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Analysis of process parameters influence on syngas yields and biomass gasification rates in a continuous particle-fed solar-irradiated gasifier
(2020-12-11)
Chuayboon, Srirat
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Abanades, Stéphane
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Rodat, Sylvain
Steam gasification of biomass was experimentally investigated with different lignocellulosic biomass feedstocks in a 1.5 kWth continuous particle-fed solar-irradiated gasifier at high temperatures (1100-1300 °C) utilizing highly concentrated sunlight as process heat source, demonstrating the conversion of intermittent solar energy and biomass into synthesis gas without CO2 emissions. Forty-nine on-sun experiments were performed in order to study the effect of process parameters (biomass feeding rate, temperature, biomass composition) on syngas production yield, biomass gasification rate (carbon conversion rate), and reactor performance. As a result, syngas yield, composition (quality), biomass gasification rate, and reactor performance increase significantly with both the biomass feeding rate and temperature because both biomass consumption rates and reaction kinetics are enhanced. However, the performance outputs are reduced when biomass feeding rate exceeds its optimal feeding point. The reactor temperature of 1300°C is recommended to operate reliably the solar biomass gasifier with the considered biomass particle size range (0.3-4 mm) in a continuous feeding mode with complete biomass conversion, as verified by the carbon consumption rate that matches closely the carbon feeding rate. By optimizing biomass feeding rate consistently with operating temperature, the calorific value of the biomass feedstock is solar upgraded by 24% with carbon conversion extent above 90% and solar-to-fuel energy conversion efficiency up to 29%.
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Stepwise Solar Methane Reforming and Water-Splitting via Lattice Oxygen Transfer in Iron and Cerium Oxides
(2020-08-01)
Chuayboon, Srirat
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Abanades, Stéphane
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Rodat, Sylvain
Chemical-looping reforming of methane (CLRM) involves lattice oxygen transfer in metal oxides. This study aims to compare iron (Fe<inf>2</inf>O<inf>3</inf>) and cerium (CeO<inf>2</inf>) oxides as oxygen carrier materials for isothermal solar-driven stepwise CH<inf>4</inf> reforming and H<inf>2</inf>O splitting. Experiments are conducted in a directly irradiated lab-scale solar reactor heated by concentrated sunlight at 950–1150 °C. Using solar energy for process heat reduces the dependence on fossil energy resources and avoids CO<inf>2</inf> emissions, while converting solar energy into chemical fuels. The performance of the oxygen carrier materials is compared and evaluated by determining the amount of oxygen transferred, methane conversion, syngas yield, and thermochemical cycling stability. As a result, iron oxide reduction with methane strongly depends on temperature and displays relatively lower reaction rate than CeO<inf>2</inf>. The reduced iron is not completely reoxidized to Fe<inf>3</inf>O<inf>4</inf> after water-splitting because of low thermal stability resulting in strong sintering and agglomeration, thereby decreasing syngas yield and leading to material deactivation. In contrast, ceria exhibits faster reaction rate and stable syngas yield with H<inf>2</inf>/CO molar ratios approaching two over repeated cycles. Stable patterns in the averaged oxygen nonstoichiometry (δ = 0.35–0.38) demonstrate excellent thermal cycling stability. Thus, using Fe<inf>2</inf>O<inf>3</inf> oxygen carrier is not suitable for solar CLRM, but iron oxide reduction with methane can be promising for solar metallurgy aiming at producing both metallic iron and syngas.
