Management of vapor release in secondary refrigeration processes based on hydrates involving CO2 as guest molecule

Abstract

When used as secondary refrigerants for cold storage and refrigeration applications, hydrate slurries offer high-energy densities due to their significant latent heat of fusion. In this context, gas hydrates exhibit a feature not yet explored in the literature: vapor is released when hydrate crystals melt in the heat exchanger supplying cold to end users. This novel feature is investigated in this paper. First, the separation of the released vapor from the solid–liquid slurry is described. This is followed by a study of how the design of the storage system can be adapted to the use of gas hydrate slurries as secondary fluid and specifically the consequences on its volume. A model is developed, based on energy and mass balances, to determine the required storage volume. Two types of hydrates involving a gas are considered: the single hydrate of carbon dioxide and the mixed hydrate of tetra-n-butylphosphonium bromide (TBPB) plus CO2. The results show that adding vapor compression to the process can save up to 75% of the total storage volume.