1. INTRODUCTION

1.1. HISTORY OF CEMENT

The word “cement” derived from "caementum" in Latin meaning hewn stone chips and

then started to be used in the meaning of “binder”. The date of the first reinforced concrete

building is 1852 but yet the use of binding agents in the construction of buildings dates

back to very old times. The first material used as binding agent is lime. Although there are

no precise findings, it is possible to say that the binding property of lime was discovered in

the early period of human history, in 2000s B.C. Examples of the use of lime as a

construction material have been encountered in different regions of the Ancient Egypt,

Cyprus, Crete and Mesopotamia. The Ancient Greeks and Romans used lime as a

hydraulic binder. Architect Vitruvius (70-25 B.C.), in his 10-volume book "On

Architecture", mentions the hydraulic properties of pozzolana and lime and even gives a

mixing ratio that can be used in the buildings to be constructed by rivers and seas.

Research results prove that the plaster used in the construction of Çatalhöyük houses in

Anatolia dates back to 7000 years ago.

Throughout the history, many different binding agents symbolizing the civilization of that

period were used in the Egyptian Pyramids and the Great Wall of China and in the castles

built at different times. Later on, nearly 2000 years ago, the Romans mixed hydrated lime

with volcanic ashes and afterwards with dusts obtained from fired brick and thus started to

use a hydraulic binder having properties similar to those of today’s cement. On the other

hand, the Ancient Greeks prepared mortar by mixing the volcanic tuffs on Santorini Island

with lime or with some sort of hydraulic lime they obtained from argillaceous limestone.

The Ancient Greeks and Romans discovered the hydraulic property of lime and pozzolona

mixtures and used such mixtures but did not have the knowledge to explain lime

acquisition or pozzolanic reactions in terms of chemistry. For instance, Pliny (Roman

scholar Gaius Plinius) writes that it is inexplicable why "the lime obtained by burning

stone in fire re-flames when it comes into contact with water." However, in the 18th

century, a significant development occurred in the quality and usage of binding agents.

John Smeaton, who was charged with rebuilding Eddystone Lighthouse in 1756, is known

to be the first person to comprehend the chemical properties of lime. The following

development is the acquisition of a binder known as "Roman Cement" by Joseph Parker.

In 1824, Joseph Aspdin, a stonemason in Leeds-England, obtained a binding agent by

firing and then grinding the mixture of fine-grain clay and limestone. Joseph Aspdin added

water and sand to that product and thus enabled it to harden in time and then saw that the

resulting material resembled the building stones obtained from England’s Portland Island.

So, on 21.10.1824, he took out a patent for that binder under the name of "Portland

Cement". Even though that binder was improved greatly in the following years, the name

"Portland" remained the same.

As a matter of fact, the binder produced by Joseph Aspdin could not have all properties of

today’s Portland Cement due to the fact that it was not fired at temperatures high enough

during production. Nonetheless, it was found out that Wakefield Arms, which is still

standing next to Kirkgate Station in England, was built with the binder produced by Joseph

Aspdin. The process of firing at high temperatures and then grinding raw materials was

realized by an Englisman called Isaac Johnson (1845).

It was seen that, in Anatolia, natural pozzolanic active materials mixed with magnesian

lime were used in the preparation of mortar in Hittite cities and in particular in the ancient

cities located in Çorum, Tokat and Malatya.

Apart from that, examples such as the use of common lime and basaltic pozzolanic matter

in the historical ruins of the Assyrians in the Southeastern Anatolia point out that cement

was used in Anatolia before the Greeks and Romans. In the ancient cities of Teos- İzmir,

Ephesus- İzmir, Aphrodisias-Aydın, Kinidos- Muğla, cement and mortar were also

encountered following wide contact with ancient Anatolian civilizations.

Although cement production and sales commenced in 1878 in the world, cement sector

was introduced to Turkey primarily in 1912 with private sector’s initiative. The 34-year

delay in question results from insufficient hydraulic lime production and the fact that those

years coincided with the fall of the Ottoman Empire.

The first cement production plant in the world was founded in 1848 in England. The first

German Cement Standard was created in 1860. And, the establishment of the American

Concrete Institut and the creation of the first American Regulations coincide with 1913.

In Turkey, however, Darıca Production Plant owned by Aslan Osmanlı Anonim Şirketi and

Eskihisar Production Plant owned by Eskihisar Portland Çimento ve Su Kireci Osmanlı

Anonim Şirketi were put into operation in 1912.

Fig. 1. Aslan Cement Plant, Darıca, Kocaeli, Turkey (1912)

In those production plants (one with wet system and the other with dry system), there were

two kilns bearing a capacity of 100- 150 tons/day and 60-70 tons/day, the installation of

which is unimaginable with today’s dimensions. Darıca Production Plant was established

by FLSmidth while Eskihisar Production Plant was established by a German company.

There was a brisk demand for cement as well as hydraulic lime and thus both production

plants were enlarged after they had been put into operation.

In the same years, 60.000 tons of hydraulic lime were produced in our country and, until

1930- 1931, hydraulic lime production was above cement production.

Those production plants, which met the need for cement of the country, entered into a

destructive and backbreaking domestic market competition with each other until 1920,

when large quantities were imported. In that period, cement prices fell considerably on the

grounds of lack of state intervention to the cement sector. As a result, those two production

plants could not resist to the backbreaking competition any more and merged in 1920

under the name Aslan ve Eskihisar Müttehit Çimento Fabrikaları A.Ş. to act together

against import cement.

