Transforming Feedstocks into Renewable Fuels: From Farm to Fuel

(Newsletter: October 2024)

Welcome to this month’s newsletter where we explore the critical role that various feedstocks – such as yellow grease, tallow, and soybean oil – play in the production of sustainable renewable fuels like green diesel, sustainable aviation fuel (SAF), and renewable naphtha. With growing concerns over climate change and environmental sustainability, these renewable fuels are increasingly replacing traditional fossil fuels in reducing carbon emissions.

Feedstocks: The Foundation of Renewable Fuels

1. Yellow Grease

Yellow grease, primarily made from used cooking oils, is one of the most cost-effective feedstocks. It’s a byproduct of restaurants and food processing plants, collected from fryers, and diverted from waste streams.

2. Tallow

Tallow is rendered fat from livestock, mainly cattle and sheep, and has been traditionally used in soap-making and other industries. Its high-energy content makes it an excellent feedstock for renewable fuel production.

3. Soybean Oil

Soybean oil, a major agricultural product, is widely used in food, but the growing demand for renewable fuels is driving its use as a feedstock. As a versatile vegetable oil, it provides a cleaner-burning, renewable option.

Logistics: Moving Feedstocks to Renewable Fuel Plants

To meet demand, these feedstocks are sourced globally and transported to processing facilities via tank trucks and rail cars. Once on-site, the feedstocks are offloaded from the bottom of the transport vehicles into large storage tanks. Here’s a breakdown of the logistics involved:

• Tank Trucks and Rail Cars: Specially designed to handle high volumes, tank trucks (for local/regional supply) and rail cars (for long-distance supply) bring feedstocks directly to the facility.
• Bottom Offloading: To minimize contamination and optimize flow, the feedstocks are “bottom offloaded” into heated storage tanks to keep them in a liquid state.
• Storage and Quality Control: Once offloaded, the feedstocks are stored in tanks where they are tested for quality and impurities. Maintaining the right temperature and stability is crucial to preserving their viability for renewable fuel production.

Converting Feedstocks into Renewable Fuels

The transformation of feedstocks into finished renewable fuels happens in several stages. At the heart of this process is hydrotreatment, where the carbon chains in the feedstocks are chemically altered to mimic conventional fossil fuels.

1. Pre-treatment: Feedstocks, especially waste oils like yellow grease and tallow, undergo a filtration and purification process to remove contaminants such as water, metals, and other impurities.
2. Hydrotreatment: In this process, hydrogen is used to break down the triglycerides and free fatty acids in the feedstocks. This converts them into hydrocarbons similar to those found in diesel or jet fuel. Hydrotreatment ensures that the final product meets strict regulatory standards for renewable fuels.
3. Hydrocracking and Isomerization: These additional refining steps help adjust the molecular structure of the fuel to meet specific requirements for renewable diesel, SAF, or renewable naphtha.
4. Fractionation: The resulting product is separated into distinct fuels:
   • Green Diesel: A direct replacement for traditional diesel.
   • SAF (Sustainable Aviation Fuel): Used for commercial and military jet engines.
   • Renewable Naphtha: A vital ingredient in petrochemical production, also used as a gasoline blendstock.

Delivering the Finished Product: Tank Trucks and Rail Cars

Once refined, the renewable fuels are ready for distribution. The finished products – whether it’s green diesel, SAF, or renewable naphtha – are transported from the facility to customers using the same logistics methods: tank trucks for shorter distances and rail cars for bulk or long-distance delivery.

• Loading for Shipment: Automated systems ensure the accurate loading of fuels into rail cars and trucks, with safety and quality checks conducted at each stage to ensure the product meets customer specifications.
• Dispatch to Customers: The renewable fuels are dispatched to various markets including fueling stations, airports, and petrochemical plants, ensuring that sustainable energy reaches every corner of the economy.

Optimizing Feedstock Unloading & Finished Product Loading with Skid Systems

In the renewable fuels industry, efficient and reliable handling of feedstocks and finished products is crucial for maintaining operational flow and minimizing downtime. Packaged unloading and loading skids are essential systems designed to streamline the process of offloading feedstocks like yellow grease, tallow, and soybean oil, and for loading finished products such as green diesel, SAF, and renewable naphtha for distribution.

These skids are fully integrated systems that include pumps, meters, controls, instruments, and loading/unloading arms, all designed to ensure precise and safe material transfer. Below, we break down how these skids work and the key engineering considerations when selecting components.

