Biofeed co-processing for fuel production Comprehensive review of corrosion operating concerns when co-processing renewables and bio-oils through existing hydrotreaters, FCC units, amine units, and other assets
Scott Sayles, Matthew Caserta, Stephen DeLude and Al Keller Becht
Renewable feedstocks: processing steps T he processing of renewable feedstocks in a refinery requires the following stages/steps:
Hydroprocessing Hydrocracking
• Feed selection • Pretreatment • Storage • Processing • Treating • Blending.
Suggested processing options
Catalytic cracking (FCC) processes
Pyrolysis/thermal cracking
Each step has aspects unique to the feed being consid- ered. An overview of production requirements indicates that biofuel production must consider the balance between food source utilisation and managing climate change. Feedstock selection is also a policy decision between pri - vate and public sectors. The use of non-food sources is the preferred path towards renewable fuels. Renewable feed supply and availability are equally challenging. Renewable feed requires oxygen removal and olefins saturation to produce fully fungible fuel components. As a result, hydrogen and hydroprocessing capacity must increase to accommodate additional demand. The eco- nomic incentive to produce renewable feeds depends on uncertain feed and product markets. Biofeed processing and co-processing may provide significant sustainability and economic benefits for fuels producers but may not be competitive without subsidies. Biofeeds are not all the same. Specifications and quality control need to be established consistent with the chosen processing scheme. For example, if not stored properly, biofeeds can degrade quickly (bio-action). Biofeeds are successfully co-processed in refinery units but only up to unique constraints for each specific unit. As biofeed concentration increases, increasing hydrogen demand, corrosion issues, and water/amine systems should be assessed based on selected processing options. These changes are predictable and can be effectively implemented with a proper engineering overview. The final renewable diesel or jet require blend recipes and/or additive require- ments that will change (quality). The final blends must meet all product quality requirements. Renewable fuels challenges Challenges face renewables fuels processing due to unique feed and product quality. Non-edible feeds are preferred
Expected l iquid (vol% recovery)
but have additional processing challenges. In general, non- edible feeds have lower CI scores, which are better for CO 2 reduction. Blends containing oleochemicals (FAME) produced from edible feeds are less desirable as blending components. The future use of FAME is questionable with the drive to create a fungible fuel market using hydrotreated renewable products. Non-edible feeds may require thermochemical upgrad - ing due to the low (C+H)/O ratio. The ratio defines the efficiency of the molecule to release heat and not form water 1. Feeds such as wood or forestry waste have low (C+H)/O ratios and require gasification, pyrolysis, and/ or Fisher Tropsch synthesis. The fast/catalytic pyrolysis, and hydrothermal liquefaction are all options that may require post-conversion and treating in traditional refin - ing processes. Conceptually, the processing options are a function of the (C+H)/O ratio and the existing process units. Hydrogen removal processes such as pyrolysis or thermal cracking have the lowest liquid yields. Catalytic or FCC pro - cesses are a hydrogen removal reaction, allowing hydrogen transfer with improved liquid selectivity. Finally, hydrogen addition processes have the highest liquid yield and can achieve greater than 100 vol%. This bespoke carbon effi - ciency is shown graphically in Figure 1 . Figure 1 Hypothetical renewable diesel liquid vs carbon efficiency
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PTQ Q3 2022
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