Cement preparation

1. Lecture # 2
Manufacturing process
of Cement

3. Traditional Process of Cement
Manufacturing
1- Aspdin mixed and ground hard limestone and
finely divided clay into a slurry
2- The slurry was calcinated in a furnace till CO₂ was
expelled
3- The calcinated mixture was then ground to a fine
powder perhaps at a lower temperature than the
clinkering temperature by Aspdin.

4. Later in 1845 Isaac Charles Johnson burnt a
mixture of clay and chalk at clinkering
temperature to make better cement .

5. Modern ways to Manufacture Cement
The process is divided into 4 main parts
– Quarrying and Grinding the raw materials
– Mixing them in a intimately in certain proportions
depending upon their purity and composition
– Burning the proportioned mix in a kiln at 1300 ⁰C
to 1500 ⁰C also called clinkering
– Grinding of clinker and adding of gypsum

6. 1-Quarrying of Raw materials
– The raw materials required are calcareous
materials like chalk or limestone and argillaceous
materials such as clay, marble or shale
– Local availability of raw material is an important
concern setting up a cement factory in order to
reduce the transportation cost .
The quarried materials are crushed, then
mixed at the plant to be fed to the kiln

7. 2-Mixing and storage of feed
Mixing is carried out by the either of the
following processes
– Wet Process
– Dry Process

8. i) Wet Process
The materials in the wet process are mixed with a
water content of about 35% to 50%

10. ii) Dry Process
In this process the materials are mixed in the
powdered form using compressed air.
The powdered material behaves like a fluid
when exposed to compressed air in a chamber
and mixing becomes possible
This is the most widely used method in the
recent years
It reduces the fuel consumption as the slurry
is already dry unlike wet process.

12. Burning or clinkering (wet process)
• A typical kiln is a large refractory lined steel tube
165 m long inclined to the
horizontal with capacity of 1050 tonnes/day
• At the lower end of tube there is a burner and
raw meal is fed from the other end
• The kiln rotates slowly at about 20-86 rph passing
material to the lower end
• The water from the slurry needs to be driven off
prior to the calcinating process

14. Zone 1: 0 - 35 min, temp is 800 – 1100 C o
Decarbonation. Formation of 3CaO•
Al2O3(C3A) above 900 Co. Melting of fluxing
compounds Al2O3 and Fe2O3.
heat
CaCO3 → CaO + CO2

15. Zone 2: 35 - 40 min, 1100 – 1300 Co
Exothermic reactions and the formation of secondary
silicate phases as follows:
heat
2CaO + SiO2 → 2CaO•SiO2

16. Zone 3: 40 - 50 min, 1300 - 1450 – 1300 Co
Sintering and reaction within the melt to form ternary silicates
and tetracalcium alumino-
ferrates:
heat+time
2CaO.SiO2 + CaO → 3CaO•SiO2
heat+time
3CaO.Al2O3 + CaO + Fe2O3 → 4CaO•Al2O3•Fe2O3

17. Zone 4: 50 - 60 min, 1300 – 1000 Co
Cooling and crystallisation of the various mineral phases formed
in the kiln.
The cooler :
Immediately following the kiln is a large cooler designed to drop
the temperature of the
clinker (as the fused material is now called) from 1000o
C to 150 Co. This is achieved by
forcing air through a bed of clinker via perforated plates in the
base of the cooler. Like cement, the clinker will react with water
and harden, but because it is
composed of 1-3 cm diameter fragments it is too coarse to be
used.

18. Cement milling
To produce the final product the clinker is mixed with gypsum
(CaSO4•2H2O), which is
added as a set retarder, and ground for approximately 30
minutes in large tube mills. The
cement flows from the inlet to the outlet of the mill (a rotating
chamber), being first ground
with 60 mm then 30 mm diameter steel balls. The first grinding
breaks up the material and
the second grinds it to a fine powder.