Dynamic study of a new design of a tanks based on metallic hydrides

It is known that the hydrogen has a very high mass energy density, in fact, that it is a lightest gas; therefore, its storage is a great problem. The aim of the hydrogen storage technologies is thus to reduce the volume that hydrogen occupies in its thermodynamically stable state under conditions close to ambient salt. Recent work on hydrogen storage is mainly based on the use of metal hydrides. These metal hydrides have a high capacity for the hydrogen storage in the operating conditions. The effecting parameters on the performance of such a metal-hydrogen reactor are its design and configuration. In this case, there are a number of problems that need to be considered in designing a reactor. Among these parameters are the reactor configuration, the thermal and the mechanical strength, the kinetics of hydrogen storage and the security. Our study is concentrated on the problem of the thermal and the mechanical strength while focusing on the nature of the metal makes the reactor. In this work, the experimental studies of the hydrogen absorption phenomenon in different reactors, based on metal hydrides, were evaluated. The characteristics of the reaction kinetics in three different reactors using the same measurement conditions were compared. A numerical model describing the reaction kinetic of the H₂ absorption by LaNi₅ alloy validates the results were obtained. Of these results, it is found that the rate constant varies from one reactor to another. Moreover, the activation energy of the absorption kinetics were identified.     

Ecotaxes and their impact in the cost of steam and electric energy generated by a steam turbine system

Ecotaxes allow the internalization of costs that are considered externalities associated with polluting industrial process emissions to the atmosphere. In this paper, ecotaxes internalize polluting emissions negative impacts that are added to electricity and steam generated costs of a steam turbine and heat recovery systems from a utilities refinery plant. Steam costs were calculated by means of an exergy analysis tool and Aspen Plus simulation models. Ecotaxes were calculated for specific substances emitted in the refinery flue gases, based on a toxicity and pollution scale. Ecotaxes were generated from a model that includes damages produced to biotic and abiotic resources and considers the relative position of those substances in a toxicity and pollution scale. These ecotaxes were internalized by an exergoeconomic analysis resulting in an increase in the cost per kWh produced. This kind of ecotax is not applied in Mexico. The values of ecotaxes used in the cost determination are referred to the values currently applied by some European countries to nitrogen oxides emissions.     

Ab-initio calculations of the elastic and finite-temperature thermodynamic properties of niobium- and magnesium hydrides

Density Functional Theory (DFT) calculations have been used for calculating the elastic and thermodynamic properties of Mg, Nb, and their hydrides. The study is motivated by a previous work that showed constraints arising from Mg/Nb layer interfaces de-stabilized the magnesium hydride and resulted in decomposition temperatures much lower than in the bulk state. The calculated mechanical properties and the difference in the volume expansion of Mg- and Nb-hydrides support the ideas of large, de-stabilizing mechanical stresses arising from significant volume expansion incompatibilities in Mg/Nb multilayers. The stress and corresponding formation of metastable phases result in significant destabilization of MgH₂ and provide ultra-low hydrogen desorption temperature in Mg/Nb multilayers.     

Economic analysis of hydrogen production through a bio-ethanol steam reforming process: Sensitivity analyses and cost estimations

In this study, the hydrogen selling price from ethanol steam reforming has been estimated for two different production scenarios in the United States, i.e. central production (150,000 kg H₂/day) and distributed (forecourt) production (1500 kg H₂/day), based on a process flowchart generated by Aspen Plus^® including downstream purification steps and economic analysis model template published by the U.S Department of Energy (DOE) [1]. The effect of several processing parameters as well as catalyst properties on the hydrogen selling price has been evaluated. $2.69/kg is estimated as the selling price for a central production process of 150,000 kg H₂/day and $4.27/kg for a distributed hydrogen production process at a scale of 1500 kg H₂/day. Among the parameters investigated through sensitivity analyses, ethanol feedstock cost, catalyst cost, and catalytic performance are found to play a significant role on determining the final hydrogen selling price.     

Reducing the hydrogen production cost by operating alkaline electrolysis as a discontinuous process in the French market context

The possible reduction of the hydrogen production cost when operating alkaline electrolysers in a discontinuous way, in order to benefit from low electricity prices, is investigated. Beside the insights about the electricity market (prices do not correlate the demand; they are related to the supply-and-demand hardness), advances in modelling discontinuous operation are proposed. An optimum production cost is found that induces a profit of 4%, with regard to a plant that would work continuously. Specific attention should be given to related overcosts: additional degradation due to frequent transitions from the minimum electrolyser load to the nominal one, higher maintenance needs, and hydrogen storage costs. Such an operating mode would also greatly benefit from a reduction of the electrolyser prices. However, the state-of-the-art as regards the electrolyser minimum loads and transition time appears satisfactory.     