1.2. ABOUT GÖLTAŞ GÖLLER BÖLGESİ ÇİMENTO SAN. VE TİC. A.Ş.

1.2.1. COMPANY

Göltaş Göller Bölgesi Çimento Sanayi ve Ticaret Anonim Şirketi was founded at Isparta in

1969 as the first private sector cement factory having 600.000 tons/year capacity and 60

Million TL capital by the participation of 2.000 shareholders. The establishment purpose of

the factory is to produce cement for Isparta, Burdur, Antalya and partially Denizli and to

perform marketing and delivery in these regions.

The Company commenced operations by completing of the investments in 1973. The

location where Göltaş Çimento has been established is extremely rich in terms of raw

material. Limestone and clay deposits which are the raw materials of Clinker Production

are existed in the factory area.

Since 1973 increasing profitability of the Company continued until 1979 where electricity

and fuel-oil shortage reached to maximum level. The Company made its first exportation

in 1981, while domestic cement demand entered in stationery state and became more

profitable due to domestic sales. A new investment was started for converting from fuel-oil

system to coal system in 1983. When the investment has been concluded at the end of 1984

the fuel was converted to coal and it provided a great economy in comparison with fuel-oil

system. Increasing of capacity, renovation and modernization investments were

commenced after 1984. The first part of the capacity increasing works was concluded in

1986. As result of these investments cement production and sales increased significantly.

Investment of the second clinker line (Bonn Line) was started in 1987. When it was

commissioned on 27 June1992 our capacity increased to 4.000 tons per day from 2.200

tons per day. The second investment was costed 35 million Dollars.

The Company passed to the registered capital system by the permission of Capital Markets

Board dated 01 December 1994 and numbered 1227. Necessary permits were received

from Capital Markets Board and other necessary associations regarding the Company in

order to be traded at the stock exchange and all par value stocks at the amount of

33.600.000.000.- were sold by seven-fold value and as of 06 March 1995, 13% of

company shares started to trade at the İstanbul Stock exchange.

The Company made its second public offering in 1997. The capital of the company was

increased from 254.1 Billion TL to 600 Billion TL; and par value stocks of the company

corresponding to 15.3% of the capital equivalent to 98.1 Billion TL were sold to abroad by

27.5 fold value at 2.524 Trillion. As of 19 August 1997 they had started to be dealted in

Istanbul Stock Exchange.

The capital that was 600 Billion in 1998 was increased to 3,6 Trillion TL and 7,2 Trillion

TL in 2002.

1.2.2. PRODUCTS

Cement types were determined in accordance with the the requirements in region and raw

material sources. Seven types cement have been produced in the factory. They are;

TS EN 197-1 CEM II/B-M (P-LL) 32,5 N

TS EN 197-1 CEM II/A-M (P-LL) 42,5 R

TS EN 197-1 CEM II/A-M (P-LL) 42,5 N

TS EN 197-1 CEM I 42,5 R

TS EN 197-1 CEM I 42,5 N

TS 10157 SDÇ 42,5 R (Sulphate Resistant Cement)

TS EN 197-1 CEM II/B-M (P-LL) 32,5 N: Total Additive in the CEM II/B-M (P-LL) 32.5

N cement, is between 21 - 35%. CEM II/B-M (P-LL) 32.5 N cement is used for general

purposes. It can be used in mass concrete applications such as foundations, retaining walls

and dams. It is a good connector in terms of chemical endurability.

TS EN 197-1 CEM II/A-M (P-LL) 42,5 R - TS EN 197-1 CEM II/A-M (P-LL) 42,5 N:

Total additive in CEM II/A-M (P-LL) 42.5 R and CEM II/A-M (P-LL) 42.5 N cements are

between 6 - 20%. CEM II/A-M (P-LL) 42.5 R and CEM II/A-M (P-LL) 42.5 N cements

are used for general purposes. They can be used in mass concrete applications such as

foundations, retaining walls and dams. They are good connectors in terms of chemical

endurability.

TS EN 197-1 CEM I 42,5 R - TS EN 197-1 CEM I 42,5 N: CEM I 42,5 R and CEM I 42,5

N cements are produced by grounding of clinker at the rate of 96% and 4% limestone in

the mills approximately. The limestone that is added during grounding process is for

adjustment of the setting period. Final resistance is obtained at the end of 28 days

regarding Portland Cements. Increasing of the resistance after this period is too few and

slow. This cements are used when high resistance concrete is required or for manufacturing

of concrete that has high strength resistance initially. Prefabricate, prestressed concretes

are suitable for tunnel form applications, which are very common at work of arts and

collective housing constructions.

TS 10157 SDÇ 42,5 R (Sulphate Resistant Cement): This cement is manufactured by

grounding of specially produced clinker with limestone in the mill. The rate of C3A

(tricalcium aluminat) should be maximum 5% and the amount of C4Af + 2C3A should be

makximum 25% in the cement. This production that requires intensive labor and technique

from preparation of the raw material to kilning them in the kiln privately therefore it is

made by less number factories in our country. This cement shows resistance against cement

sulphate waters; therefore it is used at harbors, waste water systems, dams, underground

water pipes, foundations, sewers, irrigation canals and treatment plants. It is appropriate

cement for using at the structures that require resistancy against chemical effects such as

sea water and sulphate environments.

