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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.

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Oil Tanker Safety Guide
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.

crude-oil-refining -process
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
  1. obtaining fuel that meets proper specifications and receiving accurate fuel analyses,
  2. installing additional tanks (or dividing tanks) and fuel transfer systems to minimize fuel mixing and contamination,
  3. diligent cleaning of fuel system hardware, and
  4. 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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