Electricity,hydrogen—competitors,partners?

Electricity, hydrogen—What they have in common, where they are unique.Electricity and hydrogen have in common that they are secondary energies which can be generated from any primary energy (raw materials). Once generated they are environmentally and climatically clean along the entire length of their respective energy conversion chains. Both electricity and hydrogen are grid delivered (with exceptions); they are interchangeable via electrolysis and fuel cell. Both are operational worldwide, although in absolutely dissimilar capacities. And their peculiarities? Electricity stores and transports information, hydrogen does not. Hydrogen stores and transports energy, electricity transports energy but does not store it (in large quantities). For long (i.e., continental) transport routes, hydrogen has advantages. The electricity sector is part of the established energy economy. Hydrogen, on the other hand, takes two pathways: one where it has been in use materially in the hydrogen economy almost since its discovery in the later 18th century; today, it is traded worldwide as a commodity up to an amount of some 50 million tonnes p.a., e.g., in methanol or ammonia syntheses, for fat hardening in the food industry, as a cleansing agent in glass or electronics manufacturing, and the like. And along the other pathway it serves as an energy carrier in the up coming hydrogen energy economy which started with the advent of the space launching business after WW II. Essentially, the hydrogen energy economy deals with the introduction of the, after electricity, now second major secondary energy carrier, hydrogen, together with its conversion technologies, e.g., fuel cells, into portable electronic equipment such as television cameras, laptops, cellular phones, etc., into the distributed stationary electricity and heat supply in the capacity range of kilowatts to megawatts, and into transport vehicles on earth, at sea, in the air, or space-borne. It is never a question of the energy carrier alone, be it either hydrogen or hydrogen reformat. On the contrary, environmentally and climatically clean hydrogen energy technologies along the entire length of the energy conversion chain, from production via storage, transport and distribution to, finally, end use, are what is of overarching importance. Of course, technologies are not energies, but they are as good as energies. Efficient energy technologies provide more energy services from less primary energy (raw materials). Energy efficiency gains are energies! Especially for energy poor, but technology-rich countries, efficiency gains compare well to indigenous energy sources! The trend is clearly visible: increasingly, the world is moving from national fuels to global fuels, and energy technologies serve as their opening valves. CO₂ capture and sequestration technologies bring hydrogen-dependent clean fossil fuels to life, and hydrogen supported fuel cell technology activates dormant virtual distributed power. Both technologies are key for the hydrogen energy economy which, thus, becomes the linchpin of future world energy.     

Screening of water-splitting thermochemical cycles potentially attractive for hydrogen production by concentrated solar energy

Hydrogen, a promising and clean energy carrier, could potentially replace the use of fossil fuels in the transportation sector. Currently, no environmentally attractive, large-scale, low-cost and high-efficiency hydrogen production process is available for commercialization. Solar-driven water-splitting thermochemical cycles may constitute one of the ultimate options for CO₂-free production of hydrogen. The method is environmentally friendly since it uses only water and solar energy. First, the potentially attractive thermochemical cycles must be identified based on a set of criteria. To reach this goal, a database that contains 280 referenced cycles was established. Then, the selection and evaluation of the promising cycles was performed in the temperature range of 900–2000 °C, suitable to the use of concentrated solar energy. About 30 cycles selected for further investigations are presented in this paper. The principles and basis for a thermodynamic evaluation of the cycles are also given.     

Synergistic roles of off-peak electrolysis and thermochemical production of hydrogen from nuclear energy in Canada

Hydrogen as a clean energy carrier is frequently identified as a major solution to the environmental problem of greenhouse gases, resulting from worldwide dependence on fossil fuels. However, most of the world's hydrogen (about 96%) is currently produced from fossil fuels, which does not address the issue of greenhouse gases. Although there is a large motivation of the “hydrogen economy”, for improvement of urban air quality, energy security, and integration of intermittent renewable energy sources, CO₂ free energy sources are critical to hydrogen becoming a significant energy carrier. Two technologies, applied in tandem, have a promising potential to generate hydrogen without leading to greenhouse gas emissions: 1) electrolysis and 2) thermochemical decomposition of water. This paper will investigate their unique complementary roles to reduce costs of hydrogen production. Together they have a unique potential to serve both de-centralized hydrogen needs in periods of low-demand electricity, and centralized base-load production from a nuclear station. Thermochemical methods have a significantly higher thermal efficiency, but electrolysis can take advantage of low electricity prices during off-peak hours, as well as intermittent and de-centralized supplies like wind, solar or tidal power. By effectively linking these systems, water-based production of hydrogen can become more competitive against the predominant existing technology, SMR (steam-methane reforming).     

