Dehydration kinetic study of a chemical heat storage material with lithium bromide for a magnesium oxide/water chemical heat pump

Myagmarjav, Odtsetseg; Ryu, Junichi; Kato, Yukitaka

doi:10.1016/j.pnucene.2014.07.026

Cited by 15 publications

(18 citation statements)

References 12 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[15,16] Although the Mg(OH) 2 /MgO TCES cycle is well known, [15,[17][18][19][20] low cycle stability and incomplete hydration impede application. In literature, different efforts were made to improve the reactivity and thermal conductivity of the material by addition of lithium salts, [21][22][23] increasing the reaction rate, and the preparation of composite materials with expanded graphite. [20,[24][25][26] The issue of limited reactivity and low cycle stability is mainly related to the kinetic inhibition of the critical dissociation of water on the MgO surface.…”

mentioning

confidence: 99%

Calcium Doping Facilitates Water Dissociation in Magnesium Oxide

Müller

Knöll

Ruh

et al. 2017

Advanced Sustainable Systems

View full text Add to dashboard Cite

is the most ubiquitously used form of energy, including in electricity generation, power plants, or industry. [5] In this context, in 2011, the International Energy Agency estimated in a report entitled "Solutions for a low-carbon energy future" that global energy loss through waste heat accounts for two-third of the overall energy production. [6] Therefore, methods suitable for reduction of waste heat or reutilization thereof could contribute significantly to a sustainable energy management. [7][8][9] Among the different approaches to this challenge, thermochemical energy storage (TCES) is a highly appealing concept, since by means of a reversible chemical reaction, a suitable material energy is converted from thermal to chemical energy. The charged material may be stored for any period of time without further losses or additional infrastructure (such as insulation), until, by addition of the proper reactant, the discharging reaction, releasing the stored energy in form of heat, is initiated. [2,[10][11][12] The economic benefit of implementing TCES cycles in the energy management was demonstrated by several economic feasibility studies, illustrating that, e.g., with the waste heat from Lenzing AG, [13] Calcium doping of magnesium oxide results in significantly increased water dissociation rates, thus enhancing both hydration rate and reaction completeness of hydration compared to pure MgO. For a series of mixed magnesiumcalcium oxides (Mg x Ca 1−x O) with varying Ca contents between 0% and 40%, the material of a composition Mg 0.9 Ca 0.1 O shows the fastest rehydration, transforming completely within 80 min to the mixed hydroxide. In consecutive dehydration/rehydration cycles, reasonable cycle stability is found. A "regeneration" of the aged material (reactivity reduced by excessive cycling) in liquid water re-establishes the initial rehydration reactivity. Density functional theory calculations support the experimental findings, confirming that calcium doping can reduce the energy of the rate limiting water dissociation reaction, exploiting both electronic and steric (size) effects. Three major requirements for future sustainable energy management have been established including reduction of greenhouse gas emissions, promotion and increased use of renewable energy sources, and enhancing the efficiency of energy use. [1,2] Whereas the first two issues are widely discussed and the subject of international treaties such as the Kyoto protocol [3] and the Paris agreement, [4] awareness of the poor overall efficiency of today's energy economy is rather limited. Heat

show abstract

mentioning

confidence: 99%

Calcium Doping Facilitates Water Dissociation in Magnesium Oxide

Müller

Knöll

Ruh

et al. 2017

Advanced Sustainable Systems

View full text Add to dashboard Cite

show abstract

“…Their research has focused first on the development of a new magnesium oxide material using ultra fine oxide powder as precursor in order to improve its durability [20]. Subsequently, the same developed material has been used to test the performance of different packed bed reactor configurations of MgO/Mg(OH)2 chemical heat pumps [22,23], to study the reaction mechanism of the material mixed with different additives such as LiCl [24], LiBr [25][26][27] and CaCl2 [28,29], and to improve its thermal properties by addition of expanded graphite [30][31][32]. The related results have shown the potential of the studied material to meet the requirements of the chemical heat storage/chemical heat pump technology.…”

Section: Thermochemical Heat Storage Mediamentioning

confidence: 99%

“…Indeed, referring to Kato and coworkers studies [26,28], the Mg/Mg(OH)2 system can store heat at around 300 o C (lower than the PCM melting temperature) under vacuum while achieving reasonable dehydration reaction rates.…”

Section: Thermodynamic Considerationsmentioning

confidence: 99%

Feasibility analysis of a novel solid-state H2 storage reactor concept based on thermochemical heat storage: MgH2 and Mg(OH)2 as reference materials

Bhouri

Bürger

Linder

2016

International Journal of Hydrogen Energy

View full text Add to dashboard Cite

This paper discusses the feasibility of a novel adiabatic magnesium hydride (MgH2) reactor concept based on thermochemical heat storage. In such a concept, the heat of reaction released during the absorption of hydrogen is stored by a thermochemical material in order to be reused in a subsequent desorption stage. Magnesium hydroxide (Mg(OH)2) has been selected as the suitable material for integration into the MgH2 storage system due to its thermodynamic properties. An analytical formulation of hydrogen absorption time is used to determine the range of the geometrical characteristics of the two storage media, their properties and their operating conditions. The advantage of the proposed new concept is the possibility to reduce the mass of the heat storage media by a factor of 4 compared to phase change material, improving then the gravimetric system capacity as well as its total cost. The second advantage is an improved flexibility of the operating pressure conditions for MgH2 absorption reaction and Mg(OH)2 dehydration reaction that enables shorter hydrogen absorption times by ensuring larger temperature gradients between the two storage media.

show abstract

“…For further studies of determining the optimal mixing ratios of LiBr and EG in the EML composite, the experiments were carried out at five different mixing molar ratios of LiBr-to-Mg(OH) 2 , a: were the optimal mixing molar and mass ratios based on the evaluation of kinetic parameters [17,18]. Thereby the EML composite (a ¼ 0.10 and w ¼ 0.83) was suggested as the desired material.…”

Section: Sample Preparationmentioning

confidence: 99%

“…For further studies of determining the optimal mixing ratios of LiBr and EG in the EML composite, the experiments were carried out at five different mixing molar ratios of LiBr-to-Mg(OH) 2 , a: 0.300, 0.100, 0.050, 0.010, 0.005, and seven different mixing mass ratios of EG-to-Mg(OH) 2 , w: 0.50, 0.67, 0.75, 0.80, 0.83, 0.86 and 0.88 from which the kinetic parameters, i.e., the reaction rate constants and activation energies, were obtained for both reactions. The investigation revealed a of 0.10 (Mg(OH) 2 :LiBr ¼ 10:1) and w of 0.83 (Mg(OH) 2 :EG ¼ 5:1) were the optimal mixing molar and mass ratios based on the evaluation of kinetic parameters [17,18].…”

Section: Introductionmentioning

confidence: 99%