Hydrogen production through renewable and non-renewable energy processes and their impact on climate change

The urbanization and increase in the human population has significantly influenced the global energy demands. The utilization of non-renewable fossil fuel-based energy infrastructure involves air pollution, global warming due to CO₂ emissions, greenhouse gas emissions, acid rains, diminishing energy resources, and environmental degradation leading to climate change due to global warming. These factors demand the exploration of alternative energy sources based on renewable sources. Hydrogen, an efficient energy carrier, has emerged as an alternative fuel to meet energy demands and green hydrogen production with zero carbon emission has gained scientific attraction in recent years. This review is focused on the production of hydrogen from renewable sources such as biomass, solar, wind, geothermal, and algae and conventional non-renewable sources including natural gas, coal, nuclear and thermochemical processes. Moreover, the cost analysis for hydrogen production from each source of energy is discussed. Finally, the impact of these hydrogen production processes on the environment and their implications are summarized.     

The future cost of uranium enrichment: Technology and economics

The cost of uranium enrichment is the most important factor determining the fuel cost of nuclear energy. This paper attempts to forecast the future direction of the price of separative work by examining the forces that determine it. It is argued that the interplay among the characteristics of enrichment technologies, the structure of the international market, and the balance of supply and demand determine the enrichment price. The analysis indicates that all forces point towards a price much lower than the current one. It is predicted that, depending on the technological advances, the price of separative work unit for uranium enrichment will range between $40 and $90 by the year 2000.     

Numerical simulation and innovation on magnesium reduction process

The thermal process of L.M.Pidgeon's reduction art,widely used in magnesium production,is numericallysimulated.It is shown that the thermal efficiency will be highly enhanced with the increase of heat-exchange areaor the intensification of heat exchange between flame and the outer surface of the reduction jars.An innovationhas been made by fuel-shifting(from coal to Coal-Water Mixture),up-draft reduction furnace configuration,multi-layer jars installation and waste heat recovery.A bench scale furnace has been constructed and put intooperation to identify the simulation and new design.     

Integrating safety and economics in designing a steam methane reforming process

The recent explosion at a steam reforming facility producing hydrogen in California, U.S., suggests the need to revisit the design of the traditional steam methane reforming (SMR) process from a safety perspective to further enable the growth of the hydrogen economy. Specifically, it is important to analyze the interaction between process, economic and safety variables within the SMR process through an integrated model approach to maintain positive economics of hydrogen production while making the process safer. The integrated model described within this study consists of process synthesis, quantitative risk assessment and economic analysis sub-models facilitating a holistic design for the SMR process. The usefulness of the integrated model is demonstrated by evaluating alternatives based on the inherently safer design philosophy. For the considered base design, it was found that decreasing the pressure of purge gas exiting the purge gas compressor leads to a reduction in the jet-fire axial risk distance of purge gas with minor economic benefits. Also, increasing the temperature of syngas entering the condensation unit leads to a reduction in the jet-fire axial risk distance for both purge gas and syngas with slight decrease in process economics.     

Projected economic and environmental impact of hydrogen: The case for Ontario

The Summary Report of the Ontario Hydrogen Energy Task Force, which was issued in September 1981, identifies the market potential for electrolytic hydrogen in Ontario by the year 2000 as approximately 257 PJ y⁻¹ of which it suggests a penetration of 45 PJ y⁻¹ as a realistically attainable target.

This report examines the gross economic and environmental impact that would result from this target penetration. It also creates a scenario for that portion of the penetration attributable to the growth of hydrogen leverage technologies, and quantifies the direct economic and employment activity in new manufacturing industries based on these hydrogen leverage technologies.     

Comparative study of the formation-decomposition mechanisms and kinetics in LaNi5 and magnesium reversible hydrides

Comparison of kinetics and formation decomposition mechanisms between Mg and LaNi₅ hydrides is carried out as a function of the number of cycles.Kinetic studies are performed, as a function of pressure and temperature domains either by high sensitivity thermogravimetry or by differential manometry. Mechanisms are confirmed by microscopic observations. Differences in mechanical properties and temperature-pressure domains and the absence of an insertion solid-solution of H₂ in Mg give quite different mechanisms:For LaNi₅, the β-hydride results from a precipitation of the new phase in the whole sample volume, the reaction speed is probably controlled by the stress-density.For Mg, MgH₂ formation appears by superficial nucleation and growth of a gas-proof hydride without fragmentation of the sample.     

