Inventory and comparative characteristics of dryers used in the sub-Saharan zone: Criteria influencing dryer choice

A survey was carried out in Togo, Benin and Burkina Faso involving 140 respondents and three climatic zones. Ten typical types of dryers with batch operating and natural convection were inventoried. Analysis of the results showed that: (1) Traditional sun dryers were widely used everywhere from 1 to 4000 kg per cycle, costing ?0 to ?7.63 per m2 drying area. (2) Low power solar dryers were mostly used in the Sahel and Sudan-Sahel tropical climate, from 5 to 1000 kg, costing from ?9.11 to ?238.55 per m2 of tray. (3) Gas dryers were used in all climatic zones at around 100 kg per cycle, with a high drying power, costing from ?107.52 to ?181.75 per m2 of tray. The acquisition of dryers depended mostly on the distance between provider and user and on the means of dissemination. A thermo-economic analysis was carried out to determine which dryers were most successfully adopted. These dryers will be re-employed by the users when the investment and maintenance costs enable profit to be made from the drying operation. Two types of dryers met those conditions: the traditional simple sun dryer used by families and groups: a study of an application on maize showed costs of ?0.01/kg of evaporated water equal to 7% of daily capital gain; the Atesta gas dryer used by small and medium-sized enterprises: applied to pineapple, cost ?0.07/kg of evaporated water equal to 9% of daily capital gain. New criteria had to be added to all those listed from the literature in order to choose a dryer properly: characteristics of the product to be dried, product added value, local energy availability and cost, labour skills and availability, local material availability and user investment capacity. (Resume d'auteur)