raw material handling and grinding

8/18/2019 Raw Material Handling and Grinding

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RAW MATERIAL HANDLINGRAW MATERIAL HANDLING

AND GRINDINGAND GRINDING


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INTRODUCTION

In a cement plant the Cement Manufacturing Process consists of the

following:

Raw material handling

Raw Material Grinding

Coal handling

Coal GrindingPyro – Process

Cement Grinding

Cement PackingThese processes are are shown in the flow chart.


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Raw Material

andling

Raw Material

Grinding

Coal

andling

Coal

Grinding

Pyro ! Process

Cement

Grinding

Cement Packing


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Raw Material Handling

The raw materials use in cement plants are limestone" laterite"

#au$ite and iron ore. The ma%or raw material &a#out '()* is

limestone" which is supplied from limestone mines. The

limestone supplied from mines is of si+e up to one cu#ic meter

and therefore re,uires crushing for reducing to the re,uired

si+es. -ther raw materials are normally of re,uired si+e. The

raw material handling consists of the following operations and

is shown #y flow chart..

imestone crushing

imestone /tacking and /torage

imestone Reclaiming

0eeding to limestone and additi1e hoppers


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imestone Crushing

2elt con1eyors

imestone

/tacking 3 /torage

imestone

Reclaiming

2elt con1eyors

imestone opper

4dditi1e /tockyard

2elt con1eyors

4dditi1e

opper no.54dditi1e

opper no.6


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Raw Material Crushing

imestone mined from limestone mines ha1ing si+e up to one cu#ic

meter ha1e to #e crushed to the re,uired si+es depending on the typeof raw material grinding system a1aila#le in the plant. There are

different types of crushing as gi1en #elow.

/ingle stage crushing

Primary crushing

/econdary crushing

Tertiary crushing


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Different tyes !f "rushers used f!r li#est!ne "rushing are

gi$en %el!w&

7aw Crusher

Gyratory Crusher

7aw type Gyratory Crushers

Cone Crusher

Roll Crusher

ammer Crushers

Impact Crushers

Impact!hammer crusher


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Different Tyes Crushers

'( )aw Crusher: ! It is mainly designed for medium hard to 1ery hard

materials and usually installed as primary crusher. There are twotypes of %aw crushers. /ingle toggle %aw crushers are ideally suited

to hard and tough" #ut not so a#rasi1e materials. 8ou#le toggle %aw

crusher are suited for highly a#rasi1e e$tremely hard and tough

material. Capacities of 6( – 59 tph are a1aila#le with a reduction

ratio of ;!wh per ton of material.

*( Gyrat!ry Crusher: ! In cement industry gyratory crusher is used

for primary crushing of limestone of medium hard to 1ery hard for

higher capacities of around 5


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+( )aw tye Gyrat!ry Crushers& ,

These crushers are designed to handle e1en #igger feed lumps

than the compara#le si+e of the gyratory crusher with the samecone diameter. These crushers can #e installed for single stage

crushing. These crushers can #e installed for crushing all type of

material from 1ery hard to soft e$cept wet or sticky material.

The main features of gyratory crushers are:

ower power re,uirement

igh throughput rates

Possi#ility of direct feed


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@o idle strokes due to continuous crushing

ow fines content in the crushed material" if re,uired

/tart under load possi#le

ow operating and maintenance cost

-( C!ne Crusher&

In this type of crusher the positions of the crushing cone and conical

crushing ring are arranged with each other. These crushers are

mainly installed as secondary or tertiary crushers. The reduction

ratio is in the order of < to 5. It is used for hard to 1ery hard

&moderately a#rasi1e* to fria#le material. The specific powerconsumption of this crusher is .9 – .= >wh per ton of material.


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.( R!ll Crusher&

These crushers are speciali+ed machines to medium strength" highly

sticky material such as limestone contaminated with clay" coal" marl

and o1er#urden. Comminution in a roll crusher is #ased on the passing

of material #etween two rotating rolls which crush the material #y

compression. These are used for primary" secondary or tertiary crushing

and achie1e crushing ratios of 9:5 to ;:5. The specific powerconsumption of this crusher is .( – .? >wh per ton of material


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/( Ha##er Crushers& ,

These are widely used in cement industry. They are used for si+e

reduction of hard to medium hard limestone and sometimes forwet and sticky material. ammer mills work with reduction ratios

as high as 5:= to 5:; as primary and 5(:5 as secondary crushers.

