Is there a future for bunker? Part II

In October 2008, the 58th IMO MEPC session adopted significant changes to Annex VI under Resolution MEPC 176(58). This introduced a reduction in the global sulfur fuel limit to 3.5% from January 2012 with a further global reduction to 0.5% from January 2020.

The implementation date of 2020 is to be reviewed in 2018 to assess the availability of fuel oil to meet the 0.5% limit. This review will determine whether the implementation date is to be extended to 2025.

Inside of Environment Control Areas (ECA) the vessel must leads to an emissions equivalents to the consumption of a fuel with 0.1% of sulfur, and outside of these areas (open waters), emissions equivalents to a fuel of 0.5% of sulfur content.

Ship designers, owners and operators have three general routes to achieve SOx regulatory compliance:

A)     Use low sulfur residual or distillate marine fuel in existing machinery,

B)     Install an exhaust gas cleaning (EGC) after treatment system, or

C)     Install new machinery designed to operate liquefied natural gas (LNG)

Systems description in modern merchant vessels and ISO 8217.

The most of merchant vessels are designed by the “unifuel” concept, i.e., the same type of fuel is consumed by two strokes engines at propulsion, and consumed by four strokes engines in generators sets. The two strokes engines has a concept where the combustion products don’t reach the space of crankshaft and bearings, once there is a separation between combustion chamber and the main gear. A gasket package assembled at piston rods divide the spaces. The bearings are lubricated by a lube oil slightly alkaline (5~6 mg KOH/g) unlike of cylinders liners and piston rings package where an oil type with high alkalinity (60~70 mg KOH/g). In cylinders the lube oil alkalinity shall be in a “delicate” balance with fuel sulfur content. If there is a sulfur content higher of 1,5%, the 70 mg KOH/g oil shall be used, otherwise a 60 or 50 mg KOH/g is used. In case of unbalance between lube oil alkalinity and sulfur content the parts at reciprocal running, cylinder liners and piston rings, there will be corrosion (S%>TBN) or scuffing (TBN>S%).

Scuffing means adhesive wear, where piston rings parts of metallurgical particles are “welded” with other particles of cylinder liner matrix. The wear rate of scuffing is very high, inside of 48 hours all cylinder liners and piston rings would be collapse, this as meaning that vessel becoming without propulsion at relative short time.

At the four strokes engines, where the combustion products and even some fuel leakage from fuel pumps reach the main gear, the chemicals relations are more complicated. Here a contamination of lube oil reduces the viscosity if the engine is under diesel operation and inversely the viscosity will be increased if the engine is under heavy fuel operation. High TBN oils shall be used in way to promote the necessary detergency to keep the sump and pistons in acceptable state of cleanliness.

A tip: the marine engines volume of lube oil may estimate by a “rule of thumb”, e.g., in a main engine of 17 MW the volume of lube oil shall be 17000 x 1.5= 25,500 liters. For an engine of a gen set of 900 kW, will be 900 x 1.5=1,350 liters.

ISO 8217

The maritime regulation specification ISO 8217 for fuels distillates and residuals rules the parameters of the fuel as supplied, namely the bunker fuel is a product not ready for use as supplied. Thus, the sampling is to be drawn at custody transfer point, i.e., at vessel manifold, between the supplier and vessel tanks by dripping over time of supply.

The International Organization for Standardization (ISO) based at marine fuel specification BSMA100:1982 of British Standards Institution, published at 1987, the first edition of a standard for residual and distillates marine fuels, assuring the safe handling and consumption of fuels by the vessels and allowing that all parts involved in the business (oil companies, engine builders, ship designers, owners, operators and charterers) could work with the same parameters of fuel quality, following the revised editions in 1996, 2005, 2010, 2012 and 2017. Over the years new characteristics have been introduced because of the development of the required test methods or an identification of needs and certain limits have been tightened.

Given the basic framework of ISO 8217, the assessment of quality of a fuel as supplied shall be divided into three parts, namely statutory (flash point and sulfur content), defined limits (contaminants content and physical properties) and general requirements, i.e., the parameters of ISO 8217 ensure that fuel can be handling and cleaning on board of the vessel.

The purpose of the fuel treatment system is:

1.      Cleaning the fuel oil by removal water, solids and suspended matter to protect the engine from excessive wear and corrosion.

2.      Conditioning of the fuel oil to prepare for best possible properties for injection to the engine and a good combustion

3.      To take care of oily sludge streams from separators, self-cleaning filters etc., with the task to:

-         Reduce the sludge volume which must be landed or incinerated,

-         Recover usable fuel oil

-         Extract water to be transferred to the bilge water system

The cleaning system is divided in four sub systems:

-         Settling Tanks (there are two settling tanks in machinery space, each one has the fuel volume enough for two days of operation at full speed. The fuel is kept at 60~70 deg. C)

-         Pumping

-         Heating for separation using centrifugal (80~90 deg. C).

-         Diary tank or service tank that have the volume of fuel enough for one day of operation at full speed (Keeping the oil under 80~90 deg. C).

 

The conditioning system for fuel oil with part-systems for:

-         Fuel oil supply and pressuring (two sets, the first one pressurizes until 4 bars and the second until 8~12 bars)

-         Filtering by automatic filter (monitored back pressure).

-         Circulation and mixing (the returned oil is kept under 6 bar of pressure).

-         Heating controlled by viscometer (in line), from 135 to 154 deg. C.

-         Consumption measurement (flowmeter).

Regardless of the fuel oil viscosity as supplied, the fuel will be consumed in engines at 12~17 centistoke (cst.). The energy necessary for heat the fuel oil in tanks, purifiers, and at engine inlet come from the economizers that use the heat energy of main engine exhaust gas while ocean going sail.

