Production & Supply Chain
Time-phased Geospatial Siting Analysis for Renewable Hydrogen Production Facilities under a Billion-kilogram-scale Build-out using California as an Example
Jun 2022
Publication
For renewable hydrogen to be a significant part of the future decarbonized energy and transportation sectors a rapid and massive build-out of hydrogen production facilities will be needed. This paper describes a geospatial modeling approach to identifying the optimal locations for renewable hydrogen fuel production throughout the state of California based on least-cost generation and transport. This is accomplished by (1) estimating and projecting California renewable hydrogen demand scenarios through the year 2050 (2) identifying feedstock locations (3) excluding areas not suitable for development and (4) selecting optimal site locations using commercial geospatial modeling software. The findings indicate that there is a need for hundreds of new renewable hydrogen production facilities in the decades preceding the year 2050. In selecting sites for development feedstock availability by technology type is the driving factor."
Machine Learning-based Energy Optimization for On-site SMR Hydrogen Production
Jun 2021
Publication
The production and application of hydrogen an environmentally friendly energy source have been attracting increasing interest of late. Although steam methane reforming (SMR) method is used to produce hydrogen it is difficult to build a high-fidelity model because the existing equation-oriented theoretical model cannot be used to clearly understand the heat-transfer phenomenon of a complicated reforming reactor. Herein we developed an artificial neural network (ANN)-based data-driven model using 485710 actual operation datasets for optimizing the SMR process. Data preprocessing including outlier removal and noise filtering was performed to improve the data quality. A model with high accuracy (average R2 = 0.9987) was developed which can predict six variables through hyperparameter tuning of a neural network model as follows: syngas flow rate; CO CO2 CH4 and H2 compositions; and steam temperature. During optimization the search spaces for nine operating variables namely the natural gas flow rate for the feed and fuel hydrogen flow rate for desulfurization water flow rate and temperature air flow rate SMR inlet temperature and pressure and low-temperature shift (LTS) inlet temperature were defined and applied to the developed model for predicting the thermal efficiencies for 387420489 cases. Subsequently five constraints were established to consider the feasibility of the process and the decision variables with the highest process thermal efficiency were determined. The process operating conditions showed a thermal efficiency of 85.6%.
Modeling of a High Temperature Heat Exchanger to Supply Hydrogen Required by Fuel Cells Through Reforming Process
Sep 2021
Publication
Hydrogen as a clean fuel and a new energy source can be produced by various methods. One of these common and economical methods of hydrogen production is hydrocarbon vapor modification. This research studies hydrogen production using a propane steam reforming process inside a high temperature heat exchanger. The application of this high temperature heat exchanger in the path of the power supply line is a fuel cell stack unit to supply the required hydrogen of the device. The heat exchanger consists of a set of cylindrical tubes housed inside a packed-bed called a reformer. The energy required to perform the reaction is supplied through these tubes in which high temperature gas is injected and the heat exchanger is insulated to prevent energy loss. The results show that at maximum temperature and velocity of hot gases (900 K and 1.5 m s−1 ) complete consumption of propane can be observed before the outlet of the reformer. Also in the mentioned conditions the maximum hydrogen production (above 92%) is obtained. The best permeability under which the system can perform best is 1×10−9 m2.