It can #e installed for single stage crushing" primary crushing or

secondary crushing. Two types of hammer crushers are

manufacturedA single shaft and dou#le shaft hammer crushers and

work with the impact effect of the hammers. Capacities up to 6

tph are a1aila#le. The material crushed in dou#le rotor hammer

crushers is limited to certain characteristics of its properties. The

specific power consumption of this crusher is 5. – 5.< >wh perton of material


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These limits are:

Compressi1e strength: ! B 6wh per ton of material


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Impact crushers are capa#le of capacities of more than 6 tph.

The si+e reduction work of impact crushers is limited to certain

,uality characteristics of the crusher feed. These limits are:Compressi1e strength: ! B 9( l# per s,.inch

Mohs hardness: ! B =.(

Moisture: ! ma$ 6)

Clay content: ! )

1( I#a"t,ha##er "rusher& ,

It is a com#ination of impact and hammer crusher. The limestone is

crushed in a single operation to a finished product of '() minus 6(mm. It can #e fed with rocks of 5 – 6 m9 si+e with an edge length up

to 6 meter. The specific power consumption of this crusher is .' –

5.5 >wh per ton of material


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CRITERIA 2OR CRU3HER 3ELECTION

5. Material to #e crushed:

! nature! a#rasi1eness &) of silica*

! resistance to compression &kg per cm6*

! hardness

! moisture content

6. Ma$imum feed si+e

9. Percentage of fines in the feed

=. 8esired Production rate

(. 8esired granulometry of crushed material


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4hysi"al Chara"teristi"s !f Li#est!ne

5. 2ond work inde$ : ! range ( – 5? " normal 5 – 55

6. ardness #y Mohs scale : ! 9 – (

9. 2ulk density : ! 5(6 >g per m9

=. Compressi1e strength : ! 5( – 6( >g per s,. cm

(. Moisture content : ! 5 – 6( )


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Wear in the Crusher

In %aw crusher" the greatest wear shows at the lower part of the fi$ed

%aw plateA ne$t the lower part of swing %aw plate. The specific wearrate of %aw liners is in the range of ( – 9 grams per ton of crushed

material.

iners in gyratory crushers ha1e to #e replaced more often than %aw

crushers and also the re1ersal of liners performed in %aw crusher isimpossi#le in gyratory crushers.

8epending upon the hardness of limestone" the specific wear rate of

impact hammers is 5.( to 9 grams per ton of crushed limestone.

The wear rate of impact crusher is .; ! 9 gm per ton of limestonecrushed.


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Li#est!ne 3ta"5ing 6 3t!rage

The crushed limestone is transported #y #elt con1eyors to the

limestone storage yard and is stacked in the limestone storage

yard. /tacking is done for pre!#lending of limestone.

What is 4re,%lending: ! Pre!#lending system consists of stacker

and reclaimer. It is a method of stacking limestone of widely

1arying ,uality in layers or piles and reclaiming it in such a

manner that the ,uality 1ariations in the output stream are

su#stantially lower than those in the input stream.

4RE 7LENDING O2 RAW MATERIAL


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4RE,7LENDING O2 RAW MATERIAL

Essentials !f 4re,%lending: ! Today with the technological

ad1ancements in cement industry and increase in the specific kiln

1olumes" a uniform ,uality of kiln feed has #ecome pr!re,uisites not

only for optimum kiln output #ut also for ,uality of the clinker. 0orgetting uniform ,uality of kiln feed the pneumatic homogeni+ation of

ground raw meal alone is not sufficient and hence it has #ecome

necessary to prehomogenise the raw material #y pre!#lending #efore it is

fed to the grinding mills. It has another ad1antage of pre!homogeni+ation

of raw materials from non!homogeneous materials mined #y selecti1e

mining" manual mining or mechani+ed mining o1er a wider area.

Tyes 4re,%lenders& ,

Pre!#lending consists of stacking and reclaiming.3ta"5ing: ! The stacking is the process of depositing material of non!

uniform ,uality in layers &longitudinal or circular* o1er a period of time.

The following are different methods of stacking.


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'( L!ngitudinal st!"5iles

a* Roof!type stockpiles &Che1ron – method*

#* ine!type stacking &Dindow – method*

c* Com#ination of che1ron 3 window method

d* /trata method

e* Conical method

f* ayer method

*( Cir"ular st!"5iles

a* /ection – style Che1ron method

#* Continuous che1ron stacking

c* ayer method


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Che$r!n Meth!d 8Linear9: ! In this" a stacker continuously tra1els

#ack and forth o1er the stockpile along its length and deposits the

material in cone shaped layers. The stockpiling is performed either

#y a #elt con1eyor tripper or #y a stacker with rigid #oom" whichmo1es alongside the stockpile.The material dumped centrally o1er

the ridge flows on each side of the pile to form the re,uired layers.

