Thermodynamic simulation and mechanistic analysis of a dual-pathway biomass chemical looping gasification–steam reaction system for hydrogen production from typical aquatic invasive biomass

The utilization of invasive aquatic biomass for hydrogen production offers a promising route for simultaneously addressing invasive species management and low-carbon energy supply. This study employed alligator weed ( Alternanthera philoxeroides , AP) and water hyacinth ( Eichhornia crassipes , EC) as feedstocks to construct a dual-pathway biomass chemical looping gasification–steam reaction (BCLG-SR) hydrogen production system consisting of a fuel reactor (FR), water–gas shift reactor (WGSR), steam reactor (SR), air reactor (AR), and pressure swing adsorption (PSA) unit. A steady-state thermodynamic equilibrium model was developed using a process simulation framework, incorporating RYield for biomass decomposition, RGibbs based on Gibbs free-energy minimization for the main reaction equilibria, and REquil for the WGS reaction. The Peng–Robinson equation of state was used for gas-phase thermodynamic property calculations. The effects of reaction temperature (600–900 °C), steam-to-biomass mass ratio (S/B = 0.6–2.0, defined as the mass ratio of the total H 2 O feed to the dry biomass feed), and oxygen carrier (OC) type (Fe 2 O 3 , Fe 2 O 3 /Al 2 O 3 , and CoFe 2 O 4 ) on hydrogen production performance, gas composition, and carbon conversion behavior were systematically investigated. In addition, the system was comprehensively evaluated in terms of energy utilization efficiency and environmental impact. The results showed that, for AP at an S/B ratio of 1.5, the hydrogen production rate reached a maximum at approximately 750 °C. Under the fixed dry biomass feed rate of 600 kg·h −1 , the CoFe 2 O 4 system achieved the highest H 2 production rate of 58.36 kg · h −1 , corresponding to 97.27 g H 2 per kg of dry biomass processed. Increasing the S/B ratio significantly increased the H 2 molar fraction, which reached approximately 64% in the CoFe 2 O 4 system. Different oxygen carriers (OCs) exhibited distinct influences on system performance, with the Fe 2 O 3 system exhibiting higher H 2 selectivity ( Se l H 2 ) and a higher lower heating value (LHV) of the product gas. Carbon in the system was mainly enriched in the form of CO 2 , with the CO 2 fraction at the outlet of the water–gas shift (WGS) pathway remaining above 98% under most operating conditions. Under representative operating conditions for Fe 2 O 3 (800 °C, S/B = 1.5), the overall energy utilization efficiency of the system was 68.96%, while the biomass-to-hydrogen energy conversion efficiency ( η BH ) reached 72.65%. The results confirmed that the BCLG-SR system enables efficient hydrogen production and sustainable conversion of aquatic invasiv e biomass, providing a reference for process optimization and engineering applications.