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VPS: Shipowners turn to ‘highly reactive’ Cashew Nut Shell Liquid (CNSL) biofuel blends for marine fuel

17 Feb 2023

The drive towards decarbonisation has lately brought shipowners to adopt Cashew Nut Shell Liquid (CNSL) as a biologically renewable resource for marine fuel, learned bunkering publication Manifold Times.

“One of the latest biofuels to come into the marine market is CNSL,” said Steve Bee, Group Commercial Director, VPS at the VPS Biofuels Seminar on Wednesday (15 February).

“CNSL is a bio component used instead of FAME and is a naturally occurring byproduct of the cashew nut industry. It’s a substituted phenol, a low-cost renewable substance, and chemically reactive.”

Competition for Fatty Acid Methyl Esters (FAME), a traditional component of biodiesel, from the aviation and road transportation sectors have resulted in some shipowners resorting to adopt more readily available CNSL blends as biofuels for their vessels, explained Bee.

He highlighted properties of CNSL seemed to conform with the ISO 8217:2012 standard for marine distillate and marine residual fuels, but warned CNSL-blended fuels with MGO, VLSFO or HSFO have shown mixed reactions to vessel operations.

“Some CNSL-blends have been stored and burnt without issue, whereas others have given rise to operational problems including fuel sludging, injector failure, filter clogging, system deposits, corrosion of turbocharger nozzle rings, and damage to SCR units, amongst others,” he shared.

“The thing to remember is CNSL, though not corrosive to copper or steel, is a reactive phenolic compound which can polymerise forming gums while also creating fuel deposits.”

According to Bee, CNSL is used as an effective monomer in many industrial plastic applications such as resin manufacturing, adhesives, laminates, and surface coatings production due to its ability to polymerise when heated above 200°C.

“CNSL is a long chain substituted phenol, which as a monomer is highly reactive,” he highlighted.

“The thing to be aware of for CNSL is it exhibits very high acid values usually greater than 3mg KOH/g; and considering the ISO 8217 limit is 2.5mg KOH/g, pure CNSL is highly corrosive.

“In terms of its iodine value, these are also very high at greater than 300 g I2/100g so it’s highly reactive and less stable.

“Further, potassium levels within CNSL are typically high leading to potential post-combustion deposits and corrosion of turbocharger nozzle rings.”

Bee recommended shipowners to not use 100% CNSL as a marine fuel and advised stakeholders to initiate discussions with their OEMs on the material compatibility of CNSL-based biodiesel blended products.

“Though blending 100% CNSL will reduce its high acid number, reactivity and potassium levels while increasing energy content, the operation may increase sulphur, cold-flow and sediment potential issues instead,” he pointed out.

“CNSL blends can also significantly reduce hydrocarbon, CO/CO2 and smoke emissions, although they raise NOx emissions slightly.

“Absence of sulphur in CNSL will require marine engine lubrication oils with low TBN and high detergency in order to provide efficient engine lubrication and prevent scuffing.

“Don’t try and store this material for longer than three months. And if that is unavoidable, then tests every couple of months for acid number, iodine value, plus obviously ISO 8217 parameters will have to be done.”

Moving forward, Bee was keen to introduce an Additional Protection Service for biofuels based on VPS’ experience of having tested more than 1,000 biofuels as marine fuels.

“Biofuels will certainly reduce carbon dioxide emissions from ships and certainly help towards a reduction in pollution from the global fleet,” he stated.

“But they do come with their own individual considerations in terms of transfer, storage and use. Good fuel management and understanding of the pros and cons of biofuels should mitigate the risks of using this particular material.

“My final message is please use VPS’ experienced expertise to support you, in your use of biofuels, to protect your assets, to protect the crew, and protect the environment.”

Related: VPS organises seminar on biofuel bunkers in Singapore
Related: VPS launches APS-BIO offering biofuels protection service against potential damage


Photo credit: Manifold Times
Published: 17 February, 2023

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