The recently concluded (Maritime Environment Protection Committee) MEPC 74 meeting held in London last month for the prevention and control of marine pollution from ships, has set a guideline report for possible safety implications relating to fuel oils, meeting the 0.50% m/m sulphur limit. Here’s a detailed insight on the same as made public by IMO.
Identified potential safety implications
The potential safety implications identified are listed below, but are not limited to, the following:
- stability of blended fuel oil;
- compatibility, including new tests and metrics appropriate for future fuels;
- cold flow properties;
- acid number;
- flash point;
- ignition and combustion quality;
- cat fines;
- low viscosity; and
- unusual components.
Additional technical information including potential challenges and remarks of the possible potential safety implications is set out below.
Blended Fuel Oil Stability Challenges
The consequences of a ship receiving an unstable fuel, or one that becomes unstable during storage, or handling, can be serious. Sludge may build up in the storage tanks, piping systems or centrifuges and filters can become totally blocked by voluminous amounts of sludge.
- The challenge for the fuel producer is to blend a fuel which is not only stable but also has a degree of reserve stability such that it will remain stable during periods of storage and treatment at elevated temperatures.
- More paraffinic blend components are expected for Very Low Sulphur Fuel Oil (VLSFO) compared to existing fuel. Whereas aromatic components have a stabilizing effect on asphaltenes, paraffins do not. Fuel suppliers are responsible for ensuring that the supplied fuel is stable.
Challenges Related To Compatibility Issues
Challenges are the same as with the case of stability.
- An incompatible mix may be harmful to ship’s operation. VLSFOs are expected to be paraffinic based in some regions and aromatic based in other regions.
- There is a risk of experiencing incompatibility when mixing an aromatic fuel with a paraffinic fuel.
- The same risk exists today, but with the wide range of products which may exist post 2020, it is important to segregate fuels as far as possible and to be cautious of how to manage/handle incompatible fuels on board.
Cold flow properties and Pour Point Challenges
ISO 8217:2017 limits the cold flow properties of a fuel through setting a limit on the pour point (PP). However, given that wax crystals form at temperatures above the PP, fuels that meet the specification in terms of PP can still be challenging when operating in colder regions. Wax particles can rapidly block filters, potentially plugging them completely. The paraffins may crystallize and/or deposit in the storage tanks leading to blockages at the filters and reduced fuel flow to the machinery plants. If fuels are held at temperatures below the pour point, wax will begin to precipitate. This wax may cause blocking of filters and can deposit on heat exchangers. In severe cases the wax will build up in storage tank bottoms and on heating coils, which can restrict the coils from heating the fuel (fuel will become unpumpable from the bunker tanks).
- VLSFO products are expected to be more paraffinic compared to existing fuels. As such, it is important to know the cold flow properties of the bunkered fuel in order to ensure proper temperature management on board.
- It is important to note that for additives to be effective, they have to be applied before crystallization has occurred in the fuel.
Acid Number Challenges
The fuel shall be free from strong, inorganic acids. Fuels with high acid number test results arising from acidic compounds cause accelerated damage to marine diesel engines. Such damage is found primarily within the fuel injection equipment.
There is no currently no recognized correlation between an acid number test result and the corrosive activity of the fuel.
Flashpoint Challenges
Flashpoint is considered to be a useful indicator of the fire hazard associated with the storage of marine fuels. Even if fuels are stored at temperatures below the determined flash point, flammable vapours may still develop in the tank headspace.
Problems Pertaining to Ignition and combustion quality
Fuels with poor ignition & combustion properties can, in extreme cases, result in serious operational problems, engine damage and even total breakdown. Poor combustion performance is normally characterized by an extended combustion period and/or poor rates of pressure increase and low “p max” resulting in incomplete combustion of the fuel. The resulting effects are increased levels of unburned fuel and soot that may be deposited in the combustion chamber, on the exhaust valves and in the turbocharger system, exhaust after treatment devices, waste heat recovery units and other exhaust system components. Extended combustion periods may also result in exposure of the cylinder liner to high temperatures which may disrupt the lubricating oil film, leading to increased wear rates and scuffing. Unburnt fuel droplets may also carry over impinging on the liner surfaces causing further risk of damage to the liner.
- High and medium-speed engines are more prone to experience operational difficulties due to poor ignition and combustion properties than low speed two stroke types. With four stroke engines, poor ignition can result in excessive exhaust gas system deposits, black smoke, engine knocking and difficulties operating at low load.
- If the ignition process is delayed for too long a period by virtue of some chemical quality of the fuel, too large a quantity of fuel will be injected into the engine cylinders and will ignite at once, producing a rapid pressure and heat rise and causing associated damage to the piston rings and cylinder liners of the engine.
Cat fines Related Issues
Cat fines will cause abrasive wear of cylinder liners, piston rings and fuel injection equipment if not reduced sufficiently by the fuel treatment system. High wear in the combustion chamber can result.
- Major engine manufacturers recommend that the fuel’s cat fines content does not exceed 10 mg/kg (ppm) at engine inlet.
Low Viscosity Issues
Low-viscosity fuels (less that 2 CST at engine inlet) challenge the function of the fuel pump in the following ways:
- Breakdown of the oil film, which could result in seizures;
- Insufficient injection pressure, which results in difficulties during start-up and low-load operation; and
- Insufficient fuel index margin, which limits acceleration.
How does it effect?
- Low fuel viscosity does not only affect the engine fuel pumps. Most pumps in the external fuel oil system (supply pumps, circulating pumps, transfer pumps and feed pumps for the centrifuge) also need viscosities above 2 CST to function properly.
- Viscosity is highly temperature dependent and the crew must take proper care of the fuel oil temperature management to avoid viscosity related issues.
Unusual components Hazard Issues
The below components and group of components can be linked to the risk of encountering the following problems:
Polymers (e.g. polystyrene, polyethylene, polypropylene)
Associated with filter blocking
Polymethacrylates
Associated with fuel pump sticking
Phenols
Occasionally Associated with filter blocking/fuel oil pump sticking
Tall oils
Associated with filter blocking
Chlorinated hydrocarbons
Associated with fuel pump seizures
Estonian shale oil
Associated in the past with excessive separator sludging
Organic acids
Associated with corrosion as well as fuel pump sticking
How to tackle them?
Only for few components, there exists a clear cause and effect between component and associated operational problems.
There is no statistical study performed of which components are typically found in marine fuels and in which concentration.
As per ISO 8217:2017, annex B: The marine industry continues to build on its understanding of the impact of specific chemical species and the respective critical concentrations at which detrimental effects are observed on the operational characteristics of marine fuels in use.
Only in some of the past cases the origin of the unusual components found in bunkers were revealed and were due to various reasons such as:
- Russia/Baltic states 1997, cross contamination in storage/piping (polypropylene);
- Singapore 2001, 4 bunker barges received material from road tanker which, in addition to transporting fuel, also collected/transported waste oil from shipyards and motor shops (esters);
- Ventspils 2007, Estonian shale oil to convert HSHFOs to LSFOs; and
- Houston 2010/11, bunker barges that were not cleaned between cargoes (polyacrylates).
Did you subscribe to our daily newsletter?
It’s Free! Click here to Subscribe!
Source: IMO
