Assessing the waste heat recovery potential of liquid organic hydrogen carrier chains

Proper thermal management can improve the efficiency of hydrogen storage chains based on liquid organic hydrogen carriers (LOHC). The energy and exergy efficiencies of 24 LOHC chains, which are differentiated by two hydrogen sources (SEL: hydrogen from electrolyzer and SINDU: industrial by-product), three hydrogen consumers (CPEMFC: proton exchange membrane fuel cell, CSOFC: solid oxide fuel cell, and CINDU: industrial consumer), and four LOHC pairs are calculated based on thermodynamic modeling. Possible strategies for the heat integration between the heat sources (including hydrogenation heat, heat generated by hydrogen consumer, and the high-temperature LOHC fluids) and the heat sinks (including LOHC preheating, hydrogen preheating, dehydrogenation, and external heating purposes) are designed for these chains. In the four selected LOHC pairs, dibenzyltoluene (DBT) is found to be the most favorable LOHC pair for the implementation of WHR strategies, mainly because of low heat demand for preheating (8.9% of the stored hydrogen energy) and a high dehydrogenation rate. The WHR strategies significantly improve the energy efficiency of LOHC chains by up to 21.7% points for the chains with CINDU and 40.8% points for chains with CSOFC or CPEMFC, which makes LOHC chains more efficient than traditional compressed or liquid hydrogen chains in several scenarios, i.e., the DBT chain with CPEMFC have the highest energy efficiency (70.4% for SEL/69.5% for SINDU), while the DBT chain with SINDU and CSOFC has the highest exergy efficiency (60.6%). For the remaining combinations of the remaining hydrogen sources and consumers, the compressed hydrogen chains are the most efficient

Methane steam reforming reaction in solid oxide fuel cells:Influence of electrochemical reaction and anode thickness

The influence of operation temperature, inlet gas composition, current density and the anode thickness on the methane steam reforming reaction over nickel yttria-stabilized zirconia anodes was experimentally studied in solid oxide fuel cells. The experimental results were analyzed using data fitting in Power-Law and Langmuir–Hinshelwood kinetic models. Similar trends of dependence of methane and steam partial pressures were observed in both models. The methane reaction order is positive. Negative influence of steam partial pressure on the methane steam reforming reaction rate are found. The electrochemical reaction and anode thickness affect the reforming kinetics parameters. The anodes thickness shows particular influences on the steam reaction order, and the activation energy when a current is produced. The model evaluation suggests that the two models are comparable and the extra parameters within the Langmuir–Hinshelwood kinetic model are contributing to the lower mean absolute percentage error and higher coefficient of determination

The effect of H₂S on internal dry reforming in biogas fuelled solid oxide fuel cells

Internal dry reforming of methane is envisaged as a possibility to reduce on capital and operation costs of biogas fuelled solid oxide fuel cells (SOFCs) system by using the CO2 present in the biogas. Due to envisaged internal dry reforming, the requirement for biogas upgrading becomes obsolete, thereby simplifying the system complexity and increasing its technology readiness level. However, impurities prevailing in biogas such as H2S have been reported in literature as one of the parameters which affect the internal reforming process in SOFCs. This research has been carried out to investigate the effects of H2S on internal dry reforming of methane on nickel-scandia-stabilised zirconia (Ni-ScSZ) electrolyte supported SOFCs. Results showed that at 800°C and a CH4:CO2 ratio of 2:3, H2S at concentrations as low as 0.125 ppm affects both the catalytic and electric performance of a SOFC. At 0.125 ppm H2S concentration, the CH4 reforming process is affected and it is reduced from over 95% to below 10% in 10 h. Therefore, future biogas SOFC cost reduction seems to become a trade-off between biogas upgrading for CO2 removal and biogas cleaning of impurities to facilitate efficient internal dry reforming

Thermodynamic analysis of supercritical water gasification combined with a reversible solid oxide cell

The low cost of electricity in some areas facilitates the adoption of high-temperature electrolysis plants for the large-scale storage of electricity. Supercritical water gasification (SCWG) is a promising method of syngas production from wet biomass. Additionally, it is a potential source of steam for electrochemical plants. However, the commercialisation of standalone SCWG systems is hindered by low efficiency and high operating cost. Accordingly, we propose the integration of SCWG with a reversible solid oxide cell (rSOC) to realise simultaneous syngas or power generation and wet biomass conversion. This technique would make the process feasible in terms of energy, allowing engineers to use SCWG to combine power generation with fuel production. The wet syngas from the SCWG is fed to the rSOC powered by excess renewable electricity in electrolysis mode, where steam is reduced to H2 to produce dry syngas with a higher calorific value. The energy efficiency of the proposed system is 91% in electrolysis mode and 47% in fuel cell mode. The electrolysis increases the syngas yield by a factor of thirteen and the use of total syngas generates twelve times more power in fuel cell mode compared to the use of only fresh syngas from SCWG.</p

