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Technological Trends in Cement Industry

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Technological Trends in Cement Industry - Energy and Environmental impact G. Jayaraman Associate Director, Price Waterhouse, Chennai About the author: Mr. G. Jayaraman, graduate in Mechanical Engineering with Post Graduate Diplomas in Industrial Engineering, SQC and OR, is presently Associate Director, Price Waterhouse, Chennai. He has more than 40 years of experience in cement, refractory, chemicals and fertilisers industries. He has made notable contribution in cement engineering and technolo
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  Technological Trends in Cement Industry - Energy and Environmentalimpact G. JayaramanAssociate Director, Price Waterhouse, ChennaiAbout the author  : Mr. G. Jayaraman ,graduate in Mechanical Engineering with Post Graduate Diplomas inIndustrial Engineering, SQC and OR, is presently Associate Director, Price Waterhouse, Chennai.He has more than 40 years of experience in cement, refractory, chemicals and fertilisersindustries. He has made notable contribution in cement engineering and technology, qualityassurance and R&D. He has headed cement plants in the Associated Cement Companies (ACC)and Aditya Birla group's cement business. He spear-headed their expansion and up-gradation.He is associated with several institutions like Indian Value Engineering Society (INVEST),National Council for Cement and Building Materials (NCB), Confederation of Indian Industry (CII)Institution of Engineers (India), Institution of Industrial engineers, Compute society of India,Operations research society of India.He is also a member of the energy and environmental sub-committee of the Confederation of Indian Industry (CII). He has contributed a number of papers on cement and other engineeringsubjects. Introduction Indian cement industry has come a long way in technological upgradation, production and quality.India today, is the second largest cement producing country in the world with an installed capacityof 119 million metric tons per annum. The cement industry in India has a distinction of operatingvery large to very small capacity and very modern to very old technology plants. Some of themodern plants can be compared to the best plants in the world in terms of quality, variety of cements produced and energy efficiency. Indian cement industry has been very proactive inadopting various technological advancements taking place all over the world. This wasparticularly triggered by the partial decontrol of cement industry in 1982 followed by full decontrolin 1989 giving the resultant free market competition an opportunity for growth in production andproductivity.The share of energy inefficient wet process plants had slowly decreased from 94.4% in 1960 to61.6% in 1980. Thereafter as a result of quantum jump in production capacities throughinstallation of modern dry process plants as well as conversion of some of the wet process plants,the share of wet process has reduced to less than 5% today.During the last two decades (80's and 90's), major technological advancements took place indesign of cement plant equipment/systems basically in the following major areas  a) pre-calcinationb) high pressure grindingc) automation in process controld) high efficiency particle separatione) clinker coolingThese resulted in sea change developments globally and the Indian cement industry followed theinternational trend. The special features noticeable were:(i) standard size of the new plants neared a million tonnes per annum(ii) large areas of limestone even in remote areas exploited by cluster of plants(iii) active search made for the latest type of technology and equipment to continually bringdown the energy costs(iv) large number of old wet process plants closed down or converted into dry process onaccount of high cost of operation(v) introduction of multiple grades of cement on strength parameters surpassing theBureau of Indian Standards (BIS) specifications(vi) many plants taking to automation, computer controlled systems and man power reduction(vii) Improvement in packaging with the use of HDPE/PP/paper bags in place of conventional jute bags(viii) shift in the marketing strategy with specific emphasis on quality associated with brandThe industry never looked back. The financial investments were justified on energyconservation, quality enhancement and environmental consideration. Energy Conservation  A typical modern cement plant has heat consumption of 680-720 kcal/kg clinker and power consumption of 70 - 85 Kwh/tonne of (OPC-43) cement. A few recent technologies that helped Indian cement industry to consolidate in sustained energysavings are broadly discussed below. Raw Material Grinding Raw material grinding is a critical mechanical operation predominantly determining the sizing of equipment in a cement plant. Raw grinding process consumes about 20% of the total energyconsumed in the plant. Various grinding systems used in Indian cement industry for raw materialgrinding are:a) Ball millsb) Vertical Roller Mills (VRM)c) Ball mills with high pressure grinding rolls.d) High pressure grinding rollse) Horizontal roller millsSelection of type of grinding mill depends on the raw material's several physical characteristicsmost important amongst which are hardness of the material and moisture content. Availability of the major grinding equipment in appropriate capacity decides complexity or otherwise of layout,auxiliary equipment sizing etc. which ultimately decide plant's pyro-processing capacity.Vertical roller mills have been widely accepted for combined grinding and drying of moist rawmaterials in view of their excellent drying capacity and low energy consumption. Although theprinciple of the vertical roller mill did not change over the years, many improvements have been  made in design of mill and other equipment in the grinding circuit resulting in less energyconsumption and improved reliability. Introduction of external re-circulation of material, adjustablelouvre ring and modification of mill body to improve the air and material trajectories are examplesof such design changes.While a number of plants are still using ball mills, many have installed pre-grinders like roller press to improve energy efficiency. Here, the extent to which the roller press is loaded determinesthe efficiency of