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cement internship report

  1. 1. 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.
  2. 2. In 1824, Joseph Aspdin, a stonemason in Leeds-England, obtained a binding agent byfiring and then grinding the mixture of fine-grain clay and limestone. Joseph Aspdin addedwater and sand to that product and thus enabled it to harden in time and then saw that theresulting 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 "PortlandCement". 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 oftoday‟s Portland Cement due to the fact that it was not fired at temperatures high enoughduring production. Nonetheless, it was found out that Wakefield Arms, which is stillstanding next to Kirkgate Station in England, was built with the binder produced by JosephAspdin. The process of firing at high temperatures and then grinding raw materials wasrealized by an Englisman called Isaac Johnson (1845).It was seen that, in Anatolia, natural pozzolanic active materials mixed with magnesianlime were used in the preparation of mortar in Hittite cities and in particular in the ancientcities located in Çorum, Tokat and Malatya.Apart from that, examples such as the use of common lime and basaltic pozzolanic matterin the historical ruins of the Assyrians in the Southeastern Anatolia point out that cementwas 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 alsoencountered following wide contact with ancient Anatolian civilizations.Although cement production and sales commenced in 1878 in the world, cement sectorwas introduced to Turkey primarily in 1912 with private sector‟s initiative. The 34-yeardelay in question results from insufficient hydraulic lime production and the fact that thoseyears coincided with the fall of the Ottoman Empire.The first cement production plant in the world was founded in 1848 in England. The firstGerman Cement Standard was created in 1860. And, the establishment of the AmericanConcrete Institut and the creation of the first American Regulations coincide with 1913.
  3. 3. In Turkey, however, Darıca Production Plant owned by Aslan Osmanlı Anonim Şirketi andEskihisar Production Plant owned by Eskihisar Portland Çimento ve Su Kireci OsmanlıAnonim 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 weretwo kilns bearing a capacity of 100- 150 tons/day and 60-70 tons/day, the installation ofwhich is unimaginable with today‟s dimensions. Darıca Production Plant was establishedby 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 productionplants 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, until1930- 1931, hydraulic lime production was above cement production.Those production plants, which met the need for cement of the country, entered into adestructive and backbreaking domestic market competition with each other until 1920,when large quantities were imported. In that period, cement prices fell considerably on thegrounds of lack of state intervention to the cement sector. As a result, those two productionplants could not resist to the backbreaking competition any more and merged in 1920under the name Aslan ve Eskihisar Müttehit Çimento Fabrikaları A.Ş. to act togetheragainst import cement.
  4. 4. 1.2. ABOUT GÖLTAŞ GÖLLER BÖLGESİ ÇİMENTO SAN. VE TİC. A.Ş. 1.2.1. COMPANYGöltaş Göller Bölgesi Çimento Sanayi ve Ticaret Anonim Şirketi was founded at Isparta in1969 as the first private sector cement factory having 600.000 tons/year capacity and 60Million TL capital by the participation of 2.000 shareholders. The establishment purpose ofthe factory is to produce cement for Isparta, Burdur, Antalya and partially Denizli and toperform marketing and delivery in these regions.The Company commenced operations by completing of the investments in 1973. Thelocation where Göltaş Çimento has been established is extremely rich in terms of rawmaterial. Limestone and clay deposits which are the raw materials of Clinker Productionare existed in the factory area.Since 1973 increasing profitability of the Company continued until 1979 where electricityand fuel-oil shortage reached to maximum level. The Company made its first exportationin 1981, while domestic cement demand entered in stationery state and became moreprofitable due to domestic sales. A new investment was started for converting from fuel-oilsystem to coal system in 1983. When the investment has been concluded at the end of 1984the fuel was converted to coal and it provided a great economy in comparison with fuel-oilsystem. Increasing of capacity, renovation and modernization investments werecommenced after 1984. The first part of the capacity increasing works was concluded in1986. 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 wascommissioned on 27 June1992 our capacity increased to 4.000 tons per day from 2.200tons per day. The second investment was costed 35 million Dollars.The Company passed to the registered capital system by the permission of Capital MarketsBoard dated 01 December 1994 and numbered 1227. Necessary permits were receivedfrom Capital Markets Board and other necessary associations regarding the Company inorder to be traded at the stock exchange and all par value stocks at the amount of33.600.000.000.- were sold by seven-fold value and as of 06 March 1995, 13% ofcompany shares started to trade at the İstanbul Stock exchange.
