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Intern report

  2. 2. 2 Contents P.g# Preface 4 Acknowledgments 5 Summary of cement production 6 1. Introduction to cement 7 1.1 History of cement 1.2Types of cement 1.3 Stages in the production 8 1.4 Production processes 2. Raw material for cement 9 2.1Prepartion of raw material 2.2Crushing of raw material 10 2.2.1Hammer crusher 2.2.2 Working and condition 2.2.3 Production of crusher 2.3 Limestone yard 11 2.4Proportionating tower 2.5Weigh feeder 12 2.6Vertical raw mill or raw mill 2.7Coal grinding 13 2.8Homogenization of grinded raw material 3.Multistage pre-heaters and pre-calcination 14 3.1Advantages of Pre-heater 15
  3. 3. 3 4.Burning in a kiln – formation of cement clinker 4.1Reaction zones 16 4.2 Properties of the major cement minerals 18 4.3 Composition of clinker 20 4.4Influence of compound composition on characteristics of p.c 4.5 Cooling and storage of clinker 5.Cement mill 21 6.Packing plant 22 References 23
  4. 4. 4 PREFACE This report documents the work done during the summer internship at Lucky Cement Limited (LCL), Lucky Cement Limited (LCL) is Pakistan’s largest producer and leading exporter of quality cement with the production capacity of 7.75 million tons per annum. The report first shall give an overview of the tasks completed during the period of internship with technical details. Then the results obtained shall be discussed and analyzed.We have tried our best to keep report simple yet technically correct. We hope we succeed in our attempt. M.SALEEM CHOHAN M.SHAFIQ NABEEL KHAN AMEEN REHMAN M.FAISAL MUBUSHIR AHMED
  5. 5. 5 ACKNOWLEDGMENTS First of all we would like to thanks Al-mighty Allah , The Most Beneficent and Merciful . We are very happy to avail this golden opportunity of getting training at lucky cement plant . We are thankful to General Manager of Lucky cement plant at Karachi Mr. Mashkoor Ahmed and HR Manager Mr.Fahad who provided us such a valuable opportunity. A lot of thanks to Manager Imran Ansari who provided us assistance in such a friendly environment. We are also thankful to all the managers /heads of each department we visited during internship for providing us information about the plants.and its operations Their kindness thus improving this report with their Additional technical knowledge has contributed mightly to the quality of this work. We got much practical knowledge which was not possible to gain in the university during studies. we are thankful to all the Officers & the workers of Lucky cement as well.
  6. 6. 6 Summary of Production Process Cement is typically made from limestone and clay or shale. These raw materials are extracted from the quarry crushed to a very fine powder and then blended in the correct proportions. This blended raw material is called the 'raw feed' or 'kiln feed' and is heated in a rotary kiln where it reaches a temperature of about 1400 C to 1500 C. In its simplest form, the rotary kiln is a tube up to 64 meter in length and total dia of kiln is 4.3 meter and effective dia is 3.9 meter, with a long flame at one end. The raw feed enters the kiln at the cool end and gradually passes down to the hot end, then falls out of the kiln and cools down. The material formed in the kiln is described as 'clinker' and is typically composed of rounded nodules between 1mm and 25mm across. After cooling, the clinker may be stored temporarily in a clinker store, or it may pass directly to the cement mill. The cement mill grinds the clinker to a fine powder. A small amount of gypsum - a form of calcium sulfate - is normally ground up with the clinker. The gypsum controls the setting properties of the cement when water is added.
  7. 7. 7 1. INTRODUCTION TO CEMENT The term cement is commonly used to refer to powdered materials which develop strong adhesive qualities when combined with water. Cement is a fine grayish powder which, when mixed with water, forms a thick paste. When this paste is mixed with sand and gravel and allowed to dry it is called concrete 1.1 HISTORY OF CEMENT Cement was first invented by the Egyptians. Cement was later reinvented by the Greeks and the Babylonians who made their mortar out of lime. Later, the Romans produced cement from pozzolana, an ash found in all of the volcanic areas of Italy, by mixing the ash with lime. 1.2 TYPES OF CEMENT The differences between these cement types are rather subtle. All five types contain about 75 wt% calcium silicate minerals, and the properties of mature concretes made with all five are quite similar. Thus these five types are often described by the term “ordinary portland cement”, or OPC.