the grinding circuit. Use of roller press alone as a finish grinding equipment togive the final product is also a new development.Horizontal roller mill is yet another improvement in grinding systems incorporating the advantagesof vertical roller mill and roller press. An additional advantage with the horizontal roller mill is itslow space requirement due its compact size. A compact horizontal roller mill with an in-builtseparator is now in the process of development. This kind of a mill would eliminate many smallconveyors carrying material to separator and from separator.The efficiency of the grinding circuit and power consumption of the mill fan greatly depend on theperformance of the classifier. Perhaps classifier is the part that has undergone maximumchanges and has been the target part for efficiency improvement. A variety of high efficiencyclassifiers are employed in grinding circuits. Apart from the main equipment viz., mill, classifier and fan the efforts have been on improving theperformance of internals e.g. table liners in case of vertical roller mills and classifying liners incase of ball mills. Use of mechanical conveying systems like bucket elevators is becoming morecommon in place of pneumatic conveying giving substantial savings in energy. Pyro-processing Pyro-processing section in a cement plant comprises preheater, rotary kiln and clinker cooler.Pyro-processing section is considered to be the heart of a cement plant as actual cement clinker formation takes place in kiln. The size of a cement plant is determined based on pyro-processingsection and the sizes of all other equipment are determined to match pyro-processing. The shapeof cement plants changed with the advent of preheater in 70's. With the introduction of pre-calciners in 80's, the size of cement plant had considerably increased. A 600 tpd considered to beeconomic size of kiln earlier went up to 3300 tpd in 80's and further to 7000 tpd currently. Avariety of preheaters with different designs of precalciners have come into existence.Preheaters can be classified into the following 5 categories irrespective of the manufacturer.a) preheater without calciner b) inline calciner with air passing through the kilnc) inline calciner with external tertiary air ductd) separate line calciner e) separate line calciner with inline calciner With the above five modes of operation, different equipment manufacturers came out withdifferent designs normally designated in the manufacturing company's name. Cyclones are basicunits in a preheater system. Pressure drop and change of temperature of gas across each stagedetermines the efficiency of cyclones. Introduction of Low Pressure drop (LP) cyclones hasbrought the pressure drop across each stage to around 50 mm WG from around 150 mm WG inconventional cyclones. This has resulted in more and more plants adopting 5 or 6 stages of preheater. A typical 6 stage preheater with LP cyclones will have a preheater exhaust gastemperature of around 2500C and draught of around 500 mm WG. This in turn lead to decrease  in preheater fan power consumption. The reduced temperatures at preheater exhaust contributeto environmental improvement.The burners also play an important role in determining the thermal efficiency of the pyroprocessing system. There has been a continuous effort on operating the burners with the leastpossible primary air. The advent of multi-channel burners taking only 5% primary air are beinginstalled in many plants giving a direct thermal energy saving of 15 kcal/kg clinker. Apart fromsaving thermal energy, the modern burners also enable easy flame control.Clinker cooler is a critical equipment and the size of clinker cooler some times becomes a bottle-neck for increasing production from rotary kiln. The function of a clinker cooler in a cement plantis dual i.e. reducing the temperature of the clinker to a level that is acceptable for further transportand grinding and recover energy from the sensible heat of the hot clinker by heating the coolingair. Thus thermal efficiency of clinker cooler is very important in deciding about the type of cooler.Mainly two types of clinker coolers are used at present in cement industry. They area) Grate cooler b) Planetary cooler In majority of the existing plants, conventional grate coolers are used. These coolers have lower recuperation efficiency, occupy more space and need more cooling air. Inspite of these drawbacks, grate coolers are more widely used than planetary coolers primarily due to comparativelyhigher thermal efficiency. There have been a number of design improvements in grate coolers inrecent times, mainly on grate plate to improve the efficiencies simultaneously reducing thecooling air intake. The specific load of clinker on grate plate can be as high as 50 tpd/m2. Thesemodern coolers are compact in size. High efficiency coolers operate on the principle of Horizontalaeration. More and more cement plants with conventional grate coolers are retrofitting the coolerswith high efficiency coolers.By installing high efficiency coolers, it is possible to reduce the cooling air to about 1.8 Nm3/kgclinker from conventional value of more than 3 Nm3/kg clinker. This has resulted in low electricalenergy consumption in cooling air fans and also in cooler ID fan. Thus high efficiency coolers giverise to both thermal and electrical energy conservation.The inlet and outlet seals of kiln are important, as they help to reduce the air infiltration into thesystem. With the improved kiln seals available today, not only heat loss is reduced but also theenvironment around kiln has become almost dust free. A pneumatic seal for kiln inlet and springloaded mechanical seal for kiln outlet are considered to be very effective in modern kilns.Cement GrindingCement grinding is another energy intensive operation in cement manufacture Cement grindingconsumes around 25-30% of the total energy consumed in a cement plant. Typical cementgrinding systems in use area) open circuit millsb) closed circuit millsc) roller press with open circuit ball milld) roller press with closed circuit ball mill.e) roller press in finished modef) vertical roller millg) horizontal roller millBall mills have traditionally been in use for many years in open circuit and closed circuit mode. Inrecent past, roll press as pre grinders have been introduced. This has given a substantial benefit
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