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INTRODUCTION OF BIRLA CEMENT WORKS
1.1 History Behind Birla Cement
Grasim Industries Limited, a flagship company of the Aditya Birla Group, ranks among India’s largest private sector companies. Starting as a textiles manufacturer in 1948, six years later Grasim pioneered the production of viscose staple fibre (VSF), a man-made biodegradable fibre with characteristics akin to cotton. Today, Grasim is the country’s largest producer of VSF and the largest manufacturer of caustic soda, which is used in the production VSF.
In mid 1980s, with the opening up of the cement industry, Grasim diversified into cement. In 1998, Grasim acquired from its group company – Indian Rayon & Industries Ltd., a cement capacity of 3.2 million tonnes. In 1999, it acquired Shree Digvijay Cement Company Ltd. (SDCCL) from the Kolkata based Bangurs. SDCCL had a cement plant of 1.1 million tonnes
ADITYA BIRLA GROUP is a multi product, multi interest Rs. 5000/- crore plus conglomerate. It plays significant roles in the cement, jute products, blended yarn, PVC floor covering, carbide, industrial gases, auto trim and steel casting industries.
The story of Birla Corporation Limited began 85 years ago, when the young G. D. Birla came to the then Calcutta. A man of vision and Enterprise, Shri Ganshyam Dasji set up the first Indian owned jute mill near Kolkata. The year was 1919.
The name of the company was changed to Birla Jute & Industries Ltd. in 1983. In view of the opportunities offered by the liberalized, fast growing economy and to promote brand equity and international image, the name was changed to Birla Corp Limited in 1997. In 1998, the name was changed to Birla Corporation Limited, to establish the size, image and conglomerate character of the company.
It was Shri Madhav Prasadji Birla (nephew of Shri G.D. Birla) who gave shape to the world of Birla Corporation Limited. As chairman of the company he helped transform it from a manufacturer of jute goods to a leading multiproduct corporation with widespread activities.
Cement can be defined as any substance, which can join or unite two or more pieces of some other substance together to form a unit mass. Cement, as used in construction industries, is a fine powder which when mixed with water and allowed to set and harden can join different components or members together to give a mechanically strong structure.
2.1. History of Cement
The history of cement is the story of civilization from Egyptians utilized gypsum plaster as cementing material as early as 3000 BC building their monuments. However, It was in 1824, sixty-eighty years after the discovery of hydraulic properties of lime Joseph Aspdin patented his product, which was called "Portland Cement" The plants manufacturing portland cement outside England were commissioned in Belgium and Germany in 1855. The interest that is evoked in the technology of cement resulted in the development of Rotary kilns in 1886. Modern cement is the outcome of the combined research and development efforts of chemists, technologists and architects.
Limestone (calcareous) and clays (argillaceous) are the conventional raw materials mostly used in cement industry. Sometimes sandstone (siliceous),bauxite (aluminous) and iron ore (ferruginous) are used, as corrective material to maintain desired composition for potential property of clinker.
2.2.2. Technological Assessment of Raw Material
Raw materials are characterized by
• Chemical composition
• Mineral composition
• Physical composition
• Mechanical characteristics
2.3. Composition of Ordinary Cement
Ordinary Portland Cement is the basic cement and it has three grades namely 33, 43 and 53 respectively.
Cement consumption growth is highly correlated to the GDP growth and serves as a leading indicator.
There are three production lines involving five significant manufacturing stages, namely crushing, raw meal grinding, clinkerisation, cement grinding and packing.
Basic steps involved in the manufacture of cement are :
3.3. Stacking and reclaiming
3.4. Raw material grinding
3.5. Raw meal storage & blending
3.6. Preheating and burning
3.7. Clinker cooling
3.8. Clinker storage
3.9. Clinker grinding
3.10. Cement storage in silos
3.11. Packing & dispatch
Most of the raw materials used are extracted from the earth through mining and quarrying and can be divided into the following groups:
lime (calcareous), silica (siliceous), alumina (argillaceous) and iron (ferriferous).