Thermodynamic analysis of a new process for hydrogen and electric power production by using carbonaceous fuels and high-temperature process heat

A new process for the simultaneous production of hydrogen and electrical power by using carbonaceous fuels and high-temperature process heat is presented in this paper. In an electrolytic cell, sulfur dioxide dissolved in an aqueous solution of sulfuric acid is electrochemically oxidized to sulfuric acid at the anode, while hydrogen gas is evolved at the cathode. The sulfuric acid produced in the cell provides the oxygen for the fuel combustion which subsequently takes place at high pressure. The combustion gas consisting mainly of CO₂, SO₂ and H₂O expands in a turbine in order to produce electrical power. After the expansion, the components sulfur dioxide and water are separated from the combustion gas and fed together with added water into the electrolysis cell.The process shows some advantages compared with already existing or proposed processes for the production of hydrogen or electric power. The influence of the sulfuric acid concentration and some other important process parameters on the energetic and exergetic efficiency of the total process is shown. The results shown in this paper have been obtained by using carbon (as a substitute for coal which is the preferred fuel) and a nuclear heat production plant (as an example of providing the required high-temperature process heat).     

Hydrolysis of Mg-based alloys and their hydrides for efficient hydrogen generation

The hydrolysis of Mg-based alloys and their hydrides with high abundance on the earth and low cost could produce hydrogen with high theoretical capacity and the formation of by-products that have no pollution to the environment. Hence, it has been regarded as one of the most promising way for hydrogen generation. Particularly, a gravimetric capacity of 6.4 wt% and 3.4 wt% H₂ could be produced from the hydrolysis of pure Mg and MgH₂, respectively, even when stoichiometric water is included for calculation. The formation of passive magnesium hydroxides with dense structure, however, could immediately interrupt the hydrolysis reaction of Mg/MgH₂, which leads to ultralow yield and sluggish hydrogen generation rate. Recent studies have demonstrated that the hydrolysis reaction of Mg/MgH₂ could be effectively enhanced in terms of both yield and kinetics by the formation of Mg-based alloys and their hydrides. This review aims to summarize the recent progress in the hydrolysis of Mg-based alloys and their hydrides and the involved hydrolysis mechanisms.     

New process for high temperature polybenzimidazole membrane production and its impact on the membrane and the membrane electrode assembly

Water addition is a key step in the new process developed at BASF Fuel Cell Inc. (BFC) for polybenzimidazole (PBI) membrane production. The added water prevents further polymerization and controls the solution viscosity for easier membrane casting. For large-scale PBI membrane production, a certain amount of tension is necessary during membrane upwinding. The applied tension could affect the polymer orientation and result in anisotropic membrane mechanical properties and proton conductivity. The membrane prepared with tension shows higher elastic modulus and proton conductivity in machine direction, which might suggest some degree of polymer chain orientation. However, the membrane electrode assembly (MEA) performance is not affected by the membrane's apparent anisotropic character. However, we observed performance variation as a function of MEA break-in condition, which might be explained by the formation of a phosphate anion concentration gradient during MEA operation.     

Monitoring and control of a hydrogen production and storage system consisting of water electrolysis and metal hydrides

Renewable energy sources such as wind turbines and solar photovoltaic are energy sources that cannot generate continuous electric power. The seasonal storage of solar or wind energy in the form of hydrogen can provide the basis for a completely renewable energy system. In this way, water electrolysis is a convenient method for converting electrical energy into a chemical form. The power required for hydrogen generation can be supplied through a photovoltaic array. Hydrogen can be stored as metal hydrides and can be converted back into electricity using a fuel cell. The elements of these systems, i.e. the photovoltaic array, electrolyzer, fuel cell and hydrogen storage system in the form of metal hydrides, need a control and monitoring system for optimal operation. This work has been performed within a Research and Development contract on Hydrogen Production granted by Solar Iniciativas Tecnológicas, S.L. (SITEC), to the Politechnic University of Valencia and to the AIJU, and deals with the development of a system to control and monitor the operation parameters of an electrolyzer and a metal hydride storage system that allow to get a continuous production of hydrogen.     

