Experimental and numerical analysis of a packed-bed thermal energy storage system designed to recover high temperature waste heat: an industrial scale up

Abstract

An industrial-scale air-ceramic horizontal packed-bed thermal energy storage (Eco-Stock®) has been designed and built by Eco-Tech Ceram and tested during an experimental campaign of 500h. The goal is to provide experimental data and analysis of a horizontal and containerized packed bed TES at high temperature, with performance indicators specific to waste heat recovery. A single charge-discharge at 525°C and 3 cycles at 500°C were carried out (300 kW Th for charge, 350 kW Th for discharge). The unit was able to store up to 1.9 MWh Th in a TES system (1.7 × 1.7 × 3.08 m 3 ) composed by 16-ton of bauxite ceramic media. The packed bed was able to valorize up to 90% of the heat source, which demonstrates the system ability to recover waste heat up to 525°C at industrial scale. No channeling effect and moderate radial thermal gradient were detected, even though the tank had a horizontal geometry. The plug and play TES presents a non-negligible part of its energy stored in the insulant, which can be recovered during discharge. To take into account such phenomenon, a one-dimension 3 temperature model is proposed. The model fitted well with experimental results, with a root mean standard deviation of the model below 20°C for the temperature profiles.

Energy analysis and life cycle assessment of a thermal energy storage unit involving conventional or recycled storage materials and devoted to industrial waste heat valorisation

“…The charge efficiency includes the thermal loses due to the piping and mostly to the non-valorisation of low-temperature waste heat (a threshold is set at 150 • C), while the discharge efficiency is only affected by the piping thermal loses and potentially by a self-discharge depending on the use conditions (the whole heat is valorised up to ambient temperature). Those efficiencies are consistent with similar systems in the literature (Touzo et al, 2020), adjusted by the specific temperature threshold corresponding to the industrial application, as this parameter is known to be of major influence (Fasquelle et al, 2018). The storage porosity corresponds to a homogeneous and disordered granular media porosity that is about 30%-40% (Nellis and Klein, 2008), usually set closely to 40% in real systems (Ortega-Fernández and Rodríguez-Aseguinolaza, 2019) and even increased by the use of internal separators (Fasquelle et al, 2018).…”

“…2015., 2015), the valorisation potential would be about 2.8 GWh per year. The storage system has an 80% charging efficiency (accounting for the ducts thermal losses and the low-temperature waste heat fraction that is not recovered) and 92% discharging (accounting for the ducts thermal losses) (Touzo et al, 2020). The two tanks operate 3 charge/discharge cycles per 24 h h 7/7days with a two weeks plant closure, totalizing 1050 cycles per year that is to say 2 GWh year − 1 valorised.…”

Influence of solar heat sources on packed bed TES performances

“…This storage unit weights 28 tons in total (ceramic medium, insulation and tank), which makes transportation by truck possible. The packed-bed has been able to store up to 1.9 MWhth at 525°C during a reference test described in a previous work 3 . The skid is a system which enables to properly handle the air flux in the storage using the air admission, a fan, an electric air heater (500 kWe), a chimney and a set of valves.…”

Thermocline thermal energy storage optimisation combining exergy and life cycle assessment

“…The objective of the present work is to optimise the environmental impacts and the exergy efficiency of an industrial tank, named Eco-Stock® [32] (Fig. 2), developed and commercialised by Eco-Tech Ceram [33], to valorise industrial waste heat.…”