Performance simulation of a heat pump drying system using r744 as refrigerant.

Drying is an energy intensive thermal process. The specific energy consumption in industrial systems is normally higher than 0.8 kWh/kg of evaporated water and the thermal energy demand in most drying systems is provided through burning of fossil fuels. The potential of using R744 (CO2) as working media in a heat pump drier was investigated for a drying process at 45°C, 60°C and 70°C. The trans-critical temperature glide of CO2 reduces the large temperature differences during re-heating of the drying air. The obtained Coefficients of Performance were between 3.4 and 4.3 resulting in specific energy consumption in the range of 0.24 to 0.27 kWh/kg of evaporated water for the different drying processes. The simulations confirm that heat pump assisted drying has the potential to reduce the energy demand by around 70% in general and shows the feasibility of applying heat pump drying also at drying conditions up to 70°C.