Quarry operations consist of drilling, blasting, excavating, handling, loading, hauling, crushing, screening, stockpiling, and storing.
Mining Functions :
Planning and executing a systematic exploration programme.
Draw scope of drilling campaign. How to carry out survey and perform drilling activities for exploration purpose.
Establish system for computerized mine-planning in order to ensure supply of limestone with consistent quality.
Planning and executing drilling and blasting program in normal course at site to take optimum output from blasting as well as achieving economy in explosive consumption.
Loading and transportation of lime stone boulders to crusher site.
Implementing statutory requirement for safety and environment.
Approximate boulder size : 1.0 M *
It is a process in which the limestone from the mines comes into the crusher for further size reduction. This process is based on the reduction ratio ®.
The size is reduced from 1.0M * 1.4M * 1.1M boulder to 25mm size of limestone pieces.
R = largest linear dimension of material before crushing
largest linear dimension of material after crushing
Common type of Crushers used are :
• Double Toggle Jaw Crusher is used as primary crusher & capacity is 400 TPH.
• Swing Hammer Crusher is used as secondary crusher & capacity is 200 TPH.
• Compound Impactor is combined unit of primary and secondary crusher & capacity is 800 TPH.
Stacker : The stacker moves on longitudinal rails longitudinal pile is formed.
Details of Piles: 20000 – 30000 tonnes per pile. Height of pile upto 11.00 meters.
Rated capacity : 1000 tonnes per hour. It varies from plant to plant depending upon the production requirement. In stacking, limestone and clay are metered and fed simultaneously to the feed conveyor for Homogenization process.
There are two major Stacking systems :
• Chevron : Stacking is done in layers along single axis with the feed conveyor sweeping backwards and forward along the length of pile on the longitudinal rail.
• Windrow : Stacking is done in longitudinal strips side by side and then in successive layers. This avoids segregation which is the characteristics shown by Chevron Stacking. Windrow requires more complex and expensive stacking belt arrangement.
Reclaimer cuts Stack Pile in slice from parallel to face of pile. Shifting material (limestone) to belt with the help of scrapper. The Reclaimer reclaims the stack piles of raw meal using a Bridge Scrapper type Reclaimer which cuts stack pile into slice from parallel to face of pile shifting limestone to belt.of the scrapper.
Type: Bridge Scrapper Type.
Rated Capacity : 600 tonnes per hour. It will vary from plant to plant depending on the production requirement (in TPD).
There are two types of Reclaims are available:
• End Reclaim : The Reclaim Drag Chain scraps the end of the pile and limestone is shifted to the discharge conveyor.
• Side Reclaim : The Reclaim Drag Chain scraps the pile sideways and reclaim boom provide raw material to the discharge conveyor.
3.5. RAW MILL GRINDING
Raw milling involves mixing the extracted raw materials to obtain the correct chemical configuration and grinding them to achieve the proper particle-size, to ensure optimal fuel efficiency in the cement kiln and strength in the final concrete product.
Transport belt conveyor transfers the blended raw materials to ball mills where it is ground. The chemical analysis is again checked to ensure excellent quality control of the product. The resulting ground and dried raw meal is sent to a homogenizing and storage silo for further blending before being burnt in the kilns.
In the dry process, each raw material is proportioned to meet a desired chemical composition and fed to either a rotating ball mill or vertical roller mill. The raw materials are dried with waste process gases and ground to a size where the majority of the materials are less than 75 microns. The dry materials exiting either type of mill are called "kiln feed". The kiln feed is pneumatically blended to insure the chemical composition of the kiln feed is well homogenized and then stored in silos until required.
3.6. RAW MEAL STORAGE AND BLENDING
Raw meal after Grinding is stored in large silos until required for further process.
The rawmix is formulated to a very tight chemical specification. Calcium and silicon are present in order to form the strength-producing calcium silicates. Aluminium and iron are used in order to produce liquid ("flux") in the kiln burning zone. The liquid acts as a solvent for the silicate-forming reactions, and allows these to occur at an economically low temperature. Insufficient aluminum and iron lead to difficult burning of the clinker, while excessive amounts lead to low strength due to dilution of the silicates by aluminates and ferrites. The relative amounts of each oxide are therefore kept constant in order to maintain steady conditions in the kiln, and to maintain constant product properties. Remaining chemical variation is minimized by passing the raw mix through a blending system that homogenizes up to a day's supply of rawmix (15,000 tonnes in the case of a large kiln).
