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

• Published in: Science and technology for energy transition Vol. 78; p. 29
• Main Author: Pons, Michel
• Format: Journal Article
• Language: English
• Published: IFP Énergies nouvelles (IFPEN), Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA) 2023; EDP Sciences
• Subjects: co2; Engineering Sciences; gas-hydrate; mixed-hydrate; secondary refrigeration; tbpb; thermodynamics; Thermodynamics; Gas-hydrate; Secondary refrigeration; Mixed-hydrate; CO2; TBPB
• ISSN: 2804-7699; 2804-7699
• DOI: 10.2516/stet/2023027

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.