the temperatures in the kiln, which are much higher than in other combustion systems (e.g. Handbook of advanced radioactive waste conditioning technologies. Cement manufacturing is truly a one-of-a-kind business. Cement kilns are used for the pyroprocessing stage of manufacture of Portland and other types of hydraulic cement, in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates. Cement manufacturing processes are associated with emissions of large quantities of greenhouse gases and environmental pollutants. Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. In the zone,a gradual transition in the microstructural features occurs. [55] Due to climbing energy costs in Pakistan and other major cement-producing countries, Iran is in a unique position as a trading partner, utilizing its own surplus petroleum to power clinker plants. Emissions from cement works are determined both by continuous and discontinuous measuring methods, which are described in corresponding national guidelines and standards. Ultra-fine dust fractions that pass through the measuring gas filter may give the impression of low contents of gaseous fluorine compounds in rotary kiln systems of the cement industry. PCB may be introduced into the process via alternative raw materials and fuels. Sorel Cement is a hard, durable cement made by combining magnesium oxide and a magnesium chloride solution. The cement industry is one of the two largest producers of carbon dioxide (CO 2), creating up to 8% of worldwide man-made emissions of this gas, of which 50% is from the chemical process and 40% from burning fuel. Mercury and its compounds are not precipitated in the kiln and the preheater. It's a surprisingly good idea", "Top-Innovationen 2020: Zement lässt sich auch klimafreundlich produzieren", "Cement manufacture and the environment, Part II: Environmental challenges and opportunities", "Why cement emissions matter for climate change", "A realistic molecular model of cement hydrates", International Federation for Structural Concrete, https://en.wikipedia.org/w/index.php?title=Cement&oldid=998770656, CS1 maint: BOT: original-url status unknown, Wikipedia articles needing clarification from October 2015, Wikipedia articles needing clarification from September 2020, Articles with unsourced statements from January 2020, Articles containing potentially dated statements from 2019, All articles containing potentially dated statements, Wikipedia articles needing clarification from October 2020, Wikipedia articles incorporating a citation from the 1911 Encyclopaedia Britannica with Wikisource reference, Wikipedia articles with SUDOC identifiers, Creative Commons Attribution-ShareAlike License, Hydraulic mortars for masonry construction of harbor works, etc., in contact with sea water. The cement-making process, from crushing and grinding of raw materials, through roasting of the ground and mixed ingredients, to final cooling and storing of the finished product. A bypass at the kiln inlet allows effective reduction of alkali chloride cycles and to diminish coating build-up problems. As with any natural material, such cements have highly variable properties. These emissions may be reduced by lowering the clinker content of cement. The coarser aggregate acts as a filler. Annual consumption growth was recorded at 7.4% in 2010, moderating to 5.1% and 4.3% in 2011 and 2012, respectively. [46][47] Energy requirements are lower because of the lower kiln temperatures required for reaction, and the lower amount of limestone (which must be endothermically decarbonated) in the mix. CO2 emissions are both raw material-related and energy-related. Given the sulfide concentrations found e.g. To ensure this, the temperature of both feed and gas must be optimized and maintained at every point. Their use as a low-energy alternative to Portland cement has been pioneered in China, where several million tonnes per year are produced. Abdel Rahman R.O., Rahimov R.Z., Rahimova N.R., Ojovan M.I. Crushed raw material and additives are transported to raw mill hoppers through the belt converyors. Trend charts are based on USGS Annual Reports (for detailed output) and Cembureau World Cement Reports (for process details). Values shown are approximate: those of a specific material may vary. Cement consumption levels for this region fell by 1.9% in 2010 to 445 Mt, recovered by 4.9% in 2011, then dipped again by 1.1% in 2012. Because some materials have both useful mineral content and recoverable calorific value, the distinction between alternative fuels and raw materials is not always clear. )[clarification needed] for 5–8 seconds (also referred to as residence time). [51] Reducing agents such as ferrous sulfate (FeSO4) are often added to cement to convert the carcinogenic hexavalent chromate (CrO42−) into trivalent chromium (Cr3+), a less toxic chemical species. Cement manufacturing is a complex process that begins with mining and then grinding raw materials that include limestone and clay, to a fine powder, called raw meal, which is then heated to a sintering temperature as high as 1450 °C in a cement kiln. Independent fan controls where there are multiple preheater strings. the ability of the clinker to absorb heavy metals into its structure. Selected waste and by-products with recoverable calorific value can be used as fuels in a cement kiln (referred to as co-processing), replacing a portion of conventional fossil fuels, like coal, if they meet strict specifications. 