Spray dryer experiment

1.0

INTRODUCTION

1.1

Background of Experiment Spray drying is a very widely applied, technical method used to dry aqueous or organic

solutions, emulsion and others in industrial chemistry and food industry. Dry milk powder, detergents and dyes are just a few spray dried products currently available. Spray drying can be used to preserve food or simply as a quick drying method. It also provides the advantage of weight and volume reduction. It is the transformation of feed from a fluid state into a dried particulate form by spraying the feed into a hot drying medium. The spray drying is the most widely used in industrial process for particle formation and drying. It is well suited for continuous production of dry solids in powder, granulate or agglomerate form from a liquid feed. Basically, spray drying is accomplished by atomizing feed liquid into a drying chamber through a rotating wheel or nozzle, where the small droplets are subjected to a stream of hot air and converted to powder particles as a result of moisture evaporation. The resulting rapid evaporation maintains a low droplet temperature so that high drying air temperatures can be applied without affecting the product. As the powder is discharged from the drying chamber, it is passed through a powder/air separator and collected for packaging. Most spray dryers are equipped for primary powder collection at efficiency of about 99.5 % and most can be supplied with secondary collection equipment if necessary.

1.2

Objectives of Experiment To study the process of spray drying which is applied to dry aqueous organic solutions,

emulsion and others.

Experiment 5: Spray Dryer | 4SKKK SECTION 04

1

1.3

Scope of Experiment The experiment was conducted by a group of four people in Separation 2 Laboratory,

University Technology Malaysia. All the apparatus setup was provided in the laboratory and the experiment was carried out on the 21th September 2014. This experiment is only as a fundamental reference for further laboratory study.


2

2.0

Theory

2.1

Spray dryer

Spray drying is widely used in the industry for conversion of a suspension or solution into a dry products. In spray drying the suspension or solution feed is atomized and the droplet formed comes into contact with hot gas. When the droplets and the heated gas come into contact, the solvent in the droplets evaporate, leaving a dry powdered product. This method usually used in industrial technique used on large scale for drying and powdering very thermally sensitive materials such as foods and pharmaceuticals. A spray dryer is a device used in the spray drying method. The spray dryer used some type of atomizer or spray nozzle in order to disperse the liquid into a controlled drop size spray. It takes liquid stream and separates the solute as a solid and the solvent into a vapor. Usually the solid is collected in a drum or cyclone. The liquid input stream is sprayed through a nozzle into a hot vapor stream and then vaporized. The solids form moisture quickly leaves the droplets. The function of the nozzle is to make the droplets as small as possible, maximizing heat transfer and the rate of water vaporization. Generally, the range of droplets size is between 20 to 180µm depending on the nozzle. Furthermore, the spray dryer can dry the product very quickly compared with other methods of drying. The liquid state turn into dried powder in a single step, which can be advantageous for profit maximization and process simplification. In order to reduce the dusts and increase the flow ability of the powders, multiple of spray dryer effects are used to dry the liquid in one stage. There are two steps in drying process which are one at the top (as per single effect) and an integrated static bed at the bottom of the chamber. The bottom of the chamber allows the fluidizing powder inside a humid atmosphere to agglomerate to fine the particles with medium particle size. Then, the fines generated by the first stage drying can be recycled in continuous flow either at the top chamber or at the bottom of the chamber. The drying of the powder can be finalized on the external vibrating fluidized bed. The hot drying gas can be passed as a co- current or counter current flow to the atomizer direction. The co- current flow enables the particles to have a lower residence time within the system and Experiment 5: Spray Dryer | 4SKKK SECTION 04

3

the particle separator operates more efficiently. Usually, the counter- current flow method enables a greater residence time of the particles in the chamber and usually is paired of spray dryer in food and drug production.

Figure 2.1: The spray Dryer

2.2

I.

Application of spray dryer

Food industry: milk powder, coffee, tea, eggs, cereal, spices, flavorings, starch, and

II. III.

starch derivatives, vitamins, enzymes, stevia, and colorings. Pharmaceutical: antibiotics, medical ingredients, additives Industrial: paint pigments, ceramic materials, catalyst supports and microalgae.

2.3

Function of spray dryer


4

I. II.

A device used to produce dried foods Produce a good quality final product with low water activity and reduce the weight, resulting in easy storage and transportation.

2.4

I.

