Performance evaluation of a solarized gas turbine system integrated to a high temperature electrolyzer for hydrogen production

In this paper, the performance of a solar gas turbine (SGT) system integrated to a high temperature electrolyzer (HTE) to generate hybrid electrical power and hydrogen fuel is analyzed. The idea behind this design is to mitigate the losses in the electrical power transmission and use the enthalpy of exhaust gases released from the gas turbine (GT) to make steam for the HTE. In this context, a GT system is coupled with a solar tower including heliostat solar field and central receiver to generate electrical power. To make steam for the HTE, a flameless boiler is integrated to the SGT system applying the SGT extremely high temperature exhaust gases as the oxidizer. The results indicate that by increasing the solar receiver outlet temperature from 800 K to 1300 K, the solar share increases from 22.1% to 42.38% and the overall fuel consumption of the plant reduces from 7 kg/s to 2.7 kg/s. Furthermore, flameless mode is achievable in the boiler while the turbine inlet temperature (TIT) is maintained at the temperatures higher than 1314 K. Using constant amounts of the SGT electrical power, the HTE voltage decreases by enhancing the HTE steam temperature which result in the augmentation of the overall hydrogen production. To increase the HTE steam temperature from 950 K to 1350 K, the rate of fuel consumption in the flameless boiler increases from 0.1 m/s to 0.8 m/s; however, since the HTE hydrogen production increases from 4.24 mol/s to 16 mol/s it can be interpreted that the higher steam temperatures would be affordable. The presented hybrid system in this paper can be employed to perform more thermochemical analyses to achieve insightful understanding of the hybrid electrical power-hydrogen production systems.     

Design and computational analysis of a metal hydride hydrogen storage system with hexagonal honeycomb based heat transfer enhancements-part A

In this study, design and performance analysis is carried out for a 10 kWh metal hydride based hydrogen storage system. The system is equipped with distinctive aluminium hexagonal honeycomb based heat transfer enhancements (HTE) having higher surface area to volume ratio for effective heat transfer combined with low system weight addition. The system performance was studied under different operating conditions. The optimum absorption condition was achieved at 35 bar with water at room temperature as heat transfer fluid where up to 90% absorption was completed in 7200 s. The performance of the reactor was observed to significantly improve upon the addition of the HTE network at a minimal system weight penalty.     

Determination of the potential of cyanobacterial strains for hydrogen production

Hydrogen (H₂) is a renewable, abundant, and nonpolluting source of energy. Photosynthetic organisms capture sunlight very efficiently and convert it into organic molecules. Cyanobacteria produce H₂ by breaking down organic compounds and water. In this study, biological H₂ was produced from various strains of cyanobacteria. Moreover, H₂ accumulation by Synechocystis sp. PCC 6803 was as high as 0.037 μmol/mg Chl/h within 120 h in the dark. The wild-type, filamentous, non-heterocystous cyanobacterium Desertifilum sp. IPPAS B-1220 was found to produce a maximum of 0.229 μmol/mg Chl/h in the gas phase within 166 h in the light, which was on par with the maximum yield reported in the literature. DCMU at 10 μM increased H₂ production by Desertifilum sp. IPPAS B-1220 by 1.5-fold to 0.348 μmol H₂/mg Chl/h. This is the first report on the capability of Desertifilum cyanobacterium to produce H₂.     

Economic viability assessment of sustainable hydrogen production,storage, and utilisation technologies integrated into on- and off-grid micro-grids: A performance comparison of different meta-heuristics

In recent years, there has been considerable interest in the development of zero-emissions, sustainable energy systems utilising the potential of hydrogen energy technologies. However, the improper long-term economic assessment of costs and consequences of such hydrogen-based renewable energy systems has hindered the transition to the so-called hydrogen economy in many cases. One of the main reasons for this is the inefficiency of the optimization techniques employed to estimate the whole-life costs of such systems. Owing to the highly nonlinear and non-convex nature of the life-cycle cost optimization problems of sustainable energy systems using hydrogen as an energy carrier, meta-heuristic optimization techniques must be utilised to solve them. To this end, using a specifically developed artificial intelligence-based micro-grid capacity planning method, this paper examines the performances of twenty meta-heuristics in solving the optimal design problems of three conceptualised hydrogen-based micro-grids, as test-case systems. Accordingly, the obtained numeric simulation results using MATLAB indicate that some of the newly introduced meta-heuristics can play a key role in facilitating the successful, cost-effective development and implementation of hydrogen supply chain models. Notably, the moth-flame optimization algorithm is found capable of reducing the life-cycle costs of micro-grids by up to 6.5% as compared to the dragonfly algorithm.     

