Technical and economic performance of a tray dryer for medicinal and aromatic plants

This research considers engineering design, operation, functional performan ce and economic analysis of a heated-air tray dryer designed for medicinal and aromatic plants. In investigating the performance of the dryer, six dry ing tests with varying loading density were conducted with Mentha piperita and Hypericum perforatum. The drying process which reduced the product mois ture contents from 59 to 80% (w.b.) to moisture content below 15% (w.b.) to ok 6-9 h depending on the material being dried and loading density. To obta in the high-quality dried products in terms of flavour and colour, the temp erature of the drying air was controlled at 46 +/- 4 degreesC during drying experiments. This dryer can be successfully used to dry 145 kg of M. piper ita and 120 kg of H. perforatum in each drying batch. The specific heat ene rgy consumption of the dryer for M. piperita and H. perforatum were determi ned as 4840 and 7694 kJkg(-1) [water], respectively, when the dryer was ope rated at maximum capacity. The payback period of the dryer is estimated to be less than 2.0 months for M. piperita drying and less than 0.5 months for H. perforatum drying. (C) 2001 Silsoe Research Institute.