An equation of state and a phase diagram for gas-hydrate-forming slurries in gas-shortage

Michel Pons (1)

1 COMET - COuplages Multiphysiques Et Transferts - LISN

Slurries of gas hydrates, especially mixed hydrates of CO 2 and TBPB (Tetra-n-Butyl Phosphonium Bromide), are currently under consideration for secondary refrigeration. Secondary refrigeration circuits contain wide sections where the two-phase slurry (solid + liquid), separated from the gas phase, undergoes transformations that would if gas were present, lead to both hydrate formation and gas dissolution. The absence of gas hinders these processes: the slurry is in gas shortage . The analysis demonstrates that, although thermodynamically distant from three-phase equilibria, slurries in gas-shortage are in equilibrium. For describing their thermodynamic state, the notion of CO 2 partial pressure in a gas mixture is introduced, which leads to an equation of state and a new phase diagram with temperature or enthalpy versus CO 2 mass-fraction. This diagram complements those commonly used for three-phase systems. The thermal behavior of slurries in gas shortage is then investigated, leading to the possibility of future experimental validation of the present analysis.

Mots clés: Gas-hydrate; Mixed-hydrate; Secondary refrigeration; CO2; TBPB; Thermodynamics

Domaines: Sciences de l'ingénieur [physics]

Michel Pons. An equation of state and a phase diagram for gas-hydrate-forming slurries in gas-shortage. Science and Technology for Energy Transition, 2023, 78, pp.29. ⟨10.2516/stet/2023027⟩. ⟨hal-04253845⟩