Environmental sustainability assessment of large-scale hydrogen production using prospective life cycle analysis

The need for a rapid transformation to low-carbon economies has rekindled hydrogen as a promising energy carrier. Yet, the full range of environmental consequences of large-scale hydrogen production remains unclear. Here, prospective life cycle analysis is used to compare different options to produce 500 Mt/yr of hydrogen, including scenarios that consider likely changes to future supply chains. The resulting environmental and human health impacts of such production levels are further put into context with the Planetary Boundaries framework, known human health burdens, the impacts of the world economy, and the externality-priced production costs that embody the environmental impact. The results indicate that climate change impacts of projected production levels are 3.3–5.4 times higher than the allocated planetary boundary, with only green hydrogen from wind energy staying below the boundary. Human health impacts and other environmental impacts are less severe in comparison but metal depletion and ecotoxicity impacts of green hydrogen deserve further attention. Priced-in environmental damages increase the cost most strongly for blue hydrogen (from ～2 to ～5 USD/kg hydrogen), while such true costs drop most strongly for green hydrogen from solar photovoltaic (from ～7 to ～3 USD/kg hydrogen) when applying prospective life cycle analysis. This perspective helps to evaluate potentially unintended consequences and contributes to the debate about blue and green hydrogen.     

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.     

Recent advances in artificial neural network research for modeling hydrogen production processes

Artificial Neural Networks (ANN) have been widely used by scientists in a variety of energy modes (biomass, wind, solar, geothermal, and hydroelectric). This review highlights the assistance of ANN for researchers in the quest for discovering more advanced materials/processes for efficient hydrogen production (HP). The review is divided into two parts in this context. The first section briefly mentions, in terms of technologies, economy, energy consumption, and costs symmetrically outlined the advantages and disadvantages of various HP routes such as fossil fuel/biomass conversion, water electrolysis, microbial fermentation, and photocatalysis. Subsequently, ANN and ANN hybrid studies implemented in HP research were evaluated. Finally, statistics of hybrid studies with ANN are given, and future research proposals and hot research topics are briefly discussed. This research, which touches upon the types of ANNs applied to HP methods and their comparison with other modeling techniques, has an essential place in its field.     

System optimization for effective hydrogen production via anaerobic digestion and biogas steam reforming

To construct a system for the effective hydrogen production from food waste, the conditions of anaerobic digestion and biogas reforming have been investigated and optimized. The type of agitator and reactor shape affect the performance of anaerobic digestion reactors. Reactors with a cubical shape and hydrofoil agitator exhibit high performance due to the enhanced axial flow and turbulence as confirmed by simulation of computational fluid dynamics. The stability of an optimized anaerobic digestion reactor has been tested for 60 days. As a result, 84 L of biogas is produced from 1 kg of food waste. Reaction conditions, such as reaction temperature and steam/methane ratio, affect the biogas steam reforming reaction. The reactant conversions, product yields, and hydrogen production are influenced by reaction conditions. The optimized reaction conditions include a reaction temperature of 700 °C and H₂O/CH₄ ratio of 1.0. Under these conditions, hydrogen can be produced via steam reforming of biogas generated from a two-stage anaerobic digestion reactor for 25 h without significant deactivation and fluctuation.     

