Modeling of Contact Dryers

Abstract

Contact drying of stagnant or agitated beds can be reliably described by the penetration model under vacuum or inert conditions. However, the penetration model has disadvantages in the consideration of granular mechanics and statistics due its continuous nature. The fact that such disadvantages can be avoided by discrete approaches is illustrated by application of the discrete element method to the problem of heating of particles in a rotary drum. Important limiting cases are treated, along with conditions for equivalence between continuous and discrete model. Time constants and scaling aspects are addressed and opportunities of combined product and process engineering are pointed out.

Drying of Solid Materials

“…In contrast, the mixing intensity has a stronger influence on the drying rate of fine-grained materials than on the drying rate of coarse-grained ones. The physical explanation for this behavior can be found in [14,15]. The maximum drying rate that can be expected is given by…”

“…The temperature that the solid reaches in the first drying period T I can be found by inserting Equation (15) for mass transfer and Equation (17) for heat transfer into the energy balance of Equation (13). The result is…”

“…If the temperature of the solid T I and either the heat-transfer coefficient a 0 or the mass-transfer coefficient b 0 g are known, then the drying rate can be determined numerically either with Equations (17) and (13) or with Equation (15).…”

A Review of Dehydration of Various Industrial Sludges

“…[59] Sludge type, conditioning of sludge, dewatering devices, and operating conditions are the main factors that have influence on sludge dewatering efficiency. [63][64][65][66] The cost of sludge dewatering ranges from about US $34 to 57 t À1 of dry solids, using a high throughput centrifuge capable of processing 60-150 t day À1 of sludge. In the case of belt filter presses, the cost would be US $40-64, respectively.…”

Modeling of a continuous sewage sludge paddle dryer by coupling Markov chains with penetration theory

“…As emphasized in [34], the correlation obtained by Mollekopf and presented in [33] may not be valid with any products or stirrer designs: the determination of an appropriate value for N mix is thus not straightforward. In the latter reference, the authors deduced a = 9 and b = 0.05 from experimental studies on two paddle dryers of different scales.…”