The pile increases uniformly up to its ma$imum height. -ne

draw#ack of this method is the segregation of the material into larger

and smaller particles as it tum#les down the sides of the pile. 8ue to

simplicity of operation this is the most commonly used method.

Wind!w Meth!d 8Linear9: ! In this method piles are #uilt!up in a

num#er of rows of limited cross section one a#o1e other. This

method eliminates the disad1antage of material segregation as inche1ron method" #ut it is less adopted due to re,uirement of more

ela#orate stacking arrangement.


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C!#%inati!n !f Che$r!n 6 Wind!w #eth!d 8Linear9: ! 0rom the

1iew point of #lending efficiency this is the #est" #ut is rarely

adopted due to comple$ity of stacking arrangement.

3trata Meth!d 8Linear9: ! /trata method is more intendedreclaiming #y the side acting scrapper.

C!ni"al Meth!d 8Linear9: ! 4 #elt con1eyor tra1eling longitudinally

o1er the piles deposits a succession of conical shaped layers. This

method is suita#le for sideways reclaiming or for under floore$traction of material. The #lending effect is poor in this case.

Layer Meth!d 8Linear9: ! In this method relati1ely wide and thin

layers of material are deposited one upon another. 4 #ridge or gantry

tra1els in the longitudinal direction of the stockpile and a distri#uting

#elt con1eyor mo1es trans1ersely to and fro.


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3e"ti!nal,style Che$r!n 3ta"5ing 8Cir"ular9& , The

stockpiling is performed #y a #elt con1eyor which is swi1el!

mounted in the #eds center point. The cross section of a circular

stockpile can either triangular or trape+oidal. /tacking in thismethod is relati1ely straightforward and can #e compared to

longitudinal #eds. owe1er" this method produces su#stantial

1ariations in the ,uality in the transition +ones from one section

to other.

C!ntinu!us Che$r!n 3ta"5ing 8Cir"ular9& , This is the most

common method applied in circular stockpiling and it gi1es a

larger 1olume of fully homogeni+ed material with ma$imum

storage capacity.

Layer Meth!d 8Cir"ular9: ! The material is deposited #y a #elt

con1eyor system. The stacker #elt mo1es in circular directions

to and fro and has a luffing #oom.


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Re"lai#ing: ! Reclaiming is the process of e$tracting the


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material from the stockpile #y cross!cutting of material from the

o1erall height and width of the stockpile and the reclaimed

material slice is e,ui1alent to the a1erage ,uality of the #lending

#ed. The following are the methods of reclaiming used.5. /ide Reclaiming

6. 0ront end Reclaiming

a* uffing /craper Chain 4ssem#ly

#* ori+ontal /craper Chain

c* 2ucket Dheel Reclaimer

d* 2arrel Reclaimer

9. E$ca1ating

a* 2ucket Dheel on Pi1oted 2ooms

# 2ucket Chain / stem


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'( 3ide Re"lai#ing: ! E,uipment for side reclaiming comprises of a

tra1eling #oom e$tending o1er the pile and reclaiming is

achie1ed #y the scraping action of a luffing scraper chain

assem#ly on one face of the pile. The material rakes down the

#ase of the pile where it is remo1ed #y a longitudinal #elt

con1eyor under floor or to one side of the stockpile. /uch

reclaiming is normally used for stockpiles #ased on strata system

or conical system.*( 2r!nt end Re"lai#ing: ! It comprises a tra1eling #ridge

operating on rail tracks on either side of the stockpile. The

reclaimed material is remo1ed #y a #elt con1eyor. The reclaiming

in this case is done #y any of the following methods


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i9 Luffing 3"raer Chain Asse#%ly: ! This is #asically the same

e,uipment as in case of side reclaiming e$cept that it is mounted on

a tra1eling #ridge on rail tracks and reclaims the material from the

front end &cross section* of the stockpile. This method is used forfiner grain si+es up to 9 – = tph capacity.

ii9 H!ri:!ntal 3"raer Chain: ! In this case" material is dislodged #y

a triangular harrows or wire rope" which partly co1ers the end face

of the stockpile along its angle of repose and mo1es hori+ontally toand fro across it. The #lades on the scraper chain transfer the

dislodged material to a #elt con1eyor. Dith this e,uipment it is

possi#le to reclaim from stockpiles 6 – ; meter in width at rates

up to 5 tph.

