The second period of the project has allowed the consortium to carry out the construction and commissioning of the individual units and their integration into a pilot plant in which an extensive experimental campaign has been carried out to demonstrate the feasibility of the thermochemical energy storage concept and the calcination/carbonation reactions under SOCRATCES conditions. The successful experimental campaign included calcination and carbonation tests and cyclic processes at different temperatures and materials.
The relevant results obtained show the potential of the SOCRATCES technology on a larger scale. The SOCRATCES project has successfully contributed to reducing the technological risks from TRL-4 level (laboratory validated technology) to TRL-5 level (technology validated in a relevant environment).
During the second period, an important effort has been made to characterise the different potential raw materials (CaO precursors) proposed within SOCRATCES, mainly limestones (CaCO3) and dolomites (CaMg(CO3)2) under pilot plant conditions, which had already been previously characterised at laboratory scale, by X-ray diffraction (XRD), X-ray fluorescence chemical analysis (XRF), particle size distribution (PSD), scanning electron microscopy (SEM), specific surface area analysis and thermogravimetric analysis (TGA) tests. The operational tests of the project have demonstrated the feasibility of the thermochemical energy storage concept at a scale non addressed before, achieving successful processes with mass flows over 20kg/h. They show that the application of the CaL process to energy storage for CSP applications is possible at a relevant scale. The pilot plant has been operated continuously, and in the last part of the project valid and representative operating conditions have been obtained.
The kinetic models validated during the first period were used to design and model the carbonator reactor. Tests on the prototype confirm the results previously obtained in the laboratory. The carbonation of small particles at 700-800ºC under a CO2-rich atmosphere occurs in very short residence times, with different materials and flow rates. Similarly, after the analysis of the CSP-calciner integration of the first period, which provided key information to estimate the calcination behaviour, expected to occur in a few seconds under the conditions of the SOCRATCES concept (temperatures around 930ºC), the calciner reactor was designed and modelled. Tests on the prototype validate that the reaction occurs within a few seconds in the designed reactor under SOCRATCES conditions, with different materials and temperatures (from 900ºC-1030ºC), and various flow rates in the solids flow. Success in the calcination and carbonation processes has been achieved with the current designs of the calcination and carbonation reactors. Values above 50% have been obtained for both. The entrained flow designs of both reactors ensure calcination and carbonation at more than reasonable levels.
Solids transport is highly improved with reduced silica mixed with the original material (values between 1-2% by weight). Materials with particle sizes greater than 74 microns have shown excellent transport and reaction development behaviour. Materials with finer particle sizes do not show better behaviour in calcination or carbonation. The multi-cyclic operation does not drastically affect the behaviour of the material in a reduced number of cycles. Extended multicycle operation (modifying the prototype to support faster calcination and carbonation tests) corroborates this result.
The path to commercial level is expected to go through a SOCRATCES ALPHA with a prototype cavity receiver in the 300-500 kWth range connected to a 150 kWth power block with indirect CSP-CaL integration of a Brayton cycle and a SOCRATCES GAMMA with a commercial CSP plant in the 5-10 MWth range and fully integrated into the power grid.
In WP8, analyses and documents of vital importance for the technology have been developed, such as risk analysis, failure mode and effect analysis, life cycle analysis or life cycle cost analysis. Work Package 9 dissemination activities have greatly contributed to the visibility of the project.
Interaction with the Advisory Board with relevant members from the solar thermal, limestone, energy and cement industries has contributed to the development of the project. In addition, synergies with similar projects have been established, and the project has been part of the group "H2020 Projects on Concentrated Solar Power".
The development of WPs has been successful with a high level of execution and excellent outcomes regarding main components, pilot plant operation, and laboratory results. New models were developed and tested. The technology costs, environmental impact and potential exploitation assessments developed show high potential for future developments. All tasks, milestones and deliverables have been successfully completed. The project has ended successfully with new capacities for the partners and optimistic perspectives for the technology or variations derived from the gained knowledge.
