particle technology 7

8/19/2019 Particle Technology 7

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Particle Technology

Dr. Muhammad Waqas Anjum


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Size Enlargement

• Problems with fne particles•

There are many situations where fne articles aredi!cult to handle mainly due to the "act thatarticles in #ul$ do not %ow readily

• &ine articles may #e di!cult to discharge "romhoers as articles may cling to the walls

• &iner the articles' the greater is their secifcsur"ace' and the gra(itational "orces acting on thearticles may not #e great enough to $ee themaart during %ow.

•

&ine articles o"ten gi(e rise to seriousen(ironmental and health ro#lems' articularlyas they may "orm dust clouds when loaded into(ehicles

• Although the articles may #e inert' #ut cancause serious resiratory ro#lems i" these are


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Size Enlargement

Purpose o size enlargement

• Size enlargement concerns those rocesses that

#ring together fne owder articles into larger

masses to imro(e the roerties o" the owders

• Size enlargement oerations are used in the

rocess industries with di)erent aims such as

imro(ing handling and %owa#ility' reducing

dusting or material losses' roducing structural

use"ul "orms' enhancing aearance' etc.


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Size Enlargement

Processes used "or article size enlargement

1. Compaction is achie(ed either #y comressionor e*trusion. +omression is done either into amold to gi(e a fnal shae or into a sheet or #loc$that is later #ro$en u to roer sizes. E*trudates

are "ormed under ressure in dies o" a (ariety o"cross sections, as they lea(e the die they are#ro$en u or cut to size.

2. Agglomeration is accomlished undertum#ling or otherwise

agitated conditions' with or without #indingagents. Size is

controlled #y adjusting the residence time and#y gradual addition

o" "eed and #inder' slurry or solution.3. Heat bondin - in which material is tum#led


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Size EnlargementEquiment

4. lobulation is the "ormation o" drolets o" solution'

slurry' or melt "ollowed #y solidifcation #y rilling' sray

drying' or %uidized #ed oeration. +ontrol o" article size

is #est achie(ed in %uidized #eds.

!. "locculation' coagulation and growth o" articles in

dilute slurries' to assist in su#sequent sedimentation and

fltration.


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Size Enlargement methods#ndustrial methods used or size

enlargement

a. Sray drying

#. Prilling

c. &luidized #eds

d. Drum agglomerators

e. Pug mills and e*truders

". Ele(ated temeratures

g. Pressure comaction


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Size Enlargement methods

$pra% dr%ing


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$pra% dr%ing

•

Particle size is largely determined #y the size o" the droleto" liquid or susension' controlled #y a suita#ly designed

sray nozzle.

• The aggregates o" dried material are held together as a

result o" the deosition o" small amounts o" solute on the

sur"ace o" the articles.

• &or a gi(en nozzle' the dro sizes will #e a "unction o" #oth

%ow rate and liquid roerties' articularly (iscosity' and to

a lesser e*tent o" outlet temerature.

• n general' (iscous liquids tend to "orm large dros yielding

large aggregates.


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Prilling


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Prilling

•

/elati(ely coarse drolets are introduced into theto o" a tall' narrow tower and allowed to "allagainst an uward %ow o" air.

• This results in somewhat larger articles than those

"ormed in sray dryers.• 0sed in "ertilizer industry and detergent owders.

• Per"ect sherical shae articles are o#tained #ythis technique.

• 1oth oerations' cooling and article "ormationoccur in the long tower.

• As they tra(el to the #ottom o" the tower' theysolidi"y.


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"luidized bed

• n this case' an atomized liquidor susension is srayed on to a#ed o" hot %uidized articles andlayers o" solid #uild u to gi(eenlarged articles

• The size o" which is largelydeendent on their residencetime.$pouted bed is gas2solid

contactor in which the gas is

introduced through a single

orifce "rom the center o" a %at

#ase' instead o" a multi2orifce

system' resulting in a systematic

cyclic attern o" solid mo(ement


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&rum agglomerators

• Machines used to #ring together fnes in the

resence o" moisture (ia a large rotating drum.

• Particles are 3tum#led4 in an oen cylinder with

roughened walls and su#jected to a com#ination o"

gra(itational and centri"ugal "orces.• n order to aid agglomeration' liquid may #e srayed

on to the sur"ace o" the #ed or introduced through

distri#ution ies under the #ed.


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&isc Pelletizer

•Disc Pelletizer is an adjusta#le

an de(ice utilized in micro2

elletizing' elletizing and

conditioning alications o"ten

equied with equied with a

#inder sray system which

includes iing' tu#ing' or

nozzles.

• t can #e used to elletize

materials such as coer' and


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Pug 'ills

• Pug mills are also re"erred to as

#lungers' ug mi*ers' and

addle mi*ers. These are

e*amles o" mi*er

agglomerations• They imart a comle*

$neading action that is acom#ination o" ri##ing' shearingand mi*ing.

• They ha(e two sha"ts alignedhorizontally. As the twin #ladesmo(e in oosite directions'material is thrown into the

center and the agglomerates


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Size Enlargement methodsPressure compaction

" a material is su#jected to (ery high comaction

"orces' it may #e "ormed into sheets or ta#lets.

The frst ste in ressure agglomeration is the

alication o" a small "orce to rearrange the articles inorder to fll any large (oids.

6e*t' the ressure is increased in the comression

ste' causing #rittle articles to #rea$ and de"orm. Thisste decreases the amount o" air surrounding each

article.

Since the le(el o" "orce alied is the most


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P())(* '#))$

n the ta#leting machines used "or roducing ills

o" harmaceuticals' the owder is comressed into

dies' either with or without the addition o" a #inder.

Pellet mills comact owder in a confned sace (ia

a rocess called ressure agglomeration.


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$intering +(le,ation o temperatures-

• With many materials' agglomeration may #e

achie(ed #y heating as a result o" which so"tening

occurs in the sur"ace layers

• n agglomeration using heat 7sintering8' atoms and

molecules #egin to migrate across the inter"ace

where articles touch each other.

• This haens at a certain ele(ated temerature'

which is di)erent "or (arious materials.

• While still in solid state' di)used matter "orms

#ridge2li$e structures #etween the sur"aces' which

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