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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - SOCRATCES (SOlar Calcium-looping integRAtion for Thermo-Chemical Energy Storage)

Teaser

Summary

Energy storage is one of the greatest challenges for a short-term deeper penetration of renewable energy sources. The Ca-Looping(CaL) process based upon the reversible carbonation/calcination of CaO is one of the most promising technologies for thermochemical energy storage(TCES). The wide availability of natural limestone(almost pure CaCO3) and its low price(~10â‚¬/ton) are key factors for the feasibility and sustainability of the CaL process.
SOCRATCES global objective is to demonstrate the CSP-CaL storage concept. The project will advance in the knowledge of processes and systems under CaL energy storage conditions though the development of prototypes of components and integrated system. Their construction and their operation will be used to reduce the core risks of scaling up the technology, to identify and to solve challenges and to understand and optimize the operation conditions; with the longer-term goal of enabling highly competitive and sustainable CSP plants. SOCRATCES departs from previous laboratory and simulation results of the partners in the consortium(TRL4) for testing the concept in a relevant environment(TRL5).

Work performed

Significant advances have been achieved during the 1st reporting period. Briefly, the first year of the project has served to advance the knowledge of reactions and systems by modeling and test performance at laboratory scale. The important result reached have been the basis for the Front-End Engineering Design (FEED). Currently, there is a close relation between the lab-scale work packages(WP2, WP3 and WP4), the systems integration(WP5) and the Engineering and procurement tasks(WP6), in which the consortium is currently fully involved. As expected, the prototype construction will start by the beginning of 2020 and the experimental campaigns(WP7) will be finished before the end of 2020.
During the reporting period an important effort has been made to characterize the raw materials (CaO precursors) proposed within SOCRATCES, which mainly are limestones(CaCO3) and dolomites(CaMg(CO3)2) but also steel slags or synthetic sorbents. Samples were characterized by X-ray diffraction, X-ray fluorescence chemical analysis, particle size distribution, scanning electron microscopy, specific surface area analysis and thermogravimetric analysis tests. Many carbonation tests have been carried to assess the kinetics of the reaction. Under the specific conditions applied in the SOCRATCES concept(carbonation of small size particles at around 700-800ÂºC under rich CO2 atmosphere), lab-scale tests confirm that carbonation is expected to occur in very short residence times. Results from the validated kinetics model have been used for the design and modelling of the carbonator reactor, in which the stored energy is released at high temperature. Mathematical models for the carbonator reactors have been developed to take decisions about the reactorâ€™s dimensions, geometry and operating conditions. A proper understanding of the heat transfer mechanisms is needed to properly analyse the heat released in the carbonator reactor and its capacity for power generation. A dedicated model has been developed as a useful tool to evaluate the heat transfer from the highly exothermic carbonation.
Similarly, experiments determining the calcination kinetics and the multicyclic CaO precursors behaviour have been performed. Results have been validated from well-known kinetics. From this lab-scale experience, the solar calciner have been designed and simulated under a wide range of operating conditions by computational methods. Analysis on the CSP-calciner integration provides key information to estimate the calcination behaviour, which is expected to occur in just few seconds under the SOCRATCES concept conditions, namely, temperatures around 930ÂºC under rich CO2 atmosphere.
Regarding the power cycle development, thermodynamic analysis of integration from direct and indirect approaches at both prototype and large scale have been performed. Several carbonator side configurations have been assessed with the aim of obtain preliminary conclusions for the integration at large scale. Thus, the analysis at large scale of closed-loop direct integration(CO2 Brayton cycle) and the indirect integration of Organic Rankine cycles, steam Rankine cycles and Brayton-Joule cycle with supercritical CO2 have been carried out in order to understand most promising scaling up routes to be taken as reference for current analyses. Among the studied, the most interesting integration from a complexity and efficiency point of view is the closed-loop CO2 Brayton cycle, with efficiencies up to 45% (not including solar side losses). An important achievement has been the detailed carbonator-Stirling engine integration at SOCRATCES prototype scale, including a CFD analysis of the heater of the engine(Beta type).
A complete layout simulation has been performed, which has been the basis for the development of the 1st version of the control system. In addition, the power plant management and an analysis of the grid connection have been proposed. Engineering and procurement task are being devel

Final results

SOCRATCES is intended to open a new pathway for next generation of CSP tower plants, technologically feasible, economically viable and sustainable (environmental, social and economic).
Main expected impacts are: Demonstration of CSP-CaL storage concept. The main outcome of the project will be the demonstration of the SOCRATCES concept for energy storage at pilot scale (~10 kWth); Identification of challenges and solutions for developing the concept at commercial scale; Demonstration of the use of abundant, cheap and non-toxic natural CaO precursors for massive energy storage systems; Creation of a pathway to fostering the use of solar energy and reducing the EU energy dependency, thus improving security and reinforcing EU energy industry capacities. The first Innovation evaluation report provides the first picture of the possible Key Exploitable Results (KERs): 22 KERs were identified by the consortium. Within the reported period, project partners have identified 28 innovation with exploitation potential.