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Performance improvement of the proton-conducting solid oxide electrolysis cell coupled with dry methane reforming
(2023-02-28)
Patcharavorachot, Yaneeporn
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Chalee, Wissawa
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Saebea, Dang
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Arpornwichanop, Amornchai
The proton-conducting solid oxide electrolysis cell (H-SOEC) is a clean technology for syngas production from H<inf>2</inf>O and CO<inf>2</inf> through electrochemical and chemical reactions. However, it provides a low CO<inf>2</inf> conversion and produces a syngas product with a high H<inf>2</inf>O content. To improve the H-SOEC for syngas production, H-SOEC coupled with a dry methane reforming process (H-SOEC/DMR) was proposed in this work. The process flowsheet of the H-SOEC/DMR was developed and further used to evaluate the performance of the H-SOEC/DMR process. From the performance analysis of the H-SOEC/DMR process, it was found that the CO<inf>2</inf> and CH<inf>4</inf> conversions were higher than 90% and 80%, respectively, when the process was operated in the temperature range of 1073–1273 K. In addition, the result showed that a syngas product with a low H<inf>2</inf>O content could be obtained. Energy efficiency was then considered and the results indicated that the highest energy efficiency of 72.80% could be achieved when the H-SOEC/DMR process was operated at a temperature of 1123 K, pressure of 1 atm, and current density of 2500 A m<sup>−2</sup>. Based on a pinch analysis, a heat exchanger network was applied to the H-SOEC/DMR process that improved the energy efficiency to 81.46%. Finally, an exergy analysis was performed and showed that the H-SOEC/DMR unit had the lowest exergy efficiency as a high-temperature exhaust gas was released.
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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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Clean magnesium production using concentrated solar heat in a high-temperature cavity-type thermochemical reactor
(2019-09-20)
Chuayboon, Srirat
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Abanades, Stéphane
The synthesis of magnesium from the corresponding oxide via a solar carbo-thermal and methano-thermal reduction process using high-temperature concentrated solar heat was investigated. The reduction of magnesium oxide (MgO) was experimentally demonstrated in a directly-irradiated prototype solar reactor at reduced pressure and temperature up to ∼1650 °C. The solar reactor was successfully operated with a variety of reducing agents (carbon and CH<inf>4</inf>) in batch and continuous modes under atmospheric and low pressure conditions (0.1–0.9 bar), thus representing the first process demonstration of MgO carbothermal reduction with continuous reactant injection in vacuum condition. A parametric study regarding operating pressure, carbon feedstock type, and C/MgO molar ratio was conducted to emphasize their effect on products yield (Mg and CO) and solar reactor performance. MgO conversion, reduction rate, and CO yield increased with decreasing pressure, in agreement with thermodynamic analysis. Utilizing activated charcoal as reducing agent showed the highest MgO conversion and CO yield. High MgO conversion over 99% was demonstrated with maximal CO yield up to 24.59 mmol/g<inf>MgO</inf>, closely approaching theoretical maximum value (24.81 mmol/g<inf>MgO</inf>). Employing methane as a reducing agent was also shown to be an alternative option to produce Mg, although methane cracking occurred simultaneously at the elevated reaction temperature. Mg recovery in the outlet products was identified as one of the most critical process challenges because of the pyrophoric property of the produced nanopowder and its strong oxidation reactivity with air.
1
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Effect of sintering additives on barium cerate based solid oxide electrolysis cell for syngas production from carbon dioxide and steam
(2018-05-01)
Likhittaphon, S.
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Pukkrueapun, T.
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Seeharaj, P.
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Wetwathana Hartley, U.
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Laosiripojana, N.
The effect of sintering additives (NiO, Co<inf>2</inf>O<inf>3</inf>, and ZnO) on the performance of barium-cerate-based solid oxide electrolysis cell (SOEC) is investigated. The performance of the SOEC with different sintering additives is determined in terms of relative density, electrochemical performance, and catalytic activity toward reverse water gas shift reaction. BaCeO<inf>3</inf> (BC) and BaCe<inf>0.9</inf>Gd<inf>0.1</inf>O<inf>3−δ</inf> (BCG) are synthesized using conventional precipitation method, comparing to ultrasonic-assisted precipitation. The sintering additives promote both densification and grain growth. The relative density of the BCG without sintering additive is 69% while that of the BCG with 1 wt% of Co<inf>2</inf>O<inf>3</inf>, NiO and ZnO is 95%, 95% and 88%, respectively. The SEM images indicate that the BCG with sintering additives exhibits dense grains with relatively large grain size. Although the BGC with NiO and Co<inf>2</inf>O<inf>3</inf> exhibit maximum relative density, the sample with ZnO shows relatively highest conductivity with the lowest activation energy of conduction and the sample with NiO provides the largest CO yield and CO<inf>2</inf> conversion. The activation energy of conduction is found to be 375.41, 70.06, 66.86 and 61.80 kJ mol<sup>−1</sup> for BCG, BCG with 1 wt% Co<inf>2</inf>O<inf>3</inf>, NiO and ZnO, respectively. The BCG with 1 wt% NiO provides the highest CO<inf>2</inf> conversion and CO yield at temperature below 700 °C (62% CO<inf>2</inf> conversion and 32% CO yield at 700 °C). Temperature program of oxidation (TPO) reveals that carbon deposition can cause the low CO yield at the operating temperature above 700 °C.
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Experimental analysis of continuous steam gasification of wood biomass for syngas production in a high-temperature particle-fed solar reactor
(2018-03-01)
Chuayboon, Srirat
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Abanades, Stéphane
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Rodat, Sylvain
Solar steam gasification of beech wood biomass has been performed in a novel high-temperature continuously-fed solar reactor for the thermochemical conversion of low-grade carbonaceous feedstock into transportable and storable gaseous fuels (syngas). The 1.5 kW<inf>th</inf> cavity-type solar reactor was operated in the temperature range of 1100–1300 °C. Large wood biomass particles (3–5 mm size) were continuously fed and gasified with the oxidizing agent to produce syngas, thus demonstrating the reactor suitability for large particle size processing. Operating parameters were varied in order to optimize the syngas production. The effect of steam flow-rate, carrier gas flow-rate, temperature, and biomass feeding rate on the syngas yield and reactor performances was experimentally investigated. The increase of steam flow-rate favored H<inf>2</inf>, CO<inf>2</inf> and CH<inf>4</inf> and reduced CO production. A noteworthy increase of the syngas yield with the temperature was highlighted, while the increase of carrier gas flow-rate was detrimental to the amount of syngas produced because of lowered gas residence time. The increase of biomass feeding rate (in the range of 0.8–1.8 g/min) showed noteworthy impact on the syngas composition without affecting the reactor performance, yielding high-quality syngas with a carbon conversion rate above 80%, while the total syngas yield was stable at about 70 mmol/g<inf>biomass</inf>.
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