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RAW MATERIAL HANDLING
AND 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 used in cement plants are mainly limestone"
laterite" #au$ite and iron ore. The ma%or raw material is
limestone" which is supplied from limestone mines. The
limestone supplied from mines is of si&e up to one cu#ic meter
and therefore re'uires crushing for reducing to the re'uired
si&es. (ther raw materials are normally of re'uired si&e. The
raw material handling consists of the following operations and
is shown #y flow chart..
)imestone crushing
)imestone *tacking and *torage
)imestone Reclaiming
+eeding to limestone and additi,e hoppers
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)imestone Crushing
-elt con,eyors
)imestone
*tacking *torage
)imestone
Reclaiming
-elt con,eyors
)imestone opper
/dditi,e *tockyard
-elt con,eyors
/dditi,e
opper no.0/dditi,e
opper no.1
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Raw Material Crushing
)imestone mined from limestone mines ha,ing si&e up to
one cu#ic meter ha,e to #e crushed to the re'uired si&esdepending on the type of raw material grinding system
a,aila#le in the plant. There are different types of crushing
as gi,en #elow.
*ingle stage crushing
Primary crushing
*econdary crushingTertiary crushing
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Different tyes !f "rushers used f!r li#est!ne "rushing are
gi$en %el!w&
2aw Crusher
Gyratory Crusher
2aw 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 ,ery hard materials and usually installed as primary crusher. There are two types of %aw
crushers. *ingle toggle %aw crushers is ideally
suited to hard and tough" #ut not so a#rasi,e
materials. 3ou#le toggle %aw crusher are suited for
highly a#rasi,e e$tremely hard and tough material.
Capacities of 14 – 0566 tph are a,aila#le with a
reduction ratio of 7!8: 0. *pecific powerconsumption of this crusher is 6.1 – 6.9 wh per
ton of material.
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*( Gyrat!ry Crusher: ! In cement industry
gyratory crusher is used for primarycrushing of limestone of medium hard to
,ery hard for higher capacities of around
0866 tph. It has a two to three times
capacity of %aw crusher for the same si&es
of feed opening and discharge slot. The
reduction ratio of this crusher is ;:0 to
04:0. The specific power consumption ofthis crusher is 0.5 to 5.7 times more than
the %aw crusher.
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+( )aw tye Gyrat!ry Crushers& ,
These crushers are designed to handle e,en #igger feed lumps than the compara#le si&e of the
gyratory crusher with the same cone diameter.
These crushers can #e installed for single stage
crushing. These crushers can #e installed for
crushing all type of material from ,ery hard to
soft e$cept wet or sticky material.
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-( C!ne Crusher&
In this type of crusher" the positions of the crushingcone and conical crushing ring are ad%acent to each
other. These crushers are mainly installed as secondary
or tertiary crushers. The reduction ratio is in the order
of 8 to 0. It is used for hard to ,ery hard =moderatelya#rasi,e> to fria#le material. The specific power
consumption of this crusher is 6.5 – 6.9 wh per ton
of material.
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/( Ha##er Crushers& ,
These are widely used in cement industry. They areused for si&e reduction of hard to medium hard
limestone and sometimes for wet and sticky material.
ammer mills work with reduction ratios as high as
0:96 to 0:76 as primary and 04:0 as secondarycrushers. It can #e installed for single stage crushing"
primary crushing or secondary crushing. Two types
of hammer crushers are manufactured? single shaft
and dou#le shaft hammer crushers and work with theimpact effect of the hammers. Capacities up to 1666
tph are a,aila#le.
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0( I#a"t Crushers& ,
These crushers are suita#le for non!a#rasi,e" from soft
to hard" slightly wet materials. The predominant stressused is impact" howe,er cut and attrition are also used.
The ma$imum reduction ratios are 96:0. There are two
types? single rotor impact and dou#le rotor impact
crushers. The specific power consumption of this
crusher is 6.9 – 0.6 wh per ton of material
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Impact crushers are capa#le of capacities of more
than 1666 tph.
The si&e reduction work of impact crushers is
limited to certain 'uality characteristics of the
crusher feed. These limits are:
Compressi,e strength: !@ 54666 l# per s'.inch
MohAs hardness: ! @ 9.4
Moisture: ! ma$ 16BClay content: ! 6B
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C A O C 3 3 C O
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CRITERIA 2OR CRU3HER 3ELECTION
0. Material to #e crushed:
! nature
! a#rasi,eness =B of silica>
! resistance to compression =kg per cm1>
! hardness
! moisture content
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4RE,7LENDING O2 RAW MATERIAL
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4RE 7LENDING O2 RAW MATERIAL
Essentials !f 4re,%lending: ! Today with the technological
ad,ancements in cement industry and increase in the specific
kiln ,olumes" a uniform 'uality of kiln feed has #ecome pre!re'uisites not only for optimum kiln output #ut also for 'uality
of the clinker. +or getting 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 ad,antage of pre!
homogeni&ation of raw materials from non!homogeneous
materials mined #y selecti,e mining" manual mining ormechani&ed mining o,er a wider area.
