HEAT PUMP DRYING: SIMULATION AND EVALUATION OF A DRYING SYSTEM FOR CLIPFISH WITH MAIN AND STORAGE DRYING

A process simulation of industrial heat pump drying of clipfish is performed and the energy consumption for different systems is compared. The components of the heat pump (evaporator, compressor, 2 condensers, expansion valve and controller) were dimensioned for a 250 kW (thermal) system and a drying model based on the similarity between heat and mass transfer is used to develop a batch tunnel drying model. The investigation was performed with the natural refrigerant Ammonia (R717). The energy consumption for heat pump drying was simulated to be 222.6 kWh per ton of produced clipfish compared to 973.8 kWh per ton of clipfish for a drying system using heated ambient air. The moisture profile through the tunnel is significant and is a limitation for industrial batch tunnel driers. Measures to increase process efficiency are discussed by means of energy consumption, specific dehydration rate and heat flows. A new drying concept is proposed, using the excess energy of the secondary condenser for a final drying period in storage facilities. Using the same dimensions of the heat pump it was possible to increase the productivity of the heat pump drier by 40%, while at the same time the production costs were decreased to 133.6 kWh per ton of clipfish. Also the moisture profile through the batch tunnel drier is minimized by the proposed system.