Assessing the waste heat recovery potential of liquid organic hydrogen carrier chains

Proper thermal management can improve the efficiency of hydrogen storage chains based on liquid organic hydrogen carriers (LOHC). The energy and exergy efficiencies of 24 LOHC chains, which are differentiated by two hydrogen sources (SEL: hydrogen from electrolyzer and SINDU: industrial by-product), three hydrogen consumers (CPEMFC: proton exchange membrane fuel cell, CSOFC: solid oxide fuel cell, and CINDU: industrial consumer), and four LOHC pairs are calculated based on thermodynamic modeling. Possible strategies for the heat integration between the heat sources (including hydrogenation heat, heat generated by hydrogen consumer, and the high-temperature LOHC fluids) and the heat sinks (including LOHC preheating, hydrogen preheating, dehydrogenation, and external heating purposes) are designed for these chains. In the four selected LOHC pairs, dibenzyltoluene (DBT) is found to be the most favorable LOHC pair for the implementation of WHR strategies, mainly because of low heat demand for preheating (8.9% of the stored hydrogen energy) and a high dehydrogenation rate. The WHR strategies significantly improve the energy efficiency of LOHC chains by up to 21.7% points for the chains with CINDU and 40.8% points for chains with CSOFC or CPEMFC, which makes LOHC chains more efficient than traditional compressed or liquid hydrogen chains in several scenarios, i.e., the DBT chain with CPEMFC have the highest energy efficiency (70.4% for SEL/69.5% for SINDU), while the DBT chain with SINDU and CSOFC has the highest exergy efficiency (60.6%). For the remaining combinations of the remaining hydrogen sources and consumers, the compressed hydrogen chains are the most efficient

Methane reforming in solid oxide fuel cells:Challenges and strategies

Methane, mainly derived from fossil fuels, coal and natural gas, is a widely used industrial resource for hydrogen production via the reforming process. However, due to their unsustainability and the high carbon emission during the reforming process, more effective utilization of precious natural resources is desired. Therefore, sustainable resources such as biogas derived from biomass are attracting more and more attention for hydrogen and power production. A renewed interest in the flexible application of biogas in solid oxide fuel cells has recently attracted attention as a green pathway for hydrogen and power production driven by the fast development of fuel cell technology, especially in material technologies. However, the methane reforming process in solid oxide fuel cells suffers from low long-term operability, such as carbon deposition and sulphur poisoning over the anode materials. Therefore, the operational strategies for safe and stable operations are first discussed. Following that, the development of the anode materials to facilitate the methane reforming reaction while mitigating the subsequent insufficient catalyst stability such as deformation and degradation is conducted. Hopefully, this review can provide a practical perspective for sustainable hydrogen and power production in solid oxide fuel cells using biogas

Advances on methane reforming in solid oxide fuel cells

With the demand for anticipated green hydrogen and power production, novel and upgraded catalytic processes are desired for more effective utilization of precious natural resources. Methane steam reforming is an advanced and matured technology for converting methane to hydrogen and syngas. As a renewable energy resource containing a large amount of methane, biogas is a promising fuel for green hydrogen production. Because of the fuel flexibility and high efficiency relative to alternative technologies, solid oxide fuel cells with internal methane reforming capabilities may become an economically viable technology for hydrogen and power generation. A renewed interest in the flexible application of biogas in solid oxide fuel cells for the co-generation of green hydrogen and power has emerged recently, driven by the spectacular advances in fuel cell technology. However, the methane reforming process suffers from inaccurate or unprecise descriptions. Knowledge of the factors influencing the reforming reaction rate on the novel and improved reforming anode catalysts in solid oxide fuel cells are still required to design and operate such systems. Therefore, a comprehensive review of recent advances in methane steam reforming provides meaningful insight into technological progress. Herein, major descriptors of the methane steam reforming reaction engineering are reviewed to provide a practical perspective for the direct application of biogas in solid oxide fuel cells, which serves as an alternative sustainable, flexible process for green hydrogen and power co-production. Current advances and challenges are evaluated, and perspectives for future work are discussed