Heat Exchangers in Renewable Diesel Production

As the biofuel industry moves from first generation oil-based biodiesel production to second- and third-generation renewable diesel, the role of heat exchangers in renewable diesel production is also changing.
By John Michelin | June 01, 2022

Although the COVID-19 pandemic reduced demand for all types of fuel, as the economy recovers, demand for gasoline and diesel is recovering rapidly. The price of biodiesel in North America rose more than 50% last year, partly driven by the discrepancy between demand and production capacity. According to Advanced Biofuels Canada, Canadian biodiesel consumption in 2020 amounted to 334 million litres (88.2 million gallons).

A recent report filed with the USDA Foreign Agricultural Service’s Global Agricultural Information Network suggests that Canada could have 3.27 billion liters (863.84 million gallons) of renewable diesel production capacity in place within the next four years. A number of high-profile biodiesel and renewable diesel projects have been announced in the country to help meet this growing demand.

Biodiesel is traditionally produced by the transesterification of vegetable oil or animal fats into fatty acid methyl esters (FAME) via the addition of methanol to the fatty triglycerides found in the vegetable oil at high temperatures and pressures. The resulting biodiesel is then usually blended with mineral diesel (typically at rates between 5% and 20%) for use as a road fuel. In 2021, the average rate of biodiesel blending in Canada was 2.8%.

The production of this traditional biodiesel relies on the use of heat exchangers in many areas, such as heating and cooling methanol, evaporation and condensing, as well as heating biodiesel to improve flow rates, heat recovery and the thermal hydrolysis of advanced feedstocks.

A Changing Role
One use of heat exchangers in the biodiesel production process is the condensation of methanol (either pure methanol or a mixture of gas vapor phases) to recover and purify the methanol from the biodiesel after esterification and transesterification. This recovery is often vital to the renewable nature of the process, and to help reduce production costs. To ensure that the recovered methanol is of suitable purity, the heat exchangers used for the condensation (often under vacuum conditions) must be carefully designed to meet tight thermal tolerances. However, as the biofuel industry moves from first generation oil-based biodiesel production (using feedstocks such as canola oil) to second- and third-generation renewable diesel (based on woody biomass), the role of heat exchangers in renewable diesel production is also changing. They are becoming an intrinsic part of the new and novel production processes that are being developed.

Calgary-based Exchanger Industries Limited is working with a number of clients on renewable diesel projects. Some of them are looking to add renewable diesel production to existing refineries using a wide range of agricultural feedstocks. These often have interesting service requirements that utilize significant amounts of hydrogen at high operating temperatures and pressures. Hydrogen is generally used in refineries to “clean” and lower the sulphur content of diesel fuels, but it is also the smallest known molecule that can diffuse into certain materials and welds, so metallurgical selection, design features and fabrication procedures are of utmost importance for equipment and plant reliability.

When using specialist materials in such challenging environments, it is important that the thermal and mechanical design is properly configured and assessed to ensure the heat exchanger functions correctly and reliably, and that it produces the product required to an exacting specification. Therefore, it is critical to engage a provider with extensive experience and familiarity with the sort of high-temperature, high-pressure working environments that occur in renewable diesel production.

Author: John Michelin
Vice President and General Manager, Commercial
Exchanger Industries Ltd.

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