Post on 23-Oct-2020
1
1.1 Beginning of Cement "Cement" as Portland Cement was first made in ashaft kiln using dry process and later in rotary kilns.
That "Slaked" lime hardens with water was wellknown and was used as "Mortar" with sand inconstruction industry before the advent of cement.
Some "Natural rocks" contained all ingredients likeCaO, SiO2, Al2O3 and Fe2O3 in approximately rightproportions so that they did not need any additions andwhen ground calcined and sintered in a kiln producedclinker which when ground with 5% gypsum producedwhat has come to be known as "Portland Cement".
Cement has hydraulic properties like slaked limeand hardens when mixed with water. Compressivestrength increases in time and reaches its practical toplimit after 28 days.
Mixing crushed stone, sand, cement and watermakes "Concrete". When hardened it is like rock andhence is called "Synthetic rock". It has similar propertiesof high compressive but low tensile strengths.
When concrete is poured around steel it becomesReinforced Cement Concrete - popularly known asRCC - and has high tensile strength also.
RCC has revolutionized construction industry andit is well nigh unimaginable to construct roads, dams,skyscrapers and silos and many other large and heavybuildings for residential or for industrial purpose withoutRCC.
Cement the main strength giving and bindingingredients is thus an all-important part of RCC andthus plays a vital role in the progress and developmentof a nation.
At present there is no substitute for cement.Hence, it will continue to play an all-important role inconstruction industry.
Yardsticks like inter alia per capita consumption ofsteel, power and cement are used to indicate state ofdevelopment of countries. Advanced and developedcountries have per capita consumption of cement of400-500 kgs. As against it, in India per capitaconsumption of cement is only about 195/200 kgs.
1.2 Making CementCement Industry started in a very small way, first asshaft kilns using dry process.
When it was found that the proper composition ofraw mix required to making good quality clinker almostalways needed, additions or correcting materials tocompensate for constituents like Silica, Alumina andIron Oxides, it became necessary to "Blend" theconstituents after "Grinding".
Blending was then more convenient in wet stage inthe form of slurry.
By this time Rotary Kiln had come to be used tomake Cement. It would conveniently receive slurry aswell. Thus process of cement making changed fromDry to Wet.
1.3 Dry to Wet to DryProcess of Manufacture
Wet Cement plants continued to grow in number andsize and wet process was the predominant process ofmanufacture of cement till 1950 or so. It continued tobe the dominant process in India for another twodecades.
CHAPTER 1
OVERVIEW OF MANUFACTURE OF CEMENT
Section 1. BASICS2
Wet process was simple and required less processcontrol and instrumentation and manpower. But itconsumed a large quantity of water and also heat energyin drying the slurry.
As fuel costs rose, alternative processes wereinvestigated to reduce water content of slurry andthereby fuel consumption.
1.4 Semi-dry ProcessThus came into use 'semi-dry' process which neededonly 8-10% water compared to 35-36% for wet slurry.Raw materials were ground and blended dry. Waterwas added to dry raw mix in a revolving pan to makenodules. The nodules were dried on a travelling gratepreheater before feeding them to a rotary kiln or to ashaft kiln.
1.4.1 V. S. KilnsVertical Shaft Kilns also came to be developed forcapacities up to 300 tpd (in Europe). They needed lowvolatile fuels like coke breeze.
1.5 Dry ProcessWhen wet process plants had reached their peakcapacity of 750-1000 tpd, developments in processesand machinery took place that once again changedthe course of cement making.
1.6 Suspension Preheaters In early 50s of the 20th Century, an epoch makingconcept was developed - that of Suspension Preheater.
The suspension preheater, with rotary kiln and gratecooler formed the heart of the cement plant and 'dryprocess' came to be adopted fast and number of wetprocess plants and semi dry process plants declined.
Even in India, which had predominance in wetprocess plants in numbers and capacity as late assixties, the percentage has decreased to less than 3% now.
1.7 Vertical Mills and CalcinersOther epoch making developments took place in 70s.They were using Vertical mills for grinding rawmaterials and coal and development of calciners whichcalcined raw meal before it entered the kiln. With acalciner, output of the same kiln could be increased byabout two and a half times.
Vertical mills have also came to be used for grindingcement clinker and slag.
Roller Presses are also now part of grinding syatemsThese two developments gave tremendous boost
to the size of the plant and also to economies in powerconsumption.