  8. 8. 8 1.3 STAGES IN THE PRODUCTION There are three fundamental stages in the production of Portland cement: 1. Preparation of the raw mixture 2. Production of the clinker 3. Preparation of the cement 1.4 PRODUCTION PROCESSES The production of cement takes place with several steps in different stages :  Quarrying of limestone and shale  Crushing  Prehomogenization  Grinding in Vertical Raw Mill  Preheating  Rotary kiln Process  Cooler  Clinker Storage  Cement Grinding  Cement silos and Packaging
  9. 9. 9 2. RAW MATERIAL FOR CEMENT There are two types of raw materials which are combined to make cement:  Lime-containing materials, such as limestone, marble, oyster shells, marl, chalk, etc.  Clay and clay-like materials, such as shale, slag from blast furnaces, bauxite, iron ore, silica, sand, etc 2.1 PREPARTION OF RAW MATERIAL The first step in the manufacture of portland cement is to combine a variety of raw ingredients so that the resulting cement will have the desired chemical composition. . Since the final composition and properties of portland cement are specified within rather strict bounds, it might be supposed that the requirements for the raw mix would be similarly strict. As it turns out, this is not the case. While it is important to have the correct proportions of calcium, silicon, aluminum, and iron, the overall chemical composition and structure of the individual raw ingredients can vary considerably. The reason for this is that at the very high temperatures in the kiln, many chemical components in the raw ingredients are burned off and replaced with oxygen from the air. Table below lists just some of the many possible raw ingredients that can be used to provide each of the main cement elements. The ingredients listed above include both naturally occurring materials such as limestone and clay, and industrial byproduct materials such as slag and fly ash. From Table above it may seem as if just about any material that contains one of the main cement elements can be tossed into the kiln, but this is not quite true. Materials that contain more than minor (or in some cases trace) amounts of metallic elements such as magnesium, sodium, potassium, strontium, and various heavy metals cannot be used, as these will not burn off in the kiln and will negatively affect the cement. Another consideration is the reactivity, which is a function of both the chemical structure and the fineness. Clays are ideal because they are made of fine particles already and thus need little processing prior to use, and are the most common source of silica and alumina. Calcium is most often obtained from quarried rock, particularly limestone (calcium carbonate) which must be crushed and ground before entering the kiln.
  10. 10. 10 2.2 CRUSHING OF RAW MATERiAL 2.2.1 HAMMER CRUSHER In lucky cement industry hammer crusher are used for crushing the lime stone The hammer crusher contain 5 rows and 9 hammers in each row it means that hammer crusher has 45 hammers. A hammer mill is a machine whose purpose is to shred material into fine particles. 2.2.2 WORKING AND CONDITION The basic principle is straightforward. A hammer mill is essentially a steel drum containing a vertical or horizontal rotating shaft or drum on which hammers are mounted. The hammers are free to swing on the ends of the cross, or fixed to the central rotor. The rotor is spun at a high speed inside the drum while material is fed into a feed hopper. The material is impacted by the hammer bars and is thereby shredded and expelled through screens in the drum of a selected size. Small grain hammer mills can be operated on household current. Large automobile shredders can use one or more 2000 horsepower (1.5 MW) diesel engines to power the hammer mill. The Screen less hammer mill uses air flow to separate small particles from larger ones. It is designed to be more reliable, and is also claimed to be much cheaper and more energy efficient than regular hammer mills. 2.2.3 PRODUCTION OF CRUSHER In lucky cement industry two lime stone crusher are Assembled both are hammer crusher Hammer mill at lucky reduces the size of I meter stone into 70 to 80 mm The crushing capacity of hammer mill is 800 to 900 ton/hour . The weight of each hammer is 120 kg .
