Final Report Summary - HYDROSOL-PLANT (Thermochemical HYDROgen production in a SOLar monolithic reactor: construction and operation of a 750 kWth PLANT)
Executive Summary:
The HYDROSOL-technology series of projects are based on the utilization of concentrated solar thermal power for the production of Hydrogen from the dissociation of water via the redox-pair metal oxide based two-step thermochemical cycles. The redox material is a metal oxide or a combination of metal oxides (e.g. ferrites, cerium oxide etc.) with cations that have the ability to obtain different oxidation states and thus these materials can exchange oxygen through their lattice. The HYDROSOL-technology differentiates from other conventional Hydrogen production technologies mainly in two ways; the utilization of renewable and practically inexhaustible raw materials (solar energy and water), and the utilization of modular structured reactors. In the HYDROSOL-Plant project several advancements were introduced related to large scale redox materials’ synthesis, shaping into porous structures, reactor design, etc. The HYDROSOL-Plant is the largest demonstration facility (0.75MWth) of its kind, worldwide. The ultimate objective was to achieve the production of H2 at a level of 3 kg/week as set also in the AIP2012. With the end of the project the solar H2 production on the HYDROSOL-Plant platform has been achieved for the first time on the full scale reactors, however at a lower level than the initial target. The scale of implementation of the HYDROSOL-Plant project allowed the identification of several challenges and development gaps that exist and need to be addressed and revisited during the evolutionary process of bringing the technology of solar redox thermochemical H2 production to commercial level.
Project Context and Objectives:
The HYDROSOL-Plant project is the continuation of a series of successful research projects (HYDROSOL, HYDROSOL-II and HYDROSOL-3D) focusing on the production of H₂ from the two-step solar thermochemical water splitting based on redox structured reactors. The principal objective of HYDROSOL-PLANT is the development and operation of a plant for solar thermo-chemical hydrogen production from water in a 0.750 MWth scale on a solar tower, based on the HYDROSOL technology. The HYDROSOL-plant consortium consists of 3 Research Centers from Greece, Germany and Spain (APTL which is the coordinator of the project, DLR and CIEMAT), 1 SME from the Netherlands (HYGEAR) and 1 Industry from Greece (HELPE).
The predecessor projects HYDROSOL and HYDROSOL-II have introduced the concept of redox structured monolithic solar reactors for the production of solar H2 from water. The proof of concept at lab-scale was presented in the first HYDROSOL project, while the feasibility of the main principles of the process for longer-term cyclic operation at a pilot reactor set-up in a scale of 100 kWth at the Plataforma Solar de Almeria (PSA) was proven in HYDROSOL-II project. In the third project of the series, HYDROSOL-3D, the relevant design aspects necessary to prepare the erection of a solar demonstration plant at the 1 MWth scale were addressed. However, the actual realization of a solar demonstration plant near the MW scale (0.75MWth) was achieved in the HYDROSOL-Plant project.
The specific Scientific and Technical Objectives of HYDROSOL-3D were:
• Define all key components and aspects necessary for the erection and operation of a 750 kWth solar plant for H2O splitting (heliostat field, solar reactors, overall process monitoring and control, feedstock conditioning, etc.)
• Develop tailored heliostat field technology (field layout, aiming strategies, monitoring and control software) that enables accurate temperature control of the solar reactors.
• Scale-up the HYDROSOL reactor while advancing the state-of-the-art (redox materials, monolithic honeycomb fabrication and functionalization) for optimum hydrogen yield.
• Design the overall chemical process, covering reactants and products conditioning, heat exchange/recovery, use of excess/waste heat, monitoring and control.
• Construct a solar hydrogen production demonstration plant in the 750 kWth range to verify the developed technologies for solar H2O splitting.
• Operate the plant and demonstrate hydrogen production and storage on site (at levels > 3 kg/week).
Project Results:
The HYDROSOL-PLANT project website was launched and is fully operational since April 2014. The website has a public area, providing non-confidential information about the project as well as the ability to contact the project coordinator requesting further information or making comments about the project. There is also a ‘member’ area granting access to the partners and the officer to the project’s confidential documents.
WP2: Process Layout
Major objectives:
• To prepare a detailed design of the complete demonstration plant.
• To provide the basis for the development of system control schemes.
• To enable the final definition of all necessary plant components and interfaces.
A detailed design of the complete demonstration plant flowsheet was developed. The flow sheet incorporates all process design improvement, identified within the previous project (HYDROSOL-3D), mainly concerning heat recovery, water and hydrogen separation and steam generation as well as the final refinements of the reactor’s design. Furthermore, it contains the main results of the simulation of the plant, which has been carried out by using the simulation tool Aspen Plus. Based on this flow sheet, a piping and instrumentation diagram (P&ID) was developed, which will provide the piping of the process flow diagram together with the installed equipment and instrumentation in order to define the control strategy of the plant. The flow sheet involves all necessary components for the operation of the plant by taking into account also existing facilities on the PSA in Almeria.
Some aspects of the process, although significant for the operation of a real plant, such as the recycling/reuse of N2 that is consumed in the process, were not addressed in the final process layout, since the project focuses on the H2 production part and not so much on the peripherals. In a real plant operation, recycling of the N2 used in the process would be of high economic/commercial significance, but at the scale of the current research project this was put aside.
WP3: Manufacture of Hydrogen production unit
Major objectives:
• Development and manufacture of a complete 750 kWth scale dual receiver/reactor unit for solar thermochemical splitting of water.
Work was focused on the finalization of the reactor design. The initial reactor concept of the HYDROSOL technology (HYDROSOL, HYDROSOL-II and HYDROSOL-3D) involved a dual reactor system. The reactors consisted of porous monolithic structures constructed either from re-crystallized SiC (ReSiC, for the case of the HYDROSOL project and the single chamber and dual-chamber 3 kW solar reactors) or from siliconized SiC (silicon-infiltrated Si-SiC, for the case of the HYDROSOL-II and HYDROSOL-3D 100 kW reactor) coated with the redox material. These monolithic structures were selected because besides their capability of operating as volumetric receivers/ absorbers of concentrated solar irradiation and achieving and sustaining the required high temperatures, their multi-channeled structure provided high gas-solid contact area and facilitated the access of steam to the reaction sites of the redox material.
In the previous project (HYDROSOL-3D), a point of improvement of the reactor’s design was the change of the geometry of the reactor from flat to spherical, since the latter provides the most efficient exploitation of the solar flux. Another aspect that was considered had to do with the fact that the substrate occupies the majority of the reactor volume (and weight) compared to the active redox material (the amount of the latter used so far on the SiC structures was about 20 %wt). Since the water splitting reaction based on redox materials depends also on the mass of the redox material on the reactor, the hydrogen yield per reactor volume would be rather low. A solution that would tackle this limitation was to produce the monolithic segments that constitute the reactor body entirely from the redox material.
Within the HYDROSOL-PLANT project, the design of the reactor was revisited, based also on the results of the previous project (HYDROSOL-3D), and the number and geometry of the reactors was defined. The final reactor design involves a set-up of 3 reactors put in a triangular arrangement. In the previous projects it was shown that although the flat geometry is the least complex in terms of manufacturing and maintenance, the conical and spherical geometries are likely to achieve better flux distributions. Ray-tracing simulations showed that the best shape that would allow the highest quality of flux distribution in the absorber would be the spherical shape [HYDROSOL-3D project]. However, this reactor concept had also some disadvantages mainly regarding the shapes of the monoliths and the supporting of the different segments to achieve the spherical shape of the absorber.
Consequently, in HYDROSOL-PLANT a new reactor design was developed based on previous cavity reactor designs that were employed in solar applications (REFOS, SOLREF and EMPOLI).
The new Hydrosol reactors consist of five main parts: 1) the secondary concentrator extension, 2) the front flange, 3) the quartz window, 4) the volumetric absorber and 5) the vessel.
The absorber consists of several porous monolithic structures. These blocks have to be assembled in such a manner that would create a cavity, so that the radiation crossing the window can be absorbed by the material more efficiently and uniformly. A first target in the Hydrosol-Plant design was to increase the volume of the blocks that form the cavity reactor in order to further increase the quantity of redox material that can be incorporated on the reactor. For this reason the cavity was made longer and thicker, compared to the previous reactor designs, to accommodate more material. The reactor is formed by 6 parallel rings, one as inlet and five as outlet, and each ring is made by 18 blocks. The total active material volume inside the cavity was increased to about 95 liters/reactor.
A dome window design was chosen and the front flange was designed to hold both the secondary concentrator and the window. A cooling network is essential to keep the window flange at appropriate temperatures for the sealing during operation under solar flux.
The three reactors would be placed on the solar tower on a steel structure able to bear their weight and to point the reaction chambers to the middle of the heliostat field. The reactors are placed at about 26 m high from the ground and the heliostats field has twelve lines: the horizontal distance between the frontal face of the tower and the seventh line is 106 m. The arctangent of this triangle gives 14° as result and so the structure has to tilt the reactors at this angle. A support for each reactor is designed to make easier the assembly and then both are placed on a turntable, which makes possible the maintenance of the reactor itself.
A secondary concentrator at the entrance of the reactor was considered for the minimization of the thermal losses from the reactor window and for focusing the sun rays inside the active reactor area. The secondary concentrators that used in the HYDROSOL-PLANT project are based on existing systems. The purpose of that component is to use the spillage in the reactor instead of losing it, to homogenize the solar radiation as much as possible hitting the reactor window and to protect the front flange from the direct radiation coming from the heliostats.
Furthermore an investigation on the porous structures that will form the cavity of the reactor (main reactor body) was conducted with the aim to increase the capacity/reactor volume. Certain specifications had to be covered (such as platform space and weight limitations, reactor volume, scalability of the redox porous structures, and also budget limitations) that affect also the final reactors’ design. Monoliths as well as foams consisting entirely of the redox material were considered as possible structures for the building of the reactor body and were developed and evaluated. In addition the durability of the redox structure was assessed.
Based on past experience NiFe2O4 synthesized via the Self-Propagating High temperature Synthesis (SHS) method was considered the redox material of choice to be applied in the reactor. This material possesses the appropriate characteristics for the current solar plant, i.e. it has a significant splitting performance at moderately high temperatures (Tsplitting: 1100C) without the need of extremely high temperatures for its regeneration/reduction (Treduction: 1400C). Also it is a formulation that has been extensively investigated in the previous HYDROSOL projects and has been applied at the previous solar reactor concept under the actual conditions at the current solar platform facility where the new plant is going to be located.
The use of inert lightweight monoliths as substrates for the redox material was initially investigated. Al2O3 based monolith was considered as the most appropriate substrate since it has small weight, can operate at the high temperatures of the process and does not participate in the water splitting reaction. NiFe2O4 synthesized via the SHS process was deposited on an Al2O3 monolith via impregnation in a slurry of the redox material. This solution was finally rejected since there was an indication of possible interaction of the NiFe2O4 coating with the Al2O3 substrate detected via X-ray diffraction analysis on fresh and processed samples, although this was limited to an interface where NiFe2O4 is in direct contact with the Al2O3.
