Community Research and Development Information Service - CORDIS

FP7

SOL2HY2 Report Summary

Project ID: 325320
Funded under: FP7-JTI
Country: Italy

Final Report Summary - SOL2HY2 (Solar To Hydrogen Hybrid Cycles)

Executive Summary:
The FCH JU strategy has identified hydrogen production by water decomposition pathways powered by renewables such as solar energy to be a major component for sustainable and carbon-free hydrogen supply. It is well reported by previous studies and experiments that solar-powered thermo-chemical and hybrid cycles are capable to directly transfer concentrated sunlight into chemical energy by a series of chemical and electrochemical reactions.
Despite many thermo-chemical cycles have proven to be theoretically possible, only few of them might be feasible for practical realization. Previously finalized IEA Task 25 “High-temperature processes for hydrogen production” and some other parallel studies have ranked the hybrid-sulphur (HyS) cycle, also known as Westinghouse cycle, to be the most promising one. However, the main attention with respect to heat sources of the HyS cycle has been earlier focused on nuclear power as the H2 production was evaluated to be more economic compared to using pure solar power.
The challenges in HyS realization are mostly in materials (for electrolyser, concentrator, sulphuric acid cracker and balance of plant components), combined with the whole process optimization, which must be tailored to specific solar input and plant site location. The previous research projects have brought some solutions for these challenges, but still did not manage to present a consolidated, optimized plant and process design capable to comply with imposed costs, operational constrains and the whole process chain objectives. Materials stability, costs and the whole solar-based HyS-plant issues still remain unsolved.
It has been also identified that recent technology level and large-scale (400-800 MW) hydrogen production plant concepts are unlikely to achieve hydrogen costs below 3.0-3.5 €/kg. For smaller scale plants (which might be more reasonable), the H2 costs might be substantially higher. Additional associated technical and operational risks do not encourage industries to start such plants construction, which does not allow examination of realistic bottlenecks and make necessary improvements.
The SOL2HY2 project has focused on these bottle-necks solving materials research and development challenges, and demonstration of the relevant key components of the solar-powered, CO2-free hybrid water splitting cycles, complemented by their advanced modelling and processes simulation with added conditions-specific technical-economical assessment, optimization, quantification and evaluation.
The main results and achievements of the project are reported in the analysis, development and validation of new process flowsheets to include solar power input for key units of the plant, targeted at selected locations (specified by user) and allowing a flexible combination of different sources, inclusive of the new Outotec Open Cycle, where sulphuric acid is directed to be a commercial by-product to hydrogen rather than to be cracked and returned to the HyS cycle. This allows increase of the renewable sources share, improve waste heat utilization and ensure 24/7 plant operation, eliminating solar input instability, combined with reasonable capital costs and balance of the products streams. In the electrolyzer unit - the core of H2 generation - most of the challenges were solved - elimination of platinum-group metals catalysts, control of parasitic reactions, lowering the capital costs (e.g. ~3 times vs. existing analogues). The operation of the developed sulphuric acid cracking unit was successfully demonstrated on-sun at the solar tower Jülich (Germany).
An extra development of the software for plant design and optimisation was also carried out allowing the user to analyse and optimise the hydrogen production process in an interactive and guided way, through the use of user-friendly graphical user interfaces. This enables any user to evaluate technical and economical performance of a hydrogen production plant in any feasible location well before field studies.

