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The objective of this study to develop and undertake a comprehensive CFD analysis of an effective state-of-the-art 250 kg/day hydrogen generation unit for an on-site hydrogen refueling station (HRS), an essential part of the infrastructure required for fuel cell vehicles and various aspects of hydrogen mobility. This design consists of twelve reforming tubes and one newly designed metal fiber burner to ensure superior emission standards and performance. Experimental and computational modeling steps are conducted to investigate the effects of various operating conditions, the excess air ratio (EAR) at the burner, the gas hourly space velocity (GHSV), the process gas inlet temperature, and the operating pressure on the hydrogen production rate and thermal efficiency. The results indicate that the performance of the steam methane reforming reactor increased significantly by improving the combustion characteristics and preventing local peak temperatures along the reforming tube. It is shown that EAR should be chosen appropriately to maximize the hydrogen production rate and lifetime operation of the reformer tube. It is found that high inlet process gas temperatures and low operating pressure are beneficial, but these parameters have to be chosen carefully to ensure proper efficiency. Also, a high GHSV shortens the residence time and provides unfavorable heat transfer in the bed, leading to decreased conversion efficiency. Thus, a moderate GHSV should be used. It is shown that heat transfer is an essential factor for obtaining increased hydrogen production. This study addresses the pressing need for the HRS to adopt such a compact system, whose processes can ensure greater hydrogen production rates as well as better durability, reliability, and convenience. • A hydrogen generation unit for an on-site hydrogen refueling station is studied. • An effective surface-stabilized burner ensuring superior performances is developed. • A 3D numerical model of the proposed hydrogen generation unit is established. • SMR unit performance outcomes over a range of operating conditions are evaluated. [ABSTRACT FROM AUTHOR]

Achieving higher efficiency of direct ammonia solid oxide fuel cells (DA-SOFC) requires high compatibility between cell design and temperature distribution during NH 3 decomposition. Therefore, this work aims to provide a comprehensive study of the DA-SOFC different design configurations and parameter optimization. Three main flow configurations are co-flow, counter-flow, and cross-flow. In addition, a detailed parametric study of the cross-flow configuration is performed to optimize cell performance by minimizing thermal stress, considering thermal management, efficiency, and manufacturing advantages. The model is experimentally validated, and the mean relative error and root mean square error is found to be less than 2%. The co-flow configuration has shown lower power output at higher current densities than the counter and cross-flow configurations. At the same time, co-flow possesses minimum thermal stress across the cell cross-section. In cross-flow design, the maximum electrical efficiency of 51.4% with 152 K cell temperature difference is established at 60% fuel utilization, 3% air utilization, fuel intake temperature, and air inlet temperature at 923 K. This study is expected to help optimize the design and operating parameters to maximize DA-SOFC stacking performance and durability and minimize cost. [Display omitted] • Multi-scale 3-D model for direct NH 3 decomposition in SOFC was developed. • Optimum operating conditions and cell flow configuration were established. • Co-flow exhibits less temperature difference, but lower efficiency. • Counter and crossflow exhibit higher temperature differences and higher efficiency. • High performances are highlighted in the cross-flow by minimizing thermal stress. [ABSTRACT FROM AUTHOR]

Hydrogen production by supercritical water gasification (SCWG) of valine as a model for protein was examined in a fixed-bed reactor at 28 MPa. The effect of reaction temperature (500–710 °C), type of catalyst (AC, Ni–Y/AC, Ni–Pt/AC, and Ni–Pd/AC), and LHSV (24–72 h −1 ) on the extent of gasification and gas composition was investigated. Total gas yield increased with increasing temperature up to 710 °C while carbon gasification efficiency (CGE) reached the highest value of 98.1% at 600 °C over the Ni–Y/AC catalyst. The three Ni-based catalysts promoted hydrogen formation reactions greater than the AC. In particular the Ni–Pt/AC and Ni–Pd/AC catalysts effectively reformed C 2+ hydrocarbons intermediates to H 2 and CO 2 . The Ni–Y/AC catalyst at 650 °C completely destroyed nitrogen-containing organic intermediates such as amines in the liquid effluent. The presence of Pt and Pd significantly suppressed the crystallization of Ni metal supported on AC in supercritical water. [ABSTRACT FROM AUTHOR]