In parallel the extrusion of honeycomb monoliths consisting entirely of NiFe2O4 (activity pursued for the first time ever based on open literature) was also investigated employing a lab-scale piston extruder. Optimization of the extrusion process allowed the production of thin-wall extruded monoliths with good structural stability. The structure was subsequently subjected to multiple H2O splitting/thermal reduction cycles. The evaluation started within the first period of the project and continued also in the second project period. The durability assessment involved consecutive water splitting (60 vol% H2O concentration in N2) and thermal reduction cycles (N2 flow). The 1000h operation target of the project was achieved and with the exposure of the structure in approximately 600 consecutive cycles (corresponding to a time-span of approximately 6 months of on-sun operation) at temperatures from 1100 to 1400oC and alternating vapor and inert gas atmosphere. After approx. 400h activity was more or less stabilized to ~0.1 mmoles/gmonolith. In addition, “cast” monoliths prepared by using 3D-printed molds were evaluated during the first period of the project and had a prominent performance.
Although the performance of the all-redox extruded and 3D-printed cast honeycomb monoliths was appreciable, difficulties in the scaling-up of the different segment geometries that comprise the reactor cavity could not be overcome especially within the scope and the limited timeframe of the project
Based on:
- the complexity of the reactor cavity segments’ geometries that increases machining difficulty for the case of honeycomb monoliths and subsequently the cost of the whole structure.
- communications with experts in the field of honeycomb monoliths manufacturing for commercial applications
- the experience gained in another project coordinated by APTL (RESTRUCTURE project, FP7-283015), for the scaling-up of the extrusion of honeycomb monolithic structures from lab-scale dimensions to actual full-scale dimensions,
- and finally the limited time for the construction of all reactors and the completion of the plant facility
, it was decided that other geometries with more facile scaling-up potential, such as foam structures, should be chosen as a fallback option for the construction of the cavity reactors. Preliminary work on small scale foams took place within the first project period showing encouraging results.
Therefore, within the first months of the second project period the activities were focused on the scaling-up of the production of NiFe2O4 powder to be used as the starting material for the manufacturing of all-redox NiFe2O4 foams. The capacity of the method for powder production at the laboratory was of the order of 100-200 g/d at the beginning of the project. The final scale-up of the NiFe2O4 synthesis reached 15 kg/day.
Several problems occurred during the scaling-up of the foam structures that had not been previously identified during the investigation of producing small scale foams that consist entirely of the redox material. The problems that had occurred spanned from foam structures melting in the furnace during heating, to shape deformation and cracking. Thermal testing at APTL of the prepared large scale foam segments, both in conventional electrical furnace as well as in the solar simulator, revealed the challenges in the preparation of robust all-redox full-scale foam structures.
Those challenges, along with the low tolerance in the dimensions of the different segments (in order to achieve perfect fit of the segments in the cavity reactor) and the limitations in the available raw material and also in the time left for the completion of all the reactors, led the consortium to take the decision of using commercially available foams that would be coated with the redox material. 54 pieces with three different geometries were already manufactured consisting entirely of NiFe2O4 while the rest of the foams i.e. 55 pieces to complete the 1st reactor and 220 pieces to complete the 2nd and 3rd reactors would be prepared via coating of NiFe2O4 and CeO2 (for comparison purposes. CeO2 has been investigated in the past with respect to its potential in water splitting with promising results) on standard foam substrates (e.g. ZrO2).
Comparison at the laboratory scale of all-redox NiFe2O4 foams with NiFe2O4 coated foams with respect to their redox activity did not show significant differences. Comparison of the NiFe2O4 coated foam with the CeO2 coated foam showed significant differences mainly in the rate of the reaction and the total H2 produced which was higher in the case of the NiFe2O4 at the specific experimental conditions.
The assembly of the reactors with the foams and the different supporting components was done manually and involved multiple disassembling and reassembling of the components in order to find the best fit and to achieve stability of the structure. In addition kipping tests were conducted, prior to transportation to the solar tower at the Plataforma Solar de Almeria to ensure the integrity of the unit during transport, lifting or when tilted.
WP4: Development of balance of plant components
Major objectives:
• To address all - besides the hydrogen production unit - necessary components’ sizing and detailed design.
• To accordingly manufacture/procure these components.
• To select and procure all necessary sub-components and equipment needed for process automation and control.
The SPSS-CRS (small solar power central-receiver system), consists of an autonomous field of heliostats and a metallic tower 43 meters high. SSPS-CRS tower is equipped with a large quantity of auxiliary devices that allow the execution of a wide range of tests in the field of solar thermal chemistry. All test levels have access to pressurized air (29 dm3/s, 8bar), pure nitrogen supplied by two batteries of 23 standard-bottles (50 dm3/225bar) each, cooling water with a capacity of up to 700 kW, demineralized water (ASTM type 2) from a 8 m3 buffer tank for use in steam generators or directly in the process, and the data network infrastructure consisting of Ethernet cable and optical fiber.
The HYDROSOL-Plant consists of two distinct parts: 1) the solar reactor with steam generator, heat exchangers and condensation units; 2) the gas cleaning unit consisting of a buffer vessel, a product vessel, a compressor and a small PSA-system. The main components are integrated on the metallic tower using flexible pipes in the evaporation part, the reaction part, the H2 purification part, and the nitrogen supply part.
The solar reactor system consists of 4 main blocks. First water is converted into steam in the steam generation part. The steam is then going to the reactor system, where it is converted to hydrogen. The wet hydrogen then goes to the condensation part to dry. Subsequently it flows to the PSA system to be purified and stored. For regeneration of the reactors Nitrogen is needed, which is supplied via the Nitrogen part.
Based on this process layout and the work conducted in WP2 and WP3, all BoP and sub-BoP components were defined and procured. Such components are the cryogenic unit which was installed at the facility for the supply of adequate N2 flow to the solar platform, the demineralized water plant and the steam generator for the supply of water, the product purification unit (PSA) with the buffer and PSA vessels and the cooler/condenser. The plant peripherals, such as valves, mass flow controllers, pressure sensors, thermocouples, etc. were also identified and procured. Furthermore the product gas purification unit, based on Pressure Swing Adsorption (PSA) was constructed, taking into account the needs of the solar process which is characterized from high vapor concentrations and low H2 flow rates and is intermittent (the diurnal nature of solar energy in contrast to the PSA which needs to be operated continuously to achieve good performance), and.
WP5: Set-up of demonstration plant.
Major objectives:
• To adapt the solar tower platform to the hydrogen plant operation requirements.
• To install the fully assembled solar hydrogen production reactor on the solar tower.
• To install all other necessary plant components.
• To integrate the operation of the whole plant via the implementation of suitable control software, hardware and plant’s infrastructure.
The relevant activities necessary to prepare the erection of a HYDROSOL technology-based 0.75 MWth solar demonstration plant involve the completion of the whole plant including the solar hydrogen reactor and all necessary upstream and downstream units needed to feed in the reactants and separate the products.
The HYDROSOL-Plant facility was installed at the SSPS-CRS platform at the Plataforma Solar de Almeria in Spain. The activities involved preparation of the solar field facilities (heliostats, tower, control rooms), the installation of the solar reactors and the coupling to the peripherals (heat exchangers, purification units etc.).
The SSPS-CRS plant was inaugurated as part of the International Energy Agency’s SSPS (Small Solar Power Systems) project in September 1981. Originally conceived to demonstrate continuous electricity generation, it used a receiver cooled by liquid sodium that also acted as the thermal storage medium. At present, this test facility is mainly devoted to testing small solar receivers in the 200 to 500-kWth capacity range.
During the first 18 months of the project, work has been focused in preparing the solar platform facilities to house the HYDROSOL-Plant platform. The preparation of the solar platform involved improvements not only in structural works at the 27m height platform but also of the performance of the plant (renovation of the facets, new control program). Some actions that have taken place on this task were:
• Improvement of the communication of heliostats by wiring all heliostats.
• Re-moderation of control room
• Addition of new functionalities in the control program
• Renovation of the facets of the heliostat field.
• Conditioning of the platform.
The heliostats’ facets were renovated (high reflectivity mirrors that contribute to the improvement of the efficiency of the captured solar radiation on the reactor, under typical conditions of 950 W/m2, total field capacity is 2.5 MWth and peak flux is 2.5 MW/m2). The platform that would host the plant was enlarged by 20m2. In addition a deck was added below the main deck to host the purification unit and peripherals and the electrical control cabinets. The main deck was reformed for the installation of the 3 reactors. The positioning of the reactors was proposed to be triangular, for the most efficient irradiation, with two of the reactors placed on the floor and one hanged from the roof. The specific assembly of the reactors in a triangular configuration required the design of a support structure on a wagon, which also hosts all main peripherals that would provide flexibility during maintenance and service works. In addition changes in the façade of the solar tower for the appropriate attachment of the secondary concentrators were necessary. Flux measurement systems equipped on the solar tower allowed the calculation of the solar flux on the new reactors’ configuration. The installation of the three reactors was conducted with the aid of cranes while the mounting of the optical components on the reactors was done on the platform. During the reactors installation, an accident on the positioning of the top reactor caused the destruction of the cavity and as a consequence the platform completion was significantly delayed. However, no damage of the redox foams occurred which indicated the rigidity of the structures. In addition, all installation of hardware (control cabinets, data acquisition workstations) and the development of the software interfaces for the control and monitoring of the different solar facility components (i.e. heliostat field, peripherals control based on the process layout, solar reactors interface, PSA interface etc.) were developed and completed. The new control program provides much more information for the design of a supervisory system (monitoring and diagnosis displays, definition of alarms, meter readings, equipment status reports etc.). A ray tracing tool for the simulation of the solar flux distribution on the reactors was developed with the potential to be validated by solar flux measurements based on a camera moving bar system on the solar tower with the target to simulate the process and eventually replace the moving bar technology.
All peripherals and the three reactors coupled with the optical components were successfully integrated to the SSPS-CRS solar facility in Plataforma Solar de Almeria. A HAZOP analysis was conducted to identify the existing potential hazards resulting from process deviations, and when necessary, propose possible actions to reach safety and operability risk levels that are acceptable.
WP6: Operation and validation of demonstration plant.
Major objectives:
• To demonstrate the feasibility of the proposed process for solar hydrogen production in the 750 kWth scale.
• To validate the performance of key plant materials and components with respect to economic operation.
• To assess the technology vs. the targets set and evaluate its potential for further scale-up.
The HYDROSOL-technology relates to the utilization of renewable and practically inexhaustible raw materials (solar energy and water), and the utilization of structured reactors. The predecessor projects HYDROSOL and HYDROSOL-II have introduced the concept of redox structured monolithic solar reactors for the production of solar Hydrogen from water. The proof of concept at lab-scale was presented in the first HYDROSOL project, while the feasibility of the main principles of the process for longer-term cyclic operation at a pilot reactor set-up in a scale of 100 kWth at the Plataforma Solar de Almeria (PSA) was proven in HYDROSOL-II project. In the third project of the series, HYDROSOL-3D, the relevant design aspects necessary to prepare the erection of a solar demonstration plant at the 1 MWth scale were addressed. However, the actual realization of the construction of a solar demonstration plant near the MW scale (0.75MWth) was achieved in the HYDROSOL-Plant project. Several advancements were introduced, with the ultimate objective to achieve a production of Hydrogen at a level of 3 kg/week. The HYDROSOL-Plant is the largest demonstration facility of its kind, worldwide.
The activities that took place within the last period of the project involve the pre-testing, debugging and testing of the different components of the solar platform. The tests were conducted under atmospheric conditions as well as under solar radiation conditions. Several problems and bottlenecks were encountered on critical for the operation of the reactors components.