Hydrogen Production from Surplus Electricity Generated by an Autonomous Renewable System: Scenario 2040 on Grand Canary Island, Spain
Sep 2022
Publication
The electrification of final energy uses is a key strategy to reach the desired scenario with zero greenhouse gas emissions. Many of them can be electrified with more or less difficulty but there is a part that is difficult to electrify at a competitive cost: heavy road transport maritime and air transport and some industrial processes are some examples. For this reason the possibility of using other energy vectors rather than electricity should be explored. Hydrogen can be considered a real alternative especially considering that this transition should not be carried out immediately because initially the electrification would be carried out in those energy uses that are considered most feasible for this conversion. The Canary Islands’ government is making considerable efforts to promote a carbon-free energy mix starting with renewable energy for electricity generation. Still in the early–mid 2030s it will be necessary to substitute heavy transport fossil fuel. For this purpose HOMER software was used to analyze the feasibility of hydrogen production using surplus electricity produced by the future electricity system. The results of previous research on the optimal generation MIX for Grand Canary Island based exclusively on renewable sources were used. This previous research considers three possible scenarios where electricity surplus is in the range of 2.3–4.9 TWh/year. Several optimized scenarios using demand-side management techniques were also studied. Therefore based on the electricity surpluses of these scenarios the optimization of hydrogen production and storage systems was carried out always covering at least the final hydrogen demand of the island. As a result it is concluded that it would be possible to produce 3.5 × 104 to 7.68 × 104 t of H2/year. In these scenarios 3.15 × 105 to 6.91 × 105 t of water per year would be required and there could be a potential production of 2.8 × 105 to 6.14 × 105 t of O2 per year.
Roadmap to Hybrid Offshore System with Hydrogen and Power Co-generation
Sep 2021
Publication
Constrained by the expansion of the power grid the development of offshore wind farms may be hindered and begin to experience severe curtailment or restriction. The combination of hydrogen production through electrolysis and hydrogen-to-power is considered to be a potential option to achieve the goal of low-carbon and energy security. This work investigates the competitiveness of different system configurations to export hydrogen and/or electricity from offshore plants with particular emphasis on unloading the mixture of hydrogen and electricity to end-users on land. Including the levelized energy cost and net present value a comprehensive techno-economic assessment method is proposed to analyze the offshore system for five scenarios. Assuming that the baseline distance is 10 km the results show that exporting hydrogen to land through pipelines shows the best economic performance with the levelized energy cost of 3.40 $/kg. For every 10 km increase in offshore distance the net present value of the project will be reduced by 5.69 MU$ and the project benefit will be positive only when the offshore distance is less than 53.5 km. An important finding is that the hybrid system under ship transportation mode is not greatly affected by the offshore distance. Every 10% increase in the proportion of hydrogen in the range of 70%–100% can increase the net present value by 1.43–1.70 MU$ which will increase by 7.36–7.37 MU$ under pipeline transportation mode. Finally a sensitivity analysis was carried out to analyze the wind speed electricity and hydrogen prices on the economic performance of these systems.
The Impact of Operating Conditions on the Performance of a CH4 Dry Reforming Membrane Reactor for H2 Production
May 2020
Publication
Biogas is a promising resource for the production of H2 since it liberates energy by recycling waste along with the reduction of CO2. In this paper the biogas dry reforming membrane reactor is proposed to produce H2 for use in fuel cells. Pd/Cu alloy membrane is used to enhance the performance of the biogas dry reforming reactor. This study aims at understanding the effect of operating parameters such as feed ratio of sweep gas pressure in the reactor and reaction temperature on the performance of the biogas dry reforming membrane reactor. The effect of the molar ratio of the supplied CH4:CO2 feed ratio of the sweep gas and the valve located at the outlet of the reaction chamber on the performance of biogas dry reforming are investigated. Besides the thermal efficiency of the proposed reactor is also evaluated. The results show that the concentration of H2 in the closed valve condition is higher than that of the open valve and the optimum feed ratio of the sweep gas to produce H2 is 1 irrespective of the molar ratio of supplied CH4:CO2. Also H2 selectivity and CO selectivity increases and decreases respectively when the reaction temperature increases irrespective of the molar ratio of supplied CH4:CO2. Therefore the thermal efficiency of the closed valve is higher than that of the opened valve. Also the thermal efficiency is the maximum when the feed ratio of the sweep gas is 1 due to high H2 production performance.