1.2.3. PRODUCTION UNITS AND CAPACITY

Two Pieces Rotating Kiln:

1st 2.200 Tons/Day Clinker

2nd 4.000 Tons/Day Clinker

Three Pieces Raw Material Crusher:

1st Raw Material Crusher 350 Tons/Hour

2nd Raw Material Crusher 450 Tons/Hour

One Piece Pozzolanas Crusher 150 Tons/Hour

Three Pieces Raw Meal Mill:

1st Raw Meal Mill with Horizontal Ball 160 Tons/Hour

2nd Raw Meal Mill with Vertical Roller 130 Tons/Hour

3rd Raw Meal Mill with Vertical Roller 175 Tons/Hour

One Piece Coal Crusher: 100 Tons/Hour

Two Pieces Coal Mill:

1st Line Coal Mill with Vertical Vals 18 Tons/Hour

2nd Line Coal Mill with Horizontal Ball 18 Tons/Hour

Four Pieces Cement Mill:

1st Mill with pre-crusher, ball and separator 65 Tons/Hour

2nd Mill with pre-crusher, ball and separator 65 Tons/Hour

3rd Mill with ball and separator 70 Tons/Hour

4th Mill with ball and separator 140 Tons/Hour

Pozzolanas Drying Two Pieces Trommel (with spare): 100 Tons/Hour

Packaging Unit:

4 pieces 2.500 Tons Bunker/Silo

1 Pieces 10.000 Tons Bunker/Silo

8 Pieces Rotary Weigh-Bridge 800 Tons/Hour

5 Pieces Bulk Cement Line 500 Tons/Hour

7 Pieces Big-Bag Filing Facility

- 3.000 Tons/Day for CEM I 42,5 R

- 1.500 Tons/Day for CEM II/A-M (P-LL) 42,5 R Sling-Bag

- 3.750 Tons/Day for CEM I 42,5 R

2. MANUFACTURING

Fundamentally, cement is defined as a hydraulic binding agent which is obtained as the

mixture of natural limestone and clay is heated at a high temperature and then ground.

Hydraulic binding agents create a hard mass as a result of reacting with water and then do

not dissolve in water but retain or increase their hardness and strength.

Like other binding agents, cements are comprised of alkaline elements such as CaO and

MgO and hydraulic elements such as SiO2, Al2O3 and Fe2O3. The rates of alkaline and

hydraulic elements determine the quality of binding agents.

Fig. 2. The basic components of the cement production process

2.1. RAW MATERIALS

2.1.1. LIMESTONE

Limestone requirement of the factory has been

provided by factory’s limestone quarries, which are

about 3 kms away. Minerals that contain rich

minerals (includes minimum 90% CaCO3 in its

chemical composition) in terms of tertial aged lime

are called as limestonea (calcerous) and they are

indicated as CaCO3. For producing of clinker, all

geological types CaCO3 is suitable. The purest types

of limestone are Calcite and Aragonite.

Limestone and chalk are the most common types. Marble is the type of calcite that has

visible crystal grainy structure.

The hardness of the calcerous is 3 and specific gravity is 2,5 - 2,7 gr/cm3. Limestone

deposits occur as travertine by the effect of underground waters, and by the effect of

chemical, organic and mechanic precipatition of the sea-water and fresh waters. It can be

seen at yellow, brown and black colors because of subsidiary various substances and

compounds taking part in its structure. Close location of the limestone deposits that have

been used as raw material of cement, easy operation of the quarry, having low humidity

Fig. 3. Limestone

and homogeneous characteristics are the most important factors that affect production

costs.

Rock units that have existed around the Göltaş Çimento A.Ş. are at the time interval

between upper cretaceous and oligocene. The rock units at the environment are forme by

carbonated rocks and detrital sedimentaries. Upper cretaceous aged carbonated rock mass

has been separated in two different units as Söbüdağ Limestone and Senirce Limestone.

The Limestone that is required by Göltaş Çimento A.Ş., is supplied from Söbüdağ

Limestone Quarry that displays wide expansion in the south of the factory area. The

operated limestone area has been limited by the Göltaş fault from the North. The width of

the hydrothermal separation zone that has developed alongside of the fault, changes

between 150 and 250 meters. Hydrothermal solutions and gasses that have increased

alongside of the Göltaş Fault, which is a deep originated fault, have affected the compound

and structure of the limestones, which exist at the close locations to the fault.

2.1.2. CLAY

Limestone that has silica, clayish materials and iron

oxide is called Marn. Since it has existed on a vast

scale on the earth, it is the most common used material

in terms of cement production.

In terms of geological point of view, Marn is a

sedimentary rock that occurred as the result of the

precipitation of CaCO3 and Clayish substances at the

same time. In terms of formation it is sedimentary completely, had diagenesis, and exists

usually as regular bedded. Marn formation mainly occurs at the quiet environments where

tectonic and orogenic movements have calmed down. Color of the Marn changes from

yellow to grayish black depends on the clayis materials.

In comparison with calcerous, Marn can be educted easily because of being softer and

energy consumption of crushing and grounding becomes lower as well.

Marn deposits that exist around the Göltaş Çimento A.Ş. have located in Eocene aged

Kayıköy formation. The marn deposit that exists at the environment is observed as a

stratigraphic scale, which can be monitored horizontally within the Kayıköy Formation.

