Towards a complete CO2 hydrate slurry-based cooling application – COOLHYD

With a cost equivalent to 20% of global electricity consumption, and highly regulated refrigerants, the refrigeration industry must face several challenges of sustainable development while ensuring its fundamental role for various sectors (food, air conditioning…). The use of phase change material (PCM) slurries in secondary refrigeration is a solution to reduce the amount of refrigerants and improve energy performances. These PCM suspensions can indeed store and convey large quantities of cold by latent heat, an asset for the design and efficiency of installations. CO2 hydrates are high potential PCMs: they have the best latent heat among all PCMs in refrigeration and are stable over a wide range of temperature; they can be produced by gas injection, avoiding energetically penalizing scraping processes; finally, they are green materials because they are made up of water and CO2. A secondary refrigeration system is based on 3 main stages: generation, transport and use (cold restitution). Thus, slurries must meet various constraints related to these stages to ensure good process continuity. In particular, controlling the kinetics of hydrate crystallization and slurry flow conditions, with suitable crystal size distribution (CSD), is still a major stake. By associating three internationally recognized laboratories in complementary fields, Hydrates/Cooling (FRISE), Fluid Mechanics (IMFT) and Process Engineering (LGPM), and relying on different experimental approaches (hydrate slurry pilot system, rheology of cohesive synthetic suspensions, controlled heat flow tubes) and modeling (mass/thermal balance, population balance, rheological models, global dynamic simulation model), the overall objective of the COOLHYD project is to propose a fundamental and systematic approach to address the kinetic, rheology and continuity issues involved in the application of CO2 hydrate slurry-based cooling. We will focus on: understanding the impact of slurry generation conditions on critical properties for the process (CSD, suspended solid fraction, flow regimes); developing models linking these critical properties to rheological (for slurry transport) and thermal (for slurry use) properties; optimizing the energy performance of the overall process, as a function of device architecture and control variables related to generation, transport, and use conditions, in order to provide recommendations for the design of an efficient secondary refrigeration system.