Low Sulphur Fuel Oil Compliance Requirement for Merchant Ships
The significant change to the 2020 International Maritime Organization global marine fuels sulfur rule
poses many challenges to the shipping industry. Beginning January 1, 2020, there was a massive shift from high-sulfur residual-based heavy fuel oils (HFO), which are blended mainly for viscosity,
to new fuels blended to contain 0.50 wt.% sulfur, also known as very low sulfur fuel oil (VLSFO).
Increases in distillate production and desulfurization of refinery streams are anticipated as part of meeting
marine fuel demand. It brings some uncertainty concerning the compliance of the fuel supply and much
uncertainty concerning fuel composition. Furthermore, the change in fuel properties will drive significant
changes for lubricants, equipment, operating procedures, and shipping economics. The consensus is that
the initial use of 0.50 wt.% sulfur marine fuel oils will increase operating costs since this fuel will be
more expensive than high-sulfur HFO. The existing onboard fueling infrastructure and operational
protocols are expected to be suitable for use with most of the 0.50 wt.% sulfur fuels available.
However, more economical operation and quality control will be needed to ensure trouble-free operation. These
practices will take the forms of proper sampling, frequent and more diligent cleaning, and tighter control
of temperatures (viscosities) during fuel handling, switchover, and blended operations.
Compliance needs
to be followed to minimize the potential for any problems. If recommended practices are not followed,
a buildup of piston deposits or erosion by catalyst fines could cause excessive wear and damage to engines.
Also, fuel incompatibility due to asphaltene precipitation could lead to system plugging and poor engine
operation.
Fig: A Crude oil refining process shown in diagram for different use
Fuel Compatibility
VLSFO blends are expected to be derived from a broad range of refinery streams and to vary broadly in
properties as suppliers try to meet the 0.50 wt.% specification. Stability and compatibility concerns are
paramount, at least soon. For instance, some VLSFO blends could be mainly paraffinic. It increases the risk of asphaltene precipitation during fuel-mixing operations, including switchover. Also,
some paraffinic fuels have an affinity to precipitate solids in cold conditions, and more attention to this
problem will be required in some regions.
Catalyst fines are expected to be present in many VLSFO
blends, and therefore cleaning these fuels will be critical. Recommendations to avoid
compatibility problems during switchover and blending center primarily on
obtaining fuel that meets
proper specifications and receiving accurate fuel analyses,
installing additional tanks (or dividing
tanks) and fuel transfer systems to minimize fuel mixing and contamination,
diligent cleaning of fuel
system hardware, and
maintaining and following proper protocols for purifiers to remove catalyst
fines.
Frequent cleaning and following operational guidelines are necessary to maintain compatibility.
In many cases, changes will be made in ship equipment and operating procedures because of the switch to
VLSFO. Because blends of VLSFO are expected to vary widely in viscosity, there will be a need for
compatible pumps, better temperature control, centrifugal purifiers, and other equipment. Engines and
boilers might need to be carefully evaluated for compatibility and safe operation with the new fuels.
These considerations point to the need for many ships to undergo capital upgrades at a time of increasing
fuel costs and financial uncertainty.
Catalyst Fines
An increased presence of catalyst fines in VLSFO is anticipated for some fuel suppliers or in some
regions. Heavy-cycle fuel oil from a catalytic cracker has low sulfur content and is expected to be blended
into low-sulfur fuel oils. Fuel purifiers will need to be appropriately operated and settling tanks to be drained
of bottom contaminants at proper intervals to remove catalyst fines effectively. Rough weather and high seas can entrain tank sediment, and special attention to purification will be needed under these conditions.
Fuel filters may also need more frequent cleaning and maintenance.
Fuel Handling and Processing
The HFO handling and processing systems onboard ships may require some modifications beyond the
need for additional fuel storage tanks to separate different fuel chemistries. It could include the
addition of a chiller, which might be needed to increase the viscosity for some lowest viscosity fuels.
Since VLSFO may contain catalyst fines, the fuel cleaning system will need to be effective for a wide
spectrum of fuel viscosities. Water will need to be removed, and surfaces cleaned. It would minimize the risk
associated with microbially induced corrosion (MIC) with more paraffinic fuels. The use of biocide fuel
additives and inspections might become more frequent as a result.
Fuel switchover from distillate to HFO or VLSFO when exiting an emission control area will require
a careful operation to mitigate potential compatibility issues. It is recommended that a
small mixing tank be employed to assess compatibility when conducting a switchover operation. It would minimize risk. When
switching from distillate to a high-viscosity fuel, it is vital to keep the rate of temperature increase
low to protect fuel system components. Switching from heavy fuel to a distillate fuel (such as marine
diesel oil or marine gas oil) might require a controlled slowdown. In both instances, leak checks and
operation of the fuel pumps will need to be monitored to ensure smooth operation.
Corrosion and Wear
With most ships featuring crosshead engines switching to VLSFO, a shift away from rapid cold corrosion
risk is expected. However, the potential for MIC may be increased for fuels with high paraffin content.
MIC can be mitigated by maintaining cleanliness, removing standing water, and biocide treatments.
Another area of concern with VLSFO use is the greater risk of deposit-related problems from both
excessive bases in cylinder lubrication oil (CLO) or a lack of detergency. New operating procedures
concerning cylinder lubrication may be required, and new developments in CLO formulation are
forthcoming.
It may be beneficial to have more varieties of CLO available onboard. Hard deposit
formation on the piston or rings can negatively affect the lubricating film by causing bore polishing and
interfering with rings and the CLO film on the cylinder liner. One approach being considered to mitigate
this effect is to intermittently use a lower base number CLO to prevent hard deposits and to allow slight
beneficial corrosion of the liner surface to open the graphite lamella structure, which provides oil pockets
to maintain a good oil film.
The economics of shipping will be changed and challenged by the switch from HFO to VLSFO. This
transition will not be seamless, and problems are likely to be encountered due to different fuel chemistries
and improper lubricant selection or management. Fueling protocols may need to be recalibrated to ensure
that problems are prevented or mitigated. Capital investments to make ships perform better with VLSFO
will be made by some but resisted by many because of challenging economics. The most successful ship
operators will be those who undertake great diligence and understand the potential problems and solutions.
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