Process improvement analysis of pyrolysis/gasification of biomass and waste plastics with carbon capture and utilisation through process simulation

Excessive utilisation of fossil fuels to meet increasing energy demand results in increasing global CO2 emissions. It is a promising solution to apply carbon capture and utilisation (CCU) for pyrolysis/gasification of biomass and waste plastics, which recycles captured CO2 from pyrolysis/gasification to the reforming stage to serve as the second gasification agent. This paper aims to analyse the potential of combining the pyrolysis/gasification process with CCU and to investigate how to improve this process through process simulation using Aspen Plus®. Process analysis is carried out based on the validated model to investigate the impact of recycling captured CO2 on the product gas production and CO2 conversion when changing various operating conditions (i.e. the amount of recycled CO2, reforming temperature and steam-to-feed ratio). The target is to ensure high H2 production and to promote CO2 conversion. Simulation results indicated that: (i) Applying CCU for pyrolysis/gasification can inhibit the production of H2 andCO2, but it can promote the production of CO; (ii) The H2/CO ratio of gas products can be adjusted flexibly after recycling CO2 to the reforming stage; (iii) Increase of CO2 recycle amount and steam-to-feed ratio results in lower CO2 conversion while the increase of reforming temperature improves the CO2 conversion; (iv) It is suggested to add solid carbon (e.g. bio-char or carbon-based catalyst) in the reforming stage together with adjusting the operating conditions (i.e. relatively high reforming temperature (e.g. 600 ∼ 700 °C) and low steam-to-feed ratio (e.g. 3 ∼ 4)) simultaneously to protect H2 production and achieve high CO2 conversion. The findings in this paper will be very useful for future large-scale commercial deployment of applying CCU for pyrolysis/gasification.