The Diesel oil is used on board of vessels like a backup fuel, i.e., in case of problems in handling the fuel oil, the crew shall do a changeover from heavy fuel to diesel (is not too fast operation).

Some aspects regarding the crude oil quality and the use of new blends in refineries shall be examined:

1.      Crude oil quality variability,

In the oil segment of the global energy industry, feedstocks are moving toward the heavier end.

Light crude oil it is easier to process and has lower operational cost of refining. However, world reserves are decreasing and the production of heavier crude oils is increasing. They contain relatively small amounts of paraffinic components and are more naphthenic and aromatic in nature. They contain also lower sulfur and higher nitrogen content than lighters crude.

It should be noticed that heavy crude leads to the production of large quantities of atmospheric residue and vacuum residue of the crude oil distillation step.

The high temperatures currently used for atmospheric and vacuum residues processing and the presence of acid compounds (naphthenic, sulphur acids etc.) in these residues can drive to a higher value of Total Acid Number (TAN) at end of process than occurs when processing light crudes.

Supply trends impact will undoubtedly continue to affect refining capabilities. Most existing refineries were not originally designed to be feedstock flexible or to accommodate heavy feeds. So, many authors agree that Middle East is forecast to become the biggest regional exporters by 2025 tripling volumes traded, once their focus on increased refinery capacity to capture value of product versus crude sales.

2.      Refinery process.

Additional units have been added to process larger numbers of different blend streams, and these can be made available to the middle distillate stream to make up the diesel pool. However, these additional steams typically come from units designed to improve the refinery economics.

In way to meet with approval of new legislation limits, some additional processes must be used by refiners, the most important of them is the level of hydrogenation and dewaxing used.

It happens that process causes a significative lubricity and flash point temperature reduction, increase of pour point temperature and Cold Filter Plugging Point (CFPP) of the final products.

To keep those parameters inside of preserving operational viability, additives will be used by refiners. So, the future maritime fuels are not the simple blend of the straight run middle distillates but the mixing of diverse streams including a very complex hydrocarbon and perhaps some additives, furthermore bio fuel contamination and addition of used lube oil and waste chemicals are possible.

A)     Use low sulfur residual or distillate marine fuel in existing machinery,

There are two alternatives here:

1.      Using ultra low sulfur diesel (ULSD) only when at long side in harbors inside of ECA.

Whether the implementation date is to be extended to 2025, the operators can operate their vessels with main engines consuming HFO until sulfur content of 3.5/0.5%, and doing a changeover for ULSD inside of ECA.

Some tanks are to be prepared or even built to store and allow the handling of the new kind of diesel. The engines and boiler shall be prepared to ULSD consumption.

In gen sets engines the returned ULSD must be cooled, avoiding the viscosity decrease due the temperature rising, considering a viscosity low limit of 2 cst, once ULSD have the lubricity reduced due the refineries process.

On the boilers the low lubricity will change the shape and length of spray, so, renewing burners and pumping system could be necessary by units designed especially for the new fuel.

At main engine the changeover procedure from bunker heavy fuel for ULSD shall be done under extreme care in case of manual procedure but there are automatic devices available in the market. If the duration of operation be higher than 8 hours is suggested consult the engine maker regarding cylinders lubrication.

2.      Consuming ULSF full time.

This route may be a good option for vessels that sail inside of ECA, keeping the existing vessel design. All fuel tanks would be completely dedicated for the ULSD utilization.

A tip: In both above cases (intermittent or regular use of ULSD) the operators shall proceed a main engine cylinder oil drained analysis to confirm the wear rate expectation of cylinder liners and piston rings confirming the correct balance between lube oil TBN and the diesel sulfur content.

In gensets engines the frequency of oil sump sampling shall be increased to check if there are fuel pump plunger’s corrosion or lacquering. In case of contamination of lube oil by the fuel the lube oil viscosity will be reduced (consider a limit of 25%), and some damage of bearings is expected if the viscosity become beyond of the limit.

Would we prepared to attend the future necessities, especially regarding chemicals waste contents, instability and incompatibility, only using ISO8217?

By analysis of some key parameters one can estimate the used lube oil content in fuel, but there are not protocols for waste chemicals analysis yet and laboratories of fuel testing services doesn’t have this kind of analysis in their contracts, once is almost impossible to detect at delivery since the usual routine bunker fuel sample is insufficient to be contain traces of polymers, so where this is suspected verification additional analysis must be required (GCMS/FTIR).

There are many available routes for increasing low sulphur marine fuel production, but is expected an increasing the risk of compatibility and instabilities of the different fuel types, e.g., the low sulphur heavy fuel oil (HFO) can be produced from a blend of De-asphalt oil, Vacuum gas oil, gas oil and unconverted oil. But on the other hand, ignition and combustion duration will be an unknows results once the ISO 8217 still have this issue under General Requirements.

Ultra-Low Sulfur Diesel doesn’t mean that is free of cat fines and water, the diesel must be purified.

Blends between the different sources bunkers shall be avoided on board, keeping one settling tank empty before the transfer the bunker from deck tanks.

The operators shall improve their knowledge and planning of the bunker quality prior the operation of bunkering. So, the detailed analysis of reports from Bunker Services Companies, regarding non-conform qualities off or even beyond of the ISO 8217 will be necessary.

The fuel management will be essential in the short term not as logistical issue anymore, but a question regarding the survival of the business.

When bunkering a new fuel, keep one of the auxiliary engines set up with the previous fuel on board which was consumed whitout any troubles until do a test of the new fuel at another engine.

Get smart.