Characterization and modelling of K2CO3 cycles for thermochemical energy storage applications

Research output: Contribution to conferencePaperAcademic

Abstract

Thermochemical heat storage in salt hydrates is a promising concept to bridge the gap between supply and demand of solar thermal energy in the built environment. Using a suitable thermochemical material (TCM), a heat battery can be created to supply low-temperature thermal energy during colder time periods. The principle is based on a reversible hydration-dehydration reaction with water vapour. The TCM can be charged (dehydrated) at a temperature of 120°C by using solar thermal collectors. Conversely, the discharge (hydration) occurs at room temperature using a constant water vapour pressure of 12 mbar. Previous studies have indicated that potassium carbonate (K2CO3) is a good candidate to fulfil the role of TCM in built environment applications. To generate adequate power from a heat battery for hot tap water or space heating, the kinetics of the TCM need to be sufficiently fast. It is hypothesized that the kinetics of the material improve over multiple charge and discharge cycles due to crack formation and volume increase of the grains. The aim of this work is to evaluate the kinetics of 500-700 µm K2CO3 grains using thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), and to quantify the improvement in kinetics over multiple charge and discharge cycles. The kinetics serve as input for an existing nucleation and growth model, simulating the fractional conversion at grain level. In the TGA/DSC experiments, the material was charged and discharged numerous times under a constant water vapour pressure of 12 mbar. The cycling temperature varies from room temperature to a maximum temperature of 120°C. The conversion time of each cycle was monitored. Additionally, using an optical microscope, cycling experiments of K2CO3 were performed in a micro climate chamber with the same conditions as in the TGA/DSC experiments. This allows tracking of the apparent surface area of the grains and the observation of crack formation for each cycle. The existing nucleation and growth model is enhanced by incorporating grain growth and crack formation observed from the optical experiments. Thermal characterization by means of TGA/DSC has indicated that indeed the kinetics of the material improve over multiple cycles. Typical conversion rates are increased by a factor 10 comparing the first and the 12th cycle. Preliminary optical microscope experiments show an increase of the apparent grain surface area of approximately 55%. Additionally, crack formation is observed over multiple hydration and dehydration cycles leading to increased inter-particle porosity, likely adding to the improved kinetics.
Translated title of the contributionKarakterisatie en modelleren van K2CO3 cycli voor thermochemische warmteopslag
LanguageEnglish
StatePublished - 2019
EventEurotherm Seminar 112- Advances in Thermal Energy Storage - Lleida, Spain
Duration: 15 May 201917 May 2019

Conference

ConferenceEurotherm Seminar 112- Advances in Thermal Energy Storage
CountrySpain
CityLleida
Period15/05/1917/05/19

Fingerprint

kinetics
calorimetry
crack
modeling
hydration
water vapor
vapor pressure
dehydration
experiment
temperature
nucleation
surface area
microclimate
energy storage
material
energy
potassium
porosity
salt
heating

Keywords

  • Thermochemical heat storage
  • Nucleation and growth model
  • TGA/DSC
  • Heat Battery
  • Salt Hydrate

