NEW APPLICATIONS OF HEAT PUMPS IN DRYING PROCESSES

Abstract

ABSTRACT Heat pumps in combination with fluidized bed driers have been investigated extensively at The Norwegian Institute of Technology. A laboratory plant was constructed and a series of experiments on different types of temperature sensitive products were executed. By using heat pump, good temperature and humidity regulation is achieved. Drying temperatures can be regulated from −20°C to 50°C. This gives the possibility of freeze-drying at atmospheric pressure, and drying at temperatures above 0°C in the same plant. By using a temperature program, including an initial period of freeze drying, it is possible to regulate the products' physical properties. Examples are: the sinking velocity of fish fry feed, rehydration ability, colour and taste of dried fish, meat and vegetable products. Further, biotechnological products like bacterial cells and biomolecules/enzymes were dried with improved biological activity of the products compared to traditional drying methods like vacuum freeze drying or spray drying.