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T : 목차정보

International journal of hydrogen energy 51건

  1. [해외논문]   Optimization of a counter-flow microchannel reactor using hydrogen assisted catalytic combustion for steam reforming of methane   SCI SCIE

    Jeon, S.W. , Yoon, W.J. , Jeong, M.W. , Kim, Y.
    International journal of hydrogen energy v.39 no.12 ,pp. 6470 - 6478 , 2014 , 0360-3199 ,

    초록

    The objective of this study is to optimize a microchannel reactor using hydrogen assisted catalytic combustion for steam reforming of methane. Hydrogen assisted catalytic combustion does not require preheating because the catalytic combustion of hydrogen occurs at room temperature. After start-up by hydrogen catalytic combustion, fuels of hydrogen and methane were changed to methane. The geometric configuration of the counter-flow reactor was optimized by the simulation model under steady state condition. The hydrogen flow rate in the counter-flow reactor was also optimized by transient simulations using the response surface methodology. As a result, the counter-flow reactor showed extremely short start-up time because of the optimized configuration and the optimized hydrogen flow rate. Hot spots were avoided because of the hydrogen shut-off after start-up. The operating characteristics of the counter-flow reactor were compared with those of the co-flow reactor.

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  2. [해외논문]   Thermodynamic performance assessment and comparison of IGCC with solid cycling process for CO2 capture at high and medium temperatures   SCI SCIE

    Chi, J. , Zhao, L. , Wang, B. , Li, Z. , Xiao, Y. , Duan, Y.
    International journal of hydrogen energy v.39 no.12 ,pp. 6479 - 6491 , 2014 , 0360-3199 ,

    초록

    Solid sorbents can be used to capture CO 2 from pre-combustion sources at various temperatures. MgO and CaO are typical medium- and high-temperature CO 2 sorbents. However, pure MgO is not active toward CO 2 . The addition of Na 2 CO 3 increases the operating temperature and significantly increases the reactivity of sorbents to capture CO 2 . Na 2 CO 3 -promoted MgO is a promising medium-temperature CO 2 sorbent. In this study, the thermodynamic performance of integrated gasification combined cycle (IGCC) systems with Na 2 CO 3 -MgO-based warm gas decarbonation (WGDC) and CaO-based hot gas decarbonation (HGDC) is evaluated and compared with that of an IGCC system with methyldiethanolamine (MDEA)-based cold gas decarbonation (CGDC). Assuming that the average CO 2 capture capacities of solid sorbents are one-third of their theoretical maxima, we reveal that the IGCC system undergoes approximately 2.8% and 3.6% improvement on net efficiency when switching from CGDC to WGDC and to HGDC, respectively. The net efficiency of the system is increased by improving the CO 2 capture capacity of the sorbent. The IGCC with Na 2 CO 3 -MgO experiences more significant increase in efficiency than that with CaO along with the improvement of sorbent average CO 2 capture capacity. The efficiency of the IGCC systems reaches the same value when the average CO 2 capture capacities of both sorbents are 53% of their theoretical levels. The effects of gas turbine combustor fuel gas inlet temperature on IGCC system performance are analyzed. Results show that the efficiency of the IGCC systems with HGDC and WGDC increases by 0.74% and 0.53% respectively as the fuel gas inlet temperature increases from 250 o C to 650 o C.

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  3. [해외논문]   Improving temperature uniformity and performance of CO preferential oxidation for hydrogen-rich reformate with a heat pipe   SCI SCIE

    Wong, S.C. , Hsiao, H.C. , Lo, K.F.
    International journal of hydrogen energy v.39 no.12 ,pp. 6492 - 6496 , 2014 , 0360-3199 ,

    초록

    Preferential oxidation (PROX) is an effective, but highly temperature-sensitive, method of CO removal for hydrogen-rich reformates. In a packed-bed catalytic reactor, oxidation is strongest at the inlet side and the local catalyst pellets become over-heated with poor heat conduction. As a result, the enhanced parasitic H 2 oxidation consumes oxygen and suppresses CO conversion. This study applies a heat pipe to improve the temperature uniformity in a tubular one-stage packed-bed reactor by transporting heat downstream and thereby improve CO removal. In the experiments, the fuel mixture containing 2% of CO, 75% of H 2 , and 23% of CO 2 , further mixed with air at O 2 /CO = 0.75, 1.0 or 1.25, is supplied with stepwise increase of feeding rate under a fixed environmental temperature of 99 +/- 1 o C. The proposed simple method is found to significantly improve temperature uniformity and CO removal for the present test conditions with O 2 /CO = 1.0 and 1.25.

