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Thermochemical HYDROgen production in a SOLar structured reactor:facing the challenges and beyond

Periodic Reporting for period 2 - HYDROSOL-beyond (Thermochemical HYDROgen production in a SOLar structured reactor:facing the challenges and beyond)

Reporting period: 2021-01-01 to 2022-06-30

It has been globally recognized that the promotion of renewable energy production penetration is a top priority for tackling the adverse effects of the traditional dominant industrial processes both on the environment and human health. The greenhouse gas emissions targets are becoming more restricted in order to keep in line with the global treaties (Kyoto protocol and Paris Agreement) and establish a sustainable anti-pollution policy. The complete substitution of fossil fuels by a mixture of renewable and sustainable energy sources, assuring the production of carbon-neutral or ultimately even carbon-free energy chemical products, is one of the most persistent quests both within the EU and globally as it seems the only vital solution for the preservation of the future of mankind.
Amongst the wide variety of alternative fuels, Hydrogen has been increasingly investigated as a potential energy carrier and storage medium in the last few decades. 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 hydrogen production processes, many research programs have been focused on developing environmentally friendly H production routes. These efforts aim to compete the conventional hydrogen production process, which is methane reforming, a relatively “carbon-rich” chemical process..
The current project continues the series of HYDROSOL-related research programs and its main goal is to increase the efficiency of the already existing 750kW solar plant in Almeria, Spain. The solar platform takes advantage of the HYDROSOL technology in order to produce renewable green hydrogen. HYDROSOL concept is based on the utilization of concentrated solar thermal power for the production of Hydrogen from the dissociation of water via redox-pair-based thermochemical cycles.
The main objectives of HYDROSOL-beyond are:
• the minimization of the energy losses of the system mostly related to the high consumption of inert gas
• the efficient recovery of heat at rates >60%
• the development of redox materials and structures with enhanced stability (>1,000 cycles) and with production of hydrogen ~three times higher than the current state-of-the-art Ni-ferrite foams
• the development of a technology with annual solar-to-fuel efficiency of ≥10%
• the improvement of the reactor design and introduction of novel reactor concepts
• the development of smart process control strategies and systems for the optimized operation of the plant
• the demonstration of efficiency >5% in the field tests, i.e. during operation at the 750kWth HYDROSOL solar platform (PSA, Spain)
Once these targets are meet then the proposed technology will be able to compete the traditional, low-cost hydrogen production routes employed nowadays.
Continuing the work that has been done in the first project period, the activities on the investigation, design and development of novel concepts that are going to be integrated in the existing plant (novel hybrid heat exchanger, reverse pressure swing adsorption for N2 purification) and the tasks and activities undertaken in the solar field at Plataforma Solar de Almeria in order to be able to perform solar experiments, run in parallel.
Novel lattice structures of existing redox oxides have been manufactured and evaluated at the laboratory scale both for the water splitting as well as for the oxygen trapping concept. The final long-term durability on the qualified structures will run until the end of the project and in parallel to the experimental campaigns at the solar platform.
The hybrid high-temperature heat exchanger was constructed and its performance was assessed, leading to valuable results for the optimization of its design and construction the final prototype that will be directly integrated on the solar platform for testing under real plant conditions.
Full scale experiments on the modified directly heated solar cavity reactor coupled to conventional heat exchanger took place at the high flux solar simulator at Jullich. The performance analysis of an alternative indirectly heated tube reactor concept has been reported. Analysis for both reactor types reveals the issues and limitations in the operation and that there is a margin for improvement, however, inherent characteristics of the directly heated solar cavity reactor design and materials limit the potential increase of the efficiency.
The repair and restore actions on the HYDROSOL solar platform at the Plataforma Solar de Almeria in Spain focused on the secondary concentrators and the quartz window fitting on the reactor. Several tests were performed and significant progress has been made with the operation of the plant. H2 production was achieved on the solar platform in one of the two directly heated solar cavity reactors, with the highest production recorded since the Hydrosol-Plant project. Several issues were identified in the case of the quartz window and the effect of reactor degradation on the window optical properties as well as in the case of temperature distribution in the reactor cavity.
Data have been collected for setting up the technoeconomic analysis and the life cycle assessment of the HYDROSOL-beyond process. A preliminary LCA was initiated with data from the previous project and the original platform of the HYDROSOL-Plant during as a benchmark for future comparison with the corresponding analysis of the Hydrosol-beyond modified platform.
A significant goal of the project is the design and development of a novel hybrid ceramic-metallic heat-exchanger (HX) capable of operating at extremely high temperatures. Up to now, a small-scale prototype has been constructed and tested and the results provided valuable information for the design optimization to reach the final version of the full scale prototype that will be integrated on the HYDROSOL solar platform. The several computational studies that have been conducted in order to investigate and assess the performance of the HX have helped to understand in-depth the critical parameters that affect its operation.
Additionally the decrease of the amount of the inert gas is expected to be attained. The reduction will be achieved mainly through the reduction of the inert gas flow rate during the thermal regeneration step and from the purification of the effluent stream and its subsequent recycling into the process loop. Until now, various methods have been investigated in order to minimize the nitrogen that is used and the results are encouraging; as a result, there is strong evidence that the target will be achieved. This will have a strong impact on the overall process efficiency, upgrading the process into a sincere and sustainable option for green hydrogen production.
Finally, a major challenge of the proposed technology is the really high-temperature of the process (typically above 1000oC). At these levels it is observed at the full scale solar experiments that there is a degradation effect on the materials of the reactor along with the rest of the equipment that is challenging the longterm operation. However, the consortium has gained valuable information and in-depth knowledge of the process (from the entire series of HYDROSOL projects) and from the theoretical investigation of the process potential and will focus towards targeted changes to progress the solar-aided hydrogen production.