Fig. 4. Clay

The marn that has been required by Göltaş Çimento A.Ş. is supplied from marn quarries

that exist approximately 3 km away in the northwest of the factory area.

2.1.3. IRON ORE

Iron Ore exists in the nature mostly as hematite. The

color of hematite is red and is used in cement factory.

The mole weight is 150.68 and its density is 4,9 - 5,3

gr/cm3. Determination of the melting point is

impossible; because the Fe2O3 that is heated under the

atmospheric conditions dissolved and becomes

magnetic together with oxygen. The color of the ore in

amorphous conditions is reddish. Iron ore is procured by purchasing from producer

companies.

2.1.4. BAUXITE

Bauxite is an aluminum ore and has occurred from oxides and contains hydration water. It

exists mainly at the hot regions. It occurs from decomposition of the aluminum silicate

rocks such as granite, gneiss by aerifying. Its structure is flabby and earthy. Its color is

usally white and because of iron oxide admixtures it is brownish or reddish. The hardness

degree is 1-3 and its density is 2,5 - 3,0 gr/cm3. Buxite that is occurred by SiO2, Al2O3,

Fe2O3 ve H2O virtually, can have (~%3) TiO2 in small quantities. Bauxite ore is procured

by purchasing from producer companies.

2.1.5. AXUILIARY MATERIALS AND ADDITIVES

Gypsum (CaSO4.2H2O): Gypsum is seen between the sedimentary masses, which were

precipitated at the dry, semi-dry climate regions in the ancient geological eras. It exists in

the nature as massive mass, as well as mixed with bitumen, clay, limestone and iron oxide.

Since it is a precipitated sedimentary mass mineral, it isn’t dissolved in acides easily. It’s

hardness is 2,0 - 2,4 and specific gravity is 2,2 - 2,4 gr/cm3. Gypsum is expressed by the

(CaSO4.2H2O) chemical formula and by losing some of its water at 120 0C and hydrates.

Addition to the clinker between 3-5% is to control starting and ending of the cement

freezing. Both minority and majority of the amount of limestone has role in terms of

accelerating of the freezing period. Therefors it is essential addition of it at specific rates.

Gypsum ore is procured by purchasing from producer companies.

Fig. 5. Iron ore

Pozzolanas: According to TS 25, pozzolanas is a kind of volcanic rock that does not have

hydraulic connective attributes, however can constitute connective substances when it is

mixed with other substances such as tinny grounded limestone or cement and provides

chemical resistance to cement, where it is added. Pozzolanas constitutes the most important

section of the natural pozzuolanas those are used as additive in cement and known as

trachyte andesitic tuff.

Pozzolanas requirement of plant has been supplied from its own quarries at Dereboğazı,

which is about 25 km away. There are trias, jura, cretaceous aged volcanites at the working

area and close environment. The substance that will be used as additive should have high

pozzolanic activity and low SO3 amount. According to chemical experiments and

pozzolanic activity experiment that will be performed in accordance with TS 25 it is

decided, whether pozzolanas will be used as additive.

2.2. RAW MATERIALS PREPARATION

Raw materials preparation starts with extraction of the main components, which are

limestone and clay. The main raw materials come from natural rocks existing in the

quarries. They are supplied to crushers and then transferred to storage. Other (corrective)

materials such as iron ore, bauxite, gypsum or pozzolanas are added with a varying

percentage to reach the optimum chemical composition of each type of cement.

2.2.1. QUARRY

Quarry is the place from where

raw material in extracted. Drilling

and blasting is done to extractthe

material. A hole of about 10-15 m

is drilled and ammonium nitrate in

filled as an explosive in different

sizes. These pieces are then

loaded on the dumper trucks and

conveyod to the crushers. It is

located about 2 km from the plant.

Fig. 6. Limestone quarry

Fig. 8. Ball mill

2.2.2. CRUSHER

Raw material such as limestone, clay and

pozzolanas dumped into hoppers by dump trucks

and enteredinto a hammer crusher through an apron

feeder. Inside hammer crusher there are hammers

each having aweight of 100-102 kg. They rotate at a

speed of 1200-1300 rpm and is capable of crushing

feed of very large sizes.

2.3. GRINDING AND HOMOGENIZATION

The grinding process takes place in a raw mill to reduce the particle size of the components

to a typical value of 10-15 % residue on a 90 μm sieve. There are three raw mill in the

plant, a ball mill and two vertical roller mills. The output of the grinding process – called

‘raw meal’ – is transferred to a homogenization silo before the clinker manufacturing

process.

2.3.1. BALL MILL

Ball Mill grinds

material by

rotating a cylinder

with steel

grinding balls,

causing the balls

to fall back into

the cylinder and

onto the material

to be ground. The

rotation is usually

between 4 to 20

revolutions per minute, depending

upon the diameter of the mill. The larger the diameter, the slower the rotation. If the

peripheral speed of the mill is too great, it begins to act like a centrifuge and the balls do

Fig. 7. Hammer crusher

not fall back, but stay on the perimeter of the mill. The point where the mill becomes a

centrifuge is called the "Critical Speed", and ball mills usually operate at 65% to 75% of

the critical speed.

Ball Mills are generally used to grind material 1/4 inch and finer, down to the particle size

of 20 to 75 microns. To achieve a reasonable efficiency with ball mills, they must be

operated in a closed system, with oversize material continuously being recirculated back

into the mill to be reduced.