The parameters of spray dryer

Inlet temperature: The higher the temperature inlet, the faster is the moisture evaporation but the powder is subjected to higher temperatures, which may distort the

II.

chemical/ physical properties of heat- sensitive products. Outlet temperature: This governs the sizing of powder recovery equipment, and the higher the outlet temperature, the larger will be the size of powder recovery equipment and conveying ducts. The outlet temperature also controls the final moisture content of

III.

the powder. Volume of particulate powder obtained: V P =V

R

[ ( )]

P1 −1 P2

Where: Vp = Volume of particulate powder, cm3 VR = Standard volume, cm3 P1 = Pressure after applying pressure on the standard density P2 = Pressure after taking Vc into account

IV.

Overall thermal efficiency: ηoverall =

[

]

T Ai−T ×100 T Ai −T ∞ Ao


5

Where: TAi = The inlet air temperature TAo = The outlet air temperature T∞ = The ambient temperature 2.5 Principle of spray dryer

There are three fundamental steps involved in spray drying: i. Atomization of a liquid feed into fine droplets. ii. Mixing of these spray droplets with a heated gas stream, allowing the iii.

liquid to evaporate and leave dried solids. Dried powder is separate from gas steam and collected.

2.6 Benefits of spray dryer

i. ii. iii. iv. v. vi. vii.

Typical application in pre- formulated products Microencapsulation, solid solutions Improved bioavailability, improved product stability Products with unusual or difficult characteristics Sticky or hygroscopic products Difficult to isolate products Rapid drying for temperature sensitive materials.

2.7 Advantages of spray drying technology i.

Pharmaceuticals: Some pharmaceuticals occur in crystal form, making them difficult to use. It do not easily dissolve in water and are absorbed slowly, so they are currently unused because of bioavailability. So, the spray dryer dry

ii.

the compound once it has been dissolved in water for easier absorption. Food products: The quick process of spray drying keeps flavor loss to a minimum. Dairy products, such as milk, cheese, butter and dry creamer are common items made using the spray drying technique. Other than that, instant coffee, dry creamer and instant soups also can be spraydried and previously Experiment 5: Spray Dryer | 4SKKK SECTION 04

6

spraydried foods often serve as baby foods. Spray drying keeps the retail price of such foods low, because of the process extends the product’s shelf iii.

life. Industrial products: Spray dryers give an advantage in many commercial and industrial industries. For example, in fabrics and clothing, and spraydried pigments appear in many wall paints. Spray dryers reduce the size of particles found in dyes to allow more consistent and convenient dispersion into paints. The dyes are allowed to dissolve in liquids that can then dye

iv.

clothes and fabrics. The production of milk powder using spray drying technique: Milk powder production is an example of spray drying. During the process of milk powder production, after cooling stages, the milk emulsion is concentrated and after that the concentrated emulsion becomes ready for spray drying. The concentrated emulsion is atomized into droplets by a centrifuged atomizer or high pressure spray nozzle, which located at the top of the spray chamber. The droplets fall into the spray chamber in a concurrent flow with a hot air, the moisture in the emulsion droplets is removed by hot air. Milk droplets shrink in size as water is evaporated from its surface. Finally, the droplets lost most of their moisture and become particles with a solid crust formed at their surfaces

3.0

Methodology

3.1

General Set-up Procedures 1. 2. 3. 4. 5. 6. 7. 8.

The cyclone chamber on the holder is installed The nozzle housing is installed The sample (liquid) is prepared the power supply and the main switch in a panel spray drier is switched on Set the temperature (inlet) The blower and the heater is switched on Outlet temperature increased until 100°C The feed pump is switched on


7

3.2

General Shut-down Procedures 1. 2. 3. 4.

The feed pump and the blower The heater is switched off and temperature outlet is decreased in range 35-40°C The main switch in a panel spray drier and the power supply The sample is taken out while the cyclone chamber and housing nozzle is removed

4.0

RESULT Table 4.1: Experiment result of particulate powder’s density

Data Test 1 Volume of particles 12.426 powder, Vp (cm3) Density of 54.321

Test 2

Test 3

Average

6.754

6.754

8.645

99.941

99.941

84.734

particulate powder,⍴ (kg/m3)

Table 4.2: Experiment result of inlet and outlet temperature Operation state Before experiment During experiment After experiment

Inlet temperature (⁰C) 199 200 199

Outlet Temperature (⁰C) 100 93 89


8

Thermal efficiency (ŋoverall) = 61.14%

5.0

DISCUSSION

Figure 5.1

Process Flow Diagram for Entire Spray Drying System Experiment 5: Spray Dryer | 4SKKK SECTION 04

9

Figure 5.2

Process Block Diagram for Entire Spray Drying System

Spray drying process is one of the drying techniques used for production of food powders. It is the simplest technique used by commercial industry to convert the fluid material into solid or semi-solid particles where the product is heat sensitive or heat resistant. In spray drying process, the spray dryer uses hot air to evaporate water from the product. The hot air used is air or inert gas (nitrogen gas). The main driving force is the temperature difference between the surrounding air and the temperature of particle or known as the wet bulb temperature of the inlet air.

