Production & Supply Chain
Numerical Analysis of VPSA Technology Retrofitted to Steam Reforming Hydrogen Plants to Capture CO2 and Produce Blue H2
Feb 2022
Publication
The increasing demand for energy and commodities has led to escalating greenhouse gas emissions the chief of which is represented by carbon dioxide (CO2). Blue hydrogen (H2) a lowcarbon hydrogen produced from natural gas with carbon capture technologies applied has been suggested as a possible alternative to fossil fuels in processes with hard-to-abate emission sources including refining chemical petrochemical and transport sectors. Due to the recent international directives aimed to combat climate change even existing hydrogen plants should be retrofitted with carbon capture units. To optimize the process economics of such retrofit it has been proposed to remove CO2 from the pressure swing adsorption (PSA) tail gas to exploit the relatively high CO2 concentration. This study aimed to design and numerically investigate a vacuum pressure swing adsorption (VPSA) process capable of capturing CO2 from the PSA tail gas of an industrial steam methane reforming (SMR)-based hydrogen plant using NaX zeolite adsorbent. The effect of operating conditions such as purge-to-feed ratio and desorption pressure were evaluated in relation to CO2 purity CO2 recovery bed productivity and specific energy consumption. We found that conventional cycle configurations namely a 2-bed 4-step Skarstrom cycle and a 2-bed 6-step modified Skarstrom cycle with pressure equalization were able to concentrate CO2 to a purity greater than 95% with a CO2 recovery of around 77% and 90% respectively. Therefore the latter configuration could serve as an efficient process to decarbonize existing hydrogen plants and produce blue H2.
Setting Thresholds to Define Indifferences and Preferences in PROMETHEE for Life Cycle Sustainability Assessment of European Hydrogen Production
Jun 2021
Publication
The Life Cycle Sustainability Assessment (LCSA) is a proven method for sustainability assessment. However the interpretation phase of an LCSA is challenging because many different single results are obtained. Additionally performing a Multi-Criteria Decision Analysis (MCDA) is one way—not only for LCSA—to gain clarity about how to interpret the results. One common form of MCDAs are outranking methods. For these type of methods it becomes of utmost importance to clarify when results become preferable. Thus thresholds are commonly used to prevent decisions based on results that are actually indifferent between the analyzed options. In this paper a new approach is presented to identify and quantify such thresholds for Preference Ranking Organization METHod for Enrichment Evaluation (PROMETHEE) based on uncertainty of Life Cycle Impact Assessment (LCIA) methods. Common thresholds and this new approach are discussed using a case study on finding a preferred location for sustainable industrial hydrogen production comparing three locations in European countries. The single LCSA results indicated different preferences for the environmental economic and social assessment. The application of PROMETHEE helped to find a clear solution. The comparison of the newly-specified thresholds based on LCIA uncertainty with default thresholds provided important insights of how to interpret the LCSA results regarding industrial hydrogen production.
A Multiobjective Optimization of a Catalyst Distribution in a Methane/Steam Reforming Reactor Using a Genetic Algorithm
May 2020
Publication
The presented research focuses on an optimization design of a catalyst distribution inside a small-scale methane/steam reforming reactor. A genetic algorithm was used for the multiobjective optimization which included the search for an optimum of methane conversion rate and a minimum of the difference between highest and lowest temperatures in the reactor. For the sake of computational time the maximal number of the segment with different catalyst densities was set to be thirty in this study. During the entire optimization process every part of the reactor could be filled either with a catalyst material or non-catalytic metallic foam. In both cases the porosity and pore size was also specified. The impact of the porosity and pore size on the active reaction surface and permeability was incorporated using graph theory and three-dimensional digital material representation. Calculations start with the generation of a random set of possible reactors each with a different catalyst distribution. The algorithm calls reforming simulation over each of the reactors and after obtaining concentration and temperature fields the algorithms calculated fitness function. The properties of the best reactors are combined to generate a new population of solutions. The procedure is repeated and after meeting the coverage criteria the optimal catalyst distribution was proposed. The paper is summarized with the optimal catalyst distribution for the given size and working conditions of the system.