Pneumatic dry Blending involves consists of porous ceramic plates or fibers covered boxes permeable to air. The is passed into the raw meal through the porous plates where the fine air current fluidize the raw meal.
3.7. PREHEATING AND BURNING
The raw meal is fed into the preheater tower equipped with four cyclone stages. In the dry process, Preheater Tower is150 meters high. Material from the preheater tower is discharged to a rotary kiln having the same diameter as a wet process kiln i.e.2-3 meters but the length is much shorter approximately 45.0 m. The preheater tower and rotary kiln are made of steel and lined with special refractory materials to protect it from the high process temperatures As raw meal falls in the preheater tower, the meal is heated up by the rising hot gases and reaches 800°C. At this temperature, the meal dehydrates and partially decarbonizes.
In per-heater kiln, the first five transformations will take place in pre-heater tower.
The decomposition of limestone and other carbonates will primarily take place in the calciner vessel where the calculate of temperature is maintained by injection of fuel. The last two transformations will take place in the rotary kiln.
The carbonate CaCO3 decomposes between 600 – 800oC to form CaO. Quartz and clay will have started decomposing slightly before that to liberate free reactive Al2O3 and SiO2.
The CaO being formed at this stage, now reacts with SiO2 to form C2S and later with more CaO to form C3S. Some CaO will also react with Al2O3 and Fe2O3 to form various intermediate components such as CA, C12A7 and others, which will decompose at higher temperature at later stage.
C2S content is seen to grow steadily during the heating and reach maximum content at approx. 1300oC which is a point where liquid phase appears. The major part of C2S is then transformed to C3S in the liquid phase and the final content of C2S in the clinker is less than the content of C3S.
The meal then enters a sloping rotary kiln, which is heated by a 1,800°C flame, which completes the burning process of the meal. The meal is heated to a temperature of at least 1450°C. At this temperature the chemical changes required to produce cement clinker are achieved. The dry process kiln is shorter than the wet process kiln and is the most fuel-efficient method of cement production available.
In order to manufacture cement from the raw mix, it is required to heat raw meal to a temperature of 1450oC, thus carrying out SINTERING OR CLINKERISATION. The burning process requires an oxidising atmosphere in the kiln, the clinker of brown colour (contrary to the normal greenish –gray) will be formed and the resulting cement will be quicker setting and with lower strength. Clinkers are hard, gray, spherical nodules with diameters ranging from 0.32 - 5.0 cm (1/8 - 2") created from the chemical reactions between the raw mtrs.
The pyroprocessing system involves three steps:
a. Drying or Preheating (dehydration of the argillaceous minerals)
b. Calcining (decarbonisation or expulsion of CO2)
c. Burning (reactions in solid phase and reactions with the participation of one liquid phase and crystallizations)
The raw mix is supplied to the system as a slurry (wet process), a powder (dry process). For the wet and dry processes, all pyroprocessing operations take place in the rotary kiln, while drying and preheating and some of the calcination are performed outside the kiln on moving grates supplied with hot kiln gases. These processes are influenced by chemical factors in the raw meal (such as its chemical composition), by mineralogical factors (its mineralogical composition), by physical factors (fineness or particle size in the raw meal), homogeneity and other factors. The complete course of these endothermic reactions plays a decisive role in quality of the resulting cements.