iii* 7u"5et Wheel Re"lai#er: In this case one or more #ucket


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iii* 7u"5et Wheel Re"lai#er: ! In this case one or more #ucket

wheels operate in con%unction with a raking down de1ice. The raking

down de1ice dislodges the material and #ring it down within the

reach of #uckets. These two mo1e automatically across the face of the

pile and their direction of mo1ement is re1ersed with the help of limit

switches at the #ridge ends. /imultaneously" the #ridge mo1es

forward in the longitudinal direction for a present distance. The

material scooped #y the #uckets is fed on to a #elt con1eyor mounted

on the #ridge and in turn on to a longitudinal #elt con1eyor foronward transmission.

i1* 7arrel Re"lai#er: ! In this case material is dislodged and

scooped from the entire cross section of the pile without performing

any oscillating motions. 0or this scoops are mounted on the outside of

a tu#e or drum which pick up the dislodged material and feed it on to

a #elt con1eyor installed inside the tu#e. This drum is mounted on a

#ridge type structure" which tra1els on rails and spans across the full

width of the pile.

9 E i Th i d f i d i k


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9. E;"a$ating: ! These e,uipment are used for 1ery moist and sticky

material in which there is no raking down mechanism #ut instead"

the e,uipment #ites its way through the material. Two types of such

e,uipment are descri#ed here.i9 7u"5et Wheel !n 4i$!ted 7!!#s: ! In this the #ucket wheel itself

#ites its way through the entire height of the dump in certain num#er

of slices depending on the #ucket wheel diameter. This method is

suited for coarse grained moist or sticky material.

ii9 7u"5et Chain 3yste#: ! 0or certain materials" it is prefera#le to go

in for a storage pit instead of a stockpile. 4#o1e the pit two gantries

run on tracks. 0rom the upper gantry" raw material is dumped into

the pit from a distri#ution #elt. Running on the lower gantry is a

#ucket ladder e$ca1ator which remo1es the dumped material.


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4RE,7LENDING E22ICIENC


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4RE,7LENDING E22ICIENC<

Efficiency of pre!#lending stockpile is measured #y the ratio of

standard de1iation of CaC-9 content of input material to

standard de1iation of CaC-9 content of output material. It is possi#le to achie1e a #lending efficiency of ?:5 to 5: 5.

2a"t!rs affe"ting 7lending Effi"ien"y: ! The factors affecting

the #lending efficiency are:

1ariation in the incoming material

method of formation of stockpile

no. of layers forming the #ed

,uantity of material per #ed

,uantity of material per layer


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#lending #ed capacity

method of reclaiming Fuantity of material per reclaimer slice

4ll the pre!#lending systems achie1e the re,uired #lending

efficiency #y controlling the a#o1e parameters

RAW MATERIAL GRINDING


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The raw material grinding is a process which in1ol1es preparation of

raw mi$ for making clinker. The crushed limestone along with the

additi1es such as laterite" #au$ite or iron ore in the re,uired

proportions are ground raw mills for getting raw meal of re,uiredfineness.

The right choice of a raw grinding system is influenced #y a series

of techno!economic considerations including the local conditions.

The system which has the highest operational economy" coupledwith low in1estment cost and high relia#ility" has to #e aimed at.

The important parameters which influence the design and selection

of a raw grinding system are:

4. Raw material characteristics

i* Grinda#ility

ii* 4#rasi1eness


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iii* Ci1il construction


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iii* Ci1il construction

E. En1ironmental Regulation

i* 8ustii* @oise

iii* Hi#ration

0. Maintaina#ility 3 Relia#ility

i* 8amage and Replacement of compounds

ii* /kill of plant operating staff

iii* Comple$ity of design" replacement and a1aila#ility

The most important factors in relation to a modern dry process

plant is the moisture and grinda#ility of raw material and

specific power consumption.


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Tyes !f Mills a$aila%le f!r raw #aterial grinding: ! The

following are the types of grinding systems a1aila#le for raw

material grinding.

5. 2all Mills

a* 4ir /wept Mill

#* Tandem Mill

c* End 8ischarge Mill with 8rying Cham#er

d* Central 8ischarge Mill with 8rying Cham#er

6. Hertical Roller Mills

9. Hertical Roller Mills

=. Roller Press

(. oromill


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Tyes !f Mills a$aila%le f!r raw #aterial grinding

5. 2all Mill: !Con1entionally raw materials were #eing ground in

the #all mills. The #all mills are highly inefficient with morethan '


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a* 4ir /wept Mill: ! In this mill ground raw material is swept

away #y the gases supplied at the inlet of the mill and the fine

product is separated in a separator and the coarse re%ects are

returned to the inlet of the mill.