Use of scrap tires in cement production and their impact on nitrogen and sulfur oxides emissions

Cement production is characterized by extremely high energy consumption per unit of product. Energy costs and environmental standards encouraged cement manufacturers worldwide to evaluate to what extent conventional fuels can be replaced by alternative fuels, i.e., processed waste materials, such as scrap tires. The decisive factors promoting the use of cement kilns for the utilization of scrap tires are: the high incineration temperature, the large area of the furnace, the significant length of the kiln, the long period of time the fuel stays inside the kiln, and the alkaline environment inside the kiln. The use of scrap tires in cement kilns is one of the best technologies for a complete and safe destruction of these wastes, due to the fact that there is a simultaneous benefit of destroying wastes and getting the energy. Thus, the use of scrap tires as alternative fuel in cement kilns has energy and economic justifiability, and it is environmentally friendly. In this article, monitoring results of nitrogen and sulfur oxides emissions from cement kilns in a cement factory in Serbia are given, depending on the ratio of scrap tires in total fuel quantity. Research was carried out for 0 to 15% share of scrap tires in total heat production. Nitrogen and sulfur oxides emission measurements from cement kilns were done during a trial use of scrap tires as a secondary fuel in a cement factory. During nitrogen and sulfur oxides emissions monitoring from the cement kiln, coal and petroleum coke were used as primary fuel, and whole or shredded tires were used as secondary fuel. Experimental results have shown the encouraging results: in particular, clinker characteristics were unmodified, and stack emissions of NOx and SO₂ were, in the case of tires, slightly decreased, in some cases were incremented, but remaining always below the law imposed limits.     

A study of the economics of alcohol-gasoline blend production

We show how to determine the value of methanol and ethanol as gasoline additives in the liquid-fuel market, where the alcohol-gasoline blends compete with unleaded clear gasolines. It is found that the clear gasolines are cheaper to produce than the alcohol blends of equivalent octane under the same refinery constraints. The results are based on the use of a combined model of the oil-refining and transportation sectors with optimised refinery operation and transport fleet. In the context of the national lead phaseout program, optimisation provided a viable route to producing the unleaded gasoline without recourse to alcohol-blending, while investment in heavy-end processing and isomerisation capacity increases the economic advantage of this route.     

Facile process to utilize carbonaceous waste as a carbon source for the synthesis of low cost electrocatalyst for hydrogen production

Low cost non-noble metal electrocatalysts are highly desirable for the sustainable production of hydrogen as a renewable energy source. Molybdenum carbide (Mo₂C) has been considered as the promising non-noble metal electrocatalyst for the hydrogen production via hydrogen evolution reaction (HER) through water splitting. The nanostructured nitrogen (N) incorporated carbon (C) coupled with Mo₂C is the potential candidate to boost the HER activity and electrode material for the energy conversion applications. In this work, nitrogen incorporated carbon coated Mo₂C (Mo₂C@C/N) has been synthesized in an eco-friendly way using waste plastic as the carbon source. The pure phase Mo₂C@C/N has been synthesized at 700 and 800 °C for 10 h. The relatively higher temperature synthesized phase shows enhanced HER activity with lower Tafel slope (72.9 mVdec⁻¹) and overpotential of 186.6 mV to drive current density of 10 mAcm⁻². It also exhibits stability up to 2000 cyclic voltammetry (CV) cycles and retains the current density with negligible loss for 10 h. The higher temperature synthesized phase exhibits higher electrochemical active surface area (ECSA) and enhanced HER kinetics.     

The impact of carbon sequestration on the production cost of electricity and hydrogen from coal and natural-gas technologies in Europe in the medium term

Carbon sequestration is a distinct technological option with a potential for controlling carbon emissions; it complements other measures, such as improvements in energy efficiency and utilization of renewable energy sources. The deployment of carbon sequestration technologies in electricity generation and hydrogen production will increase the production costs of these energy carriers. Our economic assessment has shown that the introduction of carbon sequestration technologies in Europe in 2020, will result in an increase in the production cost of electricity by coal and natural gas technologies of 30–55% depending on the electricity-generation technology used; gas turbines will remain the most competitive option for generating electricity; and integrated gasification combined cycle technology will become competitive. When carbon sequestration is coupled with natural-gas steam reforming or coal gasification for hydrogen production, the production cost of hydrogen will increase by 14–16%. Furthermore, natural-gas steam reforming with carbon sequestration is far more economically competitive than coal gasification.