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High-Purity and Clean Syngas and Hydrogen Production From Two-Step CH4 Reforming and H2O Splitting Through Isothermal Ceria Redox Cycle Using Concentrated Sunlight
(2020-07-17)
Chuayboon, Srirat
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Abanades, Stéphane
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Rodat, Sylvain
The thermochemical conversion of methane (CH<inf>4</inf>) and water (H<inf>2</inf>O) to syngas and hydrogen, via chemical looping using concentrated sunlight as a sustainable source of process heat, attracts considerable attention. It is likewise a means of storing intermittent solar energy into chemical fuels. In this study, solar chemical looping reforming of CH<inf>4</inf> and H<inf>2</inf>O splitting over non-stoichiometric ceria (CeO<inf>2</inf>/CeO<inf>2−δ</inf>) redox cycle were experimentally investigated in a volumetric solar reactor prototype. The cycle consists of (i) the endothermic partial oxidation of CH<inf>4</inf> and the simultaneous reduction of ceria and (ii) the subsequent exothermic splitting of H<inf>2</inf>O and the simultaneous oxidation of the reduced ceria under isothermal operation at ~1,000°C, enabling the elimination of sensible heat losses as compared to non-isothermal thermochemical cycles. Ceria-based reticulated porous ceramics with different sintering temperatures (1,000 and 1,400°C) were employed as oxygen carriers and tested with different methane flow rates (0.1–0.4 NL/min) and methane concentrations (50 and 100%). The impacts of operating conditions on the foam-averaged oxygen non-stoichiometry (reduction extent, δ), syngas yield, methane conversion, solar-to-fuel energy conversion efficiency as well as the effects of transient solar conditions were demonstrated and emphasized. As a result, clean syngas was successfully produced with H<inf>2</inf>/CO ratios approaching 2 during the first reduction step, while high-purity H<inf>2</inf> was subsequently generated during the oxidation step. Increasing methane flow rate and CH<inf>4</inf> concentration promoted syngas yields up to 8.51 mmol/g<inf>CeO<inf>2</inf></inf> and δ up to 0.38, at the expense of enhanced methane cracking reaction and reduced CH<inf>4</inf> conversion. Solar-to-fuel energy conversion efficiency, namely, the ratio of the calorific value of produced syngas to the total energy input (solar power and calorific value of converted methane), and CH<inf>4</inf> conversion were achieved in the range of 2.9–5.6% and 40.1–68.5%, respectively.
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Solar chemical looping reforming of methane combined with isothermal H2O/CO2 splitting using ceria oxygen carrier for syngas production
(2020-02-01)
Chuayboon, Srirat
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Abanades, Stéphane
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Rodat, Sylvain
The chemical looping reforming of methane through the nonstoichiometric ceria redox cycle (CeO<inf>2</inf>/CeO<inf>2</inf><inf>−</inf><inf>δ</inf>) has been experimentally investigated in a directly irradiated solar reactor to convert both solar energy and methane to syngas in the temperature range 900–1050 °C. Experiments were carried out with different ceria shapes via two-step redox cycling composed of endothermic partial reduction of ceria with methane and complete exothermic re-oxidation of reduced ceria with H<inf>2</inf>O/CO<inf>2</inf> at the same operating temperature, thereby demonstrating the capability to operate the cycle isothermally. A parametric study considering different ceria macrostructure variants (ceria packed powder, ceria packed powder mixed with inert Al<inf>2</inf>O<inf>3</inf> particles, and ceria reticulated porous foam) and operating parameters (methane flow-rate, reduction temperature, or sintering temperature) was conducted in order to unravel their impact on the bed-averaged oxygen non-stoichiometry (δ), syngas yield, methane conversion, and solar reactor performance. The ceria cycling stability was also experimentally investigated to demonstrate repeatable syngas production by alternating the flow between CH<inf>4</inf> and H<inf>2</inf>O (or CO<inf>2</inf>). A decrease in sintering temperature of the ceria foam was beneficial for increasing syngas selectivity, methane conversion, and reactor performance. Increasing both CH<inf>4</inf> concentration and reduction temperature enhanced δ with the maximum value up to 0.41 but concomitantly favored CH<inf>4</inf> cracking reaction. The ceria reticulated porous foam showed better performance in terms of effective heat transfer, due to volumetric absorption of concentrated solar radiation and uniform heating with lower solar power consumption, thereby promoting the solar-to-fuel energy conversion efficiency that reached up to 5.60%. The energy upgrade factor achieved during cycle was up to 1.19. Stable patterns in the δ and syngas yield for consecutive cycles with the ceria foam validated material performance stability.
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Experimental assessment of biomass feedstock gasification in a high-temperature continuous solar gasifier
(2019-07-25)
Chuayboon, Srirat
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Abanades, Stéphane
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Rodat, Sylvain
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Boujjat, Houssame
Solar steam gasification of biomass was performed in a 1.5 kW<inf>th</inf> continuous particle-fed solar reactor at high temperature (1100-1300 °C) using real high-flux solar radiation provided by a parabolic dish solar concentrator. A comprehensive parametric study considering different lignocellulosic biomass feedstocks, biomass feeding rates, and operating temperatures was conducted for optimizing the syngas production and assessing the gasification performance. Different biomass feedstocks were continuously fed and gasified with H<inf>2</inf>O to produce syngas, thus demonstrating the suitability of the reactor operated compatibly with different biomass variants. A significant beneficial enhancement of the syngas yield when increasing temperature was highlighted. Increasing biomass feeding rate considerably promoted the syngas yields, and the syngas production (especially H<inf>2</inf>) was more affected by the biomass feedstock (chemical composition) than by the particle size in the considered range (0.3-4 mm). Moreover, an increase in the biomass feeding rate inherently reduced the solar processing duration (for a given biomass amount processed), thus in turn promoting efficient solar energy storage into syngas with the energy upgrade factor (U) up to 1.24 and solar-to-fuel energy conversion efficiency (η<inf>solar-to-fuel</inf>) up to 29%.