  5. 5. The Company made its second public offering in 1997. The capital of the company wasincreased from 254.1 Billion TL to 600 Billion TL; and par value stocks of the companycorresponding to 15.3% of the capital equivalent to 98.1 Billion TL were sold to abroad by27.5 fold value at 2.524 Trillion. As of 19 August 1997 they had started to be dealted inIstanbul Stock Exchange.The capital that was 600 Billion in 1998 was increased to 3,6 Trillion TL and 7,2 TrillionTL in 2002. 1.2.2. PRODUCTSCement types were determined in accordance with the the requirements in region and rawmaterial 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) 32.5N cement, is between 21 - 35%.CEM II/B-M (P-LL) 32.5 N cement is used for generalpurposes. It can be used in mass concrete applications such as foundations, retaining wallsand 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 arebetween 6 - 20%.CEM II/A-M (P-LL) 42.5 R and CEM II/A-M (P-LL) 42.5 N cements areused for general purposes. They can be used in mass concrete applications such asfoundations, retaining walls and dams. They are good connectors in terms of chemicalendurability.TS EN 197-1 CEM I 42,5 R - TS EN 197-1 CEM I 42,5 N: CEM I 42,5 R andCEM I 42,5Ncements are produced by grounding of clinker at the rate of 96% and 4% limestone in the
  6. 6. mills approximately. The limestone that is added during grounding process is foradjustment of the setting period. Final resistance is obtained at the end of 28 daysregarding Portland Cements. Increasing of the resistance after this period is too few andslow.This cements are used when high resistance concrete is required or for manufacturingof concrete that has high strength resistance initially. Prefabricate, prestressed concretesare suitable for tunnel form applications, which are very common at work of arts andcollective housing constructions.TS 10157 SDÇ 42,5 R (Sulphate Resistant Cement): This cement is manufactured bygrounding 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 bemakximum 25% in the cement. This production that requires intensive labor and techniquefrom preparation of the raw material to kilning them in the kiln privately therefore it ismade by less number factories in our country.This cement shows resistance against cementsulphate waters; therefore it is used at harbors, waste water systems, dams, undergroundwater pipes, foundations, sewers, irrigation canals and treatment plants. It is appropriatecement for using at the structures that require resistancy against chemical effects such assea water and sulphate environments. 1.2.3. PRODUCTION UNITS AND CAPACITYTwo Pieces Rotating Kiln:1st 2.200 Tons/Day Clinker2nd 4.000 Tons/Day ClinkerThree Pieces Raw Material Crusher:1st Raw Material Crusher 350 Tons/Hour2nd Raw Material Crusher 450 Tons/HourOne Piece Pozzolanas Crusher 150 Tons/HourThree Pieces Raw Meal Mill:1st Raw Meal Mill with Horizontal Ball 160 Tons/Hour2nd Raw Meal Mill with Vertical Roller 130 Tons/Hour3rd Raw Meal Mill with Vertical Roller 175 Tons/Hour
  7. 7. 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 R2. 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.