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  4. [해외논문]   A small scale H2NG production plant in Italy: Techno-economic feasibility analysis and costs associated with carbon avoidance   SCI SCIE

    de Santoli, L. , Lo Basso, G. , Bruschi, D.
    International journal of hydrogen energy v.39 no.12 ,pp. 6497 - 6517 , 2014 , 0360-3199 ,

    초록

    Energy conversion from hydrogen represents a viable contribution to sustainable development. For this reason several authors have investigated clean hydrogen production and its end uses. One end use is a hydrogen storage system with a fuel cell to mitigate grid instabilities inherent to renewable power generation or intermittent reactive loads. Another end use is burning hydrogen in internal combustion engines for motive transport or remote power generation. Blending hydrogen with traditional hydrocarbon fuels is also possible. The aim of this paper is to assess the opportunity for realizing a small-scale renewable hydro methane production system in Italy. The system is completely integrated in an electrical and thermal smart grid. For this reason, a techno-economic feasibility analysis on hybrid systems was carried out to quantify the carbon avoidance cost associated with blended hydrogen fuels. Twelve different scenarios were simulated with the HOMER software and the optimal system configuration was identified by applying the levelized cost of hydrogen (LCOH) as evaluation criterion. Furthermore, a sensitivity analysis was applied to explore potential fiscal policy scenarios. The simulation results show that the lowest LCOH (8.041 @?/kg) was achieved with a 5 Nm 3 electrolyser capability (operating for about 4000 h/yr) and a grid connected 160 kW p PV array when hydrogen was produced only during the winter season. Instead considering the same operating hours and modifying the hydrogen production daily and monthly profile (i.e. hydrogen production from May to September) the best results were obtained (LCOH = 0 @?/kg). An analysis of carbon avoidance costs showed the optimal hydrogen mixture of approximately 23% by volume to provide the best economic and environmental trade-off. Finally, if the hydrogen cost is equal to 1.5587 @?/kg a null over price for decarbonisation is achievable. To obtain this result a dedicated incentive scheme to encourage the hydrogen production should be developed by Italian Government.

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  5. [해외논문]   High-pressure release and dispersion of hydrogen in a partially enclosed compartment: Effect of natural and forced ventilation   SCI SCIE

    Prasad, K.
    International journal of hydrogen energy v.39 no.12 ,pp. 6518 - 6532 , 2014 , 0360-3199 ,

    초록

    The study of compressed hydrogen releases from high-pressure storage systems has practical application for hydrogen and fuel cell technologies. Such releases may occur either due to accidental damage to a storage tank, connecting piping, or due to failure of a pressure release device (PRD). Understanding hydrogen behavior during and after the unintended release from a high-pressure storage device is important for development of appropriate hydrogen safety codes and standards and for the evaluation of risk mitigation requirements and technologies. In this paper, the natural and forced mixing and dispersion of hydrogen released from a high-pressure tank into a partially enclosed compartment is investigated using analytical models. Simple models are developed to estimate the volumetric flow rate through a choked nozzle of a high-pressure tank. The hydrogen released in the compartment is vented through buoyancy induced flow or through forced ventilation. The model is useful in understanding the important physical processes involved during the release and dispersion of hydrogen from a high-pressure tank into a compartment with vents at multiple levels. Parametric studies are presented to identify the relative importance of various parameters such as diameter of the release port and air changes per hour (ACH) characteristic of the enclosure. Compartment overpressure as a function of the size of the release port is predicted. Conditions that can lead to major damage of the compartment due to overpressure are identified. Results of the analytical model indicate that the fastest way to reduce flammable levels of hydrogen concentration in a compartment is by blowing through the vents. Model predictions for forced ventilation are presented which show that it is feasible to effectively and rapidly reduce the flammable concentration of hydrogen in the compartment following the release of hydrogen from a high-pressure tank.