Graphitic Carbon Nitride Heterojunction Photocatalysts for Solar Hydrogen Production
Sep 2021
Publication
Photocatalytic hydrogen production is considered as an ideal approach to solve global energy crisis and environmental pollution. Graphitic carbon nitride (g-C3N4) has received extensive consideration due to its facile synthesis stable physicochemical properties and easy functionalization. However the pristine g-C3N4 usually shows unsatisfactory photocatalytic activity due to the limited separation efficiency of photogenerated charge carriers. Generally introducing semiconductors or co-catalysts to construct g–C3N4–based heterojunction photocatalysts is recognized as an effective method to solve this bottleneck. In this review the advantages and characteristics of various types of g–C3N4–based heterojunction are analyzed. Subsequently the recent progress of highly efficient g–C3N4–based heterojunction photocatalysts in the field of photocatalytic water splitting is emphatically introduced. Finally a vision of future perspectives and challenges of g–C3N4–based heterojunction photocatalysts in hydrogen production are presented. Predictably this timely review will provide valuable reference for the design of efficient heterojunctions towards photocatalytic water splitting and other photoredox reactions.
Hydrogen Fuel and Electricity Generation from a New Hybrid Energy System Based on Wind and Solar Energies and Alkaline Fuel Cell
Apr 2021
Publication
Excessive consumption of fossil fuels has led to depletion of reserves and environmental crises. Therefore turning to clean energy sources is essential. However these energy sources are intermittent in nature and have problems meeting long-term energy demand. The option suggested by the researchers is to use hybrid energy systems. The aim of this paper is provide the conceptual configuration of a novel energy cycle based on clean energy resources. The novel energy cycle is composed of a wind turbine solar photovoltaic field (PV) an alkaline fuel cell (AFC) a Stirling engine and an electrolyzer. Solar PV and wind turbine convert solar light energy and wind kinetic energy into electricity respectively. Then the generated electricity is fed to water electrolyzer. The electrolyzer decomposes water into oxygen and hydrogen gases by receiving electrical power. So the fuel cell inlets are provided. Next the AFC converts the chemical energy contained in hydrogen into electricity during electrochemical reactions with by-product (heat). The purpose of the introduced cycle is to generate electricity and hydrogen fuel. The relationships defined for the components of the proposed cycle are novel and is examined for the first time. Results showed that the output of the introduced cycle is 10.5 kW of electricity and its electrical efficiency is 56.9%. In addition the electrolyzer uses 9.9 kW of electricity to produce 221.3 grams per hour of hydrogen fuel. The share of the Stirling engine in the output power of the cycle is 9.85% (1033.7 W) which is obtained from the dissipated heat of the fuel cell. In addition wind turbine is capable of generating an average of 4.1 kW of electricity. However 238.6 kW of cycle exergy is destroyed. Two different scenarios are presented for solar field design.
Main Hydrogen Production Processes: An Overview
May 2021
Publication
Due to its characteristics hydrogen is considered the energy carrier of the future. Its use as a fuel generates reduced pollution as if burned it almost exclusively produces water vapor. Hydrogen can be produced from numerous sources both of fossil and renewable origin and with as many production processes which can use renewable or non-renewable energy sources. To achieve carbon neutrality the sources must necessarily be renewable and the production processes themselves must use renewable energy sources. In this review article the main characteristics of the most used hydrogen production methods are summarized mainly focusing on renewable feedstocks furthermore a series of relevant articles published in the last year are reviewed. The production methods are grouped according to the type of energy they use; and at the end of each section the strengths and limitations of the processes are highlighted. The conclusions compare the main characteristics of the production processes studied and contextualize their possible use.
