Upgrading Waste Heat from 90 to 110 °C: The Potential of Adsorption Heat Transformation

Abstract

Low-grade heat is abundantly available below 100 °C, whereas industry mainly needs heat above 100 °C. Thus, the industry cannot directly utilize low-grade heat to save primary energy and emissions. Low-grade heat can be utilized by adsorption heat transformers (AdHTs); however, closed AdHTs to upgrade heat above 100 °C are only investigated by idealized steady-state analyses, which indicate the maximal theoretical performance. For evaluating the performance achievable in practice, this work studies a closed AdHT in a one-bed configuration using dynamic simulation. For the working pair AQSOA-Z02/H2O, the performance is optimized via the design of the adsorber heat exchanger and the control of the AdHT cycle. When heat is upgraded from 90 to 110 °C, releasing waste heat at 35 °C, the maximum exergetic coefficient of performance (COPexergetic) is 0.64, and the maximum specific heating power (SHP) is 590 W kg−1. The maximum SHP can increase by 35% when releasing waste heat at 25 °C. Both performance indicators strongly depend on design, control, and the available temperature of the waste heat. Overall, AdHTs with optimized design and control are promising to utilize low-grade waste heat.