  8. 8. 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 Fig. 3. Limestone of limestone are Calcite and Aragonite. Limestoneand chalk are the most common types. Marble is the type of calcite that has visible crystalgrainy structure.The hardness of the calcerous is 3 and specific gravity is 2,5-2,7 gr/cm3. Limestonedeposits occur as travertine by the effect of underground waters, and by the effect ofchemical, organic and mechanic precipatition of the sea-water and fresh waters. It can beseen at yellow, brown and black colors because of subsidiary various substances andcompounds taking part in its structure.Close location of the limestone deposits that havebeen used as raw material of cement, easy operation of the quarry, having low humidity
  9. 9. and homogeneous characteristics are the most important factors that affect productioncosts.Rock units that have existed around the Göltaş Çimento A.Ş. are at the time intervalbetween upper cretaceous and oligocene. The rock units at the environment are forme bycarbonated rocks and detrital sedimentaries. Upper cretaceous aged carbonated rock masshas 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 SöbüdağLimestone Quarry that displays wide expansion in the south of the factory area. Theoperated limestone area has been limited by the Göltaş fault from the North. The width ofthe hydrothermal separation zone that has developed alongside of the fault, changesbetween 150 and 250 meters. Hydrothermal solutions and gasses that have increasedalongside of the Göltaş Fault, which is a deep originated fault, have affected the compoundand 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 Fig. 4. Clay precipitation of CaCO3 and Clayish substances at thesame time. In terms of formation it is sedimentary completely, had diagenesis, and existsusually as regular bedded. Marn formation mainly occurs at the quiet environments wheretectonic and orogenic movements have calmed down. Color of the Marn changes fromyellow to grayish black depends on the clayis materials.In comparison with calcerous, Marn can be educted easily because of being softer andenergy consumption of crushing and grounding becomes lower as well.Marn deposits that exist around the Göltaş Çimento A.Ş. have located in Eocene agedKayıköy formation. The marn deposit that exists at the environment is observed as astratigraphic scale, which can be monitored horizontally within the Kayıköy Formation.
  10. 10. The marn that has been required by Göltaş Çimento A.Ş. is supplied from marn quarriesthat 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 Fig. 5. Iron ore magnetic together with oxygen. The color of the ore inamorphous conditions is reddish. Iron ore is procured by purchasing from producercompanies. 2.1.4. BAUXITEBauxite is an aluminum ore and has occurred from oxides and contains hydration water. Itexists mainly at the hot regions. It occurs from decomposition of the aluminum silicaterocks such as granite, gneiss by aerifying. Its structure is flabby and earthy. Its color isusally white and because of iron oxide admixtures it is brownish or reddish. The hardnessdegree is 1-3 and its density is 2,5-3,0 gr/cm3.Buxite that is occurred by SiO2, Al2O3, Fe2O3ve H2O virtually, can have (~%3) TiO2 in small quantities.Bauxite ore is procured bypurchasing from producer companies. 2.1.5. AXUILIARY MATERIALS AND ADDITIVESGypsum (CaSO4.2H2O):Gypsum is seen between the sedimentary masses, which wereprecipitated at the dry, semi-dry climate regions in the ancient geological eras. It exists inthe 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‟shardness 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 andhydrates.Addition to the clinker between 3-5% is to control starting and ending of thecement freezing. Both minority and majority of the amount of limestone has role in termsof accelerating of the freezing period. Therefors it is essential addition of it at specificrates.Gypsum ore is procured by purchasing from producer companies.
  11. 11. Pozzolanas:According to TS 25, pozzolanas is a kind of volcanic rock that does not havehydraulic connective attributes, however can constitute connective substances when it ismixed with other substances such as tinny grounded limestone or cement and provideschemical resistance to cement, where it is added.Pozzolanas constitutes the most importantsection of the natural pozzuolanas those are used as additive in cement and known astrachyte 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 workingarea and close environment. The substance that will be used as additive should have highpozzolanic activity and low SO3 amount.According to chemical experiments andpozzolanic activity experiment that will be performed in accordance with TS 25 it isdecided, whether pozzolanas will be used as additive. 2.2. RAW MATERIALS PREPARATIONRaw materials preparation starts with extraction of the main components, which arelimestone and clay. The main raw materials come from natural rocks existing in thequarries. 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 varyingpercentage 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 Fig. 6. Limestone quarryloaded on the dumper trucks and conveyod to the crushers. It is located about 2 km fromthe plant.