Project Context and Objectives:
The FCH JU strategy has identified hydrogen production by water decomposition pathways powered by renewables such as solar energy to be a major component for sustainable and carbon-free hydrogen supply. It is well reported by previous studies and experiments that solar-powered thermochemical and hybrid cycles are capable to directly transfer concentrated sunlight into chemical energy by a series of chemical and electrochemical reactions. Despite the many thermochemical cycles have been proven to be theoretically possible, only few of them might be feasible for practical realization. Recently finalised IEA HIA Task 25 “High-temperature processes for hydrogen production” and other parallel studies have ranked hybrid-sulphur (HyS) cycle, also known as Westinghouse cycle, to be the most promising one. However, the main attention in heat source in HyS cycle has been focused on nuclear sources as the H2 production was evaluated to be more economic when combined with nuclear power than using pure solar power. The challenges in HyS realization remain mostly in materials (for electrolyser, concentrator, ac-id decomposer/cracker and balance of plant (BOP) components) and with the whole process optimisation, which must be tailored to specific solar input and plant site location. The previous research projects have brought some solutions for these challenges, but still did not manage to present the consolidated, optimized plant and process design capable to complain with imposed costs, and operational constrains and the whole process chain objectives. Materials stability, costs and the whole solar-based HyS-plant is-sues still remain unsolved.
It has been also identified that recent technology level and large-scale (400-800 MW) hydrogen production plant concepts are unlikely to achieve hydrogen costs below 3.0-3.5 €/kg, especially combined with renewable sources as nuclear power is not generally considered as a renewable source. For smaller scale plants the H2 costs might be substantially higher. Additional associated technical and operational risks do not encourage industries to start such plants construction, which does not allow examination of realistic bottlenecks and make necessary improvements. Adding uncertainty in solar power input, the plant availability variations impose additional challenges on such plant design.
The SOL2HY2 project has focused on applied bottle-necks solving materials research, development and demonstration of the relevant key components of the solar-powered, CO2-free hybrid water splitting cycles, complemented by their advanced modelling and processes simulation with added conditions-specific technical-economical assessment, optimization, quantification and evaluation.
In this project, the consortium has provided necessary solutions for solar-powered hybrid cycle in several stages. The solar HyS cycle remains the best long-term solution, but in order to ensure economic profitability of the HyS cycle, for the short-term opportunities the consortium starts with the integration of solar-power sources with new Outotec® Open Cycle. This cycle does produce H2SO4 together with hydrogen using different sources of SO2 from chemical and metallurgical plants and allows fast, scalable build-up of smaller scale hydrogen by-production plants without affecting acid production. Simplified structure, extra revenues from acid sales and highly efficient co-use of the existing plants drops H2 costs by about 50-75% vs. traditional HyS process designs (however, this naturally depends on the plant size and share of the renewable energy sources targeted). This allows further developments to concentrate in a real-scale size technology, learning from the pilot and smaller scale production and developing key solutions for solar HyS in medium to long term.
Besides providing key materials and process solutions, for the first time the whole production chain and flowsheet will be connected with multi-objective design and optimisation (MODAO) and meta-modelling algorithms ultimately leading to hydrogen plants and technology “green concepts” commercialization.

The general objectives of the project were:

• Development of the following key components: sulphur dioxide depolarised electrolyser (SDE), solar-powered flexible energy converter (solar-to-electric, solar-to-heat - STH), solar sulphuric acid cracker (SAC)
• Modelling, “green design”, development and testing of improved critical materials solutions for SDE and acid decomposer (SAC)
• Advanced multi-objective design and optimization (MODAO) of the materials and properties for solving the most critical issues (e.g. corrosion stability, catalytic activity, thermodynamics/kinetics; chemical, thermal-mechanical stability)
• Designing and running field tests of key blocks of the hybrid cycles (SDE, STH, SAC) with their performance analysis and feedback for the materials solutions validation
• Creation of a virtual SOL2HY2 plant concept/model with sub-blocks, its running and optimisation of the whole plant operations, analysing plant structure at specific locations and sites
• Technical-economic evaluation of the new process concept and development of the technology implementation on the market, including possible spin-off solutions such as materials, components and other relevant know-how
• Development of the flexible, semi-centralised H2 production plant options using interfaces to central parts of industrial process as the starting point for renewable hydrogen by-production

In order to achieve these general objectives, the project work has included the following specific steps, for instance:

• Creation of the virtual SOL2HY2 plant concept with sub-blocks, its running and optimization, for the flexible H2 production plant options using interfaces to central parts of industrial processes
• Development of sulphur dioxide-depolarised electrolyser (SDE) stack, testing and validation of new and critical materials solutions for low-temperature stages in SDE
• Designing and running field tests of key blocks (such as SDE) with their performance analysis and feedback for the materials solutions validation
• Development, evaluation, testing and validation of high-temperature solar-powered sulphuric acid cracker (SAC), including development and testing of the critical materials solutions for high-temperature stages
• Development of high-temperature concentrated solar power interface, thermal storage and heat management of the plant with testing of critical materials solutions for high- and low-temperature stages and designing of key blocks (STH) solutions with their performance analysis

