Transcript project poc - Swedish College Of Engineering & Technology

IN THE NAME OF ALLAH ALMIGHTY,
THE MOST MERCIFUL,
THE MOST BENEVOLENT,
THE CREATOR OF ALL THE WORLDS
THE PRESERVER
SWEDISH COLLEGE OF ENGINEERING AND TECHNOLOGY
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Manufacturing of Cement
SWEDISH COLLEGE OF ENGINEERING AND TECHNOLOGY
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Submitted To:
Engr. Dr. Ayub Elahi
Submitted By:
MUHAMMAD BIN ANWAR
TALHA AKBAR BUTT
FARHAN SAJID
RANA WASEEM SAEED
MUHAMMAD RIZWAN TAHIR
SWEDISH COLLEGE OF ENGINEERING AND TECHNOLOGY
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01
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INTRODUCTION
 Definition:
“Cement is a crystalline compound
of calcium silicates and other calcium
compounds
having
hydraulic
properties”
(Macfadyen, 2006).
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 Cement is made primarily from a calcareous material, such as limestone or chalk,
and from alumina and silica found as clay or shale. Marl, a mixture of calcareous
and argillaceous materials, is also used.
 The process of manufacturing of cement consists essentially of grinding the raw
materials, mixing them intimately in certain propositions and burning in a large
rotary kiln at a temperature of up to about 1450 0 C when the material sinters and
partially fuses into the balls known as clinker. The clinker is cooled and ground to a
fine powder, with some gypsum added, and the resulting product is the commercial
Portland cement so widely used throughout the world.
 The mixing and grinding of the raw materials can be done either in water or in a
dry condition; hence the name ‘wet’ and ‘dry’ processes. The actual methods of
manufacture of cement depend also on the hardness of materials used and on
their moisture content.
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Manufacture of Portland
cement
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Raw materials
Preparation of materials
Burning
Final processing
Quality control
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RAW MATERIALS
The fundamental chemical compounds to produce cement clinker are:
Lime (CaO)
Silica (SiO2)
Alumina (Al2O3)
Iron Oxide (Fe2O3)
Raw materials used in the production of clinker cement
Fly ash: by-product of burning finely grounded coal either for industrial application or in
the production of electricity
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Raw materials
 Limestone (calcium carbonate) is a common
source of calcium oxide.
 Iron-bearing aluminosilicates are the most
common source of silica.
 Aluminum and iron oxides act as fluxing agents i.e.
lower fusion temperature of part of the raw mix to
a practical firing temperature
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Preparation of Materials
 Crush the materials and store them
 Blend the materials and grind them
 Store them and do final blending
 Blending – assure constant composition and
predictable properties.
 Wet, dry, processes.
 Burn the materials
 Grind, blend, and store the materials
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WET PROCESS
When chalk is used, it is finely broken up and dispersed in water in a wash mill;
this is a circular pit with revolving radial arms carrying rakes which break up the
lumps of solid matter.
The clay is also broken up and mixed with water, usually in a similar wash mill.
The two mixtures are now pumped so as to mix in predetermined proportions and
pass through a series of screens. The resulting cement slurry flows into storage
tanks.
When limestone is used, it has to be blasted, then crushed, usually in two
progressively smaller crushers, and then fed into a ball mill with the clay
dispersed in water. There the comminution of the limestone (to the fineness of
flour) is completed, and the resultant slurry is pumped into storage tanks.
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Raw materials are homogenized by crushing, grinding and blending
so that approximately 80% of the raw material pass a No.200 sieve.
The mix will be turned into form of slurry by adding 30 - 40% of
water.
It is then heated to about 2750 0 F(1510ºC) in horizontal revolving
kilns (76-153m) length and 3.6-4.8m in diameter.
The slurry, in its movement down the kiln, encounters a
progressively higher temperature.
At first the water is driven off and CO2 is liberated; further on, the
dry material undergoes a series of chemical reactions until finally, in
the hottest part of the kiln, some 20 to 30 percent of the material
becomes liquid, and lime, silica and alumina recombine.
The mass then fuses into balls, 3 to 25 mm (1/8 to 1 in.) in diameter,
known as clinker.
The clinker is then cooled and stored, after that its finish grinding is
done and It is stored in silos.
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CEMENT CLINKERS
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Natural gas, petroluem or coal are used for burning. High fuel requirement may
make it uneconomical compared to dry process.
Wet process is obsolete.
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DRY PROCESS
 Raw materials are homogenized by crushing, grinding and blending so
that approximately 80% of the raw material pass a No.200 sieve.
 The raw materials are crushed and fed in the correct proportions into a
grinding mill, where they are dried and reduced in size to a fine powder. The
dry powder called the ‘raw meal’ is then pumped to a blending silo, and final
adjustment is now made in the proportions of the materials required for the
manufacture of cement.
 In the dry process, the raw meal, which has a moisture content of about
0.2 percent, is passed through a pre-heater, usually of a suspension type; that
means that the raw meal particles are suspended in the rising gases. Here, the
raw meal is heated to about 800 0 C before fed into the kiln.
Mixture is fed into kiln & burned in a dry state.
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 This process provides considerable savings in fuel consumption and water usage but
the process is dustier compared to wet process that is more efficient than grinding.
 It is then heated to about 2750ºF (1510ºC) in horizontal revolving kilns (76-153m
length and 3.6-4.8m in diameter.
