Biofuels present problems for maritime industry

The increase in the production and use of biofuels for transport is set to continue, and with most biofuels transported by sea, the industry needs to take stock of its growing experience of what can go wrong aboard ship and develop safe and efficient shipping, loading, handling and storage practices.

Demand for biodiesel is expected to grow at an estimated annual compound rate of 15%, rising from 20 million metric tonnes in 2010 to 45 million tonnes in 2015. Global biodiesel and ethanol sales could reach US$247 billion by 2020, up from US$76 billion predicted for 2010. In the first half of 2008/2009, about 670 million litres of biofuels were supplied to the UK transport market, 92% of which was imported.

The UK government is stepping up its targets for forecourt sales of fuels from renewable sources to 5% by 2013/14, and the EU Renewable Energy directive would like it to be more as new sustainable biofuels come to market. By 2030, Lloyd’s Register predicts global demand for 100 million tonnes of biofuel, requiring an extra 400 handysize tankers to transport it.

According to a report by the UK P&I Club, blends of biofuels and conventional fuels are essentially mixtures of mineral oil based hydrocarbons and noxious liquid substances. The two main classes of ‘first generation‘ biofuels in widespread use are biodiesel and bioethanol.

Biodiesel is derived from vegetable oils and animal fats. Better known as Fatty Acid Methyl Esters (FAMEs), these are produced by reacting vegetable oil or animal fat with an alcohol, usually methanol. The transesterification process brings the properties of the raw materials closer to those of conventional petroleum diesel. FAME can be used neat as a fuel but is more commonly blended with petroleum diesel for use in diesel engines.

The different chemical compositions of FAME raw materials and their blend levels mean the end products vary in terms of stability, degradability and cold temperature performance. This will affect storage, handling, treatment, engine operations and emissions.

Bioethanol refers to ethanol produced by fermenting renewable sources of sugar or starch crops. Unlike FAME, bioethanol is a single chemical compound, which is volatile, colourless, miscible with water and hygroscopic. Again, bioethanol can be used neat but is generally blended with conventional gasoline.

P&I club executives are beginning to receive insurance claims stemming from biofuel problems, most of which emanate from FAMEs. There is no standardised analytical technique for detecting FAME materials in fuel oils and data on their effect on marine fuel systems is limited.

Water contamination is the main problem as FAMEs absorb water via sea water ingress, tank washing residues, atmospheric humidity in tanks‘ ullage spaces and other sources. 

FAME can hold high levels of water in suspension, rendering cargo off-specification. Water can promote hydrolytic reactions, breaking down the FAME to form free fatty acids. Such species are corrosive and may attack exposed metal surfaces. Water can separate out from FAMEs, promoting unwanted microbiological growth, which may lead to filter blocking and corrosion.

Potential shipping problems include degradation reactions by trace metals, such as copper heating coils or zinc-containing tank coatings. Thermal stability will be affected if FAME cargoes are stored next to heated tanks. Dry nitrogen blankets can help to prevent degradation reactions through air contact.

FAME can adsorb onto the walls of tanks or pipelines and de-adsorb into subsequently carried products, causing problems for multi-product pipelines or storage tanks, necessitating great care with tank cleaning and flushing and draining common lines. Switching from B5 diesel to jet fuel requires at least a hot water tank wash. Some would advocate at least three intermediate FAME free cargoes plus the hot water wash before loading jet fuel.

Tankers carrying multiple products risk inadvertently contaminating jet fuel cargo with traces of FAME. The EN590 specification for ultra-low sulphur diesel (ULSD) allows up to 7% FAME content by value.  Ships‘ tanks and lines should be completely stripped of all ULSD before loading jet fuel.

FAME acts as a solvent, taking up any organic residue, dirt or scale that may have accumulated on surfaces of tanks or pipelines. It attacks and quickens the ageing process of certain materials, including elastomers.

Unwanted water is also a major problem with bioethanol. The ethanol itself is hygroscopic and highly soluble in water. Small quantities of water can be dissolved in gasoline/bioethanol blends but, if there is too much, the ethanol will separate from the gasoline, forming an alcohol-rich water/ethanol aqueous phase and an alcohol- poor gasoline phase.

The former will collect at the bottom of the ship’s tank or storage tank and is likely to be highly corrosive and not usable as fuel. The gasoline phase may be considered a "minor hazard to either marine resources or human health" if discharged into the sea from tank cleaning or deballasting operations. 

Bioethanol also acts as a solvent, cleaning out dirty storage tanks and lines but becomes contaminated itself in the process.