REACHER: the exploration of the use of reactive working fluids for thermodynamic cycles
Silvia Lasala
Thermodynamic cycles are at the basis of the operation of thermal power plants, heat pumps and vapour-compression refrigeration systems. Nowadays, thermodynamic cycles operate with working fluids that are either pure or inert mixtures, such as water, air, organic fluids and helium.
The project REACHER aims to quantify the impact of using reactive working fluids, undergoing rapid and reversible reactions, instead of inert ones (Lasala, 2021). This investigation is divided into four primary work packages (see Figure 1).
Project work packages
- WP1 – Development of a computational tool for the prediction of thermodynamic properties of reactive fluids.
- WP2 – Discovery, or design, and full thermophysical and thermochemical characterisation of reactive working fluids suitable for power and heating applications.
- WP3 – Optimisation of the architecture of thermodynamic cycles operating with reactive working fluids.
- WP4 – Validation of our calculations on an experimental micro-gas turbine operating on a Brayton cycle.
The project spans five years (2022–2027), and we are currently concluding the first year. The team comprises six non-permanent members and three members. During the project’s first year, we have been working on WP1, WP2 and WP4. In this article, we elaborate on the methodology employed and share some of the results we have obtained. More details will be provided in more specific scientific publications.
The performances of heat pumps operating with fictitious reactive fluids
Building upon work previous to the project, we analysed (Lasala et al., 2021; Barakat et al., 2022) the performance of heat pumps operating on a Brayton and Stirling cycle using fictitious reactive working fluids of the form:
An = (n/m) Am
To this general reaction, we have associated different stoichiometries (n and m) and thermochemistry (enthalpy and entropy of reaction), giving rise to a different set of chemical reactions. We have then assessed the impact of those parameters on the cycle’s performance. The main conclusion of the study is that many reactive fluids exist for which the slight increase of the mass flow rate of the cycle (by 10 per cent, with respect to an inert fluid) can lead to a doubled coefficient of performance (COP) (Barakat et al., 2022), see Figure 2.
The characterisation of the thermodynamic properties
Assessing the performance of thermodynamic cycles requires the calculation of the thermodynamic properties of reactive working fluids (enthalpy, entropy, density, composition of the fluid, etc., in one-phase or two-phase conditions). Those properties can be determined thanks to the methodological approach we describe in a paper under submission (for more details, visit www.univ-lorraine.fr/erc-reacher). This methodology integrates quantum mechanics calculations needed to determine thermochemical properties (standard enthalpy of formation, entropy, and the heat capacity of ideal gas) and force field-based Monte Carlo simulations to enable the determination of the non-measurable temperature and pressure of the critical points of inert NO2 and N2O4 (see Figures 3 and 4).
The code produced to perform these calculations integrates algorithms for the computation of reactional and, if more than one phase is coexisting, phase equilibrium. Two codes are being realised, one for determining those properties as a function of specified independent variables and a second to plot phase equilibrium diagrams for all the studied fluids. Figure 5 shows a temperature-entropy diagram of the reactive mixture N2O4 = 2NO2. This code is scheduled to be released as open-source in 2024.
The reaction design
In the project, we developed an algorithm and computational code capable of designing thousands of dimerisation reactions. Next, we’ll employ quantum mechanics simulations to calculate their enthalpy and entropy of reaction. These properties collectively establish the equilibrium constant, governing the reaction’s behaviour under temperature and pressure variations. Subsequently, we’ll conduct an initial screening based on these properties.
The pilot
The pilot was designed (Figure 6) and is currently under construction. It is equipped with four operating units: a 3.5 kW turbine, a shell and tube heat exchanger, a 15 kW compressor, and an electric heater. The first successful test consisted of running the turbine at the highest speed, separated from the circuit operating as a motor. The second test consists of operating the pilot in an open circuit: ambient air is taken from the inlet of the compressor and is rejected into the atmosphere after the cooler. Then, during the third test, the engine will be run in a closed circuit with N2. During the last test, a mixture of N2 and a reactive working fluid will be tested in the same closed circuit. The performance will be assessed and compared to the calculated values.