From the figure above, the spray dryer pump a liquid stream into drying chamber and separate the solute as solid and the solvent into a vapour. Then, the liquid input stream is sprayed through a nozzle or atomizer by a hot vapour stream and vaporized. The hot air used is air or inert gas (nitrogen gas). Air is heated by heating element before it enters the chamber. After that, the bulk liquid will be converted into droplets or mist though a nozzle. The function of nozzle is to make droplets as small as possible to maximize heat and mass transfer and rate of Experiment 5: Spray Dryer | 4SKKK SECTION 04

10

water vaporization. In common, nozzle size varies from ranges of 20µm to 180µm. According to Singh and Dixit (2014), the choice of atomizer depends on the nature and the configuration of feed a well as desired product characteristic. When the hot air and the droplet contact with each other, it will evaporate the moisture content of droplet and changes it into powder form. The dried powder product will be separated by using a cyclone where dense particles are recovered at the drying chamber base. Drying is finished when the particle temperature is equal to the air temperature. For industrial based drying process, the spray dryers are equipped with the filters (bag filters) in order to remove the finest powder. Chemical scrubber is used to remove the remaining powder or volatile pollutants. From the result obtained, the average density of the milk particulate powder is 84.734kg/m3. However, it is different with the standard density value of milk which is 1035 kg/m3. The large difference is mainly due to the errors occurring during the experiment. The solid particles are precipitated at the bottom part of the bottle, and this causes the water cannot evaporate from the solution effectively. However, the product collected into the small sample cell for measuring density is not including the wet product, while only dried particulate is taken into account. Therefore the mass of the particulate is affected. On the other hand, the input temperature set may not the most suitable for the separation process to happen. Research need to be done in order to find a more suitable temperature for this experiment. Meanwhile, micropycnometry is not exactly calibrated at zero, due to the fluctuate of the value given by the meter. Other than that, the major difficulty in spray drying milk solutions is encountered in attempting the formation of droplets during the spray drying operation. Instead, filaments are usually formed. These are caused by premature drying of liquid filaments formed near the spray nozzle before they can be broken up into droplets. Formation of these filaments also results in a considerable loss of milk during drying because of plastering of the walls of the spray dryer and incomplete drying of the product. Using the, the performance of spray drying is calculated which is measured in terms of thermal efficiency by using temperature measured during the experiment. If the drying process is assumed to be adiabatic, that is, the heat loss is negligible, the overall thermal efficiency (ηoverall) can be approximated to the relation: Experiment 5: Spray Dryer | 4SKKK SECTION 04

11

 T  T Ao    100%  overall   Ai  T Ai  T 

where TAi and TAo are the inlet and outlet air temperatures, respectively and

T

is the ambient

air temperature. The thermal efficiency found in the experiment is 61.14%.

There are some modifications that can be made on the existing system to increase the recovery percentage of product. By increasing the inlet temperature, the recovery percentage can be increased. At higher inlet air temperatures, there is a greater temperature gradient between the atomized feed and drying air and it results the greatest driving force for water evaporation. The use of higher inlet air temperature leads to the production of larger particles and causes the higher swelling. If temperature is low, the particle remains more shrunk and smaller. Nijdam (2006) were obtained the similar results in the production of milk powder at 120°C and 200°C. The higher drying temperature is lower the moisture content and increase its hygroscopicity. This is related to the water concentration gradient between the product and the surrounding air, which is great for the less moist powder. The increase of inlet temperatures has given the higher process yield and it was due to the greater efficiency of heat and mass transfer processes occurring when higher inlet air temperatures were used. When the drying temperature is sufficiently high and the moisture is evaporated very quickly and the skin becomes dry and hard. As a result, the hollow particle cannot deflate when vapor condenses within the vacuole as the particle moves into cooler regions of the dryer. However, when the drying temperature is lower, the skin remains moist and supple for longer, so that the hollow particle can deflate and shrivel as it cools. Secondly, the rate of air flow must be at a maximum in all cases. The movement of air is decided the rate and degree of droplet evaporation by inducing, the passage of spray through the drying zone and the concentration of product in the region of the dryer walls and finally extent the semi-dried droplets and thus re-enter the hot areas around the air disperser. A lower drying air flow rate causes an increase in the product halting time in drying chamber and enforces the circulatory effects. The effect of drying air flow rate on powder solubility depends on its effect Experiment 5: Spray Dryer | 4SKKK SECTION 04