Project Results:
The chemical part of the SOL2HY2 plant (hydrogen and sulfuric acid production, evaporation, concentration, cracking and gas handling) and the solar (high-temperature part) were iterated and prepared for the technical-economical analysis and optimization. Additionally exergy scenarios were considered and calculated.
Updated data and improvements for solar part, acid plant (BOP) and SDE have been analysed and added to the flowsheet options for better flexibility. These examined extra options were sulfur burning (especially for open cycle) and photovoltaic (PV) module; their effect on variation of renewables share and costs of the hydrogen production was analysed. For example, opening of the HyS cycle by 30% were shown to drop hydrogen costs twice (plant location in Almeria, 50 MW on mirrors, hydrogen demand 33 mol/s). Addition of a dedicated power block and other options may provide up to 100% renewable sources and minimize solar power input instability. Cycle opening of 20-30% seems to be optimal keeping sufficiently high renewable energy sources share, reasonable capital costs and balance of the products streams (for instance, the costs of SDE stack is roughly ~3 times lower vs. existing PEM electrolysers analogues).
In sulfur-dioxide depolarized electrolyser (SDE) new strategy has been adopted and proven to have substantial advantages. Unlike all other R&D efforts known worldwide, here the SDE was designed to operate at room temperature and near ambient pressure, yet eliminating platinum group metals catalysts completely. This has been achieved by manufacturing and testing of new coatings concepts, which do not contain Pt or Pd nevertheless possessing proper selectivity and catalytic activity towards SO2 oxidation. The cost effective option for bipolar plates was chosen as gold-plating of steel, which have been tested in 11 experimental SDE campaigns. This allowed substantial costs reduction (~3 times vs. analogue PEM designs).
For improved protection of coated bipolar plate especially in “worst case” scenarios when gold coating may fail, semiconductive "tetrene" (tetrahedrally bound carbon) back coating was employed. Bipolar plates with and without tetrene were tested in small and large cells, and an unusual effect of acceleration of the current density at medium potentials (closer to pure gold) has been observed (extra depolarization by ~0.1-0.2 V). Furthermore, tetrene back layer has shown almost five times less corrosion current indicating it as a new promising way to protect anode (even when Au top coating fails). The single SDE cell and 5-cell stack were successfully demonstrated in a closed loop, being perhaps the only lab in the world capable to operate SDE at ambient conditions and such low costs.
As there is no yet validated single-stage titration method for a fast determination of SO2 in acidic media, the new method instead of iodometry has been developed using bichromate as a redox agent. Validation experiments were made to estimate method reliability for determination of SO2 in acidic media, which confirmed higher precision, less scatter and better reproducibility. Since now no secondary titration needed and no disturbances from present sulfuric acid take place, it takes about 5-10 min per probe with titration machines (~10 times faster than iodometry).
The analysis of an alternative integration by solar trough with thermal storage optimization of the operational parameters and interfaces was carried out, also with the possibility to produce electricity by the solar plant in order to produce 100% “green” hydrogen. In addition the development of critical materials solutions for the solar to heat and storage systems were envisaged.
In order to study the integration between the chemical and the Concentrated Solar Power (CSP) plant, different scenarios were considered. Such scenarios differed for: plant location (as example: Alghero (Italy), San Diego (CA, USA), Almeria (Spain), Ben Guerir (Morocco), Luqa (Malta), Larnaca (Cyprus), Atacama (Chile); solar power design criterion (local yearly maximum, average or minimum irradiation); extent of cycle opening (completely closed (HyS) to completely open (Outotec Open Cycle); presence of a power block and photovoltaic (PV) options. For the latter, the integration of PV technology has been analysed as additional option to reduce the costs for DC electricity production.
For high-temperature sulfuric acid cracking, a preparation method for the iron oxide (Fe2O3) supported catalyst was developed and improved and about 20 kg were prepared and shipped for large scale tests. The target to produce a cheap and feasible catalyst material for an adiabatic post solar receiver reactor was achieved. A detailed acid evaporator model was developed simulating the on-sun operation of this component with a thermal efficiency of 80 %. The modeling work of the solar high-temperature receiver was published at several international conferences and in peer-reviewed journals.
The secondary concentrator was redesigned developing water cooling concept. A control program was implemented to operate the solar field in solar tower. The gas cell for the SO2 analysis system was redesigned and new customised measurement procedure was implemented, combined with control system was developed and LabVIEW based control programs. Sectioned SiC foam absorbers were manufactured and installed in the site. Pressure sensors (for absolute and differential measurement) were connected to inlet and outlet of the system.
A storage concept was selected for the solar SO3 decomposer requiring high temperature heat in the range of 750 – 1000 °C. In order to operate the reactor continuously a special honeycomb structure was proposed. At the same time the optimization of molten salts as storage medium to drive heat demanding operations at mid-temperatures and for electricity generation has being assessed.
BOP components are integrated stepwise by firstly testing and characterizing them individually, before combining and testing them in conjunction with the energy source and other BOP components. The flowsheets developed were used to calculate the energy requirements of each unit, in terms of electric power, medium and high temperature heat. Process solutions to use appropriate heat transfer fluids from the solar heat storage system were considered. Furthermore a detailed design of all units was carried out with the aim of assessing their cost. Functions relating the energy requirement and cost of all BOP units to their operating conditions were provided for the optimization of the plant. Design and costing analysis of all BOP equipment was completed and automated procedures for scaling up the equipment and associated investment costs were developed and integrated in the optimization software. Several approaches for handling the produced O2 were also considered and costs associated with such processes were also estimated.
Multi-objective design and optimization (MODAO) of the materials solutions was performed with dedicated software and exploitation of advanced numerical procedures. The optimization process was created with the integration of the up-to-dated spreadsheets and appropriate meta-modeling strategies, which are also useful to deal with the size of the solar plant (scaling). Based on designed Excel process calculator, HSC and AspenPlus flowsheets and set conditions, a unique software prototype was developed with three main features: 1) integration of the models; 2) analysis of the whole process through multivariate data analysis techniques and visualization of quantities of interest with several types of charts; 3) multi-objective optimization of the process. The software has been developed in Scilab (open source code) and it allows the user to analyze and optimize the hydrogen production process in an interactive and guided way, through the use of user-friendly graphical user interfaces.
The DEMO activities were carried out in Solar Tower Jülich and the data of the measurements were found in a good agreement with simulations. This has allowed a more detailed model to be integrated into the process flowsheet of the process. Heat management including pinch point analysis was performed for the SAC unit deriving the share of heat demand, which can be recovered by high and low temperature heat exchangers. Implementation of the frame model was carried out including all relevant components: evaporator, super heater, reactor, heat exchangers for heat recovery. Dynamic simulation of one exemplary day to demonstrate functionality of the preliminary models was also performed.
Altogether, all objectives set for the project has been achieved and also extra results obtained (new titration method, new coatings concept, better high-temperature catalyst method, improved design of solar parts and new optimization software tool).

