A one-dimensional plug-flow model of a counter-current spray drying tower

Ali, Muzammil; Mahmud, Tariq; Heggs, Peter J.; Ghadiri, Mojtaba; Djurdjevic, D; Ahmadian, Hossein; Juan, Luis Martín de; Amador, Carlos; Bayly, Andrew E.

doi:10.1016/j.cherd.2013.08.010

Cited by 50 publications

(46 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The median age t 50 and the mean t range between 310-510 s and 710-870 s, respectively. These values are, in average, from 10-100 times higher than the residence time expected from the trajectories of the air-borne particles in similar units, 22,28 <30 s or more recent numerical simulations in the same dryer 29,30 which report much lower values for the largest particles. The large time that the particles spend at the wall may explain why current models struggle to explain how drying occurs in such short air-borne residence times.…”

Section: Residence Time Of the Re-entrained Materialsmentioning

confidence: 82%

“…This is in agreement with the particle air-borne residence times <30-45 s reported for similar units 22,28 and more recently for the same spray dryer. 29,30 The initial size distribution is very narrow and contains primarily the size fractions that later become the mean product size between 300 and 600 mm. As time progresses, the distribution spans to contain a larger proportion of small and large sizes.…”

Section: Transient Productionmentioning

confidence: 99%

See 1 more Smart Citation

The role of wall deposition and re‐entrainment in swirl spray dryers

et al. 2015

View full text Add to dashboard Cite

A new experimental method is outlined to study fouling in spray dryers and similar devices. In essence, it makes the deposits traceable so that one can quantify the material that comes off the walls, how long it remains there and how the deposits agglomerate with particles in the air. This paper investigates a countercurrent swirl spray dryer of detergent and provides sound evidence that fouling is a dynamic process: clusters form and break at the walls renewing an active layer of deposits. Remarkably, the wall generates >20% of the product and most of the large granules, and increases drastically the residence time of the powder. The assumptions of current numerical models are clearly invalid (i.e. particles rebound at the wall or deposit indefinitely). Several re-entrainment mechanisms and their times scales are identified in this work, and accordingly, a new general framework to describe fouling in spray dryers is proposed.

show abstract

Section: Residence Time Of the Re-entrained Materialsmentioning

confidence: 82%

Section: Transient Productionmentioning

confidence: 99%

The role of wall deposition and re‐entrainment in swirl spray dryers

et al. 2015

View full text Add to dashboard Cite

show abstract

“…As the gas flow in the spray drying tower is turbulent and swirling, it is necessary to use a turbulence model that is capable of reproducing the correct flow profiles. In a supplementary study [37] , the predicted distributions of the mean velocity components and turbulence intensity in single phase, isothermal swirling flow in this tower obtained using the eddy-viscosity and RST models were compared with measurements. The latter model provided the best agreement with data and hence it was used in this study.…”

Section: Continuous Phase Equationsmentioning

confidence: 99%

“…The multiphase CFD model is based on the Eulerian-Lagrangian approach. The continuous phase turbulence is modelled using the RST model which was validated using measurements in strongly swirling flow in the same tower [37] . The roughness of the tower wall caused by the deposition of materials is taken into account through modifying the wall functions.…”

Section: Scope Of the Studymentioning

confidence: 99%

See 1 more Smart Citation

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

et al. 2016

Self Cite

View full text Add to dashboard Cite

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

show abstract

An effective rate approach to modeling single‐stage spray drying

et al. 2015

View full text Add to dashboard Cite

An effective rate approach (ERA) is proposed to achieve a fast and reliable prediction of dryer outlet conditions for a given single-stage spray drying system operated under a range of scenarios. This approach is improved from existing methods based on simple mass and energy balances due to the incorporation of a reliable drying rate model, which is the reaction engineering approach for the material of interest. It allows quick solution procedure without the need to solve the partial differential equations that govern the heat and mass transfer in the spray drying process. By following a generic procedure, this technique has been exercised on the experimental results from running a monodisperse droplet spray dryer, that is, a well-established experimental platform for model validation. The proposed ERA has been shown to be rather promising. It could become a powerful approach for proactive control and optimization for existing spray drying facilities. V C 2015 American Institute of Chemical Engineers AIChE J, 61: [4140][4141][4142][4143][4144][4145][4146][4147][4148][4149][4150][4151] 2015 Keywords: spray drying, predictive modeling, effective rate approach, reaction engineering approach, proactive quality control IntroductionSpray drying is an effective process for large-scale powder production. Although this technique has been widely used in a variety of industries for many years, proactive control of powder product formation remains a challenge. [1][2][3][4][5] It is well known that the dryer inlet conditions that include the feed solution composition and operational settings all have significant influences on droplet formation through atomization, the airdroplet flow pattern, the air-droplet mass, and heat exchange in the drying chamber, and hence the dryer outlet conditions (i.e., the size, shape, moisture content, and morphology of the particles). 6,7 The quantitative relationships between dryer inlet and outlet conditions, however, remain unclear.Over the past decades, new dryer designs and optimized operations have been pursued by many research groups to deepen our scientific understanding of the spray drying process and to improve our control over powder formation dynamics. Counter-current spray drying towers are suitable for thermally stable products such as detergents and ceramics as the hot gas comes in contact with dry particles just before the particles exit the tower. Cocurrent spray dryers are the best choice for heat sensitive products like milk powders, where thermal degradation and aroma retention are of concern. Hot gas comes in contact with the droplets at the top where the droplets have maximum moisture content and are at the wet bulb temperature. 8,9 With this configuration, the driest particles are eventually coupled with the lowest temperatures Correspondence concerning this article should be addressed to J. Xiao at jie. xiao@suda.edu.cn or X. D. Chen at xdc@xmu.edu.cn; xdchen@suda.edu.cn. 4140AIChE Journal December 2015 Vol. 61, No. 12 (i.e., the outlet temperatures). A single-stream ...

show abstract

A one-dimensional plug-flow model of a counter-current spray drying tower

Cited by 50 publications

References 24 publications

The role of wall deposition and re‐entrainment in swirl spray dryers

The role of wall deposition and re‐entrainment in swirl spray dryers

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

An effective rate approach to modeling single‐stage spray drying

Contact Info

Product

Resources

About