore its alkalinity, and th
ereby able to react with the sulphur. In the process tank, the dirty wash water is removed through a low suction pipe, where it goes into the water treatment system like the open looped system, when the water has been cleaned and the residual sludge removed into the sludge tank, the water will be discharged overboard or kept in a holding tank, depending on the local regulations
Figur 8 Closed looped scrubber
Due to the different advantages of open and closed systems, a combination has been made. This system allows you to run an open system when you are not in a zero-discharge zone. And allows closed systems in zones not for filling the requirements for alkalinity contents or zones where you are not allowed to discharge.
Figur 9 Hybrid Scrubber, running as open looped
liquefied natural gas (LNG):
LNG is the liquid form for natural gas, this state is reached by cooling the liquid down to -162° C (depending on the quality of the gas), this is done by using an LNG condensator. When the liquid form is reached the volume is decreased 600 times, which makes it easy and economical to transport. A concern using LNG has previously been however there are enough, but it is estimated that we have supply enough for the next 230 years assumed that we continue our current LNG consume.
The process of cooling the natural gas requires a lot of energy, therefore the most profitable way to transport it is through a pipe system if the local infrastructure allows it. But because the natural gas often is found in very isolated areas or at places where there is no demand for natural gas, the gas is often transported as a liquid onboard ship. When offloading the liquid is heated up to gas form and then delivered to the LNG gas terminals, this means that the amount of energy natural gas takes when transported thru ships is significantly higher than through piping systems, making it less climate-friendly
Natural gas (methane) quality:
When choosing an LNG engine, the minimum methane number the engine can run on is an important factor, the methane number indicates the quality of the gas, if a gas has a methane number of 70%, its equivalent to a gas comprised of 70% methane and 30% hydrogen
if an engine with a minimum methane number of 80% is chosen, it can only use 38% of the global produced methane, which could lead to problems when large supplies of LNG is needed. Therefore the minimum methane number should be taken into account when ordering a new engine, as figure 10 shows an engine with a minimum number of 70 can use 90% of the global LNG supply. It is possible to get ridge of this problem by ordering an engine that is capable of
using all methane qualities like the MAN ME-GI
Figur 10 MAN B&W Dual Fuel Engines – Starting a New Era in Shipping PDF
Dual fuel engines running on LNG as a primal fuel, are built upon well-known diesel engine technology, this means the dual fuel engines are able to operate on 100% diesel fuel, which come in handy when idling, or doing port maneuvers. The dual fuel engine is not capable to run on 100% natural gas, because of the high self-ignition temperature, this means the combustion does not occur before a spark is present. This spark I generated by using a pilot fuel, heavy fuel oil, marine diesel oil or marine gas oil can be used as a pilot fuel.
Combustion Cycle for Two-Stroke Dual-Fuel Engine:
The ideal way to mix air with gas, is through the air intake, but because the air intake is used for scavenging air in a two-stroke engine it is not possible, therefore it is injected just as the pilot fuel, through an injector, into the compressed air.
Figur 11 Working principle of combustion with Dual fuel
Figure 11 shows the injection system for a two-stroke dual fuel engine. For the natural gas to be able to be injected into the compressed air. It must reach a pressure higher than 30Mpa, this is done by vaporizing the liquid natural gas. Because the bypass system (explained below) makes sure knocking does not occur, the changeover from fuel oil to gas can be done easy and fast.
’’Happens when the air, fuel mixture inside the combustion chamber is incorrect, making the fuel burn unevenly. In most conditions, the fuel burns in pockets, rather than in one fireball within, and when each pocket of fuel burns, a shock occurs that burns the next until all the fuel is burned in that stroke. When a knock is present, the pockets don’t burn evenly, causing shock waves at the wrong times that can damage the cylinder wall and the piston itself. This also creates the common “pinging” noise that is often described when knock is present.’’
To avoid misfiring or knocking due to the turbochargers speed, not being able to follow the rapid changes in load that can occur, a bypass air system is installed. This system purpose is to keep the excess air ratio at an acceptable zone, by adjusting the intake air flow.