An Investigation of a (Vinylbenzyl) Trimethylammonium and N-Vinylimidazole-Substituted Poly (Vinylidene Fluoride-Co-Hexafluoropropylene) Copolymer as an Anion-Exchange Membrane in a Lignin-Oxidising Electrolyser
Jun 2021
Publication
Electrolysis is seen as a promising route for the production of hydrogen from water as part of a move to a wider “hydrogen economy”. The electro-oxidation of renewable feedstocks offers an alternative anode couple to the (high-overpotential) electrochemical oxygen evolution reaction for developing low-voltage electrolysers. Meanwhile the exploration of new membrane materials is also important in order to try and reduce the capital costs of electrolysers. In this work we synthesise and characterise a previously unreported anion-exchange membrane consisting of a fluorinated polymer backbone grafted with imidazole and trimethylammonium units as the ion-conducting moieties. We then investigate the use of this membrane in a lignin-oxidising electrolyser. The new membrane performs comparably to a commercially-available anion-exchange membrane (Fumapem) for this purpose over short timescales (delivering current densities of 4.4 mA cm−2 for lignin oxidation at a cell potential of 1.2 V at 70 °C during linear sweep voltammetry) but membrane durability was found to be a significant issue over extended testing durations. This work therefore suggests that membranes of the sort described herein might be usefully employed for lignin electrolysis applications if their robustness can be improved.
Selected Aspects of Hydrogen Production via Catalytic Decomposition of Hydrocarbons
Feb 2021
Publication
Owing to the high hydrogen content hydrocarbons are considered as an alternative source for hydrogen energy purposes. Complete decomposition of hydrocarbons results in the formation of gaseous hydrogen and solid carbonaceous by-product. The process is complicated by the methane formation reaction when the released hydrogen interacts with the formed carbon deposits. The present study is focused on the effects of the reaction mixture composition. Variations in the inlet hydrogen and methane concentrations were found to influence the carbon product’s morphology and the hydrogen production efficiency. The catalyst containing NiO (82 wt%) CuO (13 wt%) and Al2O3 (5 wt%) was prepared via a mechanochemical activating procedure. Kinetics of the catalytic process of hydrocarbons decomposition was studied using a reactor equipped with McBain balances. The effects of the process parameters were explored in a tubular quartz reactor with chromatographic analysis of the outlet gaseous products. In the latter case the catalyst was loaded piecemeal. The texture and morphology of the produced carbon deposits were investigated by nitrogen adsorption and electron microscopy techniques.
How Do Dissolved Gases Affect the Sonochemical Process of Hydrogen Production: An Overview of Thermodynamic and Mechanistic Effects – On the “Hot Spot Theory”
Dec 2020
Publication
Although most of researchers agree on the elementary reactions behind the sonolytic formation of molecular hydrogen (H2) from water namely the radical attack of H2O and H2O2 and the free radicals recombination several recent papers ignore the intervention of the dissolved gas molecules in the kinetic pathways of free radicals and hence may wrongly assess the effect of dissolved gases on the sonochemical production of hydrogen. One may fairly ask to which extent is it acceptable to ignore the role of the dissolved gas and its eventual decomposition inside the acoustic cavitation bubble? The present opinion paper discusses numerically the ways in which the nature of dissolved gas i.e. N2 O2 Ar and air may influence the kinetics of sonochemical hydrogen formation. The model evaluates the extent of direct physical effects i.e. dynamics of bubble oscillation and collapse events if any against indirect chemical effects i.e. the chemical reactions of free radicals formation and consequently hydrogen emergence it demonstrates the improvement in the sonochemical hydrogen production under argon and sheds light on several misinterpretations reported in earlier works due to wrong assumptions mainly related to initial conditions. The paper also highlights the role of dissolved gases in the nature of created cavitation and hence the eventual bubble population phenomena that may prevent the achievement of the sonochemical activity. This is particularly demonstrated experimentally using a 20 kHz Sinaptec transducer and a Photron SA 5 high speed camera in the case of CO2-saturated water where degassing bubbles are formed instead of transient cavitation.