Thermophysical properties of the liquid organic hydrogen carrier system based on diphenylmethane with the byproducts fluorene or perhydrofluorene

Fluorene (H0-F) and perhydrofluorene (H12-F) represent process-related byproducts formed by a dehydrocyclization step in the liquid organic hydrogen carrier (LOHC) system based on diphenylmethane (H0-DPM) and dicyclohexylmethane (H12-DPM). The influence of these byproducts on the liquid viscosity, surface tension, and liquid density of the DPM-based system was experimentally determined by studying three dehydrogenated binary mixtures with H0-F mole fractions of 0.05, 0.10, and 0.20 as well as one hydrogenated binary mixture with an H12-F mole fraction of 0.10 close to 0.1 MPa from (283–573) K. The densities increase with increasing share of H0-F or H12-F by around 1% per added byproduct mole fraction of 0.1. For the surface tension, an increase relative to the values of H0-DPM or H12-DPM by up to 6% is found. The addition of H0-F to H0-DPM or H12-F to H12-DPM yields a relative increase in viscosity by up to 9% at the lowest temperature studied.     

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.     

Performance analysis of metal hydride based simultaneous cooling and heat transformation system

The performance of metal hydrides based simultaneous cooling and heat transformation system (MHCHT) using a combination of La_0.9Ce_0.1Ni₅–MmNi_4.4Al_0.6–MmNi_3.7Co_0.7Mn_0.3Al_0.3 hydrides is evaluated. The MHCHT is thermodynamically analysed using statically and dynamically measured PCIs and thermodynamic properties. In addition, a set of governing equations is solved in order to study the heat and hydrogen transfer between the reaction beds. The experimental PCI measurement data are compared with the numerical results and a reasonably good agreement is observed between them. From the results, the slope and hysteresis factors are determined for further thermal analyses. It is observed that the performance parameters i.e. cooling capacity, heat transformation capacity and coefficient of performance (COP) of MHCHT are significantly decreased by 42.4%, 26.7% and 19.1% respectively when dynamic property data are considered compared to static property data. In addition, the thermodynamic cycle is analysed by considering the variation in pressure during hydrogen transfer process between the metal hydride beds.     

Transition metal/carbon nanoparticle composite catalysts as platinum substitutes for bioelectrochemical hydrogen production using microbial electrolysis cells

Various metal nanoparticle catalysts supported on Vulcan XC-72 and carbon-nanomaterial-based catalysts were fabricated and compared and assessed as substitutes of platinum in microbial electrolysis cells (MECs). The metal-nanoparticle-loaded cathodes exhibited relatively better hydrogen production and electrochemical properties than cathodes coated with carbon nanoparticles (CNPs) and carbon nanotubes (CNTs) did. Catalysts containing Pt (alone or mixed with other metals) most effectively produced hydrogen in terms of overall conversion efficiency, followed by Ni alone or combined with other metals in the order: Pt/C (80.6%) > PtNi/C (76.8%) > PtCu/C (72.6%) > Ni/C (73.0%) > Cu/C (65.8%) > CNPs (47.0%) > CNTs (38.9%) > plain carbon felt (38.7%). Further, in terms of long-term catalytic stability, Ni-based catalysts degraded to a lesser extent over time than did the Cu/C catalyst (which showed the maximum degradation). Overall, the hydrogen generation efficiency, catalyst stability, and current density of the Ni-based catalysts were almost comparable to those of Pt catalysts. Thus, Ni is an effective and inexpensive alternative to Pt catalysts for hydrogen production by MECs.     

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.     

Effect of organic fraction of municipal solid waste addition to high rate activated sludge system for hydrogen production from carbon rich waste sludge

Municipal solid waste has been used for bio-methane production for many years. However, both methane and carbon dioxide that is produced during bio-methanization increases the greenhouse gas emissions; therefore, hydrogen production can be one of the alternatives for energy production from waste. Hydrogen production from the organic substance was studied in this study with the waste activated sludge from the municipal wastewater treatment. High rated activated sludge (HRAS) process was applied for the treatment to reduce energy consumption and enhance the organic composition of WAS. The highest COD removal (76%) occurred with the 12 g/L organic fraction of municipal solid waste (OFMSW) addition at a retention time of 120 min. The maximum hydrogen and methane yields for the WAS was 18.9 mL/g VS and 410 mL/g VS respectively. Total carbon emission per g VS of the substrate (OFMSW + waste activated sludge) was found as 0.087 mmol CO₂ and 28.16 mmol CO₂ for dark fermentation and bio-methanization respectively. These kinds of treatment technologies required for the wastewater treatment plantcompensate it some of the energy needs in a renewable source. In this way, the HRAS process decreases the energy requirement of wastewater treatment plant, and carbon-rich waste sludge enables green energy production via lower carbon emissions.     