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Tyes !f 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> o,er a period of
time. The following are different methods of
stacking.
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' L!ngitudinal st!"5iles
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'( L!ngitudinal st!"5iles
a> Roof!type stockpiles =Che,ron – method>
#> )ine!type stacking =Dindow – method>
c> Com#ination of che,ron window method
d> *trata method
e> Conical method
f> )ayer method
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*( Cir"ular st!"5iles
a> *ection – style Che,ron method
#> Continuous che,ron stacking
c> )ayer method
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Ch M h d 8Li 9 I hi k
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Che$r!n Meth!d 8Linear9: ! In this" a stacker
continuously tra,els #ack and forth o,er the stockpile
along its length and deposits the material in coneshaped layers. The stockpiling is performed either #y a
#elt con,eyor tripper or #y a stacker with rigid #oom"
which mo,es alongside the stockpile.The material
dumped centrally o,er the ridge flows on each side ofthe pile to form the re'uired layers. The pile increases
uniformly up to its ma$imum height. (ne draw#ack of
this method is the segregation of the material into
larger and smaller particles as it tum#les down thesides of the pile. 3ue to simplicity of operation this is
the most commonly used method.
Wind!w Meth!d 8Linear9: ! In this method piles are
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p
#uilt!up in a num#er of rows of limited cross section
one a#o,e other. This method eliminates the
disad,antage of material segregation as in che,ronmethod" #ut it is less adopted due to re'uirement of
more ela#orate stacking arrangement.
C!#%inati!n !f Che$r!n 6 Wind!w #eth!d8Linear9: ! +rom the ,iew point of #lending
efficiency this is the #est" #ut is rarely adopted due to
comple$ity of stacking arrangement.
3trata Meth!d 8Linear9: ! *trata method is more
intended reclaiming #y the side acting scrapper.
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3e"ti!nal style Che$r!n 3ta"5ing 8Cir"ular9&
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3e"ti!nal,style Che$r!n 3ta"5ing 8Cir"ular9& ,
The stockpiling in circular #lending #ed is
performed #y a #elt con,eyor" which is swi,el!
mounted in the #edAs center point. The cross
section of a circular stockpile can either triangular
or trape&oidal.
*tacking in this method is relati,elystraightforward and can #e compared to
longitudinal #eds. owe,er" this method produces
su#stantial ,ariations in the 'uality in the transition
&ones from one section to other.
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0. *ide Reclaiming
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1. +ront end Reclaiming
a> )uffing *craper Chain /ssem#ly
#> ori&ontal *craper Chain
c> -ucket Dheel Reclaimer
d> -arrel Reclaimer
5. E$ca,ating
a> -ucket Dheel on Pi,oted -ooms
#> -ucket Chain *ystem
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'( 3ide Re"lai#ing: ! E'uipment for side reclaiming
i f li # di h il
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comprises of a tra,eling #oom e$tending o,er the pile
and reclaiming is achie,ed #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
remo,ed #y a longitudinal #elt con,eyor under floor or
to one side of the stockpile. *uch reclaiming is normally
used for stockpiles #ased on strata system or conicalsystem.
*( 2r!nt end Re"lai#ing: ! It comprises a tra,eling #ridge
operating on rail tracks on either side of the stockpile.
The reclaimed material is remo,ed #y a #elt con,eyor.The reclaiming in this case is done #y any of the
following methods
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iii> 7u"5et Wheel Re"lai#er: ! In this case one or
# k h l i % i i h
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more #ucket wheels operate in con%unction with a
raking down de,ice. The raking down de,ice dislodges
the material and #rings it down within the reach of #uckets. These two mo,e automatically across the face
of the pile and their direction of mo,ement is re,ersed
with the help of limit switches at the #ridge ends.
*imultaneously" the #ridge mo,es forward in thelongitudinal direction for a present distance. The
material scooped #y the #uckets is fed on to a #elt
con,eyor mounted on the #ridge and in turn on to a
longitudinal #elt con,eyor for onward transmission.