Potential Impact:
Project Impact:
On the European level, the SOL2HY2 project has demonstrated an enhanced way of solving complex problem in utilization of renewable energy resources minimizing their fluctuation (such as solar power) and converting them into hydrogen - an energy carrier - with lower costs and flexible demand/supply, tailored for a specific application site and with a minimal investments required. SOL2HY2 has for the first time linked new concepts with solar-driven power leading to the proof-of-concept and key systems demonstration in the short-term.
An additional impact is anticipated to come from demonstration of novel "green plant design" tools (virtual production/design of materials/plants is easier without building up pilot equipment) ensuring low emission footprint and effective use of resources and further that of the processing and application will be minimal.
The overall socio-economic impact of SOL2HY2 includes environmental, economic, innovative and social aspects. Economically, the market of the hydrogen produced with the open cycle is linked to the growing sulfuric acid production which is expected to reach 285 millions ton in 2020-2025 worldwide. This means more than 5 millions ton H2 to be able to co-produce without affecting the acid production and its market. Further, this can solve problem with excess waste sulfur originating from different chemical processes, as it can be efficiently converted into acid, hydrogen and oxygen. Production of H2SO4 is a commercially available technology with hundreds of year experience in process safety and monitoring. It is much less risky than connection of hydrogen production to nuclear reactors or fossil fuel plants. Thus new SOL2HY2 processes have no intrinsic unknown safety or accidents concerns. The Outotec Open Cycle has been patented in many countries and eventually available for further implementation.
Environmentally, SOL2HY2 demonstrated a possibility for 100% renewable energy sources and for utilization of the external sulfur sources, which means substantial positive changes in environmental protection. This additionally backed with new software tool, which allows a fast estimation on profitability, scalability and feasibility of the plant in any location, leading to catalysis of investments, creation on new regional jobs and promotion of the clean fuel technologies, also beyond the Europe.

Dissemination:
Dissemination has been a crucial activity through the whole project duration. All actions have been done with the aim to disseminate to a wider public as possible, raising public awareness, not only during technical and scientific conferences and symposiums. In this regard, for example, during editions 2014 and 2015 of the International CAE Conference, some live “hydrogen experiment” demonstrations has been done explaining the importance of hydrogen “green” production. These “unusual” events roused a big public interest. In the same occasions, some interviews to main project actors were registered and videos are available on the SOL2HY2 web-site (https://sol2hy2.eucoord.com/Video/body.pe , https://sol2hy2.eucoord.com/Training/body.pe and https://sol2hy2.eucoord.com/news/body.pe?clistid=finaldisseminationevent&cid=262) . The web site has been continuously updated with publications, news and events, and its reserved area has been intensively used for dissemination activities approval and as document repository for the whole consortium.