How Packaged Unloading and Loading Skids Work

• Unloading Feedstocks: When feedstocks arrive via tank trucks or rail cars, the unloading skid system uses pumps to transfer the material from the transport vehicle into storage tanks. The skid is equipped with meters and controls to monitor the flow rate, ensuring accurate measurement of the volume unloaded.
• Loading Finished Products: After processing, renewable fuels are loaded into trucks or rail cars for shipment to customers. Loading skids utilize similar pumps and meters to ensure precise, safe transfer of the finished product into the transport vehicles.

Each skid is a self-contained unit designed for specific applications, from transferring high-viscosity tallow to low-viscosity naphtha, ensuring flexibility and efficiency in the handling of different materials.

Key Engineering Considerations for Skid Design

When designing or selecting an unloading and loading skid system for renewable fuel facilities, engineers must consider several factors to ensure both reliability and safety.

1. Pumps

• Pump Type: The choice of pump depends on the feedstock’s viscosity and the flow rate required. For high-viscosity feedstocks like tallow or yellow grease, positive displacement pumps (e.g., gear or screw pumps) are often preferred to maintain a steady flow rate. For lower-viscosity materials such as soybean oil or renewable naphtha, centrifugal pumps may be sufficient.
• Material Compatibility: The pump materials must be compatible with the feedstocks and finished products to prevent corrosion or degradation. Stainless steel is commonly used due to its resistance to chemical attack from bioderived oils and fuels.
• Temperature Requirements: Some feedstocks need to be kept at elevated temperatures to remain in liquid form (e.g., tallow). Engineers should ensure pumps are designed to handle these temperature requirements, potentially including heating jackets.

2. Meters

• Flow Measurement Accuracy: Precision in flow measurement is critical, both for regulatory compliance and cost control. Coriolis meters are highly accurate and commonly used in renewable fuel applications for both feedstock unloading and finished product loading, as they measure mass flow directly and are unaffected by changes in viscosity or temperature.
• Volume vs. Mass Measurement: Depending on the product, engineers may need to decide whether to measure by volume (e.g., for liquid-based products like soybean oil) or by mass (e.g., tallow, which may vary in density with temperature).

3. Controls and Instruments

• Automation and Control Systems: Skids are often equipped with programmable logic controllers (PLCs) or distributed control systems (DCS) to automate the loading and unloading process. These systems monitor flow rates, pressures, and temperatures, enabling operators to control the process remotely and ensure safe operation.
• Temperature and Pressure Sensors: Feedstocks and products should be monitored closely for temperature and pressure to prevent issues like cavitation in pumps or excessive wear on equipment. These sensors also trigger alarms or shutoffs if conditions exceed safe operating limits.

4. Loading and Unloading Arms

• Flexibility and Reach: Loading arms need to be flexible and durable enough to handle both the size and type of vehicle (tank trucks or rail cars). Top-loading arms are often used for rail cars, while bottom-loading arms are ideal for tank trucks.
• Material Selection: Like pumps, loading arms must be constructed from materials that are compatible with the feedstocks and fuels. Carbon steel and stainless steel are common, with specific coatings applied if needed to prevent corrosion or chemical degradation.

5. Hazardous Area Electrical Considerations

In renewable fuel facilities, many areas are classified as hazardous locations due to the flammable nature of the feedstocks and fuels being handled. Engineers must account for electrical safety in these areas.

• Explosion-Proof Equipment: All electrical equipment in hazardous zones must be explosion-proof and meet standards such as NFPA 70E to prevent sparks or electrical faults from igniting vapors.
• Grounding and Bonding: Proper grounding and bonding of equipment and vehicles are crucial to prevent static electricity from accumulating during the loading and unloading process, which could ignite combustible materials.
• Intrinsic Safety: Where applicable, intrinsically safe controls and instruments should be used to ensure that electrical circuits cannot carry enough energy to cause ignition in the event of a fault.

Conclusion: Efficiency, Safety, and Precision

Packaged unloading and loading skids are an indispensable part of renewable fuel production and distribution. By carefully selecting the right pumps, meters, controls, and instruments, and ensuring compliance with hazardous area standards, engineers can optimize material handling while minimizing risk. Whether unloading yellow grease or loading SAF for jet fuel, these skid systems help keep renewable fuel facilities running efficiently and safely, ensuring that the global shift towards sustainable energy continues without interruption.