2.3.2. VERTICAL ROLLER MILL

Material through the feed tube fell on the center of grinding plate, centrifugal force

generated from the rotation of grinding plate uniformly scatters and flattens the materials

outwards the surrounding area of grinding plate, to forms a certain thick layer of materials

bed, the material was crushed by number of rollers at the same time. Driven by the

Fig. 9. Vertical roller mill

continuous centrifugal force to keep the materials moving to the outer edge of the grinding

plate, the materials off the grinding plate rising with the hot air which enter from wind ring

into the mill, through the mill shell into the middle of the separator, in this course materials

and hot gas do a fully heat exchange, and the water quickly evaporates. Separator controls

the output size of finished product, greater than the specified size are separated and fall

back to the plate, while meet the fineness requirements are brought through the separator

into the finished product warehouse.

2.3.3. HOMOGENIZATION SILO

The silo bottom of the CF (Controlled Flow) silo is divided into seven identical hexagonal

sectors, each of which hasits centre outlet covered by a pressure relief cone made of steel.

Each of the hexagonal sectors issubdivided into six triangular segments all equipped with

open aeration boxes. Raw meal extractionfollows a sequence where three segments

positioned at three different outlets are aerated at a time. Fromthe outlets it is conveyed at

different rates to the central mixing tank installed below the silo. The aerationsequence is

cyclic in a way that all the 42 segments will be activated once within about 15 minutes.

Fig. 10. Homogenization silo

2.4. THE CLINKER MANUFACTURING PROCESS

The clinker manufacturing process starts with the extraction of the raw meal from the

homogenization silo to insure that the raw meal is stable and homogenized in order to

produce consistent clinker quality. The preheating of the material takes place in pre-heater

cyclones fitted with a pre-calciner fired with coal. The calcinations of the material begin

during this stage, changing its phase to the oxide phase for each component to be ready for

the burning process. The burning phase takes place in a rotary kiln. The clinker

temperature in the kiln burning zone has to reach 1,500°C and then it is cooled in a cooler

by air which decreases the temperature.

2.4.1. PRE-HEATER

Rawmeal is the feed material for the high temperature process in the kiln system.

"Preheating" is the first part of this system. A pre-heater is a series of vertical cyclones. As

the raw meal is passed down through these cyclones it comes into contact with the swirling

hot kiln exhaust gases moving in the opposite direction and as a result heat is transferred

from the gas to material. This pre-heats the material before it enters the kiln so that the

necessary chemical reactions will occur more quickly and efficiently. By retaining energy

from the exhaust gases, energy is saved. Depending

on the raw material moisture, a kiln may have 3 to 6

stages of cyclones with increasing heat recovery with

each extra stage.

The calciner is a combustion chamber at the bottom

of the preheater above the kiln back-end. Up to 65%

of the total energy needs of the kiln system can be

supplied to the calciner. Calciners allow for shorter

rotary kilns and for the use of lower grade alternative

fuels. Calcination is the decomposition of CaCO3 to

CaO, which releases CO2. These process emissions

comprise 60% of the total emission from a cement

kiln. The combustion of the fuel generates the rest.

2.4.2. KILN

Raw meal, more accurately termed "hot meal" at this stage then enters the rotary kiln. The

kiln is the world's largest piece of industrial equipment. Fuel is fired directly into the rotary

kiln and ash, as with the calciner, is absorbed into the material being processed. As the kiln

rotates at about 3-5 revolutions per minute, the material slides and tumbles down through

progressively hotter zones towards the flame. Coal, pet coke, natural gas and more

increasingly alternative fuels such as plastic, solvents, waste oil or meat and bone meal are

burned to feed the flame which can reach as high as 2000oC.

Fig. 11. Pre-heater

As the mixture moves down the cylinder, it progresses through four stages of

transformation. Initially, any free water in the powder is lost by evaporation. Next,

decomposition occurs from the loss of bound water and carbon dioxide. This is called

calcination. The third stage is called clinkering. During this stage, the calcium silicates are

formed. The final stage is the cooling stage. The marble-sized pieces produced by the kiln

are referred to as clinker.

Fig. 12. Schematic outline of conditions and reaction in a typical dry-process rotary kiln. When suspension preheaters are used, dehydration and initial calcination takes place outside the kiln in the preheater tower.

2.4.3. BURNER

A burner is a device to generate a flame to heat up products using a gaseous fuel such as

acetylene, natural gas or propane. Some burners have an air inlet to mix the fuel gas with

air to make a complete combustion. Acetylene is commonly used in combination with

oxygen.

Burner used for industrial furnace heating. It consists of a set the wind shell with air inlet,

the shell sets the wind even on both ends of the back seat and a burner nozzles, as

described in case the wind sets are equipped with mixing tube, the open end of the mixing

tube and burner diameter nozzle connected to

the gas tube is inserted closed end and with

the gas supply port connected on the back

seat, as described on the mixing tube closed

end and back walls of the ministry and the

open end of the circumference of the outer

wall of the wind jet holes were laid.

2.4.4. COOLING

The clinker tumbles onto a grate cooled by forced air. Once cooled the clinker is ready to

be ground into the grey powder known as Portland cement. To save energy, heat recovered

from this cooling process is re circulated back to the kiln or preheater tower.

