1 IN THE NAME OF ALLAH ALMIGHTY, THE MOST MERCIFUL, THE MOST BENEVOLENT, THE CREATOR OF ALL THE...

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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

2SWEDISH COLLEGE OF ENGINEERING AND TECHNOLOGY

Submitted To:

Engr. Dr. Ayub Elahi

Submitted By:MUHAMMAD BIN ANWAR 42TALHA AKBAR BUTT 08FARHAN SAJID 38RANA WASEEM SAEED 01MUHAMMAD RIZWAN TAHIR 34


INTRODUCTION

Definition: “Cement is a crystalline compound of calcium silicates and other calcium compounds having hydraulic properties” (Macfadyen, 2006).


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.


Manufacture of Portland cement

Raw materials Preparation of materials Burning Final processing Quality control


RAW MATERIALSThe fundamental chemical compounds to produce cement clinker are:

Lime (CaO) Silica (SiO2)Alumina (Al2O3) Iron Oxide (Fe2O3)

Fly ash: by-product of burning finely grounded coal either for industrial application or in the production of electricity

Raw materials used in the production of clinker cement


Raw materialsLimestone (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


Preparation of Materials

Crush the materials and store themBlend the materials and grind themStore them and do final blendingBlending – assure constant composition

and predictable properties.Wet, dry, processes.Burn the materialsGrind, blend, and store the materials


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.


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


Natural gas, petroluem or coal are used for burning. High fuel requirement may make it uneconomical compared to dry process.

Wet process is obsolete.


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.14SWEDISH COLLEGE OF ENGINEERING AND TECHNOLOGY

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


Burning processSintering (become a coherent mass with no melting)Fusion (complete melting)Clinkering – only about ¼ of the charge is in the liquid

stateKiln

Long steel cylinder pipeLined with refractory brickInclined a few degreesRotated at 60 to 200 rev/hTypically 6 m (20 ft) in diameter and 180 m (600 ft)

longTime 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


Calcination 600 to 1100 °C

Clay decomposes (600 °C)Limestone decomposes (700 °C) – CO2 driven offFormation 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 °CFormation of C3S

CoolingRate of cooling significantly affects the reactivity of the final cement. Clinkers should be cooled quickly to get high quality cement.

Clinkers


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.


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.


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.


KILN

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Oxides composition of cement


CEMENT SILOS

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THE CEMENT MANUFACTURING PROCESS

1. BLASTING : The raw materials that are used to manufacture cement (mainly limestone and clay) are blasted from the quarry.

Quarry face

1. BLASTING 2. TRANSPORT

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.

quarry

3. CRUSHING & TRANSPORTATION

2. TRANSPORT : The raw materials are loaded into a dumper.

crushing

conveyor

dumper

storage at the plant

loader

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1. RAW GRINDING : The raw materials are very finely ground in order to produce the raw mix.

1. RAW GRINDING

Raw grinding and burning

2. BURNING

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.

conveyor Raw mix

kiln

cooling

preheating

clinker

storage at the plant

Raw mill



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.

1. GRINDING

Grinding, storage, packing, dispatch

2. STORAGE, PACKING, DISPATCH

2. STORAGE, PACKING, DISPATCH :The cement is stored in silos before being dispatched either in bulk or in bags to its final destination.

clinker storage

Gypsum and the secondary additives are added to the clinker.

silos

dispatch

bags

Finish grinding


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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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