Catalytic and Photocatalytic Electrospun Nanofibers for Hydrogen Generation from Ammonia Borane Complex: A Review
Jul 2021
Publication
Hydrogen (H2) is a promising renewable energy source that can replace fossil fuels since it can solve several environmental and economic issues. However the widespread usage of H2 is constrained by its storage and safety issues. Many researchers consider solid materials with an excellent capacity for H2 storage and generation as the solution for most H2-related issues. Among solid materials ammonia borane (abbreviated hereafter as AB) is considered one of the best hydrogen storage materials due to its extraordinary H2 content and small density. However the process must be conducted in the presence of efficient catalysts to obtain a reasonable amount of generated H2. Electrospun nanofibrous catalysts are a new class of efficient catalysts that involves the usage of polymers. Here a comprehensive review of the ceramic-supported electrospun NF catalysts for AB hydrolysis is presented with a special focus on catalytic and photolytic performance and preparation steps. Photocatalytic AB hydrolysis was discussed in detail due to its importance and promising results. AB photocatalytic hydrolysis mechanisms under light were also explained. Electrospun catalysts show excellent activity for AB hydrolysis with good recyclability. Kinetics studies show that the AB hydrolysis reaction is independent of AB concentration and the first-order reaction of NF catalysts.
A Novel Self-Assembly Strategy for the Fabrication of Nano-Hybrid Satellite Materials with Plasmonically Enhanced Catalytic Activity
Jun 2021
Publication
The generation of hydrogen from water using light is currently one of the most promising alternative energy sources for humankind but faces significant barriers for large-scale applications due to the low efficiency of existing photo-catalysts. In this work we propose a new route to fabricate nano-hybrid materials able to deliver enhanced photo-catalytic hydrogen evolution combining within the same nanostructure a plasmonic antenna nanoparticle and semiconductor quantum dots (QDs). For each stage of our fabrication process we probed the chemical composition of the materials with nanometric spatial resolution allowing us to demonstrate that the final product is composed of a silver nanoparticle (AgNP) plasmonic core surrounded by satellite Pt decorated CdS QDs (CdS@Pt) separated by a spacer layer of SiO2 with well-controlled thickness. This new type of photoactive nanomaterial is capable of generating hydrogen when irradiated with visible light displaying efficiencies 300% higher than the constituting photo-active components. This work may open new avenues for the development of cleaner and more efficient energy sources based on photo-activated hydrogen generation.
A Holistic Consideration of Megawatt Electrolysis as a Key Component of Sector Coupling
May 2022
Publication
In the future hydrogen (H2) will play a significant role in the sustainable supply of energy and raw materials to various sectors. Therefore the electrolysis of water required for industrial‐ scale H2 production represents a key component in the generation of renewable electricity. Within the scope of fundamental research work on cell components for polymer electrolyte membrane (PEM) electrolyzers and application‐oriented living labs an MW electrolysis system was used to further improve industrial‐scale electrolysis technology in terms of its basic structure and systems‐ related integration. The planning of this work as well as the analytical and technical approaches taken along with the essential results of research and development are presented herein. The focus of this study is the test facility for a megawatt PEM electrolysis stack with the presentation of the design processing and assembly of the main components of the facility and stack.
Dynamic Model to Expand Energy Storage in Form of Battery and Hydrogen Production Using Solar Powered Water Electrolysis for Off Grid Communities
Feb 2022
Publication
In this model we used a 50 WP photovoltaic panel to produce electrical energy. This electricity production was used directly and stored in a battery. In this design we coupled batteries and hydrogen as a means of storing energy. In case of overcharging the battery it will be attached with water electrolysis to convert the excess amount of chemical energy of the battery into hydrogen energy storage. Hydrogen will be stored as a compacted gas and in chemical storage. We used PEM (proton exchange membrane) electrolysis technologies to breakdown water molecules into hydrogen and oxygen which were then stored in the designed tanks. Different supply voltages were used in our practical readings with an average gaining of 22.8 mL/min on a voltage supply of 2. While using Ansys simulation software we extrapolated hydrogen production until reaching 300 mL/min on 12 V of supply (which represents 220% higher production). By using the second phase of this model hydrogen energy was converted back into electrical energy with the help of a PEM (proton exchange membrane) fuel cell when needed. This model explores the feasibility of energy storage in the form of hydrogen and chemical energy for off-grid communities and remote areas comprising batteries water electrolysis and fuel cells. The main purpose of hydrogen storage in this system is to store and handle the extra energy of system produced through PV panel and utilize it for any desired requirements.
