Abstract
To store low-temperature heat below 100 °C, novel composite sorbents were developed by impregnating LiCl into expanded vermiculite (EVM) in this study. Five kinds of composite sorbents were prepared using different salt concentrations, and the optimal sorbent for application was selected by comparing both the sorption characteristics and energy storage density. Textural properties of composite sorbents were obtained by extreme-resolution field emission scanning electron microscopy (ER-SEM) and an automatic mercury porosimeter. After excluding two composite sorbents which would possibly exhibit solution leakage in practical thermal energy storage (TES) system, thermochemical characterizations were implemented through simulative sorption experiments at 30 °C and 60% RH. Analyses of thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) curves indicate that water uptake of EVM/LiCl composite sorbents is divided into three parts: physical adsorption of EVM, chemical adsorption of LiCl crystal, and liquid–gas absorption of LiCl solution. Energy storage potential was evaluated by theoretical calculation based on TGA/DSC curves. Overall, EVMLiCl20 was selected as the optimal composite sorbent with water uptake of 1.41 g/g, mass energy storage density of 1.21 kWh/kg, and volume energy storage density of 171.61 kWh/m3.
Highlights
Solar energy is regarded as a promising alternative to traditional energy resources, and the potential usage in residency and industry has been widely researched
With larger salt content, more salt crystals are observed on EVMLiCl20
This paper aims to develop novel composite sorbents employing expanded vermiculite (EVM), which has a macroporous structure, as host matrix rather thansorbents using traditional
Summary
Solar energy is regarded as a promising alternative to traditional energy resources, and the potential usage in residency and industry has been widely researched. Thermal energy storage (TES) is an efficient method to realize sustainable usage of solar energy [1]. Methods of TES are mainly divided into three types: latent heat storage, sensible heat storage, and thermochemical heat storage. Latent heat storage and sensible heat storage have been widely investigated in recent decades, insufficient studies on thermochemical heat storage have been carried out, which is competitive and attracting burgeoning interests owing to higher energy storage density and negligible heat loss over a long-term storage period. Water sorption materials can be generally divided into three types: physical sorbents such as silica gel and zeolite; chemical sorbents represented by LiCl and MgCl2 ; and composite sorbents, called “salt inside porous matrix (CSPM)”. CSPM was selected as the water sorption material.
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