Figur 12 The bypass system
Most dual fuel engines have 3 running modes, this gives them a big advantage compared to LNG only or fuel oil only, when in port, fuel oil mode is the preferred choice, because of the modulation needed for port maneuvers, or when sailing I areas with strict emissions tolerances, the minimum fuel oil mode is engaged. All dual fuel engines must be started in conventional diesel fuel oil mode
The 3 stages are described below:
Only fuel oil mode
Minimum fuel oil mode
Mixed gas mode
Only fuel oil mode:
Engine runs only on traditional fuel oil. This state is as mentioned chosen when maneuvering, or when gas fuel is not available.
Minimum fuel oil mode:
Is used for gas operations, this mode can only be started manually on the gas main operating panel in the control room, when running, a control system will adjust the ratio between gas and pilot fuel, in regards to the minimum amount required of pilot fuel, it is typically 1-5 % at full engine load and approx. 2% at 10% load As seen in figure 13 in start up the engine will run on fuel oil only, until it reaches approx. 10% engine load.
Figur 13 Figur 13 Min. fuel
Mixed gas mode:
This mode offers an increased fuel modulation, and a possibility to inject a constant amount of gas, after which the control system will add up fuel for the required load for the operation
Figur 14 Mixed fuel mode
Fuel choice for different running modes:
If using HFO as a pilot fuel, and tend to use fuel oil only mode for longer periods of time its recommended to install two lubrication oil tanks, one for each running mode. MAN describes having good experiences with BN 40 lubrication oil for minimum fuel oil operations, and BN 70 for fuel oil only mode
Capable of reaching tier III and 2020 SOx limits:
For the dual fuel engine to be able to comply with tier lll, it requires a lean burn principle meaning a low-pressure gas fuel injection, where the fuel and air are premixed and burned at a higher air to fuel ratio, this means adding the gas into the scavenge air at mid-stroke position, right before the piston reaches top position w
here the pilot fuel is injected at a quantity of 1%. This method requires injection timing control that allows a delay for the pre-mixing of the gas and air, this prevents the fuel-air mixture from coming in contact with the exhaust gas.
This results in an 85% reduction of NOx compared to and high pressure direct injected gas diesel engines, shown on figure 15
And a 99% lowering in SOx compared to a normal diesel engine.
Difficulties using dual fuel:
Gas fuel supply infrastructure:
Previously the lack of LNG terminals, Availability, and bunkering of LNG, was a big concern, but as shown in PDF 12 the development of LNG terminals is expanding rapidly, and many of them are placed in the ECA’s where the demand for LNG will be higher. On figure 16 is an overview of some import and export terminals, showing the rising availability of LNG supply.
Lloyd’s Registers indicates that the majority of the biggest bunkering stations for oil are placed advantageously close to LNG terminal, making the dual fuel option more interesting
Figur1 LNG stations
One key factor when considering converting to a duel engine, is bunkering of LNG onboard ship and the availability of the gas, if these requirements cannot be met, LNG does not seem to make sense, to overcome these problems several solutions can be done:
Ship to ship LNG bunkering:
Ship to ship bunkering has been recognized as a potential solution to the limited LNG storage onboard many ships, the non LNG carriers that cannot rely on their own productions of boil-off gas, are depending on their own supply of LGN, which in most cases gives a limited reach. To comprehend with this limitation, without having to go to an LGN terminal, ship to ship LNG bunkering is in the development. This year Skangas successfully made their first ship to ship delivery of LNG, and are estimating that they are able to provide ship to ship supply of LNG by 2018.
Storage of LNG onboard retrofitted ships:
To show the difficulties the size of storage tanks will have. A calculation is made, this example is based on a ship with a similar size as the Bit Viking (Shown later) To determinate the size of the LNG tank needed:
Voyage length approx. 14 days, Estimated consumption a day 50m3 (safety margin 10%)
Power increase due to bad weather 15%
Capacity_needed=days·m^3/day·10%_(safety margin)·15%_(bad weather)=
Because it is a dual fuel engine it is not needed to have a larger tank, in case of an extended voyage, or even heavier weather, it is possible to switch over to fuel oil, MDO for an example.