#* Tandem Mill: ! It is a com#ination of #all mill and hammer

mill. The lower power consumption is due to the closed #ottom

hammer mill installed in the system which results in a#out

9) of raw meal produced without #eing ground further in the

#all mill.

c* End 8ischarge Mill with 8rying Cham#er: ! These can #e of

either open circuit or close circuit. These mills will ha1e one.

two or three cham#ers separated #y diaphragms.


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i* -pen circuit mills: ! These mills do not ha1e a

separator for separating the output from the mill into

product and re%ects. The total mill output is product and the

fineness is controlled #y the grinding media loading

pattern" mill feed input rate" gas flow rate etc. The gases used

for drying raw materials in the mill is separated from fines

either in a #ag filter or Electrostatic Precipitator.

ii* Closed Circuit Mills: ! In these mills the output fromthe mill is is fed to a separator #y a #ucket ele1ator for

separating into product and re%ects. The re%ects are

returned to the mill inlet. The closed circuit mills ha1e a

#etter control on the particle si+e distri#ution and fineness

control.


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d* Central 8ischarge Mill with 8rying Cham#er: ! This mill has

two cham#ers. Raw material is fed to the first cham#er.The

material ground in the first cham#er and second cham#er are

centrally discharged and fed to a separator through a #ucketele1ator. The re%ects of the separator is fed to the second

cham#er of the mill. The gases used for drying are separated

from fines either in a #ag filter or E/P.

6. Hertical Roller Mills: ! The 1ertical roller mill has #ecome theo#1ious and preferred tool of choice for raw milling due to

higher output rates" lower energy consumption" drying capacity"

dependa#ility" 1ersatility" etc. These mills offer simplicity #y

com#ining the functions of secondary tertiary crushing"

drying" grinding and classifying in one compact machine.HRMs are a1aila#le with two" three" four and si$ rollers.


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The 1ertical roller mills are different types such as Ring Roller

Mills" Ring 2all Mills" 2owl Mills" etc. The characteristic of

these mills is that the si+e reduction is effected #y rollers oncompara#le grinding elements tra1eling o1er a circular #ed of

material. The material after passing under the rollers is su#%ected

to a preliminary classifying action #y a stream of air sweeping

through the mill. The air at high 1elocity lifts the material to the

classifier which separates the coarse and fine particles. The fine particles are entrained and the separated coarse particles fall

#ack to the ta#le. The separator could #e either static or

dynamic. The fine particles are collected later in an E/P or 2ag

0ilter. In Hertical roller mills with e$ternal recirculation" the

no++le ring 1elocity is lower & =!; m.per sec* than the millswithout e$ternal recirculation &?!


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The ad$antages !f =erti"al R!ller Mills&


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The ad$antages !f =erti"al R!ller Mills& !

HRM is comparati1ely more energy efficient and on an a1erage these

system consume 6() less energy in comparison to the con1entional

2all Mills.

HRM has higher drying capacity and can dry up to 6() moisture" as

against ma$imum drying capacity of

Mill system.

HRM is more compact and occupies less space for the e,ui1alent

capacity in comparison to a con1entional 2all Mill system.

HRM can ha1e higher capacities up to


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9. ydraulic Roll Crusher: ! It is possi#le to use a hydraulic roll

crusher to produce raw meal without a #all mill or 1ertical

roller mill. This can #e useful for kiln capacities of less than6 tpd. The recirculation rates through the rolls are as high

as ;!? times for a gi1en production. It does not ha1e clear

ad1antage o1er 1ertical roller mills and has higher risks of

mechanical difficulties. The application of RC is only

attracti1e when it is com#ined with an e$isting #all mill process.

=. Roller Press: ! Roller Presses are more energy efficient than

Hertical roller mills. It can operate in semi finish and finish

mode.

In semi finish mode" the output of roller press is further

ground in a #all mill The raw material is ground when it


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ground in a #all mill. The raw material is ground when it

passes through two rotating high pressure grinding rolls &one

is fi$ed and other is mo1ea#le*. The ground raw material

passes through a dissagglometor and then a separator eitherstatic or dynamic. The separated coarse material is fed #ack

to the roller press and the fines are fed to a #all mill for finish

grinding.

(. oromill: ! This mill works on the concept of in!#edcompression and comminution. It consists of a shell dri1en at

supercritical speed" a roller applied on the material #ed #y

means of hydraulic %acks and material fed from one side and

ground se1eral times #etween shell and the roller. It has

energy sa1ing potential of 9( to ?). It is en1ironmentalfriendly with low noise le1els" no pollution and low energy

consumption.