  11. 11. 11 2.3 LIMESTONE YARD A yard is made for the storage of crushed limestone in form of piles . A limestone pile being built by a boom stacker and prehomogenization of pile is made with the help of reclaimer. Crushed limestone is transported by a 90 m long belt to the storage yard then it drop the material on chand belt then chand belt drop on boom belt then with the help of boom stacker piles are made then after prehomogenization the lime stone is transported to the proportionating building by buckets then on long belt . 2.4 PROPORTIONATING TOWER In lucky cement there is a Proportionting tower. It is a building which store raw material Silos of individual raw materials are arranged. It has hoppers which provide feed to weigh-feeder. Accurately controlled proportions of each material are delivered onto the belt by weigh-feeders. The proportion of raw material is decided by Laboratory usually lucky cement industry works on following titration . • limestone 75 to 85 % • purchase clay 6 to 7 % • lucky clay 5 to 6 % • bauxite 1 to 2 %
  12. 12. 12 In practice, the raw material for raw mix is controlled by frequent chemical analysis (hourly by X-Ray fluorescence analysis in the laboratory, or every three minutes by prompt gamma neutron activation analysis). The analysis data is used to make automatic adjustments to raw material feed rates 2.5 WEIGH FEEDER Weigh feeder is a machine which weigh’s the material according to the defined composition and supply to the conveyer belt which take the material to the work place. 2.6VERTICAL RAW MILL or RAW MILL The motor drives the grinding table through decelerator.The materials fall down the center of grinding table from feed opening. At the same time, hot air comes into the mill from the air inlet. Due to the centrifugal force, materials move to the edge of the grinding table. The materials are pulverized by the roller when by pass of the groove on the grinding table. The crushed materials are brought up by vane high-speed airstream, the larger particles fall down to the grinding table for regrinding. When the materials in the airstream pass the separator on the top of the mill , the coarse powder fall down the grinding table for regrinding under the function of rotation rotor. The fine powder comes out with the airstream,and is gathered by the dust catcher. The materials content with moisture will be dried when they meet the hot airstream. Through adjusting the temperature of the hot airstream, it can meet different material’s requirement, and also through adjusting seperator, it can reach proper fineness of materials.
  13. 13. 13 In lucky cement plant the Vertical raw mill is used for the grinding of Raw material and coal. Approximately 180 to 210 tons of feed per hour is provided to the VRM . According to the introduction of VRM there are some rollers in the mill. VRM at lucky has 4 rollers weight of each roller is 22 ton. Inlet temperature of VRM is 287 C for 230 ton/h feed acorrding to design capacity 2.7 COAL GRINDING In Lucky Coal mill is the place where coal is grinded into fine powder for this purpose a small Roller mill or VRM (Vertical Raw Mill) is used. Coal mill design capacity is 25 tons/h and its inlet temperature is 92 C . Fine powdered coal is called Pulverize coal. The coal is grind to fine powder because the fine coal is very easy to burn in the kiln or PC (pre-calciner) 2.8 HOMOGENIZATION OF GRINDED RAW MATERIAL As the raw mix is stored in the silo that’s why its need to homogenize it for this purpose heavy compressor are used which through's air from the downward due to which a continuous motion occurs in the material and Homogenization of grinded raw material takes place.