Cite this

Beving, M., Frijns, A., Rindt, C., & Smeulders, D. (2019). Characterization and modelling of K2CO3 cycles for thermochemical energy storage applications. Paper presented at Eurotherm Seminar 112- Advances in Thermal Energy Storage, Lleida, Spain.
@conference{d881a28ab0a94004bf43a337941ff1e8,
title = "Characterization and modelling of K2CO3 cycles for thermochemical energy storage applications",
abstract = "Thermochemical heat storage in salt hydrates is a promising concept to bridge the gap between supply and demand of solar thermal energy in the built environment. Using a suitable thermochemical material (TCM), a heat battery can be created to supply low-temperature thermal energy during colder time periods. The principle is based on a reversible hydration-dehydration reaction with water vapour. The TCM can be charged (dehydrated) at a temperature of 120°C by using solar thermal collectors. Conversely, the discharge (hydration) occurs at room temperature using a constant water vapour pressure of 12 mbar. Previous studies have indicated that potassium carbonate (K2CO3) is a good candidate to fulfil the role of TCM in built environment applications. To generate adequate power from a heat battery for hot tap water or space heating, the kinetics of the TCM need to be sufficiently fast. It is hypothesized that the kinetics of the material improve over multiple charge and discharge cycles due to crack formation and volume increase of the grains. The aim of this work is to evaluate the kinetics of 500-700 µm K2CO3 grains using thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), and to quantify the improvement in kinetics over multiple charge and discharge cycles. The kinetics serve as input for an existing nucleation and growth model, simulating the fractional conversion at grain level. In the TGA/DSC experiments, the material was charged and discharged numerous times under a constant water vapour pressure of 12 mbar. The cycling temperature varies from room temperature to a maximum temperature of 120°C. The conversion time of each cycle was monitored. Additionally, using an optical microscope, cycling experiments of K2CO3 were performed in a micro climate chamber with the same conditions as in the TGA/DSC experiments. This allows tracking of the apparent surface area of the grains and the observation of crack formation for each cycle. The existing nucleation and growth model is enhanced by incorporating grain growth and crack formation observed from the optical experiments. Thermal characterization by means of TGA/DSC has indicated that indeed the kinetics of the material improve over multiple cycles. Typical conversion rates are increased by a factor 10 comparing the first and the 12th cycle. Preliminary optical microscope experiments show an increase of the apparent grain surface area of approximately 55{\%}. Additionally, crack formation is observed over multiple hydration and dehydration cycles leading to increased inter-particle porosity, likely adding to the improved kinetics.",
keywords = "Thermochemische warmteopslag, Zout hydraat, Nucliatie en groei model, TGA/DSC, K2CO3, Thermochemical heat storage, Nucleation and growth model, TGA/DSC, Heat Battery, Salt Hydrate",
author = "Max Beving and Arjan Frijns and Camilo Rindt and David Smeulders",
year = "2019",
language = "English",
note = "Eurotherm Seminar 112- Advances in Thermal Energy Storage ; Conference date: 15-05-2019 Through 17-05-2019",

}

Beving, M, Frijns, A, Rindt, C & Smeulders, D 2019, 'Characterization and modelling of K2CO3 cycles for thermochemical energy storage applications' Paper presented at Eurotherm Seminar 112- Advances in Thermal Energy Storage, Lleida, Spain, 15/05/19 - 17/05/19, .

Characterization and modelling of K2CO3 cycles for thermochemical energy storage applications. / Beving, Max; Frijns, Arjan; Rindt, Camilo; Smeulders, David.

2019. Paper presented at Eurotherm Seminar 112- Advances in Thermal Energy Storage, Lleida, Spain.

Research output: Contribution to conferencePaperAcademic

TY - CONF

T1 - Characterization and modelling of K2CO3 cycles for thermochemical energy storage applications

