Design of thermochemical heat transformer for waste heat recovery: Methodology for reactive pairs screening and dynamic aspect consideration

Abstract

Waste Heat Recovery in the industrial sector often requires to upgrade the temperature of the heat fluxes in order to make them useful for the process. Thermochemical Heat Transformer (THT) and especially 2-salt configuration, can play a major role as they can achieve high temperature lift when compared to alternative technologies. Despite various developments in recent years, this technology still suffers from several issues to make it fully attractive: rapid and reliable reactive salt selection, heat and mas transfer intensification, coupling with process heat demand, etc. This work is focused on a new methodology to achieve a rapid screening of salt pairs for a given application (i.e. source temperatures). Four criteria, based on thermodynamic considerations, are proposed allowing for an example to go from 4290 possibilities to only three most promising pairs at the end. A second part is dedicated to dynamic aspect considerations, exploring the robustness of the solution towards changes in heat transfer and kinetic coefficients as well as to changes in heat source temperatures. Knowledge on this last aspect is of great importance to achieve efficient integration to cover process heat demand.

Thermodynamic Performance of Adsorption Working Pairs for Low-Temperature Waste Heat Upgrading in Industrial Applications

“…The thermochemical approach exploits the chemical reaction occurring between a working fluid (e.g., ammonia, water) as a refrigerant and a solid phase (e.g., salts). This technology is currently under investigation, with activities dedicated to the definition of selection criteria for working pairs [9] as well as design and testing of lab-scale prototypes, showing relevant performance in terms of coefficient of performance (COP) defined as the ratio between the upgraded heat and the heat spent to drive the process, and achievable temperature lift [6]. Nevertheless, the thermochemical approach suffers from some intrinsic limitations, such as working pairs' stability and reduced process kinetics, due to the associated chemical reaction as well as mass transfer resistance inside the reactor [10].…”