Design of a fluidized bed heat exchanger for CO₂ hydrate slurry production

Abstract

CO2 hydrate slurry is a newly developed secondary cooling fluid. In order to use CO2 hydrate as a direct coolant of fresh products, a new CO2 hydrate slurry production system (a fluidized bed heat exchanger, FBHE) is under construction and it has been optimized for the expected operating conditions. A sensitivity analysis has been used to identify the optimum design for the specific operating conditions. The model includes the growth of CO2 hydrate on the fluidized bed wall as a function of the operating conditions. The heat of formation is removed by a falling film of evaporating R134a outside the fluidized bed. The maximum capacity of the set-up is 5 kW. The parameters optimized include the internal diameter of the fluidized bed heat exchanger, bed porosity, inert particles inside the FBHE, as well as the refrigerant temperature. Under specific operating conditions: pressure inside the FBHE is 35 bars and solution initial temperature is 6°C, the optimized parameters according to simulation are: internal diameter is 85 mm, bed porosity is 0.7, particle diameter is 5 mm, and refrigerant temperature is 0°C. Under these conditions the apparatus produces 13.2 kg hydrate in one hour.