INTRODUCTION

Hydrotreated Vegetable Oil (HVO) emerges as an enticing alternative fuel, offering a chemical equivalence to petroleum diesel and compatibility with diesel engines without the need for blend walls or costly modifications. As the world grapples with escalating environmental challenges and an increasing urgency to combat climate change, attention is shifting towards sustainable alternatives across various sectors. Notably, the transportation industry stands out as a substantial contributor to greenhouse gas emissions. Diverging from traditional diesel fuels, HVO is derived from renewable sources, including vegetable oils and animal fats, undergoing a sophisticated hydrotreating process that elevates its properties. This intricate process not only yields a cleaner and more stable fuel but also positions HVO as a viable “drop-in” solution for existing diesel engines, mitigating the need for expensive modifications.

This article delves into the expansive world of HVO biofuels, unraveling the intricacies of their production, exploring their engine impact, and assessing their potential to reshape the transportation landscape. As we embark on a journey towards a more sustainable future, comprehending the role of innovative biofuels like HVO becomes imperative. Such understanding is crucial for fostering a cleaner, greener, and more responsible approach to fulfilling our energy needs. The exploration of HVO biofuels is not just a glimpse into the future; it is a pivotal step in steering our collective journey towards sustainable energy solutions.

PRODUCTION

Feedstock Selection

The production of Hydrotreated Vegetable Oil (HVO) encompasses a broad spectrum of feedstock options rich in triglycerides and/or fatty acids. This inclusive range includes conventional sources such as vegetable oils, beef tallow, and used cooking oil (UCO). Notably, there is a growing utilization of unconventional materials, exemplified by non-food grade vegetable oils, subpar animal fats, sludge palm oil mill effluent (POME), distillers corn oil, and refining byproducts like acid oils from soapstock, oil recovered from bleaching earths, fatty-acid distillates, distillation pitches, and even non-glyceride feedstocks.

In a bid to align with sustainability, economic, and political considerations, producers are increasingly turning towards alternative and lower-quality waste and non-food feedstocks. This shift not only addresses ecological concerns but also establishes a more economically viable and politically resilient framework for HVO production.

The hydrogen essential for the production process predominantly originates from fossil sources. On a global scale, vegetable oil and palm oil prominently contribute to the hydrogen component.

The production process itself exhibits flexibility, allowing for the conversion of an extensive array of low-quality waste and residue materials into hydrocarbon-based drop-in fuels. This versatility ensures compliance with the stringent sustainability criteria set forth by the Renewable Energy Directive (RED) in the European Union.

Production Process

The synthesis of HVO involves a meticulous production process, primarily conducted through the hydrotreating of oils. In this process, triglycerides, the primary components of oils, undergo a reaction with hydrogen under high pressure, facilitating the removal of oxygen. The resultant hydrocarbon chains exhibit chemical equivalence to petroleum diesel fuel, marking a significant advancement in biofuel technology. The production unfolds in two key stages: hydrotreatment and hydrocracking/isomerization.

The initial stage typically transpires within the temperature range of 300 – 390°C, yielding propane as a by-product during the treatment of triglycerides. Hydrogen is introduced to double bonds in this phase, followed by additional hydrogen infusion aimed at eliminating propane through the breakdown of triglycerides into fatty acids. Subsequently, fatty acids undergo a transformation into hydrocarbons by the removal of oxygen via hydrodeoxygenation or decarboxylation processes. The resulting hydrocarbons undergo further refinement to meet end-user specifications, aligning with conventional petroleum fuel standards. This refinement is achieved through isomerization and cracking treatments, ensuring that the final product complies with the stringent criteria set for traditional petroleum fuels. The intricate series of reactions and treatments showcase the technical precision involved in producing HVO as a viable and chemically akin substitute for conventional diesel fuels.

Production Plant

Hydrotreated Vegetable Oil (HVO) can be produced in either dedicated facilities or through co-processing with fossil oil in refineries. In co-processing, biobased feeds are blended with fossil feeds, resulting in different products across refinery lines. Additionally, the HVO process can be adapted to produce renewable kerosene, suitable for applications like jet fuel. This versatility underscores HVO’s potential as a flexible and eco-friendly solution for various industries.