The platform that hosts the HYDROSOL-Plant installation is located at the 27 m level in the CRS receiver plant in Plataforma Solar de Almeria. This level also accommodated the previous HYDROSOL II and HYDROSOL 3D installations and it was a closed room, four meters high with 60 m2 available for equipment. The HYDROSOL Plant installation has been divided into two parts. The main components of the plant, such as reactors, secondary concentrators, steam generator, and main gas stream pipes are located in the main floor. The floor 4 meters below the main deck accommodates the rest of the peripheral components, mainly consisting of the purification system of the outlet gas. In the lower deck, a condenser removes the water from the outlet gas stream and prepares the gas for the purification subsystem, which is used to separate and store the hydrogen produced in the water splitting step. The system consists of three elements: two large vessels (buffer and final product) and a cabinet containing a compressor and four PSA modules.
The HYDROSOL-Plant solar thermochemical cycles consist of two steps carried out at different temperature levels with different energy requirements. The regeneration step is endothermic and takes place at 1300-1400°C; the water splitting step is slightly exothermic and takes place at 1000-1100°C. Therefore, the reactor which is under regeneration needs a higher solar flux density than the reactor that is in the water splitting mode. In fact, the latter would only need a small amount of solar energy to compensate for heat losses. This means that it is necessary to vary the flux density when the cycle state in the modules changes from regeneration to water splitting and vice versa.
The results of the previous Hydrosol II and 3D experimental campaigns formed the basis for the development of a process control strategy for Hydrosol Plant. From the experience gained in the operation of the previous reactors coupled to the solar tower facility, it could be confirmed that with the control of the heliostat field the simultaneous adjustment of the two different process temperatures could be achieved. In addition, as it had been observed on previous tests carried out in the previous projects (Hydrosol II and 3D), the inlet temperature of the feed gases in both steps (regeneration and water splitting) of the process ensured a fine adjustment of the reactor temperature.
During the first few months of the platform pre-testing and debugging campaigns, a test program was carried out to verify the behavior of all the components of the pilot plant, the feasibility of the measurement and analysis systems, the feed system, the gas treatment of the gas obtained during the water splitting step and, of course, the overall thermal behavior of the reactor.
During this period the measurement of the incident flux over the target was carried out with the current equipment installed in the PSA. To obtain the flux distribution, a white, diffusely reflecting Lambertian moving bar is rotated in front of the receiver. Then, a 14 bit Video Camera system was calibrated with one thermogage flux sensor fixed in the receiver aperture close to the measurement plane.
For a measurement, the moving bar is launched and then rotates through the focus and back. The acquired set of snap shots showing the moving bar at different positions over the background has to be assembled to a resulting image representing flux densities over the whole receiver aperture reaching up to 800 kW/m2. After exhaustive image processing, the total power can be integrated, and the rest of the magnitudes of interest, such as peak flux or statistical energy distribution parameters on the receiver can be calculated.
The gas cleaning system designed and constructed by HyGear consists of three elements, two large vessels, a cabinet with the compressor, the 4 PSA vessels and various valves. For safety on top of the cabinet a large fan is placed to avoid hydrogen accumulation in the cabinet in case of a leakage. Based on the design of the operation of the purification system, the produced gas stream from the solar reactors would be compressed by means of a 2-stage membrane compressor. The compressor delivers a pressure of around 12-13 bar. This is a suitable pressure for the Pressure Swing Adsorption system (PSA) as well as for hydrogen storage in both the buffer and final product vessels.
The buffer vessel is required to allow continuous operation of the system. The sizing (volume: 500 l) was based on a 6 h production time of the solar reactors; the PSA processes this amount in 24 h (it needs to operate continuously to achieve good performance). Due to the decreasing pressure during the hours of non-solar reactor production the gas from the buffer is fed back to the compressor, so that the operation of the PSA system cannot be paused.
The PSA vessels (four, plus one product vessel) are relatively small; this is due to the relatively short cycle time typical of PSA systems, in combination with the fact that the feed flow rate is quite low (a.o. due to the fact that it is processed in 24 h while it is produced in 6h, hence the PSA feed decreases by a factor of 4). The purified hydrogen is stored at 12 bar in the product vessel. It was sized to contain the expected production of about 3 days (volume: 900 l).
Following the completion of all installation works, the activities were focused on the ultimate target of the project; the on-sun operation of the HYDROSOL-Plant solar platform for the production of H2 from water splitting. Initially tests were conducted under atmospheric conditions, where several problems and bottlenecks were encountered that were mainly related to defective off-the-shelf products (leaks in the high temperature valves). After implementing some measures for the safe operation of the plant, thermal only tests were conducted to evaluate the performance of the cavity reactors during heating with concentrated solar radiation and their coupled operation with the plant peripherals. The main aim was to reach the target temperatures of 1100oC for the water splitting step and 1400oC for the thermal reduction step and assess the reactors’ response. In the initial thermal tests the temperature in the reactor cavity could be increased up to 900oC with the utilization of only a small number of heliostats. However, soon a significant issue occurred. The optical components failed. High temperatures were developed in the window flange and the secondary concentrator that could not be alleviated by the cooling network. As a consequence there was damage of the mirrors of the secondary concentrators and destruction of the sealing of the window flange. In addition, the decomposition of the sealing materials caused depositions on the quartz window that had to be thoroughly cleaned in order to be used again. These incidents led to further testing of a solar reactor under controlled conditions in a solar simulator (at Julich, Germany) where similar problems occurred. The design of the window flange was readdressed and the problem was solved allowing the safe operation of the reactor. Counteracting measures were also taken on the reactors at the solar platform and the experiments were continued with the target to further increase the temperature of the cavity and conduct water splitting and thermal reduction tests. During the operation of the solar platform the temperatures in the cavity reactor were limited to an average of 950-1000oC, while locally 1350oC have been also monitored. It was observed that there is significant inhomogeneity in the thermal map of the cavity with high temperature differences between the different foams. These conditions were not optimal for the thermal reduction and the water splitting reactions. Although the operation of the solar platform and the solar reactors under water splitting and thermal reduction conditions was achieved for the first time at the scale of the HYDROSOL-Plant reactors (90l cavity, 250kWth solar receiver/reactors consisting of Ni-ferrite and Ceria coated foams), the amount of H2 that was delivered was significantly lower than the initial target of 3 kg H2/week on the solar platform, as set by the project objectives and according to the mandate of the AIP2012. The main reasons are the low temperatures (at least 200-400oC lower than the optimal), as well as the low H2O flow rate. The final experiment on the solar platform delivered H2 at a rate of 0.25kg/week. Nevertheless, based on laboratory experiments for the investigation of the effect of the temperature and H2O content on the H2 production an approximation of the capacity of the solar platform, if it was operated under optimal conditions, can be made. Operation of the solar platform at the optimum water splitting temperature (to 1100oC) would increase the H2 production by a factor of 1.4 while increase of the thermal reduction temperature (to 1400oC) would cause an additional 2 times increase of the H2 production. Finally increase of the flow rate of H2O would lead to an additional 4 times increase in the H2 production. The extrapolated capacity of the solar plant under optimum conditions would be at the level of 2.8 kg H2/week.
WP7: System analysis and LCA.
Major objectives:
• To support the selection of the best suitable process options for further commercialization from an environmental point of view.
• To compare the HYDROSOL Process to other hydrogen generation processes.
• To decrease the environmental impact of the overall plant.
The LCA analysis is a very useful method for the evaluation of the total environmental impact of a product over its fabrication and construction process and operation cycle. The LCA-model was based on the flowsheet of the demonstration plant and the sizing of the components. Within the LCA-analysis of the HYDROSOL-demonstration plant, the attributional approach was selected since the impact of emissions during construction and operation on the GWP is the main focus of this analysis. Since the application of the produced hydrogen has not been defined within the HYDROSOLPlant project, the “cradle-to-gate” approach was applied to the LCA analysis.
The analysis showed that if implementing improvements on the issues that have been identified during the whole duration of the project and also by efficient exploitation of the vast amounts of heat generated in the process the total GWP of the plant would be reduced to levels comparable to those of wind-electrolysis.
WP8: Dissemination and Exploitation.
Major objectives:
• To provide for visible dissemination of the project’s results and maximize its impact to the most wide and relevant audience.
• To define the best way of exploiting the project’s results.
• To educate and train young researchers.
The HYDROSOL-Plant exploitable results are related to the:
Redox material: The redox material is the core of the HYDROSOL process. It is the main component of the HYDROSOL cavity reactor technology that facilitates the splitting of water and the production of hydrogen. The selection of the main material (NiFe2O4) was based on the experience and know-how of APTL that was gained through its research activities in all the previous HYDROSOL projects as well as from other projects in solar thermochemical process and solar chemistry. The specific material is relatively common in the field of research for the production of H2 from H2O. In HYDROSOL-Plant, however, it was achieved for the first time, the shaping of structures consisting entirely of NiFe2O4, in the form of honeycomb monolithic structures or monolithic foams either via extrusion, or casting in 3D-printed molds or via the polymeric matrix replication method, at the laboratory scale. The material was synthesized via the self-propagating high temperature synthesis route that is applied at APTL, which had to be appropriately adapted to achieve the scale-up requirements of the current project. In addition, apart from the core redox material that was investigated in HYDROSOL-Plant, another formulation was employed. CeO2 is another material of great interest in the field of solar thermochemistry. Compared to the NiFe2O4 it was not synthesized in the laboratory but it was a commercially available bulk material. Furthermore, this material was not developed from the small scale as in the case of the NiFe2O4 but it was directly deposited on inert material foam structures for implementation as building blocks for the construction of one of the three reactors that were constructed in HYDROSOL-Plant.
A significant achievement of the HYDROSOL-Plant project was the implementation of over 1000h of consecutive H2O splitting and thermal reduction cycles on a NiFe2O4 structured monolithic body (corresponding to an equivalent of over 6 months of on-sun operation or almost two years of laboratory experiments). Such a durability evaluation campaign has never before been reported in literature, and provided interesting aspects in the behavior and performance of structured ceramic materials for high temperature applications under alternating oxidizing and inert atmosphere conditions.
Another target that was achieved in the HYDROSOL-Plant project was the production of H2 at the laboratory scale corresponding to more than 3 kg/week based on novel structured monolithic bodies consisting entirely of NiFe2O4. Such results were reported for the first time and show the potential for the development of structures with enhanced properties. However, restrictions in time, budget, as well as the adaptation of the technology to an already existing platform, limited the choices for the scaling-up of the monolithic structures.
These achievements have created new foundations for the solar thermochemical H2 production based on structured solar reactors that will be exploited in the future research activities of APTL as well as in the future collaboration of the core group of the consortium in other projects.
Scale-up of redox monolithic structures: To reach the scale of implementation of the HYDROSOL-Plant significant scaling-up steps in the production of the active redox material and the shaping into structured bodies had to be achieved. The scaling-up of full size ceramic structured bodies consisting entirely of the redox material was assessed as significantly challenging. This task, although it is closely connected with the success of the implementation of the HYDROSOL-technology, it is on its own an innovation that could be exploited in applications such as solar receivers, active redox and catalytic structures for fuel production, upgrading and refining, compact reactors etc.
