Fossil feed Renewable feed
Fossil gases Renewable propane
Fossil kerosene Renewable feed
Fossil naphtha + gases Renewable propane
Fractionator
Fossil naphtha
Fossil kerosene SAF Fossil diesel Hydrotreated vegetable oil
Fossil kerosene SAF
Unconverted oil
Recycle
Hydrotreating reactor
Splitter
Modifications for co-processing Modifications required for a hydroprocessing unit to undertake co-processing depend on its existing design and objectives. However, several common areas may need to be addressed, including hydrogen availability, corrosion control, renewable feedstocks – due to their oxygen content – can consume more hydrogen than fossil feedstocks. Therefore, the suitability of the make-up gas compressor and recycle gas compressor needs to be checked to ensure sufficient hydrogen availability. Renewable feedstocks can be highly acidic and may also contain chlorides, which can lead to chlorine-induced corrosion. Depending on the point of injection of the renewable source, a material check may be required to assess potential acidity issues for corrosion control. The deposition of ammonium chloride salts may also necessitate modifications in the amount of wash water or the point of injection at the reactor outlet. Water formation also needs to be considered, water formation, and catalyst volumes. Hydrogen availability is important, as as triglyceride-based renewable feedstocks typically contain around 11% oxygen, which is converted into mostly water and small amounts of CO/CO2 during hydroprocessing. This increased water formation may require adjustments to the water boot capacity. Which refinery units are best suited The choice of processing unit is central to SAF co- processing performance. Kerosene hydrotreaters Figure 1 A hydrotreating unit with a splitter in which renewable feedstock has been introduced into the existing unit, enabling the production of a mix of fossil fuels and SAF
and hydrocrackers are available options, as they are designed for the molecular transformations required for aviation fuels. Kerosene hydrotreaters are the most optimal choice, as maximum SAF yield is achieved in this option. With relatively minor changes, they can achieve a high SAF yield. Diesel hydrotreaters, and, in most cases, hydrocrackers are not preferred options, as most of the renewable feedstock will convert into renewable diesel, limiting SAF output. Diesel hydrotreater units can also be utilised in kerosene mode of operation for co-processing and obtaining the maximum SAF yield. Refinery configuration, available hydrogen, and product slate will determine which unit can deliver the most attractive balance between SAF yield and throughput (see Figures 1-3 ) . Compliant feedstock blending ratios Feasible and compliant feedstock blending ratios for use in aviation fuel are defined by ASTM D1655, which specifies strict limits on allowable volumes. Under the current standard, up to 5 vol% co-processing is permitted for mono-, di-, and triglycerides, free fatty acids, and fatty acid esters. Similarly, a 5 vol% limit applies to hydrocarbons produced from synthesis gas via the Fischer-Tropsch process. In addition, co- processing, including co-fractionation, is allowed for hydrocarbons derived from hydroprocessed mono-, di-, and triglycerides, free fatty acids, and fatty acid esters, with the restriction that no more than 24 vol% of the feed and 10 vol% of the final product may consist of these materials. Figure 2 Hydrotreating units may have been the primary choice so far for co-processing of renewable feedstock, but hydrocracking units should not be overlooked
Refining India
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