Suitable Site Selection for Solar‐Based Green Hydrogen in Southern Thailand Using GIS‐MCDM Approach
May 2022
Publication
Climate change mitigation efforts are in dire need of greener and more versatile fuel al‐ ternatives to fossil fuels. Green hydrogen being both renewable and flexible has the potential to offset fossil fuels as the primary fuel source. Countries around the world are planning to develop their green hydrogen industries and accurate potential assessment is vital. This study employed the consolidation of a geographic information system (GIS) and the analytical hierarchy process (AHP) technique of multicriteria decision making (MCDM) for the potential assessment of green hydrogen in southern Thailand through the selection of suitable sites for solar‐based green hy‐ drogen production. Technical economic and environmental criteria with 10 sub‐criteria were con‐ sidered for the selection of suitable sites. With 0.243 (24.3%) weight the distance from protected areas turned out to be the most important sub‐criterion whereas the criterion of elevation with a 0.017 (1.7%) score was considered the least important. Southern Thailand is a well‐suited area for solar‐based green hydrogen production with a 4302 km2 area of high suitability and a 3350 km2 area of moderate suitability. These suitable areas can be utilized to develop the green hydrogen industry of Thailand and the method developed can be employed for the assessment of green hydrogen potential in other parts of the country. Studies like these are vital for the development of green hydrogen road maps for Thailand to develop its hydrogen policy and promote investments in the sector.
Water Photo-Oxidation Reaction on Clean and Doped Two-Dimensional Graphitic C2N
Apr 2020
Publication
In the search for new efficient photo-catalysts for hydrogen production through water splitting the main attention has been paid to tuning the band gap width and its position with respect to vacuum level. However actual electro-catalytic activity for the water oxidation reaction on a catalyst surface is no less important than those quantities. In this work we evaluate from first principles the thermodynamics of the reaction on relatively new candidates for water splitting: two-dimensional C2N and that doped with phosphorus. We find that the 4-step reaction usually expected for water splitting will not proceed on these systems resulting in oxygen atoms left strongly adsorbed to the surface. Another option a 3-step reaction is also found to be unfavorable. We also test an effect of higher oxygen coverage on the reaction thermodynamics as suggested elsewhere. We find that indeed the doubled O-coverage makes the 4-step reaction feasible for the doped C2N. However an unacceptably high anode potential is required to make this reaction proceed. We thus conclude that the materials under consideration may not be efficient electro-catalysts for water splitting.
Life Cycle Assessment of Hydrogen from Proton Exchange Membrane Water Electrolysis in Future Energy Systems
Jan 2019
Publication
This study discusses the potential of H2 production by proton exchange membrane water electrolysis as an effective option to reduce greenhouse gas emissions in the hydrogen sector. To address this topic a life cycle assessment is conducted to compare proton exchange membrane water electrolysis versus the reference process - steam methane reforming. As a relevant result we show that hydrogen production via proton exchange membrane water electrolysis is a promising technology to reduce CO2 emissions of the hydrogen sector by up to 75% if the electrolysis system runs exclusively on electricity generated from renewable energy sources. In a future (2050) base-load operation mode emissions are comparable to the reference system.
The results for the global warming potential show a strong reduction of greenhouse gas emissions by 2050. The thoroughly and in-depth modelled components of the electrolyser have negligible influence on impact categories; thus emissions are mainly determined by the electricity mix. With 2017 electricity mix of Germany the global warming potential corresponds to 29.5 kg CO2 eq. for each kg of produced hydrogen. Referring to the electricity mix we received from an energy model emissions can be reduced to 11.5 kg CO2 eq. in base-load operation by the year 2050. Using only the 3000 h of excess power from renewables in a year will allow for the reduction of the global warming potential to 3.3 kg CO2 eq. From this result we see that an environmentally friendly electricity mix is crucial for reducing the global warming impact of electrolytic hydrogen.
