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01 Cement Plant Overview

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OVERVIEW CEMENT PRODUCTION
CEMENT PRODUCTION
OVERVIEW
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Cement Plant overview
Quarry types
Raw material composition
Raw Material Grinding
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Burning-Process in kiln
Kiln types
Clinker Phases
Clinker Cooling
 Finish grinding
 Gypsum
 Conveying Systems
2
CEMENT PRODUCTION
„common“ cement plant
Preheater
Raw material storage and homogenisation
Raw material
from Quarry
Dispatch
3
RAW MATERIAL
QUARRY
Common quarry
Open pit
HC, Brevik (Norway)
Mine 330 m below see
1.2 Mt cement capacity
4
 Limestone: Calciumcarbonat (CaCO3)
 Clay: Aluminiumoxide and Siliciumoxide (Al2O3, SiO2)
 Ironoxide (Fe2O3)
LH, Lägerdorf (Germany)
Chalk (CaCO3), 23% humidity
1.4 Mt cement capacity
RAW MATERIAL
COMPOSITION
CaCO3
Correction materials are added if necessary to achieve the
desired composition (CaCO3, SiO2, Al2O3, Fe2O3).
Clinker phases
Formula
Short-cut
Tri-Calcium-Silicate
3 CaO SiO2
C3S
ø
63
Di-Calcium-Silicate
2 CaO SiO2
C2S
ø
16
C4AF
ø
8
C3A
ø
11
Tetra-Calcium-Alumino-Ferrite 2 CaO (Al2O3, Fe2O3)
Tri-Calcium-Aluminate
Al2O3, SiO2
5
3 CaO Al2O3
Content [M-%]
RAW MATERIAL
RAW MATERIAL GRINDING
Dry grinding process
1. Homogenization of raw material in
special storehouse.
1. Raw material are ground with water
in ball mills
2. Raw materials are ground in vertical
roller mills or ball mills (< 90µm).
2. Resulting “slurry” is stored in huge
basins, where it is continuously mixed
before being fed to the kiln.
(homogenization).
3. Homogenization of raw meal in silo,
before being fed to the kiln.
1
6
Wet grinding process
2
3
1
2
RAW MATERIAL / RAW MEAL
HOMOGENIZATION DRY GRINDING PROCESS
The main principle is to form layers of the raw
material in the longitudinal stockpile from the
mix.
When the reclaimer slices the pile from the
edge, the slice cuts through all the layers and
ensures each layer has the right proportion
according to the target chemistry.
The Homogenizing Silo of raw meal should be
at least 50-70% full of material at all times.
The aeration at the silo bottom should occur
adequately to fluidize the material.
The extraction rate and sequence is regulated
to bring about maximum mechanical
movement of layers of material.
http://pecconsultinggroup.com/newsflash/
homogenization-strategy-in-the-cement-industry
7
CLINKER PRODUCTION
REACTIONS IN THE KILN
1. Calcination:
At approximately 800⁰C, the calcium carbonate
(limestone) is burnt to Calcium oxide (lime):
CaCO₃ → CaO + CO₂
2. Clinker formation:
The lime and the other raw materials melt and
react at temperatures of 1500⁰C to form calcium
silicates and calcium aluminates, the main
components of clinker.
 Total 0,8 ton CO2/ton clinker
8
CLINKER PRODUCTION
BURNING – PROCESS TYPES
Dry process ()
 raw materials are fed to the kiln
in a dry state
 ~ 3’000 MJ thermal energy
Wet process ()
 raw material are fed into the kiln
in form of a "slurry“.
 Up to 6’000 MJ thermal energy
per ton of clinker
per ton of clinker
 Characteristic sign:
 Characteristic sign:
cyclone preheating tower
very long kilns
Slurry bassin
9
long kiln
CLINKER PRODUCTION
OVERVIEW WET PROCESS
10
CLINKER PRODUCTION
OVERVIEW DRY PROCESS
 Hot air from the kiln is used in cyclone pre-heater to drive off moisture and increase temperature of
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the raw meal.
Heated raw meal enters the kiln with a calcination degree of approx. 50%.
A higher calcination degree of up to 90% is achieved with pre-calciners (second flame).
 Kilns are 6-8 m in diameter and 60 m to 100 m long. They are set at a slight inclination
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11
and rotate 1 to 3 times per minute.
Burner is located at the lower end.
Raw materials move toward the flame.
CLINKER PRODUCTION
BURNING – PROCESS TYPES
Lepol kiln (semi-dry)
 Dry ground raw material is formed with the help of water to pellets
 The pellets are preheated on the grate preheater with exhaust air from kiln
Pellet producer
https://www.hc-museum.de/de/video-vomkalkstein-zum-zement
6’15
12
CLINKER PRODUCTION
REACTIONS IN THE KILN
13
CLINKER PRODUCTION
KILN DUST AND BY-PASS DUST
 Cement kiln dust is the dust which passes out of the
top of the preheater with the exhaust gases, or
more typically out of the back of a long wet or long
dry kiln.
 Parts of the raw material, partially processed feed
and components of the final product are entrained
in the combustion gases that flow countercurrent to
the feed.
 These particulates and combustion gas precipitates
are collected in a filter.
Alternative fuels
Many facilities return all or a significant portion of
the CKD to the kiln as a feedstock
generate BPD and CKD
which is loaded with
 Bypass dust is the dust that is drawn out of the kiln
inlet when some kiln exit gases are extracted
Chlorides, Sulfates etc.!
between the kiln and preheater to break the cycle
of volatile species between the kiln and preheater.
