A structured procedure for the selection of thermal energy storage options for utilization and conversion of industrial waste heat

Thermal energy storage is a key enabling technology for the recovery and valorisation of industrial waste heat. Nevertheless, there is a wide gap between the variety of heat storage options investigated and the recurrent few types virtually implemented in the industries. To take advantage of a wider spectrum of solutions, a structured procedure is proposed in this work for the selection of storage material and layout. The algorithm developed consists of a preliminary storage design followed by a performance estimation of the overall system where the heat storage is integrated. The preliminary design allows a first screening and ranking of sensible, latent or thermochemical materials using a quasi-stationary approach. The performance estimation leads to the final selection of the heat storage system, which is based on the analysis of the dynamic thermal response of the heat storage along with physically based or input-output models for the load. The algorithm is applied to improve the heat recovery of a discontinuous and fluctuating flue gas at medium temperature from a steel industry, targeting the production of process steam or electricity. The results show that the integration of a packed bed heat storage, either of the sensible or latent type, allows the highest amount of steam to be generated in the discharging. Moreover, the combination of the same heat storage with an organic Rankine cycle or the Kalina cycle results in the highest amount of generated electricity. The investment in a packed bed rock storage was found to result in payback times of about seven years, whereas tank-based storage units appear not profitable due to the high cost of the silicone oil.