Advanced Concrete Steam Accumulation Tanks for Energy Storage for Solar Thermal Electricity

energies Article Advanced Concrete Steam Accumulation Tanks for Energy Storage for Solar Thermal Electricity Cristina Prieto 1,2,* , David Pérez Osorio 1, Edouard Gonzalez-Roubaud 1, Sonia Fereres 1 and Luisa F. Cabeza 3,* 1 Abengoa Energía, Calle Energía Solar, 1, 41014 Sevilla, Spain; [email protected] (D.P.O.); [email protected] (E.G.-R.); [email protected] (S.F.) 2 Department of Energy Engineering, University of Seville, Calle San Fernando, 4, 41004 Sevilla, Spain 3 GREiA Research Group, University of Lleida, Pere de Cabrera s/n, 25001 Lleida, Spain * Correspondence: [email protected] (C.P.); [email protected] (L.F.C.) Abstract: Steam accumulation is one of the most effective ways of thermal energy storage (TES) for the solar thermal energy (STE) industry. However, the steam accumulator concept is penalized by a bad relationship between the volume and the energy stored; moreover, its discharge process shows a decline in pressure, failing to reach nominal conditions in the turbine. From the economic point of view, between 60% and 70% of the cost of a steam accumulator TES is that of the pressure vessel tanks (defined as US$/kWhth). Since the current trend is based on increasing hours of storage in order to improve dispatchability levels in solar plants, the possibility of cost reduction is directly related to the cost of the material of pressure vessels, which is a market price. Therefore, in the present paper, a new design for steam accumulation is presented, focusing on innovative materials developed specifically for this purpose: two special concretes that compose the accumulation tank wall. Study of dosages, Citation: Prieto, C.; Pérez Osorio, D.; selection of materials and, finally, scale up on-field tests for their proper integration, fabrication and Gonzalez-Roubaud, E.; Fereres, S.; construction in prototype are the pillars of this new steam accumulation tank. Establishing clear and Cabeza, L.F. Advanced Concrete precise requirements and instructions for successful tank construction is necessary due to the highly Steam Accumulation Tanks for sensitive and variable nature of those new concrete formulations. Energy Storage for Solar Thermal Electricity. Energies 2021, 14, 3896. Keywords: storage tank; accumulator; steam; storage; concrete; insulation refractory; high-strength; https://doi.org/10.3390/en14133896 self-compacting concrete; construction Academic Editor: Dimitrios Katsaprakakis 1. Introduction Received: 27 May 2021 Large-scale thermal energy storage (TES) is a key component of concentrating solar Accepted: 24 June 2021 Published: 28 June 2021 power plants (CSP), offering energy dispatchability by adapting the electricity power production to the demand curve [1]. The industry is looking for more economical and ◦ Publisher’s Note: MDPI stays neutral efficient TES systems, especially for process heat applications between 150–250 C. New with regard to jurisdictional claims in decarbonization strategies worldwide promote the solarization of the process heat, where published maps and institutional affil- direct steam generation is one of the most efficient technologies [2]. However, the need for iations. effective steam storage penalizes this application. Commercial solar thermal electricity plants today implement only two TES technologies: steam accumulators and molten salts storage [3]. Parabolic trough plants with thermal oil and molten salt towers use two tanks of molten salts as storage system. Molten salt is the most widespread heat transfer fluid for Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. thermal energy storage in CSP commercial applications due to its good thermal properties This article is an open access article and reasonable cost [2]. Direct TES systems, i.e., where the storage fluid is the same as that distributed under the terms and directly heated by the concentrated solar radiation, have the advantage of reducing system conditions of the Creative Commons losses and complexity by eliminating heat exchangers between the heated and the storage Attribution (CC BY) license (https:// media; this is used in commercial parabolic trough plants [4]. creativecommons.org/licenses/by/ Direct steam generation plants use steam accumulators, also known as Ruth accumu- 4.0/). lators [5]. In these systems, the steam is directly stored at high pressure in accumulator Energies 2021, 14, 3896. https://doi.org/10.3390/en14133896 https://www.mdpi.com/journal/energies Energies 2021, 14, 3896 2 of 27 Direct steam generation plants use steam accumulators, also known as Ruth accumu- Energies 2021,lators14, 3896 [5]. In these systems, the steam is directly stored at high pressure in accumulator 2 of 26 tanks. The equipment is charged with the surplus saturated