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Syngas production via solar-driven chemical looping methane reforming from redox cycling of ceria porous foam in a volumetric solar reactor
(2019-01-15)
Chuayboon, Srirat
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Abanades, Stéphane
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Rodat, Sylvain
The solar-driven chemical looping methane reforming using the non-stoichiometric ceria redox cycle (CeO<inf>2</inf>/CeO<inf>2-δ</inf>) was experimentally investigated for both syngas production and isothermal H<inf>2</inf>O/CO<inf>2</inf> splitting using a directly irradiated volumetric solar reactor in the temperature range of 950–1050 °C. Experiments were performed via two-step redox cycling encompassing endothermic ceria reduction with methane (partial oxidation of methane) and exothermic oxidation of reduced ceria with H<inf>2</inf>O/CO<inf>2</inf> under the same operating temperature. Ceria was used as oxygen carrier material in the form of reticulated porous foam structure and different operating parameters (methane flow-rate and reduction temperature) were varied in order to emphasize their impact on the bed-averaged oxygen non-stoichiometry (δ), syngas yield, methane conversion as well as solar reactor performances. The ceria cycling stability was also examined. The increase of both the methane flow-rate and reduction temperature promoted the δ in turn leading to a substantial enhancement in the syngas yields that reached up to 8.08 mmol/g<inf>CeO₂</inf>. However, they showed an adverse impact on the carbon formation associated with methane cracking reaction. Fifteen successive ceria redox cycles with stable patterns in the δ and syngas production yield validated material stability. The maximum δ achieved during ceria reduction was up to 0.38, complete oxidation yield with either water or CO<inf>2</inf> was achieved, while the highest solar-to-fuel energy conversion efficiency reached 5.22% and the energy upgrade factor was in the range of 0.97–1.10.
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Insights into the influence of biomass feedstock type, particle size and feeding rate on thermochemical performances of a continuous solar gasification reactor
(2019-01-01)
Chuayboon, Srirat
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Abanades, Stéphane
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Rodat, Sylvain
The solar-driven steam gasification of different lignocellulosic biomass feedstocks was experimentally investigated with a 1.5 kW<inf>th</inf> continuously particle-fed solar reactor at high temperature using real high-flux solar radiation provided by a parabolic dish concentrator. Experiments were carried out with five carbonaceous materials under different biomass feeding rates in the range of 0.8–2.7 g/min at 1300 °C in order to optimize the synthesis gas production and composition. Increasing biomass feeding rate (at constant slightly over-stoichiometric steam/biomass ratio) noticeably promoted the syngas yields that reached up to 83.2 mmol/g<inf>biomass</inf>. The syngas yield (especially H<inf>2</inf>) was more affected by the biomass feedstock (chemical composition) than by the particle size in the considered range (0.3–4 mm). The calorific value of the biomass was solar upgraded up to 24% through the syngas produced with a carbon conversion above 90%, thereby accomplishing efficient solar energy storage into the produced syngas. Increasing the biomass feeding rate inherently shortened the solar processing duration (for a given biomass amount). Thus, the solar energy input and the heat losses were reduced while the overall syngas production capacity was increased, which in turn drastically enhanced both the thermochemical reactor efficiency and the solar-to-fuel energy conversion efficiency with maximum values typically beyond 25%.