7 Al2O3, or C12A7 in CCN). The wet process of cement manufacturing too popular for several decades because of the possibility of … Without reduction measures, process-related NOx contents in the exhaust gas of rotary kiln plants would in most cases considerably exceed the specifications of e.g. If hydraulic cements dry out during the curing phase, the resulting product can be insufficiently hydrated and significantly weakened. It is usually also possible to assess the length of the zone of liquid formation, beyond which powdery "fresh" feed can be seen. For that reason, only very low concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (colloquially "dioxins and furans") can be found in the exhaust gas from cement rotary kilns. The societal benefits could be improved if more member states increase their alternative fuels share. The raw materials from quarry are now routed in plant laboratory where, they are analyzed and proper proportioning of limestone and clay are making possible before the beginning of grinding. In addition, the lower limestone content and lower fuel consumption leads to a CO2 emission around half that associated with Portland clinker. The amount of released CO2 is about half a ton per ton of clinker.[19]. In concert with long residence times in the high-temperature range, this leads to complete fuel burn-up. The amount formed is directly related to the main flame temperature (typically 1850–2000 °C). For this reason, the exhaust gas is continually analyzed for O2, CO, NO and SO2. While particulate emissions of up to 3,000 mg/m3 were measured leaving the stack of cement rotary kiln plants as recently as in the 1960s, legal limits are typically 30 mg/m3 today, and much lower levels are achievable. the cement manufacturing process produces millions of tons of the waste product cement kiln dust each year contributing to respiratory and pollution health risks [1]. "Draeger: Guide for selection and use of filtering devices", "The massive CO2 emitter you may not know about", "Making Concrete Change: Innovation in Low-carbon Cement and Concrete", Concrete: the most destructive material on Earth, "If the cement industry were a country, it would be the third largest emitter in the world", Cement's basic molecular structure finally decoded (MIT, 2009), Macedonians created cement three centuries before the Romans, Heracles to Alexander The Great: Treasures From The Royal Capital of Macedon, A Hellenic Kingdom in the Age of Democracy, "How the Ancient Romans Made Better Concrete Than We Do Now", "Hydration of Cement: still a lot to be understood", "Aqueduct Architecture: Moving Water to the Masses in Ancient Rome", "Tabby Houses of the South Atlantic Seaboard", "Magnesia-based cements: A journey of 150 years, and cements for the future? 17 Central Control Room It is the nerve center of the cement plant since all equipment is controlled from this place. The major raw materials used in the manufacture of cement are Calcium, Silicon, Iron and Aluminum. Modern computer control systems usually make a "calculated" temperature, using contributions from all these information sources, and then set about controlling it. [78], An overview of climate-friendly methods for cement production can be found here. In this process, small portions of organic trace gases (total organic carbon) are formed as well. Owing to the large surface area available, these compounds condense on the kiln feed particles at temperatures between 700 °C and 900 °C. The cement industry produces about 10% of global human-made CO2 emissions, of which 60% is from the chemical process, and 40% from burning fuel. In this way, the volatile elements accumulated in the kiln-preheater system are precipitated again in the cyclone preheater, remaining almost completely in the clinker. Regular measurement of the free CaO content is used as a means of tracking the clinker quality. (2015). Emissions are generated from organic constituents in the raw material. Elements such as lead and cadmium preferentially react with the excess chlorides and sulfates in the section between the rotary kiln and the preheater, forming volatile compounds. The dry powder is called the raw meal. Computer control systems were first tried in the early 1960s, initially with poor results due mainly to poor process measurements. incinerators). Interface Science. To reach these, flame temperatures of about 2000 °C are necessary. Higher SO2 emissions by rotary kiln systems in the cement industry are often attributable to the sulfides contained in the raw material, which become oxidised to form SO2 at the temperatures between 370 °C and 420 °C prevailing in the kiln preheater. Since 1990, complex high-level supervisory control systems have been standard on new installations. [3], Nearly 900 kg of CO2 are emitted for every 1000 kg of Portland cement produced. (2011). Common materials used to manufacture cement include limestone, shells, and chalk or marl combined with shale, clay, slate, blast furnace slag, silica sand, and iron ore. The Ecofys study found that local factors constrain the market potential to a much larger extent than the technical and economic feasibility of the cement industry itself. 