book of cement production process technology

cement production technology by chatterjee, anjan kumar (ebook)

The book is an outcome of the authors active professional involvement in research, manufacture and consultancy in the field of cement chemistry and process engineering. This multidisciplinary title on cement production technology covers the entire process spectrum of cement production, starting from extraction and winning of natural raw materials to the finished products including the environmental impacts and research trends. The book has an overtone of practice supported by the back-up principles.

cement production - an overview | sciencedirect topics

Cement production has undergone tremendous developments since its beginnings some 2,000years ago. While the use of cement in concrete has a very long history (Malinowsky, 1991), the industrial production of cements started in the middle of the 19 th century, first with shaft kilns, which were later replaced by rotary kilns as standard equipment worldwide. Today s annual global cement production has reached 2.8 billion tonnes, and is expected to increase to some 4 billion tonnes per year in 2050 (Schneider et al., 2011). Major growth is foreseen in countries such as China and India as well as in regions like the Middle East and Northern Africa. At the same time, the cement industry is facing challenges such as cost increases in energy supply (Lund, 2007), requirements to reduce CO2 emissions, and the supply of raw materials in sufficient qualities and amounts (WBCSD, 2008).

In this chapter, the environmental impact of cement production will be described. The chapter will first focus on the most common cementitious product: ordinary Portland cement (OPC) and will then evaluate the main perspective in terms of reduction of cement production s environmental impacts. To do so, we will describe the improvement perspective in the cement sector as well as the alternative products that could, at least partially, replace OPC.

Cement production is a thermal energy intensive process, which requires heating solid particles up to 1450C and cooling it down. The process generates hot and CO2 rich exhaust streams. Fin order to study energy efficiency of the process, authors like Mujumdar et al. (2006, 2007) developed detail models of process units, while others highlighted energy and exergy performances of plants (Kolip et al 2010). Some authors have studied the integration of cogeneration units in cement industry as an option of waste heat recovery (Wang et al 2008). The previously mentioned studies are considering, in detail, thermodynamic performances, but they are not investigating the heat integration inside the process. Some other authors, such as Murray et al (2008), Kaantee (2004), Mokrzycki (2003) have focused their analysis in the use of alternative/waste fuels, but they did not show the impact and the potential of these fuels on the heat integration between streams.

This paper explores the use of process integration techniques to improve the energy efficiency of cement plants, focusing on the dry route cement production and the integration of alternative fuels. Flow sheeting modeling, Pinch Analysis and mixed integer linear optimization techniques are applied to study an existing cement production facility.

Cement production is one of the largest industries in the world. Annual world production in 2013 was approximately 4 GT (of which, about half was in China). It is produced in kilns at around 1400oC (2500oF), and approximately 750 kg (1650 lb) of CO2 are released for each tonne (2205 lb.) that is made. This is 400 m3 (524 yd3) of gas; and CO2 normally forms only 0.04% of air. Cement production is responsible for around 7% of worldwide greenhouse gas emissions. The only larger contributors are electricity generation and transport.

Most of the CO2 released when cement is made comes from the chemical reaction. The limestone from which it is made is calcium carbonate, and when this is heated it gives off carbon dioxide, and forms calcium oxide. Thus, while some benefit has been obtained by making the process more energy efficient, there is little scope for any further reductions.

Numerous different solutions to this problem have been proposed, including carbon capture and inventing completely new cements; but the only effective method currently used to achieve significant reductions in greenhouse gas emissions is the use of cement replacements.

One process that has not been extensively investigated is carbon sequestration. In this process, the hydrated cement reacts with CO2 in the air, slowly reversing some of the processes that took place in the kiln when the cement was made (this is the carbonation process; it also causes reinforcement corrosion, see Section 25.3.2). It is estimated that this may reduce the carbon footprint of the cement industry by 35%.

Cement production is an energy-intensive process. The cost of energy constitutes more than 60% of the cost of the cement; hence cement plants have to consider minimizing the cost of energy when planning production. However, there are several challenging issues regarding the production plan. First, there are some operational constraints for the production process itself, such as keeping a proper level of inventory. Second, electricity prices are not fixed; they change on an hourly basis. Hence the cost of the electricity consumed may change substantially depending on the time of production. In this study, we developed a mixed integer programming model to minimize the cost of production (including energy, labor, and storage) by shifting working times to hours with low energy costs and trying to maintain activities during hours with high energy costs.