Greenhouse gas reduction benefits and costs of a large-scale transition to hydrogen in the USA

Hydrogen is an energy carrier able to be produced from domestic, zero-carbon sources and consumed by zero-pollution devices. A transition to a hydrogen-based economy could therefore potentially respond to climate, air quality, and energy security concerns. In a hydrogen economy, both mobile and stationary energy needs could be met through the reaction of hydrogen (H₂) with oxygen (O₂). This study applies a full fuel cycle approach to quantify the energy, greenhouse gas emissions (GHGs), and cost implications associated with a large transition to hydrogen in the United States. It explores a national and four metropolitan area transitions in two contrasting policy contexts: a “business-as-usual” (BAU) context with continued reliance on fossil fuels, and a “GHG-constrained” context with policies aimed at reducing greenhouse gas emissions. A transition in either policy context faces serious challenges, foremost among them from the highly inertial investments over the past century or so in technology and infrastructure based on petroleum, natural gas, and coal. A hydrogen transition in the USA could contribute to an effective response to climate change by helping to achieve deep reductions in GHG emissions by mid-century across all sectors of the economy; however, these reductions depend on the use of hydrogen to exploit clean, zero-carbon energy supply options.     

Synthesis of Ni/TiO2 catalyst by sol-gel method for hydrogen production from sodium borohydride

Hydrogen is a sustainable, renewable and clean energy carrier that meets the increasing energy demand. Pure hydrogen is produced by the hydrolysis of sodium borohydride (NaBH₄) using a catalyst. In this study, Ni/TiO₂ catalysts were synthesized by the sol-gel technique and characterized by X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) methods. The effects of Ni loading ratio (20–40%), catalyst amount (75–200 mg), the concentration of sodium hydroxide (NaOH, 0.25–1 M), initial amount of NaBH₄ (75–125 mg) and the reaction temperature (20–60 °C) on hydrogen production performance were examined. The hydrogen yield (100%) and hydrogen production rate (110.87 mL/g_cat.min) were determined at the reaction conditions of 5 mL of 0.25 M NaOH, 100 mg NaBH₄, 100 mg Ni/TiO₂, 60 °C. Reaction order and activation energy were calculated as 0.08 and 25.11 kJ/mol, respectively.     

Feasibility and sustainability analyses of carbon dioxide – hydrogen separation via de-sublimation process in comparison with other processes

Hydrogen (H₂) plays a vital role both as a reactant in petrochemical processes and as an energy carrier and storage medium. When produced from carbon-containing feed stocks, such as fossil fuels and biomass, hydrogen is typically produced as a mixture with carbon dioxide (CO₂), and must be subsequently separated by the associated energy, with an invertible energy penalty. In this study, the process for the removal of carbon dioxide from CO₂ - H₂ mixtures by de-sublimation was analysed. This process is particularly relevant to the production of liquid hydrogen (LH₂) at cryogenic temperatures, for which cooling of the H₂ stream is already necessary. The solid – gas equilibrium of CO₂ - H₂ was studied using the Peng-Robinson equation of state which provided a wide range of operating conditions for process simulation. The de-sublimation process was compared with selected conventional separation processes, including amine-based absorption, pressure swing adsorption and membrane separation. In the scenario in which the resulting products, carbon dioxide and hydrogen, were subsequently liquefied for transportation and storage at 10 bar and −46 °C, and 1 bar and −251.8 °C, respectively. The overall energy consumption per kg of CO₂ separated (MJ/kgCO₂₎, was found to follow the order: 8.19–11.21 for monoethanolamine (MEA) absorption; 1.81–8.93 for membrane separation; 1.53–5.69 for pressure swing adsorption; and 0.81–3.35 de-sublimation process. Each process was evaluated and compared on the bases of electricity demand, cooling water usage, high-pressure steam usage, and refrigeration energy requirements. Finally, the advantages and disadvantages were discussed and the feasibility and sustainability of the processes for application in the production of liquid hydrogen were assessed.     

