Experiment evaluation and thermodynamic analysis of pulping modification on ordered conversion of bark in supercritical water

[Display omitted] •Rheological property of bark slurry was significantly lower than 1 Pa·s.•Alkaline pulping led to the ordered conversion of bark in supercritical water.•Bark slurry prepared by KOH achieved complete gasification at 650 °C.•Pulping modification reduced a 20% carbon emission at least potentially.•Energy and exergy efficiencies of new system were 47.47% and 48.63%, respectively. Major obstacles of supercritical water gasification (SCWG) of lignocellulosic biomass, including ineffective pulping for energy self-sufficiency and a high conversion barrier significantly inhibited its large-scale development. In this study, the pulping effect of alkaline and salt pulping for high concentration bark slurry were compared systematically. The SCWG performances of bark (non-catalytic/catalytic) and bark slurry were evaluated. Based on energy self-sufficiency, a novel SCWG process of 50 wt% bark slurry was designated with a multistage reactor configuration and pulping process. The findings suggest that alkaline pulping had a wider applicability (reaching 50 wt%) and better rheological properties than salt pulping. Only 30 wt% bark slurry was capable for applying salt pulping because of solid residue with the excessive salt addition. Alkaline pulping resulted in an ordered conversion of 5 wt% and 10 wt% bark slurries during SCWG, with complete gasification of 5 wt% bark slurries prepared by KOH and NaOH at 650 and 680 °C, respectively. Besides, alkaline and salt pulping reduced the 26 % and 33 % carbon emissions, respectively. In the novel process, the optimal ratio of preheated water to bark slurry was 4 (water diversion to the primary and secondary gasification reactors of 1:3), which exhibits in energy and exergy efficiencies of 47.47 % and 48.63 %, respectively. This configuration reduces exergy losses in the gasification reactor and heat exchanger, aiding in the large-scale industrial output of SCWG.