The main dissemination activities which can be mentioned are international conference and seminar presentations, public events (from schoolchildren to general audience), publications (traditional and open source journals) and exhibitions:
11th International Hydrogen and Fuel Cell Exhibition FC EXPO 2015, 25-27 February 2015, Tokyo Big Sight, Japan
88th SolarPACES Executive Committee Meeting, Hotel Mediterraneo, , 24 March 2015, Rome, Italy
6th International Conference on Hydrogen Production ICH2P, 3 – 6 May 2015, Oshawa, Canada
IcheAP12, 12th International Conference on Chemical & Process Engineering ,May 19-22, 2015. Milan, Italy
International Conference on Energy Sustainability June 28-July 2, 2015, San Diego, California, USA
National Conference ,10.06.2015, Pori, Finland
21st SolarPACES Conference, 13-16 Oct 2015, Cape Town, South Africa
International CAE Conference , Oct. 2014 and 2015, Pacengo del Garda, Italy
World FC EXPO 2016, Tokyo, 2-4.3.2016
General public event, Foligno, (Italy), April 2016
”Millenium X” event: Helsinki, Finland, 20-22 May 2016
Fuel Cells and Hydrogen Hannover Messe, 25-29.5.2016
World Hydrogen Energy Conference 2016, Zaragoza, Spain, June 13th to 16th 2016
10th International Conference on Energy Sustainability, Charlotte, USA, June 26-30, 2016
AIP Conference Proceedings-Solarpaces 2016 International Conference, Abu Dhabi, 11-14 October 2016
International CAE Conference, Parma, Italy, October 17-18 2016
AIChE Annual Meeting 2016, San Francisco, USA, November 13-18, 2016

Main publications:
Process modelling and heat management of the solar hybrid sulfur cycle – DLR A. Guerra Niehoff, N. Bayer Botero, A. Acharya, D. Thomey, M. Roeb, C. Sattler, R. Pitz-Paal, - International Journal of Hydrogen Energy, Vol. 40 Issue 13, Elsevier
Performance of electrocatalytic gold coating on bipolar plates for SO2 depolarized electrolyser – AALTO A.Santasalo-Aarnio 1, A. Lokkiluoto, J. Virtanen1,M.M. Gasik - Journal of Power Sources, Vol. 306, Elsevier
Modelling and scaling analysis of a solar reactor for sulphuric acid cracking in a hybrid sulphur cycle process for thermochemical hydrogen production - DLR N. Bayer Botero, D. Thomey, A. Guerra Niehoff, M. Roeb, C. Sattler, R. Pitz-Paal - International Journal of Hydrogen Energy, Vol. 41, Elsevier
SO2 carry-over and sulphur formation in SO2 depolarized electrolyser – AALTO A. Santasalo-Aarnio 1 ,J. Virtanen1,M.M. Gasik - Journal of Solid State Electrochemistry, Vol: 20, Springer
Modeling of a Solar Receiver for Superheating Sulfuric Acid - DLR J. L. Lapp, A. Guerra Niehoff, H.-P. Streber, D. Thomey, M. Roeb and C. Sattler - Journal of Solar Energy Engineerin,g Vol 138, June 2016, ASME
Bichromatometry as a new method for SO2 analysis at low pH solutions – AALTO Annukka Santasalo-Aarnio*, I. Galfi, J. Virtanen, M.M. Gasik - American Institute if Chemical Engineering Wiley
Solar Thermal Water Splitting - DLR, Martin Roeb - RENEWABLE HYDROGEN TECHNOLOGIES, chapter 4, Elsevier 2013, ISBN 978-0-444-56352-1
Optimizing clean energy: solar-to-hydrogen cycles - EnginSoft SpA - EnginSoft Newsletter Autums 2013
Optimizing the integration of a chemical process with a concentrated solar power source: the SOL2HY2 project - ENEA and EnginSoft - EnginSoft Newsletter Year 11 n.2 Summer 2014
The SOL2HY2 project - DLR Dennis Thomey, Martin Roeb - EUREC (Association of European Renewable Energy Research Centers) Newsletter
Multi-Objective Optimization of a Solar Powered Hydrogen Production Process, H2 production through different solar technologies - EnginSoft, ENEA - Winter 2016

