Experimental and numerical study of a directly irradiated hybrid solar/combustion spouted bed reactor for continuous steam gasification of biomass

The concept of hybrid solar gasifiers is proposed to couple autothermal gasification with solar gasification so as to meet the requirement for stable and continuous operation under intermittent or fluctuating solar irradiation. Solar process hybridization through partial oxy-combustion of the feedstock appears to be crucial because thermochemical processes are very sensitive to small solar energy input variations, and require permanent control of thermodynamic conditions to ensure fuel production quality. This work aims to study solar-hybridized steam gasification of biomass in a novel directly-irradiated lab-scale reactor based on the principle of conical jet spouted beds. This concept was first numerically simulated to thoroughly analyze the reactor operation and to provide insights into the temperature distribution, fluid flow dynamics, reactive particle trajectories/conversion, gas species distribution and flame location inside the reactor. A two-phase flow model was developed including discrete phase model for the reactive biomass particles undergoing both combustion and pyro-gasification, and coupled heat and mass transfer. Thereafter, solar-only and mixed solar-combustion experiments were carried out under real concentrated solar flux and the effects of process hybridization on syngas yield and reactor performance were investigated. The results confirmed that O2 feeding rate is a relevant variable to control the process temperature. Accordingly, a continuous operation of the solar reactor can be ensured with variable solar energy input.