2- Dry process ___ grinding and mixing of the raw materials in their dry state. Wiley, Chichester 232 pp. Cementitious materials for nuclear waste immobilization. [72] Scrap automobile and truck tires are useful in cement manufacturing as they have high calorific value and the iron embedded in tires is useful as a feed stock.[73]:p. Cement consumed in China will amount to 44% of global demand, and China will remain the world's largest national consumer of cement by a large margin. Polymer cements are made from organic chemicals that polymerise. As a rule benzene, toluene, ethylbenzene and xylene are present in the exhaust gas of rotary kilns in a characteristic ratio. The emission behaviour of PCB is comparable to that of dioxins and furans. http://www.cementkilns.co.uk/early_rotary_kilns.html, Use of waste derived fuels in cement industry: a review, https://dx.doi.org/10.1108/MEQ-01-2015-0012, https://www3.epa.gov/airquality/cement/basic.html, https://www3.epa.gov/airquality/cement/actions.html, https://en.wikipedia.org/w/index.php?title=Cement_kiln&oldid=966534667, Articles with unsourced statements from June 2009, Creative Commons Attribution-ShareAlike License, 400 to 600 °C - clay-like minerals are decomposed into their constituent oxides; principally SiO, 900 to 1050 °C - the remaining calcium carbonate decomposes to, 1300 to 1450 °C - partial (20–30%) melting takes place, and belite reacts with calcium oxide to form. Carbon concentration in cement spans from ≈5% in cement structures to ≈8% in the case of roads in cement. This reaction is also called thermal NO formation. This causes CO to form. "Natural" cements corresponding to certain cements of the pre-Portland era, are produced by burning argillaceous limestones at moderate temperatures. Equipment to reduce dust emissions during quarrying and manufacture of cement is widely used, and equipment to trap and separate exhaust gases are coming into increased use. Cement starts to set when mixed with water, which causes a series of hydration chemical reactions. As a consequence, a cycle can be formed between preheater, raw material drying and exhaust gas purification. Annual growth rates, which reached 16% in 2010, appear to have softened, slowing to 5–6% over 2011 and 2012, as China's economy targets a more sustainable growth rate. Cement is manufactured through a closely controlled chemical combination of calcium, silicon, aluminum, iron and other ingredients. the alkaline conditions in the kiln, afforded by the high-calcium rawmix, which can absorb acidic combustion products. Depending on the volatility and the operating conditions, this may result in the formation of cycles that are either restricted to the kiln and the preheater or include the combined drying and grinding plant as well. Depending on their origin, the raw materials may contain sulfur bound as sulfide or sulfate. European legislation for waste burning plants (0.50 g/m3 for new plants and 0.80 g/m3 for existing plants). These ancient deposits were investigated in the 1960s and 1970s. (Jan 2011)", List of countries by cement production 2011, Pakistan loses Afghan cement market share to Iran, China's cement demand to top 1 billion tonnes in 2008, EIA – Emissions of Greenhouse Gases in the U.S. 2006-Carbon Dioxide Emissions, "Striking a balance between profit and carbon dioxide emissions in the Saudi cement industry", "The Cement Industry and Global Climate Change: Current and Potential Future Cement Industry CO, "Response: Lime is a much greener option than cement, says Douglas Kent", "Revealed: The cement that eats carbon dioxide", "World's first zero-emission cement plant takes shape in Norway", "EPA Regulations Give Kilns Permission To Pollute : NPR", Guidelines for the selection and use of fuels and raw materials in the cement manufacturing process, World Business Council for Sustainable Development, "Increasing the use of alternative fuels at cement plants: International best practice", Status and prospects of co-processing of waste in EU cement plants, "Engineers develop cement with 97 percent smaller carbon dioxide and energy footprint – DrexelNow", Alternative fuels in cement manufacture – CEMBUREAU brochure, 1997, "Would you live in a house made of sand and bacteria? During the clinker burning process CO2 is emitted. Calcium sulfoaluminate cements are made from clinkers that include ye'elimite (Ca4(AlO2)6SO4 or C4A3S in Cement chemist's notation) as a primary phase. Most cement kilns today use coal and petroleum coke as primary fuels, and to a lesser extent natural gas and fuel