Optimizing the CSP-Calcium Looping integration for Thermochemical Energy Storage

Thermochemical energy storage (TCES) is considered a promising technology to overcome the issues of intermittent energy generation in Concentrated Solar Power (CSP) plants and couple them with yearly electricity demand. The development of this technology could favor the commercial deployment of CSP, which is considered as a key factor for new challenges in reducing GHG emissions. Among other possibilities, using the Calcium Looping (CaL) process for TCES is an interesting choice mainly due to the low cost of natural CaO precursors such as limestone (below $10/ton) and the high energy density that can be achieved (around 3.2 GJ/m3). This manuscript explores several configurations in order to maximize the performance of the CSP-CaL integration with the focus on power cycle integration in the carbonator zone. For this purpose, firstly, a discussion about the possibility of using open and closed power cycles is carried out, which leads to the conclusion that a CO2closed cycle is more appropriate. Then, a closed regenerative CO2Brayton cycle is analyzed in further detail and optimized by means of the pinch-analysis methodology. A main output is that high plant efficiencies (of about 45%) can be achieved using a simple closed CO2Brayton power cycle. The optimized integration layout shows good performances at carbonator to turbine outlet pressure ratios around 3, thus allowing for a feasible integration of the power cycle in the CSP-CaL system.Ministerio de Economía y Competitividad CTQ2014-52763-C2-2-

Power cycles integration in concentrated solar power plants with energy storage based on calcium looping

Efficient, low-cost and environmentally friendly storage of thermal energy stands as a main challenge for large scale deployment of solar energy. This work explores the integration into concentrated solar power plants of the calcium looping process based upon the reversible carbonation/calcination of calcium oxide for thermochemical energy storage. An efficient concentrated solar power-calcium looping integration would allow storing energy in the long term by calcination of calcium carbonate thus overcoming the hurdle of variable power generation from solar. After calcination, the stored products of the reaction (calcium oxide and carbon dioxide) are brought together in a carbonator reactor whereby the high temperature exothermic reaction releases the stored energy for efficient power production when needed. This work analyses several power cycle configurations with the main goal of optimizing the performance of the overall system integration. Possible integration schemes are proposed in which power production is carried out directly (using a closed carbon dioxide Brayton power cycle) or indirectly (by means of a steam reheat Rankine cycle or a supercritical carbon dioxide Brayton cycle). The results obtained show that the highest plant efficiencies (up to 45–46%) are achievable using a closed carbon dioxide Brayton power cycle.Ministerio de Economia y Competitividad CTQ2014-52763-C2-1-R, CTQ2014- 52763-C2-2-R, MAT2013-41233-

Thermochemical energy storage of concentrated solar power by Integration of the calcium looping process and a CO2 power cycle

Energy storage is the main challenge for a deep penetration of renewable energies into the grid to overcome their intrinsic variability. Thus, the commercial expansion of renewable energy, particularly wind and solar, at large scale depends crucially on the development of cheap, efficient and non-toxic energy storage systems enabling to supply more flexibility to the grid. 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), which offers a high potential for the long-term storage of energy with relatively small storage volume. This manuscript explores the use of the CaL process to store Concentrated Solar Power (CSP). A CSPCaL integration scheme is proposed mainly characterized by the use of a CO2 closed loop for the CaL cycle and power production, which provides heat decoupled from the solar source and temperatures well above the ~550ºC limit that poses the use of molten salts currently used to store energy as sensible heat. The proposed CSP-CaL integration leads to high values of plant global efficiency (of around 45-46%) with a storage capacity that allows for long time gaps between load and discharge. Moreover, the use of environmentally benign, abundantly available and cheap raw materials such as natural limestone would mark a milestone on the road towards the industrial competitiveness of CSP

Thermochemical energy storage of concentrated solar power by integration of the calcium looping process and a CO2 power cycle

Energy storage is the main challenge for a deep penetration of renewable energies into the grid to overcome their intrinsic variability. Thus, the commercial expansion of renewable energy, particularly wind and solar, at large scale depends crucially on the development of cheap, efficient and non-toxic energy storage systems enabling to supply more flexibility to the grid. 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), which offers a high potential for the long-term storage of energy with relatively small storage volume. This manuscript explores the use of the CaL process to store Concentrated Solar Power (CSP). A CSP–CaL integration scheme is proposed mainly characterized by the use of a CO2 closed loop for the CaL cycle and power production, which provides heat decoupled from the solar source and temperatures well above the 550 C limit that poses the use of molten salts currently used to store energy as sensible heat. The proposed CSP–CaL integration leads to high values of plant global efficiency (of around 45–46%) with a storage capacity that allows for long time gaps between load and discharge. Moreover, the use of environmentally benign, abundantly available and cheap raw materials such as natural limestone would mark a milestone on the road towards the industrial competitiveness of CSP