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Valorisation énergétique des hydrates : Application à la réfrigération

Abstract : My research at Irstea aims at studying gas hydrates in order to reduce energy and environmental impact of refrigeration systems. These crystals, formed from water and gas, have a high latent heat of melting. They can thus be used for cold storage in order to optimize design, flexibility and efficiency of facilities. By dispersing hydrates in liquid phase, it is also possible to form hydrate slurries capable of carrying their cold reserves in secondary refrigeration systems dedicated to limit the use of greenhouse gas refrigerant. Two approaches have directed this work on the use of hydrate energy: the study of hydrates as storage materials (thermodynamic approach) and the implementation of hydrate slurries for cold distribution (rheological approach). This work has resulted in scientific production of eighteen publications and forty communications. My participation in the supervision of PhD thesis and postdoctoral positions has greatly contributed to the development of these themes, supported by the funding of collaborative projects mostly in coordination. Concerning the thermodynamic approach, our calorimetric studies have shown that CO2 hydrates have a high latent heat of melting (501 kJ.kgwater-1) and adjustable equilibrium conditions (T> 273 K, P> 1.4 MPa). However, in order to reduce their equilibrium pressures and improve the economic viability of the process, various thermodynamic additives (tetrahydrofuran, alkyl-onium salts) were used to form mixed hydrates with CO2, resulting in a decrease of pressure of about 80 % compared to single CO2 hydrate while maintaining good dissociation enthalpy, above 330 kJ.kgwater-1. Consequently, single/mixed hydrates have potential applications for cold storage at temperatures appropriate for different cooling procedure (process, air-conditioning…). Our results also confirmed the advantage of using these structures for gas treatment applications (natural gas/CO2 capture, storage…). In addition, the rheological properties of hydrate slurries have a strong influence on pumping energy, but also on heat exchange coefficients, i.e. the ability of hydrate slurry to transfer energy. The rheological approach consisted in studying various hydrate slurries (CO2, salt) in two devices based on the capillary viscometer principle (circulation loops with or without stirred reactor). Rheological models showed that over 10 % of crystals in solution, hydrate slurries have a shear thinning behaviour regardless of the device. In the presence of some surfactants, however, their behaviour may become Newtonian. Moreover, apparent viscosity and yield stress of CO2 hydrate slurries decreases significantly when they are formed in a stirred reactor. Thus, the present work contributed to the definition of hydrate slurries with flow conditions suitable for secondary refrigeration applications. The further work aims at completing this study according to the following three directions: the study of new mixed hydrates; the increase of transfers in hydrate formation/dissociation processes; the integration of hydrates in refrigeration systems associated with energy and environmental analysis. A fourth aspect concerns the enlargement of the subject to other application domains, in order to characterize not only the level of maturity of different hydrate-based technologies but also the potential use of hydrates in areas not yet explored.
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https://hal.inrae.fr/tel-03286925
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Submitted on : Thursday, July 15, 2021 - 11:48:09 AM
Last modification on : Tuesday, September 7, 2021 - 3:54:08 PM

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Anthony Delahaye. Valorisation énergétique des hydrates : Application à la réfrigération. Sciences de l'ingénieur [physics]. Université Pierre et Marie Curie (Paris 6), Sorbonne Universités, 2013. ⟨tel-03286925⟩

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