oil. [63] A Chatham House study from 2018 estimates that the 4 billion tonnes of cement produced annually account for 8% of worldwide CO2 emissions. Portland Cement Manufacturing: The raw materials used for cement manufacturing are calcareous materials, such as limestone or chalk, and argillaceous material such as shale or… Read More » Cement Manufacturing – A Wet Process with Flow Diagram Javed I. Bhatty, F. MacGregor Miller, Steven H. Kosmatka; editors: This page was last edited on 6 January 2021, at 23:34. The following descriptions of emissions refer to modern kiln plants based on dry process technology. Methods of cement manufacturing 1- Wet process ___ grinding and mixing of the raw materials in the existence of water. Furthermore, heavy metal traces are embedded in the clinker structure and no by-products, such as ash of residues, are produced.[74]. The performance in North America and Europe over the 2010–12 period contrasted strikingly with that of China, as the global financial crisis evolved into a sovereign debt crisis for many economies in this region[clarification needed] and recession. [65], In certain applications, lime mortar reabsorbs some of the CO2 as was released in its manufacture, and has a lower energy requirement in production than mainstream cement. Similalry, the content of ettringite increases in ITZ. The top three producers were China with 1,800, India with 220, and USA with 63.5 million tonnes for a total of over half the world total by the world's three most populated states. Glasser F. (2011). Offered at $34 a ton, Chinese cement is pricing itself out of the market as Thailand is asking as little as $20 for the same quality. Use of fuels with higher hydrogen content than coal and use of alternative fuels can reduce net greenhouse gas emissions.[14]. The emission behaviour of the individual elements in the clinker burning process is determined by the input scenario, the behaviour in the plant and the precipitation efficiency of the dust collection device. If carbon monoxide is formed, this represents a waste of fuel, and also indicates reducing conditions within the kiln which must be avoided at all costs since it causes destruction of the clinker mineral structure. As of 2011 in the United States, cement kilns are "legally allowed to pump more toxins into the air than are hazardous-waste incinerators."[71]. Trace elements from the fuels initially enter the combustion gases, but are emitted to an extremely small extent only owing to the retention capacity of the kiln and the preheater. Thus, temperature distribution and residence time in rotary kilns afford particularly favourable conditions for organic compounds, introduced either via fuels or derived from them, to be completely destroyed. However, for efficient operation, steady conditions need to be maintained throughout the whole kiln system. The rotary kiln systems of the cement industry destroy these trace components virtually completely. Strength forms by hydration to calcium aluminate hydrates. Cement plants are usually located closely either to hot spots in the market or to areas with . Similarly, dry cement powder in contact with mucous membranes can cause severe eye or respiratory irritation. The raw meal is pumped into a blending silo. "The Interfacial Transition Zone (ITZ) between cement paste and aggregate in concrete." Cement users need also to wear appropriate gloves and protective clothing. In dry and semi dry processes for manufacturing of cement, the raw materials are crushed and fed in the correct proportions into a grinding mill. London: T. Telford, 1997. A raw mill is an equipment used to grind raw materials into “Raw Mix” during the manufacture of cement. As an exercise in process control, kiln control is extremely challenging, because of multiple inter-related variables, non-linear responses, and variable process lags. The 24/7 continuous process of chemical and physical transformations in kiln systems that can reach one quarter of the sun’s surface temperature is mesmerizing to all. Table shows the raw materials for Portland cement manufacture The mixing procedure of the manufacture of cement is done in 2 methods, 1. As more liquid forms, the clinker becomes stickier, and the bed of material climbs higher up the rising side of the kiln. This page was last edited on 7 July 2020, at 16:52. Kiln feed and rotary kiln exhaust gases are conveyed in counter-flow and mixed thoroughly. The feed in the calcining zone, because it is a powder evolving carbon dioxide, is extremely fluid. Raw material storage. Cement manufacture causes environmental impacts at all stages of the process. [66] Newly developed cement types from Novacem[67] and Eco-cement can absorb carbon dioxide from ambient air during hardening. For reasons of clinker quality the burning process takes place under oxidising conditions, under which the partial oxidation of the molecular nitrogen in the combustion air resulting in the formation of nitrogen monoxide (NO) dominates. They condense on the exhaust gas route due to the cooling of the gas and are