Cement Manufacturing Process
Cement
manufacturing process involves various raw materials and processes. Cement is a
greenish grey coloured powder, made of calcined mixtures of clay and limestone.
When mixed with water becomes a hard and strong building material.
It
was first introduced by a British stone mason, Joseph Aspdin in 1824, who
cooked cement in his kitchen. He heated a mixture of limestone and clay powder
in his kitchen, and grind the mixture into powder creating cement, that hardens
when mixed with water.
Cement
is first used in the tunnel construction in the Thames River in 1828.
Manufacturing Process of Cement
There
are four stages in this whole process.
Ø Mixing of raw material
Ø Burning
Ø Grinding
Ø Storage and packaging
Mixing of raw material
Calcium,
Silicon, Iron and Aluminium are the raw materials used majorly in manufacture
of cement. There are two methods of mixing. Dry Process and Wet Process.
Ø Dry Process: The both calcareous and argillaceous raw materials
are firstly crushed in the gyratory crushers to get 2-5cm size pieces
separately. The crushed materials are again grinded to get fine particles into
ball or tube mill. After screening this finely grinded materials are stored in
hopper. Then powdered minerals are mixed and dry raw mix is stored in silos and
ready to be sent into rotary kiln.
Ø Wet Process: In this process first raw materials are crushed and
made into powdered form and stored in silos. Then clay is washed and sticky
organic matters are removed. Then powdered limestone and water washed clay are
sent to flow in the channels and transfer to grinding mills where they are
completely mixed and the paste is formed. Then grinding process is done in a
ball or tube mill or even both. Then the slurry is led into collecting basin
where composition can be adjusted. The slurry contains around 38-40% water that
is stored in storage tanks and kept ready for the rotary kiln.
Burning of Raw Materials
This
process is carried out in rotary kiln while the raw materials are rotated at
1-2rpm at its longitudinal axis. The raw mix of dry process of corrected
slurry of wet process is injected into the kiln from the upper
end. Powdered coal or oil or hot gases are used to be heated up from
the lower end of the kiln so that the long hot flames is produced. The lower
part (clinkering zone) have temperature in between 1500-1700 degree Celsius
where lime and clay are reacts to yielding calcium aluminates and calcium silicates.
This aluminates and silicates of calcium fuse to gather to form small and hard
stones are known as clinkers. The size of the clinker is varies from 5-10mm.
The clinker coming from the burning zone are very hot. To bring down the
temperature of clinkers, air is admitted in counter current direction at the
base of the rotary kiln. The cooled clinkers are collected in small trolleys.
Grinding of clinkers
The
cooled clinkers are received from the cooling pans and sent into mills. The
clinkers are grinded finely into powder in ball mill or tube mill. Powdered
gypsum is added around 2-3% as retarding agent during final grinding. The final
obtained product is cement that does not settle quickly when comes in contact
with water. After the initial setting time of the cement, the cement becomes
stiff and the gypsum retards the dissolution of tri-calcium aluminates by
forming tricalciumsulfoaluminate which is insoluble and prevents too early
further reactions of setting and hardening.
Storage and packaging
The
grinded cement is stored in silos, from which it is marketed either in
container load or 50kg bags.
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Blog
written by
Shruti Doshi
Technical
Officer – Sanghi Cement & Blogger
Blog
Managed by
Nirav
Pandya
Digital
Marketing Officer – Sanghi Cement
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