Fig. 14. Cooler

2.5. CEMENT GRINDING AND PACKING PROCESS

The clinker is ground with an amount of gypsum to a fine powder in order to regulate the

setting time of cement and to gain the most important property of cement, which is

compressive strength. To produce different types of cement (e.g. Portland Pozzolana

Cement), the required additives are ground with clinker and gypsum to a very fine powder

and then used as desired. The cement stored in silos is then packed and delivered in

different ways, e.g. bagged or bulk, as per the customer‘s requirement.

Fig. 15. Finish grinding circuit

2.5.1. CEMENT MILL

Cement clinker is usually ground using a ball mill. This is essentially a large rotating drum

containing grinding media - normally steel balls. As the drum rotates, the motion of the

balls crushes the clinker. The drum rotates approximately once every couple of seconds.

The drum is generally divided into two or three chambers, with different size grinding

media. As the clinker particles are ground down, smaller media are more efficient at

reducing the particle size still further.

Grinding clinker requires a lot of energy. How easy a particular clinker is to grind

("grindability") is difficult to predict, but rapid cooling of the clinker is thought to improve

grindability due to the presence of microcracks in alite and to the finer crystal size of the

flux phases. It is frequently observed that belite crystals, which have a characteristic round

shape, tend to separate and form single crystal grains during grinding.

As part of the grinding process, calcium sulfate is added as a set regulator, usually in the

form of gypsum (CaSO4.2H2O). Natural anhydrite may also be added to discourage

lumpiness of the gypsum due to its water content.

Since the clinker gets hot in the mill due to the heat generated by grinding, gypsum can be

partly dehydrated. It then forms hemihydrate, or plaster of Paris - 2CaSO4.H2O. On further

heating, hemihydrate dehydrates further to a form of calcium sulfate known as soluble

anhydrite (~CaSO4). This has a similar solubility in water to hemihydrate, which in turn

has a higher solubility than either gypsum or natural anhydrite.

Cement mills need to be cooled to limit the temperature rise of the cement. This is done by

a mixture of both air-cooling and water-cooling, including spraying water inside the mill.

The relative proportions and different solubilities of these various types of calcium sulfate

are of importance in controlling the rate the rate of C3A hydration and consequently of

cement set retardation. Problems associated with setting and strength characteristics of

concrete can often be traced to changes in the quantity of gypsum and hemihydrate, or with

variations in cooling rate of the clinker in the kiln and subsequent changes in the

proportions or size of the C3A crystals.

For set regulation, the most important feature of aluminate is not necessarily the absolute

amount present, but the amount of surface which is available to water for reaction. This

will be governed by many factors, such as the surface area of the cement, the grinding

characteristics of the different phases and also the size of the aluminate crystals. Over-large

crystals can lead to erratic setting characteristics.

Fig. 16. Cement mill

2.5.2. PACKAGING AND SHIPMENT

The cement is stored in silos before being delivered in bulk using tanker trucks or

packaged into 25 – 35 kg bags and stacked on pallets. Varrious means of transport may be

used according to the local infrastructure and topography.

The cement bags are attached manually to the rotating packer which fills the cement bag.

When the bag is filled up to the required weight, it automatically falls on the conveyor balt

which takes the bags to the roller conveyor. From these rollers the bags slide to different

channels and finally cement bags are loaded on the trucks for dispatch.

The used of transportation methods with a low carbon footprint (in particular river or rail)

is given preference whereever possible. Since the market for constraction materials is a

local market, transportation distances are relatively short.

3. CLINKER

3.1. PHASES

Alite or 3CaO•SiO2 or C3S

Hydrates & hardens quickly

High early strength

Higher heat of hydration (setting)

Belite or 2CaO• SiO2 or C2S

Hydrates & hardens slower than alite

Gives off less heat

High late strength (> 7 days)

Aluminate or 3CaO• Al2O3 or C3A

Fig. 17. Loading terminal

Very high heat of hydration

Some contribution to early strength

Low C3A for sulfate resistance

Ferrite or 4CaO• Al2O3 • Fe2O3 or C4AF

Little contribution to strength

Lowers clinkering temperature

Controls the color of cement

3.2. REACTIONS IN THE KILN

The reactions which take place in the kiln can be considered under three broad headings:

Decomposition of raw materials - reactions at temperatures up to about 1300oC.

Alite formation and other reactions at 1300oC - 1450oC in the burning zone.

Cooling of the clinker.

3.2.1. DECOMPOSITION OF RAW MATERIALS

This includes:

Water evaporation in the raw feed, if any.

Loss of carbon dioxide from the limestone (ie: calcining).

Decomposition of the siliceous and aluminosilicate fractions of the feed.

Formation of a sulfate melt phase.

The decomposition products react with lime to form intermediate compounds which in turn

form other compounds as clinkering proceeds.

i. Water Evaporation

In wet-process kilns, and their derivatives, water must first be driven off. In a wet-process

kiln, calcining takes place after the water has been driven off, about a third of the way

down the kiln. In the more modern pre-calciner kilns, the feed is calcined prior to entering

the kiln.

i. Calcining

In isolation, decarbonation of calcium carbonate at 1 atmosphere takes place at 894 C. This

temperature is reduced to 500oC - 6000C if the reaction takes place in contact with quartz

or the decomposition products of clay minerals, which react with the calcium oxide as it

forms.

In a wet-process or preheater system without a pre-calciner, most of the calcination takes

place in the rotary kiln within a moving mass of feed. This situation is not ideal for

calcination because heat transfer has to take place through a large mass of material and

CO2 has to escape outwards as heat moves inwards.

