In fossil refineries, crude oil is separated in various fractions via distillation. These are further processed, by catalytic upgrading and blending, to useable products (refinery gases, gasoline, jet and diesel). Another core process is the vacuum distillation, where VGO (vacuum gas oil) is separated from heavy components. The operations of a fossil refinery are complex, due to various interconnections between processes. Each refinery is unique regarding product composition and quantities. In order to reduce consumption of crude oil, vegetable or pyrolysis oil can be co-processed. The integration is possible either in the hydrotreatment step of kerosene or light gasoil, or during fluid catalytic cracking of VGO. As a result of co-processing, all products, such as transport fuels, include bio-components.
Source: BIOFIT Project
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Another option for fossil refineries is the complete re-purposing of a refinery to the production of HVO from various oils and fats. This has been done e.g. in the eni refinery at Porto Maghera and the Total refinery in La Mede.