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  6. [해외논문]   Para-H2 to ortho-H2 conversion in a full-scale automotive cryogenic pressurized hydrogen storage up to 345 bar   SCI SCIE

    Petitpas, G. , Aceves, S.M. , Matthews, M.J. , Smith, J.R.
    International journal of hydrogen energy v.39 no.12 ,pp. 6533 - 6547 , 2014 , 0360-3199 ,

    초록

    Hydrogen vehicles offer the potential to improve energy independence and lower emissions but suffer from reduced driving range. Cryogenic pressure vessel storage (also known as cryo-compressed storage) offers the advantage of higher densities than room temperature compressed although it has the disadvantage of cryogenic operating temperatures which results in boil-off when the temperature of the gas increases. In order to understand and optimize the time prior to boil-off, we have examined heat absorption from the transition between the two quantum states of the hydrogen molecule (para-ortho) in a full-scale (151 L internal volume) automotive cryogenic pressure vessel at pressures and temperatures up to 345 bar and 300 K, and densities between 14 and 67 g/L (2.1-10.1 kg H 2 ). The relative concentration of the two species was measured using rotational Raman scattering and verified by calorimetry. In fifteen experiments spanning a full year, we repeatedly filled the vessel with saturated LH 2 at near ambient pressure (2-3 bar), very low temperatures (20.3-25 K), varying densities, and very high para-H 2 fraction (99.7%). We subsequently monitored vessel pressure and temperature while performing periodic ortho-H 2 concentration measurements with rotational Raman scattering as the vessel warmed up and pressurized due to environmental heat entry. Experiments show that para-ortho H 2 conversion typically becomes active after 10-15 days of dormancy (''initiation'' stage), when H 2 temperature reaches 70-80 K. Para-ortho H 2 conversion then approaches completion (equilibrium) in 25-30 days, when the vessel reaches 100-120 K at ~50 g/L density. Warmer temperatures are necessary for conversion at lower densities, but the number of days remains unchanged. Vessel dormancy (time that the vessel can absorb heat from the environment before having to vent fuel to avoid exceeding vessel rating) increased between 3 and 7 days depending on hydrogen density, therefore indicating a potentially large benefit for reduced fuel venting in cryogenic pressurized hydrogen storage.

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  7. [해외논문]   Simulation study on the outlet flow dynamics of a hydride-based hydrogen storage canister for medical use   SCI SCIE

    Yang, F. , Zhang, Z. , Gao, D. , Wang, Y. , Chen, X.
    International journal of hydrogen energy v.39 no.12 ,pp. 6548 - 6557 , 2014 , 0360-3199 ,

    초록

    In recent years, hydrogen molecule as therapeutic antioxidant was found to be useful for the treatment of a number of diseases. To supply hydrogen safely and reliably in the hospital, a patent-pending system was proposed by the authors, including a canister filled with metal hydride, a gas mixing chamber and some other components. The outlet flow of the canister must be controlled within certain accuracy to assure the medical effect of the hydrogen intake, thus was investigated in this work. The mathematical model of hydrogen release process, which couples porous flow, heat and mass transfer was solved using a commercial software package COMSOL Multiphysics 3.5a. The outlet flow dynamics are tested in the cases of convective heating and electrical heating, and great differences are found. For the case of electrical heating that provides constant heat flux, the mass flow rate of H 2 showed little temporal variation after the initial transient. Moreover, under certain conditions a PI control strategy was successfully applied to regulate the valve openness for keeping a constant flow rate of H 2 .

