Optimal Design of Combined Two-Tank Latent and Metal Hydrides-Based Thermochemical Heat Storage Systems for High-Temperature Waste Heat Recovery

The integration of thermal energy storage systems (TES) in waste-heat recovery applications shows great potential for energy efficiency improvement. In this study, a 2D mathematical model is formulated to analyze the performance of a two-tank thermochemical heat storage system using metal hydrides pair (Mg2Ni/LaNi5), for high-temperature waste heat recovery. Moreover, the system integrates a phase change material (PCM) to store and restore the heat of reaction of LaNi5. The effects of key properties of the PCM on the dynamics of the heat storage system were analyzed. Then, the TES was optimized using a genetic algorithm-based multi-objective optimization tool (NSGA-II), to maximize the power density, the energy density and storage efficiency simultaneously. The results indicate that the melting point Tm and the effective thermal conductivity of the PCM greatly affect the energy storage density and power output. For the range of melting point Tm = 30–50 °C used in this study, it was shown that a PCM with Tm = 47–49 °C leads to a maximum heat storage performance. Indeed, at that melting point narrow range, the thermodynamic driving force of reaction between metal hydrides during the heat charging and discharging processes is almost equal. The increase in the effective thermal conductivity by the addition of graphite brings about a tradeoff between increasing power output and decreasing the energy storage density. Finally, the hysteresis behavior (the difference between the melting and freezing point) only negatively impacts energy storage and power density during the heat discharging process by up to 9%. This study paves the way for the selection of PCMs for such combined thermochemical-latent heat storage systems.

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Metal Hydride Beds-Phase Change Materials: Dual Mode Thermal Energy Storage for Medium-High Temperature Industrial Waste Heat Recovery

Energies ◽

10.3390/en12203949 ◽

2019 ◽

Vol 12 (20) ◽

pp. 3949 ◽

Cited By ~ 6

Author(s):

Serge Nyallang Nyamsi ◽

Ivan Tolj ◽

Mykhaylo Lototskyy

Keyword(s):

Phase Change ◽

Latent Heat ◽

Metal Hydride ◽

Heat Recovery ◽

Waste Heat Recovery ◽

Heat Storage ◽

Waste Heat ◽

Metal Hydrides ◽

Thermochemical Heat Storage ◽

Change Material

Heat storage systems based on two-tank thermochemical heat storage are gaining momentum for their utilization in solar power plants or industrial waste heat recovery since they can efficiently store heat for future usage. However, their performance is generally limited by reactor configuration, design, and optimization on the one hand and most importantly on the selection of appropriate thermochemical materials. Metal hydrides, although at the early stage of research and development (in heat storage applications), can offer several advantages over other thermochemical materials (salt hydrates, metal hydroxides, oxide, and carbonates) such as high energy storage density and power density. This study presents a system that combines latent heat and thermochemical heat storage based on two-tank metal hydrides. The systems consist of two metal hydrides tanks coupled and equipped with a phase change material (PCM) jacket. During the heat charging process, the high-temperature metal hydride (HTMH) desorbs hydrogen, which is stored in the low-temperature metal hydride (LTMH). In the meantime, the heat generated from hydrogen absorption in the LTMH tank is stored as latent heat in a phase change material (PCM) jacket surrounding the LTMH tank, to be reused during the heat discharging. A 2D axis-symmetric mathematical model was developed to investigate the heat and mass transfer phenomena inside the beds and the PCM jacket. The effects of the thermo-physical properties of the PCM and the PCM jacket size on the performance indicators (energy density, power output, and energy recovery efficiency) of the heat storage system are analyzed and discussed. The results showed that the PCM melting point, the latent heat of fusion, the density and the thermal conductivity had significant impacts on these performance indicators.

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Application of Borehole Thermal Energy Storage in Waste Heat Recovery from Diesel Generators in Remote Cold Climate Locations

Energies ◽

10.3390/en12040656 ◽

2019 ◽

Vol 12 (4) ◽

pp. 656 ◽

Cited By ~ 4

Author(s):

Seyed Ghoreishi-Madiseh ◽

Ali Fahrettin Kuyuk ◽

Marco Rodrigues de Brito ◽

Durjoy Baidya ◽

Zahra Torabigoodarzi ◽

...

Keyword(s):

Energy Storage ◽

Thermal Energy ◽

Thermal Energy Storage ◽

Heat Recovery ◽

Waste Heat Recovery ◽

Waste Heat ◽

Storage System ◽

Thermal Storage ◽

Cold Climate ◽

Diesel Generators

Remote communities that have limited or no access to the power grid commonly employ diesel generators for communal electricity provision. Nearly 65% of the overall thermal energy input of diesel generators is wasted through exhaust and other mechanical components such as water-jackets, intercoolers, aftercoolers, and friction. If recovered, this waste heat could help address the energy demands of such communities. A viable solution would be to recover this heat and use it for direct heating applications, as conversion to mechanical power comes with significant efficiency losses. Despite a few examples of waste heat recovery from water-jackets during winter, this valuable thermal energy is often discarded into the atmosphere during the summer season. However, seasonal thermal energy storage techniques can mitigate this issue with reliable performance. Storing the recovered heat from diesel generators during low heat demand periods and reusing it when the demand peaks can be a promising alternative. At this point, seasonal thermal storage in shallow geothermal reserves can be an economically feasible method. This paper proposes the novel concept of coupling the heat recovery unit of diesel generators to a borehole seasonal thermal storage system to store discarded heat during summer and provide upgraded heat when required during the winter season on a cold, remote Canadian community. The performance of the proposed ground-coupled thermal storage system is investigated by developing a Computational Fluid Dynamics and Heat Transfer model.

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The Experiment Research on Storage Characteristic of PCM Storage Device by Spheres Piled Encapsulated for Vehicle Waste Heat

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.983.383 ◽

2014 ◽

Vol 983 ◽

pp. 383-387 ◽

Cited By ~ 1

Author(s):

Tian Shi Zhang ◽

Qi Yi Wang ◽

Guo Hua Wang ◽

Chun Gao ◽

Qing Gao

Keyword(s):

Melting Point ◽

Flow Rate ◽

Heat Recovery ◽

Waste Heat Recovery ◽

Heat Storage ◽

Waste Heat ◽

Thermal Environment ◽

Melting Rate ◽

Storage Device ◽

Medium Flow

For the thermal environment and the warming requirement of Vehicle, carry out experiment study on heat storage characteristic of phase change materials (PCM) encapsulated by Spherical stack. heat storage and release experiment process , changing factors such as medium flow rate and melting point which impact on PCM heat transfer characteristics , melting rate and response time have been analyzed. The results show that within the scope of experiment high medium flow rate is conducive to promote PCM melting rate and heat storage. In the experiments process, high melting point of PCM storage heat grade is high, but the low melting point of PCM is more suitable for vehicle motor, batteries in low temperature waste heat recovery. At the same time, multi-melting point PCM storage device with spheres piled encapsulated delamination mixed stowage was better satisfy the different condition of waste heat recovery and utilization than single melting point of PCM.

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