Although the shaping of oxide powders into structured ceramic bodies (e.g. monoliths with parallel channels (honeycombs) or with an open interconnected porous network (foams)) is based on well-established commercial processes, the actual challenges that HYDROSOL-Plant had to overcome, surpassed any initial prediction. The active redox materials, employed as the raw material for the shaping of the ceramic structures, in combination with:
-the geometries of the main building blocks of the specific cavity reactor design i.e. in total seven (7) different geometries with rather strict and non-commercially available dimensions and shapes that required precision machining
-the production scale concerning both the quantity of the required redox material but mostly the size of the required full-scale dimensioned monoliths, which for example in the case of extruded monoliths would require infrastructure with capabilities beyond the commercially available ones
-the nature of the intended application itself; cyclic operation at elevated temperatures with constant “expansion and contraction” of the redox material lattice and finally
-the fact that all of the above innovations/challenges were simultaneously attempted for the first time
describes the degree of complexity that the project had to overcome.
Despite the fact that the shaping of stable large-scale green bodies turned out to be a relatively normal task to achieve, the main problems were encountered during the sintering and the post-calcination steps involved in the preparation process. The development process required time, manpower dedication, numerous efforts and close collaboration with an experienced technical ceramics manufacturer for the scaled-up production. However, there were still several issues that were encountered, (e.g. the melting of structures or the poor mechanical stability of fragile and brittle sintered bodies) that affected the delivery time of the main building blocks of the reactors. A process for the production of sufficiently stable large scale monolithic foams consisting entirely of the active redox material (i.e. NiFe2O4), was finally developed. However, time and budget restrictions, limited the production to only a few series of segments that could partially cover the construction of one reactor. Unavoidably the implementation of the fallback option of the preparation of the same geometries and blocks but from already commercially available inert materials and the application of the active redox material as a coating, was followed in order to cover the construction of the rest of the reactors.
Nevertheless, the achievement of the production of small and large scale monolithic structures consisting entirely of the NiFe2O4 represents an important development in the sector of ceramics’ fabrication methods and fields of application which is of particular interest for specialized technical ceramics manufacturers. In addition it has paved the way towards new shaping techniques that will be exploited in the future especially by the Research partners.
HYDROSOL solar reactors design: The HYDROSOL technology is based on directly irradiated solar monolithic reactors. Until the current project the designs that had been implemented in the previous projects were based on the same principle but with the construction of flat reactors (12l active volume). In the previous HYDROSOL-3D project the possibility of designing cavity reactors consisting of monolithic segments was investigated. However, it was not until the HYDROSOL-Plant project, that an actual redox cavity reactor was constructed. The design of the current reactors is based on an already successful design that was initially developed by DLR for a methane reforming process. However, the difference in the HYDROSOL-Plant reactors was that the main building blocks that are the actual active component and are based on foam monolithic structures, had to be constructed with a higher thickness (2-times thicker foams) so that the appropriate amount of active material could be incorporated in the available space of the already existing solar platform.
Within the project the development and construction of three such reactors was realized for the first time at the scale of 90l active volume each. This positions these reactors as the largest structured reactors in the world for the production of solar H2 based on the two step redox thermochemical splitting of water.
Moreover, a significant component of the reactors was the secondary optics, i.e. the secondary concentrator that enhances the incoming solar flux in the reactor cavity. These components were again based on the experience and know-how within the consortium and was chosen as the most optimum solution to achieve the targets set in the project. However, unexpectedly, these components that were state-of-the-art and had been previously successfully employed in other concentrated solar applications, failed during operation at the solar platform and consequently affected the proper operation of the reactors and the accomplishment of the ultimate project target.
Therefore, retrospectively, a development gap is identified both in the scaling up of the reactors as well as in the utilization of already existing and validated components, which enhanced the challenges both in the construction as well as in the operation of the reactors.
The experience that was gained from the HYDROSOL-Plant project will be exploited by the Research partners in the future by addressing the issues that were identified within the project and in addition by adapting new approaches within the framework of the follow-up proposed collaborative project.
The HYDROSOL-Plant solar platform at the Plataforma Solar de Almeria: The proof of concept of the two step solar thermochemical water splitting for H₂ production based on structured redox materials has been demonstrated in the first HYDROSOL project while a scaled up version of the technology (up to 100 kWth) was confirmed in the two HYDROSOL projects that followed. The aim of the HYDROSOL-Plant project was to prove the feasibility of further scalability of the technology to a near MW scale that would provide more solid evidence about its potential future commercial exploitation.
In the HYDROSOL-Plant project the development of the technology had to evolve in parallel in several different fields involving:
-the production of the active redox material that had to be scaled up from a few hundreds of grams to several hundreds of kilograms (a total of ~600 kg of NiFe2O4 were synthesized for the needs of the shaping and scaling-up of foam structures), to
-the scaling of the reactor size, from a total reactor volume of 12l to 90l per reactor
-the scale up of all peripheral components (valves, heat exchangers etc)
-the assembly of all components on the existing space at the SSPS CRS solar tower in Plataforma Solar de Almeria in Spain
-the entire process control, scaled from 0.1MWth (HYDROSOL-II platform) to 0.75MWth (HYDROSOL-Plant platform) and naturally to
-the debugging and final operation of the integrated system
The target was to implement efficient solar testing campaigns at the 0.75MWth HYDROSOL-Plant solar facility in the Plataforma Solar in Almeria, ultimately demonstrating the production of solar H2. However, several challenges during installation and debugging process led to major delays that did not allow the proper operation of the facility and subsequently the production of H2.
The most determining factors that caused significant delays in the operation of the plant were the following:
- the damage of one of the reactors (the reactor that consisted of CeO2 coated foams) during its installation to the holding structure on the platform.
- the detection of leaks in the commercially acquired high temperature valves. The solving of this problem was of high importance because it compromised the safe operation of the plant.
- the problematic operation of the secondary concentrators related mainly to inadequate cooling.
- the Weather. Realistic solar experiments in the actual solar platform environment depend on weather conditions (e.g. high percentage of cloud coverage, strong winds etc.). Weather instability with poor insolation and/or high winds do not allow the operation of the platform. This minimized the window of opportunity for successful solar.
The aforementioned reasons did not allow the implementation of solar H2 producing experiments at the solar platform at the scale that was targeted in the beginning of the project and according to the AIP2012.
However, the HYDROSOL-Plant platform was operated for a period of over 3 months including 3 months after the end of the project to acquire as much as possible data and experience in its operation. This data will serve as a starting point for improvements that are envisaged to be implemented in a future collaborative project and for further efforts for solar hydrogen production at similar scales.
As a conclusion, the determination of improvement actions is probably the most valuable outcome that could be exploited in future relevant research efforts with the aim of: a) demonstrating H2 production at the 0.75MWth scale; b) further increasing the targeted H₂ production; c) improving the reactor design and its peripherals; d) further reducing the cost and the production duration of the redox materials and the respective monolithic structures; e) additional assessment of the long-term stability and overall performance of the redox structured reactors under solar radiation; f) suggesting ways for rapid comparative evaluation of different materials and structured geometries under realistic conditions, g) minimization of the inert gas utilized mainly for the thermal reduction step, h) maximization of the heat recovery.
The project progress and results were disseminated through publications in scientific journals and conference proceedings, presentations in conferences and forums, as well as via other public dissemination mechanisms (EU, FHC-JU platforms, Horizon Magazine, exhibitions, trade fairs, business and technological forums, webinars, web newsletters, etc.). In addition, a workshop was organized at the HYDROSOL-Plant facility at the Plataforma Solar de Almeria in Spain for the presentation of the major project achievements and the demonstration of the completed solar platform.
Potential Impact:
The promotion of renewable energy penetration is a top priority for the tackling of the adverse effects of the current dominant energy production processes on the environment, and the achievement of Europe’s and worldwide energy efficiency and climate and greenhouse gas emissions specific targets especially the very ambitious ones set for the mid- to long-term future. The complete substitution of fossil fuels by a mixture of renewable and sustainable energy sources, thus assuring the production of carbon-neutral or ultimately even carbon-free energy and the decarbonisation of transportation and modern economy in general, is one of the most persistent quests both within the EU as well as globally that if successful could be the sole solution for significant socio-economic benefits (independence from fossil fuels, improvement of living standards, health and safety, potential for job creation and employment).
Amongst the wide variety of alternative fuels, H2 has been increasingly investigated as a potential alternative energy carrier and storage medium in the last few decades and, especially in Europe, after the establishment of the FCH-JU as the “sponsor” of research and development activities that are related to sustainable and renewable H2 production processes. Currently the dominant H2 production process is via steam reforming mainly of methane, which is a relatively “carbon-rich” chemical process, and is the main competitor of renewable hydrogen both in terms of mass production and efficiency of production as well as financially.
Therefore, there are several challenges that need to be overcome so that a reliable and low cost, renewable hydrogen can be produced. To achieve this, the exploitation of the vast and practically inexhaustible solar potential is an attractive primary solution. Introducing a chemical process (two-step thermochemical water splitting), such as the production of H2, in a solar tower (e.g. employed for the production of heat for the generation of electricity), facilitates the storage of solar energy into a chemical, an energy carrier, which has no temporal or local limitations and can be used, when needed, in several different ways either as clean transportation fuel or as a feed into other chemical processes.
The HYDROSOL-Plant project pursued to address the challenges of realizing the scaling-up of the process at a near the MW level and adapting the solar plant in an already existing solar platform at the Plataforma Solar de Almeria in Spain. The essence of “scaling-up things” is inherently challenging. It is a common problem that all processes may more or less face when evolving towards technological maturity. Although there are significant endeavors worldwide for the development of solar thermochemical processes for the production of hydrogen based on redox water splitting, only a few examples exited the laboratory and were deployed at realistic scale. The HYDROSOL-Plant project, was the first worldwide to deal with the demonstration of the scalability of the technology near the MW scale. The implementation of the project revealed the potential of the technology but also the significant “bottlenecks” that almost naturally appear when stepping out of the controlled environment of the lab and of simulated operating conditions.
By the end of the project, a complete solar plant for the production of H2 based on redox thermochemical splitting of water had been integrated to the solar tower at the Plataforma Solar de Almeria in Spain. This success had also profound challenges. The systematic operation of the plant in the H2 production mode at optimum conditions was not achieved until the end of the project. Currently the temperatures that have been achieved at the reactors are not high enough to fully promote the two steps of the process (thermal reduction and water splitting). Nevertheless, even at such non-optimum conditions some Hydrogen has been produced, validating more or less the laboratory findings that had shown an activity of the materials, however low, at such conditions. These results give a taste of the potential of the process, which, needs further development in order to confront the challenges that are emerging when operating at that scale. Future targets are focused on the exploitation of the most substantial benefit of the technology, which is the significant amounts of high temperature solar heat produced during the redox cycles. Employing efficient heat recovery at the high temperature levels of the process would have an impressive effect both on the efficiency of the process as well as on the environmental assessment of the plant.
