Experimental assessment of woody biomass gasification in a hybridized solar powered reactor featuring direct and indirect heating modes

Abstract

Solar thermochemical gasification is an opportunity for the production of sustainable fuels from carbonaceous resources including biomass. Substituting conventional gasification processes by solardriven technologies may enable cleaner production of H 2 -rich syngas while saving feedstock resources and alleviating CO 2 emissions. This work addresses hybrid solar-autothermal gasification of mm-sized beech wood particles in a lab-scale 1.5 kW th spouted-bed reactor. Hybridization under reduced solar power input was performed by injecting oxygen and additional biomass inside the gasifier for complementary heat supply. Increasing O 2 :C molar ratios (in the range 0.14-0.58) allowed to heat the reactor cavity and walls progressively, while gradually impairing the reactor performance with an increase of the syngas CO 2 content and a decrease of the reactor cold gas efficiency (CGE). Gasification with mixed H 2 O and O 2 was then assessed at thermodynamic equilibrium and global trends were validated experimentally, showing that control of H 2 :CO ratio was compatible with in-situ combustion. The impact of reaction temperature (1200-1300°C) and heating mode (direct or indirect) was experimentally studied during both allothermal and hybrid gasification. Higher H 2 and CO yields were achieved at high temperatures (1300°C) under direct reactor heating. Hybridization was able to counterbalance a 40% drop of the nominal solar power input, and the measured CGE reached 0.82, versus values higher than 1 during allothermal gasification.

Design and validation of reactant feeding control strategies for the solar-autothermal hybrid gasification of woody biomass

“…Regarding the injection of oxygen, typical results showed a significant decrease of the H 2 content and an increase of the CO 2 content due to combustion reactions, which did not systematically come with a decrease of the CO mole fraction [23,24]. The CO content only seemed to decrease at high inlet O 2 :C molar ratios [25], which was also pointed out in recent investigations about spouted-bed hybridization [22]. This shows that hydrogen combustion (Equation 3) tends to be favored in comparison with carbon monoxide combustion (Equation 4).…”

“…The hybridization of the spouted-bed gasifier by injecting oxygen and additional wood was already investigated in previous studies [19,22,38]. They showed a reactor cavity temperature maintained above 1300 °C, while the solar power input decreased by about 40% (from 1200 W to 700 W).…”

“…In our previous work [22], it was stated that altered syngas production rates could have been caused by a progressive decrease of the wood injection rate in the reactor. A new effort was thus undertaken to calibrate the screw driver, and provide more stable wood injection rates.…”

“…Thus, T cavity remained at 1300 °C ± 10 °C (like in Figure 2). This temperature was chosen based on a previous study showing improved performance compared to 1200 °C [22,37]. A record of the shutter aperture was kept, so the solar power input could be deduced at each instant (time-step of 3 s) and averaged over gasification periods.…”

“…Boujjat et al also investigated SAHG both experimentally [19] and numerically [20], using a hybridized spouted-bed reactor and eventually proposing an application to solid-recovered fuel gasification [21]. Recent experimental investigations of the hybridized spouted-bed revealed the impact of O 2 injection rate, operating temperature (in the range 1200-1300 °C) and reactor heating mode (direct versus indirect heating of the cavity) [22].…”