Drying of Liquid Feedstocks in a Spout‐Fluid‐Bed with Draft‐Tube Submerged in Inert Solids: Hydrodynamics and Drying Performance

Abstract

T he method for drying suspensions and solutions in a bed of inert particles of spoutable size, was first developed at the former Leningrad Institute of Technology for applications where the dried solids were ultimately required in the form of a fine powder (Reger et al., 1967;Romankov and Rashkovskaya, 1968;Minchev et al., 1969a, b). Since then, this technique has been used for drying chemicals (Mathur and Epstein, 1974;Ormos and Blickle, 1980) as well as biological products such as: animal blood, animal blood plasma, egg white, and protein-containing solutions, among others (Fane et al., 1980;Pham and Pooley, 1981;Pham, 1983;Rashkovskaya et al., 1979;Kutsakova and Utkin, 1983). More recently, reports by Markowski (1992), Reyes et al. (1998), Brereton and Lim (1993), Ochoa-Martínez et al. (1993), Szentmarjay et al. (1996) and Tia et al. (1995) who dried a variety of products, ranging from chemicals to liquid foods, have shown the feasibility of the process to obtain good quality dry powdered solids, which make the system, a low-cost, compact alternative to spray drying. Most of these authors have worked with conventional spouted beds, and practically none of them mention any limitations to the system employed.On this topic, Osorio (1990) and Ochoa-Martínez et al. (1993) reported that in spite of the great superficial area present in the bed of inert particles in a conventional spouted bed dryer, only a small fraction of this is really used during the drying process (2% to 10% of the total area, depending on the operating conditions). The effective area, increased slightly with the spouting velocity, but nevertheless this fraction remained small in contrast to the available area. These authors also reported that the maximum bed wet fraction that can be utilized in the drying process for a given inlet temperature, spouting velocity and feed conditions, is limited by the stability of the fountain. If the wet fraction of the bed exceeds a certain value, fixed by operations conditions, the spouting becomes unstable.On the other hand, the amount of heat that the annular region of the bed can provide for the evaporation of moisture, is practically unaffected by the spouting velocity. As the spouting velocity increases, a larger pro-

Analysis of pressure fluctuations during water evaporation in spouted bed

“…In some of our experimental conditions we could see evaporation rates up to 2.4 L/h. This result agrees with the observation of other authors (Barret et al, 1985;Osorio-Revilla et al, 2004) which showed higher volumetric evaporative capacities for SBs when compared to spray-dryers. However, many authors have reported that the maximum evaporation capacities drop dramatically when drying pastes, solutions, and suspensions in SBDIs (Berni and Freitas, 2007;Marreto et al, 2007;Tacon and Freitas, 2007).…”

Residence time distribution in spouted bed drying of maltodextrin solutions on a bed of inert particles

“…This equipment was described in detail elsewhere (Osorio-Revilla et al, 2004) but, in summary, the drying chamber was also made of Perspex with a 0.143 m internal diameter (D c ). The conical base, made of stainless steel, had an included angle of 60…”

Low temperature drying of pomace in spout and spout-fluid beds

“…This limitation is even more obvious when wet and sticky materials are treated in the fluidization units: in this situation, a separate control of gas flows to the spout (mainly acting as a mixing means, besides promoting effective mass transfer, though for a very short time) and to the annulus (where equilibrium between the moving phases can be easily reached, thus stopping the phenomenon) is desirable (Hattori et al, 2001). The addition of a draft tube (Arsenijevic et al, 2004;Hattori et al, 2001;Ijichi, Miyauchi, Uemura, & Hatate, 1998;Ishikura, Nagashima, & Ide, 2003;Ji, Tsutsumi, & Yoshida, 1997Khoe & Van Brakel, 1983;Muir, Berruti, & Behie, 1990;Osorio Revilla et al, 2004a;Osorio Revilla et al, 2004b;Stocker et al, 1989) has proven to act as a beneficial constraint and helps in terms of a better definition of both the gas distribution and the solids motion pattern during various processes such as drying (Khoe & Van Brakel, 1983;Tulasidas et al, 1993), coal gasification, combustion (Konduri et al, 1995, Konduri, Altwicker, & Morgan, 1999 pyrolysis of hydrocarbons (Stocker et al, 1989) and production of pharmaceuticals (Fukumori & Ichikawa, 1997;Littman, Morgan, & Morgan, 1997). A paste-like agglomerate surely benefits from such a geometrical configuration which assures the intermixing of the solids and close contact with the drying fluid medium.…”

“…Spouted beds are therefore suitable for different physical and chemical operations, ranging from coating, which has extensively been studied for nuclear and pharmaceutical applications (Bridgwater, 1985;De Oliveira, Freire, & Coury, 1997;Jono, Ichikawa, Miyamoto, & Fukumori, 2000;Mathur & Epstein, 1974;Olazar, Jose, & Bilbao, 1996;Pissinati & Pereira Oliveira, 2003), for catalyzed reactions, coal gasification and combustion (Konduri, Altwicker, & Morgan, 1995Lim et al, 1988;Olazar, Arandes, Zabala, Aguayo, & Bilbao, 1997;Piccinini, Grace, & Mathur, 1979;Rovero, Piccinini, Grace, Epstein, & Brereton, 1983;Stocker, Eng, Svrcek, & Behie, 1989) and for solids to fluid mass transfer operations, such as drying (Arsenijevic, Grbavcic, & Garic-Grulovic, 2004; Di Bartolo, Marmo, Rovero, & Mazzarino, 1996;Hattori, Morimoto, Yamaguchi, Onezawa, & Arai, 2001;Izadifar & Mowla, 2003;Khoe & Van Brakel, 1983;Nagaraju, Murthy, Ramalaksmi, & Srinivasa Rao, 1997;Olazar et al, 1996;Osorio Revilla, Lopez-Suarez, & Gallardo Velazquez, 2004a, Osorio Revilla, Elias-Serrano, & Gallardo Velazquez, 2004bShuhama, Aguiar, Oliveira, & Freitas, 2003;Tulasidas, Kudra, Raghavan, & Mujumdar, 1993;Viswanathan, Lyall, & Raychaudhuri, 1986). Some applications concerning desulfurization in combustion processes have also been presented (Xu, Guo, Kaneko, & Kato, 2000).…”