In case our study finds that a dual fuel engine retrofit would be the best answer, for Britta Maersk, an option for fitting an LNG tank could be on deck, just like Wärtsilä’s retrofit solution for the Bit Viking, see figure 15
Figur 15 Service tank for LNG on deck
The retrofit solution means building the old engine into and dual fuel engine. Both Wärtsilä and MAN offer this option on many of their current engines, and a retrofitting period that does not extend the standard docking period (approx. 30 days). For companies interested in an environmental propulsion solution. For an example, if they are operating In ECA areas. This could be a good alternative, especially because some dual fuel engines have achieved to for fill the requirements in the 2020 legislation.
Britta Maersk is fitted with a 5S50MC engine, unfortunately, MAN only delivers retrofit kits for the ME platform, the ME platform is upgraded with a system, that does not use a camshaft, but instead uses hydraulic oil for operating the exhaust and valve lifting. And an improved combustion due to an electronic control of the fuel injection
This means a dual fuel option requires an entirely new engine, making it quite an expensive implementation.
ULSFO or HFO:
To find out if the ULSFO could be an affordable solution as the preferred fuel for Britta Mærsk the following calculations have been made.
Information regarding fuel prizes is found 16-11-2017 at the port of Hamburg.
Engine power P_E = 6084kW
Specific fuel consumption F_cb =167,5 g/kWh
Engine speed = 127 rpm
Lower calorific value ULSFO = 42700 kJ/kg
Lower calorific value IFO380 = 39500 kJ/kg
Britta Maersk sailing 24 hours a day, 330 days a year.
Fuel Lower calorific value Price $/mt
IFO380 39500 kJ/kg 350.50
ULSFO 42700 kJ/kg 511.50
As shown above, the ULSFO have a better Lower calorific value, this leads to a new calculation of the SFOC value:
Fuel consumption for IFO380 (HFO)
F_ch(HFO) =F_cb(HFO) ·P_E=167,5·6084=1019070=1,02 (ton )/h
Fuel consumption for ULSFO
F_ch(ULSFO) =F_cb(ULSFO) ·P_E=154,947·6084≈942697,55=0,94 ton/h
Yearly cost using HFO:
Yearly cost_HFO=F_ch(HFO) ·hours·days·price_HFO
Yearly cost using ULSFO:
Yearly cost_ULSFO=F_ch(ULSFO) ·hours·days·price_ULSFO
0,94·24·330·511.50 ≈3808015,2 $/year
Increased cost when using ULSFO compared to HFO over a one-year period:
Yearly cost_ULSFO-Yearly cost_HFO=3808015,2-2831479,2 =976536,2 $/year
This shows a drastic increase in fuel expenses, making ULSFO as the only fuel, a very cost ineffective method to reach the SOx requirements. A solution could be having to service tanks for fuel, ULSFO for ECA, and HFO combined with a scrubber outside ECA.
Service tank for implantation of LSDFO:
Onboard Britta Maersk is located two tanks used for LSHFO, a service tank, and a settling tank, these tanks allow a possible change from LSHFO to ULSFO which content less Sulphur and thereby a way to comply with the MARPOL Annex VI requirements and the requirements for sailing into the ECA, however the changeover has shown some difficulties, that must be considered before implementing the change of fuel.
Problems with lubrication:
when changing to ULSFO, a problem with lubrication has previously been discovered. HFO has a certain content of Sulphur, as mentioned around 2,5-3,5%. When choosing lubrication oil the BN (base number) has to be sufficient for your fuel. The base number is a “measure of the acid neutralizing power in a lubrication oil, also known as Total Base Number”. If the same lubrication oil as used for HFO with a content of 3,5% is used for ULSDO with a Sulphur content around 0,1% the BN would not be sufficient for that.
Lubrication oil base consists primarily of calcium carbonate (limestone – CaCO3) and after reaction with the Sulphur, Calcium sulphate (gypson -CaSO4) is formed . However, since the lubrication oil used was designed for a higher sulpher content there will be unreacted CaSO3 left in the combustion chamber. It can form a very hard type of deposit, if this
deposit is formed the lubrication film can be disrupted and sudden severe wear may take place.