Moreover, among the measurements performed on the pilot, Raman spectroscopy measurements will be obtained before and after each pilot unit to validate the expected evolution of the chemical reaction. A preliminary experimental activity, already under development, consists of analysing the Raman spectra of some reactive fluids and calibrating the probes.
Next challenges
We will continue to improve the thermodynamic model based on our calculations, the thermodynamic code and the authomatisation of the final characterisation of each designed reactive fluid. To conclude, we are beginning with the optimisation of the cycle architecture.
Acknowledgements
This project has received funding from the European Research Council (ERC) under the European Union’s Horizon Europe research and innovation programme (grant agreement No. 101040994). The author wishes to thank the association APSIIS for the kind support in the sizing of the power plant.
References
Barakat, A., Lasala, S., Arpentinier, P., Jaubert, J.-N. (2022) ‘The Original and Impactful Exploitation of Chemical Energy in Heat Pumps’, Chemical Engineering Journal Advances, 12, 100400. doi: 10.1016/j.ceja.2022.100400.
Lasala, S, Privat, R., Herbinet, O., Arpentinier, P., Bonalumi, D. and Jaubert, J.-N. (2021) ‘Thermo-Chemical Engines: Unexploited High-Potential Energy Converters’, Energy Conservation and Management, 229, 113685. doi: 10.1016/j.enconman.2020.113685.
Lasala, S. (2022) ‘Reactive fluids for intensified thermal energy conversion’, The Project Repository Journal, 13, pp. 102–105. doi: 10.54050/PRJ1318808.
Project summary
With the aim to effectively increase the performances of power plants, refrigeration systems and heat pumps, this project proposes the use of equilibrated reactive working fluids instead of inert ones. It applies an original methodology that integrates thermodynamic and kinetic predictive tools to discover and characterise suitable reactive fluids, allowing for the quantification of the effects of reaction features on system performance and optimal architecture.
Project lead profile
Silvia Lasala, principal investigator in REACHER, is currently assistant professor at the University of Lorraine, ENSIC-LRGP (France). In 2016, she got her PhD at Politecnico di Milano (Italy) with a thesis aiming at improving the thermodynamic modelling of CO2-based streams in CO2-capture-and-storage systems. During her PhD, she also worked in designing and characterising inert working fluids for thermodynamic cycles. Then, she carried out a postdoc at LRGP (France), investigating the kinetics and thermodynamics of liquefying hydrogen and researching the possible use of inert and novel reactive working fluids in power and trigeneration plants.
Project contacts
Silvia Lasala
Laboratoire Réactions et Génie des Procédés, UMR 7274, Université de Lorraine – CNRS, Nancy Cédex, France
silvia.lasala@univ-lorraine.fr
www.researchgate.net/profile/Silvia-Lasala
Funding
This project has received funding from the European Research Council (ERC) under the European Union’s Horizon Europe research and innovation programme under grant agreement No. 101040994.
Image legends
Figure 1: The project plan.
Figure 2: The ratio of the COP of a heat pump operating with a reactive working fluid and the COP of a heat pump using inert working fluids as a function of the ratio between the mass flow rate of the reactive fluid heat pump with respect to the inert one. In both cases (inert or reactive fluid), the thermal power output of the heat pump is the same. Each black point of the cycle represents a different fictitious fluid.
Figure 3: Monte Carlo simulations for the system NO2 – saturation density-temperature curve.
Figure 4: Monte Carlo simulations for the system N2O4 – saturation density-temperature curve.
Figure 5: Temperature-entropy diagram of the reactive mixture N2O4 = 2NO2. The two curves make reference to the same calculation done with different sets of input critical properties for the equation of state.
Figure 6: Pilot under realisation.