  12. 12. 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. Insidehammer 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 Fig. 7. Hammer crusherfeed of very large sizes. 2.3. GRINDING AND HOMOGENIZATIONThe grinding process takes place in a raw mill to reduce the particle size of the componentsto a typical value of 10-15 % residue on a 90 μm sieve. There are three raw mill in theplant, 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 manufacturingprocess. 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 Fig. 8. Ball mill revolutions per minute, dependingupon the diameter of the mill. The larger the diameter, the slower the rotation. If the
  13. 13. peripheral speed of the mill is too great, it begins to act like a centrifuge and the balls donot fall back, but stay on the perimeter of the mill.The point where the mill becomes acentrifuge is called the "Critical Speed", and ball mills usually operate at 65% to 75% ofthe critical speed.Ball Mills are generally used to grind material 1/4 inch and finer, down to the particle sizeof 20 to 75 microns. To achieve a reasonable efficiency with ball mills, they must beoperated in a closed system, with oversize material continuously being recirculated backinto the mill to be reduced. 2.3.2. VERTICAL ROLLER MILL Fig. 9. Vertical roller millMaterial through the feed tube fell on the center of grinding plate, centrifugal forcegenerated from the rotation of grinding plate uniformly scatters and flattens the materials
  14. 14. outwards the surrounding area of grinding plate, to forms a certain thick layer of materialsbed, the material was crushed by number of rollers at the same time. Driven by thecontinuous centrifugal force to keep the materials moving to the outer edge of the grindingplate, the materials off the grinding plate rising with the hot air which enter from wind ringinto the mill, through the mill shell into the middle of the separator, in this course materialsand hot gas do a fully heat exchange, and the water quickly evaporates. Separator controlsthe output size of finished product, greater than the specified size are separated and fallback to the plate, while meet the fineness requirements are brought through the separatorinto the finished product warehouse. 2.3.3. HOMOGENIZATION SILOThe silo bottom of the CF (Controlled Flow) silo is divided into seven identical hexagonalsectors, 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 withopen aeration boxes. Raw meal extractionfollows a sequence where three segmentspositioned at three different outlets are aerated at a time. Fromthe outlets it is conveyed atdifferent rates to the central mixing tank installed below the silo. The aerationsequence iscyclic 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 PROCESSThe clinker manufacturing process starts with the extraction of the raw meal from thehomogenization silo to insure that the raw meal is stable and homogenized in order toproduce consistent clinker quality. The preheating of the material takes place in pre-heatercyclones fitted with a pre-calciner fired with coal. The calcinations of the material begin
  15. 15. during this stage, changing its phase to the oxide phase for each component to be ready forthe burning process. The burning phase takes place in a rotary kiln. The clinkertemperature in the kiln burning zone has to reach 1,500°C and then it is cooled in a coolerby air which decreases the temperature. 2.4.1. PRE-HEATERRawmeal 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. Asthe raw meal is passed down through these cyclones it comes into contact with the swirlinghot kiln exhaust gases moving in the opposite direction and as a result heat is transferredfrom the gas to material. This pre-heats the material before it enters the kiln so that thenecessary 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 Fig. 11. Pre-heater comprise 60% of the total emission from a cementkiln. The combustion of the fuel generates the rest. 2.4.2. KILNRaw meal, more accurately termed "hot meal" at this stage then enters the rotary kiln. Thekiln is the worlds largest piece of industrial equipment. Fuel is fired directly into the rotarykiln and ash, as with the calciner, is absorbed into the material being processed. As the kilnrotates at about 3-5 revolutions per minute, the material slides and tumbles down throughprogressively hotter zones towards the flame. Coal, pet coke, natural gas and moreincreasingly alternative fuels such as plastic, solvents, waste oil or meat and bone meal areburned to feed the flame which can reach as high as 2000oC.
