Exergetic, economic and carbon emission studies of bio-olefin production via indirect steam gasification process

The indirect steam gasification of biomass to olefins (IDBTO) coupled with CO₂ utilization was proposed and simulated. Energy and exergy efficiencies, net CO₂ emissions, and economic evaluation were performed against IDBTO as well as the direct oxygen-steam gasification of biomass to olifins (DBTO). The influences of unreacted gas recycling fraction (RU) and CO₂ to dry biomass mass ratio (CO₂/B) on the thermodynamic performance of the processes were also studied. The results showed that the yields of olefins of DBTO and IDBTO were 17 wt% and 19 wt%, respectively, the overall energy and exergy efficiencies of the IDBTO were around 49% and 44%, which were 8% and 7% higher than those of the DBTO process, respectively. A higher RU was found favor higher energy and exergy efficiencies for both routes. Besides, for the IDBTO process, it is found that the addition of CO₂ to gasification system led to an improvement in both energy efficiency and exergy efficiency by around 1.6%. Moreover, life-cycle net CO₂ emission was predicted to be −4.4 kg CO₂ eq./kg olefins for IDBTO, while for DBTO, it was −8.7 kg CO₂ eq./kg. However, the quantitative economic performance of IDBTO was superior to that of the DBTO process.