Refueling-station costs for metal hydride storage tanks on board hydrogen fuel cell vehicles

Refueling costs account for much of the fuel cost for light-duty hydrogen fuel-cell electric vehicles. We estimate cost savings for hydrogen dispensing if metal hydride (MH) storage tanks are used on board instead of 700-bar tanks. We consider a low-temperature, low-enthalpy scenario and a high-temperature, high-enthalpy scenario to bracket the design space. The refueling costs are insensitive to most uncertainties. Uncertainties associated with the cooling duty, coolant pump pressure, heat exchanger (HX) fan, and HX operating time have little effect on cost. The largest sensitivities are to tank pressure and station labor. The cost of a full-service attendant, if the refueling interconnect were to prevent self-service, is the single largest cost uncertainty. MH scenarios achieve $0.71–$0.75/kg-H₂ savings by reducing compressor costs without incurring the cryogenics costs associated with cold-storage alternatives. Practical refueling station considerations are likely to affect the choice of the MH and tank design.     

Review of hydrogen economy in Malaysia and its way forward

Heavy fossil fuels consumption has raised concerns over the energy security and climate change while hydrogen is regarded as the fuel of future to decarbonize global energy use. Hydrogen is commonly used as feedstocks in chemical industries and has a wide range of energy applications such as vehicle fuel, boiler fuel, and energy storage. However, the development of hydrogen energy in Malaysia is sluggish despite the predefined targets in hydrogen roadmap. This paper aims to study the future directions of hydrogen economy in Malaysia considering a variety of hydrogen applications. The potential approaches for hydrogen production, storage, distribution and application in Malaysia have been reviewed and the challenges of hydrogen economy are discussed. A conceptual framework for the accomplishment of hydrogen economy has been proposed where renewable hydrogen could penetrate Malaysia market in three phases. In the first phase, the market should aim to utilize the hydrogen as feedstock for chemical industries. Once the hydrogen production side is matured in the second phase, hydrogen should be used as fuel in internal combustion engines or burners. In the final phase hydrogen should be used as fuel for automobiles (using fuel cell), fuel-cell combined heat and power (CHP) and as energy storage.     

The economic feasibility study of a 100-MW Power-to-Gas plant

Power-to-Gas (PtG) is a grid-scale energy storage technology by which electricity is converted into gas fuel as an energy carrier. PtG utilizes surplus renewable electricity to generate hydrogen from Solid-Oxide-Cell, and the hydrogen is then combined with CO₂ in the Sabatier process to produce the methane. The transportation of methane is mature and energy-efficient within the existing natural gas pipeline or town gas network. Additionally, it is ideal to make use of the reverse function of SOC, the Solid-Oxide-Fuel-Cell, to generate electricity when the grid is weak in power. This study estimated the cost of building a hypothetical 100-MW PtG power plant with energy storage and power generation capabilities. The emphasis is on the effects of SOC cost, fuel cost and capacity factor to the Levelized Cost of Energy of the PtG plant. The net present value of the plant is analyzed to estimate the lowest affordable contract price to secure a positive present value. Besides, the plant payback period and CO₂ emission are estimated.     

Exploring N-best solution space for heat integrated hydrogen regeneration network using sequential graph-theoretic approach

To achieve the ever-stringent sustainable goals, this paper aims to synthesize a heat integrated hydrogen regeneration network (HIHRN) using a graph-theoretic-based sequential method. Firstly, the optimal and near-optimal structures for a hydrogen regeneration networks (HRN) are determined using P-graph model with consideration of both impurity and pressure constraints. These networks are then used as inputs in P-HENS software to generate a list of optimal and near-optimal heat exchanger network (HEN) structures. An eight source and sink problem is used to demonstrate the effectiveness of the proposed method. There are 199,677 feasible HIHRN structures identified, while the 6 near-optimal solutions which are within 0.05% tolerance of the optimal network cost (i.e., less than 33.04 M$/y) are presented together with the top four HEN designs that can offer comparable costs (～115,500 $/y). In addition, the impacts of pressure swing adsorber (PSA) pressure drop consideration and minimum temperature difference on the optimal design are also presented.     

