System analysis and optimization of replacing surplus refinery fuel gas by coprocessing with HTL bio-crude off-gas in oil refineries

This study evaluates the introduction of Carbon Capture and Utilization (CCU) process in two Colombian refineries, focusing on their potential to reduce CO2 emissions and their associated impacts under a scenario aligned with the Net Zero Emissions by 2050 Scenario defined in the 2023 IEA report. The work uses a MILP programming tool (Linny-R) to model the operational processes of refinery sites, incorporating a net total cost calculation to optimize process performance over five-year intervals. This optimization was constrained by the maximum allowable CO2 emissions. The methodology includes the calculation of surplus refinery off-gas availability, the selection of products and CCU technologies, and the systematic collection of data from refinery operations, as well as scientific and industrial publications. The results indicate that integrating surplus refinery fuel gas (originally used for combustion processes) and HTL bio-crude off-gas (as a source of biogenic CO2) can significantly lower scope 1 and 2 CO2 emissions, aligning with long-term decarbonization goals. However, these advantages carry additional costs due to significant increases in utility demands. In the high-complexity refinery, electricity consumption increases by a factor of 10, and steam demand and water usage each increase by a factor of 2.5 and 3, respectively. Similarly, in the medium-complexity refinery, electricity consumption rises by a factor of 11, steam demand by a factor of 4, and water usage by a factor of 6. The renewable energy requirements for water electrolyzers and CO2 capture units primarily drive these increases. Furthermore, despite achieving CO2 neutrality in scope 1 and 2 emissions by 2050, scope 3 emissions increase due to additional CO2-based methanol production. Economic analyses highlight profit opportunities in the long term. The production costs of CO2-based methanol are lower than the forecasted cost of production of fossil-based methanol, enhancing their economic viability in the long term. The study emphasizes the critical influence of refinery complexity levels on the scale and timeline for implementing these technologies to achieve short- and long-term CO2 reduction targets. However, further evaluation is necessary to align these results with national electrical grid capacity, water supply availability, and expansion plans.