A pre-calciner calcines the raw material much more efficiently than a wet-process kiln.

Raw meal is dispersed in the hot gas and calcination takes place in seconds, rather than the

half an hour or so inside a kiln at the same temperature.

ii. Formation Of Early And Intermediate Compounds

During calcination, the lime produced starts to react with other components of the raw

feed. The initial silicate product is belite. Some calcium aluminate and ferrite phases also

start to form.

A number of phases are formed in the clinker feed before the burning zone proper is

reached. These intermediate phases dissociate in the burning zone and are not therefore

found in clinker but assist in forming the final clinker minerals.

iii. Sulfate Melt Phase

At intermediate temperatures, sulfates combined with calcium and alkalis form a liquid

phase. This is separate from the aluminate and aluminoferrite-based liquid formed in the

burning zone - the two liquids are immiscible.

As with the main liquid phase, the sulfate liquid phase contributes to ion mobility and

promotes combination.

3.2.2. ALITE FORMATION AND OTHER REACTIONS

In the burning zone, above about 1300oC, reactions take place quickly. The clinker is in the

burning zone for perhaps 10-20 minutes but in this time a lot happens:

The proportion of clinker liquid increases and nodules form.

Intermediate phases dissociate to form liquid and belite.

Belite reacts with free lime to form alite.

Some volatile phases evaporate.

i. Clinker Liquid And Nodule Formation

Above about 1300oC the proportion of liquid starts to increase - by 1450oC, perhaps 20-

30% of the mix is liquid. The liquid forms from melting ferrite and aluminate phases and

some belite. The liquid content is more than the sum of the aluminate and ferrite phases in

the cooled clinker because of the dissolved lime and silica.

The additional liquid causes coalescence of clinker particles, leading to the formation of

nodules.

ii. Dissociation Of Intermediate Phases

The intermediate phases dissociate to form mainly aluminate phase, which then becomes

part of the liquid, and belite.

iii. Alite Formation

Alite forms by the transition of some of the belite to alite and also directly from free lime

and silica to alite. These reactions occur rapidly once the clinker temperature is above

about 1400oC.

iv. Evaporation Of Volatiles

Volatile phases in the cement kiln are principally alkali sulfates, with a much smaller

proportion of alkali chlorides. As the part-burned feed approaches the burning zone, these

volatile phases are in liquid form and a proportion volatilizes, the remainder passing out of

the kiln in the clinker as inclusions within the pores.

The volatilized material passes back down the kiln, where it condenses on the relatively

cool incoming feed. It again becomes part of the sulfate melt phase, promoting reactions,

and is once again carried within the clinker towards the burning zone.

This recirculating load of alkali and sulfate can occasionally become excessively high.

Large quantities of condensing volatiles can then cause blockages in the kiln or in the

preheater as the condensed liquid sticks feed particles together, forming accretions.

3.2.3. COOLING OF THE CLINKER

As the clinker cools, the main liquid phase crystallizes to form aluminate phase, ferrite and

a little belite.

Fast cooling of clinker is advantageous - it makes for more hydraulically-reactive silicates

and lots of small, intergrown, aluminate and ferrite crystals.

Slow cooling gives less hydraulically-reactive silicates and produces coarse crystals of

aluminate and ferrite - over-large aluminate crystals can lead to erratic cement setting

characteristics. Very slow cooling allows alite to decompose to belite and free lime.

Fig. 18. Process of clinker

3.3. COMPOSITIONAL PARAMETERS

Parameters based on the oxide composition are very useful in describing clinker

characteristics. The following parameters are widely used (chemical formulae represent

weight percentages).

3.3.1. LIME SATURATION FACTOR (LSF)

The LSF is a ratio of CaO to the other three main oxides. Applied to clinker, it is calculated

as:

LSF = CaO / (2.8 SiO2 + 1.2 Al2O3 + 0.65 Fe2O3)

Often, this is referred to as a percentage and therefore multiplied by 100.

The LSF controls the ratio of alite to belite in the clinker. A clinker with a higher LSF will

have a higher proportion of alite to belite than will a clinker with a low LSF.

Typical LSF values in modern clinkers are 0.92 - 0.98, or 92% - 98%.

Values above 1.0 indicate that free lime is likely to be present in the clinker. This is

because, in principle, at LSF = 1.0 all the free lime should have combined with belite to

form alite. If the LSF is higher than 1.0, the surplus free lime has nothing with which to

combine and will remain as free lime.

In practice, the mixing of raw materials is never perfect and there are always regions

within the clinker where the LSF is locally a little above, or a little below, the target for the

clinker as a whole. This means that there is almost always some residual free lime, even

where the LSF is considerably below 1.0. It also means that to convert virtually all the

belite to alite, an LSF slightly above 1.0 is needed.

The LSF calculation can also be applied to portland cement containing clinker and gypsum

if (0.7 x SO3) is subtracted from the CaO content. (NB: This calculation (ie: 0.7 x SO3)

does not account for sulfate present as clinker sulfate in the form of potassium and sodium

sulfates and this will introduce a slight error. More particularly, it does not account for fine

limestone or other material such as slag or fly ash in the cement. If these materials are

present, calculation of the original clinker LSF becomes more complex. Limestone can be

quantified by measuring the CO2 content and the formula adjusted accordingly, but if slag

or fly ash are present, calculation of the original clinker LSF may not be conveniently

practicable.)