The results for the global warming potential show a strong reduction of greenhouse gas emissions by 2050. The thoroughly and in-depth modelled components of the electrolyser have negligible influence on impact categories; thus emissions are mainly determined by the electricity mix. With 2017 electricity mix of Germany the global warming potential corresponds to 29.5 kg CO2 eq. for each kg of produced hydrogen. Referring to the electricity mix we received from an energy model emissions can be reduced to 11.5 kg CO2 eq. in base-load operation by the year 2050. Using only the 3000 h of excess power from renewables in a year will allow for the reduction of the global warming potential to 3.3 kg CO2 eq. From this result we see that an environmentally friendly electricity mix is crucial for reducing the global warming impact of electrolytic hydrogen.
EU Hydrogen Strategy: A Case for Urgent Action Towards Implementation
Jul 2020
Publication
Interest in hydrogen as one route to the decarbonisation of energy systems has risen rapidly over the past few years with the publication of a number of hydrogen strategies from countries across the global energy economy. The momentum in Europe has increased sharply this month with the publication of an EU strategy to incorporate hydrogen into its plans for a net zero emission future. This Comment reviews the key elements of this strategy and provides an initial commentary on the main goals. We highlight the challenges that will be faced in meeting hydrogen production targets in particular via the “green hydrogen” route and analyse the plans for expanding the consumption of hydrogen in Europe. We also assess the infrastructure questions that will need to be answered if and when hydrogen takes on a greater role in the region and note the extensive state support that will be needed in the early years of the implementation of the strategy. Despite this though we applaud the ambition laid out by the EU and look forward to the provision of more detailed plans over the coming months and years.
Link to document on OIES website
Link to document on OIES website
Current Legislative Framework for Green Hydrogen Production by Electrolysis Plants in Germany
Mar 2022
Publication
(1) The German energy system transformation towards an entirely renewable supply is expected to incorporate the extensive use of green hydrogen. This carbon-free fuel allows the decarbonization of end-use sectors such as industrial high-temperature processes or heavy-duty transport that remain challenging to be covered by green electricity only. However it remains unclear whether the current legislative framework supports green hydrogen production or is an obstacle to its rollout. (2) This work analyzes the relevant laws and ordinances regarding their implications on potential hydrogen production plant operators. (3) Due to unbundling-related constraints potential operators from the group of electricity transport system and distribution system operators face lacking permission to operate production plants. Moreover ownership remains forbidden for them. The same applies to natural gas transport system operators. The case is less clear for natural gas distribution system operators where explicit regulation is missing. (4) It is finally analyzed if the production of green hydrogen is currently supported in competition with fossil hydrogen production not only by the legal framework but also by the National Hydrogen Strategy and the Amendment of the Renewable Energies Act. It can be concluded that in recent amendments of German energy legislation regulatory support for green hydrogen in Germany was found. The latest legislation has clarified crucial points concerning the ownership and operation of electrolyzers and the treatment of green hydrogen as a renewable energy carrier.
Numerical Study on Optics and Heat Transfer of Solar Reactor for Methane Thermal Decomposition
Oct 2021
Publication
This study aims to reduce greenhouse gas emissions to the atmosphere and effectively utilize wasted resources by converting methane the main component of biogas into hydrogen. Therefore a reactor was developed to decompose methane into carbon and hydrogen using solar thermal sources instead of traditional energy sources such as coal and petroleum. The optical distributions were analyzed using TracePro a Monte Carlo ray-tracing-based program. In addition Fluent a computational fluid dynamics program was used for the heat and mass transfer and chemical reaction. The cylindrical indirect heating reactor rotates at a constant speed to prevent damage by the heat source concentrated at the solar furnace. The inside of the reactor was filled with a porous catalyst for methane decomposition and the outside was surrounded by insulation to reduce heat loss. The performance of the reactor according to the cavity model was calculated when solar heat was concentrated on the reactor surface and methane was supplied into the reactor in an environment with a solar irradiance of 700 W/m2 wind speed of 1 m/s and outdoor temperature of 25 °C. As a result temperature methane mass fraction distribution and heat loss amounts for the two cavities were obtained and it was found that the effect on the conversion rate was largely dependent on a temperature over 1000 °C in the reactor. Moreover the heat loss of the full-cavity model decreased by 12.5% and the methane conversion rate increased by 33.5% compared to the semi-cavity model. In conclusion the high-temperature environment of the reactor has a significant effect on the increase in conversion rate with an additional effect of reducing heat loss.