  14. 14. 14 3. MULTISTAGE PRE-HEATERS AND PRE-CALCINATION Multistage preheaters and pre-calciners make use of the waste heat from the kiln and clinker cooler to pre-heat and pre-process the kiln feed, and thereby allow for considerable energy savings. Kiln systems with five cyclone preheater stages and precalciner are considered standard technology for ordinary new plants. Pre-heater is divided into two section • Cyclones of pre-heater where heat exchange takes place between the feed (raw mix) and hot air . • Precalciner (P.C)
  15. 15. 15 3.1 ADVANTAGES OF PRE-HEATER Pre-heater is used for heat exchange and calcinations . In lucky cement plant Pre-heater’s inlet temperature is 800 to 1000 C and out let temperature is 250 to 280 C . The raw material is burned in the pre-heater for 52 seconds and then it is sent to kiln . 75-80 % calcination is done.It increases the production capacity, it reduces the specific heat consumption also reduces specific power consumption. It also Improves kiln operation efficiency and reduces production cost. 4. BURNING IN A KILN – FORMATION OF CEMENT CLINKER After pre heating and pre calcinated material enters in burning and clinker zone of kilns where temp ranges from 1000C-1350C. Here CaO reacts with other oxides to form cementeous materal. Burning of kiln involves the following steps ; 1. evaporation of free water at temperature upto 100 C 2. removal of absorbed water in clay material 100-300 C 3. removal of chemically bounded water 450-900 C 4. calcinations of carbonate materials 700-850 C 5. formation of C2S, Aluminates and ferrite’s 800-1250 C 6. formation of liquid phase melt > 1250 C 7. formation of C3S 1330-1450 C 8. cooling of clinker to solidify liquid phase 1300-1240 C 9. final clinker microstructure frozen in clinker < 1200 C 10. clinker cooled in cooler 1250-100 C the final product as it comes out the kiln is known as clinker .
  16. 16. 16 4.1 REACTION ZONES Dehydration zone (up to ~ 450˚C): This is simply the evaporation and removal of the free water. Even in the “dry process” there is some adsorbed moisture in the raw mix. Although the temperatures required to do this are not high, this requires significant time and energy. In the wet process, the dehydration zone would require up to half the length of the kiln, while the dry process requires a somewhat shorter distance. Calcination zone (450˚C – 900˚C): The term calcination refers to the process of decomposing a solid material so that one of its constituents is driven off as a gas. At about 600˚C the bound water is driven out of the clays, and by 900˚C the calcium carbonate is decomposed, releasing carbon dioxide. By the end of the calcination zone, the mix consists of oxides of the four main elements which are ready to undergo further reaction into cement minerals. Because calcination does not involve melting, the mix is still a free-flowing powder at this point. Solid-state reaction zone (900˚ - 1300˚C): This zone slightly overlaps, and is sometimes included with, the calcination zone. As the temperature continues to increase above ~ 900˚C there is still no melting, but solid-state reactions begin to occur. CaO and reactive silica combine to form small crystals of C2S (dicalcium silicate), one of the four main cement minerals. In addition, intermediate calcium aluminates and calcium ferrite compounds form. These play an important role in the clinkering process as fluxing agents, in that they melt at a relatively low temperature of ~ 1300˚C, allowing a significant increase in the rate of reaction. Without these fluxing agents, the formation of the calcium silicate cement minerals would be slow and difficult. In fact, the formation of fluxing agents is the primary reason that portland (calcium silicate) cements contain aluminum and iron at all. The final aluminum- and iron-containing cement minerals (C3A and C4AF) in a portland cement contribute little to the final properties. As the mix passes through solid-state reaction zone it becomes “sticky” due to the tendency for adjacent particles to fuse together. Clinkering zone (1300˚C – 1550˚C): This is the hottest zone where the formation of the most important cement mineral, C3S (alite), occurs. The zone begins as soon as the intermediate calcium aluminate and ferrite phases melt. The presence of the melt phase causes the mix to agglomerate into relatively large nodules about the size of marbles consisting of many small solid particles bound together by a thin layer of liquid Inside the liquid phase, C3S forms by reaction between C2S crystals and CaO. Crystals of solid C3S grow within the liquid, while crystals of belite formed earlier decrease in number but grow in size. The clinkering process is complete when all of silica is in the C3S and C2S crystals and the amount of free lime (CaO) is reduced to a minimal level (<1%).