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Wear in raw #ill and re#edial #easures


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Dear of grinding media" rollers and liners in raw mill grinding 1aries

with the physical and chemical characteristics of the raw material to

#e ground. The important factors are:

Grinda#ility – work inde$ #y 2ond

4#rasi1eness

/ilica and ,uart+ content

In #all mills" wear of the following are to #e considered.

5.Grinding media

6.Mill liners

9.8iaphragm plates

The wear rate of grinding media and liner plates can #e reduced #y


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selecting proper alloys" which are wear resistant as material for

construction of grinding media and liner plates. The common

material used are forged steel. Dhite cast iron and chromium alloyedcast media.

In 1ertical roller mills wear of the following are important.

JRollers

JTa#le liners

2y proper selection of material of construction and #y hard facing

uilding of wear resistant surface #y welding with special

electrodes* life of rollers and ta#le liners can #e impro1ed.

In Roller Press and ydraulic Roll Crusher also #y proper selection

of material wear rate can #e reduced.

Raw Mi; 2ineness: !


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The ad$antages !f in"reasing the raw #i; fineness are:

/horter time re,uired for preheating of suspended raw mi$ in

preheater.

0aster calcination and clinkeri+ation reactions.

Increase in clinker production rate.

Reduction in specific fuel consumption.

The disad$antages !f in"reasing the raw #i; fineness are:

Increase in specific power consumption of raw mi$ grinding.

8epending on chemical and physical characteristics of the raw mi$"optimum fineness has to fi$ed #y considering all the a#o1e

mentioned factors.

R!le !f 3earat!r in 2ineness "!ntr!l

4 ma%or role in controlling the fineness of raw meal.


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Raw meal grinding systems of air swept #all mills" central

discharge #all mills" 1ertical roller mills" RC" oromill and roller

press can not work without separators.

In case end discharge #all mills separator is installed for close

circuiting the mill to ha1e a #etter particle si+e distri#ution of the

product.

/eparator efficiencies are different for different kinds of

separators.

/pecific power consumption of raw material grinding 1aries

depending on the efficiencies of the separator installed in the circuit.

Two important parameters of separators are recycle ratio and

separator efficiency.

Re"y"le rati! is the ratio of ,uantity of separator feed to ,uantity


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Re"y"le rati! is the ratio of ,uantity of separator feed to ,uantity

of separator fines.

/eparator efficiency K&/f L / a* $ &&/ a! /g* L &&/ f ! /g** $ 5

/f K ) passage of separator fines of one grain si+e

/a K ) passage of separator feed of one grain si+e

/g K ) passage of separator re%ects of one grain si+e

2ineness is "!ntr!lled %y:

/peed of the separator

4ir to material ratio4ngle and shape of stationary and rotating separator 1anes

4ir 1elocity through the separator

Tr!# Cur$e


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Tr!# Cur$e

4 common method used to determine the ,uality of the separator

classification sharpness is determining the distri#ution densityusing a tromp distri#ution cur1e &so called Tromp cur1e*.

It is determined #ased on the weight components of the indi1idual

particle fractions of three separator flows" i.eA feed" grits and

product. The result of calculation is one distri#ution figure

&percent #y weight* for a particular particle si+e fraction. 0rom

numerous points you get the function depicted in the graph of the

distri#ution figure T &)* as function of particle si+e &micron m*.

The cur1e indicates for each particle si+e of the separator feed

material what percentage share &weight* passed into the grits andwhat percentage passed into the product. 4#o1e the cur1e you can

find the shares in the fines" #eneath the cur1e" those in the grits.

To e1aluate the classification sharpness of the separator it is


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p p

important to determine the steepness of the Tromp cur1e and where

it is located in the graph.

The steeper the cur1e &the right a$is* the more efficiently the

separator handled the classification" that is" the more coarse

particles are there in grits and fine particles in the product.

The ideal cur1e would #e one in which the coarse range in the

distri#ution function would run 5) hori+ontally up to the desired

separating particle si+e and then drop 1ertically and drop down to

the distri#ution figure in the fine range. This would mean that all

the particles in the feed which are larger than the separator particle

si+e passed into grits and all the smaller particles into the product.


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4r!"ess !f drying raw #aterials in Raw Mills

The characteristic feat re of the dr ing grinding process is that


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The characteristic feature of the drying!grinding process is that

two different processes are generally performed in the grinding

mill. The heat re,uired for drying the raw material is supplied #y

hot gases from preheater or cooler or hot air generator and #y the

heat generated #y comminution in the grinding process.