On figure 16 is shown how to choose your lubrication oil depending on your Sulphur content in the injected fuel.
Figur 16 Comparison of Base number and Sulphur content
Another problem with the high BN number is “the lack of corrosion”, it is believed by some engine designers, that a limited degree of corrosion keeps the structure of the cylinder liner surface open which allows the lubrication oil better conditions to create the necessary oil film layer is can be seen on figure 17.
So, regarding a changeover, it is important to change lubrication oil with a BN which has enough alkalinity to keep the neutralization and corrosion controlled, in order to avoid unreacted CaCo3 that will deposit on the piston crown or piston rings and to avoid bore polishing.
Figur 17 Deposit and bore polishing
Problems with incompatibility:
When the changeover takes place, there will be a mix for an extended period of time of two very different products. This can result in the asphaltenes in the HFO to precipitate as heavy sludge, which might result in filter clogging. This can be avoided by checking the compatibility between the fuels before leaving quay, since it may take some time for the results, it is likely the ship has already left the harbor before receiving the results. The test can be done manually, however, this test might be a little late since the fuel already onboard the ship and has most likely left the harbor.
When the changeover takes place, there is a period of time where it is a mixture between HFO and ULSFO in the pipelines, which has to be taken into account when entering the ECA. The level of Sulphur content in the exhaust gas, will while it is a mixture in the pipeline be higher than the 0,1% Sulphur content of ULSFO. The flushover time can be estimated by some known factors of the system. The calculation depends on the system capacity (total fuel pipeline) and consumption rate, and some high variables and uncontrollable unknowns the system can be fully flushed within 2 hours or days depending on the system. Some of the high variables are the deposits and associated sludge adhering to pipe walls and system components, since the LSDFO will tend to have a cleaning effect on the fuel system, the amount of these will depend on how often the ship changeover to LSDO.
Due to the change of fluid, different in viscosity, and the cleaning effect the LSDO has inside the pipelines, leakage through flanges, joints, seams etc. might occur however this is a question of proper maintenance.
Loss of power and propulsion:
When using HFO the normal temperature at the injectors are controlled to give a viscosity around 12-15cSt at which point operating with a relatively worn fuel pump with a clearance between the plunger and barrel can be operated . However, when running on LSDFO the viscosity can in some cases be around 3-6 cSt at the injectors. This change in viscosity change, might cause the LSDFO to leak through the clearance between the plunger and barrel, which leads to excessive leakage flow and hence an inability to create a sufficient injection pressure, this might lead to loss of power, or even no power depending on the fuel pump. Similar problems can occur with other pumps in the fuel system. This is relative easy problem to solve, since the worn components can be replaced.
Temperature and viscosity:
While running on HFO, heaters are needed to reach the operating viscosity, however when using LSDO a problem can be to keep the fuel sufficiently cool, so they maintain a sufficient viscosity to provide supporting hydrodynamic lubrication to the fuel oil system components. Therefore, it is necessary to control the heaters and ensure heat flows from elsewhere is controlled this could be from the main engine which while running on HFO was a benefit, but can be a problem due to the controlling the viscosity of the LSDO. The solution has been to install coolers in the fuel system, to keep the viscosity sufficient, and ensure the supporting lubrication of the pumps, and thereby avoid wear, followed by seizures on the pumps.
The difficulties can be solved by proper maintenance of the system, the leakage that might occur because of the change in viscosity can be solved by replacing worn equipment and tighten the pipeline flanges. The condition of the fuel pumps must be checked and a maintenance plan for the pump should be made in order to ensure stable operation conditions, otherwise, the problem with loss of power as mentioned above earlier might occur
However, for the changeover to be successful, the temperature and viscosity problem must be solved in a proper way, to ensure a stable and efficient performance of the main engine. The viscosity can be controlled by adding a cooler to the system, which cools the ULSDO to a sufficient temperature where the required viscosity is achieved.
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