12

on powder moisture content and density of powder. Density variation can arise from temperature changes and migrating pollution. By using COMSOL multi physics we can able to get the exact solution which is used for both temperature and concentration changes. The rising of air flow rate was led to the increased of powder moisture content and decrease in powder solubility (Papadakis, 1998). Lastly, at higher atomizer speed, the smaller droplets were produced and more moisture was evaporated resulting from an increased contact surface.

6.0

CONCLUSION

The objective of this experiment had been achieved as the milk which was fed in liquid had been evaporated into dry particulates through the spray dryer. The density measured was 84.734 kg/m3 and overall thermal efficiency for the spray dryer was 61.14%. The measured density of milk is different with the standard value which is 1035 kg/m 3. This may due to some errors occurred during the experiment. The spray drying system needs to be modified in order to have better efficiency in recovering products.


13

REFERENCES 1. Felix Engman, Spray Drying as an Appropriate Technology for the Food and Pharmaceutical Industries, Journal of Environment Science, Computer Science and Engineering & Technology,September- November 2012, Vol. 1, No. 3, 467- 476. 2. Dr. Mukesh Gohel, 2009, Spray Dryer:A Review, http://www.pharmainfo.net/reviews/spray-drying-review, retrieved on 27 September 2014. 3. V.S Birchal, M.L. Passos, Modeling and simulation of milk emulsion drying in spray dryers, Brazilian Journal of Chemical Engineering, June 2005, Vol. 22, No. 2, 272284. 4. Phisut. N, Spray drying technique of fruit juice powder: some factors influencing the properties of products, International Food Research Journal, 2012, 19(4), 1297- 1306. 5. Viviane S. Birchall, M. Laura Passos, Cloria R.S. Wildhagen and Arun. S. Mujumdar, The Influence of Spray Dryer operation variables on Milk Powder Quality, Drying 2004- Proceedings of the 14th International Symposium (IDS 2004), 22-25 August 2004, vol. A, 389-396.


14

6. E.Donz, P. Boiron, J.L Courthaudon, Characterization of industrial dried whey emulsion at different stages of spray drying, Journal of Food Engineering, 2014, 126, 190-197. 7. Charles Onwulata, 2005, Spray Drying, https://www.princeton.edu/~achaney/tmve/wiki100k/docs/Spray_drying.html, retrieved on 27 September 2014. 8. Samatha Singh, Deepa Dixit, A review on spray drying: Emerging technology in Food Industry, International Journal of Applied Engineering and Technology, 2014, Vol. 4(1), 1-8.

APPENDIX Table Appendix 1: Experimental result of calculation of particulate density Data for calculation of particulate powder’s density Total weight (g) 5.105 Weight of beaker (g) 4.430 Weight of sample (g) 0.675 Standard volume, VR (cm3) 6.28 3 Volume of sample cell, Vc (cm ) 11.67 Total drying time (min) 24 min 40 s

Table Appendix 2: Experimental result of pressure Data P1 P2 Where:

Test 1 Test 2 Test 3 16.493 16.732 16.402 5.537 8.062 7.903 P1 = Pressure; after applying pressure on the standard density P2 = Pressure; after taking Vc into account


15

Sample calculation (A) Calculation of volume of particulate powder, Vp (cm3) V p=V R

[( ) ] P1 −1 P2

for test 1, V p=6.28

[(

16.493 −1 5.537

)

]

V p=12.426 (B) Calculation of particulate powder’s density (kg/m 3)

density , ρ=

mass of particulate powder ( g) 1000 kg 3 3 volume of particulate powder (cm ) m

for test 1, ρ=

0.675 ( g ) 1000 kg 12.426( cm3 ) m3 3

ρ=54.321 kg /m

(C) Calculation of thermal efficiency (ŋoverall)

(

ŋoverall =

T Ai−T Ao ×100 T Ai−T ∞

)

×100 ( 200−93 200−25 )

ŋoverall =

ŋoverall =61.14 Experiment 5: Spray Dryer | 4SKKK SECTION 04

16


17

Spray dryer experiment

Recommend Documents