Effect of catalytic washcoat shape and properties on mass transfer characteristics of microstructured steam-methanol reformers for hydrogen production

Many attempts have been made to improve mass transfer by reducing the size of reactors. However, such reduction will fairly quickly reach practical limitations and numerous difficulties still remain. Catalytic washcoat shape and properties may be critical design factors, but the mechanisms for their effects on mass transfer characteristics are still not fully understood. To effectively eliminate problems associated with mass transport phenomena in microstructured steam-methanol reformers, the effects of washcoat shape and properties were investigated in various situations by performing computational fluid dynamics simulations. The dependence of the solution on mass transfer characteristics was reduced to a small number of dimensionless parameters. A dimensionless mass transfer analysis was carried out in terms of the Sherwood, Schmidt, and pore Reynolds numbers. The results indicated that the rate of mass transfer is predominantly controlled by washcoat properties, and porosity and effective thermal conductivity are fundamentally important. The rate of the reforming reaction is typically controlled by kinetics at a temperature of 480 K and limited by mass transfer at a temperature of 580 K. The shape of washcoats affects the overall mass transfer characteristics, depending on the structural and thermal properties of washcoats. The shape effect is limited by heat transfer. A three-fold increase in effectiveness factor can be achieved by increasing the effective thermal conductivity of the washcoat. Design recommendations were finally made to improve transport characteristics for the systems.     

Generation-IV reactors and nuclear hydrogen production

There are dozens of hydrogen production methods and techniques from many sources such as fossil fuels, renewable energy sources and nuclear energy in the literature. Thermo-chemical methods are more efficient at higher temperatures to produce large quantities of hydrogen. In this study, a comparative overview of Generation VI nuclear reactor types for major hydrogen production methods have been researched in the literature and suggestions have been carried out.This research work is addressing that both electric power cycle and hydrogen production based on nuclear technologies need to be developed. Generation IV nuclear reactors can provide hydrogen for a worldwide hydrogen economy. Both thermo-chemical and electrolysis (hybrid) processes in hydrogen production have a promising future, especially when integrated with Generation IV nuclear power plants. Efficient heat transfer is required for both high temperature thermodynamic cycles and the high temperature steam electrolysis. Hence, highly efficient heat exchanger designs are one of the key technologies for that purpose.     

A review on hydrogen generation,explosion, and mitigation during severe accidents in light water nuclear reactors

Progress of severe accident (SA) can be divided into core degradation and post core meltdown. An important phenomena during severe accidents is the hydrogen generation from exothermal reaction between oxidation of core components, and molten core concrete interaction (MCCI). During the severe accidents, a large amounts of hydrogen is produced, deflagrated and consequently the containment integrity is violated. Therefore, the main objectives of this study is to highlight the source of hydrogen production during SA. First, a thorough literature review and main sources of hydrogen production, hydrogen reduction systems are introduced and discussed. Based on the available results, the amount of produced hydrogen in a typical pressurized water reactor (PWR) and a boiling water reactor (BWR) are estimated to be 1000 and 4000 kg, respectively during in-vessel phase. The average rate of hydrogen production is about 1 kg/s during reflooding of a degraded core. Also, about 2000 kg hydrogen is produced during MCCI for a PWR. The lower and upper range of hydrogen required to initiate combustion is 4.1 and 74 vol percent, respectively. In this paper a review is provided of what has been done in the literature with regard to hydrogen generation in severe accidents of nuclear power plants. In addition, the review identifies the literature gaps and underlines the need of developing a systematic hydrogen management strategy. A hydrogen management strategy is proposed in order to maintain the containment integrity against the probable combustion or hydrogen explosion loads.     

From sustainability to sustainizability

Following the recent introduction of the Sustainability over Sets (SOS) concept as a sustainability analysis tool with broad flexibility in incorporating human input, in this work, the concepts of Sustainizability (SIZ) and Sustainizability over Sets (SIZOS) are introduced, as novel frameworks for sustainable system synthesis. Springing off the conceptual foundation of sustainability, SIZ (and SIZOS) refers to the existence of allowable external actions, and/or design changes that can render sustainable (sustainable over a set) an unsustainable (unsustainable over a set) system. Utilizing earlier mathematical results for SOS, rigorous necessary and sufficient conditions for SIZOS are presented. Two case studies, on a two-dimensional biological waste treatment system, and a three-dimensional food chain system, are then presented to illustrate the developed necessary and sufficient conditions for SIZOS.     

Fixed‐Bed Heat Storage – Mathematical Modeling Approaches

While renewable heat makes up only 13 % of overall German heat consumption, the share of renewable electricity produced from wind, solar, water, and geothermal power already reached 36 % of overall electricity consumption in 2017. One measure to support the integration of renewable heat in the German energy system is the use of heat storage systems. Although water‐based heat storage systems for temperatures up to 100 °C are state of the art, systems for temperatures up to several hundred degrees Celsius are still under investigation or in the demonstration phase. Therefore, this work focuses on the development of a simulation model for analyzing and engineering fixed‐bed thermal storage systems that are filled with an inert bulk material such as stone fragments.     

Monolithic Ag-Mt dispersed Z-scheme pCN-TiO2 heterojunction for dynamic photocatalytic H2 evolution using liquid and gas phase photoreactors

Fabricating montmorillonite (Mt) dispersed Ag/pCN-TiO₂ heterojunction for stimulating photocatalytic H₂ evolution using two/three phases photo-reactor systems has been investigated. Using Ag–Mt/pCN–TiO₂ composite in three-phase, H₂ rate of 667 μmolh⁻¹ was obtained, much greater than TiO₂-based samples due to superior charges separation with Ag SPR and Mt mediated effect. Among parameters, 0.15 g catalyst loading at pH 7 gives highest H₂ yield with glycerol sacrificial reagents. More interestingly, liquid system with glycerol gave best H₂ rate while gas-phase with methanol encouraged H₂ productivity. Furthermore, H₂ rate increased to 8230 μmolh⁻¹ using two-phase monolith reactor, 9.01 and 12.34 times greater than two-phase fixed-bed and three-phase slurry systems. Comparatively, highest AQY and SY of 39.85% and 54.86 μmolh⁻¹cm⁻³ were obtained using monolith. This superior efficiency was due to efficient photon-flux consumption, effective mass-transfer and large light-fluxed. These findings would be fruitful for further development for clean hydrogen production through photocatalytic water splitting.     

Inline Spectroscopy-Based Optimization of Chemical Reactions Considering Dynamic Process Conditions

The demand for sustainable energy sources, like biomass, solar energy, hydro and wind power, is connected to challenges like energy storage and fluctuating energy supply. Regarding the second challenge, industry has to evolve their existing processes from steady state processes to dynamic ones. This work is concerned with the conception of an inline spectroscopy-based optimization routine for chemical reactions under dynamic process conditions, which implements the search for a well applicable optimization algorithm. The studied reaction to reach this goal is a nitroaldol condensation.     

Study on estimating electric potential in space between parallel electrodes

We have been studying on estimating distribution of permittivity between measurement electrodes using capacitance and electric potential. Two arc electrodes were separated by long distance and there electrodes were surrounded by additional electrodes respectively. In past research work, we carried out numerical electric analysis for calculating the capacitance and electric potential using Finite Element Method (FEM) and compared with experimental and numerical results. The capacitance values were almost agreed with experimental and numerical results. However, the electric potential values were different between experimental and numerical results in conventional studies. In this paper, we proposed an equivalent circuit including the stray capacity and measurement method for capacitance, the electric potential in space between long distance electrodes was estimated.