Techno-economic analysis of carbon-based additives and process optimization for enhanced hydrogen production in integrated pyrolysis/gasification and carbon capture systems

Overexploitation of fossil fuels leads to issues of energy security and environmental pollution. Integrating carbon capture and utilisation (CCU) with biomass and waste plastics pyrolysis/gasification offers a promising route for simultaneous hydrogen production and CO₂ mitigation. However, hydrogen yield is often limited in such integrated systems. This study developed an Aspen Plus model to evaluate the effects of carbon-based additives, steam flow rate, and reforming temperature on H₂ production and process economics. Results show that application of CCU to pyrolysis/gasification decreases H2 yield from 5.28 to 4.61 mol/hr, and only a small quantity of carbon additives (0.13 additives-to-feed ratio) can restore the H2 yield to 5.33 mol/hr, which is higher than the original level of 5.28 mol/hr when no CCU is applied. An optimal steam flowrate is required to balance enhanced H₂ generation against the undesired increase in CO₂ formation that may offset the benefit of carbon capture. 600 °C is identified as the optimal temperature with the highest H2 yield. Economic analysis also indicates the levelized cost of hydrogen (LCOH) at different operating conditions. A multi-objective optimisation was also performed to find an optimal operating point at 1.50 g/min carbon addition, 8.75 g/min steam flowrate, and 669.92 °C reforming temperature, corresponding to an H₂ yield of 14.04 mol/h and an LCOH of 3.49 $/kg. The findings provide quantitative guidance for optimising integrated pyrolysis/gasification–CCU systems toward industrial deployment.