  16. 16. As the mixture moves down the cylinder, it progresses through four stages oftransformation. 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 calledcalcination. The third stage is called clinkering. During this stage, the calcium silicates areformed. The final stage is the cooling stage.The marble-sized pieces produced by the kilnare referred to as clinker.Fig. 12. Schematic outline of conditions and reaction in a typical dry-process rotary kiln. Whensuspension preheaters are used, dehydration and initial calcination takes place outside the kiln in thepreheater tower. 2.4.3. BURNERA burner is a device to generate a flame to heat up products using a gaseous fuel such asacetylene, natural gas or propane. Some burners have an air inlet to mix the fuel gas withair to make a complete combustion. Acetylene is commonly used in combination withoxygen.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, asdescribed in case the wind sets are equipped with mixing tube, the open end of the mixing
  17. 17. 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. Fig. 13. Burner pipe 2.4.4. COOLINGThe clinker tumbles onto a grate cooled by forced air. Once cooled the clinker is ready tobe ground into the grey powder known as Portland cement. To save energy, heat recoveredfrom this cooling process is re circulated back to the kiln or preheater tower. Fig. 14. Cooler 2.5. CEMENT GRINDING AND PACKING PROCESSThe clinker is ground with an amount of gypsum to a fine powder in order to regulate thesetting time of cement and to gain the most important property of cement, which iscompressive strength. To produce different types of cement (e.g. Portland PozzolanaCement), the required additives are ground with clinker and gypsum to a very fine powder
  18. 18. and then used as desired. The cement stored in silos is then packed and delivered indifferent ways, e.g. bagged or bulk, as per the customer„s requirement. Fig. 15. Finish grinding circuit 2.5.1. CEMENT MILLCement clinker is usually ground using a ball mill. This is essentially a large rotating drumcontaining grinding media - normally steel balls. As the drum rotates, the motion of theballs 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 grindingmedia. As the clinker particles are ground down, smaller media are more efficient atreducing 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 improvegrindability due to the presence of microcracks in alite and to the finer crystal size of theflux phases. It is frequently observed that belite crystals, which have a characteristic roundshape, 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 theform of gypsum (CaSO4.2H2O). Natural anhydrite may also be added to discouragelumpiness of the gypsum due to its water content.
  19. 19. Since the clinker gets hot in the mill due to the heat generated by grinding, gypsum can bepartly dehydrated. It then forms hemihydrate, or plaster of Paris - 2CaSO4.H2O. On furtherheating, hemihydrate dehydrates further to a form of calcium sulfate known as solubleanhydrite (~CaSO4). This has a similar solubility in water to hemihydrate, which in turnhas 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 bya 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 sulfateare of importance in controlling the rate the rate of C3A hydration and consequently ofcement set retardation. Problems associated with setting and strength characteristics ofconcrete can often be traced to changes in the quantity of gypsum and hemihydrate, or withvariations in cooling rate of the clinker in the kiln and subsequent changes in theproportions or size of the C3A crystals.For set regulation, the most important feature of aluminate is not necessarily the absoluteamount present, but the amount of surface which is available to water for reaction. Thiswill be governed by many factors, such as the surface area of the cement, the grindingcharacteristics of the different phases and also the size of the aluminate crystals. Over-largecrystals can lead to erratic setting characteristics. Fig. 16. Cement mill
  20. 20. 2.5.2. PACKAGING AND SHIPMENTThe cement is stored in silos before being delivered in bulk using tanker trucks orpackaged into 25 – 35kg bags and stacked on pallets. Varrious means of transport may beused 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 baltwhich takes the bags to the roller conveyor. From these rollers the bags slide to differentchannels and finally cement bags are loaded on the trucks for dispatch.The usedof transportation methods with a low carbon footprint (in particular river or rail) isgiven preference whereever possible. Since the market for constraction materials is a localmarket, transportation distances are relatively short. Fig. 17. Loading terminal3. 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 Very high heat of hydration
  21. 21. 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 KILNThe 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 MATERIALSThis includes: Water evaporation in the raw feed, if any.