Cement production processes can be categorized as dry, semidry, semiwet, and wet processes depending on the handling of raw material before being fed to the rotary kiln. Nowadays, almost all new plants are based on the dry process and many old wet plants are also remodeled to dry or semidry processes. Dry cement manufacture has three fundamental stages: preparation of feedstocks, production of clinker, and preparation of cement [15,16].

Preparation of feedstock. This stage includes the process of siege, crushing, and prehomogenization. Typical raw materials used for cement production have 85% cayenne, 13% clay or blackboard, and under 1% each of materials such as silica, alumina, and iron ore. These feedstocks are crushed into particles with a diameter of less than 20mm and mixed with a prehomogenization pile [17].

Clinker production. As shown in Fig.6.6, the feedstock first enters the raw material to make a fine powder (raw feed), where 85% of the material is slightly smaller than 88m. Then, the feed is transferred to the homogenizing silos to impair the material difference. After that,the meal is thrown into the precalciner tower to start the chemical change to cement. Precyclone towers intermix with raw feed and almost 1000C of exhaust gas to recover energy, preheat feed, and initiate chemical reactions that result in cement. Gases straight from the kiln, but in precalciner facilities, gasoline, and air are provided by a combustion vessel inside the tower and kiln. Typically, 60% of burned calciner and more than 90% calcination have been reached before the material enters the rotary kiln. Inside the kiln, temperatures reach approximately 1400C to complete the process of chemical reactions and produce calcium silicates, called clinkers, with a diameter of 1025mm. The gas from the preheater tower is usually blended in a rawmill, which will help stabilize the future feedstock. After flowing through the rawmill, the gases are eventually released by a dust collector, which also obtains good particles when feedstuffs are milled. The dust will then be recycled into homogenizing silos and served as part of the kiln feed.

Preparation of cement. This stage completes the manufacturing process where clinker nodules are milled into cement. Following clinker milling, the cement is ready for use as a binder in various concrete mixes.

The cement production process, for example, starts with mining of limestone, which is then crushed and ground to powder. It is then preheated to save energy before being transferred to the kiln, the heart of the process. The kiln is then heated to a high temperature of up to 1480 degrees to convert the material to a molten form called clinker. The clinker is then cooled and ground to a fine powder with other additives and transferred to storage silos for bagging or bulk transportation (Portland Cement Association, 2014). The production of cement is either through the wet or dry process with the dry process as the preferred option because of the lower energy intensity. Cement production accounts for about 5% of total anthropogenic emissions (IFC, 2017). Cement-based structures constitute the largest surface area of all man-made structures (Odigure, 2009). World cement demand was about 2.283 billion tons in 2005, 2035 million tons in 2007, and 2836 million tons in 2010 with an annual estimated increase of about 130 million tons (Madlool, Saidur, Hossaina & Rahim, 2011; Odigure, 2009). World total cement production for 2016 was about 4.2 billion tons with emerging markets playing a dominant role (IFC, 2017). The energy intensity of cement production ranges from 3.6 to 6.5 GJ/ton depending on production process and location of the production (Hammond and Jones, 2011; Ohunakin et al., 2013; Worrell et al., 2000).

Cement production is one of the largest contributors to CO2 emissions. SCMs have been partially or completely used as replacement of cement or fine aggregates in construction to reduce the demand of cement and corresponding CO2 emissions (Al-Harthy etal., 2003; Babu and Kumar, 2000; Bondar and Coakley, 2014; Cheng etal., 2005; Jia, 2012; Khan and Siddique, 2011; Kunal etal., 2012; Limbachiya and Roberts, 2004; Lothenbach etal., 2011; Maslehuddin etal., 2009; Najim etal., 2014; Nochaiya etal., 2010; Siddique, 2011; Siddique and Bennacer, 2012; Toutanji etal., 2004). Some of the established SCMs are fly ash, silica fume, blast furnace slag, steel slag, etc. Pozzolanic materials, such as fly ash, steel slag, and cement kiln dust (CKD) when used as replacement to cement, improve the long-term performance of concrete as the pozzolanic reaction takes time. But, the early age strength of SCMs is a concern, as the reduction in cement content causes lesser hydration and, consequently, lesser formation of CSH gel (Lothenbach etal., 2011). The problem of low early strength of SCMs can be solved by using carbonation curing at early ages.