The bypass is therefore positioned between the kiln
inlet and the preheater.
14
CLINKER PRODUCTION
OVERVIEW COOLING
Target
 cool the material as quickly as
possible below 800°C
 cause solidification of the clinker
 freeze composition of clinker phases
 maintain the C3S content
(high reactivity + easy grindable)
 Slow cooling leads to chemical
changes: C3S reacts back to C2S
discharged from lower end of kiln
15
CLINKER PRODUCTION
COOLER TYPES
Grate-Cooler
 most commonly used
 very quick cooling down to 100⁰C
 Efficient heat recovery
Satellite/Planetary-Cooler
 cooling tubes around the kiln end
 higher remaining temperature of
clinker (slower cooling)
 Lower heat recovery
CLINKER PRODUCTION
GRATE COOLER
Clinker
Return of heat into
kiln ventilation air
Adjustable airstream
 Spread the
clinker
 Initial cooling
 clinker moves over grating
system
 adjustable cooling fans
 Fine-adjustment of
temperature
 crusher
CLINKER PRODUCTION
GRATE COOLER
Cross bar cooler
CLINKER PRODUCTION
VIEW INTO A GRATE COOLER
CLINKER PRODUCTION
SATELLITE COOLER
 Hot clinker leaves kiln and falls into the cooling
tubes at the kiln end
(10 - 11 tubes around the circumference).
 Increased surface leads to a cooling effect.
Lifter pattern in the satellite tubes cause
turbulence and promote cooling air contact.
 For kilns up to 3000 t/day
Dis-advantage:
 only as much cooling air possible as required
for burning because all air has to pass the kiln
 Slow cooling
Advantage:
 no need for de-dusting equipment
Airstream
Clinker
Ambient Air
CLINKER PRODUCTION
PHASE COMPOSITION
Clinker
phases
Formula
Tri-Calcium3 CaO SiO2
Silicate
Di-CalciumSilicate
2 CaO SiO2
TetraCalcium- 2 CaO (Al2O3,
AluminoFe2O3)
Ferrite
Tri-Calcium3 CaO Al2O3
Aluminate
Free Lime
21
CaO
Short-cut
C3S
C2S
C4AF
C3A
Content [M-%]
high
80
average
63
low
45
high
32
average
16
low
0
high
14
average
8
low
4
high
15
average
11
low
7
high
3
average
1
low
0,1
C4AF
10%
C3A
10%
C2S
20%
C3S
60%
C4AF
10%
C3A
10%
C2S
20%
C3S
60%
Compressive Strength [N/mm²]
CLINKER PRODUCTION
PHASE COMPOSITION AND STRENGTH
C3S
C2S
C3A
C4AF
Age [day]
22
CEMENT PRODUCTION
FINISH GRINDING
Grinding of clinker in a mill to obtain fine powder
Addition of:
 Gypsum (setting regulator)
 Secondary cementitious materials (SCM)
 Kiln dust, by-pass dust
 Chromium reducers
CEMENT HYDRATION
SET REGULATION WITH GYPSUM
 Without set regulation:
 C3A + water → Tetracalciumaluminiumhydrate
 Big, leaf-shaped crystals. Bridge building microstructure.
 Immediate reaction and setting
 With Gypsum:
 On C3A surface a thin cover of calciumaluminatsulfat (Ettringit) is formed
 This film delays the reaction of C3A with water
 High Reactivity of C3A
 High Fineness of cement
 High temperature at application
24
→ more gypsum
CEMENT HYDRATION
MAIN TYPES OF GYPSUM
 Gypsum:
CaSO4 ∙ 2H2O
Natural or from flue gas desulfuriation FGD
 Anhydrite:
CaSO4
Natural or by dehydration of FGD
 Hemihydrate: CaSO4 ∙ ½H2O
Dehydration of Gypsum at > 120⁰C:
CaSO4 ∙ 2H2O → CaSO4 ∙ ½H2O + 1 ½H2O
 Dehydration can take place in mill
 Each type of «Sulfate» has different solubility
25
CEMENT HYDRATION
SOLUBILITY OF GYPSUM
12
solubility [g CaSO4/l]
10
Optimum for cement:
Blend of gypsum and Anhydrit
β-hemihydrate
8
6
α-hemi-hydrate
4
anhydrite II
2
gypsum
Reality:
 Availability
 Economy
0
0
26
20
40
60
80
100
temperature [°C]
120
140
160
180
CEMENT PRODUCTION
FINISH GRINDING - OVERVIEW MILL TYPES
The cooled clinker is blended with certain additions and ground into a fine powder
to make cement.
There are mainly 4 different Milling Systems used:
 Ball mill
 Roller-Press mill
 Vertical Roller Mill
 Horizontal Roller Mill
CEMENT PRODUCTION
CONVEYING SYSTEMS
Air Slide
Conveying the cement powder in an air
Stream (low pressure)
Screw-conveyor
Conveying the cement powder in a
closed tube with a turning Screw
Conveyor-Belt
Conveying the cement powder on an
open Belt
CEMENT PRODUCTION
WORKING PRINCIPLE AIR SLIDE
Cement conveying
in air flow
Membrane to separate air & cement flow
Air pressure
QUESTIONS?
• Where can we support the cement plant?
• How much CO2 is produced per ton of clinker?
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