The effect of pyrolysis temperature on the optimal conversion of residual biomass to clean syngas through fast-pyrolysis/steam gasification integration

Abstract

The present work examines the performance of an integrated pyrolysis/gasification energy system, considering biochar as a key element of integration, and assessing the impact of pyrolytic pretreatment on the system behavior. Firstly, softwood pellet (SWP) and spent coffee grounds (SCG) were pyrolyzed using a screw-type reactor in semi-continuous operation (at 400 °C and 500 °C). The steam gasification of biochar at 850 °C was then simulated using a kinetic model based on the results of devolatilization tests performed in a lab-scale fluidized-bed reactor. The results showed that pyrolytic pretreatment significantly reduced tar contamination in the gasification syngas to 0.3g/Nm 3 , compared to 24.2 and 18.7g/Nm 3 resulting for raw SCG and SWP, respectively. Furthermore, the comprehensive evaluation of the integrated system confirmed that cold gas efficiency and carbon conversion efficiency of the integrated processes were not affected, despite the different quality of the syngas produced, also highlighting the differences in H 2 production between the two feedstocks. • Pyro-gasification integration and conventional steam gasification is compared. • Hydrogen up to 112.7 g/kg Biochar was predicted from biochar steam gasification. • Down to 0.3g/Nm 3 syngas tar content was obtained from biochar gasification. • A different behavior of SWP and SCG biochar for hydrogen production was noticed. • Pyrolysis at 500 and 400 °C raise SWP and SCG biochar steam gasification reactivity.