Drying of Suspensions in a Modified Spouted Bed Drier With an Inert Packing

Szentmarjay, T.; Pallai, E.

doi:10.1080/07373938908916607

Cited by 29 publications

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“…In addition to this, any means used to keep the fountain stable at higher bed wet fractions, would probably significantly enhance the performance and capacity of the dryer. This could be achieved by mechanical means (Szentmarjay and Pallai, 1989) or by the use of a draft tube.…”

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

Osorio-Revilla¹,

Elías-Serrano²,

Gallardo-Velázquez³

2004

Can J Chem Eng

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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-

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confidence: 99%

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

Osorio-Revilla¹,

Elías-Serrano²,

Gallardo-Velázquez³

2004

Can J Chem Eng

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“…In F i e 5 the temperature disbibudons of the air and the particles along the bed b e t are shown. It can be seen that the air temperature became constant above the bed level SZENTMARTAY, PALLAI, AND SZALAY Air -in FIGURE 4 Mechanically spouted bed dryer with inert particles I4yer. 2-inen paniclu.…”

Section: Drying Experlmentsmentioning

confidence: 96%

“…The heat transfer coefficient for the bottom part of the bed of intensive gassolid contan was calculated by Equation (4). The height of the w m g zone was determined by the temperature variation along the bed height.…”

Section: Calculation Of the Heat Transfer Coefficientmentioning

confidence: 99%

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Drying Process on Inert Particles in Mechanically Spouted Bed Dryer

1995

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Suspensio-M e s and paste-like materials can be dried in the Mechanically Spouted Bed (MSB) dryer wilh inert packing. The circulation of the men particles characteristic of classical spouted beds is provided with a houseless conveyor screw mounted in the vertical axis of the bed. Radioactive isotopic tracer technique was used for measurement of the cycle time distribution (CI1D) of the spherical inert particles as a function of the operational parametm of drymg. The variances (a2) of the C T D s and the particle velocity in the various zones of the MSB dryer were calculated. The circulation of the inert particles can be characterised by nearly plug flow. According to the physical model of drying on inert packing the heat and mass wansfer coefficients were calculated. Que to the relatively uniform film-like, w n coating formed on the surface of the spheical inen particles, the drying process may be characterised with the constant rate of drymg A method has been elaborated for calculation of drying time, hereby the partial processes of drymg on inert particles can be synchronised.

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“…Schneider and Bridgwater (1993) investigated the stability of a wet spouted bed, while Benali and Amazouz (2002) studied the effect of drying-aid agents on jet-spouted bed stability. Szentmarjay and Pallai (1989) and Kudra et al (1989) investigated the drying of different materials including paste-like materials in a screw-type spouted bed with inert particles.…”

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Drying of Suspensions in the Draft Tube Spouted Bed

2004

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Drying of suspensions is a very important process in the chemical, pharmaceutical and food processing industries. This unit operation is a most energy-consuming operation. Although there are hundreds of variants actually used in drying, the research efforts throughout the world are associated with the development of more sophisticated systems. In general, the trends in drying technology are associated with higher energy efficiency, enhanced drying rates and the development of more compact dryers, better control for enhanced quality and optimal capacity, developments of multi-processing units, etc. Mujumdar (1990Mujumdar ( , 1995 pointed out that numerous new or improved drying technologies are currently at various stages of development. Each type of dryer has specific characteristics, which make it suitable or unsuitable for specific applications.An efficient drying system should include good quality of the final product as well as meet several conditions: high values of heat and mass transfer coefficients, high contact area, high input of heat carrier gas, uniform temperature distribution over the drying chamber, the use of concentrated suspensions (as high as possible) in order to minimize the water amount to be evaporated and the use of a high inlet air temperature as much as possible. However, many of these conditions are in conflicts.Drying of suspensions of inert particles is a relatively novel technology to produce powdery materials. It was originally developed for drying pigments, chemicals and some biomaterials to eliminate the constrains of spray, drum and paddle dryers. Independent of the hydrodynamic configuration of the dryer, the principle behind this technology is based on the drying of a thin slurry layer that coats the surface of inert particles. Depending on the dryer type, these particles can be vibrated, fluidized or spouted either by hot air only, or in combination with a mechanical device installed within the dryer, such as an agitator or conveyor screw (Kudra and Mujumdar, 2002).In our prior investigations, a fluid bed dryer with inert particles was used for drying solutions, suspensions and pastes, as described in detail in Grbavcic et al. (1998). With respect to the main efficiency criteria, i.e. specific water evaporation rate, specific heat consumption and specific air consumption, a fluidized bed dryer with inert particles represents a very attractive alternative to other drying technologies. A high drying efficiency results from the large contact area and from the large temperature difference between the inlet and outlet air.The most important disadvantage of a fluid bed dryer with inert particles lies in the possibility of bed sintering in certain applications. For example, our experimental trials of drying several organic and biologi-*Author to whom correspondence may be addressed. E-mail address: grbavcic@elab.tmf.bg.ac.yu A draft tube spouted bed dryer with inert particles was used for drying suspensions. The effects of the operating conditions on dryer throughput and product ...

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Drying of Suspensions in a Modified Spouted Bed Drier With an Inert Packing

Cited by 29 publications

References 0 publications

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

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

Drying Process on Inert Particles in Mechanically Spouted Bed Dryer

Drying of Suspensions in the Draft Tube Spouted Bed

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