List of Websites:
http://hydrosol-plant.certh.gr/root.en.aspx
Coordinator: Athanasios G. Konstandopoulos
CENTER FOR RESEARCH AND TECHNOLOGY HELLAS
6th km Charilaou-Thermi rd, 57001 Thessaloniki, Greece
E-mail: agk@cperi.certh.gr
tel: +30 2310 498 192
Coordinator contact: Souzana Lorentzou
CENTER FOR RESEARCH AND TECHNOLOGY HELLAS
6th km Charilaou-Thermi rd, 57001 Thessaloniki, Greece
E-mail: souzana@cperi.certh.gr
tel: +30 2310 498 421
The HYDROSOL-technology series of projects are based on the utilization of concentrated solar thermal power for the production of Hydrogen from the dissociation of water via the redox-pair metal oxide based two-step thermochemical cycles. The redox material is a metal oxide or a combination of metal oxides (e.g. ferrites, cerium oxide etc.) with cations that have the ability to obtain different oxidation states and thus these materials can exchange oxygen through their lattice. The HYDROSOL-technology differentiates from other conventional Hydrogen production technologies mainly in two ways; the utilization of renewable and practically inexhaustible raw materials (solar energy and water), and the utilization of modular structured reactors. In the HYDROSOL-Plant project several advancements were introduced related to large scale redox materials’ synthesis, shaping into porous structures, reactor design, etc. The HYDROSOL-Plant is the largest demonstration facility (0.75MWth) of its kind, worldwide. The ultimate objective was to achieve the production of H2 at a level of 3 kg/week as set also in the AIP2012. With the end of the project the solar H2 production on the HYDROSOL-Plant platform has been achieved for the first time on the full scale reactors, however at a lower level than the initial target. The scale of implementation of the HYDROSOL-Plant project allowed the identification of several challenges and development gaps that exist and need to be addressed and revisited during the evolutionary process of bringing the technology of solar redox thermochemical H2 production to commercial level.
Project Context and Objectives:
The HYDROSOL-Plant project is the continuation of a series of successful research projects (HYDROSOL, HYDROSOL-II and HYDROSOL-3D) focusing on the production of H₂ from the two-step solar thermochemical water splitting based on redox structured reactors. The principal objective of HYDROSOL-PLANT is the development and operation of a plant for solar thermo-chemical hydrogen production from water in a 0.750 MWth scale on a solar tower, based on the HYDROSOL technology. The HYDROSOL-plant consortium consists of 3 Research Centers from Greece, Germany and Spain (APTL which is the coordinator of the project, DLR and CIEMAT), 1 SME from the Netherlands (HYGEAR) and 1 Industry from Greece (HELPE).
The predecessor projects HYDROSOL and HYDROSOL-II have introduced the concept of redox structured monolithic solar reactors for the production of solar H2 from water. The proof of concept at lab-scale was presented in the first HYDROSOL project, while the feasibility of the main principles of the process for longer-term cyclic operation at a pilot reactor set-up in a scale of 100 kWth at the Plataforma Solar de Almeria (PSA) was proven in HYDROSOL-II project. In the third project of the series, HYDROSOL-3D, the relevant design aspects necessary to prepare the erection of a solar demonstration plant at the 1 MWth scale were addressed. However, the actual realization of a solar demonstration plant near the MW scale (0.75MWth) was achieved in the HYDROSOL-Plant project.
The specific Scientific and Technical Objectives of HYDROSOL-3D were:
• Define all key components and aspects necessary for the erection and operation of a 750 kWth solar plant for H2O splitting (heliostat field, solar reactors, overall process monitoring and control, feedstock conditioning, etc.)
• Develop tailored heliostat field technology (field layout, aiming strategies, monitoring and control software) that enables accurate temperature control of the solar reactors.
• Scale-up the HYDROSOL reactor while advancing the state-of-the-art (redox materials, monolithic honeycomb fabrication and functionalization) for optimum hydrogen yield.
• Design the overall chemical process, covering reactants and products conditioning, heat exchange/recovery, use of excess/waste heat, monitoring and control.
• Construct a solar hydrogen production demonstration plant in the 750 kWth range to verify the developed technologies for solar H2O splitting.
• Operate the plant and demonstrate hydrogen production and storage on site (at levels > 3 kg/week).
Project Results:
The HYDROSOL-PLANT project website was launched and is fully operational since April 2014. The website has a public area, providing non-confidential information about the project as well as the ability to contact the project coordinator requesting further information or making comments about the project. There is also a ‘member’ area granting access to the partners and the officer to the project’s confidential documents.
WP2: Process Layout
Major objectives:
• To prepare a detailed design of the complete demonstration plant.
• To provide the basis for the development of system control schemes.
• To enable the final definition of all necessary plant components and interfaces.
A detailed design of the complete demonstration plant flowsheet was developed. The flow sheet incorporates all process design improvement, identified within the previous project (HYDROSOL-3D), mainly concerning heat recovery, water and hydrogen separation and steam generation as well as the final refinements of the reactor’s design. Furthermore, it contains the main results of the simulation of the plant, which has been carried out by using the simulation tool Aspen Plus. Based on this flow sheet, a piping and instrumentation diagram (P&ID) was developed, which will provide the piping of the process flow diagram together with the installed equipment and instrumentation in order to define the control strategy of the plant. The flow sheet involves all necessary components for the operation of the plant by taking into account also existing facilities on the PSA in Almeria.
Some aspects of the process, although significant for the operation of a real plant, such as the recycling/reuse of N2 that is consumed in the process, were not addressed in the final process layout, since the project focuses on the H2 production part and not so much on the peripherals. In a real plant operation, recycling of the N2 used in the process would be of high economic/commercial significance, but at the scale of the current research project this was put aside.
WP3: Manufacture of Hydrogen production unit
Major objectives:
• Development and manufacture of a complete 750 kWth scale dual receiver/reactor unit for solar thermochemical splitting of water.
Work was focused on the finalization of the reactor design. The initial reactor concept of the HYDROSOL technology (HYDROSOL, HYDROSOL-II and HYDROSOL-3D) involved a dual reactor system. The reactors consisted of porous monolithic structures constructed either from re-crystallized SiC (ReSiC, for the case of the HYDROSOL project and the single chamber and dual-chamber 3 kW solar reactors) or from siliconized SiC (silicon-infiltrated Si-SiC, for the case of the HYDROSOL-II and HYDROSOL-3D 100 kW reactor) coated with the redox material. These monolithic structures were selected because besides their capability of operating as volumetric receivers/ absorbers of concentrated solar irradiation and achieving and sustaining the required high temperatures, their multi-channeled structure provided high gas-solid contact area and facilitated the access of steam to the reaction sites of the redox material.
In the previous project (HYDROSOL-3D), a point of improvement of the reactor’s design was the change of the geometry of the reactor from flat to spherical, since the latter provides the most efficient exploitation of the solar flux. Another aspect that was considered had to do with the fact that the substrate occupies the majority of the reactor volume (and weight) compared to the active redox material (the amount of the latter used so far on the SiC structures was about 20 %wt). Since the water splitting reaction based on redox materials depends also on the mass of the redox material on the reactor, the hydrogen yield per reactor volume would be rather low. A solution that would tackle this limitation was to produce the monolithic segments that constitute the reactor body entirely from the redox material.
Within the HYDROSOL-PLANT project, the design of the reactor was revisited, based also on the results of the previous project (HYDROSOL-3D), and the number and geometry of the reactors was defined. The final reactor design involves a set-up of 3 reactors put in a triangular arrangement. In the previous projects it was shown that although the flat geometry is the least complex in terms of manufacturing and maintenance, the conical and spherical geometries are likely to achieve better flux distributions. Ray-tracing simulations showed that the best shape that would allow the highest quality of flux distribution in the absorber would be the spherical shape [HYDROSOL-3D project]. However, this reactor concept had also some disadvantages mainly regarding the shapes of the monoliths and the supporting of the different segments to achieve the spherical shape of the absorber.
Consequently, in HYDROSOL-PLANT a new reactor design was developed based on previous cavity reactor designs that were employed in solar applications (REFOS, SOLREF and EMPOLI).
The new Hydrosol reactors consist of five main parts: 1) the secondary concentrator extension, 2) the front flange, 3) the quartz window, 4) the volumetric absorber and 5) the vessel.
The absorber consists of several porous monolithic structures. These blocks have to be assembled in such a manner that would create a cavity, so that the radiation crossing the window can be absorbed by the material more efficiently and uniformly. A first target in the Hydrosol-Plant design was to increase the volume of the blocks that form the cavity reactor in order to further increase the quantity of redox material that can be incorporated on the reactor. For this reason the cavity was made longer and thicker, compared to the previous reactor designs, to accommodate more material. The reactor is formed by 6 parallel rings, one as inlet and five as outlet, and each ring is made by 18 blocks. The total active material volume inside the cavity was increased to about 95 liters/reactor.
A dome window design was chosen and the front flange was designed to hold both the secondary concentrator and the window. A cooling network is essential to keep the window flange at appropriate temperatures for the sealing during operation under solar flux.
The three reactors would be placed on the solar tower on a steel structure able to bear their weight and to point the reaction chambers to the middle of the heliostat field. The reactors are placed at about 26 m high from the ground and the heliostats field has twelve lines: the horizontal distance between the frontal face of the tower and the seventh line is 106 m. The arctangent of this triangle gives 14° as result and so the structure has to tilt the reactors at this angle. A support for each reactor is designed to make easier the assembly and then both are placed on a turntable, which makes possible the maintenance of the reactor itself.
A secondary concentrator at the entrance of the reactor was considered for the minimization of the thermal losses from the reactor window and for focusing the sun rays inside the active reactor area. The secondary concentrators that used in the HYDROSOL-PLANT project are based on existing systems. The purpose of that component is to use the spillage in the reactor instead of losing it, to homogenize the solar radiation as much as possible hitting the reactor window and to protect the front flange from the direct radiation coming from the heliostats.
Furthermore an investigation on the porous structures that will form the cavity of the reactor (main reactor body) was conducted with the aim to increase the capacity/reactor volume. Certain specifications had to be covered (such as platform space and weight limitations, reactor volume, scalability of the redox porous structures, and also budget limitations) that affect also the final reactors’ design. Monoliths as well as foams consisting entirely of the redox material were considered as possible structures for the building of the reactor body and were developed and evaluated. In addition the durability of the redox structure was assessed.
Based on past experience NiFe2O4 synthesized via the Self-Propagating High temperature Synthesis (SHS) method was considered the redox material of choice to be applied in the reactor. This material possesses the appropriate characteristics for the current solar plant, i.e. it has a significant splitting performance at moderately high temperatures (Tsplitting: 1100C) without the need of extremely high temperatures for its regeneration/reduction (Treduction: 1400C). Also it is a formulation that has been extensively investigated in the previous HYDROSOL projects and has been applied at the previous solar reactor concept under the actual conditions at the current solar platform facility where the new plant is going to be located.
The use of inert lightweight monoliths as substrates for the redox material was initially investigated. Al2O3 based monolith was considered as the most appropriate substrate since it has small weight, can operate at the high temperatures of the process and does not participate in the water splitting reaction. NiFe2O4 synthesized via the SHS process was deposited on an Al2O3 monolith via impregnation in a slurry of the redox material. This solution was finally rejected since there was an indication of possible interaction of the NiFe2O4 coating with the Al2O3 substrate detected via X-ray diffraction analysis on fresh and processed samples, although this was limited to an interface where NiFe2O4 is in direct contact with the Al2O3.