In #all mills for drying of raw material a drying compartment is

arranged in front of the grinding compartment of the mill. The

drying cham#er is e,uipped with lifters" #ut has no grinding

media.

In the traditional #all mill the drying capacity is limited #y its

geometry. E1en at sufficient hot gas amount it was difficult to get

all necessary gas flow to pass the mill. The gas flow and dryingcapacity was normally decreased with mill si+e &grinding

capacity*.

In other mills like 1ertical roller mills #oth grinding and drying

take place together inside the mill #y the hot gases supplied


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through the mill. The 1ertical roller mills are usually designed to

ha1e a rather constant ratio #etween air flow and grinding

capacity. HRMs of all si+es ha1e the same drying capacities upto 6().

Dhen calculating the amount of e$it gases from a drying!

grinding mill" the following should #e taken into consideration:

5. The amount of water 1apor generated from the moisture contentof raw material

6. The heat re,uired for e1aporation" using a practical figure of

56( kcal per kg of water.

9. The amount of flue gas when generating the re,uired heat.


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C!ntr!l L!!s in Raw Mill aut!#ati!n


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The system has the following control loops:

Material feed to mill is controlled #y differential pressure across themill.

Control of gas flow though the mill increase or decrease of mill fan

speed or damper.

Mill inlet temperature control #y controlling GCT water spray orheat generated from hot air generator.

Mill outlet temperature control #y controlling mill internal water

spray.

Preheater fan e$it draft control #y controlling recirculation air to mill

#y controlling damper in recirculation duct.

Meth!d !f De,dusting raw #ill gases

8e!dusting of raw mill e$haust gases are done #y the


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8e!dusting of raw mill e$haust gases are done #y the

following methods:

Gra$ity settling "ha#%ers: ! It has the importance of pre!cleaning of high dust laden gasesA they work on the principle

of remo1ing the dust #y reducing the 1elocity of gas stream.

/ometimes it is e,uipped with deflectors. The efficiency of

gra1ity settling cham#ers are 9!?).

Cy"l!nes: ! cyclones are low cost dust collectors and it

consists of two sectionsA a cylindrical and conical one. 4t the

top of the cylindrical section the dust laden gas enters

tangentially. It spirals along the walls downward and upward

to the outlet thim#le. 8ust is separated from the gases #y thecentrifugal forces. The efficiency of cyclones decreases with

decreasing particle si+es and in1ersely proportional to its

diameter. It is used as a pre!collector.

Multi"y"l!nes: ! Multicyclones are units of cyclones installed in


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com#inations of series and parallel for high throughput and high

efficiency. The efficiency of multicyclones is in the range of


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#* Re1erse air

c* Pulse pressure

d* /onic cleaning

Gra$el %ed filters: ! The principle of a granular layer of pe##les

is also used for gas cleaning. It works in com#ination with

cyclone precipitators. This filter is immune to high temperature

up to ( o C and efficiency can #e up to ''.').

Ele"tr!stati" 4re"iitat!r 8E349& ! The principle of dust

collection is #ased on the utili+ation of the effect of gas

ioni+ation in a strong electric field" which is formed #y discharge

electrodes &corona effect" negati1e* and #y collecting electrodes&positi1e*. Collection of efficiencies of ''.?() is attaina#le

under fa1ora#le conditions.

Merits and De#erits !f using 7ag filter and E34


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The E/P si+ing depends on the outlet emissions desired.

/i+e of the #ag filter is almost independent of the outlet emission.

The cost of E/P increases with the reduction in the emission

norms.

Dith the a1aila#ility of latest PT0E #ags" #ag filter is the most

techno!economic solution to achie1e emissions #elow ( mg per

@m9.

0or the clinker cooler dust e$traction" E/P is still the most

economical solution due to large particle si+e.

The cost of #ag filter is less than E/P.

The power consumption #y #oth e,uipment is same.

The process condition in E/P 1aries during raw mill and coal mill

shutdowns and the E/P performance 1aries


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shutdowns and the E/P performance 1aries.

The tripping of E/Ps with increase in C- content in the kiln e$haust

gases due to process fluctuations are 1ery common.

The disad1antage of #ag filter is it can not with stand high

temperatures which happens during plant start up and upset conditions.

2ag filter system re,uires regular maintenance of cleaning system

and timely replacement of filter #ags.

The disad1antage of E/P is the snapping of electrodes and plant

stoppage for its rectification.

Essentials !f g!!d %lending !f raw #i;


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0or sta#le running of kiln which is the heart of cement plant"

uniform ,uality of raw meal is 1ery much essential.