 In the kiln, water from the raw material is driven off and limestone is decomposed
into lime and Carbon Dioxide.
limestone
lime + Carbon Dioxide
 In the burning zone, portion of the kiln, silica and alumina from the clay undergo solid
state chemical reaction with lime to produce calcium aluminate.
silica & alumina + lime
calcium aluminate
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Burning process
 Sintering (become a coherent mass with no melting)
 Fusion (complete melting)
 Clinkering – only about ¼ of the charge is in the liquid state
 Kiln
 Long steel cylinder pipe
 Lined with refractory brick
 Inclined a few degrees
 Rotated at 60 to 200 rev/h
 Typically 6 m (20 ft) in diameter and 180 m (600 ft) long
 Time in the kiln from 2 h (wet process) to 1 h (dry process) or even (20
min) modern heat exchangers
 Four processes take place in the kiln
 Evaporation 240 to 450 °C
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Calcination 600 to 1100 °C
Clay decomposes (600 °C)
Limestone decomposes (700 °C) – CO2 driven off
Formation of initial compounds (1000 °C)
Initial formation of C2S (1200 °C), formation of calcium aluminates
and Ferrites
Formation of melt (flux compounds melt) (1350 °C)
Clinkering – charge temperature is 1400 to 1600 °C
Formation of C3S
Cooling
Rate of cooling significantly affects the reactivity of the final cement. Clinkers
should be cooled quickly to get high quality cement.
 Clinkers
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 The rotation and shape of kiln allow the blend to flow down the kiln,
submitting it to gradually increasing temperature.
 As the material moves through hotter regions in the kiln, calcium silicates
are formed.
 These products, that are black or greenish black in color are in the form of
small pellets, called cement clinkers.
 Cement clinkers are hard, irregular and ball shaped particles about 18mm in
diameter.
 On exit from kiln, regardless of the type of process, the clinker is cooled, the
heat being used to preheat the combustion air.
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 The cool clinker, which is characteristically black, glistering, and hard, is
interground with gypsum in order to prevent fresh setting of cement.
 The grinding is done in ball mill consisting of several compartments with
progressively smaller steel balls, sometimes preceded by passing through a roll
press.
 In most plants a closed-circuit grinding system is used; the cement discharged by
the mill is passed through a separator, fine particles being moved to the storage
silo by an air current, while the coarser particles are passed through the mill once
again.
 The performance of a ball mill can be improved by pre-grinding the clinker in a
horizontal impact crusher.
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 The cement clinkers are cooled to about 150ºF (51ºC) and stored in clinker
silos.
 When needed, clinker are mixed with 2-5% gypsum to retard the setting
time of cement when it is mixed with water.
 Then, it is grounded to a fine powder and then the cement is stored in
storage bins or cement silos or bagged.
 Once the cement has been satisfactorily ground, when it have as many as
1.1 × 1012 particles per kg (5 × 1011 per lb), it is ready for transport in bulk.
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 Less commonly, the cement is packed in bags or drums.
 However, some types of cement, such as white, hydrophobic, expansive,
regulated-set, oil-well, and high alumina, are always packed in bags or drums.
 A standard bag in the United Kingdom contains 50 kg (110 lb) of cement; a
US sack weighs 94 lb (42.6 kg); other bag sizes are also used. Bags of 25 kg are
becoming popular.
 Cement bags should be stored on pallets in a dry place.
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COMPARISON OF WET AND DRY PROCESS
 Except when the raw materials necessitate the use of the wet process, the
dry process is used now a days in order to minimize the energy required for
burning.
 Typically, the burning process represents 40 to 60 percent of the
production cost, while the extraction of the raw materials for the
manufacture of cement represents only 10 percent of the total cost of
cement.
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KILN
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Oxides composition of cement
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CEMENT SILOS
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THE CEMENT MANUFACTURING PROCESS
quarry
dumper
loader
Quarry face
1. BLASTING
2. TRANSPORT
storage at
the plant
crushing
conveyor
3. CRUSHING & TRANSPORTATION
1. BLASTING : The raw materials that are used to manufacture cement (mainly limestone and clay) are blasted
from the quarry.
2. TRANSPORT : The raw materials are loaded into a dumper.
3. CRUSHING AND TRANSPORTATION : The raw materials, after crushing, are
transported to the plant by conveyor. The plant stores the materials before they are
homogenized.
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THE CEMENT MANUFACTURING PROCESS
Raw grinding and burning
storage at
the plant
Raw mill
conveyor
Raw mix
1. RAW GRINDING
preheating
kiln
cooling
clinker
2. BURNING
1. RAW GRINDING : The raw materials are very finely ground in order to produce the raw mix.
2. BURNING : The raw mix is preheated before it goes into the kiln, which is heated by a flame that can
be as hot as 2000 °C. The raw mix burns at 1500 °C producing clinker which, when it leaves the kiln, is
rapidly cooled with air fans. So, the raw mix is burnt to produce clinker : the basic material needed to
make cement.
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THE CEMENT MANUFACTURING PROCESS
Grinding, storage, packing, dispatch
Gypsum and the secondary additives are added
to the clinker.
clinker
storage
Finish grinding
1. GRINDING
silos
dispatch
bags
2. STORAGE, PACKING, DISPATCH
1.GRINDING : The clinker and the gypsum are very finely ground giving a “pure cement”. Other secondary
additives and cementitious materials can also be added to make a blended cement.
2. STORAGE, PACKING, DISPATCH :The cement is stored in silos before being dispatched either in
bulk or in bags to its final destination.
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 In addition to the main processes, there are also processes of manufacture
of cement, of which one, using gypsum instead of lime.
 Gypsum, clay and coke with sand and iron oxide are burnt in a rotary kiln,
the end products being Portland cement and sulfur dioxide which is further
converted into sulfuric acid.
 In areas where only a small production is required or whole investment
capital is limited, a vertical kiln of the Gottlieb type can be used. This fires
nodules of raw meal and fine coal powder combined, and produces
agglomerated clinker which is then broken up. A single kiln, 10 m (33 feet)
high, produces up to 300 tonnes of cement a day.
 China uses several thousand of such kilns.
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