Recent advances in membrane technologies for hydrogen purification

Planet Earth is facing accelerated global warming due to greenhouse gas emissions from human activities. The United Nations agreement at the Paris Climate Conference in 2015 highlighted the importance of reducing CO₂ emissions from fossil fuel combustion. Hydrogen is a clean and efficient energy carrier and a hydrogen-based economy is now widely regarded as a potential solution for the future of energy security and sustainability. Although hydrogen can be produced from water electrolysis, economic reasons dictate that most of the H₂ produced worldwide, currently comes from the steam reforming of natural gas and this situation is set to continue in the foreseeable future. This production process delivers a H₂-rich mixture of gases from which H₂ needs to be purified up to the ultra-high purity levels required by fuel cells (99.97%). This driving force pushes for the development of newer H₂ purification technologies that can be highly selective and more energy efficient than the traditional energy intensive processes of pressure swing adsorption and cryogenic distillation. Membrane technology appears as an obvious energy efficient alternative for producing the ultra-pure H₂ required for fuel cells. However, membrane technology for H₂ purification has still not reached the maturity level required for its ubiquitous industrial application. This review article covers the major aspects of the current research in membrane separation technology for H₂ purification, focusing on four major types of emerging membrane technologies (carbon molecular sieve membranes; ionic-liquid based membranes; palladium-based membranes and electrochemical hydrogen pumping membranes) and establishes a comparison between them in terms of advantages and limitations.     

Roadmap to economically viable hydrogen liquefaction

The distribution of hydrogen in liquid state has several advantages because of its higher volumetric density compared to compressed hydrogen gas. The demand for liquid hydrogen (LH₂), particularly driven by clean fuel cell applications, is expected to rise in the near future. Large-scale hydrogen liquefaction plants will play a major role within the hydrogen supply chain. The barriers of built hydrogen liquefiers is the low exergy efficiency and the high specific liquefaction costs. Exergy efficiency improvements, however, are limited by economic viability. The focus of this paper is to present a roadmap for the scale-up of hydrogen liquefaction technology, from state-of-the-art plants to newly developed large-scale liquefaction processes. The work is aimed at reducing the specific liquefaction costs by finding an optimal trade-off between capital costs and operating costs. To this end, two developed hydrogen liquefaction processes were optimized for specific energy consumption and specific liquefaction costs, showing the potential to reduce the specific liquefaction costs by 67% for a 100 tpd LH₂ plant compared to a conventional 5 tpd LH₂ plant while achieving a specific energy consumption between 5.9 and 6.6 kWh per kg LH₂ with technology that is or will be available within 5 years. The results make liquid hydrogen a viable distribution route for hydrogen for mobility.     

Electric system management through hydrogen production – A market driven approach in the French context

Hydrogen is usually presented as a promising energy carrier that has a major role to play in low carbon transportation, through the use of fuel cells. However, such a development is not expected in the short term. In the meantime, hydrogen may also contribute to reduce carbon emissions in diverse sectors among which methanol production. Methanol can be produced by combining carbon dioxide and hydrogen, hence facilitating carbon dioxide emission mitigation while providing a beneficial tool to manage the electric system, if hydrogen is produced by alkaline electrolysis operated in a variable way driven by the spot and balancing electricity markets. Such a concept is promoted by the VItESSE² project (Industrial and Energy value of CO₂ through Efficient use of CO₂-free electricity - Electricity Network System Control & Electricity Storage). Through the proposed market driven approach, hydrogen production offers a possibility to help managing the electric system, together with an opportunity to reduce hydrogen production costs.     