Dark fermentative biohydrogen production using pretreated Scenedesmus obliquus biomass under an integrated paradigm of biorefinery

In recent times, biohydrogen production from microalgal feedstock has garnered considerable research interests to sustainably replace the fossil fuels. The present work adapted an integrated approach of utilizing deoiled Scenedesmus obliquus biomass as feedstock for biohydrogen production and valorization of dark fermentation (DF) effluent via biomethanation. The microalgae was cultivated under different CO₂ concentration. CO₂-air sparging of 5% v/v supported maximum microalgal growth and carbohydrate production with CO₂ fixation ability of 727.7 mg L^?1 d^?1. Thereafter, lipid present in microalgae was extracted for biodiesel production and the deoiled microalgal biomass (DMB) was subjected to different pretreatment techniques to maximize the carbohydrate recovery and biohydrogen yield. Steam heating (121 °C) in coherence with H₂SO₄ (0.5 N) documented highest carbohydrate recovery of 87.5%. DF of acid-thermal pretreated DMB resulted in maximum H₂ yield of 97.6 mL g^?1 VS which was almost 10 times higher as compared to untreated DMB (9.8 mL g^?1 VS). Subsequent utilization of DF effluent in biomethanation process resulted in cumulative methane production of 1060 mL L^?1. The total substrate energy recovered from integrated biofuel production system was 30%. The present study envisages a microalgal biorefinery to produce biohydrogen via DF coupled with concomitant CO₂ sequestration.     

Current situation and development prospects of metallurgical by-product gas utilization in China's steel industry

China's annual metallurgical by-product gas production exceeds 1400 billion Nm³, the calorific equivalent of ∼266 million tonnes of coal. The widely-studied blast furnace gas used in hydrogen-enriched carbonic oxide recycling oxygenate furnaces ensures carbon-reduction. Converter gas contains abundant heat resources, equivalent to ∼6.5 million tonnes of coal. Using high-temperature by-product gas online reforming methods to convert thermal energy into chemical energy and combining it with power generation and other industries imparts physical heat recovery exceeding 60%. China's annual coke oven gas (COG) production could support more than 100 million tonnes of direct reduced iron production, thus reducing CO₂ emissions by more than 150 million tonnes (nearly 10% of China's steel industry CO₂ emissions). We summarise the characteristics, availability, and steel-chemical co-production utilisation of three by-product gases, and discuss the application of COG in direct reduced iron production and development of metallurgical by-product gas utilisation for carbon reduction in China.     

Harvest of electrical energy from fermented microalgal residue using a microbial fuel cell

The application of microalgal biomass for fermentation has been highlighted as a means of producing a range of value-added biofuels and chemicals. On the other hand, the microalgal residue from the fermentation process still contains as much as 50% organic contaminants, which can be a valuable substrate for further bioenergy recovery. In this study, a microbial fuel cell and automatic external load control by maximum power point tracking (MPPT) were implemented to harvest the electrical energy from waste fermented microalgal residue (FMR). The MFC with MPPT produced the highest amount of energy (1.82 kJ/L) compared to the other MFCs with fixed resistances: 0.98 (1000 Ω), 1.16 (500 Ω), and 1.17 kJ/L (300 Ω). The MFC with MPPT also showed the highest maximum power density (88.6 mW/m²) and COD removal efficiency (620.0 mg COD/L removal with 85% removal efficiency). The implementation of MPPT gained an approximate 12.9% energy yield compared to the previous fermentation stage. These results suggest that FMR can be an appropriate feedstock for electrical energy recovery using MFCs, and the combined fermentation and MFC system improves significantly the energy recovery and treatment efficiency from FMR.     

A techno-economic study for a hydrogen storage system in a microgrid located in baja California,Mexico. Levelized cost of energy for power to gas to power scenarios

In this work a techno economic feasibility study is carried out to implement a Hydrogen based Power to Gas to Power (P2G2P) in a Microgrid, located in a rural area in Baja California, Mexico. The study aims to define the feasibility to store energy throughout seasons with this novel alternative using an electrolyzer to produce green hydrogen from excess renewable energy in winter, to store it during months and re inject it to the grid as electricity by a fuel cell in the high energy demanding season. The Microgrid was modeled in Homer software and simulations of the P2G2P lead to Levelized Cost of Energy data to compare between the P2G2P scenarios and the current diesel-battery based solution to complete the high demand by the community. This study shows that using hydrogen and fuel cells to substitute diesel generators it is possible to reduce CO₂ emissions up to a 27% and that in order for the P2G2P to be cost competitive, the fuel cell should reduce its cost in 50%; confirming that, in the medium to long term, the hydrogen storage system is a coherent alternative towards decarbonization of the distributed energy generation.     

