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Processes
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Advances in Thermochemical Energy Storage
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Advances in Thermochemical Energy Storage

A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Energy Systems".

Deadline for manuscript submissions: closed (10 August 2023) | Viewed by 10416

Special Issue Editors

Prof. Dr. Wolfgang Krumm

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Guest Editor
Department of Mechanical Engineering, University of Siegen, 57076 Siegen, Germany
Interests: thermochemical energy conversion; process engineering; mathematical modeling and simulation of process engineering systems
Dr. Sandra Afflerbach

E-Mail Website
Assistant Guest Editor
Institute for Energy Technology, Technical University Berlin, 10587 Berlin, Germany
Interests: reversible gas–solid reactions; materials science; materials engineering; sustainable materials; chemical reaction engineering
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The transition to climate-friendly, sustainable, efficient and affordable energy production is one of the key factors in recent research. To balance the temporal intermittency of energy generation from renewable resources, such as sun, tidal or wind, storage technologies have to be developed to match the demand and constraints of the various applications in the different energy sectors. Therein, thermal storage technologies are developed for application in primary energy generation by solar thermal power or for increasing the efficiency of energy utilization by waste heat recovery as well as for sector coupling and housing. Due to their unique features as long-term and loss-free storage options accompanied by high storage densities, thermochemical storage systems comprise key advantages compared to sensible or latent thermal storage technologies. However, the degree of technological readiness of thermochemical storage systems is still low. Reasons may be found in the complexity of the performance of bulk materials undergoing cyclic charging and discharging, demanding feasible solutions of reactor and process design.

This Special Issue “Advances in Thermochemical Energy Storage” is to promote future developments and invite high-quality contributions from all related disciplines, such as chemistry, material science, engineering and economics, to provide a comprehensive coverage of the latest state of the art in this field. Topics include, but are not limited to:

  • Identification of suitable reaction systems for thermochemical energy storage;
  • Material design and modification for optimized properties during cyclic charging and discharging;
  • Design and demonstration of thermochemical reactors from lab to pilot scale;
  • Process engineering for efficient charging and discharging characteristics;
  • Economic evaluations identifying promising scenarios for the commercial implementation of thermochemical storage systems.

Prof. Dr. Wolfgang Krumm
Dr. Sandra Afflerbach
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Processes is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • thermochemical energy storage
  • thermochemical energy conversion
  • methanation
  • thermal storage
  • concentrated solar power
  • waste heat recovery
  • energy transition
  • energy storage technologies
  • gas–solid reaction
  • reversible chemical reaction.

Published Papers (4 papers)