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i9 7u"5et Wheel !n 4i$!ted 7!!#s: ! In this the #ucket
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wheel itself #ites its way through the entire height of
the dump in certain num#er of slices depending on the
#ucket wheel diameter. This method is suited forcoarse!grained moist or sticky material.
ii9 7u"5et Chain 3yste#: ! +or certain materials" it is
prefera#le to go in for a storage pit instead of astockpile. /#o,e the pit two gantries run on tracks.
+rom the upper gantry" raw material is dumped into
the pit from a distri#ution #elt. Running on the lower
gantry is a #ucket ladder e$ca,ator" which remo,es thedumped material.
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4RE,7LENDING E22ICIENC
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Efficiency of pre!#lending stockpile is measured
#y the ratio of standard de,iation of CaC(5
content of input material to standard de,iation of
CaC(5 content of output material. It is possi#le to
achie,e a #lending efficiency of ;:0 to 06: 0.
2a"t!rs affe"ting 7lending Effi"ien"y: ! The
factors affecting the #lending efficiency are:
,ariation in the incoming material
method of formation of stockpile
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RAW MATERIAL GRINDING
The raw material grinding is a process" which in,ol,es
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The raw material grinding is a process" which in,ol,es
preparation of raw mi$ for making clinker. The crushed
limestone along with the additi,es such as laterite" #au$ite
or iron ore in the re'uired proportions are ground raw
mills for getting raw meal of re'uired fineness.
The right choice of a raw grinding system is influenced #y
a series of techno!economic considerations including thelocal conditions. The system which has the highest
operational economy" coupled with low in,estment cost
and high relia#ility" has to #e aimed at.
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C. (perating Cost
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i> Energy
ii> Dear
iii> Manpower
3. In,estment Costs
i> Plant and Machinery
ii> Electricals and control system
iii> Ci,il construction
E. En,ironmental Regulation
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g
i> 3ust
ii> Hi#ration
+. Maintaina#ility Relia#ility
i> 3amage and Replacement of compounds
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i> 3amage and Replacement of compounds
ii> *kill of plant operating staff
iii> Comple$ity of design" replacement and
a,aila#ility
The most important factors in relation to a
modern dry process plant are the moisture
and grinda#ility of raw material and
specific power consumption.
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The ,ertical roller mills are different types such as Ring Roller
Mills" Ring -all Mills" -owl Mills" etc. The characteristic of
th ill i th t th i d ti i ff t d # ll
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these mills is that the si&e reduction is effected #y rollers on
compara#le grinding elements tra,eling o,er a circular #ed of
material. The material after passing under the rollers is su#%ectedto a preliminary classifying action #y a stream of air sweeping
through the mill. The air at high ,elocity 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 -ag
+ilter. In Hertical roller mills with e$ternal recirculation" the
no&&le ring ,elocity is lower = 96!76 m.per sec> than the mills
without e$ternal recirculation =;6!86 m. per sec>.
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Raw Mi; 2ineness: !
The ad$antages !f in"reasing the raw #i; fineness are:
*h t ti i d f h ti f d d i i
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*horter time re'uired for preheating of suspended raw mi$ in
preheater.
+aster 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.
3epending on chemical and physical characteristics of the raw mi$"
optimum fineness has to fi$ed #y considering all the a#o,e
mentioned factors.
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4r!"ess !f drying raw #aterials in Raw Mills
The characteristic feature of the drying!grinding process is that
two different processes are generally performed in the grinding
mill The heat re' ired for dr ing the ra material is s pplied #
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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 theheat 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 grindingmedia.
In the traditional #all mill the drying capacity is limited #y its
geometry. E,en 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>.
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Meth!d !f De,dusting raw #ill gases
3e!dusting of raw mill e$haust gases are done #y the
following methods:
Gra$ity settling "ha#%ers:
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y g
Cy"l!nes
Multi"l!nes
7ag 2ilters
Gra$el %ed filter
Ele"tr!stati" 4re"iitat!r
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C
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Cyclones are low cost dustcollectors and it consists of twosections? a cylindrical and conicalone. /t the top of the cylindricalsection the dust laden gas enterstangentially. It spirals along the
walls downward and upward to theoutlet thim#le. 3ust is separatedfrom the gases #y the centrifugalforces. The efficiency of cyclonesdecreases with decreasing particlesi&es and in,ersely proportional toits diameter. It is used as a pre!collector.
MULTICLONE3
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Multicyclones are units ofcyclones installed in
com#inations of series and
parallel for high throughput
and high efficiency. The
efficiency of multicyclones
is in the range of 84!9B.