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Comprehensive performance assessment of a continuous solar-driven biomass gasifier
(2018-12-15)
Chuayboon, Srirat
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Abanades, Stéphane
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Rodat, Sylvain
The experimental performance assessment of a continuous solar-driven biomass gasifier using real high-flux concentrated solar radiation as the source of process heat has been performed. A comprehensive parametric study considering different lignocellulosic biomass feedstocks (wood type), biomass feeding rates (0.6–2.7 g/min), steam/biomass molar ratios (1.6–2.8), carrier gas flow rates (2–3.3 Nl/min) and reaction temperatures (1100–1300 °C) was conducted for optimizing the syngas production capacity and evaluating the gasification performances. Different wood biomass feedstocks were continuously fed as particles and gasified with H<inf>2</inf>O for producing syngas, thus successfully demonstrating the reliability of the reactor that was operated compatibly with different particle sizes and shapes. A small excess of water with respect to stoichiometry was beneficial for biomass gasification regarding the increase of H<inf>2</inf> and CO and the decrease of CH<inf>4</inf>, CO<inf>2</inf> and C<inf>2</inf>H<inf>m</inf> production. An increase in the gas residence time resulted in the improvement of the syngas yields and quality. Significant enhancement of syngas yields and production rates through the rise of operating temperature was highlighted with activation energy in the range of 24–29 kJ/mol. Increasing biomass feeding rate improved the syngas yields and gasification rates, enabling efficient solar energy storage into syngas and enhancing the energy upgrade factor (U) above 1.20, the solar-to-fuel energy conversion efficiency (η<inf>solar-to-fuel</inf>) above 29% and the thermochemical reactor efficiency (η<inf>reactor</inf>) above 27%.
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Co-production of syngas and zinc via combined solar-driven biomass gasification and ZnO carbo-thermal reduction in a continuously-operated solar reactor
(2018-11-08)
Chuayboon, Srirat
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Abanades, Stéphane
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Rodat, Sylvain
The solar thermochemical gasification of biomass with in-situ ZnO carbo-thermal reduction was carried out in a lab-scale (1.5 kW) continuously-fed solar reactor. The objective of this study was to demonstrate the feasibility of the combined process involving wood biomass gasification with ZnO as an oxidizing agent under continuous process operation for co-production of syngas and metallic Zn. A controlled mixture of biomass and ZnO particles was injected in a cavity-type receiver directly irradiated by concentrated solar radiation. The influence of temperature (1050-1250°C) on syngas production was experimentally investigated and compared to the case of a pyrolysis process (without any oxidizing agent). H<inf>2</inf> production increased drastically, CO production tended also to increase, while CH<inf>4</inf> and CO<inf>2</inf> concentrations decreased when increasing the temperature. The global syngas production of the combined gasification and ZnO carbo-thermal reduction was higher in comparison with pyrolysis. Collected products at the reactor outlet indicated high Zn content, with low recombination to ZnO in the solid products. The energy content of the feedstock was upgraded by the solar power input in the form of both syngas and Zn, thus outperforming pyrolysis in addition to delivering higher syngas output per unit of feedstock.
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A novel high-temperature solar chemical reactor for syngas production from solar-driven thermochemical gasification of wood biomass
(2018-11-08)
Rodat, Sylvain
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Bellouard, Quentin
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Abanades, Stéphane
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Chuayboon, Srirat
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Frayssines, Pierre Eric
Solar energy is the most abundant renewable energy source on earth and its contribution in the energy mix is growing fast, especially for electricity production via photovoltaic panels and to a lesser extent for concentrated solar energy. However, concentrated solar energy can also provide high temperature heat for process applications. Solar fuels are envisioned as alternative fuels that would enable long term storage and transport of solar energy. Solar thermochemical gasification of lignocellulosic biomass has been investigated in this objective. The use of concentrated solar energy as the external heat source for the high-temperature reaction allows producing high-value syngas with both higher energy conversion efficiency and reduced cost of gas cleaning and separation, while saving biomass feedstock. A 1.5 kW<inf>th</inf> solar reactor was successfully tested for continuous solar driven gasification of millimetric wood particles under real solar irradiation using a parabolic dish concentrator. Investigated temperatures ranged from 1100°C to 1400°C. The influence of temperature, oxidizing agent nature (H<inf>2</inf>O or CO<inf>2</inf>), heating configuration (direct or indirect irradiation), on gas yield and energy conversion efficiency was investigated. The syngas yield drastically increased with the temperature for both steam and CO<inf>2</inf> gasification, while increasing the steam content favored H<inf>2</inf> production over CO. Continuous biomass conversion was demonstrated with a global solar-to-fuel energy conversion efficiency of 26% at 1300°C and a cold gas efficiency as high as 1.16, confirming efficient solar up-grade of the feedstock energy content.

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