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Feb-2025

Solutions for heat tracing in renewable diesel production

The production and processing of renewable diesel require careful heat management throughout different steps of the refining process.

Mike Allenspach, Jeff Fabry and Pele Myers
nVent

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Article Summary

With global decarbonisation strategies and sustainability requirements, renewable diesel has emerged as a promising alternative to conventional fossil fuels. The US Energy Information Administration (EIA) predicts a 30% increase in renewable diesel production in 2024 and 2025 (US EIA, 2024).

Renewable diesel, derived from biological materials, offers significant environmental benefits such as reduced greenhouse gas emissions and decreased reliance on non-renewable resources. However, its production and processing present unique challenges, especially in process heat tracing. This article delves into these complexities and presents innovative solutions to address them.

Comprehending renewable diesel
What is renewable diesel?

Renewable diesel, also known as hydrotreated vegetable oil (HVO), is a biofuel produced from renewable resources like vegetable oils, animal fats, and waste cooking oils. Unlike biodiesel, which is made through transesterification, renewable diesel is produced through hydrotreating. This process removes oxygen and creates a fuel that is chemically similar to petroleum diesel.

Benefits of renewable diesel
The advantages of renewable diesel are manifold. It offers a drop-in replacement for conventional diesel, meaning it can be used in existing diesel engines without any modifications. Renewable diesel also boasts superior performance characteristics, such as higher cetane numbers and better cold-flow properties. Additionally, it significantly reduces greenhouse gas emissions and particulate matter, contributing to improved air quality and public health.

Role of process heat tracing
Importance of heat tracing

In industrial processes, maintaining the proper temperature of fluids is crucial to ensure efficient operation and product quality. Heat tracing is the process of applying heat to pipes, vessels, and other equipment to maintain or raise their temperature. This is especially important in cold climates or processes involving high-viscosity fluids, where the risk of solidification or freezing is high.

Challenges in renewable diesel feedstocks
Renewable diesel feedstocks, such as vegetable oils and animal fats, present unique challenges for heat tracing. These feedstocks have higher viscosity and lower pour points than comparable petroleum-based feedstocks, making them more prone to solidification at lower temperatures. Secondly, the presence of impurities and variability in feedstock composition can further complicate the heat tracing process. Finally, as with petroleum-based feedstocks, plant oil and animal waste feedstocks for renewable diesel may arrive at the refinery via rail, ship, truck, or pipeline. To ensure flow, these feedstocks require a prescribed temperature maintenance from unloading and distribution areas to storage facilities 100% of the time.

Innovative solutions for heat tracing challenges
Addressing the challenges of renewable diesel feedstock requires a comprehensive heat management system (HMS). This system includes engineering, power distribution, electric heat trace products, control and monitoring, thermal insulation, and instrument winterisation.

Designing an HMS solution for the feedstock area of a renewable diesel refinery depends on the location of the feedstock unloading system and the availability of power distribution to support electrical heat tracing. For instance, unloading feedstocks from a ship may involve long piping distribution systems from piers and jetties, while unloading from a truck or in-plant railcar may offer closer access to the operating refinery. When the feedstock delivery system is near the refinery, self-regulating (SR) technology is ideal for heating cables.

Self-regulating heating cables
SR heating cables are an effective solution for maintaining consistent temperatures for the movement and storage of renewable diesel feedstock. These cables adjust their heat output based on the surrounding temperature, ensuring energy efficiency and preventing overheating. Their ability to provide uniform heating makes them ideal for use in pipelines and storage tanks.

Since sustainability is a key component of the energy transition, Raychem SR heating cable with high power retention (HPR) technology and a 30-year design life, ensures the performance and long product design life to meet critical sustainability requirements.

Electrical contractors typically prefer to work with SR heat tracing cables whenever possible because they are easy to design and install. This is a result of the unconditional T ratings and cut-to-length installation. The process maintain temperatures of the typical feedstocks in this industry are also a great fit for the power temperature curves of the high-temperature SR heating cables displayed in Figure 1. In this case, 277V is the optimum power, if available, to ensure maximum designed circuit lengths while minimising the impact on the overall power distribution of new or retrofit refinery operations.

Longline heating systems
When the renewable diesel feedstock delivery points are on ship docks or from distant railway access, this often means greater distances between the delivery point and the refinery itself. Due to the heat management requirement of the feedstocks, the piping distribution systems in these scenarios are best designed using longline heat tracing technologies like Skin-effect Tracing Systems (STS), which can carry heating power longer distances, as shown in Figure 2.

STS systems can be designed to operate for up to 50 km from a single power point. The critical solution that this heat tracing technology brings to this industry is the opportunity to provide the feedstock process temperature maintenance desired with little power distribution required, often from a single power point location. If the long pipeline from the ship unloading to the refinery were heat traced with SR technology, multiple power circuits would be required, which means more breakers, power distribution cabling, resistance temperature detectors (RTDs), controllers, and SR connection kits.

Integration with process control systems
SR and longline heating technologies both depend on connected advanced electrical heat trace (EHT) control and monitoring systems to ensure operational reliability, maintenance, energy efficiency, and performance. Process temperature maintenance control of the feedstocks can be achieved using RTDs for line sensing process control or thermocouples for direct process temperature control. One challenge not referenced is the potential variability of the feedstocks being delivered to a renewable diesel refinery. Delivery of plant oils, animal fats, and waste will certainly vary, and this could result in the need for unique process maintenance temperatures depending on the feedstock and the feedstock mix.


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