2a%ri" 2ilters: ! These are generally of #ag type" i.e. tu#es
with 566 mm diameter or less" and up to 06 m high? they
consists of wo,en or felted cloth" made from natural or
synthetic fi#ers. +a#ric filters can handle small particles in the
su# micron range at high efficiencies of .4B. The dust laden
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gases flow through the porous medium of ! the filter fa#ric!and deposits particles in the ,oids. /fter filling the ,oids" a
cake starts to #uild up on the fa#ricAs surface" which does most
of the filtering. Dhen the dust layer #ecomes too thick" an
increase in pressure drop results? this re'uires cleaning of the
fa#ric. 3epending on the characteristic of the dust and type offa#rics" the following methods are applied for cleaning.
a> -ag swinging
#> Re,erse air
c> Pulse pressure
d> *onic cleaning
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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" negati,e> and #y collecting electrodes
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electrodes =corona effect" negati,e> and #y collecting electrodes
=positi,e>. Collection of efficiencies of .;4B is attaina#leunder fa,ora#le conditions.
The complete electrostatic precipitation process consists of fi,e
#asic steps that operate on a continuous #asis:
0. Gas distri#ution into treatment &one
1. Particle charging L corona discharge =gas conduction>
5. 3eposition of dust on collecting electrodes
9. /ccumulation of dust
4. Remo,al of the collected material
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The process condition in E*P ,aries during raw mill and coal mill
shutdowns and the E*P performance ,aries.
The tripping of E*Ps with increase in C( content in the kiln e$haust
gases due to process fluctuations are ,ery common
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gases due to process fluctuations are ,ery common.
The disad,antage of #ag filter is it can not withstand high
temperatures" which happens during plant start!up and upset
conditions.
-ag filter system re'uires regular maintenance of cleaning system
and timely replacement of filter #ags.
The disad,antage of E*P is the snapping of electrodes and plant
stoppage for its rectification.
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Tyes !f 7lending
omogeni&ation of cement raw mi$ can #e performed on a #atch
#asis as well as continuously
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#asis as well as continuously.
7at"h %lending: ! +or #atch system two #lending silos? normally
one is called as #lending silo and other as storage silo. The
homogeni&ation process starts during the filling of #lending silo.
/fter filling the #lending silo" homogeni&ation process continues for
a#out one hour. Then it is discharged to the storage silo normallylocated at the #ottom of the #lending silo" where it is homogeni&ed
continuously and e$tracted for kiln feed. -atch type homogeni&ation
is applied in cases where the 'uality of the raw material widely
fluctuates and in relati,ely long time inter,als.
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R!le !f 7lending 3il! in ?uality C!ntr!l !f Raw Mi;
-lending silos ha,e a ma%or role in achie,ing uniform and consistent
'uality of raw mi$" which is essentially re'uired for getting ma$imum
output from the kiln and optimi&ing specific fuel and power
consumption. -lending silos" #y #lending process reduces the 'uality
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,ariation in the raw mi$. There are ,arious types #lending silos ha,ing #lending factor from 7:0 to 04:0. The #asic principle of #lending
process is one or com#ination of the following mechanisms.
3istri#ution of input raw meal at the #lending silo top.
Pneumatic dry #lending #y aeration of raw meal #y the aerationunits placed at the #ottom of silo.
*egmental aeration =octant or 'uadrant system> with difference in
the pressure of air supplied for aeration of ,arious segments for
thorough mi$ing of raw mi$.
Method of e$traction to kiln feed
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7lending 2a"t!r
+or calculation of #lending factor of a silo" input and output raw meal
samples are to #e collected in regular inter,als and to #e tested for
CaC(5 content.
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*ilo input samples to #e collected for a period of one theoretical filling
of silo with an inter,al not e$ceeding 0.4 hours and a minimum 96
samples are to #e collected. +or optimum #lending efficiency silo should
#e filled more than ;6B. The output samples are to #e collected at an
inter,al of 5 to 4 minutes after the input samples are collected and aminimum of 16 samples are to #e collected.
The standard de,iation of the input samples as well as output samples
are to #e calculated. The #lending factor is the ratio of standard
de,iation of input raw meal to standard de,iation of output raw meal.
The more the #lending factor" the #lending is more effecti,e.
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Fui&
0.3escri#e the o,er all processes found in cement industry
1.Dhat is raw material handling 3escri#e it in #lock diagram
5.)ist at least three types of crushers
9.There are two types of crushing . 3escri#e in detail
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4.Dhat is pre#lending7.Mention the e'uipments used for pre#lending
;.Dhat is stacking
8.ow many methods of stacking are there Mention stackers under
them.Drite all types of #all mill
06.Dhat is separator
00.Is tandem mill air swept mill
01.Dhat is the ad,antage of ,ertical roller mill o,er #all mill05.Hertical roller mill is air swept mill. True or +alse