1.8 Benchmarks in Manufacture of CementProgress in making cement described above has beenshown in Table 1.1.1 and pictorially in Figs. 1.1.1(a),1.1.1(b) and 1.1.2
1.9 Fuel and Power ConsumptionFuel consumption was also steadily brought down from1500 Kcal/kg clinker for wet process kilns to 800 Kcal/kg clinker for dry process kilns with 4 stage preheaterand grate cooler. This has further come down to lessthan 700 Kcal/kg by using 6 stage preheaters.
Power Consumption has come down to 85-90 Kwh/Ton.
1.10 Green CementCement industry is now conscious of the emission ofgreen house gases emitted in the process of makingcement. Green house gases cause global warming.
Cement Industry is therefore taking steps to reducethese emissions. Therefore it makes ' blended cements'like Pozzolana cement (PPC) and slag cement ( BFSC)wherever possible. It also uses Alternate fuels toreduce emissions arising out of combustion.
Cement Industry in countries, like India which wereshort of power, had begun to install captive power plantsto ensure continuity of power. This is taken one stepfurther by using waste heat in exit gases from kiln andcooler to generate power.
These new developments have been dealt with inthis new edition to the extent cement plant engineersare commonly required to deal with them.
1.11 Differences in ProcessesDifferences in various processes of making cementand equipment used therein have been brought outin Tables 1.1.2 and 1.1.3 and in Fig. 1.1.2.
1.12 Size of the PlantFrom beginning with a 20-30 t.p.d. capacity, individualkilns have gone up in size upto 7500-10,000 tpdcapacity. Plants of 3-4 mtpa capacity in one place havealso become common.
Overview of Manufacture of Cement 3
Fig.
1.1
.1 (a
)B
ench
mar
ks in
man
ufac
ture
of c
emen
t.
Section 1. BASICS4
Fig.
1.1
.1 (b
)B
ench
mar
ks in
man
ufac
ture
of c
emen
t.
Overview of Manufacture of Cement 5
BenchmarksKilns Shaft kiln-Rotary Kiln - Wet - Long dry - Short - Semi dry and Dry
preheater kilnsCoolers Rotary Cooler – planetary cooler;
Traveling and Reciprocating grate coolers;Static grate, pendulum coolers and cross bar coolers
Preheaters Calciners in wet kilns, traveling grate preheaters;Suspension preheaters 4 – 6 stages.
Mills Ball and tube mills – mills with slide shoe bearings;Vertical ring and roller mills;
Roller press and ball mill combinations;Horizontal Roller mill
Blending Slurry blending – slurry mixer;Air merge blending – batch and continuous
Classifiers Wet classifiers;Dry classifiers- grit separators, mechanical air separators;
High efficiency separatorsCrushers Jaw, Hammer, Roll and Impact, mobile and semi mobile
crushersPacking machines Stationary – rotary – rotary electronic
Calciners In and off line; spouted bed, fluidized bed and many othersDespatches Mechanized-automated loading of bagged cement;
Bulk cement by road and rail and seaDust collectors Cyclones; poly and multiclones;
Bag filters- glass bag filters;Gravel Bed filters;
Electrostatic Precipitators
Table 1.1.1 Benchmarks in manufacture of cement.
The trend even in India is to go in for large plantsto avail of economies of scale which can be achievedby using machineries (Vertical Mills, ESPS, etc.) whichare suitable for and affordable by large plants.
The days of small plants and particularly those ofVSKs are over and they would not be considered forany future cement projects.
1.13 Sizes of Cement Plants in IndiaEven in conventional plants using rotary kilns, therewas a distinction.
1. Mini Plants of capacity - 300 tpd - to start with-but expanded to 1000-1200 tpd capacity byinstalling calciners
2. Large Plants of capacity - 600 tpd and aboveearlier, 3000 tpd and now to 10000 tpd above
Thus as far as process and types of machinery usedare concerned, the distinctions between large and smallplants have almost blurred. New projects are almostinvariably for dry process plants of +1.0 MTPAcapacity.
1.13.1 Large Cement PlantsThere are already about 183 cement plants of +1MTPA capacity. Average capacity per plant is 1.7mtpa. Total installed capacity is 480 mtpa.
Section 1. BASICS6
Tab
le 1
.1.2
Con
td...
.
Tabl
e 1.
1.2
Bas
ic D
iffer
ence
s be
twee
n Va
rious
Pro
cess
es o
f Man
ufac
ture
of C
emen
t.
