increase catalyst deactivation. Additionally, economic feasibility depends on the cost and availability of these biofeedstocks. Integration with steam crackers Steam cracking is the main interface between the refinery and petrochemical plants. In the steam cracking process, the steam is used to break down heavier (longer chain) hydrocarbons to produce hydrogen and light olefins, including ethylene, propylene, and butadiene. Thus, integrating bio-based feedstocks in the steam cracker feed can yield renewable olefins and chemicals. The process operates between 750°C and 875°C and at short residence times to convert saturated hydrocarbons into unsaturated ones. Unlike FCC, steam cracking relies on thermal decomposition and is non-catalytic. Suitable bio-based feedstocks include bioethanol, biogas, and pyrolysis oils. Bioethanol can be dehydrated to bio-ethylene, while biogas can be converted to syngas for use in the methanol-to-olefins (MTO) processes. Biomass- derived pyrolysis oils can be used directly or blended with conventional feedstocks. Integration involves pretreating biofeedstocks to remove contaminants and adjust properties. For instance, bioethanol needs dehydration, and biogas requires reforming to produce syngas for further chemical conversion. After pretreatment, the feedstocks are preheated and mixed with steam in the furnace. The steam lowers the partial pressure of hydrocarbons, reducing coke formation. The mixture is then rapidly cooled to stabilise the products. Cracked gases are separated into fractions using fractionation columns. The different fractions are then compressed, cooled, and further separated through distillation. The olefins produced from steam cracking bio-based feedstocks are the building blocks for renewable polyolefins and synthetic rubbers. The benefits of using bio-based feedstocks include renewable product output and reduced carbon intensity. The process can be adapted to biofeedstocks with minimal changes to existing infrastructure. Again, challenges include feedstock variability, contaminants, and the need for adjustments in operating conditions. Bio- derived pyrolysis oils often contain higher levels of oxygenates, unsaturated compounds, and
impurities, leading to increased coke formation in the cracker furnaces. Coke build-up on furnace walls reduces heat transfer efficiency, leading to higher energy consumption and frequent maintenance shutdowns for decoking. The presence of contaminants like alkali metals can accelerate coke deposition, requiring a more rigorous pretreatment and precise control of cracking conditions. Additionally, fluctuations in biofeedstock quality can affect the rate of coke formation, creating operational challenges. Along with the cost of the biofeedstocks, economic feasibility is also impacted by their availability, as they may require significant adjustments to optimise the process conditions and minimise coking issues. Integration of syngas from biomass gasification into petroleum refineries Syngas from biomass gasification can be integrated into existing petroleum refineries at multiple points within the refinery process line- up. The most common insertion point is within the hydrocracking or catalytic reforming units. In these units, syngas can be used to produce hydrogen and, with the carbon, can be converted into valuable liquid fuels and chemicals. Challenges in integrating biomass-derived syngas into petroleum refineries include variability in syngas composition, which affects process efficiency and product quality. Impurities in the syngas, such as sulphur compounds and particulates, can damage equipment and require clean-up. Existing refinery infrastructure may need modifications to accommodate syngas, and the economic feasibility depends on the cost and availability of biomass feedstocks. Biomass-derived syngas can be converted into hydrogen for refining processes or used to produce liquid fuels such as diesel and gasoline via Fischer-Tropsch synthesis and chemicals such as methanol. Additionally, it can be used in combined heat and power systems to provide energy for refinery operations, reducing reliance on external sources. Effective biomass integration often involves a combination of these insertion points, with the choice depending on the type of biomass, conversion technologies available, and the specific goals of the refinery. A thorough analysis of the existing infrastructure and the characteristics of
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