Heat integration is a well-established approach to increase the energy efficiency in chemical processes. However, conventional steady-state approaches fail in dynamically operated Power-to-chemicals processes where production rate follows the renewable energy generation profiles and the reactor consequently experiences temperature fluctuations. Herein, we present a novel strategy to store and release heat by exploiting the high reaction enthalpy of absorption of ammonia (or water) in cheaply available metal halides, where the heat storage temperature can be tuned between 300 and 500 °C. Modelling of the system provides guidance for the tailored design of the heat storage system by balancing heat loses, heat transfer and heat storage rates, with a maximum theoretical efficiency of ~80%. In addition, this heat integration strategy can store heat closer to the temperature at which will be subsequently utilized, maximizing the heat quality. The novel heat storage approach is demonstrated for the dynamic operation of a (exothermic) Haber-Bosch reactor for green ammonia synthesis. In comparison to storing sensible heat using a ceramic material, the absorption-based heat storage system can store up to ~12× more heat on a volume basis with a temperature swing of only 10 °C to maximize the heat quality. Additionally, it keeps the HB reactor hot for up to 10× longer than the reactor alone during idle operation, facilitating the fast re-starts with no energy requirements while transiently increasing the production due to in-situ cooling. The dynamic reactor operation enabled by this new absorption-based heat storage approach highlights the importance of re-designing of Power-to-X processes with novel technologies to enhance their economic feasibility. • Demonstration of a novel heat storage system using ammonia absorption. • Heat storage temperature can be tuned between 300 and 500 °C • Absorptive heat storage compares favourably with sensible heat storage in ceramics • This passive heat storage can buffer temperature fluctuations • Particularly relevant for heat integration in dynamically operated systems.
Smith et al. (Fri,) studied this question.