CO2 hydrate, Type-III Antifreeze Proteins, thermodynamic model
CO2 hydrate slurry is a favourable direct coolant of fresh products due to its large latent heat and phase change temperature around 5°C. Continuous production of this slurry is, however, difficult to realise due to the high rate of hydrate formation. The use of additives is proposed with the purpose of decreasing the formation rate so that the controllability of the process is improved. Type-III Antifreeze Proteins (AFPs) are non-poisonous additives which have proven to be inhibitors of hydrate formation. These additives have also shown to protect the bio-cells of fresh products from damaging by freezing. The effect of these additives on the CO2 hydrate formation rate is experimentally investigated. The experiments have been performed in a coil heat exchanger with 6 mm internal diameter under operating conditions corresponding to hydrate formation conditions. The concentration of Type-III AFPs has been varied: no additives, 5 ppm and 10 ppm. The mixture of additives and CO2-water solution is cooled down until the hydrate formation conditions are attained. The growth rate of hydrates on the wall of the heat exchanger has been derived from the variation of the overall heat transfer coefficient with time. Results show that the addition of AFPs changes the supersaturation degree of CO2 water solution needed to initiate the hydrate formation process. A low concentration of the proposed additives is sufficient to slow down the formation rate of CO2 hydrate improving significantly the controllability of the hydrate production process.