Experimental investigation of an open thermochemical process operating with a hydrate salt for thermal storage of solar energy: Local reactive bed evolution

Abstract

Their high energy density and low heat losses between storage and recovery times make thermochemical processes a promising way to achieve long-term (seasonal) storage. Among the available reactor configurations, open systems using a packed bed of reactive solid are simple and efficient. This paper reports on the local operation and reactive bed behavior of such systems. Mass transfer changes within the reactive bed, which is the main limitation of such systems, was investigated using several state variables (reaction advancement, pressure drop across the salt bed and bed temperatures). Results from two experimental setups were analyzed: a small bench for mass transfer characterization, and a prototype at a larger scale. Both used SrBr 2 /H 2 O as reactive pair. A salt bed temperature analysis evidenced a reaction front moving within the reactive layer from the moist air inlet to its outlet. A mass transfer study showed marked changes in the reactive bed permeability during the reaction (by one order of magnitude) and with the reactive bed density (from 10 −9 to 10 −12 m 2 when density range from 300 to 600 kWh•m −3). During the reaction an asymmetric time course of the bed permeability was also highlighted: as f(X) in dehydration and f(1/X) in hydration.

Hybrid strontium bromide-natural graphite composites for low to medium temperature thermochemical energy storage: Formulation, fabrication and performance investigation

“…The TG measurement data shown in Fig. 7 clearly indicate that the dehydration reaction occurs in two distinct steps with one step losing five H2O molecules and the other step losing one H2O molecule, in line with previous investigations on pure SrBr2 [22,27] The onset temperatures of the two reaction steps are respectively at 64.7°C and 160.1°C. The total water loss of the TCS composite in the two steps is in line with theoretical predictions: the composites with 40% and 80% SrBr2 give respectively 40% and 80% water loss expected by pure SrBr2•6H2O.…”

“…MgSO4, CaCl2 and LiBr) in different structural materials including zeolite, silica gel and activated carbon [12,17,18]. Composite TCS containing SrBr2, however, remains largely unexplored, and the published studies were primarily on energy storage density [19][20][21] or on the performance of pure SrBr2 at the reactor scale [8,22] [23]. To our knowledge, no studies have been published on linkage between the performance and structure of the composite TCS containing SrBr2the main motivation of this paper.…”

Analysis of thermochemical energy storage in an elemental configuration

“…Mass conservation of humid air in the channel:where ρ f is the humid air density. The changes in water vapor content do not impact the humid air properties 30 .…”

“…The model equations are given by the following conservation laws:Mass conservation of humid air in the channel:where ρ f is the humid air density. The changes in water vapor content do not impact the humid air properties 30 .Mass conservation of water vapor in the channel (necessary to link with the water vapor diffusion through the salt):where c is the water vapor concentration, and D v , f is the vapor diffusion coefficient in the fluid (air).Mass conservation of water vapor in the salt:Momentum conservation of humid air in the channel, in laminar regime:where u is the velocity vector.Energy conservation along the tube:Energy conservation through the salt:Reaction kinetic:…”

Modeling and assessment of a thermochemical energy storage using salt hydrates

“…The thermochemical energy storage (TCS) materials are characterized by higher energy storage density due to their high enthalpy of reactions . Moreover, they require smaller volume size and their heat loss is smaller in comparison with conventional methods such as phase‐changing materials . TCS systems allow for storing the heat provided by the solar energy during the hot seasons to be released and used during the cold seasons.…”