The potential role of hydrogen as a sustainable transportation fuel to combat global warming

Hydrogen is recognized as a key source of the sustainable energy solutions. The transportation sector is known as one of the largest fuel consumers of the global energy market. Hydrogen can become a promising fuel for sustainable transportation by providing clean, reliable, safe, convenient, customer friendly, and affordable energy. In this study, the possibility of hydrogen as the major fuel for transportation systems is investigated comprehensively based on the recent data published in the literature. Due to its several characteristic advantages, such as energy density, abundance, ease of transportation, a wide variety of production methods from clean and renewable fuels with zero or minimal emissions; hydrogen appears to be a great chemical fuel which can potentially replace fossil fuel use in internal combustion engines. In order to take advantage of hydrogen as an internal combustion engine fuel, existing engines should be redesigned to avoid abnormal combustion. Hydrogen use in internal combustion engines could enhance system efficiencies, offer higher power outputs per vehicle, and emit lower amounts of greenhouse gases. Even though hydrogen-powered fuel cells have lower emissions than internal combustion engines, they require additional space and weight and they are generally more expensive. Therefore, the scope of this study is hydrogen-fueled internal combustion engines. It is also highlighted that in order to become a truly sustainable and clean fuel, hydrogen should be produced from renewable energy and material resources with zero or minimal emissions at high efficiencies. In addition, in this study, conventional, hybrid, electric, biofuel, fuel cell, and hydrogen fueled ICE vehicles are comparatively assessed based on their CO₂ and SO₂ emissions, social cost of carbon, energy and exergy efficiencies, fuel consumption, fuel price, and driving range. The results show that when all of these criteria are taken into account, fuel cell vehicles have the highest average performance ranking (4.97/10), followed by hydrogen fueled ICEs (4.81/10) and biofuel vehicles (4.71/10). On the other hand, conventional vehicles have the lowest average performance ranking (1.21/10), followed by electric vehicles (4.24/10) and hybrid vehicles (4.53/10).     

A flexible techno-economic analysis tool for regional hydrogen hubs – A case study for Ireland

The increasing urgency with which climate change must be addressed has led to an unprecedented level of interest in hydrogen as a clean energy carrier. Much of the analysis of hydrogen until this point has focused predominantly on hydrogen production. This paper aims to address this by developing a flexible techno-economic analysis (TEA) tool that can be used to evaluate the potential of future scenarios where hydrogen is produced, stored, and distributed within a region. The tool takes a full year of hourly data for renewables availability and dispatch down (the sum of curtailment and constraint), wholesale electricity market prices, and hydrogen demand, as well as other user-defined inputs, and sizes electrolyser capacity in order to minimise cost. The model is applied to a number of case studies on the island of Ireland, which includes Ireland and Northern Ireland. For the scenarios analysed, the overall LCOH ranges from €2.75–3.95/kgH₂. Higher costs for scenarios without access to geological storage indicate the importance of cost-effective storage to allow flexible hydrogen production to reduce electricity costs whilst consistently meeting a set demand.     

Transition to hydrogen economy in the United States: A 2006 status report

Energy crises in the latter part of the 20th century, as well as the current increase in the cost of oil, emphasize the need for alternate sources of energy in the United States. Concerns about climate change dictate that the source be clean and not contribute to global warming. Hydrogen has been identified as such a source for many years and the transition to a hydrogen economy was predicted to occur from the mid-1970s to 2000. This paper reports on the status of this transition in the year 2006. Instead of being a clean source of energy, most of the hydrogen produced in the US results from steam reforming of fossil fuels, releasing _CO2${\mathrm{CO}}_2$ and other pollutants to the atmosphere. Nuclear process heat is ideally suited for the production of hydrogen, either using electricity for electrolysis of water, or heat for thermochemical hydrogen production or reforming of fossil fuels. However, no new nuclear plants have been ordered or built in the United States since 1979, and it may be many years before high-temperature nuclear reactors are available for production of hydrogen. Considerable research and development efforts are focused on commercializing hydrogen-powered vehicles to lessen the dependence of the transportation sector on imported oil. However, the use of hydrogen fuel cell vehicles (FCV) in 2006 is two orders-of-magnitude less than what has been predicted. Although it makes little sense environmentally or economically, hydrogen is also used as fuel in internal combustion engines. Development of hydrogen economy will require a strong intervention by external forces.     