steam produced by the plant. During the discharge, steam is produced by lowering the pressure of the saturated liquid stored within thetanks. tank. TheSteam equipment has the is added charged benefit with the of surplus being saturateda common steam working produced fluid by for the plant. power generationDuring cycles, the also discharge, eliminating steam isthe produced need for by heat lowering exchangers the pressure between of the saturatedthe solar liquid field and the powerstored block. within the tank. Steam has the added benefit of being a common working fluid for power generation cycles, also eliminating the need for heat exchangers between the solar First generation STE towers use saturated steam technology. As of January 2016, field and the power block. there were only two Firstcommercial generation CSP STE plants towers in use operation saturated using steam steam technology. accumulator As of January TES: 2016, PS10 and PS20, boththere located were only in Spain. two commercial They started CSP commercial plants in operation operation using in steam 2007 accumulator and 2009, TES: respectively, andPS10 they and were PS20, the both first located two comme in Spain.rcial They central started receiver commercial solar operation plants in in the 2007 and world and the starting2009, respectively, point for the and operation they were theof firstthe direct two commercial steam generation central receiver (DSG) solar tech- plants in nology. Figure 1the represents world and schematically the starting point a flow for the diagram operation of of the the PS10 direct and steam PS20 generation direct (DSG) technology. Figure1 represents schematically a flow diagram of the PS10 and PS20 direct steam generationsteam tower generation plant with tower a steam plant withaccumulator a steam accumulator thermal energy thermal storage energy storage system. system. FigureFigure 1. Schematic 1. Schematic flow diagram flow ofdiagram a direct of steam a di generationrect steam tower generation plant (saturated tower pl steam)ant (saturated with steam steam) accumulator with thermalsteam energy accumulator storage system thermal (Source: energy Abengoa). storage system (Source: Abengoa). The PS10 central receiver plant uses a 11 MWe saturated steam Rankine cycle with The PS10 centralsteam receiver accumulator plant thermal uses energya 11 MWe storage. saturated PS10 has steam 624 heliostats Rankine (120 cycle m2 witheach) for a steam accumulatortotal thermal reflective energy surface storage. of around PS10 75,000 has 624 m2. heliostats It is arranged (120 in m circular2 each) rowsfor a aroundtotal the reflective surfacetower, of around concentrating 75,000 solarm2. It radiation is arranged on a saturated in circular steam rows cavity around receiver the placed tower, on top of concentrating solara 115 radiation m tower. on The a storagesaturated system steam provides cavity 20 receiver MWh of storageplaced capacity,on top of giving a 115 50 min m tower. The storageeffective system operational provides capacity 20 MWh at 50% of storage turbine workload.capacity, giving The system 50 min has effective four tanks that are operated sequentially in relation to their charge status. During full load operation of operational capacity at 50% turbine workload. The system has four tanks that are operated the plant, the steam accumulators are charged with a proportion of the steam produced at sequentially in relationthe receiver to their at 250 charge◦C and status. 45 bars. During When afull transient load operation period needs of tothe be plant, covered, the energy steam accumulatorsfrom are the charged saturated with water a will propor be recoveredtion of atthe variable steam pressure. produced Figure at the2 shows receiver the steam at 250 °C and 45 accumulatorsbars. When ata transient PS10. period needs to be covered, energy from the sat- 2 urated water will be Therecovered PS20 central at variable receiver pressure. plant has 1255 Figure heliostats 2 shows (with the a surface steam of accumula- 120 m each) and tors at PS10. uses the same technology as PS10 but its power cycle reaches 20 MWe with an equivalent storage capacity of 50 min at 50% turbine workload using two steam accumulators that are discharged in sequence. Energies 2021, 14, 3896 3 of 27 EnergiesEnergies 20212021, ,1414, ,3896 3896 3 of 26 3 of 27 Figure 2. Steam accumulators of PS10 plant (Source: Abengoa). The PS20 central receiver plant has 1255 heliostats (with a surface of 120 m2 each) and uses the same technology as PS10 but its power cycle reaches 20 MWe with an equivalent storage capacity of 50 min at 50% turbine workload using two steam accumulators that areFigureFigure discharged 2. 2.Steam Steam accumulators in accumulators sequence. of PS10 of PS10

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