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Research

22 pages, 7124 KiB  
Article
Development of a Moving Bed Reactor for Thermochemical Heat Storage Based on Granulated Ca(OH)2
by Aldo Cosquillo Mejia, Sandra Afflerbach, Marc Linder and Matthias Schmidt
Processes 2022, 10(9), 1680; https://doi.org/10.3390/pr10091680 - 24 Aug 2022
Cited by 5 | Viewed by 2366
Abstract
Calcium hydroxide is promising for thermal energy storage due to its low cost and high energy density. Nevertheless, the powdered material is cohesive and has low thermal conductivity which is a major challenge for the operation of moving bed reactors. One approach to [...] Read more.
Calcium hydroxide is promising for thermal energy storage due to its low cost and high energy density. Nevertheless, the powdered material is cohesive and has low thermal conductivity which is a major challenge for the operation of moving bed reactors. One approach to facilitate the movement of the reaction bed is the stabilisation of the particles through the coating of Ca(OH)2 granules with Al2O3 particles. In this work, a newly designed reactor concept was specifically developed for testing coated Ca(OH)2 granules. The design allows for the movement of the reaction bed by gravity assistance and direct heating of the particles by a counter current gas flow. The operation was successfully demonstrated and proved to achieve high heat transfer between gas and granules. Furthermore, the movement of the reaction bed was achieved after the discharging phase. Two batches of uncoated and coated Ca(OH)2 granules were subject of 10 thermochemical cycles in this reactor. The cycling stability, structural integrity, mechanical stability, morphology and phase composition of the granules were analysed. Full conversion of both samples was demonstrated for the entire experimental series. It was found that the alumina coating enhances the mechanical stability of the granules under reaction conditions. Full article
(This article belongs to the Special Issue Advances in Thermochemical Energy Storage)
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36 pages, 6156 KiB  
Article
Thermal Operation Maps for Lamm–Honigmann Thermo-Chemical Energy Storage—A Quasi-Stationary Model for Process Analysis
by Elisabeth Thiele and Felix Ziegler
Processes 2022, 10(5), 977; https://doi.org/10.3390/pr10050977 - 13 May 2022
Viewed by 3317
Abstract
The Lamm–Honigmann energy storage is a sorption-based storage that can be arbitrarily charged and discharged with both heat and electrical power. The mechanical charging and discharging processes of this storage are characterized by an internal heat transfer between the main components, absorber/desorber and [...] Read more.
The Lamm–Honigmann energy storage is a sorption-based storage that can be arbitrarily charged and discharged with both heat and electrical power. The mechanical charging and discharging processes of this storage are characterized by an internal heat transfer between the main components, absorber/desorber and evaporator/condenser, that is driven by the working-fluid mass transferred between those components with the help of an expansion or compression device, respectively. In this paper, thermal operation maps for the mechanical charging and discharging processes are developed from energy balances in order to predict power output and storage efficiency depending on the system state, which, in particular, is defined by the mass flow rate of vapor and the salt mass fraction of the absorbent. The conducted method is applied for the working-fluid pair LiBr/H2O. In a first step, a thermal efficiency is defined to account for second-order losses due to the internal heat transfer; e.g., for discharging from a salt mass fraction of 0.7 to one of 0.5 (kg LiBr)/(kg sol.) at a temperature of 130 °C, it is found that the reversible shaft work output is reduced by 1.1–2.9%/(K driving temperature difference). For lower operating temperatures, the reduction is larger; e.g., at 80 °C, the efficiency loss due to heat transfer rises to 3.5%/K for a salt mass fraction of 0.5 (kg LiBr)/(kg sol.). In a second step, a quasi-stationary assumption leads to the thermal operation map from which the discharging characteristics can be found; e.g., at an operating temperature of 130 °C for a constant power output of 0.4 kW/m2 heat exchanger area at volumetric and inner machine efficiencies of ηi=ηvol=0.8 and for an overall heat-transfer coefficient of 1500 W/(K m2), the mass flow rate has to rise continuously from 1.5 to 4.2 g/(s m2), while the thermal efficiency is reduced from 97% to 83% due to this rise and due to the dilution of the sorbent. For this discharging scenario, the corresponding discharge time is 4.4 (min·m2)/(kg salt). This results in an exergetic storage density of around 29 Wh/(kg salt mass). For a charge-to-discharge ratio of 2 (charging times equals two times discharging time) and with the same heat-transfer characteristic and machine efficiencies for constant power charging with adiabatic compression, the system is charged at around 0.75 kW/m2, resulting in a round-trip efficiency of around 27%. Besides those predictions for arbitrary charging and discharging scenarios, the derived thermal maps are especially useful for the dimensioning of the storage system and for the development of control strategies. It has to be noted that the operation maps do not illustrate the transient behavior of the system but its quasi-stationary state. However, it is shown, mathematically, that the system tends to return to this state when disturbed. Full article