  17. 17. 17 Cooling zone: As the clinker moves past the bottom of the kiln the temperature drops rapidly and the liquid phase solidifies, forming the other two cement minerals C3A (aluminate) and C4AF (ferrite). In addition, alkalis (primarily K) and sulfate dissolved in the liquid combine to form K2SO4 and Na2SO4. The nodules formed in the clinkering zone are now hard, and the resulting product is called cement clinker. The rate of cooling from the maximum temperature down to about 1100˚C is important, with rapid cooling giving a more reactive cement. This occurs because in this temperature range the C3S can decompose back into C2S and CaO, among other reasons. It is thus typical to blow air or spray water onto the clinker to cool it more rapidly as it exits the kiln. REACTIONS:
  18. 18. 18 4.3 PROPERTIES OF THE MAJOR CEMENT MINERALS About 90-95% of a Portland cement is comprised of the four main cement minerals, which are C3S, C2S, C3A, and C4AF, with the remainder consisting of calcium sulfate, alkali sulfates, unreacted (free) CaO, MgO, and other minor constituents left over from the clinkering and grinding steps. The four cement minerals play very different roles in the hydration process that converts the dry cement into hardened cement paste. The C3S and the C2S contribute virtually all of the beneficial properties by generating the main hydration product, C-S-H gel. However, the C3S hydrates much more quickly than the C2S and thus is responsible for the early strength development. The C3A and C4AF minerals also hydrate, but the products that are formed contribute little to the properties of the cement paste. The crystal structures of the cement minerals are quite complex, and since these structures do not play an important role in the properties of cement paste and concrete we will only present the most important features here. Tricalcium Silicate (C3S) C3S is the most abundant mineral in portland cement, occupying 40–70 wt% of the cement, and it is also the most important. The hydration of C3S gives cement paste most of its strength, particularly at early times. Pure C3S can form with three different crystal structures. At temperatures below 980˚C the equilibrium structure is triclinic. At temperatures between 980˚C – 1070˚C the structure is monoclinic, and above 1070˚C it is rhombohedral. In addition, the triclinic and monoclinic structures each have three polymorphs, so there are a total of seven possible structures. However, all of these structures are rather similar and there are no significant differences in the reactivity. The most important feature of the structure is an awkward and asymmetric packing of the calcium and oxygen ions that leaves large “holes” in the crystal lattice. Essentially, the ions do not fit together very well, causing the crystal structure to have a high internal energy. As a result, C3S is highly reactive. The C3S that forms in a cement clinker contains about 3-4% of oxides other than CaO and SiO2. Strictly speaking, this mineral should therefore be called alite rather than C3S. However, as discussed in Section 3.2, we will avoid using mineral names in this monograph. In a typical clinker the C3S would contain about 1 wt% each of MgO, Al2O3, and Fe2O3, along with much smaller amounts of Na2O, K2O, P2O5, and SO3 [2]. These amounts can vary considerably with the composition of the raw materials used to make the cement, however. Of the three major impurities, Mg and Fe replace Ca, while Al replaces Si. One effect of the impurities is to “stabilize” the monoclinic structure, meaning that the structural transformation from monoclinic to triclinic that would normally occur on cooling is prevented. Most cements thus contain one of the monoclinic polymorphs of C3S.