Sr. N
o.S
ectio
nW
etS
emi
Wet
Sem
i D
ryD
ryD
ry w
ithca
lcin
er
(A)
Raw
mat
eria
l pr
epar
atio
n
1.C
rush
ing
Com
mon
to a
ll pr
oces
ses;
mac
hine
ry s
elec
ted
depe
nds
on s
ize
of p
lant
and
pro
perti
es o
f sto
ne
2.G
rindi
ngW
et g
rindi
ng in
bal
l mill
sD
ry g
rindi
ng; d
ryin
g du
ring
grin
ding
; mos
tly in
clo
sed
som
etim
es i
n cl
osed
circ
uit;
circ
uit;
usin
g ki
ln g
ases
for
dry
ing.
prod
uct s
lurr
y w
ith 3
5-40
% w
ater
ball
mill
s, v
ertic
al m
ills
and
rolle
r pr
ess
in h
ybrid
grin
ding
prod
uct d
ry r
aw m
eal w
ith le
ss th
an 1
% m
oist
ure
3.H
omog
enis
ing
wet
, air
and
mec
hani
cal a
gita
tion
fluid
isat
ion
tech
inqu
es fo
r bl
endi
ng d
ry p
ulve
rised
raw
mea
lpr
oduc
t ble
nded
slu
rry
wth
35
% w
ater
batc
h or
con
tinuo
us b
lend
ing;
cont
inuo
us b
lend
ing
will
be p
rece
ded
by p
reho
mog
enis
ing
in s
tock
pile
s;pr
oduc
t dry
ble
nded
raw
mix
4.K
iln fe
edsl
urry
with
~ 3
4 %
eith
er e
xtru
ded
pelle
ts w
ith 8
-10%
dry
pulv
eris
ed ra
w m
eal f
ed th
roug
hm
oist
ure
pelle
ts w
ith 1
5%%
moi
stur
evo
lum
etric
or g
ravi
met
ic fe
eder
ssy
nchr
onis
ed w
ithm
oist
ure
or,
dry
kiln
raw
mea
l drie
din
flas
h dr
yer
Overview of Manufacture of Cement 7
Sr. N
o.S
ectio
nW
etS
emi
Wet
Sem
i D
ryD
ry
Dry
with
c
alci
ner
(B)
Pyro
proc
essi
ng
1.dr
ying
in k
ilndr
ying
of
pel
lets
dryi
ng o
f nod
ules
preh
eatin
g in
kiln
p
rehe
atin
g ou
tsid
e2.
preh
eatin
gin
kiln
in tr
avel
ling
grat
e pr
ehea
ter
for
long
dry
kiln
k
iln in
dry
pre
heat
erpr
ehea
ting
in p
rehe
ater
k
ilns;
mos
tly
cyc
lone
pre
heat
ers
3.ca
lcin
ing
in k
ilndi
ssoc
iatio
n of
CO
2 be
ginn
ing
at ~
600
oC
and
com
plet
ing
at ~
950
oC
in k
ilnla
rgel
y in
kiln
partl
y in
pre
heat
er
alm
ost
tota
lly o
utba
lanc
e in
kiln
o
f kiln
in c
alci
ner
4.si
nter
ing
f
orm
atio
n of
clin
ker
at 1
250-
1450
oC
in k
iln
5.cl
inke
r co
olin
g
co
olin
g of
clin
ker
to 6
5- 1
50 o
C c
omm
on to
all
proc
esse
s
now
mos
tly r
ecip
roca
ting
grat
e co
oler
s w
ith v
aria
tions
like
sta
tic g
rate
, co
ntro
lled
flow
and
pen
dulu
mty
pe a
re u
sed
Section 1. BASICS8
Sr. N
o.Pr
oces
sW
etSe
mi W
etSe
mi D
ryDr
yD
ry w
ith C
alci
ner
1.
crus
hing
com
mon
to a
lltw
o st
age
crus
hing
for b
all m
ills;
sin
gle
stag
e cr
ushi
ng fo
r Ver
tical
mill
s an
d R
olle
r Pre
sses
Jaw
cru
sher
– H
amm
er c
rush
er c
ombi
natio
n fo
r tw
o st
age
crus
hing
Impa
ctor
s –
sing
le o
r tw
o st
age
for s
ingl
e st
age
crus
hing
sem
i mob
ile, m
obile
cru
sher
s fo
r lar
ge p
lant
s
2.