3.8. CLINKER COOLING
The clinker cooling operation recovers up to 30% of kiln system heat, preserves the ideal product qualities, and enables the cooled clinker to be maneuvered by conveyors. The clinker discharging from the kiln is cooled by air to a temperature of 70°C above ambient temperature and heat is recovered for the process to improve fuel efficiency. The most common types of clinker coolers are reciprocating grate, planetary, and rotary. Air sent through the clinker to cool it is directed to the rotary kiln where it nourishes fuel combustion. The fairly coarse dust collected from clinker coolers is comprised of cement minerals and is restored to the operation. Based on the cooling efficiency and desired cooled temperature, the amount of air used in this cooling process is approximately 1-2 kg/kg of clinker. The rotary kiln discharges the red-hot clinker under the intense flame into a clinker cooler. The clinker cooler recovers heat from the clinker and returns the heat to the pyroprocessing system thus reducing fuel consumption and improving energy efficiency. Clinker leaving the clinker cooler is at a temperature conducive to being handled on standard conveying equipment.
3.9. CLINKER STORAGE
Some of the air from the cooler is dedusted and supplied to the coal grinding Plant. The remaining air is used as preheated secondary air for the main combustion burner in the kiln. Clinker is analyzed to ensure consistent product quality as it leaves the cooler. Metal conveyors transport the clinker to closed storage areas.
The black, nodular clinker is stored on site in silos or clinker domes until needed for cement production, a plant can normally store 5-25% of the total clinker. Equipment such as conveyors and bucket elevators is used to transfer the clinkers from coolers to storage areas and to the finish mill. Gravity drops and transfer points typically are vented to dust collectors.
3.10. CLINKER GRINDING
Fineness of output materials
• Raw Mix : 15 – 17 % Residue
1.8 – 2.2 % Residue
• Coal Powder : 15 – 17% Residue
18-22 % Residue
• Cement : 33 Grade – 2600 To 2800 Blaine
43 Grade – 2850 To 3000 Blaine 53 Grade – 3200 To 3400 Blaine
Grinding Systems :
• Ball Mill
• Vertical Roller Mill
• Combination of Roller Press and Ball Mill
(Generally open circuit is used in wet process and closed circuit is used in dry process. In closed circuit systems, fixed and dynamic separators are used.)
In the manufacture of Portland cement, clinker is the solid material produced by the cement kiln stage that has sintered into lumps or nodules, typically of diameter 3-25 mm. Clinker is ground (usually with the addition of a little gypsum, that is, calcium sulfate dihydrate) to become Portland cement. It may also be combined with other active ingredients or organic compounds to avoid powder agglomeration. Triethanolamine (TEA) is commonly used at 0.1 wt. % and is proved to be very effective. Other additives are sometimes used, such as ethylene glycol, oleic acid, dodecylbenzene sulfonic acid.
During the final ,,stage of portland cement production known as finish milling, the clinker is ground with other materials (which impart special characteristics to the finished product) into a fine powder. Up to 5% gypsum or natural anhydrite is added to regulate the setting time of the cement. Other chemicals, such as those which regulate flowability or air entrainment, may also be added. Many plants use a roll crusher to achieve a preliminary size reduction of the clinker and gypsum. These materials are then sent through ball or tube mills (rotating, horizontal steel cylinders containing steel alloy balls) which perform the remaining grinding. The grinding process occurs in a closed system with an air separator that divides the cement particles according to size. Material that has not been completely ground is sent through the system again.
http://en.wikipediawiki/File:LDFMBallMill.jpgA ball mill is a horizontal cylinder partly filled with steel ball that rotates on its axis, imparting a tumbling and cascading action to the balls. Material fed through the mill is crushed by impact and ground by attrition between the balls. The smaller grades are occasionally cylindrical ("pebs") rather than spherical. Ball mills are normally operated at around 75% of critical speed, so a mill with diameter 5 meters will turn at around 14 rpm.
The mill is usually divided into two chambers, allowing the use of different sizes of grinding media. The grinding media are usually made of high-chromium steel. Large balls are used at the inlet, to crush clinker nodules (which can be over 25 mm in diameter). Ball diameter here is in the range 60-80 mm. In a two-chamber mill, the media in the second chamber are typically in the range 15-40 mm, although media down to 5 mm are sometimes encountered.
A current of air is passed through the mill. This helps keep the mill cool, and sweeps out evaporated moisture which would otherwise cause hydration and disrupt material flow. The dusty exhaust air is cleaned, usually with bag filters.