Study of hydrogen generation from heavy oil gasification based on ramped temperature oxidation experiments

Hydrogen is a clean energy because of its high energy density and pollution-free combustion. The main ways of hydrogen generation are from coal and methane, as well as hydrogen generation from by-products of chemical plants. It had been reported that heavy oil reservoir in Margaret Lake in Canada produced up to 15 mol% hydrogen indicating that it is feasible to produce hydrogen by in-situ gasification (ISG) from heavy oil reservoir. However, there are relatively few studies on the mechanism and characteristics of hydrogen generation from ISG of heavy oil, the lower limit of hydrogen-production temperature, the interaction of produced gas and so on. Previous studies focused on the upgrading of heavy oil rather than hydrogen generation. In order to study the hydrogen generation mechanisms of different samples, The 4 types samples covering heavy oil, light oil, carbon samples were used and the saturate, aromatic, resin and asphaltene (SARA) components was measured by thin layer chromatography and flame ionization detection (TLC-FID). Then, the ramped temperature oxidation (RTO) experiments of 7 Runs of reservoir cores and sand-filling model were designed. The compositions and molar contents of produced gas were analyzed combined with gas chromatography (GC), and the lower limit temperature and the advantages of hydrogen generation from heavy oil were analyzed under different air/nitrogen injection rates based on a constant water injection rate. The results showed that the lower limit temperature of hydrogen generation from crude oil was about 500–550 °C and that of carbon was 700–750 °C. The reservoir core may had catalytic effect, which can promote hydrogen production. The highest hydrogen rate of RTO experiment with reservoir core can reach 55–60mol%, while that of sand-filling experiment was only 5–10mol%. The main chemical reactions for hydrogen generation from crude oil were coke gasification and water-gas shift. Therefore, the hydrogen production of heavy oil with high hydrocarbon ratio was significantly greater than that of thin oil. It showed the advantages of hydrogen generation from heavy oil. In addition, in order to quantitatively evaluate the efficiency of hydrogen production by gasification, the definition and calculation equation of hydrogen generation efficiency (HGE) were given. The HGE was defined as the ratio of hydrogen production volume and hydrogen consumption volume in a certain period of time (Δt). The E_hg can be used to quantitatively represent HGE, and the calculation of E_hg is the ratio of hydrogen production and twice of oxygen consumption in a period of time. The E_hg of Run1 and Run3 were calculated to be 1.47 and 0.15. It indicated that the hydrogen production efficiency of Run1 was about 10 times higher than that of Run3.     

Hydrogen as an export commodity – Capital expenditure and energy evaluation of hydrogen carriers

In this paper, we describe a case-study exploring the use of 600 MW of power from New Zealand's Manapouri Power Station to produce hydrogen for export via water electrolysis. Three H₂ carriers were considered: liquid H₂, ammonia, and toluene hydrogenation/methylcyclohexane dehydrogenation. Processes were simulated in Aspen's HYSYS for each of the carriers to determine their associated energy and annualised capital expenditure costs. We found that the total capital investment for all carriers was surprisingly consistent, but with quite different splits between the electrolysis and carrier formation plants. Based on our analysis the energy availability for liquid H₂ ranged from 53.9 to 60.7% depending on the energy cost associated with cryogenic H₂ liquefaction. The energy availability for liquid ammonia was 37.5% after conversion back to H₂, or 53.6% if the ammonia can be used directly as a fuel. For toluene/methylcyclohexane the energy availability was 41.2%. The total of the electricity and annualised capital costs per kg of H₂ ranged from NZ$5.63 to NZ$6.43 for liquid H₂, NZ$6.24 to NZ$8.91 for ammonia and was NZ$7.86 for toluene/methylcyclohexane, using a net electricity cost of NZ$70/MWh. The cost of hydrogen (or energy in the case of direct use ammonia) was more strongly influenced by the efficiency of energy retention than on capital investment, as the electricity costs contributed approximately two thirds of total costs. In the long-term, liquid hydrogen looks to be the most versatile H₂ carrier, but significant infrastructure investment is required.     

