Fluidized bed drying of solids

Abstract

A kinetic model is d e v e l o p e d for t h e drying of solids in fluidized b e d s , assuming a falling rate period following a constant rate period. Experimental d a t a obtained using b a t c h a n d continuous single a n d spiral fluidized b e d s are satisfactorily m a t c h e d with t h e assumed drying kinetics a n d t h e r e s i d e n c e time distribution of solids appropriate for t h e t y p e of dryer.

A simplified approach to the drying of solids in a batch fluidised bed

“…Experimental data from Chandran et al (1990), McKenzie and Bahu (1991), Thomas (1993) and Srinivasakannan et al (1994) are compared with the model. Details of the experimental conditions used by these authors are reported in Table 1.…”

“…The models based on transfer coefficients are generally or related with the Reynolds number, while the empirical approach relates the drying rate with system variables such as solids hold-up, gas velocity, gas temperature, humidity, etc., using a wide range of experimental data (Kettenring et al, 1950;Syromyatnikov et al, 1967;Kunni and Levenspiel, 1969;Anantharaman and Ibrahim, 1982;Chandran et al, 1990;Srinivasakannan et al, 1995 and others). On the other hand, theoretical models involving heat and mass transfer between the bubble, cloud and dense phases are too complicated, which results in differential equations for prediction of the drying rate (Hoebink and Rietema, 1980a,b;Albregtse, 1986;Palancz, 1983;Srinivasakannan et al, 1994 and others).…”

Combined resistance bubbling bed model for drying of solids in fluidized beds

“…The amount of moisture evaporated from the solids (m * ) is estimated from experimental drying data [5].…”

“…The first approach relates transfer coefficients to the dimension less numbers such as Reynolds number, Prandtl number/Schmidt number [2,3], while the second approach relates the drying rate to the system variables such as solids hold-up, gas velocity, gas temperature, humidity, material characteristics using a wide range of experimental data [4,5]. Both the approaches do not pay attention to fluidization characteristics or hydrodynamics of the bed, such as bubble formation, bubble growth, rise velocity and heat and mass transfer inside the bed, limiting their application only to the specific range of experimental data.…”

Thermal analysis of a fluidized bed drying process for crops. Part I: Mathematical modeling

“…They, however, did not consider the presence of bubbles inside the bed and assumed thermal equilibrium. Chandran et al (1990) combined the drying kinetics and the residence time-density function appropriate for the mixing of solids in the bed to predict the average moisture content of the products for a continuous #uidized bed. Abid et al (1990) used the principle of irreversible thermodynamics, and accounted for the transfer of water by di!usion under the in#uence of a concentration gradient of the moisture, and by thermodi!usion under the in#uence of temperature gradient.…”