FUEL PROPERTIES
Chemical Formula: HVO adheres to the general formula of straight-chain paraffinic hydrocarbons, expressed as CnH2n+2.

Density and Energy Content: HVO sets itself apart with a lower density compared to traditional European diesel fuels, thanks to its light hydrocarbon composition. This unique attribute translates into higher energy content per kilogram and per liter, making HVO an efficient biofuel that requires less mass and volume to meet specified bioenergy mandates.

Heating Value and Blending Ratios: In contrast to standard diesel fuel and FAME (Fatty Acid Methyl Ester), HVO exhibits a higher heating value per mass, attributed to its elevated hydrogen content.

Oxidation Stability: HVO boasts superior oxidation stability due to its oxygen-free composition, surpassing market diesel in this crucial aspect.

Aromatics and Naphthenes: HVO distinguishes itself by being practically free of aromatics and naphthenes, making it highly favorable for clean combustion processes.

Filterability and Water Content: Unlike some biofuels, HVO avoids issues related to filter blocking, and its low water solubility simplifies fuel logistics, ensuring smoother operations.

Microbial Growth and Appearance: With its low water dissolving property, HVO presents a similar risk of microbial growth as fossil diesel, requiring no additional precautions. The fuel maintains a clear and bright appearance above the cloud point, accompanied by minimal odor, reinforcing its appeal as a reliable and aesthetically pleasing biofuel.
HVO : Material Compatibility

General Compatibility:

HVO (Hydrotreated Vegetable Oil) exhibits a compatibility profile similar to fossil diesel, ensuring its suitability for a range of materials commonly used in transportation and fuel storage infrastructure. Components such as seals, hoses, diaphragms, and mechanical seals of pumps, along with construction materials like carbon and stainless steel, demonstrate resilience when exposed to HVO. Both welded and riveted tanks, including those with internal floating roofs made of aluminum, are considered appropriate for use with HVO, and nitrogen blanketing can be employed.

Elastomer Compatibility:

Specifically, HVO showcases compatibility with elastomers such as nitriles (NBR), fluoroelastomer (FKM), PTFE (polytetrafluoroethylene), as well as vinyl ester resins and epoxy resins. While the absence of aromatic compounds in HVO may theoretically lead to the contraction of elastomers previously swollen by aromatic or FAME-containing fuels, it’s noteworthy that no instances of fuel leakages have been observed during 12 years of practical usage in the field. To maintain optimal compatibility, it is advisable to avoid significant changes in fuel composition.

HVO AND OTHER MARINE FUELS

HVO can reduce emissions compared to standard diesel. However, the level of greenhouse gas emissions savings can vary by product. Savings are based on a life-cycle, well-to-wheel calculation, taking into account feedstock, production processes and transportation.

HVO does not require a different tank so businesses can use existing tanks to store the fuel. Like all flammable fuel, HVO must be stored in a cool, dry place and should not be exposed to direct sunlight.

HVO also offers a longer shelf life to conventional diesel. It is also less harmful to the environment in the event of a leak or spillage, as it is biodegradable.

HVO offers benefits over FAME, such as reduced nitrogen oxide (NOx) and particulate emissions, better storage stability and better cold-flow properties.

It can be used in existing diesel engines without blending limitations. there are maintenance issues related to biodiesel, including clogged filters, which can significantly impact machinery or vehicle downtime. HVO is FAME-free, which means it does not experience the same operational issues.