Thesis and project works:
“Methodology for the Design of a solar reactor for sulphuric acid splitting at industrial scale and technology assessment in context to the HyS-cycle” - Alejandro Guerra Niehoff - RWTH Aachen University
"Study of the Hybrid Sulfur Water-splitting Cycle Powered by Solar Energy" - Maria Rosaria Ferrara- ENEA and Università di Roma “La Sapienza”
Produzione di idrogeno mediante ciclo Zolfo Ibrido: analisi dei consumi energetici e integrazione del processo con fonte solare” - Alessia Cavaliere - ENEA and Sapienza Università di Roma
"Analisi della sezione ad alta temperatura del processo zolfo ibrido alimentato da energia solare per la produzione di idrogeno da acqua" - Giorgia Panno - ENEA and Sapienza Università di Roma
Generic Hydro DLL Unit - Julius Eerola- Outotec and Aalto University
Simulation of an air heated reactor for solar sulphuric acid splitting with integrated heat recovery - Florian Binder - TH Koln
Solar thermochemical heat storage: Optimization of an experimental set-up for long-term performance testing of catalysts for decomposition of sulfuric acid- Mikus, Martin- Fachhochschule Köln (University of Applied Sciences Cologne).
“Auslegung und Konstruktion eines Solarreceivers zur Schwefelsäurespaltung und Visualisierung einer Gesamtanlage des Schwefelsäure-Hybrid-Prozess im industriellen Maßstab” - Jan Drescher - Fachhochschule Köln (University of Applied Sciences Cologne).
Elimination of Sulphur in SDE process- Otso Matikainen - Aalto University
Materials and methods for storing hydrogen - Joel Mälkönen - Aalto University
“Silicon carbide based composites for energy applications” - Sini Bäckman - Aalto University
“Strömungssimulation eines Solarreceivers: Optimierung der Einströmung für den Solarreceiver des Sol2Hy2-Projekts” - Stefan Peter Schwan- Fachhochschule Köln (University of Applied Sciences Cologne).
“Design and start-up of a scrubber for neutralisation of sulphur dioxide” - Christopher Ziegs - University of Applied Sciences Cologne
“Corrosion behavior of advanced interlayer carbon coating on gold coated bipolar plates” - Johanna Valio - Aalto University
“SiC layers for flow fields in SDE system” - Maria Carmen Gamero Rodriguez - Aalto University

Final Dissemination Event
Finally, the Sol2Hy2 Final Dissemination Event was organized in conjunction with FCH JU Programme Review Days 2016, at the end of the first day, November 21st. The event, introduced by the Officer, Dr. Lymperopoulos, presented the key innovative results of the project: the new sulphur oxide depolarized electrolyzer, the software platform for the optimization of the hydrogen production plant plus innovative systems and components designed for solar thermochemical water-splitting cycle pilot plant.

Exploitation:
The main results and achievements of the project are reported in the analysis, development and validation of new process flowsheets to include solar power input for key units of the plant, targeted at selected locations (specified by user) and allowing a flexible combination of different sources, inclusive of new Outotec Open Cycle, where sulfuric acid was directed to be a commercial by-product to hydrogen rather than to be cracked and returned to the HyS cycle. This allows increase of the renewable sources share, improve waste heat utilization and ensure 24/7 plant operation, eliminating solar input instability, combined with reasonable capital costs and balance of the products streams. In the electrolyzer unit - the core of H2 generation - most of the challenges were solved - elimination of platinum-group metals catalysts, control of parasitic reactions, lowering the capital costs (e.g. ~3 times vs. existing analogues). The operation was successfully demonstrated on-sun at the solar tower Jülich (Germany). An extra development of the software for plan design and optimisation was also carried out allowing the user to analyze and optimize the hydrogen production process in an interactive and guided way, through the use of user-friendly graphical user interfaces.
Based on these results, 9 exploitable results and related exploitation routes have been identified:

ER 1.a Working models of the SDE key components
Sulphuric oxide depolarised electrolyzer (SDE) is a key unit and step for sulphur-based thermochemical cycles like the hybrid sulphur cycle (HyS) for hydrogen production. It utilizes feed of SO2 dissolved in weak sulphuric acid, oxidized by electrolysis to produce hydrogen and more concentrated sulphuric acid. Via the SDE hydrogen is collected and purified and acid is being fed to the next stage for concentration (if cycle is open) or cracking (if cycle is closed).
To develop a feasible large scale SDE, a proper working model was developed which solves the questions of upscaling, operation parameters (flows, concentrations, voltage, current), combination of different units and their interaction to minimize energy losses and to achieve optimal output (in combination with other plant units). Model of SDE has been validated by experimental results from a small cell and larger 5-cell stack application (at pilot scale), and integrated into an overall process simulation.
The SDE presents several advantages with respect to existing experimental values and most of the empirical models (mainly by US researchers) that are mainly based on the high-temperature, high-pressure SDE solutions with a significant amount of catalysts.
The potential commercial applications of this solution, possibly associated with ER2.a, are in industrial sulphuric acid plants or processes where SO2 is generated and has to be recycled (coal, oil plants, chemical processing), who have similar components.
Some examples of this kind of companies are OUTOTEC, General Atomics (USA), ENEA, Savannah Rivers National Laboratory (USA)

ER 1.b Working models of the SAC key components
Sulphuric acid cracking (SAC) is a key step for sulphur based thermochemical cycles like the hybrid sulphur cycle (HyS) for hydrogen production. Via the SAC step concentrated solar power (CSP) can be coupled into the HyS process so that it is driven by renewable energy and generates green hydrogen.
The development of experimentally validated models of the SAC key components of the HyS integrated into an overall process simulation allows fast design of the required process units and adapts to any projected or existing plant.
Potential commercial applications are in industrial sulphuric acid plants who have similar components compared to a solar SAC unit of a HyS plant. In case the site has sufficient solar radiation, those plants could be combined.
Some examples of this kind of companies are DLR, OTT, General Atomics (USA), ENEA, Savannah Rivers National Laboratory (USA).