  22. 22. 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 turnform other compounds as clinkering proceeds. i. Water EvaporationIn wet-process kilns, and their derivatives, water must first be driven off. In a wet-processkiln, calcining takes place after the water has been driven off, about a third of the waydown the kiln. In the more modern pre-calciner kilns, the feed is calcined prior to enteringthe kiln. i. CalciningIn isolation, decarbonation of calcium carbonate at 1 atmosphere takes place at 894 C. Thistemperature is reduced to 500oC-6000C if the reaction takes place in contact with quartz orthe decomposition products of clay minerals, which react with the calcium oxide as itforms.In a wet-process or preheater system without a pre-calciner, most of the calcination takesplace in the rotary kiln within a moving mass of feed. This situation is not ideal forcalcination because heat transfer has to take place through a large mass of material andCO2 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 thehalf an hour or so inside a kiln at the same temperature. ii. Formation Of Early And Intermediate CompoundsDuring calcination, the lime produced starts to react with other components of the rawfeed. The initial silicate product is belite. Some calcium aluminate and ferrite phases alsostart to form.
  23. 23. A number of phases are formed in the clinker feed before the burning zone proper isreached. These intermediate phases dissociate in the burning zone and are not thereforefound in clinker but assist in forming the final clinker minerals. iii. Sulfate Melt PhaseAt intermediate temperatures, sulfates combined with calcium and alkalis form a liquidphase. This is separate from the aluminate and aluminoferrite-based liquid formed in theburning zone - the two liquids are immiscible.As with the main liquid phase, the sulfate liquid phase contributes to ion mobility andpromotes combination. 3.2.2. ALITE FORMATION AND OTHER REACTIONSIn the burning zone, above about 1300oC, reactions take place quickly. The clinker is in theburning 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 FormationAbove 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 andsome belite. The liquid content is more than the sum of the aluminate and ferrite phases inthe cooled clinker because of the dissolved lime and silica.The additional liquid causes coalescence of clinker particles, leading to the formation ofnodules. ii. Dissociation Of Intermediate PhasesThe intermediate phases dissociate to form mainly aluminate phase, which then becomespart of the liquid, and belite. iii. Alite Formation
  24. 24. Alite forms by the transition of some of the belite to alite and also directly from free limeand silica to alite. These reactions occur rapidly once the clinker temperature is aboveabout 1400oC. iv. Evaporation Of VolatilesVolatile phases in the cement kiln are principally alkali sulfates, with a much smallerproportion of alkali chlorides. As the part-burned feed approaches the burning zone, thesevolatile phases are in liquid form and a proportion volatilizes, the remainder passing out ofthe kiln in the clinker as inclusions within the pores.The volatilized material passes back down the kiln, where it condenses on the relativelycool 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 thepreheater as the condensed liquid sticks feed particles together, forming accretions. 3.2.3. COOLING OF THE CLINKERAs the clinker cools, the main liquid phase crystallizes to form aluminate phase, ferrite anda little belite.Fast cooling of clinker is advantageous - it makes for more hydraulically-reactive silicatesand lots of small, intergrown, aluminate and ferrite crystals.Slow cooling gives less hydraulically-reactive silicates and produces coarse crystals ofaluminate and ferrite - over-large aluminate crystals can lead to erratic cement settingcharacteristics. Very slow cooling allows alite to decompose to belite and free lime.
