• Tall oil pitch • Wastewater oil collections (such as fats, oil and grease, or FOG) These feeds are the next-level processing opportunities as the edible feedstocks are removed from renewable feed processing. Lignocelluloses The lignocellulosic materials are the most difficult to convert and require pretreating to remove contaminants prior to entering the refinery. The woody biomass and waste are the largest quantity of the lignocellulosic feeds and are typically pretreated by pyrolysis, gasification, or hydrothermal liquefaction. These processing steps are most economically performed at the site of production due to the large quantiles of water that would be shipped if the raw wood waste were moved. The molecular structure of lignin is complex and constitutes interlinked aromatic rings by oxygen and hydrogen bonds (Frey, et al. , 2015 ) Fast pyrolysis The use of fast pyrolysis converts biomass into a liquid that is high in water content and oxygen compounds. Several different reactors and designs are used to produce pyrolysis oil. The high aldehyde and phenol content polymerises and can form a solid within minutes of heating above 150ºC (Frey, et al. , 2015), (Elliott, 2015), (De Miguel Mercader, 2010). Further processing is required to produce a stable transportation fuel. The pyrolysis oil and fossil fuel are incompatible and produce sediment that fouls equipment when mixed. As this is not a recommended option, dedicated assets for the pyrolysis oil will be required. Gasification Gasification converts all carbon- containing molecules into H₂, CO, (syngas) and CO₂ (with other contaminants converted to slag). The feeds can be solid, liquid, or gas. The products are further converted to additional H₂ or, via Fisher-Tropsch reactions, into many different molecular combinations. Hydrothermal liquefaction Hydroprocessing thermal liquefaction (HTL) is an upgrading option to convert biomass at moderate temperatures and high pressure via depolymerisation and deoxygenation to simpler molecules (Frey, et
al ., 2015), (Jensen, et al ., 2015), (Holladay, 2014), (Albrecht, et al., 2011), (Borugadda, et al. , 2020), (Cabrera-Jiminez, et al. , 2021), (Hoffmann, et al ., 2014), (Hoffmann, et al. , 2016), (Sharma, et al. , 2021), (Calemma, et al., 2000), (Ramirez, et al ., 2017). If not stabilised, the product polymerises, thereby forming larger molecules. The product is dehydrated and hydrogen deficient, with aldehydes and olefins as primary product content. Water is a key reactant in the process. Temperatures are 280- 370ºC, and deoxygenation does occur, providing a product approximating a fossil fuel. Metallurgy requirements are suitable for 1,500-4,000 psi units. The product has a high acid level and chlorides. Product yields are feed-dependent. An interesting observation is the formation of asphaltenes in the HTL product (Bjelic, et al., 2018). This makes the bottoms cut from the HTL product suitable for a coker feedstock. Refinery feeds The refinery will need to process renewable and fossil feeds in two separate trains. In general, fossil and renewable feeds are incompatible, requiring separate processing until the renewable oxygen content is reduced to nearly zero. After hydroprocessing or thermal processing to the point the oxygen is removed, the streams are compatible and can be combined. The refinery will need two feed tankage systems, one for fossil streams and the other for renewables. Product tankage will be shared and ‘common’, given the target of compatibility and adherence to current liquid fuels product specifications. Options The conceptual configuration for the biorefinery depends on the viewpoint and risk profile of the operator. The following gives examples of biorefineries and the progression to the scale required to meet the current transportation fuel demand (Holladay, 2014), (Amaroso, et al ., 2013), (Cascone, et al., 2010), (Malode, et al., 2020). Fossil processing train The fossil feed train is the same as the existing refinery systems of today. No change is anticipated.
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