In parallel the extrusion of honeycomb monoliths consisting entirely of NiFe2O4 (activity pursued for the first time ever based on open literature) was also investigated employing a lab-scale piston extruder. Optimization of the extrusion process allowed the production of thin-wall extruded monoliths with good structural stability. The structure was subsequently subjected to multiple H2O splitting/thermal reduction cycles. The evaluation started within the first period of the project and continued also in the second project period. The durability assessment involved consecutive water splitting (60 vol% H2O concentration in N2) and thermal reduction cycles (N2 flow). The 1000h operation target of the project was achieved and with the exposure of the structure in approximately 600 consecutive cycles (corresponding to a time-span of approximately 6 months of on-sun operation) at temperatures from 1100 to 1400oC and alternating vapor and inert gas atmosphere. After approx. 400h activity was more or less stabilized to ~0.1 mmoles/gmonolith. In addition, “cast” monoliths prepared by using 3D-printed molds were evaluated during the first period of the project and had a prominent performance.
Although the performance of the all-redox extruded and 3D-printed cast honeycomb monoliths was appreciable, difficulties in the scaling-up of the different segment geometries that comprise the reactor cavity could not be overcome especially within the scope and the limited timeframe of the project
Based on:
- the complexity of the reactor cavity segments’ geometries that increases machining difficulty for the case of honeycomb monoliths and subsequently the cost of the whole structure.
- communications with experts in the field of honeycomb monoliths manufacturing for commercial applications
- the experience gained in another project coordinated by APTL (RESTRUCTURE project, FP7-283015), for the scaling-up of the extrusion of honeycomb monolithic structures from lab-scale dimensions to actual full-scale dimensions,
- and finally the limited time for the construction of all reactors and the completion of the plant facility
, it was decided that other geometries with more facile scaling-up potential, such as foam structures, should be chosen as a fallback option for the construction of the cavity reactors. Preliminary work on small scale foams took place within the first project period showing encouraging results.
Therefore, within the first months of the second project period the activities were focused on the scaling-up of the production of NiFe2O4 powder to be used as the starting material for the manufacturing of all-redox NiFe2O4 foams. The capacity of the method for powder production at the laboratory was of the order of 100-200 g/d at the beginning of the project. The final scale-up of the NiFe2O4 synthesis reached 15 kg/day.
Several problems occurred during the scaling-up of the foam structures that had not been previously identified during the investigation of producing small scale foams that consist entirely of the redox material. The problems that had occurred spanned from foam structures melting in the furnace during heating, to shape deformation and cracking. Thermal testing at APTL of the prepared large scale foam segments, both in conventional electrical furnace as well as in the solar simulator, revealed the challenges in the preparation of robust all-redox full-scale foam structures.
Those challenges, along with the low tolerance in the dimensions of the different segments (in order to achieve perfect fit of the segments in the cavity reactor) and the limitations in the available raw material and also in the time left for the completion of all the reactors, led the consortium to take the decision of using commercially available foams that would be coated with the redox material. 54 pieces with three different geometries were already manufactured consisting entirely of NiFe2O4 while the rest of the foams i.e. 55 pieces to complete the 1st reactor and 220 pieces to complete the 2nd and 3rd reactors would be prepared via coating of NiFe2O4 and CeO2 (for comparison purposes. CeO2 has been investigated in the past with respect to its potential in water splitting with promising results) on standard foam substrates (e.g. ZrO2).
Comparison at the laboratory scale of all-redox NiFe2O4 foams with NiFe2O4 coated foams with respect to their redox activity did not show significant differences. Comparison of the NiFe2O4 coated foam with the CeO2 coated foam showed significant differences mainly in the rate of the reaction and the total H2 produced which was higher in the case of the NiFe2O4 at the specific experimental conditions.
The assembly of the reactors with the foams and the different supporting components was done manually and involved multiple disassembling and reassembling of the components in order to find the best fit and to achieve stability of the structure. In addition kipping tests were conducted, prior to transportation to the solar tower at the Plataforma Solar de Almeria to ensure the integrity of the unit during transport, lifting or when tilted.
WP4: Development of balance of plant components
Major objectives:
• To address all - besides the hydrogen production unit - necessary components’ sizing and detailed design.
• To accordingly manufacture/procure these components.
• To select and procure all necessary sub-components and equipment needed for process automation and control.
The SPSS-CRS (small solar power central-receiver system), consists of an autonomous field of heliostats and a metallic tower 43 meters high. SSPS-CRS tower is equipped with a large quantity of auxiliary devices that allow the execution of a wide range of tests in the field of solar thermal chemistry. All test levels have access to pressurized air (29 dm3/s, 8bar), pure nitrogen supplied by two batteries of 23 standard-bottles (50 dm3/225bar) each, cooling water with a capacity of up to 700 kW, demineralized water (ASTM type 2) from a 8 m3 buffer tank for use in steam generators or directly in the process, and the data network infrastructure consisting of Ethernet cable and optical fiber.
The HYDROSOL-Plant consists of two distinct parts: 1) the solar reactor with steam generator, heat exchangers and condensation units; 2) the gas cleaning unit consisting of a buffer vessel, a product vessel, a compressor and a small PSA-system. The main components are integrated on the metallic tower using flexible pipes in the evaporation part, the reaction part, the H2 purification part, and the nitrogen supply part.
The solar reactor system consists of 4 main blocks. First water is converted into steam in the steam generation part. The steam is then going to the reactor system, where it is converted to hydrogen. The wet hydrogen then goes to the condensation part to dry. Subsequently it flows to the PSA system to be purified and stored. For regeneration of the reactors Nitrogen is needed, which is supplied via the Nitrogen part.
Based on this process layout and the work conducted in WP2 and WP3, all BoP and sub-BoP components were defined and procured. Such components are the cryogenic unit which was installed at the facility for the supply of adequate N2 flow to the solar platform, the demineralized water plant and the steam generator for the supply of water, the product purification unit (PSA) with the buffer and PSA vessels and the cooler/condenser. The plant peripherals, such as valves, mass flow controllers, pressure sensors, thermocouples, etc. were also identified and procured. Furthermore the product gas purification unit, based on Pressure Swing Adsorption (PSA) was constructed, taking into account the needs of the solar process which is characterized from high vapor concentrations and low H2 flow rates and is intermittent (the diurnal nature of solar energy in contrast to the PSA which needs to be operated continuously to achieve good performance), and.
WP5: Set-up of demonstration plant.
Major objectives:
• To adapt the solar tower platform to the hydrogen plant operation requirements.
• To install the fully assembled solar hydrogen production reactor on the solar tower.
• To install all other necessary plant components.
• To integrate the operation of the whole plant via the implementation of suitable control software, hardware and plant’s infrastructure.
The relevant activities necessary to prepare the erection of a HYDROSOL technology-based 0.75 MWth solar demonstration plant involve the completion of the whole plant including the solar hydrogen reactor and all necessary upstream and downstream units needed to feed in the reactants and separate the products.
The HYDROSOL-Plant facility was installed at the SSPS-CRS platform at the Plataforma Solar de Almeria in Spain. The activities involved preparation of the solar field facilities (heliostats, tower, control rooms), the installation of the solar reactors and the coupling to the peripherals (heat exchangers, purification units etc.).
The SSPS-CRS plant was inaugurated as part of the International Energy Agency’s SSPS (Small Solar Power Systems) project in September 1981. Originally conceived to demonstrate continuous electricity generation, it used a receiver cooled by liquid sodium that also acted as the thermal storage medium. At present, this test facility is mainly devoted to testing small solar receivers in the 200 to 500-kWth capacity range.
During the first 18 months of the project, work has been focused in preparing the solar platform facilities to house the HYDROSOL-Plant platform. The preparation of the solar platform involved improvements not only in structural works at the 27m height platform but also of the performance of the plant (renovation of the facets, new control program). Some actions that have taken place on this task were:
• Improvement of the communication of heliostats by wiring all heliostats.
• Re-moderation of control room
• Addition of new functionalities in the control program
• Renovation of the facets of the heliostat field.
• Conditioning of the platform.
The heliostats’ facets were renovated (high reflectivity mirrors that contribute to the improvement of the efficiency of the captured solar radiation on the reactor, under typical conditions of 950 W/m2, total field capacity is 2.5 MWth and peak flux is 2.5 MW/m2). The platform that would host the plant was enlarged by 20m2. In addition a deck was added below the main deck to host the purification unit and peripherals and the electrical control cabinets. The main deck was reformed for the installation of the 3 reactors. The positioning of the reactors was proposed to be triangular, for the most efficient irradiation, with two of the reactors placed on the floor and one hanged from the roof. The specific assembly of the reactors in a triangular configuration required the design of a support structure on a wagon, which also hosts all main peripherals that would provide flexibility during maintenance and service works. In addition changes in the façade of the solar tower for the appropriate attachment of the secondary concentrators were necessary. Flux measurement systems equipped on the solar tower allowed the calculation of the solar flux on the new reactors’ configuration. The installation of the three reactors was conducted with the aid of cranes while the mounting of the optical components on the reactors was done on the platform. During the reactors installation, an accident on the positioning of the top reactor caused the destruction of the cavity and as a consequence the platform completion was significantly delayed. However, no damage of the redox foams occurred which indicated the rigidity of the structures. In addition, all installation of hardware (control cabinets, data acquisition workstations) and the development of the software interfaces for the control and monitoring of the different solar facility components (i.e. heliostat field, peripherals control based on the process layout, solar reactors interface, PSA interface etc.) were developed and completed. The new control program provides much more information for the design of a supervisory system (monitoring and diagnosis displays, definition of alarms, meter readings, equipment status reports etc.). A ray tracing tool for the simulation of the solar flux distribution on the reactors was developed with the potential to be validated by solar flux measurements based on a camera moving bar system on the solar tower with the target to simulate the process and eventually replace the moving bar technology.
All peripherals and the three reactors coupled with the optical components were successfully integrated to the SSPS-CRS solar facility in Plataforma Solar de Almeria. A HAZOP analysis was conducted to identify the existing potential hazards resulting from process deviations, and when necessary, propose possible actions to reach safety and operability risk levels that are acceptable.
WP6: Operation and validation of demonstration plant.
Major objectives:
• To demonstrate the feasibility of the proposed process for solar hydrogen production in the 750 kWth scale.
• To validate the performance of key plant materials and components with respect to economic operation.
• To assess the technology vs. the targets set and evaluate its potential for further scale-up.
The HYDROSOL-technology relates to the utilization of renewable and practically inexhaustible raw materials (solar energy and water), and the utilization of structured reactors. The predecessor projects HYDROSOL and HYDROSOL-II have introduced the concept of redox structured monolithic solar reactors for the production of solar Hydrogen from water. The proof of concept at lab-scale was presented in the first HYDROSOL project, while the feasibility of the main principles of the process for longer-term cyclic operation at a pilot reactor set-up in a scale of 100 kWth at the Plataforma Solar de Almeria (PSA) was proven in HYDROSOL-II project. In the third project of the series, HYDROSOL-3D, the relevant design aspects necessary to prepare the erection of a solar demonstration plant at the 1 MWth scale were addressed. However, the actual realization of the construction of a solar demonstration plant near the MW scale (0.75MWth) was achieved in the HYDROSOL-Plant project. Several advancements were introduced, with the ultimate objective to achieve a production of Hydrogen at a level of 3 kg/week. The HYDROSOL-Plant is the largest demonstration facility of its kind, worldwide.
The activities that took place within the last period of the project involve the pre-testing, debugging and testing of the different components of the solar platform. The tests were conducted under atmospheric conditions as well as under solar radiation conditions. Several problems and bottlenecks were encountered on critical for the operation of the reactors components.