Experimental study on hydrogen-rich syngas production via gasification of pine cone particles and wood pellets in a fixed bed downdraft gasifier

The main objective of this research is to investigate gasification of pine cones particles and wood pellets in a pilot scale 10 kWth downdraft fixed bed gasifier using air as an oxidizing agent. In this work, it was found that syngas produced by gasification of pinecones particles is rich in environmentally friendly hydrogen and that would be a clean alternative energy carrier for the production of clean energy. In addition, the effect of gasification temperature and equivalence ratio on the composition of syngas and gasification performance for pine cones and wood pellet were analysed comparatively. During the experimental works gasification took place with air, in a temperature range of 701–1046 °C, for various air equivalence ratios (0.14–0.37) and under atmospheric pressure. It is found that H₂ and CO production increased by increasing reactor temperature. Another finding is that the mean cold gas efficiency was 65% for pinecone particles and 80% for wood pellet gasification.     

Bulk nanocomposite MgH2/10 wt% (8 Nb2O5/2 Ni) solid-hydrogen storage system for fuel cell applications

Hydrogen, which holds tremendous promise as a new clean energy option is considered as an efficient source of primary energy. Unluckily, hydrogen storage presents the most crucial difficulty restricting utilization of hydrogen energy for real applications. However, Mg metal is the best known cheap solid-state hydrogen storage media with high hydrogen capacity and operational cost effectiveness; it shows high thermal stability and poor hydrogenation/dehydrogenation kinetics. In the present work we have succeeded to prepare nanocrystalline MgH₂ powders doped with a mixture of 8 wt% Nb₂O₅/2 wt% Ni nanocatalytic system. The synthesized nanocomposite powders possessed superior hydrogenation/dehydrogenation kinetics (2.6 min/3 min) at relatively low temperature (250 °C) with long cycle-life-time (400 h). The powders were consolidated into green-compacts, using cold pressing technique. The compacts were utilized as solid-state hydrogen source needed for charging a battery of a cell-phone device, using integrated Ti-tank/commercial proton-exchange membrane fuel cell system.     

Synthesis of potential nanostructures based on strontium hexaferrite for electrochemical hydrogen storage

Today, the reduction of fossil fuel resources and the increase of their destructive environmental effects are important challenges. One strategy to this problem is application of new sources of energy supply. Hydrogen can play an important role in future energy supplies due to its unique properties such as clean combustion and high energy content relative to mass. In addition, hydrogen is considered as a green energy because it can be produced from renewable sources and is not polluting. The most important issue in hydrogen as a fuel is its storage. Hydrogen must be stored reversibly in a completely safe manner as well as with high storage efficiencies. One of the best ways to store hydrogen is using of new nanostructured adsorbents. In this study, first strontium hexaferrite (SrFe₁₂O₁₉) nanostructures are synthesized by sol-gel auto-combustion method. Then, the samples structure is studied using various techniques. Furthermore, the nanostructures are used as hydrogen storage materials. Using electrochemical techniques, the hydrogen storage properties of the materials are investigated in alkaline media. The obtained electrochemical results show that the maximum hydrogen storage capacity of SrFe₁₂O₁₉ nanostructures is about 3100 mAh/g.     

The prospects for liquid hydrogen fueled aircraft

Because the world's annual production of petroleum is expected to peak in the 1990 decade, alternative energy sources and fuels must be developed. Due to the global nature of its requirements selection of an alternate fuel for transport aircraft is a special problem: the fuel must be producible or available anywhere in the world.This requirement can be met by liquid hydrogen because it can be produced from water using any locally available energy source. It does not depend on the availability of fossil resources. Using conventional production technologies LH₂ may cost more per unit energy than hydrocarbon alternatives; however, because of their weight advantage, LH₂ aircraft are more efficient and their direct operating cost is competitive. With advanced technologies which have been identified, it is shown that LH₂ can provide cost and energy advantages.A program plan to develop LH₂ technology on an international basis has been proposed which can provide for timely introduction of LH₂ as a fuel for transport aircraft.