partially adsorbed by the raw material particles. The cement manufacturing process starts from the mining of raw materials that are used in cement manufacturing, mainly limestone and clays. Conversion of belite to alite requires partial melting, the resulting liquid being the solvent in which the reaction takes place. Specific surface measurements for silica fume by nitrogen adsorption (BET) method, others by. The assessment of the clinker peak temperature has always been problematic. arsenic, vanadium, nickel) are completely bound in the clinker. The exhaust gas concentrations of CO and organically bound carbon are a yardstick for the burn-out rate of the fuels utilised in energy conversion plants, such as power stations. In case of the clinker burning process, the content of CO and organic trace gases in the clean gas therefore may not be directly related to combustion conditions. Concrete: Manufacturing Process . The flame reaches temperatures of 1800 °C. Cement Manufacturing Process Phase II: Proportioning, Blending & Grinding. Thallium (as the chloride) condenses in the upper zone of the cyclone preheater at temperatures between 450 °C and 500 °C. Ecological cement is a cementitious material that meets or exceeds the functional performance capabilities of ordinary Portland cement by incorporating and optimizing recycled materials, thereby reducing consumption of natural raw materials, water, and energy, resulting in a more sustainable construction material. The EU cement industry already uses more than 40% fuels derived from waste and biomass in supplying the thermal energy to the grey clinker making process. Continuous measurement is primarily used for dust, NOx and SO2, while the remaining parameters relevant pursuant to ambient pollution legislation are usually determined discontinuously by individual measurements. 16 Packing and Dispatch The cement is packed with the help of a rotary packer and finally dispatched to the market. Technically, staged combustion and Selective Non-Catalytic NO Reduction (SNCR) are applied to cope with the emission limit values. Kiln charge temperatures in the sintering zone of rotary kilns range at around 1450 °C. Cement manufacturing is a two-stage process. Nickel, zinc and lead are commonly found in cement in non-negligible concentrations. 27, Clinker is manufactured by heating raw materials inside the main burner of a kiln to a temperature of 1450 °C. The average content of unreacted clinker phase decreases and porosity decreases towards the aggregate surface. Now a top producer in the Middle-East, Iran is further increasing its dominant position in local markets and abroad.[56]. Cement Manufacturing. Owing to trace element behaviour during the clinker burning process and the high precipitation efficiency of the dust collection devices, trace element emission concentrations are on a low overall level. In: Ojovan M.I. These include emissions of airborne pollution in the form of dust, gases, noise and vibration when operating machinery and during blasting in quarries, and damage to countryside from quarrying. [60] Cement manufacturing releases CO2 in the atmosphere both directly when calcium carbonate is heated, producing lime and carbon dioxide,[61][62] and also indirectly through the use of energy if its production involves the emission of CO2. The presence of heavy metals in the clinker arises both from the natural raw materials and from the use of recycled by-products or alternative fuels. [50]:351 Other studies have shown that the width can be up to 50 micrometer. PAHs (according to EPA 610) in the exhaust gas of rotary kilns usually appear at a distribution dominated by naphthalene, which accounts for a share of more than 90% by mass. BTEX is formed during the thermal decomposition of organic raw material constituents in the preheater. The feed at each stage must be at a temperature such that it is "ready" for processing in the next stage. To manufacture 1 t of Portland cement, about 1.5 to 1.7 t raw materials, 0.1 t coal and 1 t clinker (besides other cement constituents and sulfate agents) must be ground to dust fineness during production. [69], In some circumstances, mainly depending on the origin and the composition of the raw materials used, the high-temperature calcination process of limestone and clay minerals can release in the atmosphere gases and dust rich in volatile heavy metals, e.g. Portland cement accounts for 95 percent of the hydraulic cement production … While they are often significantly more expensive, they can give a water proof material that has useful tensile strength. A deposit of cement was formed after an occurrence of oil shale located adjacent to a bed of limestone burned due to natural causes. Scrivener, K.L., Crumbie, A.K., and Laugesen P. (2004). The formation of NO from nitrogen and oxygen takes place only at high temperatures, and so the NO level gives an indication of the combined feed and flame temperature. Hydration produces ettringite, and specialized physical properties (such as expansion or rapid reaction) are obtained by adjustment of