Modeling and Simulation of Crossflow Moving Bed Grain Dryers

Abstract

The drying of grain in dryers of a crossflow moving bed type was theoretically and excerimentally studied. Two different duer configurations were analyzed. a drver Gith centrdkr distribution and another wilh multl'ole air ducts. ~xoenmental in~ormallun was obtained in p~lot-size dryers A mathem;ticnl model lo rikulalc llx process was developed Hindered drylng u;l\ accounrerl lor by uslng the conccpl of relative drvine rate.-~n adiustable fact06 s~ecific to the drver8. wasised to account for the un~er(~>nt~es of the>ontacl area nnd'the umsfer c&ffic~ents mcountercd in the literature. Agreement between ex~rimental rcsulls and simul.!lions WL. farly eood. Simulatiins showed that distance between inlet air and outlet devices. air to -solid flow ratlo and dryer height to crurs seclion muo havc great ~nflucnce on the process The mathematicd model may be a uceful tool for process explor~tion and optimization of this type of dryers INTRODUCTION

Moisture, acidity and temperature evolution during cacao drying

“…Grain drying theory was reported since 40 years ago (Barre, Baughman, & Hamdy, 1971;Henderson & Pabis, 1961, 1962Spencer, 1969). The models proposed by these first authors have been used practically without changes by the modern researcher (Barrozo, Murata, & Costa, 1998;Bruce & Giner, 1993;Torrez, Gustafsson, Schreil, & Martinez, 1998). All of them are based in four differential equations (for product moisture, product temperature, air moisture and air temperature), in which the water mass transfer is represented by an empirical expression.…”

“…All of them are based in four differential equations (for product moisture, product temperature, air moisture and air temperature), in which the water mass transfer is represented by an empirical expression. Some authors presented a theoretical analysis over the relation of this empirical expression with respect to water diffusivity in the grain (Barre et al, 1971;Barrozo et al, 1998;Henderson & Pabis, 1961, 1962Spencer, 1969), while others reduce the analysis to the determination of an empirical parameter (Bruce & Giner, 1993;Torrez et al, 1998). A mechanistic approach of deep-bed drying (not specific for grains) has been suggested by Herman-Lara, SalgadoCervantes, and García-Alvarado (2005), in which each one of the differential equation is a function of specific heat or mass transfer coefficient, and each coefficient depends upon the transfer mechanism.…”

Modeling heat and mass transfer during drying of green coffee beans using prolate spheroidal geometry

“…(25) is a differential equation that represents the average moisture kinetic during drying of a half prolate spheroid. This procedure is common in beans drying design (Henderson & Pabis, 1961;Henderson & Pabis, 1962;Spencer, 1969;Barre et al, 1971;Bruce & Giner, 1993;Barrozo et al, 1998;Torrez et al, 1998;Pérez-Alegría & Ciro-Velásquez, 2001), but in the case of Eq. (26) the geometry is taking in account.…”

“…Pérez-Alegría and Ciro-Velásquez (2001) recognized this variation and modeled the coffee cherry drying with a set of four differential equations. Other models, similar to Pérez-Alegría and Ciro-Velásquez (2001), have been reported for bean dryers: Henderson and Pabis (1961); Henderson and Pabis (1962); Spencer (1969); Barre, Baughman, and Hamdy (1971); Bruce and Giner (1993); Barrozo, Murata, and Costa (1998) ;Torrez, Gustafsson, Schreil, and Martinez (1998); Herman-Lara, -Cervantes, and García-Alvarado (2005). This last mathematical representation (Herman-Lara et al, 2005) is particularly useful because it is built from heat and mass transfer properties of both phases involved, and the discontinuous phase (dried product) properties can be deduced from its water effective diffusivity and its thermal conductivity.…”

Formation of amorphous sugar in the syrup film – a key factor in modelling of industrial sugar drying

“…However, several mathematically similar models describing crossflow moving-bed dryers (e.g. conveyor belt dryers) have been used widely in the agriculture industry to simulate the process of grain drying ( Thomson, Peart, & Foster, 1968;Tórrez, Gustafsson, Schreil, & Martínez, 1998). Qi and Krishnan (1996) proposed a model suitable for continuous cross-flow dryers operating in a moisture diffusion-controlled regime in which the dryer is treated as a series of gas-solid contact stages, each purged by a stream of drying gas while wet solids are passing through.…”