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  8. [해외논문]   Theoretical study of hydrogen adsorption on nitrogen doped graphene decorated with palladium clusters   SCI SCIE

    Rangel, E. , Sansores, E.
    International journal of hydrogen energy v.39 no.12 ,pp. 6558 - 6566 , 2014 , 0360-3199 ,

    초록

    Density functional theory was used to study the adsorption of hydrogen on small palladium clusters (Pd n , n = 1-4) supported on pyridine-like nitrogen doped graphene. Charge transfer and strong binding (up to four times higher than binding energy of Pd cluster supported on graphene) between graphene-nitrogen and palladium clusters prevent detachment of clusters and leads to three types of adsorption states of hydrogen. The first type is a molecular hydrogen physisorbed, the second one is an activated state of H 2 without adsorption barriers where H-H bond is relaxed and the third type is dissociated state. In dissociated cases, we found barriers below 0.56 eV. This means the process might occur spontaneously at room temperature. We also show that metal-N-vacancy complexes are very stable and involve nitrogen sp 2 and p z , carbon p z and palladium d orbitals. Besides, these systems exhibit an interesting magnetic behavior.

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  9. [해외논문]   Kinetic modeling of self-hydrolysis of aqueous NaBH4 solutions by model-based isoconversional method   SCI SCIE

    Retnamma, R. , Novais, A.Q. , Rangel, C.M. , Yu, L. , Matthews, M.A.
    International journal of hydrogen energy v.39 no.12 ,pp. 6567 - 6576 , 2014 , 0360-3199 ,

    초록

    The present work reports the kinetic modeling of self-hydrolysis of non-buffered, non-stabilized NaBH 4 solutions by model-based isoconversional method. The overall kinetics is described by a 'reaction-order' model in a practical operating window of 10-20 wt% NaBH 4 solutions at 25-80 o C and 0-50% conversions. The apparent activation energy and pre-exponential factor are interrelated through a kinetic compensation effect (KCE). The apparent reaction order remains constant at a given temperature irrespective of extent of conversion and decreases with increase in temperature. It decreases from first-order to 0.26 with increase in temperature from 25 to 80 o C. The apparent activation energy is found to increase from 65 +/- 11 to 162 +/- 2 kJ mol -1 with increase in extent of conversion from 0 to 50%. The variation of parameters with extent of conversion is discussed based on changes in solution properties during the progress of hydrolysis reaction.

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  10. [해외논문]   Improved de/hydrogenation properties and favorable reaction mechanism of CeH2 + KH co-doped sodium aluminum hydride   SCI SCIE

    Xiao, X. , Wang, S. , Fan, X. , Xu, C. , Sun, J. , Wang, Q. , Chen, L.
    International journal of hydrogen energy v.39 no.12 ,pp. 6577 - 6587 , 2014 , 0360-3199 ,

    초록

    Sodium aluminum hydride (NaAlH 4 ) was directly synthesized by ball milling NaH/Al co-doped with CeCl 3 + KH under a hydrogen pressure of 3 MPa at room temperature. Out of various samples corresponding to xNaH/Al + 0.02CeCl 3 + yKH (x + y = 1; y = 0, 0.02, 0.04 mol%) composites, the composite with y = 0.02 exhibits the optimum de/hydrogenation properties. It shows that the addition of KH can effectively improve the dehydrogenation properties of second step reaction of NaAIH 4 system. The composite with y = 0.02 starts to release hydrogen from 87 o C and completes dehydrogenation within 20 min at 170 o C, with good cycling de/hydrogenation kinetics at relatively lower temperature (100-140 o C). After ball milling, the CeCl 3 precursor can be changed into CeH 2 catalytic active component in the first several de/hydrogenation cycles. Apparent activation energy of the second decomposition step of NaAIH 4 system can be effectively decreased by addition of KH, resulting in the decrease of desorption temperatures. Based on the microstructure analyses combined with hydrogen storage performances, the improved dehydrogenation properties of sodium aluminum hydride system are ascribed to the lattice volume expansion of Na 3 AlH 6 during the dehydrogenation process resulted from the addition of KH. Moreover, by analyzing the reaction kinetics of CeCl 3 + KH co-doped sample, both of the decomposition steps of composite with y = 0.02 were conformed to the two-dimension phase-boundary growth mechanism. The mechanistic investigations gained here could help to understand the de/rehydrogenation behaviors of catalyzed complex metal hydride systems.

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