Abstract
For the thermochemical performance implementation of Mg(OH)2 as a heat storage medium, several hybrid materials have been investigated. For this study, high-performance hybrid materials have been developed by exploiting the authors’ previous findings. Expanded graphite (EG)/carbon nanotubes (CNTs)-Mg(OH)2 hybrid materials have been prepared through Mg(OH)2 deposition-precipitation over functionalized, i.e., oxidized, or un-functionalized EG or CNTs. The heat storage performances of the carbon-based hybrid materials have been investigated through a laboratory-scale experimental simulation of the heat storage/release cycles, carried out by a thermogravimetric apparatus. This study offers a critical evaluation of the thermochemical performances of developed materials through their comparison in terms of heat storage and output capacities per mass and volume unit. It was demonstrated that both EG and CNTs improves the thermochemical performances of the storage medium in terms of reaction rate and conversion with respect to pure Mg(OH)2. With functionalized EG/CNTs-Mg(OH)2, (i) the potential heat storage and output capacities per mass unit of Mg(OH)2 have been completely exploited; and (ii) higher heat storage and output capacities per volume unit were obtained. That means, for technological applications, as smaller volume at equal stored/released heat.
Highlights
About 20%–50% of the energy consumed by industrial processes is lost as waste heat contained in streams of hot exhaust gases and liquids, as well as through heat conduction, convection, and radiation from hot equipment surfaces and from heated product streams [1]
Expanded graphite (EG) has been supplied by TIMREX C-THERM 002 TIMCAL Ltd. (Bironico, Switzerland), while carbon nanotubes (CNTs) were prepared by catalytic chemical vapor deposition (CCVD) of iso-butane (i-C4 H10 ) as the C source in the presence of Fe dispersed on an Al2 O3 catalyst, purified to eliminate the catalyst residue [23]
In the case of the NM sample, few Mg(OH)2 clusters (Figure 1c white circles) are sparse among the CNT bundles (Figure 1c black arrow). Both in GM and NM samples it cannot be excluded that bulk Mg(OH)2 precipitation occurs without carbon (EG/CNTs) interaction
Summary
About 20%–50% of the energy consumed by industrial processes is lost as waste heat contained in streams of hot exhaust gases and liquids, as well as through heat conduction, convection, and radiation from hot equipment surfaces and from heated product streams [1]. This waste heat is produced whenever the operation is running. Through TES technologies, industrial users can put wasted energy back into the process that. Reducing peak demand, energy consumption, CO2 emissions and costs, while increasing overall efficiency of the processes. Since the energetic demand of industrial processes may vary during any given day and from one day to TES systems can help to balance energetic demand and supply on a daily, weekly and even seasonal basis
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