  19. 19. 19 Dicalcium Silicate (C2S) As with C3S, C2S can form with a variety of different structures. There is a high temperature a structure with three polymorphs, a b structure in that is in equilibrium at intermediate temperatures, and a low temperature g structure. An important aspect of C2S is that g-C2S has a very stable crystal structure that is completely unreactive in water. Fortunately, the b structure is easily stabilized by the other oxide components of the clinker and thus the g form is never present in portland cement. The crystal structure of b-C2S is irregular, but considerably less so than that of C3S, and this accounts for the lower reactivity of C2S. The C2S in cement contains slightly higher levels of impurities than C3S ,the overall substitution of oxides is 4-6%, with significant amounts of Al2O3, Fe2O3, and K2O. Tricalcium Aluminate (C3A) Tricalcium aluminate (C3A) comprises anywhere from zero to 14% of a portland cement. Like C3S, it is highly reactive, releasing a significant amount of exothermic heat during the early hydration period. Unfortunately, the hydration products of formed from C3A contribute little to the strength or other engineering properties of cement paste. In certain environmental conditions (i.e., the presence of sulfate ions), C3A and its products can actually harm the concrete by participating in expansive reactions that lead to stress and cracking. Pure C3A forms only with a cubic crystal structure. The structure is characterized by Ca+2 atoms and rings of six AlO4 tetrahedra. As with C3S, the bonds are distorted from their equilibrium positions, leading to a high internal energy and thus a high reactivity. Significant amounts of CaO and the Al2O3 in the C3A structure can be replaced by other oxides, and at high levels of substitution this can lead to other crystal structures. The C3A in portland cement clinker, which typically contains about 13% oxide substitution, is primarily cubic, with smaller amounts of orthorhombic C3A. The C3A and C4AF minerals form by simultaneous precipitation as the liquid phase formed during the clinkering process cools, and thus they are closely intermixed. This makes it difficult to ascertain the exact compositions of the two phases. The cubic form generally contains ~4% substitution of SiO2, ~5% substitution of Fe2O3, and about 1% each of Na2O, K2O, and MgO. The orthorhombic form has similar levels, but with a greater (~5%) substitution of K2O. Tetracalcium Aluminoferrite (C4AF) A stable compound with any composition between C2A and C2F can be formed, and the cement mineral termed C4AF is an approximation that simply the represents the midpoint of this compositional series. The crystal structure is complex, and is believed to be related to that of the mineral perovskite. The actual composition of C4AF in cement clinker is generally higher in aluminum than in iron, and there is considerable substitution of SiO2 and MgO.
  20. 20. 20 4.4 COMPOSITION OF CLINKER C3S 55-56% C2S 21-22% C3A 5-6(FOR OPC) C3A <3.5(FOR SRC) C4AF 12-13(FOR OPC) C4AF 16-17(FOR SRC 4.5 INFLUENCE OF COMPOUND COMPOSİTİON ON CHARACTERİSTİCS OF P.C C3S C2S C3A C4AF Rate of Reaction Moderate Slow Fast Moderate Heat Liberation High Low Very High Moderate Early Cementitious Value Good Poor Good Poor Ultimate Cementitious Value Good Good Poor Poor 4.6 COOLING AND STORAGE OF CLINKER In lucky cement a grate cooler is used to cool the clinker . These coolers have two main advantages: they cool the clinker rapidly, which is desirable from a quality point of view, 8 Fans are also used to force air through the cooler bed or grates.
  21. 21. 21 5. CEMENT MILL Cement mill is the area where finally cement is manufacture by the addition of second stage raw materials (Slag , Gypsum and clinker) it consist of following parts  Roller press or crusher  Crushing Separator  Storage bin  Ball mill The length of ball mill is 13 meter . it is divided into two chambers . Its 1st chamber is 3 meter long and 2nd chamber is 10 meter long . The efficiency of ball mill depends on the size and weight of media or grinding medium.Media size in 1st chamber is 30,40,50 and 60 mm and in 2nd chamber is 10x12 , 12x14 mm . Weight of media in ball mill is 180 ton
  22. 22. 22 6.PACKING PLANT Lucky cement also export loose cement by loading it into through bunker. Daily it export ton per day. loose cement storage and ship loading terminal at berth -25 west wharf karachi port. Latest technology is being utilized in packing plant to meet customer demand.
  23. 23. 23 References:  Cement Engineers’ handbook by B .Kohlhaas  Rotary Kilns (Transport Phenomena andTransport Processes) by Akwasi A. Boateng