Rheological characterisation of CO2-containing hydrate slurries for refrigeration applications
Abstract
In the present paper, the suitability of CO2 hydrate slurries in secondary refrigeration was
investigated by relying on a rheological characterization in a dynamic loop. CO2 hydrate slurry
was formed in an experimental loop by direct injection of CO2 in a pre-cooled aqueous solution.
A Herschel-Bulkley rheological model that takes into account the hydrate solid fraction was
employed. Good agreement was found between model and experimental results especially for low
hydrate fraction (<16%). Agglomerations of CO2 hydrates during injection, in particular in the
gas-liquid interface, were observed when no additive was employed. Systematic pressure and
temperature instabilities some hours after the end of the injection were observed too. The effect of
three additives on the kinetic of dissolution of CO2 in water was tested in a DTA device in order
to favor homogeneous formation of hydrate crystals within the liquid. Results showed after the
firsts ten seconds of injection that the average rate of dissolution of CO2 in water at 2 MPa and
293 K is increased by all the additives and can be multiplied by a factor 1.8 in the presence of one
of the tested surfactants. The anti-agglomeration capacity of the additives and their effect on the
CO2 injection process were also tested in the dynamic loop. Results in the dynamic loop showed
that anti-agglomeration capacity of additives is not appreciable, but they favor the CO2 injection
process and the production of a homogeneous slurry.