Drying of Solids in Fluidized Beds

Kannan, Chellapandian; Thomas, P.; Varma, Y. B. G.

doi:10.1021/ie00048a018

Cited by 38 publications

(15 citation statements)

References 6 publications

(11 reference statements)

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“…One of them is the constant rate period, and the second is the falling rate period followed by the first period when the moisture reaches the critical moisture content. Similar findings were obtained in both the drying of coal and of other solids (Diamond et al, 1990;Chandran et al, 1990;DiMattia et al, 1996;Kannan et al, 1995). In addition, a slightly visible period in which the initial adjustment occurs (Treybal, 1980) before the constant rate period is present.…”

Section: Resultssupporting

confidence: 79%

“…The effect of temperature on the rate is related to the increase of evaporation rate, while the lignite surface temperature increases at the constant rate period. At the falling rate period, this may be due to the increase of intraparticle moisture transport, as the particle temperature increases (Kannan et al, 1995). As shown in Figure 2, the effect of air temperature on the rate has more significance as the drying progresses, due to the increasing temperature difference between the lignite surface and the evaporation front as the drying air temperature increases.…”

Section: Resultsmentioning

confidence: 96%

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Drying of a Turkish Lignite in a Batch Fluidized Bed

Çalban

Erşahan

2003

Energy Sources

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Section: Resultssupporting

confidence: 79%

Section: Resultsmentioning

confidence: 96%

Drying of a Turkish Lignite in a Batch Fluidized Bed

Çalban

Erşahan

2003

Energy Sources

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“…The RTD of the solids particle is therefore quite broad, leading to non-uniform final solids moisture content. A very popular approach is to directly transform batch data for use in the continuous model by integrating the batch fluidized bed drying curve with the RTD of the solids to calculate the average solids moisture content at the outlet of the continuous dryer [10,[14][15][16][17][18][19][20][21]:…”

Section: Back-mixed Continuous Fluidized Bed Modelsmentioning

confidence: 99%

Fluidized Bed Dryers — Recent Advances

Daud¹

2008

adv powder technol

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Although industrial fluidized bed dryers have been used successfully for the drying of wet solid particles for many years, the development of industrial fluidized bed dryers for any particular application is fraught with difficulties such as scaling-up, poor fluidization and non-uniform product quality. Scaling-up is the major problem and there are very few good, reliable theoretical models that can replace the expensive laboratory work and pilot-plant trials. This problem is mainly due to the different behavior of bubbles and mixing regimes in fluidized bed dryers of different size. Simple transformation of laboratory batch drying data to continuous back-mixed dryers using the residence time distribution of the solids is insufficient to account for the complex flow and heat and mass transfer phenomena occurring in the bed. Although time scaling using temperature driving forces and solids mass flux for the same change in moisture content in the batch and continuous dryers has been successful in predicting moisture content profiles in the continuous dryer at the constant rate period, it does not take into account solid mixing. Two-phase Davidson-Harrison models have been used in modeling of the continuous back-mixed dryer with various degrees of success. On the other hand, the three-phase Kunii-Levenspiel model is seldom used in modeling fluidized bed dryers because it is too complex to handle. A combination of multi-phase models and residence time distribution could improve predicting power for back-mixed dryers because this combination takes into account both the bubbles and solid mixing phenomena. Incremental models were widely used to model continuous plug flow fluidized bed dryers, but the cross-flow of drying medium has not been sufficiently modeled except by the author. In some incremental models, axial dispersion is modeled using the Peclet number, Pe. A combination of an incremental model with an axial dispersion and cross-flow model of drying medium would improve predicting power. Poor fluidization of Geldart group C particles could be improved by the assistance of external means such as vibration, agitation, rotation and centrifugation. Both vibrated and agitated fluidized bed dryers have been successfully used in industry, but rotating or centrifugal fluidized bed dryers are still not available for industrial use. Nomenclature A bed area (m 2 ) E(t) RTD curve (-) ε bed porosity (-) F dry basis solid flow rate (kg/h) f falling rate drying factor ( • C) G dry basis gas flow rate (kg/h) h bed height (m) L total length of dryer (m) m B mass of bed (kg) N V local solids dying rate (kg/h/m 2 ) NTU number of transfer units (-) Nu nusselt number (-) Pe Peclet number (-)Pr Prandtl number (-) Re p particle Reynolds number (-) T G local gas temperature ( • C) T GI initial gas temperature ( • C) T i inlet gas tenmperature ( • C) T o exhaust gas temperature ( • C) T S local solids temperature ( • C) T wb wet bulb temperature ( • C) t time (s) τ residence time (s) X dry basis solids moisture content (kg/kg) X i inle...

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“…In evaporative drying of the coal, heat is provided to remove water from the coal particle. In references [5,11] and [12], it is stated that effective parameters on drying of lignite are temperature, drying media flow rate, sample thickness, and particle size. Many studies have been done about lignite drying.…”

Section: Introductionmentioning

confidence: 99%