Design of Experiment Analysis of the Spray Drying of Powders

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ACKNOWLEDGEMENT

I would take this opportunity to thank my research supervisor, family and friends for their support and guidance without which this research would not have been possible.

DECLARATION

I, [type your full first names and surname here], declare that the contents of this dissertation/thesis represent my own unaided work, and that the dissertation/thesis has not previously been submitted for academic examination towards any qualification. Furthermore, it represents my own opinions and not necessarily those of the University.

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ACKNOWLEDGEMENTII

DECLARATIONIII

CHAPTER 1: INTRODUCTION1

1.1 Introduction1

1.2 Significance of the study1

1.3 Theoretical framework2

1.4 Aim and objective of the study4

CHAPTER 2: LITERATURE REVIEW5

2.1 Introduction5

2.1.1 Historical development6

2.1.2 Structure and morphology9

2.2 Fundamental analysis of particle formation in spray drying10

2.2.1 Atomization process11

2.2.2 Droplet drying kinetics13

2.2.2.1 Spray Drying15

2.2.2.2 Preparation and characterization of solutions15

2.2.2.3 Particle characterization16

2.2.3 Modeling tools16

2.2.3.1 Droplet size estimation16

2.2.3.2 Droplet drying kinetics17

2.2.3.3Particle size analysis19

2.2.3.4 Particle morphology analysis20

2.2.3.5 Inflated and string-like particles23

2.4 Conclusion27

2.3 The basics of spray drying28

2.3.1 The spray drying process34

2.4 Drying chamber design tendencies35

2.4.1 Indirect heating36

2.4.2 Direct heating37

2.4.3 Air distribution37

2.4.4 Dry Blending38

2.4.5 Wet Blending - Spray Drying39

CHAPTER 3: METHODOLOGY42

3.1 Introduction42

3.2 Methods & experiment43

REFERENCES46

CHAPTER 1: INTRODUCTION

1.1 Introduction

Spray drying has become the most important method for the dehydration of fluid foods such as milk, coffee and egg powder, and is also used extensively in the pharmaceutical and chemical industries. It is a method whereby solutions or slurries are rapidly dried to particulate form by atomizing the liquid in a heated chamber [1]. Typically performed using aqueous systems, spray drying can also be undertaken with solvent-based systems under controlled conditions. Spray drying consists of the following unit operations:

Pre-concentration of liquid (for more economic operation, since evaporation is expensive)

Atomization (creation of droplets)

Drying in stream of hot, dry gas (usually air)

Separation of powder from moist gas

Cooling

Packaging of product

1.2 Significance of the study

Relatively high temperatures are needed for spray drying operations. Heat damage to products is generally only slight, however, because of an evaporative cooling effect during the critical drying period and because the subsequent time of exposure of the dry materials to high temperatures may be only very short. The typical surface temperature of a particle during the constant drying period is 45-50 °C. For this reason, it is possible to spray dry some bacterial suspensions without destroying the organisms. The physical properties of the products are intimately associated with the powder structure generated during spray drying. It is possible to control many of the factors that influence powder structure in order to obtain the desired properties [2].

Compaction of spray-dried ceramic powders by die-pressing currently is the predominant forming technique used in fabricating advanced ceramics for technical applications. Moreover, due to its ability to form complex shapes in high volume, die-pressing will continue to be used more than any other technique into the foreseeable future. However, one significant disadvantage of die-pressing is that it leads to variations in compact density throughout the component due to the influence of powder-die wall friction. These variations ultimately result in shrinkage variability later in the sintering process, often requiring costly ...