Hydrogen-rich syngas production by gasification of Urea-formaldehyde plastics in supercritical water

Supercritical water is a promising medium to convert plastics into hydrogen and other recyclable products efficiently. In previous research, supercritical water gasification characteristics investigations focus on thermoplastics instead of thermoset plastics due to its chemical, thermal and mechanical stability. Urea-formaldehyde (UF) plastics were selected as a typical kind of thermoset plastics for investigation in this paper and quartz tubes were used as the reactor in order to avoid the potential catalytic effect of metal reactor wall. Conversion characteristic were studied and the influence of different operating parameters such as temperature, reaction time, feedstock mass fraction and pressure were investigated respectively. The molar fraction of hydrogen could reach about 70% in 700 °C. Products in gas phase and solid phase were analyzed, and properties, chemical structures and inhibition mechanism of thermoset plastics was analyzed after comparing with polystyrene (PS) plastics. The result showed that increase of high temperature and long reaction time could promote gasification process, meanwhile the increase in the feedstock mass fraction would result in suppression of the gasification process. Finally, kinetic study of UF was carried out and the activation energy and pre-exponential factor of the Arrhenius equation were calculated as 30.09 ± 1.62 kJ/mol and 0.1199 ± 0.0049 min⁻¹, respectively.     

Detonation propagation characteristics of H2/O2/AR in multi-angle bifurcation tubes

The propagation characteristics of the detonation wave in the bifurcated tube with the angular variation range of 30°–90° are simulated with 25% AR as dilution gas for H₂/O₂ mixture fuel at chemical equivalence ratio using the solver DCRFoam built on the OpenFOAM platform. The diffraction and reflection phenomena of detonation waves passing through bifurcation tubes with different angles are studied and analyzed. The results show that the distance from regular reflection to Mach reflection increases with the increase of the bifurcation angle so that after one reflection, the detonation forms three reflection forms with the angle of the different bifurcation tubes. After the first reflection, the detonation waves are more likely to induce the formation of transverse waves in the low-angle bifurcation tube. The lowest collision pressure after the detonation collides with the upper wall to form a secondary reflection occurs in the bifurcation tube between 50° and 60°.     

Hydrogen production from phototrophic microorganisms: Reality and perspectives

Hydrogen is a promising alternative to fossil fuel for a source of clean energy due to its high energy content. Some strains of phototrophic microorganisms are known as important object of scientific research and they are being explored to raise biohydrogen (BioH₂) yield. BioH₂ is still not commonly used in industrial area because of the low biomass yield and valuable down streaming process. This article deals with the methods of the hydrogen production with the help of two large groups of phototrophic microorganisms – microalgae and cyanobacteria. Microalgal hydrogen is environmentally friendly alternative to conventional fossil fuels. Algal biomass has been considered as an attractive raw source for hydrogen production. Genetic modified strains of cyanobacteria are used as a perspective object for obtaining hydrogen. The modern photobioreactors and outdoor air systems have been used to obtain the biomass used for hydrogen production. At present time a variety of immobilization matrices and methods are being examined for their suitability to make immobilized H₂ producers.     

Hydrofluoroolefin-based mixed refrigerant for enhanced performance of hydrogen liquefaction process

Hydrogen has the highest gravimetric energy density of all fuels; however, it has a low volumetric energy density, unfavorable for storage and transportation. Hydrogen is usually liquefied to meet the bulk transportation needs. The exothermic interconversion of its spin isomers is an additional activity to an already energy-intensive process. The most significant temperature drop occurs in the precooling cycle (between ?150 °C and up to ?180 °C) and consumes more than 50% of the required energy. To reduce the energy consumption and improve the exergy efficiency of the hydrogen liquefaction process, a new high-boiling component, Hydrofluoroolefin (HFO-1234yf), is added to the precooled mixed refrigerant. As a result, the specific energy consumption of precooling cycle reduces by 41.8%, from 10.15 kWh/kg_LH2 to 5.90 kWh/kg_LH2, for the overall process. The exergy efficiency of the proposed case increases by 43.7%; however, the total equipment cost is also the highest. The inflated cost is primarily due to the added ortho-to-para hydrogen conversion reactor, boosting the para-hydrogen concentration. From the perspective of bulk storage and transportation of liquid hydrogen, the simplicity of design and low energy consumption build a convincing case for considering the commercialization of the process.     

