study of spray dryer

7/30/2019 Study of Spray Dryer

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Summary

The main objective of this experiment was to study about the spray dryers and the mechanism

of the spray drying process. The experiment was carried with mixed flow spray dryer which

contains a two-flow atomizer. A cyclone separator was used for the separation of solid. In our

experiment, a solution of known amount of powder milk was spray dried to observe the

performance of the spray dryer. In this experiment, 1000.1 gm liquor milk was taken which

contains 50 gm milk powder. And after the drying process 12.4 gm milk powder was

recovered from the solution. Hence, 24.8% milk powder was recovered. The probable reasons

for the poor recovery are highlighted in the discussion.


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Experimental Setup

Figure 2: Schematic diagram of experimental setup of a spray drying system

Air blower

Chamber Tem .

Heater

Drying chamber

Air

Compressor

Powder milk

container

Cyclone separatorHot air

Thermometer

Exhaust pipe

Air water vapor

Feed milk container


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Observed data

Working pressure, P = 20 psig

Inlet temperature, Ti = 150 C

Initial outlet temperature of air, To = 78.5 C

Final outlet temperature of air, To = 64 C

Total time required for drying, t = 38 min

= 2280 sec

Weight of milk powder, m = 50 gm

Weight of water, mw = 950.1 gm

Weight of liquid milk, Mt = (mw + ms) = (950.1+50) gm

= 1000.1 gm

Weight of empty beaker, m1 = 554.1 gm

Weight of beaker with recovered milk powder, m2 = 566.5 mg


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Calculated data

Weight of solid recovered, MR = (Weight of beaker + recovered milk powder) Weight of

empty beaker

= m2m1

= (566.5554.1) gm

= 12.4 gm

%100akenintially tsolidtheofweight

recoveredsolidtheofweight

recoveryPercentage

%100m

M

R

%24.8

%10050

12.4

dryingoftimeTotal

waterofweightrateDrying

t

m

W

gm/sec0.42

gm/sec0.41671

gm/sec2280

950.1


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Result

Weight of solid recovered, MR= 12.4 gm

Percentage recovery of milk powder = 24.8%

Drying rate = 0.42 gm/sec


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Discussion

From the experiment result the percentages recovery of milk indicates some losses in the

system. Probable reason behind such low recovery are stated below

1. Some milk powder may accumulate in the apparatus.2. Air is exhausted from the cyclone separator which may contain milk powder.3. A considerable portion of milk was stuck on the separator wall, which also reduced

the milk powder recovery.

4. The experiment was done in a very small scale and the dryer had been used forseveral years. So, the depreciation factor of the pilot plant has caused lower recovery

of milk powder.

5. The milk that is supplied has some moisture content but after drying only dry milkpowder was obtained. So loss in the weight of milk powder was found.

6. If the paste was not prepared perfectly, then some powder might clot. Clotted powdermight create problem while flowing throw pipe and spraying.

7. The feed had been entered the dryer at a quite high flow rate to conduct the dryingprocess quickly, if the rate was lower the drying process would be more efficient

8. Before the experiment there were some water in the nozzle for some operatingproblem. That is why dried powder may again dissolved in the water. It may be a

reason for low percentage recovery.


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Process Block Diagram (PBD)

Figure 2: Process block diagram of a spray drying system

Compressed air

P= 20 psig

Milk powder solution

Milk powder=4.9995%

Water=95.0005%

Air

Blower

Heater

Hot air, T=150

Spray

Dryer

Cyclone

Separator

Recovered milk

powder

Air

Milk powder

Water vapor

Air and Water

vapor


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Process Flow Diagram

Figure 3: Process flow diagram of a spray drying system

Air

Air

Hot air, T=150

Air

Compressed air

P= 20 psig

Feed

Milk powder=4.9995%

Water=95.0005%

Air and Water

vapor

Recovered milk

powder


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Modification

It is essential for both economic and environmental reasons to recover as much powder as

possible from the system. Three modifications are available-

1. Bag filters2. Wet scrubber3. Electrostatic precipitator (ESP)

Bag filters

Bag filters are in general frequently used for dust removal in industrial applications. So as it

is used for recovery of particle in spray drying of solid. The flow can be from the outside to

the inside of the filter or the other way around, depending on the application. The particles

are normally captured on the internal surface of the bag filter. Bag filters are in general not

designed for replacement when they are clogged, but some bag filters, like particle removers,

can be cleaned, for example by mechanical shaking or by backwashing with compressed air

(so called reverse-flow bag filters). Bag filters are mostly surface-type filters.

Figure 4: Bag filter

Wet scrubber

Wet scrubbers are the most economical outlet air cleaner. It can be used in spray drying for

higher recovery of solid dust powder. The principle of a wet scrubber is to dissolve any dust

powder left in the air stream into either water or the feed stream by spraying the wash stream

through the air. This also recovers heat from the exiting air and evaporates some of the water

in the feed stream (if used as the wash water).

Made of fabrics

(Holds milk powder but

removes gases)

Exhaust Air


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Figure 5: Scrubber

Electrostatic precipitator

An electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate collection device

that removes particles from a flowing gas (such as air) using the force of an induced

electrostatic charge. Electrostatic precipitators are highly efficient filtration devices that can

easily remove fine particulate matter such as dust and smoke from the air stream. In contrast

to wet scrubbers which apply energy directly to the flowing fluid medium, an ESP applies

energy only to the particulate matter being collected and therefore is very efficient in its

consumption of energy (in the form of electricity).

Figure 6: Electrostatic precipitator

Exhaust air

Water

Li uid milk

Charged collecting

plate

Collected particle

Exhaust gas

containing particle

Exhaust gas

Without particle

study of spray dryer

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