ER 1.c Working models of the key STH/STE components
The whole SOL2HY2 project is aimed at developing material and process solutions to power the Hybrid Sulfur Cycle with solar heat and electricity. Therefore Solar to Heat (STH) and Solar To Electricity (STE) solutions are part of the key process blocks.
Models of the solar thermal collection plants, thermal storage system, power block, backup heater and photovoltaic system have been collected and combined together in order to provide an integrated model of the STH and STE solutions tailored to the SOL2HY2 plant. The model interfaces account for the process solutions developed in the chemical plant.
Potential commercial applications are in industrial sulphuric acid plants who have similar components compared to a solar SAC unit of a HyS plant. In case the site has sufficient solar radiation, those plants could be combined.
The potential market is represented by Chemical industry interested in using renewable process heat and power (e.g., solar powered production of sulphuric acid and hydrogen) and by Solar power plants (chemical storage of solar energy as hydrogen)

ER 2.a MODAO (MultiObjective Design Analysis and Optimization) and meta-modelling tools in new fields of physics and chemistry
This result consists on the integration of different process models into an optimization and statistical analysis environment. Besides providing key materials and process solutions, for the first time the whole production chain and flowsheet will be connected with multiobjective design and optimisation (MODAO) and metamodeling algorithms ultimately leading to hydrogen plants and technology “green concepts” commercialisation.
The optimization process allows to find out some optimal quantities which reflect on the SDE (SO2 depolarised electrolyser) as constraints. This allows to perform a local optimization on the single SDE component model.
It combins the usage of existing MODAO, data analysis (statistics), meta-modeling and approximation techniques in a new application field.
Statistics techniques, in particular correlation, are useful to point out hidden relations between the input and/or the output variables of a process, helping thus to reduce the number of significant variables to be considered and downsize the search space of optimal solutions.
The software tool for the study of the SOL2HY2 process offers a single interactive and accessible application with a graphical user interface.
The usage of optimization and metamodeling techniques drastically speeds up the tuning of the optimal configuration of a new Hydrogen production plant.
The software can be profitably exploited by companies designing Hydrogen production plants powered by solar energy to increase efficiency of hydrogen production, reduce costs, take into account constrains such as plant location and logistics inputs.

ER 2.b MODAO and meta-modelling tools in new fields of physics and chemistry (ENEA)
The optimal design and operating conditions of a concentrating solar thermal plant are strongly dependent on the hourly Direct Normal Irradiance (DNI) distribution throughout the year at the specific installation site. The same clearly applies to a chemical plant that is coupled with a CSP plant, as required for the hydrogen production process developed in the SOL2HY2 project. In this second case, the problem is even more complex, because of the increased number of design variables and operating conditions.
The identification of the optimal configuration and operating conditions of a hydrogen production plant based on the SOL2HY2 process is therefore a complex MODAO problem, whose solutions requires proper tools for the simulation of the coupled solar and chemical plant operation.
A software based on a dynamic Excel spreadsheet has been developed by implementing several components:
• Mathematical models developed with ER1a (part developed by ENEA)
• Mathematical models developed with ER1c
• Models of other key process blocks and balance of plant units.
• Costing models of the plant equipment (both solar and chemical)
Such software takes the following main input:
• hourly DNI distribution at the specific plant location
• solar and chemical plant configuration (e.g., presence of a power block PV system, backup sulfur burner etc.)
• solar and chemical plant operating conditions
and allows to dynamically calculate the behaviour of the plant as well as relevant performance indicators such as
• hydrogen production costs
• share of renewables in the energy input.
Potential commercial applications are in industrial sulphuric acid plants who have similar components compared to a solar SAC unit of a HyS plant.

