Small-scale litchi dryer performance at mountainous regions of Northern Thailand

Publication Type

Contribution to conference

Authors

Precoppe M F; Nagle M; Janjai S; Mahayothee B; Müller J

Year of publication

2010

Conference name

International Symposium ‘Sustainable Land Use and Rural Development in Mountainous Regions of Southeast Asia'

Conference location

Hanoi (Vietnam)

Conference date

21-23 July 2010

https://www.uni-hohenheim.de/sfb564/uplands2010/presentations/112.pdf

In Thailand litchi has significant economical importance. It is produced primarily by smallholders in the northern mountainous regions of the country. However, due to unstable farmgate prices and insufficient access to markets litchi orchards are being substituted by seasonal field crops, a process that increases erosion, pesticide use and water demand. Local production of dried litchis by farmer cooperatives allows to decouple producer from the unstable fresh market and to eliminate the middle man from the value chain. However, small-scale drying technology in northern Thailand is still in the early stages of development. Producers face difficulties in achieving uniform batches with the desired product properties. Aiming to improve a locally-available dryer for producing high-quality dried fruits at affordable cost, the performance of a batch dryer used for litchi on a farmers' cooperative at the mountainous region was studied. Performance indices were calculated and plotted against time. The analysis of those time-based indices were used to devise possible modifications to the dryer design and operation. Each batch yielded approximately 15 kg of dried litchi and required about 15 kg of liquefied petroleum gas. To evaporate 1 kg of water 10 MJ was required. To produce 1 kg of dried fruit 47 MJ were consumed. Main heat losses identified was through exhaust air. At the drying chamber non-uniform vertical and horizontal temperature distribution was observed. Batch color, moisture content and water activity were, consequently, heterogeneous. Energy performance of the dryer could be improved by adjusting the relative humidity of the exhaust air close to saturation. This could be done by reducing air flow rate or increasing the proportion of air recirculation. Quality performance could be improved by re-designing the chamber's air inlet to obtain a better air flow distribution. Overall, it is believed that those simple modifications can improve significantly dryer performance without impacting equipment price.