Design and performance of a solar dryer for processing of coffee beans in Colombia

Ing. Eduardo Duque Dussan

Disertační práce

Abstract:

This research aimed to provide a comprehensive set of tools to understand, simulate, predict and control the coffee drying process in different scenarios: Natural convection, forced convection and mixed. In different coffee-producing countries, the drying process poses a challenge to the coffee growers due to the complex phenomenon, considering that large amounts of water should be removed from the grain to protect it from bacteria, fungi and mould development. However, the process must be thoroughly controlled to preserve the quality of the beans; this stands as an issue to the growers that are usually considered small because of their plot size and socio-economic conditions. In Colombia, around 96% of the 540000 coffee-growing families are considered small-scale farmers; this percentage relies mainly on sun-drying techniques to process their coffee. Nevertheless, the dependence of sun drying on the weather conditions is an issue since the harvesting times usually coincide with the rainy seasons, which are not the optimal conditions to dry coffee through natural convection due to the high ambient relative humidity and low temperatures. Therefore, mechanical dryers appeared as a solution seeing that the drying times are drastically reduced. Nonetheless, their elevated price and running costs prevent small-sized growers from acquiring these technologies. Therefore, wet coffee commercialization emerged as an answer, though the growers’ selling prices dropped drastically. Hence, a solution for the coffee growers seemed to be in place, integrating the product quality of sun-dried coffee and the technologies already existing in the farms (solar parabolic and tunnel dryers) with the rapid drying dynamics of mechanical dryers: a hybrid solar dryer. However, to achieve a proper design, independent studies were carried out on natural and forced convection drying of a coffee seed to provide predictive models to stochastic processes through Finite Element Methods (FEM) on mechanical drying to obtain mathematical models that simulate and characterize deep and thin bed drying of coffee and also, the thermal and physical properties of parchment coffee of new Colombian varieties were calculated not only to sharpen the mathematical and FEM and computational fluid dynamics models but also to update the literature. With this information, a hybrid solar drying unit was designed that provides a solution to coffee growers.

Keywords

Computational fluid dynamics, Hybrid solar dryer, Parchment coffee, Solar drying, Mathematical modelling, Mechanical Drying

Jazyk práce: angličtina

Datum vytvoření / odevzdání či podání práce: 6. 11. 2023

Obhajoba závěrečné práce

• Vedoucí: prof. Ing. Jan Banout, Ph.D.
• Oponent: František Kumhála, prof. Dr. Ing., Hector Andres Tinoco, externi, Aída Esther Peñuela Martínez, externi

Česká zemědělská univerzita v Praze

Fakulta tropického zemědělství

Doktorský studijní program:
Sustainable Rural Development