Blending with diesel fuels

lending Hydrotreated Vegetable Oil (HVO) with diesel fuel creates a premium-grade blend, meeting standards like EN 590 and ASTM D 975. HVO’s increased cetane number and reduced aromatic content lead to lower emissions and improved cold-start performance. Its blending flexibility, absent density limitations with ASTM D975 fuel, allows for seamless integration at various ratios. HVO’s composition of n- and i-paraffins enables it to serve as a “drop-in fuel” without constraints from vehicle technology or fuel logistics. The Fuel Quality Directive 2009/30/EC supports HVO’s versatile blending capabilities, with no prescribed limit for hydrocarbon biofuels resembling diesel. Considerations like temperature, density, and compatibility with additives in the blending process align with logistics practices. HVO’s stability, compatibility with standard additives, and low water affinity make it a reliable blending component. Practical blending limitations, often 30-50% in EN 590 due to density, can be surpassed with higher base diesel fuel density. ASTM D975, with no density limits, offers flexibility. For oil refineries, HVO proves valuable by enhancing base diesel fuel properties, reducing aromatic and sulfur content, and positively impacting cetane number and boiling points. HVO’s cold operability benefits further influence the final blend’s cold properties, serving as a corrective component for regulatory requirements when the base fuel falls short.

Blending with FAME
EN 15940 stipulates a maximum of 7% FAME content in diesel, but the quality of FAME is a crucial factor that can lead to issues, especially at lower concentrations. The precipitation risk of impurities in FAME increases with higher blending content. When blending FAME with HVO, it is essential to use blending temperatures well above the cloud points of both FAME and HVO, as the precipitation risk diminishes at higher temperatures. Additionally, the significant difference in densities between FAME and HVO should be considered during blending. It is advisable to store the neat components separately for the long term and blend the final fuel just before its use.

ENGINE PERFORMANCE

• No vessel modifications needed with HVO.
• Comparable torque and maximum power to fossil diesel in modern engines.
• No cold operability issues, even in severe winter conditions.
• Low tendency to form deposits in the fuel injection system and injectors.
• No engine oil dilution or chemical incompatibility concerns.
• Potential for designing more fuel-efficient, low-emission diesel engines (“diesel-FFV-vehicles”).
• Endorsed in the Worldwide Fuel Charter by automotive and engine manufacturers.

Diesel engines, once prevalent in robust applications, are now common in various vehicles, driven by customer demand for convenience. Stringent emissions regulations have spurred advancements in engine technology and fuel systems, emphasizing the importance of fuel properties.

HVO, as a biofuel component, enhances fuel quality, improving ignition characteristics, viscosity, heating value, oxidation stability, and distillation behavior for optimal engine operation and durability. The high cetane number of HVO, exceeding 70, ensures superior ignition quality, particularly advantageous in cold climates.

Fuel economy is influenced by heating value, where HVO’s higher mass heating value compensates for its lower volume heating value. Additionally, HVO outperforms FAME in energy content per liter and per kilogram. HVO’s viscosity aligns with specification limits, crucial for proper atomization.

Maintaining lubricity is essential to prevent excessive wear on fuel pumps and injectors. Although hydrotreated fuels typically lack natural lubricity, this issue is easily addressed with lubricity additives, ensuring smooth engine operation.

HVO’s excellent oxidation stability significantly reduces the risk of deposits in the fuel injection system and injectors, enhancing overall engine performance and durability. In summary, HVO stands out with improved operation, reduced emissions, and enhanced durability, attributed to its higher cetane number, optimal distillation range, exceptional heating value, suitable viscosity, and superior oxidation stability compared to conventional diesel fuels.

CONCLUSION
HVO proves to be a viable alternative fuel due to its “drop-in” nature, serving as a direct substitute for traditional petroleum-based fuels. However, its adoption faces challenges, given its high cost, limited production capacity, and scarcity of bunkering facilities, raising concerns about scalability for maritime applications. Moreover, addressing NOx and PM emissions requires the incorporation of exhaust gas treatment systems to meet current and anticipated regulations. While HVO is utilized in three ferries in Norway without reported issues, its overall uptake in the shipping industry remains limited. The scarcity of biomass for HVO production poses a potential challenge, competing with other sectors like road and aviation for fuel availability. Despite these challenges, from an engine perspective, HVO performs nearly as well as fossil diesel, making it a feasible drop-in fuel without requiring modifications to existing engine, fuel supply, and storage technologies.

– Riya Yadav