3.3.2. SILICA RATIO (SR)

The silica ratio is defined as:

SR = SiO2 / (Al2O3 + Fe2O3)

A high silica ratio means that more calcium silicates are present in the clinker and less

aluminate and ferrite. SR is typically between 2.0 and 3.0.

The silica ratio is sometimes called the ‘silica modulus’.

3.3.3. ALUMINA RATIO (AR)

The alumina ratio is defined as:

AR = (Al2O3 / (Fe2O3)

This determines the potential relative proportions of aluminate and ferrite phase in the

clinker.

An increase in clinker AR (also sometimes written as A/F) means there will be

proportionally more aluminate and less ferrite in the clinker. In ordinary Portland cement

clinker, the AR is usually between 1 and 4.

The above three parameters are those most commonly used. A fourth, the 'Lime

Combination Factor' (LCF) is the same as the LSF parameter, but with the clinker free lime

content subtracted from the total CaO content. With an LCF = 1.0, therefore, the maximum

amount of silica is present as C3S.

3.4. COMBINABILITY OF MIXES

The ease of combination ("combinability", or "burnability") are about how easily the raw

materials react with each other to produce the clinker minerals.

Clinker composition is evidently one of the key factors which determine cement quality.

Composition is controlled mainly by suitable blending of raw materials, but there are

limitations to what can be achieved.

Before considering these limitations, a summary of the clinkering process, and of the role

of the liquid phase, may be useful.

The essential reactions in making portland cement are the calcination of limestone to

produce lime (calcium oxide) and the combination of this lime with silica to make belite

and, especially, alite.

During clinkering, the clinker contains solid phases and a liquid phase. The bulk of the

clinker remains as a solid. At the highest temperatures reached by the clinker, perhaps only

about 25% of the clinker is a liquid. The solid phases are mainly alite, belite and free lime.

The liquid is vital in that it acts a flux, promoting reactions by ion transfer; without the

liquid phase, combinability would be poor and it would be very difficult to make cement.

The liquid phase is composed largely of oxides of calcium, iron and aluminium, with some

silicon and other minor elements. As the clinker leaves the kiln and cools, crystals of

aluminate and ferrite form from the liquid.

3.4.1. COMBINATION

The combinability of a raw mix will depend largely on:

The fineness of the raw materials - fine material will evidently react more readily

than will coarser material, so finer material makes for better combinability.

Lime Saturation Factor - higher LSF mixes are more difficult to combine than are

lower LSF mixes, so a higher LSF makes for poorer combinability.

Silica Ratio - mixes of higher SR are more difficult to combine because there is less

liquid flux present, so a higher SR makes for poorer combinability.

Alumina Ratio - mixes of AR approximately equal to 1.4 will be easier to burn than

if the AR is higher or lower. This is because at an AR of about 1.4, there is more

clinker liquid at a lower temperature and combinability is optimised. (Minor

constituents such as MgO can alter this optimum AR).

The intrinsic reactivity of the raw materials - some types of silica, for example, will

react more easily than will others.

Ideally, a cement producer would like to control all three clinker compositional parameters,

LSF, SR and AR. That would define the approximate proportions of the four main minerals

in the clinker.

3.4.2. BLENDING AND PROPORTIONING

Suppose the cement producer has a source of limestone and a source of clay and that he

knows the chemical composition of each.

He can blend the limestone and clay in the correct proportions to give whatever value for

LSF he likes, say 98%. However, the SR and AR will then be fixed by whatever the

composition of the raw materials determines them to be. Although there will probably be

some SiO2, Al2O3 and Fe2O3 in the limestone, these oxides will be mainly contributed by

the clay. In this example, therefore, it is the clay composition which will largely determine

SR and AR.

In general terms, two types of raw material, such as limestone and clay, can be

proportioned to fix any one parameter only, say the LSF.

To fix x parameters, x+1 materials of suitable composition are needed, so to control all

three parameters, LSF, SR and AR, a cement works needs to blend four different materials

of suitable composition. On a coal-fired works, the composition of the coal ash also needs

to be allowed for, since the ash falls onto the part-reacted feed and combines with it.

In practice, a works may have 5 or 6 raw materials in order to control composition.

Alite is the clinker mineral that contributes most to strength in concrete, especially earlier

strengths. Therefore, where high early strengths are important, the cement producer may

want to maximise the alite content; it might appear logical that he would want all the

silicates to be present as alite, with no belite present in the clinker. This may be so but

often it isn't quite that simple.

3.4.3. OPTIMUM BURNING REGIME

For a given mix, there will be an optimum burning regime. Under-burning will not

combine most of the lime to make alite. However, over-burned clinker is likely to contain

silicates that are less hydraulically reactive - they react more slowly with water. Harder

burning, at a higher temperature or a longer period of time or both, may therefore combine

more free lime but at the expense of silicate reactivity.

If the manufacturer tries to increase the alite content too far, he may produce a clinker that

has more alite, but less-reactive alite. Overall, the clinker may produce better strengths

with a slightly lower proportion of more reactive alite.

3.4.4. EFFECT OF COAL ASH

Where coal is the fuel for the kiln, the raw mix composition has also to take into account

the effect of coal ash, as much of the ash will become incorporated into the clinker. The

quantity of ash is enough to have a significant effect on clinker composition - ash may

represent perhaps 2% - 3%, or more, of the clinker.