Evaluating influences of impurities on hydrogen production in the reaction of Si with water using Si sludge

Hydrogen has attracted much attention as a next-generation energy resource. Among various technologies, one of the promising approaches for hydrogen production is the use of the reaction between Si and water, which does not require any heat, electricity, and light energy as an input. Notwithstanding the usefulness of Si as a prospective raw material of hydrogen production, the manufacturing process of Si requires a significant amount of energy. Therefore, as an alternative to pure Si, this study used a wasted Si sludge, generated though the manufacturing process of Si wafer, for the direct reuse. Thus, the Si-water reaction for the hydrogen generation was investigated in comparison with pure Si and Si sludge by employing X-ray absorption near edge structure (XANES) to evaluate the feasibility of hydrogen production with the use of Si sludge and to identify the influence of impurities contained in Si sludge. As a result, hydrogen was not produced with the use of Si sludge because of containing Al compound as the impurity. Through the XANES analysis, the formation of SiO(OH)₂ was found as core-shell structure, which potentially would hinder the hydrogen generation.     

Comparative techno-economic study of typically combustion-less hydrogen production alternatives

A techno-economic study is performed for a large scale combustion-less hydrogen production process based on Steam Methane Reforming (SMR). Two process versions relying on different renewable heat sources are compared: (1) direct solar heating from a concentrated solar power system, and (2) radiation from resistive electrical heaters (electric SMR). Both processes are developed around an integrated micro-reactor technology, incorporating in a monolithic block most sub-processes needed to perform SMR. A baseline techno-economic scenario with low-cost feedstock and electricity, priced at $4/MMBtu and $0.04/kWh respectively, results in an LCOH of $2.31/kg_H2 for solar SMR and $1.59/kg_H2 for electric SMR. Results further show that solar SMR is currently more attractive economically than electric SMR coupled with distributed wind power systems, but electric SMR is more favourable in the long term due to the expected future improvements in the LCOE and capacity factor of wind power systems.     

Renewable-powered hydrogen economy from Australia's perspective

This article broadly reviews the state-of-the-art technologies for hydrogen production routes, and methods of renewable integration. It outlines the main techno-economic enabler factors for Australia to transform and lead the regional energy market. Two main categories for competitive and commercial-scale hydrogen production routes in Australia are identified: 1) electrolysis powered by renewable, and 2) fossil fuel cracking via steam methane reforming (SMR) or coal gasification which must be coupled with carbon capture and sequestration (CCS). It is reported that Australia is able to competitively lower the levelized cost of hydrogen (LCOH) to a record $(1.88–2.30)/kg_H2 for SMR technologies, and $(2.02–2.47)/kg_H2 for black-coal gasification technologies. Comparatively, the LCOH via electrolysis technologies is in the range of $(4.78–5.84)/kg_H2 for the alkaline electrolysis (AE) and $(6.08–7.43)/kg_H2 for the proton exchange membrane (PEM) counterparts. Nevertheless, hydrogen production must be linked to the right infrastructure in transport-storage-conversion to demonstrate appealing business models.     

Biogas from lignocellulosic feedstock: A review on the main pretreatments,inocula and operational variables involved in anaerobic reactor efficiency

Research focused on reusing lignocellulosic waste has been gaining ground, both for the purpose of obtaining energy from renewable sources, as well as for reducing feedstock costs and preventing environmental pollution. Despite being currently evaluated as a promising feedstock, large-scale application of lignocellulosic waste to obtain bioenergy is still scarce. One of the obstacles in terms of reusing it is its recalcitrant composition, often requiring pretreatment applications to break its fibers, increasing its bioavailability. In addition to the type of substrate, there are many operational parameters that may affect the process efficiency, including the type of reactor, temperature, pH, inoculum source, among others. Considering this, it is interesting to consider using statistical tools instead of “one-factor-at-a-time” methods for simultaneous optimization of these variables to increase the production of value-added compounds, such as Plackett-Burman screening design and Central Composite Rotational Design. In this context, this review aimed at compiling data regarding obtaining value-added compounds, focusing on bio-H₂ and bio-CH₄, from different lignocellulosic waste, such as sugarcane bagasse, citrus peel waste, coffee and cereal husks, brewer's spent grain, cocoa processing waste, sawdust, among others, considering the main operational parameters involved (temperature, pH, inoculum) and the type of pretreatment applied (physical, chemical and/or biological). The results described here may support future research on reusing residual lignocellulosic waste, in addition to elucidating the importance of different operational parameters to convert this waste into H₂ and/or CH₄.     