  25. 25. Fig. 18. Process of clinker
  26. 26. 3.3. COMPOSITIONAL PARAMETERSParameters based on the oxide composition are very useful in describing clinkercharacteristics. The following parameters are widely used (chemical formulae representweight 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 calculatedas:LSF=CaO/(2.8SiO2 + 1.2Al2O3 + 0.65Fe2O3)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 willhave 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 isbecause, in principle, at LSF=1.0 all the free lime should have combined with belite toform alite. If the LSF is higher than 1.0, the surplus free lime has nothing with which tocombine and will remain as free lime.In practice, the mixing of raw materials is never perfect and there are always regionswithin the clinker where the LSF is locally a little above, or a little below, the target for theclinker as a whole. This means that there is almost always some residual free lime, evenwhere the LSF is considerably below 1.0. It also means that to convert virtually all thebelite to alite, an LSF slightly above 1.0 is needed.The LSF calculation can also be applied to portland cement containing clinker and gypsumif (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 sodiumsulfates and this will introduce a slight error. More particularly, it does not account for finelimestone or other material such as slag or fly ash in the cement. If these materials are
  27. 27. present, calculation of the original clinker LSF becomes more complex. Limestone can bequantified by measuring the CO2 content and the formula adjusted accordingly, but if slagor fly ash are present, calculation of the original clinker LSF may not be convenientlypracticable.) 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 lessaluminate 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 theclinker.An increase in clinker AR (also sometimes written as A/F) means there will beproportionally more aluminate and less ferrite in the clinker. In ordinary Portland cementclinker, the AR is usually between 1 and 4.The above three parameters are those most commonly used. A fourth, the LimeCombination Factor (LCF) is the same as the LSF parameter, but with the clinker free limecontent subtracted from the total CaO content. With an LCF=1.0, therefore, the maximumamount of silica is present as C3S. 3.4. COMBINABILITY OF MIXESThe ease of combination ("combinability", or "burnability") are about how easily the rawmaterials react with each other to produce the clinker minerals.
  28. 28. 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 arelimitations to what can be achieved.Before considering these limitations, a summary of the clinkering process, and of the roleof the liquid phase, may be useful.The essential reactions in making portland cement are the calcination of limestone toproduce lime (calcium oxide) and the combination of this lime with silica to make beliteand, especially, alite.During clinkering, the clinker contains solid phases and a liquid phase. The bulk of theclinker remains as a solid. At the highest temperatures reached by the clinker, perhaps onlyabout 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 theliquid 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 somesilicon and other minor elements. As the clinker leaves the kiln and cools, crystals ofaluminate and ferrite form from the liquid. 3.4.1. COMBINATIONThe 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).
  29. 29. 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 mineralsin the clinker. 3.4.2. BLENDING AND PROPORTIONINGSuppose the cement producer has a source of limestone and a source of clay and that heknows the chemical composition of each.He can blend the limestone and clay in the correct proportions to give whatever value forLSF he likes, say 98%. However, the SR and AR will then be fixed by whatever thecomposition of the raw materials determines them to be. Although there will probably besome SiO2, Al2O3 and Fe2O3 in the limestone, these oxides will be mainly contributed bythe clay. In this example, therefore, it is the clay composition which will largely determineSR and AR.In general terms, two types of raw material, such as limestone and clay, can beproportioned to fix any one parameter only, say the LSF.To fix x parameters, x+1 materials of suitable composition are needed, so to control allthree parameters, LSF, SR and AR, a cement works needs to blend four different materialsof suitable composition. On a coal-fired works, the composition of the coal ash also needsto 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 earlierstrengths. Therefore, where high early strengths are important, the cement producer maywant to maximise the alite content; it might appear logical that he would want all thesilicates to be present as alite, with no belite present in the clinker. This may be so butoften it isnt quite that simple.
  30. 30. 3.4.3. OPTIMUM BURNING REGIMEFor a given mix, there will be an optimum burning regime. Under-burning will notcombine most of the lime to make alite. However, over-burned clinker is likely to containsilicates that are less hydraulically reactive - they react more slowly with water. Harderburning, at a higher temperature or a longer period of time or both, may therefore combinemore 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 thathas more alite, but less-reactive alite. Overall, the clinker may produce better strengthswith a slightly lower proportion of more reactive alite. 3.4.4. EFFECT OF COAL ASHWhere coal is the fuel for the kiln, the raw mix composition has also to take into accountthe effect of coal ash, as much of the ash will become incorporated into the clinker. Thequantity of ash is enough to have a significant effect on clinker composition - ash mayrepresent perhaps 2%-3%, or more, of the clinker.