Modelling Tomato Dehydration in a Tunnel Dryer Using Geothermal Energy

Abstract

Low-temperature geothermal waters can be used efficiently in drying various vegetables and fruits, replacing sun-drying or drying using conventional fuels. A “geothermal” tomato dehydration plant has been operating since 2001 in Neo Erasmio, northern Greece, producing high-quality, “sun-dried” tomatoes. The unit uses low-cost geothermal water to heat atmospheric air to 56–58°C, which is introduced in a specially designed tunnel-type dryer. The scope of this work is to model the aforementioned tomato-drying process that uses low-enthalpy geothermal energy. The modelling procedure consists of two stages: the first stage focuses on the modelling of a single tomato piece, whereas the second stage is concerned with the modelling of air drying of tomatoes in a tunnel with trays moving in batches. The influence of air velocity, air temperature, and tomato tray loading on the drying process was investigated. The effect of flow configuration, i.e., co-current or counter-current operation, on the drying characteristics was also explored. The model can be used for the design and optimization of the continuous drying process existing in Neo Erasmio and can be easily extended and modified to deal with other agricultural products and tunnel designs.

Keywords:

• Air drying
• Drying kinetics
• Geothermal water
• Tunnel dryer
• Vegetable drying

ACKNOWLEDGMENTS

The authors would like to thank the managers of the N. Erasmio plant, Drs. N. Kolios and P. Dalampakis, for useful discussions and providing the data for the tomato-drying process.