AU - Beving,Max

AU - Frijns,Arjan

AU - Rindt,Camilo

AU - Smeulders,David

PY - 2019

Y1 - 2019

N2 - Thermochemical heat storage in salt hydrates is a promising concept to bridge the gap between supply and demand of solar thermal energy in the built environment. Using a suitable thermochemical material (TCM), a heat battery can be created to supply low-temperature thermal energy during colder time periods. The principle is based on a reversible hydration-dehydration reaction with water vapour. The TCM can be charged (dehydrated) at a temperature of 120°C by using solar thermal collectors. Conversely, the discharge (hydration) occurs at room temperature using a constant water vapour pressure of 12 mbar. Previous studies have indicated that potassium carbonate (K2CO3) is a good candidate to fulfil the role of TCM in built environment applications. To generate adequate power from a heat battery for hot tap water or space heating, the kinetics of the TCM need to be sufficiently fast. It is hypothesized that the kinetics of the material improve over multiple charge and discharge cycles due to crack formation and volume increase of the grains. The aim of this work is to evaluate the kinetics of 500-700 µm K2CO3 grains using thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), and to quantify the improvement in kinetics over multiple charge and discharge cycles. The kinetics serve as input for an existing nucleation and growth model, simulating the fractional conversion at grain level. In the TGA/DSC experiments, the material was charged and discharged numerous times under a constant water vapour pressure of 12 mbar. The cycling temperature varies from room temperature to a maximum temperature of 120°C. The conversion time of each cycle was monitored. Additionally, using an optical microscope, cycling experiments of K2CO3 were performed in a micro climate chamber with the same conditions as in the TGA/DSC experiments. This allows tracking of the apparent surface area of the grains and the observation of crack formation for each cycle. The existing nucleation and growth model is enhanced by incorporating grain growth and crack formation observed from the optical experiments. Thermal characterization by means of TGA/DSC has indicated that indeed the kinetics of the material improve over multiple cycles. Typical conversion rates are increased by a factor 10 comparing the first and the 12th cycle. Preliminary optical microscope experiments show an increase of the apparent grain surface area of approximately 55%. Additionally, crack formation is observed over multiple hydration and dehydration cycles leading to increased inter-particle porosity, likely adding to the improved kinetics.

AB - Thermochemical heat storage in salt hydrates is a promising concept to bridge the gap between supply and demand of solar thermal energy in the built environment. Using a suitable thermochemical material (TCM), a heat battery can be created to supply low-temperature thermal energy during colder time periods. The principle is based on a reversible hydration-dehydration reaction with water vapour. The TCM can be charged (dehydrated) at a temperature of 120°C by using solar thermal collectors. Conversely, the discharge (hydration) occurs at room temperature using a constant water vapour pressure of 12 mbar. Previous studies have indicated that potassium carbonate (K2CO3) is a good candidate to fulfil the role of TCM in built environment applications. To generate adequate power from a heat battery for hot tap water or space heating, the kinetics of the TCM need to be sufficiently fast. It is hypothesized that the kinetics of the material improve over multiple charge and discharge cycles due to crack formation and volume increase of the grains. The aim of this work is to evaluate the kinetics of 500-700 µm K2CO3 grains using thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), and to quantify the improvement in kinetics over multiple charge and discharge cycles. The kinetics serve as input for an existing nucleation and growth model, simulating the fractional conversion at grain level. In the TGA/DSC experiments, the material was charged and discharged numerous times under a constant water vapour pressure of 12 mbar. The cycling temperature varies from room temperature to a maximum temperature of 120°C. The conversion time of each cycle was monitored. Additionally, using an optical microscope, cycling experiments of K2CO3 were performed in a micro climate chamber with the same conditions as in the TGA/DSC experiments. This allows tracking of the apparent surface area of the grains and the observation of crack formation for each cycle. The existing nucleation and growth model is enhanced by incorporating grain growth and crack formation observed from the optical experiments. Thermal characterization by means of TGA/DSC has indicated that indeed the kinetics of the material improve over multiple cycles. Typical conversion rates are increased by a factor 10 comparing the first and the 12th cycle. Preliminary optical microscope experiments show an increase of the apparent grain surface area of approximately 55%. Additionally, crack formation is observed over multiple hydration and dehydration cycles leading to increased inter-particle porosity, likely adding to the improved kinetics.

KW - Thermochemische warmteopslag

KW - Zout hydraat

KW - Nucliatie en groei model

KW - TGA/DSC

KW - K2CO3

KW - Thermochemical heat storage

KW - Nucleation and growth model

KW - TGA/DSC

KW - Heat Battery

KW - Salt Hydrate

M3 - Paper

ER -

Beving M, Frijns A, Rindt C, Smeulders D. Characterization and modelling of K2CO3 cycles for thermochemical energy storage applications. 2019. Paper presented at Eurotherm Seminar 112- Advances in Thermal Energy Storage, Lleida, Spain.