Solar Thermochemical Hydrogen Production in the USA
Jul 2021
Publication
Hydrogen produced from renewable energy has the potential to decarbonize parts of the transport sector and many other industries. For a sustainable replacement of fossil energy carriers both the environmental and economic performance of its production are important. Here the solar thermochemical hydrogen pathway is characterized with a techno-economic and life-cycle analysis. Assuming a further increase of conversion efficiency and a reduction of investment costs it is found that hydrogen can be produced in the United States of America at costs of 2.1–3.2 EUR/kg (2.4–3.6 USD/kg) at specific greenhouse gas emissions of 1.4 kg CO2-eq/kg. A geographical potential analysis shows that a maximum of 8.4 × 1011 kg per year can be produced which corresponds to about twelve times the current global and about 80 times the current US hydrogen production. The best locations are found in the Southwest of the US which have a high solar irradiation and short distances to the sea which is beneficial for access to desalinated water. Unlike for petrochemical products the transport of hydrogen could potentially present an obstacle in terms of cost and emissions under unfavorable circumstances. Given a large-scale deployment low-cost transport seems however feasible.
Modelling Decentralized Hydrogen Systems: Lessons Learned and Challenges from German Regions
Feb 2022
Publication
Green hydrogen produced by power‐to‐gas will play a major role in the defossilization of the energy system as it offers both carbon‐neutral chemical energy and the chance to provide flexibility. This paper provides an extensive analysis of hydrogen production in decentralized energy systems as well as possible operation modes (H2 generation or system flexibility). Modelling was realized for municipalities—the lowest administrative unit in Germany thus providing high spatial resolution—in the linear optimization framework OEMOF. The results allowed for a detailed regional analysis of the specific operating modes and were analyzed using full‐load hours share of used negative residual load installed capacity and levelized cost of hydrogen to derive the operation mode of power‐to‐gas to produce hydrogen. The results show that power‐to‐gas is mainly characterized by constant hydrogen production and rarely provides flexibility to the system. Main drivers of this dominant operation mode include future demand for hydrogen and the fact that high full‐load hours reduce hydrogen‐production costs. However changes in the regulatory market and technical framework could promote more flexibility and support possible use cases for the central technology to succeed in the energy transition.