grin
ding
bal
l mill
ope
n or
clo
sed
circ
uit
ba
ll m
ills-
air-
swep
t or b
ucke
t ele
vato
r in
clos
ed c
ircui
t
a
utog
enou
s m
ill
w
ith c
onve
ntio
nal o
r hig
h ef
ficie
ncy
sepa
rato
rs
v
ertic
al ro
ller m
ills
- vrm
s w
ith e
xter
nal c
ircui
t
an
d hi
gh e
ffici
ency
sep
arat
ors
ro
ller p
ress
and
bal
l mill
in v
ario
us c
ombi
natio
ns
3.
preh
omog
enis
ing
st
acke
r rec
laim
er s
yste
ms
used
for p
reho
mog
enis
ing
of li
mes
tone
s an
d co
al d
urin
g bu
ildin
g up
of a
nd
ext
ract
ion
from
sto
ck p
iles
4.
hom
ogen
isin
gpn
eum
atic
and
mec
hani
cal a
gita
tion
b
lend
ing
syst
ems
base
don
‘flui
disi
ng’ t
echn
ique
s
slu
rry
mix
ers
b
atch
and
con
tinuo
us b
lend
ing
syst
ems
5.
kiln
feed
met
erin
g of
slu
rry
filte
r pre
ss a
ndno
dulis
er w
ithw
eigh
feed
er o
r sol
ids
flow
met
ers
sync
hron
ised
with
disa
gglo
mer
ator
varia
ble
spee
d
w
ith p
refe
eder
ski
lnan
d fla
sh d
ryer
or fi
lter p
ress
and
extru
der
Tab
le 1
.1.3
Con
td...
.
Tabl
e 1.
1.3
Diff
eren
t typ
es o
f Equ
ipm
ent u
sed
in v
ario
us P
roce
sses
.al
so s
ee F
ig. 1
.1.2
Overview of Manufacture of Cement 9
Sr. N
o.Pr
oces
sW
etSe
mi W
etSe
mi D
ryDr
yD
ry w
ith C
alci
ner
6.
preh
eate
rca
lcin
ator
trave
lling
grat
etra
vellin
g gr
ate
susp
ensi
on p
rehe
ater
or s
haft
kiln
preh
eate
r or
preh
eate
r or
susp
ensi
onsu
spen
sion
preh
eate
rpr
ehea
ter o
rsh
aft k
iln
7.
calc
inin
gca
lcin
ers
in o
r off
line
8.
clin
kerin
gro
tary
long
kiln
rota
ry s
hort
kiln
rota
ry s
hort
kiln
rota
ry s
hort
kiln
rota
ry s
hort
kiln
shaf
t kiln
rota
ry lo
ng k
iln
9.
clin
ker c
oolin
g c
omm
on to
all;
rota
ry a
nd p
lane
tary
coo
lers
for s
mal
l pla
nts
– no
w a
lmos
t dis
card
ed;
rec
ipro
catin
g gr
ate
cool
ers
of v
ario
us d
esig
ns li
ke s
tatic
gra
te, c
ontro
lled
flow
gra
te
p
endu
lum
coo
ler
cros
s ba
r coo
ler e
tc.
Follo
win
g pr
oces
ses
are
com
mon
to c
emen
t pla
nts
of a
ll ty
pes
diffe
ring
in s
cale
acc
ordi
ng
to
size
of p
lant
10.
coal
grin
ding
ba
ll or
ver
tical
mill
s w
ith d
ryin
g fa
cilit
ies
11.
cem
ent g
rindi
ng
b
all m
ills
in c
lose
d ci
rcui
t and
hig
h ef
ficie
ncy
sepa
rato
rs
verti
cal m
ills
with
ext
erna
l circ
uit a
nd h
igh
effic
ienc
y se
para
tors
ro
ller p
ress
and
bal
l mill
and
hig
h ef
ficie
ncy
sepa
rato
rs in
a n
umbe
r of w
ays
12.
cem
ent p
acki
ng
rota
ry o
r sta
tiona
ry p
acke
rs to
pac
k ce
men
t in
jute
/pap
er b
ags
loos
e ce
men
t
ce
men
t sen
t in
bulk
in b
ulk
carr
iers
by
road
bys
hips
etc
.
13.
cem
ent
by
road
or r
ail o
f bag
ged
cem
ent u
sing
sem
i or f
ully
mec
hani
sed
load
ing
mac
hine
sde
spat
ches
a
lso
by s
hip
load
s fo
r exp
ort
Section 1. BASICS10
Fig.
1.1
.2 E
quip
men
t use
d in
man
ufac
ture
of c
emen
t.