4 uniform ,uality of kiln feed to kiln ensures optimum kiln output"

reduced specific heat and power consumption and uniform ,uality of

clinker resulting consistent cement ,uality.

To get uniform ,uality of raw meal from limestone of 1arying

,uality from limestone mine operated in different phases or locations.

Though the 1ariation in the limestone ,uality can #e reduced to

some e$tend #y pre!#lending" to achie1e uniform and consistent

,uality of raw meal #lending of raw meal is essential.

Tyes !f 7lending


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Tyes !f 7lending

omogeni+ation of cement raw mi$ can #e performed on a #atch

#asis as well as continuously.

7at"h %lending: ! 0or #atch system two two #lending silosA

normally one is called as #lending silo and other as storage silo. The

homogeni+ation process starts during the filling of #lending silo.

4fter filling the #lending silo" homogeni+ation process continues fora#out one hour. Then it is discharged to the storage silo normally

located at the #ottom of the #lending silo" where it is homogeni+ed

continuously and e$tracted for kiln feed. 2atch type homogeni+ation

is applied in cases where the ,uality of the raw material widely

fluctuates and in relati1ely long time inter1als.

C!ntinu!us %lending: ! The continuous #lending is applied in

cases where the ,uality of raw material is allowed to fluctuate only


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within narrow limits and in short period of time. Continuous

#lending can #e done with single" two and three silos. Two or three

silos work in series for continuous #lending depending on the

fluctuations in the ,uality of raw material. /ingle continuous

homogeni+ing silo work with raw materials of less ,uality

fluctuations and is #est applied in cases where the raw material is

already pre!#lended. /ingle continuous #lending silo can #e of #ottom discharge or side discharge types. In case of side discharge

type o1erflow discharge is taken from the opening in the side wall

of continuous #lending silo and stored in a storage silo. In case of

#ottom discharge silo" kiln feed e$traction is taken from the

#ottom of the continuous #lending silo.

R!le !f 7lending 3il! in >uality C!ntr!l !f Raw Mi;

2lending silos ha1e a ma%or role in achie1ing uniform and consistent


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2lending silos ha1e a ma%or role in achie1ing uniform and consistent

,uality of raw mi$" which is essentially re,uired for getting ma$imum

output from the kiln and optimi+ing specific fuel and powerconsumption. 2lending silos" #y #lending process reduces the ,uality

1ariation in the raw mi$. There are 1arious types #lending silos ha1ing

#lending factor from ;:5 to 5(:5. The #asic principle of #lending

process is one or com#ination of the following mechanisms.

8istri#ution of input raw meal at the #lending silo top.

Pneumatic dry #lending #y aeration of raw meal #y the aeration

units placed at the #ottom of silo.

/egmental aeration &octant or ,uadrant system* with difference inthe pressure of air supplied for aeration of 1arious segments for

thorough mi$ing of raw mi$.

Method of e$traction to kiln feed

7lending 2a"t!r

0or calculation of #lending factor of a silo" input and output raw meal


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samples are to #e collected in regular inter1als and to #e tested for

CaC-9 content.

/ilo input samples to #e collected for a period of one theoretical filling

of silo with an inter1al not e$ceeding 5.( hours and a minimum =

samples are to #e collected. 0or optimum #lending efficiency silo should

#e filled more than ?). The output samples are to #e collected at an

inter1al of 9 to ( minutes after the input samples are collected and a

minimum of 6 samples are to #e collected.

The standard de1iation of the input samples as well as output samples

are to #e calculated. The #lending factor is the ratio of standard

de1iation of input raw meal to standard de1iation of output raw meal.The more the #lending factor" the #lending is more effecti1e.

C!lle"ti!n and Dis!sal !f artially "al"ined reheater dust

Th i f d d f diff kil i


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The ,uantity of dust generated from different cement kilns is

estimated to 1ary from < to 5( percent. The dust generated from the

kiln" which goes out with preheater e$it gases are collected #yelectrostatic precipitators or #ag filters or other kinds of dust

separators. 8isposal of the partially calcined preheater dust is as

important as its disposal. ndou#tedly recycling of the dust is the

most practical solution. In dry process" the dust can #e either mi$ed

with kiln feed or raw mill output. Dhere1er preheater gases are used

for drying of raw material in raw mills" a ma%or part of the dust gets

mi$ed with the raw mill output and only the dust collected in GCT

and during raw mill shutdown is to #e recycled. 8ue to changes in

the chemical composition of the dust" sometimes the recycling ofdust causes #uild ups in kiln or preheater ducts. In such cases the

solution for the disposal of the dust is #y #lending with ordinary

portland cement.

raw material handling and grinding

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