Drying of medicinal plants with a closed-circuit heat pump dryer

A closed circuit heat pump dryer system was tested to run drying cycles on six different species of medicianl plants (Melissa officinalis L., Achillea millefolium L., Alchemilla vulgaris L., Menta x piperita L., Urtica dioica L. and Lippia triphylla (Verbena Odorosa)). The purpose was to introduce this system into the supply chain traditionally applied in Valle Camonica (Lombardy region, Italy), evaluating, in particular, the energy consumption as a function of the dried species. During 2005, a total of 27 trials were carried out, measuring the initial green mass (kg) and corresponding moisture content (% wb), the average power absorbed by the system (kWel), the electrical energy consumption (kWhel), the final dried mass (kg) and corresponding moisture content (% wb), the specific energy consumption (kWhel/kgdried and kWhel/kgH2O), and the duration of the cycle (h). Three indexes were used to evaluate the mechanical loss (k1), production (k2) and energy consumption (k3) of each single species. The result showed that achillea millefolium L. (k1 = 1,06; k2 = 2,44 and k3 = 0,56) was the species that better responded to the method studied. Lippia triphylla (k1 = 2,76, k2 = 0,63 and k3 = 1,45) was the species that showed the worts results.