The platform that hosts the HYDROSOL-Plant installation is located at the 27 m level in the CRS receiver plant in Plataforma Solar de Almeria. This level also accommodated the previous HYDROSOL II and HYDROSOL 3D installations and it was a closed room, four meters high with 60 m2 available for equipment. The HYDROSOL Plant installation has been divided into two parts. The main components of the plant, such as reactors, secondary concentrators, steam generator, and main gas stream pipes are located in the main floor. The floor 4 meters below the main deck accommodates the rest of the peripheral components, mainly consisting of the purification system of the outlet gas. In the lower deck, a condenser removes the water from the outlet gas stream and prepares the gas for the purification subsystem, which is used to separate and store the hydrogen produced in the water splitting step. The system consists of three elements: two large vessels (buffer and final product) and a cabinet containing a compressor and four PSA modules.
The HYDROSOL-Plant solar thermochemical cycles consist of two steps carried out at different temperature levels with different energy requirements. The regeneration step is endothermic and takes place at 1300-1400°C; the water splitting step is slightly exothermic and takes place at 1000-1100°C. Therefore, the reactor which is under regeneration needs a higher solar flux density than the reactor that is in the water splitting mode. In fact, the latter would only need a small amount of solar energy to compensate for heat losses. This means that it is necessary to vary the flux density when the cycle state in the modules changes from regeneration to water splitting and vice versa.
The results of the previous Hydrosol II and 3D experimental campaigns formed the basis for the development of a process control strategy for Hydrosol Plant. From the experience gained in the operation of the previous reactors coupled to the solar tower facility, it could be confirmed that with the control of the heliostat field the simultaneous adjustment of the two different process temperatures could be achieved. In addition, as it had been observed on previous tests carried out in the previous projects (Hydrosol II and 3D), the inlet temperature of the feed gases in both steps (regeneration and water splitting) of the process ensured a fine adjustment of the reactor temperature.
During the first few months of the platform pre-testing and debugging campaigns, a test program was carried out to verify the behavior of all the components of the pilot plant, the feasibility of the measurement and analysis systems, the feed system, the gas treatment of the gas obtained during the water splitting step and, of course, the overall thermal behavior of the reactor.
During this period the measurement of the incident flux over the target was carried out with the current equipment installed in the PSA. To obtain the flux distribution, a white, diffusely reflecting Lambertian moving bar is rotated in front of the receiver. Then, a 14 bit Video Camera system was calibrated with one thermogage flux sensor fixed in the receiver aperture close to the measurement plane.
For a measurement, the moving bar is launched and then rotates through the focus and back. The acquired set of snap shots showing the moving bar at different positions over the background has to be assembled to a resulting image representing flux densities over the whole receiver aperture reaching up to 800 kW/m2. After exhaustive image processing, the total power can be integrated, and the rest of the magnitudes of interest, such as peak flux or statistical energy distribution parameters on the receiver can be calculated.
The gas cleaning system designed and constructed by HyGear consists of three elements, two large vessels, a cabinet with the compressor, the 4 PSA vessels and various valves. For safety on top of the cabinet a large fan is placed to avoid hydrogen accumulation in the cabinet in case of a leakage. Based on the design of the operation of the purification system, the produced gas stream from the solar reactors would be compressed by means of a 2-stage membrane compressor. The compressor delivers a pressure of around 12-13 bar. This is a suitable pressure for the Pressure Swing Adsorption system (PSA) as well as for hydrogen storage in both the buffer and final product vessels.
The buffer vessel is required to allow continuous operation of the system. The sizing (volume: 500 l) was based on a 6 h production time of the solar reactors; the PSA processes this amount in 24 h (it needs to operate continuously to achieve good performance). Due to the decreasing pressure during the hours of non-solar reactor production the gas from the buffer is fed back to the compressor, so that the operation of the PSA system cannot be paused.
The PSA vessels (four, plus one product vessel) are relatively small; this is due to the relatively short cycle time typical of PSA systems, in combination with the fact that the feed flow rate is quite low (a.o. due to the fact that it is processed in 24 h while it is produced in 6h, hence the PSA feed decreases by a factor of 4). The purified hydrogen is stored at 12 bar in the product vessel. It was sized to contain the expected production of about 3 days (volume: 900 l).
Following the completion of all installation works, the activities were focused on the ultimate target of the project; the on-sun operation of the HYDROSOL-Plant solar platform for the production of H2 from water splitting. Initially tests were conducted under atmospheric conditions, where several problems and bottlenecks were encountered that were mainly related to defective off-the-shelf products (leaks in the high temperature valves). After implementing some measures for the safe operation of the plant, thermal only tests were conducted to evaluate the performance of the cavity reactors during heating with concentrated solar radiation and their coupled operation with the plant peripherals. The main aim was to reach the target temperatures of 1100oC for the water splitting step and 1400oC for the thermal reduction step and assess the reactors’ response. In the initial thermal tests the temperature in the reactor cavity could be increased up to 900oC with the utilization of only a small number of heliostats. However, soon a significant issue occurred. The optical components failed. High temperatures were developed in the window flange and the secondary concentrator that could not be alleviated by the cooling network. As a consequence there was damage of the mirrors of the secondary concentrators and destruction of the sealing of the window flange. In addition, the decomposition of the sealing materials caused depositions on the quartz window that had to be thoroughly cleaned in order to be used again. These incidents led to further testing of a solar reactor under controlled conditions in a solar simulator (at Julich, Germany) where similar problems occurred. The design of the window flange was readdressed and the problem was solved allowing the safe operation of the reactor. Counteracting measures were also taken on the reactors at the solar platform and the experiments were continued with the target to further increase the temperature of the cavity and conduct water splitting and thermal reduction tests. During the operation of the solar platform the temperatures in the cavity reactor were limited to an average of 950-1000oC, while locally 1350oC have been also monitored. It was observed that there is significant inhomogeneity in the thermal map of the cavity with high temperature differences between the different foams. These conditions were not optimal for the thermal reduction and the water splitting reactions. Although the operation of the solar platform and the solar reactors under water splitting and thermal reduction conditions was achieved for the first time at the scale of the HYDROSOL-Plant reactors (90l cavity, 250kWth solar receiver/reactors consisting of Ni-ferrite and Ceria coated foams), the amount of H2 that was delivered was significantly lower than the initial target of 3 kg H2/week on the solar platform, as set by the project objectives and according to the mandate of the AIP2012. The main reasons are the low temperatures (at least 200-400oC lower than the optimal), as well as the low H2O flow rate. The final experiment on the solar platform delivered H2 at a rate of 0.25kg/week. Nevertheless, based on laboratory experiments for the investigation of the effect of the temperature and H2O content on the H2 production an approximation of the capacity of the solar platform, if it was operated under optimal conditions, can be made. Operation of the solar platform at the optimum water splitting temperature (to 1100oC) would increase the H2 production by a factor of 1.4 while increase of the thermal reduction temperature (to 1400oC) would cause an additional 2 times increase of the H2 production. Finally increase of the flow rate of H2O would lead to an additional 4 times increase in the H2 production. The extrapolated capacity of the solar plant under optimum conditions would be at the level of 2.8 kg H2/week.
WP7: System analysis and LCA.
Major objectives:
• To support the selection of the best suitable process options for further commercialization from an environmental point of view.
• To compare the HYDROSOL Process to other hydrogen generation processes.
• To decrease the environmental impact of the overall plant.
The LCA analysis is a very useful method for the evaluation of the total environmental impact of a product over its fabrication and construction process and operation cycle. The LCA-model was based on the flowsheet of the demonstration plant and the sizing of the components. Within the LCA-analysis of the HYDROSOL-demonstration plant, the attributional approach was selected since the impact of emissions during construction and operation on the GWP is the main focus of this analysis. Since the application of the produced hydrogen has not been defined within the HYDROSOLPlant project, the “cradle-to-gate” approach was applied to the LCA analysis.
The analysis showed that if implementing improvements on the issues that have been identified during the whole duration of the project and also by efficient exploitation of the vast amounts of heat generated in the process the total GWP of the plant would be reduced to levels comparable to those of wind-electrolysis.
WP8: Dissemination and Exploitation.
Major objectives:
• To provide for visible dissemination of the project’s results and maximize its impact to the most wide and relevant audience.
• To define the best way of exploiting the project’s results.
• To educate and train young researchers.
The HYDROSOL-Plant exploitable results are related to the:
Redox material: The redox material is the core of the HYDROSOL process. It is the main component of the HYDROSOL cavity reactor technology that facilitates the splitting of water and the production of hydrogen. The selection of the main material (NiFe2O4) was based on the experience and know-how of APTL that was gained through its research activities in all the previous HYDROSOL projects as well as from other projects in solar thermochemical process and solar chemistry. The specific material is relatively common in the field of research for the production of H2 from H2O. In HYDROSOL-Plant, however, it was achieved for the first time, the shaping of structures consisting entirely of NiFe2O4, in the form of honeycomb monolithic structures or monolithic foams either via extrusion, or casting in 3D-printed molds or via the polymeric matrix replication method, at the laboratory scale. The material was synthesized via the self-propagating high temperature synthesis route that is applied at APTL, which had to be appropriately adapted to achieve the scale-up requirements of the current project. In addition, apart from the core redox material that was investigated in HYDROSOL-Plant, another formulation was employed. CeO2 is another material of great interest in the field of solar thermochemistry. Compared to the NiFe2O4 it was not synthesized in the laboratory but it was a commercially available bulk material. Furthermore, this material was not developed from the small scale as in the case of the NiFe2O4 but it was directly deposited on inert material foam structures for implementation as building blocks for the construction of one of the three reactors that were constructed in HYDROSOL-Plant.
A significant achievement of the HYDROSOL-Plant project was the implementation of over 1000h of consecutive H2O splitting and thermal reduction cycles on a NiFe2O4 structured monolithic body (corresponding to an equivalent of over 6 months of on-sun operation or almost two years of laboratory experiments). Such a durability evaluation campaign has never before been reported in literature, and provided interesting aspects in the behavior and performance of structured ceramic materials for high temperature applications under alternating oxidizing and inert atmosphere conditions.
Another target that was achieved in the HYDROSOL-Plant project was the production of H2 at the laboratory scale corresponding to more than 3 kg/week based on novel structured monolithic bodies consisting entirely of NiFe2O4. Such results were reported for the first time and show the potential for the development of structures with enhanced properties. However, restrictions in time, budget, as well as the adaptation of the technology to an already existing platform, limited the choices for the scaling-up of the monolithic structures.
These achievements have created new foundations for the solar thermochemical H2 production based on structured solar reactors that will be exploited in the future research activities of APTL as well as in the future collaboration of the core group of the consortium in other projects.
Scale-up of redox monolithic structures: To reach the scale of implementation of the HYDROSOL-Plant significant scaling-up steps in the production of the active redox material and the shaping into structured bodies had to be achieved. The scaling-up of full size ceramic structured bodies consisting entirely of the redox material was assessed as significantly challenging. This task, although it is closely connected with the success of the implementation of the HYDROSOL-technology, it is on its own an innovation that could be exploited in applications such as solar receivers, active redox and catalytic structures for fuel production, upgrading and refining, compact reactors etc.