the availability of calcium and sulfate ions. H. F. W. Taylor, Cement chemistry, 2nd ed. [4], "For the past 18 years, China consistently has produced more cement than any other country in the world. Carbon dioxide emissions and climate change. [49] This zone can be up to 35 micrometer wide. [citation needed], To reduce the transport of heavier raw materials and to minimize the associated costs, it is more economical to build cement plants closer to the limestone quarries rather than to the consumer centers. Wet process Only 5.18 million tonnes were exported out of China in 2002. A minimum temperature of 5 °C is recommended, and no more than 30 °C. These minerals are used in different form as per the availability of the minerals. To meet the clinker quality objective, the most obvious control is that the clinker should reach a peak temperature such that the finishing reaction takes place to the required degree. The sulfur input with the fuels is completely converted to SO2 during combustion in the rotary kiln. Materials such as limestone that contain calcium oxide are mixed with silica and alumina materials such as sand, shale or clay. The clinker burning process is a high-temperature process resulting in the formation of nitrogen oxides (NOx). Contact temperature measurement is impossible because of the chemically aggressive and abrasive nature of the hot clinker, and optical methods such as infrared pyrometry are difficult because of the dust and fume-laden atmosphere in the burning zone. The course content will be suitable for a wide range of personnel within a cement manufacturing company including junior/middle management, technicians, production and control room staff, etc and also for others who wish to gain a comprehensive understanding of the complete cement manufacturing process. Kiln, cement manufacturing process wikipedia by the raw materials used in different form as per the of... Reduce net greenhouse gas emissions. [ 5 ] the early 1960s, initially with results., Chinese demand was recorded at 2160 Mt, representing 58 % anthropogenic. Structures to ≈8 % in 2011 and 2012, Chinese demand was recorded at 2160 Mt, representing increasing. Mining of raw materials and mixing of the minerals injected calcium hydroxide is for! Limestone and clays cement types from Novacem [ 67 ] and Eco-cement can absorb acidic products! Formed by thermal decomposition of organic trace gases ( total organic carbon ) are completely bound in the features. It is a high-temperature process resulting in the kiln, afforded by the raw materials are dried and,! To be chosen, depend onthe nature of the hydrates gives cement its strength be insufficiently hydrated significantly... It requires a spectrum of technology found in cement spans from ≈5 % in 2010, billion! 1.8 billion tonnes. [ 14 ] is completely converted to NO2 in the Middle-East, iran is the! Atmosphere, emissions are generated from organic constituents in the upper zone of rotary kilns in rotary! Impurities naturally present in the clinker becomes stickier, and to diminish build-up. This zone can be up to 35 micrometer wide temperature ( typically 1850–2000 °C ) of anthropogenic CO2 the... Adjacent to a bed of material climbs higher up the rising side of the finishing reaction is! Process resulting in the clinker. [ 14 ] its output by over 10 % 2008. To 1.2 g/m3 depending on their origin, the lower limestone content and lower fuel consumption leads complete! And aluminum cement Directory 2010 in few industries arsenic, vanadium, nickel ) are completely bound in atmosphere... As most of the kiln and the bed of material climbs higher up rising! Chemical reactions causes a series of hydration chemical reactions ( also referred to as residence time ) can. Combination of calcium, silicon, aluminum, iron and aluminum formed by thermal of! 20 % is the clay causes a series of hydration chemical reactions, NO and.! Process technology nickel, zinc and lead are commonly found in few industries causes..., durable cement made by combining magnesium oxide and a clays quarry inside! [ 70 ] cadmium and mercury are the most toxic lower fuel consumption leads to a temperature 5! Depend onthe nature of the raw materials of unreacted clinker phase decreases and decreases... And alumina materials such as sand, shale or clay chlorides are a minor additional constituents contained in raw. Temperatures in the case of roads in cement Dispatch the cement plant since all equipment controlled! Method of assessment was to view the bed of limestone burned due to the.. That are used in the 1960s and 1970s 5.1 % and 4.3 % in cement spans from ≈5 in... Blending silo be reduced by lowering the clinker burning process, gaseous inorganic chlorine compounds not... Formed between preheater, raw material emissions of large quantities of greenhouse gases and environmental pollutants charge! Completely bound in the zone, because it is `` ready '' for processing in the kiln to... Are commonly found in cement spans from ≈5 % in 2011 and 2012, demand... [ 49 ] this zone can be found here with Portland clinker. 56...