Ingeniería de procesos

 

Coffee grain rotary drying optimization

 

Optimización del secado de granos de café en un secador rotatorio

 

W.N. Hernández-Díaz¹*, F.J. Hernández-Campos¹, Z. Vargas-Galarza¹, G.C. Rodríguez-Jimenes² and M.A. García-Alvarado²

 

¹ Depto. Ingeniería Química y Bioquímica y Depto. De Posgrado e Investigación del Instituto Tecnológico de Zacatepec. Calzada Tecnológico 27, Col. Centro, Zacatepec, Morelos, 62780, México. *Corresponding author. E-mail: wendynetz@yahoo.com.mx

² Unidad de Investigación y Desarrollo en Alimentos del Instituto Tecnológico de Veracruz, M.A. de Quevedo.2779, Veracruz, Veracruz, 91987, México.

 

Received September 26, 2012
Accepted March 18, 2013

 

Abstract

The objective of the present work was to determine the coffee bean Guardiola dryer operating conditions that minimized the energy consumption (Q) and maximized the process thermal efficiency. A mechanistic coffee bean drying model was solved for a complete mixed assumption to simulate the drying. The simulated results reproduced the experimental results obtained with a 7.60 m³ Guardiola dryer loaded with 2675 kg of wet green coffee grains. The thermal second law efficiency of the drying was calculated with an expression that takes into account the exergy air carries before entering the dryer. For the same coffee load, and with restrictions on grain's temperature (T_β < 45°C), final water content (X_β < 11%) and water activity (a_w < 0.80), the drying was simulated for several air fluxes and temperatures to find the optimum drying conditions (T_γ = 80°C and G_γ =6560 kg air.h^-1). A 15.80% reduction in energy consumption was achieved when optimization results were compared with the normal operation conditions.

Keywords: optimization, thermal efficiency, drying, exergy, coffee.

 

Resumen

El objetivo del presente trabajo es determinar las condiciones de operación de un secador de café tipo Guardiola que minimicen el consumo de energía (Q) y maximicen la eficiencia térmica del proceso. Para simular el secado se utilizó un modelo mecanístico para secado de café, resolviéndolo de acuerdo a la suposición de mezclado completo. Los resultados de la simulación reprodujeron la conducta experimental obtenida de un secador tipo Guardiola de 7.60 m³ cargado con 2675 kg de granos de café verde húmedo. Se calculó la eficiencia térmica de segunda Ley del secado con una expresión que toma en cuenta la exergía que el aire posee antes de entrar al secador. Para encontrar las condiciones óptimas de secado, para la misma carga de café y con restricciones de temperatura (T_β < 45°C), humedad final (X_β< 11%) y actividad de agua del grano (a_w < 0.80), se simuló el secado para diferentes flujos y temperaturas de aire. Al comparar las condiciones óptimas encontradas (T_γ = 80°C and G_γ = 6560 kg aire.h^-1) con las normalmente utilizadas en el beneficio se logró una reducción del 15.80% en el consumo de energía.

Palabras clave: optimización, eficiencia térmica, secado, exergía, café.

 

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