Hydrogen production for energy: An overview

Power to hydrogen is a promising solution for storing variable Renewable Energy (RE) to achieve a 100% renewable and sustainable hydrogen economy. The hydrogen-based energy system (energy to hydrogen to energy) comprises four main stages; production, storage, safety and utilisation. The hydrogen-based energy system is presented as four corners (stages) of a square shaped integrated whole to demonstrate the interconnection and interdependency of these main stages. The hydrogen production pathway and specific technology selection are dependent on the type of energy and feedstock available as well as the end-use purity required. Hence, purification technologies are included in the production pathways for system integration, energy storage, utilisation or RE export. Hydrogen production pathways and associated technologies are reviewed in this paper for their interconnection and interdependence on the other corners of the hydrogen square.Despite hydrogen being zero-carbon-emission energy at the end-use point, it depends on the cleanness of the production pathway and the energy used to produce it. Thus, the guarantee of hydrogen origin is essential to consider hydrogen as clean energy. An innovative model is introduced as a hydrogen cleanness index coding for further investigation and development.     

Assessment of ammonia as energy carrier in the use with reversible solid oxide cells

Ammonia represents one of the most promising potential solutions as energy vector and hydrogen carrier, having a higher potential to transport energy than hydrogen itself in a pressurized form. Furthermore, solid oxide fuel cells (SOFCs) can directly be fed with ammonia, thus allowing for immediate electrical power and heat generation. This paper deals with the analysis of the dynamic behavior of commercial SOFCs when fueled with ammonia. Several measurements at different temperatures have been performed and performances are compared with hydrogen and a stoichiometrically equivalent mixture of H₂ and N₂ (3:1 M ratio). Higher temperature led to smaller drops in voltage for both fuels, thus providing higher efficiencies. Ammonia resulted slightly more performant (48% at 760 °C) than hydrogen (45% at 760 °C), in short stack tests. Moreover, different ammonia-to-air ratios have been investigated and the stack area-specific resistance has been studied in detail by comparing numerical modeling predictions and experimental values.     

Reducing the fuel consumption and emissions with the use of an external fuel cell hybrid power unit for electric taxiing at airports

Airport ground operations have a great impact on the environment. Various innovative solutions have been proposed for aircraft to perform taxi movements by deactivating their main engines. Although these solutions are environmentally beneficial, onboard and external electric taxiing solutions that are actively used and planned to be used in airports are not completely carbon-free. The disadvantages of the existing solutions can be alleviated by using an external fuel cell hybrid power unit to meet the energy required for taxiing that does not put additional weight on the aircraft. To reveal the power and energy required by the system, Airbus A320-200, which is a narrow-body aircraft and frequently used in airports, has been considered in this study. To determine the physical requirements of the aircraft for taxiing, a total of 900 s taxi-out movement consisting of four different periods with different runway slope, headwind, and maximum speeds were examined. According to the determined physical requirements, the conceptual design of the proposed fuel cell battery system was created and the physical data of the system for each period were obtained using the Matlab Simulink environment. As a result of the simulation, it is seen that the system consumes approximately 1.96 g of hydrogen per second. In addition, it has been calculated that 578.34 kg of CO₂ is emitted during the taxi-out movement. The results also show that as a result of using the proposed system, approximately 14.6 million tons of CO₂ emission per year can be prevented.     

Techno-economic feasibility of power to gas–oxy-fuel boiler hybrid system under uncertainty

One of the main challenges associated with utilisation of the renewable energy is the need for energy storage to handle its intermittent nature. Power-to-Gas (PtG) represents a promising option to foster the conversion of renewable electricity into energy carriers that may attend electrical, thermal, or mechanical needs on-demand. This work aimed to incorporate a stochastic approach (Artificial Neural Network combined with Monte Carlo simulations) into the thermodynamic and economic analysis of the PtG process hybridized with an oxy-fuel boiler (modelled in Aspen Plus^®). Such approach generated probability density curves for the key techno-economic performance indicators of the PtG process. Results showed that the mean utilisation of electricity from RES, accounting for the chemical energy in SNG and heat from methanators, reached 62.6%. Besides, the probability that the discounted cash flow is positive was estimated to be only 13.4%, under the set of conditions considered in the work. This work also showed that in order to make the mean net present value positive, subsidies of 68 €/MW_elh are required (with respect to the electricity consumed by PtG process from RES). This figure is similar to the financial aids received by other technologies in the current economic environment.