Hybrid thermochemical cycle for cold and electricity cogeneration: Experimental and numerical analyses of the process behavior and expander-reactor coupling

The valorization of waste heat to respond to the increase demand on electricity and cooling is an important energetic challenge. For this purpose, a hybrid thermochemical cycle is proposed. This discontinuous sorption cycle is based on reversible endothermic/exothermic solid-gas reactions, and it is able to recover medium grade waste heat (between 150 and 250 degrees C) to valorize it in a second step by providing cold production at its endothermic component and mechanical work thanks to the integration of an expander on the gas line. Moreover, the two-step operation leads to a storage functionality. This paper presents an experimental study of this new hybrid cycle prototype in different operating conditions, and a sensitivity study of the design parameters of the prototype performed through a steady state model. The experimentation shows the influence of the electrical load applied to the generator on the coupling between the expander and reactor, by affecting the rotational speed, the torque of the expander and the pressure of the reactor. The analysis of the experimental results highlighted the effect of two main limitations in the prototype: the internal leaks on the expander side (unlubricated scroll expander) and the heat transfer on the reactor side. A numerical parametric study is done on these two parameters, showing the possibility of cogenerating 125 W of mechanical power and 2.3 kW of cold for defined enhanced parameters of the prototype. These promising results prompt the next step of conducting a detailed exergetic analysis of the cycle. This analysis will aim to identify the primary sources of exergy destruction and to explore ways for reducing them by minimizing main irreversibilities in the cycle.