ER 3 - New high-temperature ceramic components capable of withstanding harsh conditions
Porous ceramics are a key component in the volumetric absorber technology for concentrated solar power. These ceramics should absorb solar radiation, and transfer the thermal energy to the flow that passes within the structure as efficiently as possible. In the specific case, the flow includes sulphuric acid. Thus, the ceramic component needs to be high temperature stable and stable in acidic environment.
The invention relates to a new application with no standard solutions. The only currently existing solution, at demo level, is given by a ceramic honeycomb. The main problem of honeycombs is the 1-D channel structure that prevents high efficiency. The straight channels of ceramic honeycombs limit flow mixing and interactions with the substrate, thus limiting heat exchange.
The use of SiC foams with a 3D channel structure increases the heat exchange along the absorber depth, allowing to increase efficiency or decrease absorber size.
The invention is very specifically intended for the field of concentrated solar power and in particular for the volumetric absorber technology with sulphuric acid environment. This application field is still in a research and development phase and may not hit the market soon. However, companies interested would be companies active in CSP-driven hydrogen production.

ER 4 New materials solutions of sulphur oxide-depolarised electrolyser components
Sulphuric oxide depolarised electrolyzer (SDE) is a key unit and step for sulphur-based thermochemical cycles like the hybrid sulphur cycle (HyS) for hydrogen production. It utilizes feed of SO2 dissolved in water (weak sulphuric acid) by electrolysis to produce hydrogen and more concentrated sulphuric acid. Via the SDE hydrogen is collected and purified and acid is being fed to the next stage for concentration (if cycle is open) or cracking (if cycle is closed).
By using gold-coated bipolar plates (validated in experiments), corrosion protection and SO2 oxidation catalysis can be integrated. This enables SDE without use of noble metals (PGM) as catalysts (zero load in µg/cm2) operating at ambient temperature and pressure, which greatly simplifies structure and costs (expected less 200-400 €/m2 of the stack).
Potential commercial applications are in industrial sulphuric acid plants or processes where SO2 is generated and has to be recycled (coal, oil plants, chemical processing), who have similar components.

ER 5 The optimized open cycle system to produce hydrogen and sulphuric acid from SO2
The open cycle (also known as Outotec Open Cycle) utilizes sulphuric oxide depolarised electrolyzer (SDE) and acid concentrator with necessary balance of plant for sulphur-based thermochemical cycles for hydrogen and sulphuric acid co-production. It utilizes feed of SO2 dissolved in water (weak sulphuric acid) by electrolysis to produce hydrogen and more concentrated sulphuric acid. The result concerns the knowledge of optimization of the cycle to produce these chemicals in the best way.
To produce hydrogen and acid simultaneously, a number of parameters need to be controlled and optimized to ensure that both outputs complement each other and the energy pinch is achieved to minimize operative costs, CAPEX and maximize efficiency.
By using smart optimization approach, the streams compositions, feeds, operative parameters cane be fit to the site and plant design to achieve the goal.
Potential commercial applications are in industrial sulphuric acid plants or processes where SO2 is generated and has to be recycled (coal, oil plants, chemical processing), who have similar components.
ER 6 First demonstration at the pilot scale for a solar thermochemical water-splitting cycle with new components
The hybrid sulphur cycle (HyS) consists of two main steps: sulphuric acid cracking (SAC) and sulphur dioxide depolarised electrolysis (SDE). Research in the past was focussed on lab scale applications. Before the invention there has been no pilot scale demonstration of the SAC using directly irradiated porous ceramic SiC absorber structures in the solar receiver unit.
Core element of the SAC unit is a solar receiver closed with a quartz glass window through which the concentrated solar power (CSP) penetrates to heat up a porous ceramic SiC absorber. Sulphuric acid vapours produced in a tube-type electrically heated evaporator pass through the SiC structure and are superheated before reaching a catalyst fixed bed in which the cracking reaction takes place in an adiabatic manner.
The invention separates the sulphuric acid cracking reaction into three sub-steps: evaporation, superheating and adiabatic reaction. It uses a tube-type evaporator for the first step and a directly irradiated porous SiC structure for the second step.
Potential commercial applications are in industrial sulphuric acid plants who have similar components compared to a solar SAC unit of a HyS plant. In case the site has sufficient solar radiation, those plants could be combined.

List of Websites:
The address of the project public website: sol2hy2.eucoord.com

Coordinator: Stefano Odorizzi, ENGINSOFT SpA
Via della Stazione,27 38123 – Trento (ITALY)
e-mail: s.odorizzi@enginsoft.it

Coordinator Main Contact: Carla Baldasso, ENGINSOFT SpA
Via Giambellino, 7 35129 – Padova (ITALY)
e-mail: c.baldasso@enginsoft.it

Scientific Coordinator: Michael Gasik, Aalto CHEM
P.O.Box 16200, FIN-00076 AALTO
e-mail: michael.gasik@aalto.fi

Related information

Reported by

ENGINSOFT SPA
Italy
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