(This article belongs to the Special Issue Advances in Thermochemical Energy Storage)
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20 pages, 5104 KiB  
Article
Experimental and Numerical Validation of the One-Process Modeling Approach for the Hydration of K2CO3 Particles
by Max Beving, Joris Romme, Pim Donkers, Arjan Frijns, Camilo Rindt and David Smeulders
Processes 2022, 10(3), 547; https://doi.org/10.3390/pr10030547 - 11 Mar 2022
Cited by 6 | Viewed by 1700
Abstract
Potassium carbonate (K2CO3) is a promising material for the long-term storage of renewable energy. A reactor vessel filled with K2CO3 can potentially be used as a domestic heat battery. The hydration and dehydration reactions of salt [...] Read more.
Potassium carbonate (K2CO3) is a promising material for the long-term storage of renewable energy. A reactor vessel filled with K2CO3 can potentially be used as a domestic heat battery. The hydration and dehydration reactions of salt hydrates in a reactor vessel are generally described using a one-process model, such as the ‘Arrhenius-f(α)’ model. However, this modeling approach cannot always be applied correctly. If the reaction does not proceed in a pseudo-steady state, and/or when nucleation and growth processes are simultaneously active during the transformation from an anhydrous to a hydrated state, the one-process modeling approach should not be applied. In this paper, it is investigated using simultaneous thermal analysis (STA) experiments whether the pseudo-steady state approximation is valid during the hydration reaction of K2CO3. Additionally, ‘jump experiments’ using STA are employed to investigate the rate-determining step (RDS) of the hydration reaction by applying step-wise changes in partial water vapor pressure. The presence of nucleation and growth processes during the hydration reaction is investigated by fitting isotropic models to STA data. The STA results showed that indeed the hydration of K2CO3 happens in a pseudo-steady state, and the reaction can be described using a RDS. An isotropic nucleation and growth model shows that the hydration reaction can be described by assuming instantaneous nucleation followed by diffusion-limited growth. This leads to the general conclusion that the one-process modeling approach, such as the Arrhenius-f(α) model, is valid to describe the hydration reaction of K2CO3 particles. Full article
(This article belongs to the Special Issue Advances in Thermochemical Energy Storage)
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23 pages, 8494 KiB  
Article
Experimental and Numerical Investigation of the Dehydration of Ca(OH)2 at Low Steam Pressures
by Kai Risthaus, Inga Bürger, Michael Lutz, Shigehiko Funayama, Yukitaka Kato, Marc Linder and Matthias Schmidt
Processes 2022, 10(2), 325; https://doi.org/10.3390/pr10020325 - 08 Feb 2022
Cited by 7 | Viewed by 2121
Abstract
The CaO/Ca(OH)2 system can be the basis for cost-efficient long-term energy storage, as the chemically stored energy is not affected by heat losses, and the raw material is cheap and abundantly available. While the hydration (thermal discharge) has already been addressed by [...] Read more.
The CaO/Ca(OH)2 system can be the basis for cost-efficient long-term energy storage, as the chemically stored energy is not affected by heat losses, and the raw material is cheap and abundantly available. While the hydration (thermal discharge) has already been addressed by several studies, for the dehydration (thermal charge) at low partial steam pressures, there is a lack of numerical studies validated at different conditions and operation modes. However, the operation at low steam pressures is important, as it decreases the dehydration temperature, which can enable the use of waste heat. Even if higher charging temperatures are available, for example by incorporating electrical energy, the reaction rate can be increased by lowering the steam pressure. At low pressures and temperatures, the limiting steps in a reactor might change compared to previous studies. In particular, the reaction kinetics might become limiting due to a decreased reaction rate at lower temperatures, or the reduced steam density at low pressures could result in high velocities, causing a gas transport limitation. Therefore, we conducted new measurements with a thermogravimetric analyzer only for the specific steam partial pressure range between 0.8 and 5.5 kPa. Based on these measurements, we derived a new mathematical fit for the reaction rate for the temperature range between 375 and 440 °C. Additionally, we performed experiments in an indirectly heated fixed bed reactor with two different operation modes in a pressure range between 2.8 and 4.8 kPa and set up a numerical model. The numerical results show that the model appropriately describes the reactor behavior and is validated within the measurement uncertainty. Moreover, our study revealed an important impact of the operation condition itself: the permeability of the reactive bulk is significantly increased if the dehydration is initiated by a rapid pressure reduction compared to an isobaric dehydration by a temperature increase. We conclude that the pressure reduction leads to structural changes in the bulk, such as channeling, which enhances the gas transport. This finding could reduce the complexity of future reactor designs. Finally, the presented model can assist the design of thermochemical reactors in the validated pressure and temperature range. Full article
(This article belongs to the Special Issue Advances in Thermochemical Energy Storage)
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