The Hydrogen Grand Challenge
Apr 2016
Publication
More than 90% of the world’s growing energy demand is satisfied by fossil fuels (BP Statistical Review … 2015)1. One consequence of the unrestrained use of this technology is the continuous increase of the CO2 level of the atmosphere2. There are also the challenges associated with the limitations of the corresponding resources (Hubbert 1956; BP Statistical Review … 2015). Climate change as a consequence of the growing CO2 level (see text footnote 2 ESRL Global Monitoring Division 2015) has been identified as one of the most critical challenges facing mankind and requires immediate action: “The Paris Agreement aims to strengthen the global response to the threat of climate change ( … ) by low greenhouse gas emissions development in a manner that does not threaten food production” (United Nations Framework … 2015). How to reach the corresponding significant reduction of CO2 emission by 2050 is not defined in this document but it implies that mankind must transform its energy technology from a fossil to a renewable basis. Numerous studies and publications have indicated that the sun’s energy and its derivatives (wind water) are by far sufficient to supply world’s energy demand (see e.g. Smalley 2005; Züttel et al. 2010); but the large daily and seasonal power variation of renewable energy is an additional complication for a wide spread replacement of fossil energy by renewable energy.
Analysis of Standard and Innovative Methods for Allocating Upstream and Refinery GHG Emissions to Oil Products
Sep 2017
Publication
Alternative fuel policies need accurate and transparent methods to find the embedded carbon intensity of individual refinery products. This study investigates different ways of allocating greenhouse gases emissions deriving from refining and upstream crude oil supply. Allocation methods based on mass energy content economic value and innovatively added-value are compared with the marginal refining emissions calculated by CONCAWE’s linear-programming model to the average EU refinery which has been adopted as reference in EU legislation. Beside the most important transportation fuels (gasoline diesel kerosene/jet fuel and heavy fuel oil) the analysis extends to petroleum coke and refinery hydrogen. Moreover novel criteria based on the implications due to hydrogen usage by each fuel pathway have been introduced to test the consistency of the analyzed approaches. It is found that only two economic-based allocation methods are consistent with the introduced criteria. These two methods also give negative refinery emissions for heavy products which is coherent with the marginal emissions calculated through the CONCAWE refinery model. The recommended allocation methods are transparent and use only publicly available statistical data so they may be useful not only for future EU legislation but also in jurisdictions where a representative refinery model is not available.