Interplay between hydrogen production and photosynthesis in a green alga expressing an active photosystem I-hydrogenase chimera

We have previously created and expressed a chimeric polypeptide joining the PsaC subunit of Photosystem I (PSI) to the HydA2 hydrogenase of Chlamydomonas reinhardtii and demonstrated that it assembles into the PSI complex and feeds electrons directly to the hydrogenase domain, allowing for prolonged photobiological hydrogen production. Here we describe a new PSI-hydrogenase chimera using HydA1, the more abundant and physiologically active endogenous hydrogenase of this alga. When the PsaC-HydA1 polypeptide was expressed in a C. reinhardtii strain lacking endogenous hydrogenases, it was assembled into active PSI-HydA1 complexes that were accumulated at a level ～75% that of PSI, which is ～5 times higher than the PSI-HydA2 chimera. Hydrogen production by the chimera could be restored after complete inactivation by oxygen without requiring new synthesis of PSI or the PsaC-HydA1 polypeptide, demonstrating that the complex could be repaired in vivo. The PSI-HydA1 chimera reduces ferredoxin in vivo to such an extent that it can drive the Calvin-Benson-Bassham cycle, leading to high O₂ production rates, and eventually resulting in inactivation of the hydrogenase; use of media that drastically diminished CO₂ fixation and an O₂-scavenging material allowed H₂ production for at least 4 days.     

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.     

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.     

Enhanced methane production using pretreated sludge in MEC-AD system: Performance,microbial activity,and implications at different applied voltages

Although various pretreatment methods are employed to promote sludge hydrolysis and thereby promoting methane production in the subsequent microbial electrolysis cell assisted anaerobic digestion (MEC-AD) system, the questions arise are, “which pretreatment method on waste activated sludge (WAS) maximises the sludge hydrolysis and what is the optimal applied voltage on anaerobic digestion (AD) to stimulates the direct interspecies electron transfer (DIET) performance and thereby accelerating the methane production fed with pretreated WAS?” was still unanswered. Herein, firstly, a series of pretreatment methods to hydrolyse and mineralise the organic matter of WAS was performed to evaluate solubilization efficiency and thereafter, the influence of different applied voltages (0.3 V, 0.6 V, and 0.9 V) on coupled MEC-AD reactors fed with pretreated WAS was investigated to apprehend the DIET promotion for methane production. The results indicated that in MEC-AD reactors, the methane yield increased by 27.2%, 44.8%, and 37.3% when the applied voltages were 0.3 V, 0.6 V, and 0.9 V, respectively. Therefore, the alkaline-thermal pretreatment (ATP) enhanced the sludge hydrolysis in WAS, followed by an applied voltage of 0.6 V in the MEC-AD reactor fed with pretreated WAS, enhanced methane production under DIET stimulation induced by the increased abundance of electroactive microorganisms (EAM) and the advanced electron transfer. Besides, the energy balance estimation validates that with an applied voltage of 0.6 V in MEC-AD could achieve higher net energy input.     

HRT control as a strategy to enhance continuous hydrogen production from sugarcane juice under mesophilic and thermophilic conditions in AFBRs

The objective of this study was to evaluate the effects of hydraulic retention time (HRT) (8–1 h) on H₂ production from sugarcane juice (5000 mg COD L⁻¹) in mesophilic (30 °C, AFBR-30) and thermophilic (55 °C, AFBR-55) anaerobic fluidized bed reactors (AFBRs). At HRTs of 8 and 1 h in AFBR-30, the H₂ production rates were 60 and 116 mL H₂ h⁻¹ L⁻¹, the hydrogen yields were 0.60 and 0.10 mol H₂ mol⁻¹ hexose, and the highest bacterial diversities were 2.47 and 2.34, respectively. In AFBR-55, the decrease in the HRT from 8 to 1 h increased the hydrogen production rate to 501 mL H₂ h⁻¹ L⁻¹ at the HRT of 1 h. The maximum hydrogen yield of 1.52 mol H₂ mol⁻¹ hexose was observed at the HRT of 2 h and was associated with the lowest bacterial diversity (0.92) and highest bacterial dominance (0.52).