An Experimental Study of the Possibility of In Situ Hydrogen Generation within Gas Reservoirs
Aug 2021
Publication
Hydrogen can be generated in situ within reservoirs containing hydrocarbons through chemical reactions. This technology could be a possible solution for low-emission hydrogen production due to of simultaneous CO2 storage. In gas fields it is possible to carry out the catalytic methane conversion (CMC) if sufficient amounts of steam catalyst and heat are ensured in the reservoir. There is no confirmation of the CMC’s feasibility at relatively low temperatures in the presence of core (reservoir rock) material. This study introduces the experimental results of the first part of the research on in situ hydrogen generation in the Promyslovskoye gas field. A set of static experiments in the autoclave reactor were performed to study the possibility of hydrogen generation under reservoir conditions. It was shown that CMC can be realized in the presence of core and ex situ prepared Ni-based catalyst under high pressure up to 207 atm but at temperatures not lower than 450 ◦C. It can be concluded that the crushed core model improves the catalytic effect but releases carbon dioxide and light hydrocarbons which interfere with the hydrogen generation. The maximum methane conversion rate to hydrogen achieved at 450 ◦C is 5.8%
Artificial Neural Networks for Predicting Hydrogen Production in Catalytic Dry Reforming: A Systematic Review
May 2021
Publication
Dry reforming of hydrocarbons alcohols and biological compounds is one of the most promising and effective avenues to increase hydrogen (H2 ) production. Catalytic dry reforming is used to facilitate the reforming process. The most popular catalysts for dry reforming are Ni-based catalysts. Due to their inactivation at high temperatures these catalysts need to use metal supports which have received special attention from researchers in recent years. Due to the existence of a wide range of metal supports and the need for accurate detection of higher H2 production in this study a systematic review and meta-analysis using ANNs were conducted to assess the hydrogen production by various catalysts in the dry reforming process. The Scopus Embase and Web of Science databases were investigated to retrieve the related articles from 1 January 2000 until 20 January 2021. Forty-seven articles containing 100 studies were included. To determine optimal models for three target factors (hydrocarbon conversion hydrogen yield and stability test time) artificial neural networks (ANNs) combined with differential evolution (DE) were applied. The best models obtained had an average relative error for the testing data of 0.52% for conversion 3.36% for stability and 0.03% for yield. These small differences between experimental results and predictions indicate a good generalization capability.
Experimental Study and Thermodynamic Analysis of Hydrogen Production through a Two-Step Chemical Regenerative Coal Gasification
Jul 2019
Publication
Hydrogen as a strategy clean fuel is receiving more and more attention recently in China in addition to the policy emphasis on H2. In this work we conceive of a hydrogen production process based on a chemical regenerative coal gasification. Instead of using a lumped coal gasification as is traditional in the H2 production process herein we used a two-step gasification process that included coking and char-steam gasification. The sensible heat of syngas accounted for 15–20% of the total energy of coal and was recovered and converted into chemical energy of syngas through thermochemical reactions. Moreover the air separation unit was eliminated due to the adoption of steam as oxidant. As a result the efficiency of coal to H2 was enhanced from 58.9% in traditional plant to 71.6% in the novel process. Further the energy consumption decreased from 183.8 MJ/kg in the traditional plant to 151.2 MJ/kg in the novel process. The components of syngas H2 and efficiency of gasification are herein investigated through experiments in fixed bed reactors. Thermodynamic performance is presented for both traditional and novel coal to hydrogen plants.
Small-Scaled Production of Blue Hydrogen with Reduced Carbon Footprint
Aug 2021
Publication
This article reviews a method of hydrogen production based on partial non-catalytic oxidation of natural gas in an original synthesis gas generator. The working principles of the unit are similar to those of liquid-propellant rocket engines. This paper presents a description of the operation and technical characteristics of the synthesis gas generator. Its application in the creation of small-scaled plants with a capacity of up to 5–7 thousand m3/h of hydrogen is justified. Hydrogen production in the developed installation requires a two-stage method and includes a technological unit for producing a hydrogen-containing gas. Typical balance compositions of hydrogen-containing gas at the synthesis gas generator’s outlet are given. To increase the hydrogen concentration it is proposed to carry out a two-stage steam catalytic conversion of carbon monoxide contained in the hydrogen-containing gas at the synthesis gas generator’s outlet using a single Cu–Zn–cementcontaining composition. Based on thermodynamic calculations quasi-optimal modes of natural gas partial oxidation with oxygen are formulated and the results of material balance calculation for the installation are presented. In order to produce “blue” hydrogen the scheme of carbon dioxide separation and liquefaction is developed. The conclusion section of the paper contains the test results of a pilot demonstration unit and the recommendations for improving the technology and preventing soot formation.