Design and Multi-scenario Optimization of a Hybrid Power System Based on a Working Gas Turbine: Energy, Exergy, Exergoeconomic and Environmental Evaluation
Sep 2022
Publication
The rising demand for electricity along with the need to minimize carbon footprints has motivated academics to investigate the flexible and efficient integration of energy conversion technologies. A novel hybrid power generation system based on environmentally friendly and cost-effective technologies to recover the waste heat of a working gas turbine is designed and assessed in different scenarios of multi-objective optimization from energy exergy exergoeconomic and environmental (4E) perspectives. In the proposed system a steam methane reformer and a water gas shift reactor are utilized for hydrogen production while a polymer electrolyte membrane fuel cell (PEMFC) and steam/organic Rankine cycles are run for generating additional power. Aspen Plus in conjunction with Fortran Microsoft Excel and MATLAB is used to model and simulate the designed plant. The response surface methodology (RSM) is utilized to determine accurate surrogate models to describe the evaluation criteria and the Non-dominated Sorting Genetic Algorithm II technique is employed to seek the optimal conditions. Moreover TOPSIS and LINMAP decision-making approaches are used to find the best final solution among Pareto frontiers. The analysis of variance (ANOVA) and sensitivity analysis are also applied to evaluate the importance of the design variables. In this regard three single-objective optimizations and four multi-objective optimization scenarios based on the maximization of the ecological coefficient of performance (ECOP) and the minimization of CO2 emissions and total system product cost (C˙ p) are carried out. It is demonstrated that the system’s evaluation criteria have the highest and lowest sensitivity to the variation of reformer temperature and ORC pressure respectively. From the triple-objective optimization procedure the decision variables including reformer temperature ORC pressure Rankine cycle I pressure and Rankine cycle II pressure are 544 ◦C 4.35 bar 158.12 bar and 52.82 bar respectively. At these conditions the total hybrid system’s energy efficiency exergy efficiency exergy destruction net generated power and total investment cost rate are 45.96% 46.83% 215.72 MW 203.67 MW and 9791 $/h respectively. The findings of this paper conclude that it is necessary to address all objective functions simultaneously in the system’s ultimate optimum design. Furthermore the objective of this paper becomes even more apparent when there is no choice but to cut greenhouse gas emissions while also addressing the rising global energy demand.
Energy and Economic Costs of Chemical Storage
May 2020
Publication
The necessity of neutralizing the increase of the temperature of the atmosphere by the reduction of greenhouse gas emissions in particular carbon dioxide (CO2) as well as replacing fossil fuels leads to a necessary energy transition that is already happening. This energy transition requires the deployment of renewable energies that will replace gradually the fossil fuels. As the renewable energy share increases energy storage will become key to avoid curtailment or polluting back-up systems. This paper considers a chemical storage process based on the use of electricity to produce hydrogen by electrolysis of water. The obtained hydrogen (H2) can then be stored directly or further converted into methane (CH4 from methanation if CO2 is available e.g. from a carbon capture facility) methanol (CH3OH again if CO2 is available) and/or ammonia (NH3 by an electrochemical process). These different fuels can be stored in liquid or gaseous forms and therefore with different energy densities depending on their physical and chemical nature. This work aims at evaluating the energy and the economic costs of the production storage and transport of these different fuels derived from renewable electricity sources. This applied study on chemical storage underlines the advantages and disadvantages of each fuel in the frame of the energy transition.
Hydrogen Bubble Growth in Alkaline Water Electrolysis: An Immersed Boundary Simulation Study
Nov 2022
Publication
Enhancing the efficiency of industrial water electrolysis for hydrogen production is important for the energy transition. In electrolysis hydrogen is produced at the cathode which forms bubbles due to the diffusion of dissolved hydrogen in the surrounding supersaturated electrolyte. Hydrogen (and oxygen) bubbles play an important role in the achievable electrolysis efficiency. The growth of the bubbles is determined by diffusive and convective mass transfer. In turn the presence and the growth of the hydrogen bubbles affect the electrolysis process at the cathode.<br/>In the present study we simulate the growth of a single hydrogen bubble attached to a vertical cathode in a 30 wt KOH solution in a cathodic compartment represented by a narrow channel. We solve the Navier-Stokes equations mass transport equations and potential equation for a tertiary current distribution. A sharp interface immersed boundary method with an artificial compressibility method for the pressure is employed. To verify the numerical accuracy of the method we performed a grid refinement study and checked the global momentum and hydrogen mass balances. We investigate the effects of flow rate and operation pressure upon bubble growth behaviour species concentrations potential and current density. We compare different cases in two ways: for the same time and for the same bubble radius. We observe that increasing the flow velocity leads to a small increase in efficiency. Increasing the operation pressure causes higher hydrogen density which slows down the bubble growth. It is remarkable that for a given bubble radius increasing the pressure leads to a small decrease in efficiency.
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