Catalytic steam gasification of pine sawdust for hydrogen-rich syngas production in a decoupled triple bed reaction system

Abstract

In the present work, a novel decoupled biomass gasification system was proposed, aiming at improving the syngas quality, particularly increasing the H₂ yield, as well as decreasing the tar and CO₂ contents. Pine sawdust was used as the raw material, and a series of gasification experiments were primarily performed in a three-stage fixed bed reactor, to investigate the effects of pyrolysis, gasification and reforming temperatures, steam flow rate, peroxide coefficient, NiO load rate and CaO/biochar mass ratio on its gasification properties. Moreover, the total gas yield, tar content, low heating value of syngas, gasification efficiency and carbon conversion efficiency were examined. The results indicated that a high reaction temperature was able to facilitate the tar cracking and H₂ production. With increasing steam flow rate and peroxide coefficient, the total gas yield and H₂ content first rose and then reduced, while the tar content showed an opposite trend. The modification of NiO on Fe-based oxygen carriers (OCs) enhanced the tar destruction and total gas yield, particularly the H₂ concentration. Furthermore, CaO/biochar played a dual role as the CO₂ sorbent at a lower temperature but as the catalyst at a higher temperature. Specially, separately adopting NiO/Fe-based OCs and CaO/biochar as the solid-phase gasification agent and CO₂ sorbent, a product syngas with the H₂ and its total gas yield of 0.54 and 0.86 Nm³/kg, and the CO₂ and tar content of 0.07 Nm³/kg and 123.43 g/Nm³ was obtained at the pyrolysis, gasification and reforming temperatures of 700, 700 and 800 °C, peroxide coefficient of 0.1, steam flow rate of 0.4 ml/min, NiO load rate of 15 %, and CaO/biochar mass ratio of 3. This study provides a basis data for the application of PS gasification.