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NEPIA interviews experts: New Fuels on the Horizon

21 Jun 2019

The following article originally titled ‘Expert Q&A: New Fuels on the Horizon’ was written by Mark Smith of The North of England P&I Association (NEPIA) and shared with Manifold Times.

Smith interviewed industry experts Chris Dyson of Exponent and Michael Banning of Innospec in an effort to bring clarity to some of the more pressing concerns regarding the characteristics of new complaint fuels and how vessels can prepare for their storage and use:

Question:  What challenges do you see ahead with the new very low sulphur fuel oil (VLSFO) products?

Michael Banning (MB): 

Stability and compatibility are the chief concerns.

The stability of a fuel is its resistance to breakdown and precipitate asphaltenic sludge under normal storage and handling conditions. If fuel is comingled on board, then we need to consider compatibility which is the ability of two or more fuels to be comingled at a defined ratio without separation or precipitation of asphaltenic sludge.

VLSFO products are likely to be produced from different lower sulphur streams from the refinery process. Distillate products are often used to further reduce the sulphur content and they may originate from different regions which creates further problems. Therefore, characteristics may differ from bunker parcel to bunker parcel which may lead to incompatibility.

Long term use of certain distillates can lead to filter blockages, injector fouling and corrosion within the fuel system.

Given the fact that 2020 fuel supply is largely anticipated to be a mixture of both VLSFO products and MGO, it may become common place that both instability of asphaltenes and gum formation will be an issue.

Chris Dyson (CD):

New VLSFO products are expected to present new challenges because distillates tend to destabilise residual fuels. It may be prudent to avoid mixing fuels whenever possible. If mixing is required then the degree of instability should be evaluated for different mixing ratios. However, it may not be possible to detect compatibility problems until significant deposits have formed.

It is possible that the low temperature performance of VLSFO products may change significantly with increase in paraffinic content. Standardised testing for low temperature performance is currently limited and it may take time to refine this process.

VLSFO products containing a higher proportion of distillates may tend towards wax deposition instead of asphaltene deposition. Wax deposition is controlled by different physical and chemical processes, so deposits may be seen in different areas of the fuel system and cause different problems.

Question:  Will long term storage of fuel be affected?

CD: The storage of incompatible fuels in the long term can lead to deposit formation in the bottom of the storage tank.

MB: The marine market may need to consider the shelf life of VLSFO products.  The majority of components ending up in VLSFO will be highly reactive short chained cracked residuals. For example ethylene cracker residue has a shelf life of days so the components should be considered.

Question:  What are your thoughts on the use of stabilisers and treatment chemicals?

MB: Dispersants and stabilisers are the most commonly used tank cleaning chemicals. Dispersants break up sludge clusters into a more manageable size. Stabilisers work to keep asphaltenes in suspension and stable within the fuel.  If a neat dispersant is used, it will break up sludge but used without a stabiliser it will shift sludge from one area in the system to another.

CD: Stabilisers and chemical treatments may be useful to remedy instability or incompatibility in fuels if used before deposits have progressed to a problematic level.

However, it is critical that the additive is chemically matched with a suitable dosage or more problems may be created. This is of even greater importance because of the expected diversity of new VLSFO blends. Lab testing may be required before adding treatment chemicals to the fuel.

There are many additive suppliers in the industry. Each uses their own chemistry so it’s important to understand the chemistry on offer and how it may affect your fuel system. It’s important to speak to the additive provider to ensure the product is best suited to your fuel system.

Question:  What challenges do you see with tank cleaning?

CD: Ships’ tanks and fuel systems should be cleaned to a satisfactory standard prior to the loading and use of compliant fuel. This should prevent any rapid removal of pre-existing deposits, residues and sediments which might cause operational issues and avoid rendering the new fuel non-compliant.

Checking the cleanliness of a ship’s fuel tank may require tank entry and inspection which brings its own risks.

To ensure compliance, analysis of samples at agreed points towards the engine inlet may be required.

Question:  How can we reliably test for stability and compatibility?

CD: Current industry tests may not be suitable or sufficient for evaluating the stability and compatibility of new VLSFO products. The deposition of sludge is a very slow process and not easily replicated in the lab. Over the years, ISO 8217 limits have been developed to understand how the fuel test results may or may not reflect fuel performance in service.

With the new VLSFO products and different chemical composition it is unclear whether the tests will provide a useful indication of fuel performance. Will the existing specification limits be appropriate?

MB: ISO 8217 recommends the hot filtration method which indicates stability of the fuel. But this doesn’t provide the dispersion of the asphaltenes and is only really an indicator of the total sediment content.

Optical scanning (Turbiscan ASTM D7061-12) provides a reserve stability number which defines the ability of a fuel oil to maintain asphaltenes in suspension during prolonged storage time and fluctuations in temperature. This is not in the ISO specifications, but is useful to predict compatibility and stability problems.

Author: Mark Smith
Executive (Loss Prevention)

Source: North of England P&I Association
Published: 21 June, 2019

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