Continuous and Discrete Phase Behavior in Countercurrent Spray Drying Process

Zbiciński, Ireneusz; Piątkowski, Marcin

doi:10.1080/07373930903383661

Cited by 22 publications

(13 citation statements)

References 6 publications

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“…4 shows that in this case, the contraction is sufficient to develop a jet across the entire cylinder, which confirms the reports of Sharma [22] or Bayly et al [28] in tall-form dryers at isothermal conditions and associated simulations (e.g. [23,24]), but in turn contrasts experimental data [29] under actual operation conditions, where the sprays seem to hinder the formation of the jet.…”

Section: Resultssupporting

confidence: 90%

“…The studies in pilot scale facilities included flow visualization and RTD analysis reported by Place et al [25], Paris et al [26] and Sharma [22] or Keey and Pham [27] in co-current units. Only in the last decade a higher level of detail has been obtained by taking advantage of laser-based flow diagnostic techniques in laboratory [28] or pilot plant units [29]. Data at production scales is much more restricted, from vane [30] to thermal anemometers [31], and a similar level of detail is not yet available.…”

Section: Introductionmentioning

confidence: 99%

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An experimental investigation of the swirling flow in a tall-form counter current spray dryer

Francia

Martín

Bayly

et al. 2015

Experimental Thermal and Fluid Science

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a b s t r a c tThis work studies the air flow in a large swirl counter-current dryer using sonic anemometry. Air velocity and turbulence fields are reported at isothermal conditions and in the absence of particles. In a tall-form unit the structure of the flow is largely influenced by the design of the exit. A contraction originates a central jet and suppresses the formation of recirculation zones despite the vortex acquires a high swirl intensity X (i.e. 1 < X < 2). Access to a full scale tower has permitted to: (a) identify asymmetries owed to the design of inlet and exhaust ducts, (b) present the first detailed turbulence data in production units, characterized by a highly anisotropic field and the axial decay of the turbulence kinetic energy, (c) study the flow stability, identifying the precession of the vortex core and oscillations at a constant Strouhal number and (d) study the impact that a rough wall has in the strength of the swirl. This work presents the first clear evidence of significant friction in spray dryers. The swirl intensity X decays exponentially in the dryer at a rate between 0.08 and 0.09, much higher than expected in pipe flow and independent of Re in the range 10 5 -2.2 Á 10 5 . Production dryers have a large characteristic wall roughness due the presence of deposits, which explains the stronger friction and the discrepancies found in the past between data at full scale or clean laboratory or pilot scale units. It is essential to address this phenomenon in current numerical models, which are validated on laboratory or pilot scale facilities and ignore the role of deposits, thus causing an overprediction of the tangential velocity above 30-40%.

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Section: Resultssupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

An experimental investigation of the swirling flow in a tall-form counter current spray dryer

Francia

Martín

Bayly

et al. 2015

Experimental Thermal and Fluid Science

View full text Add to dashboard Cite

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“…Visualisation studies were common to describe counter-current units (e.g. Paris et al, 1971;Sharma, 1990) but detailed air velocity data have only been obtained in laboratory (Bayly et al, 2004) or pilot scale facilities where laser based methods are more easily applied (Zbicinski and Piatkowski, 2009). The quantity and level of detail is much more restricted in full scale, and limited to small sections (Hassall, 2011;Wawrzyniak et al, 2012).…”

Section: Introductionmentioning

confidence: 98%

Influence of wall friction on flow regimes and scale-up of counter-current swirl spray dryers

Francia

Martín

Bayly

et al. 2015

Chemical Engineering Science

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We study the vortex flow in swirl dryers across full scale designs and conditions. Three air flow regimes are related to the effects of friction and design features. The characteristics of deposits are vital to explain the evolution of the vortex. Friction reduces the swirl drastically and it has a major impact on the turbulence. Flow regime prediction facilitates the use of new control and scale-up criteria. a b s t r a c tThe structure of the vortex flow in swirl spray dryers is investigated after having fouled the walls with deposits typical of detergent manufacture. The range of Re and swirl intensity Ω characteristic of industry are studied using three counter-current units of varying scale and design. The friction with the deposits increases the flow turbulence kinetic energy and causes a drastic attenuation of the swirl and as a result, the vortex breaks down in the chamber forming recirculation regions (i.e. areas of reverse flow). Three flow regimes (1) no recirculation, (2) central and (3) annular recirculation have been identified depending on the swirl intensity. New control and scale up strategies are proposed for swirl dryers based in predicting the decay and the flow regime using the unit geometry (i.e. initial swirl intensity Ω i ) and experimental decay rates function of the coverage and thickness of deposits. The impact in design and numerical modelling must be stressed. Adequate prediction of the swirl is vital to study fouling and recirculation, which surely play an important part in the dispersion and aggregation of the solid phase. Current models have no means to replicate these phenomena, and yet, in this case neglecting the deposits and assuming smooth walls would result in (a) over-prediction of swirl velocity up to 40 À 186% (b) under-prediction of turbulent kinetic energy up to 67 À85% and (c) failure to recognise recirculation areas.

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“…In contrast, comprehensive CFD modeling studies of spray drying in counter-current towers, which is the subject of this paper, are scarce despite many industrial applications [8,[30][31][32][33][34] . It is a poorly understood process compared with that in co-current towers [35] .…”

Section: Introductionmentioning

confidence: 99%

“…According to Zbicinski and Piatkowski [35] , complex aerodynamics resulting from a strongly swirling turbulent gas flow and associated droplet/particle trajectories, intensive coalescence/agglomeration, scarcity of experimental spray towers and difficulty in gathering reliable data for model validation are the major factors responsible for lesser modelling as well as experimental research work on counter-current spray drying towers.…”

Section: Introductionmentioning

confidence: 99%

CFD modeling of a pilot-scale countercurrent spray drying tower for the manufacture of detergent powder

et al. 2016

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A steady-state, three-dimensional, multiphase CFD modelling of a pilot-plant counter-current spray drying tower is carried out to study the drying behavior of detergent slurry droplets. The software package ANSYS Fluent is employed to solve the heat, mass and momentum transfer between the hot gas and the polydispersed droplets/particles using the Eulerian-Lagrangian approach. The continuous phase turbulence is modelled using the differential Reynolds stress model. The drying kinetics is modelled using a single droplet drying model [1] which is incorporated into the CFD code using user-defined functions. Heat loss from the insulated tower wall to the surrounding is modelled by considering thermal resistances due to deposits on the inside surface, wall, insulation and outside convective film. For the particle-wall interaction, the restitution coefficient is specified as a constant value as well as a function of particle moisture content. It is found that the variation in the value of restitution coefficient with moisture causes significant changes in the velocity, temperature and moisture profiles of the gas as well as the particles. Overall, a reasonably good agreement is obtained between the measured and predicted powder temperature, moisture content and gas temperature at the bottom and top outlets of the tower; considering the complexity of the spray drying process, simplifying assumptions made in both the CFD and droplet drying models and the errors associated with the measurements.2

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Continuous and Discrete Phase Behavior in Countercurrent Spray Drying Process

Cited by 22 publications

References 6 publications

An experimental investigation of the swirling flow in a tall-form counter current spray dryer

An experimental investigation of the swirling flow in a tall-form counter current spray dryer

Influence of wall friction on flow regimes and scale-up of counter-current swirl spray dryers

CFD modeling of a pilot-scale countercurrent spray drying tower for the manufacture of detergent powder

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