Improving the Efficiency of PEM Electrolyzers through Membrane-Specific Pressure Optimization
Feb 2020
Publication
Hydrogen produced in a polymer electrolyte membrane (PEM) electrolyzer must be stored under high pressure. It is discussed whether the gas should be compressed in subsequent gas compressors or by the electrolyzer. While gas compressor stages can be reduced in the case of electrochemical compression safety problems arise for thin membranes due to the undesired permeation of hydrogen across the membrane to the oxygen side forming an explosive gas. In this study a PEM system is modeled to evaluate the membrane-specific total system efficiency. The optimum efficiency is given depending on the external heat requirement permeation cell pressure current density and membrane thickness. It shows that the heat requirement and hydrogen permeation dominate the maximum efficiency below 1.6 V while above the cell polarization is decisive. In addition a pressure-optimized cell operation is introduced by which the optimum cathode pressure is set as a function of current density and membrane thickness. This approach indicates that thin membranes do not provide increased safety issues compared to thick membranes. However operating an N212-based system instead of an N117-based one can generate twice the amount of hydrogen at the same system efficiency while only one compressor stage must be added.
Hydrogen Production in Methane Decomposition Reactor Using Solar Thermal Energy
Nov 2021
Publication
This study investigates the decomposition of methane using solar thermal energy as a heat source. Instead of the direct thermal decomposition of the methane at a temperature of 1200 ◦C or higher a catalyst coated with carbon black on a metal foam was used to lower the temperature and activation energy required for the reaction and to increase the yield. To supply solar heat during the reaction a reactor suitable for a solar concentrating system was developed. In this process a direct heating type reactor with quartz was initially applied and a number of problems were identified. An indirect heating type reactor with an insulated cavity and a rotating part was subsequently developed followed by a thermal barrier coating application. Methane decomposition experiments were conducted in a 40 kW solar furnace at the Korea Institute of Energy Research. Conversion rates of 96.7% and 82.6% were achieved when the methane flow rate was 20 L/min and 40 L/min respectively.
A Methodology for Assessing the Sustainability of Hydrogen Production from Solid Fuels
May 2010
Publication
A methodology for assessing the sustainability of hydrogen production using solid fuels is introduced in which three sustainability dimensions (ecological sociological and technological) are considered along with ten indicators for each dimension. Values for each indicator are assigned on a 10-point scale based on a high of 1 and a low of 0 depending on the characteristic of the criteria associated with each element or process utilizing data reported in the literature. An illustrative example is presented to compare two solid fuels for hydrogen production: coal and biomass. The results suggest that qualitative sustainability indicators can be reasonably defined based on evaluations of system feasibility and that adequate flexibility and comprehensiveness is provided through the use of ten indicators for each of the dimensions for every process or element involved in hydrogen production using solid fuels. Also the assessment index values suggest that biomasses have better sustainability than coals and that it may be advantageous to use coals in combination with biomass to increase their ecological and social sustainability. The sustainability assessment methodology can be made increasingly quantitative and is likely extendable to other energy systems but additional research and development is needed to lead to a more fully developed approach.
Past, Present and Near Future: An Overview of Closed, Running and Planned Biomethanation Facilities in Europe
Sep 2021
Publication
The power-to-methane technology is promising for long-term high-capacity energy storage. Currently there are two different industrial-scale methanation methods: the chemical one (based on the Sabatier reaction) and the biological one (using microorganisms for the conversion). The second method can be used not only to methanize the mixture of pure hydrogen and carbon dioxide but also to methanize the hydrogen and carbon dioxide content of low-quality gases such as biogas or deponia gas enriching them to natural gas quality; therefore the applicability of biomethanation is very wide. In this paper we present an overview of the existing and planned industrial-scale biomethanation facilities in Europe as well as review the facilities closed in recent years after successful operation in the light of the scientific and socioeconomic context. To outline key directions for further developments this paper interconnects biomethanation projects with the competitiveness of the energy sector in Europe for the first time in the literature. The results show that future projects should have an integrative view of electrolysis and biomethanation as well as hydrogen storage and utilization with carbon capture and utilization (HSU&CCU) to increase sectoral competitiveness by enhanced decarbonization.
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