Abstract
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.
Highlights
Light olefins including ethylene and propylene are the most important petrochemicals [1], and have been widely used in the production of plastics, elastomers and rubbers [2]
For indirect steam gasification of biomass to olefins (IDBTO) process, the employment of readily CO2 from acid gas removal unit (AGR) unit as a gasifying agent could reinforce the gasification of biomass so as to offer a carbon source to enhance the CO fraction in the output syngas, leading to a possibility to reach the suitable syngas production for downstream methanol application
The simulation results of the key nodes in the direct oxygen-steam gasification of biomass to olifins (DBTO) and IDBTO processes are presented in Table 6 and Table 7 respectively
Summary
Light olefins including ethylene and propylene are the most important petrochemicals [1], and have been widely used in the production of plastics, elastomers and rubbers [2]. The employment of biomass as the raw material for the production of olefins is regarded as a sustainable decarbonization approach This scheme can be implemented through biomass gasification to methanol followed by the conversion of methanol to olefins. Hannula et al developed a biomass to olefins process via methanol as the platform product and the syngas was generated by using a fluidized-bed steam/O2 gasifier [2]. Very limited studies have been reported on the utilization of the indirect steam gasification of biomass as a source of syngas for the synthesis of olefins through methanol as the intermediate. The performance of the proposed route was evaluated in terms of olefins yield, energy and exergy efficiencies, followed by a systematic comparison with the synthesis of olefins via the direct oxygen-steam gasification of biomass. Life cycle CO2 emission and economic evaluations of these two cases were performed in this work
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