Although the shaping of oxide powders into structured ceramic bodies (e.g. monoliths with parallel channels (honeycombs) or with an open interconnected porous network (foams)) is based on well-established commercial processes, the actual challenges that HYDROSOL-Plant had to overcome, surpassed any initial prediction. The active redox materials, employed as the raw material for the shaping of the ceramic structures, in combination with:
-the geometries of the main building blocks of the specific cavity reactor design i.e. in total seven (7) different geometries with rather strict and non-commercially available dimensions and shapes that required precision machining
-the production scale concerning both the quantity of the required redox material but mostly the size of the required full-scale dimensioned monoliths, which for example in the case of extruded monoliths would require infrastructure with capabilities beyond the commercially available ones
-the nature of the intended application itself; cyclic operation at elevated temperatures with constant “expansion and contraction” of the redox material lattice and finally
-the fact that all of the above innovations/challenges were simultaneously attempted for the first time
describes the degree of complexity that the project had to overcome.
Despite the fact that the shaping of stable large-scale green bodies turned out to be a relatively normal task to achieve, the main problems were encountered during the sintering and the post-calcination steps involved in the preparation process. The development process required time, manpower dedication, numerous efforts and close collaboration with an experienced technical ceramics manufacturer for the scaled-up production. However, there were still several issues that were encountered, (e.g. the melting of structures or the poor mechanical stability of fragile and brittle sintered bodies) that affected the delivery time of the main building blocks of the reactors. A process for the production of sufficiently stable large scale monolithic foams consisting entirely of the active redox material (i.e. NiFe2O4), was finally developed. However, time and budget restrictions, limited the production to only a few series of segments that could partially cover the construction of one reactor. Unavoidably the implementation of the fallback option of the preparation of the same geometries and blocks but from already commercially available inert materials and the application of the active redox material as a coating, was followed in order to cover the construction of the rest of the reactors.
Nevertheless, the achievement of the production of small and large scale monolithic structures consisting entirely of the NiFe2O4 represents an important development in the sector of ceramics’ fabrication methods and fields of application which is of particular interest for specialized technical ceramics manufacturers. In addition it has paved the way towards new shaping techniques that will be exploited in the future especially by the Research partners.
HYDROSOL solar reactors design: The HYDROSOL technology is based on directly irradiated solar monolithic reactors. Until the current project the designs that had been implemented in the previous projects were based on the same principle but with the construction of flat reactors (12l active volume). In the previous HYDROSOL-3D project the possibility of designing cavity reactors consisting of monolithic segments was investigated. However, it was not until the HYDROSOL-Plant project, that an actual redox cavity reactor was constructed. The design of the current reactors is based on an already successful design that was initially developed by DLR for a methane reforming process. However, the difference in the HYDROSOL-Plant reactors was that the main building blocks that are the actual active component and are based on foam monolithic structures, had to be constructed with a higher thickness (2-times thicker foams) so that the appropriate amount of active material could be incorporated in the available space of the already existing solar platform.
Within the project the development and construction of three such reactors was realized for the first time at the scale of 90l active volume each. This positions these reactors as the largest structured reactors in the world for the production of solar H2 based on the two step redox thermochemical splitting of water.
Moreover, a significant component of the reactors was the secondary optics, i.e. the secondary concentrator that enhances the incoming solar flux in the reactor cavity. These components were again based on the experience and know-how within the consortium and was chosen as the most optimum solution to achieve the targets set in the project. However, unexpectedly, these components that were state-of-the-art and had been previously successfully employed in other concentrated solar applications, failed during operation at the solar platform and consequently affected the proper operation of the reactors and the accomplishment of the ultimate project target.
Therefore, retrospectively, a development gap is identified both in the scaling up of the reactors as well as in the utilization of already existing and validated components, which enhanced the challenges both in the construction as well as in the operation of the reactors.
The experience that was gained from the HYDROSOL-Plant project will be exploited by the Research partners in the future by addressing the issues that were identified within the project and in addition by adapting new approaches within the framework of the follow-up proposed collaborative project.
The HYDROSOL-Plant solar platform at the Plataforma Solar de Almeria: The proof of concept of the two step solar thermochemical water splitting for H₂ production based on structured redox materials has been demonstrated in the first HYDROSOL project while a scaled up version of the technology (up to 100 kWth) was confirmed in the two HYDROSOL projects that followed. The aim of the HYDROSOL-Plant project was to prove the feasibility of further scalability of the technology to a near MW scale that would provide more solid evidence about its potential future commercial exploitation.
In the HYDROSOL-Plant project the development of the technology had to evolve in parallel in several different fields involving:
-the production of the active redox material that had to be scaled up from a few hundreds of grams to several hundreds of kilograms (a total of ~600 kg of NiFe2O4 were synthesized for the needs of the shaping and scaling-up of foam structures), to
-the scaling of the reactor size, from a total reactor volume of 12l to 90l per reactor
-the scale up of all peripheral components (valves, heat exchangers etc)
-the assembly of all components on the existing space at the SSPS CRS solar tower in Plataforma Solar de Almeria in Spain
-the entire process control, scaled from 0.1MWth (HYDROSOL-II platform) to 0.75MWth (HYDROSOL-Plant platform) and naturally to
-the debugging and final operation of the integrated system
The target was to implement efficient solar testing campaigns at the 0.75MWth HYDROSOL-Plant solar facility in the Plataforma Solar in Almeria, ultimately demonstrating the production of solar H2. However, several challenges during installation and debugging process led to major delays that did not allow the proper operation of the facility and subsequently the production of H2.
The most determining factors that caused significant delays in the operation of the plant were the following:
- the damage of one of the reactors (the reactor that consisted of CeO2 coated foams) during its installation to the holding structure on the platform.
- the detection of leaks in the commercially acquired high temperature valves. The solving of this problem was of high importance because it compromised the safe operation of the plant.
- the problematic operation of the secondary concentrators related mainly to inadequate cooling.
- the Weather. Realistic solar experiments in the actual solar platform environment depend on weather conditions (e.g. high percentage of cloud coverage, strong winds etc.). Weather instability with poor insolation and/or high winds do not allow the operation of the platform. This minimized the window of opportunity for successful solar.
The aforementioned reasons did not allow the implementation of solar H2 producing experiments at the solar platform at the scale that was targeted in the beginning of the project and according to the AIP2012.
However, the HYDROSOL-Plant platform was operated for a period of over 3 months including 3 months after the end of the project to acquire as much as possible data and experience in its operation. This data will serve as a starting point for improvements that are envisaged to be implemented in a future collaborative project and for further efforts for solar hydrogen production at similar scales.
As a conclusion, the determination of improvement actions is probably the most valuable outcome that could be exploited in future relevant research efforts with the aim of: a) demonstrating H2 production at the 0.75MWth scale; b) further increasing the targeted H₂ production; c) improving the reactor design and its peripherals; d) further reducing the cost and the production duration of the redox materials and the respective monolithic structures; e) additional assessment of the long-term stability and overall performance of the redox structured reactors under solar radiation; f) suggesting ways for rapid comparative evaluation of different materials and structured geometries under realistic conditions, g) minimization of the inert gas utilized mainly for the thermal reduction step, h) maximization of the heat recovery.
The project progress and results were disseminated through publications in scientific journals and conference proceedings, presentations in conferences and forums, as well as via other public dissemination mechanisms (EU, FHC-JU platforms, Horizon Magazine, exhibitions, trade fairs, business and technological forums, webinars, web newsletters, etc.). In addition, a workshop was organized at the HYDROSOL-Plant facility at the Plataforma Solar de Almeria in Spain for the presentation of the major project achievements and the demonstration of the completed solar platform.
Potential Impact:
The promotion of renewable energy penetration is a top priority for the tackling of the adverse effects of the current dominant energy production processes on the environment, and the achievement of Europe’s and worldwide energy efficiency and climate and greenhouse gas emissions specific targets especially the very ambitious ones set for the mid- to long-term future. The complete substitution of fossil fuels by a mixture of renewable and sustainable energy sources, thus assuring the production of carbon-neutral or ultimately even carbon-free energy and the decarbonisation of transportation and modern economy in general, is one of the most persistent quests both within the EU as well as globally that if successful could be the sole solution for significant socio-economic benefits (independence from fossil fuels, improvement of living standards, health and safety, potential for job creation and employment).
Amongst the wide variety of alternative fuels, H2 has been increasingly investigated as a potential alternative energy carrier and storage medium in the last few decades and, especially in Europe, after the establishment of the FCH-JU as the “sponsor” of research and development activities that are related to sustainable and renewable H2 production processes. Currently the dominant H2 production process is via steam reforming mainly of methane, which is a relatively “carbon-rich” chemical process, and is the main competitor of renewable hydrogen both in terms of mass production and efficiency of production as well as financially.
Therefore, there are several challenges that need to be overcome so that a reliable and low cost, renewable hydrogen can be produced. To achieve this, the exploitation of the vast and practically inexhaustible solar potential is an attractive primary solution. Introducing a chemical process (two-step thermochemical water splitting), such as the production of H2, in a solar tower (e.g. employed for the production of heat for the generation of electricity), facilitates the storage of solar energy into a chemical, an energy carrier, which has no temporal or local limitations and can be used, when needed, in several different ways either as clean transportation fuel or as a feed into other chemical processes.
The HYDROSOL-Plant project pursued to address the challenges of realizing the scaling-up of the process at a near the MW level and adapting the solar plant in an already existing solar platform at the Plataforma Solar de Almeria in Spain. The essence of “scaling-up things” is inherently challenging. It is a common problem that all processes may more or less face when evolving towards technological maturity. Although there are significant endeavors worldwide for the development of solar thermochemical processes for the production of hydrogen based on redox water splitting, only a few examples exited the laboratory and were deployed at realistic scale. The HYDROSOL-Plant project, was the first worldwide to deal with the demonstration of the scalability of the technology near the MW scale. The implementation of the project revealed the potential of the technology but also the significant “bottlenecks” that almost naturally appear when stepping out of the controlled environment of the lab and of simulated operating conditions.
By the end of the project, a complete solar plant for the production of H2 based on redox thermochemical splitting of water had been integrated to the solar tower at the Plataforma Solar de Almeria in Spain. This success had also profound challenges. The systematic operation of the plant in the H2 production mode at optimum conditions was not achieved until the end of the project. Currently the temperatures that have been achieved at the reactors are not high enough to fully promote the two steps of the process (thermal reduction and water splitting). Nevertheless, even at such non-optimum conditions some Hydrogen has been produced, validating more or less the laboratory findings that had shown an activity of the materials, however low, at such conditions. These results give a taste of the potential of the process, which, needs further development in order to confront the challenges that are emerging when operating at that scale. Future targets are focused on the exploitation of the most substantial benefit of the technology, which is the significant amounts of high temperature solar heat produced during the redox cycles. Employing efficient heat recovery at the high temperature levels of the process would have an impressive effect both on the efficiency of the process as well as on the environmental assessment of the plant.
List of Websites:
http://hydrosol-plant.certh.gr/root.en.aspx
Coordinator: Athanasios G. Konstandopoulos
CENTER FOR RESEARCH AND TECHNOLOGY HELLAS
6th km Charilaou-Thermi rd, 57001 Thessaloniki, Greece
E-mail: agk@cperi.certh.gr
tel: +30 2310 498 192
Coordinator contact: Souzana Lorentzou
CENTER FOR RESEARCH AND TECHNOLOGY HELLAS
6th km Charilaou-Thermi rd, 57001 Thessaloniki, Greece
E-mail: souzana@cperi.certh.gr
tel: +30 2310 498 421