Apart from CO2 sequestration, carbonation curing has also been found to act as an activation mechanism for SCMs (Monkman etal., 2018). Many studies have tried to assess the effect of ACC on use of SCMs (Monkman and Shao, 2006; Sharma and Goyal, 2018; Zhan etal., 2016; Zhang etal., 2016; Zhang and Shao, 2018). ACC not only enhances the hydration degree of alternative cementitious materials but also improves the early age performance of concrete. Monkman and Shao (2006) assessed the carbonation behavior of blast furnace slag, fly ash, electric arc furnace (EAF) slag, and lime. All four materials reacted differently when subjected to carbonation curing of 2h. Fly ash and lime showed highest degrees of carbonation, followed by EAF slag, whereas ground granulated blast slag (GGBS) showed least reactivity towards CO2. Calcite was the major reaction product from fly ash, lime, and EAF slag, whereas aragonite was produced by carbonation of GGBS. Sharma and Goyal (2018) studied the effect of ACC on cement mortars made with CKD as cement replacement. ACC was found to improve the early age strength of cement mortars by 20%, even for mortars with higher CKD content. Several studies tried to assess the CO2 sequestration ability of steel slag binders (Bonenfant etal., 2008; He etal., 2013; Huijgen etal., 2005; Huijgen and Comans, 2006; Ukwattage etal., 2017). Presence of C2S component in steel slag makes it a potential cementitious material that could act as a carbon sink for CO2 sequestration (Johnson etal., 2003).

Zhang etal. (2016) in their study found that fly ash concrete was more reactive to CO2 as compared with OPC concrete. With the reduction in OPC content, a porous microstructure was generated due to insufficient hydration reaction. The enlarged distance between cement grains facilitated higher possibility of reaction with CO2, and hence, a higher degree of CO2 sequestration. The performance of SCMs subjected to carbonation curing is majorly dependent upon fineness of material and water content postcarbonation. Finer particle size of SCMs provides a higher specific area for effective carbonation reaction. Due to this, it was observed in many studies that concrete made with SCMs had better reactivity toward CO2 than OPC (Monkman and Shao, 2006). Water content postcarbonation also plays a dominant role in determining the performance of SCMs. Sufficient water content postcarbonation is necessary for complete hydration and pozzolanic reaction of SCMs (Monkman and Shao, 2006).

In Europe, cement production decreased by 26.9% from 1990 to 2012, whereas CO2 emissions decreased by 38.6%, showing an improvement in the cement production (CEMBUREAU, 2014). However, to reach the objectives of various sustainability programs, further efforts must be made in order to improve every step in the concrete production line. For concrete, the main solutions for reducing the environmental impact of modern construction are (Flatt et al., 2012):

Some other technical solutions to improve cement production are also of interest, including CO2 capture and storage. If this solution were to present a major impact on the final objective, it would need technological breakthroughs that are still in the research phase and are not planned to be ready for users before 2030, but they could potentially capture up to 45% of the CO2 produced by cement (IEA and WBCSD, 2010). By 2050 the baseline emissions will be 2.34 gigatonne (Gt) but will be reduced to blue emissions of 1.55Gt by the contribution of energy efficiency (10%), use of alternative fuels and other fuel switching (24%), clinker substitution (10%) and carbon capture and storage (56%) (IEA and WBCSD, 2010).

The worldwide use of blended cement in the production of cement is already a commonly used improvement, with significant investments for research made by cement producers (Table 15.7). Many blended cement types exist because of the great variability of usable SCMs. These cement types are produced by replacing part of clinker with SCMs, which leads to cement with unchanged or improved properties for both general and special applications. The same properties must be maintained; otherwise, for a functional unit (concrete beam) and on a product scale (cement), more cement may be necessary to obtain the same durability. Therefore the beneficial impact of replacing a part of clinker can be useless (Li et al., 2004). In the European context, binary cement incorporates up to 35% of each type of SCM even in the case of inert mineral fillers, and ternary cement uses up to 80% in mass replacement of clinker (EN 197-1, 2001). A final trend is the development of quaternary binder, but a lot of improvements remain necessary in order to ensure a better understanding of the interactions between clinker and SCMs.

As the CO2 resulting from the decarbonation of limestone during the calcination process is a fixed amount by clinker volume, the two major solutions are optimisation of the heating process to reduce the energy needed to reach 1450C and the use of blended cements.

The improvement of a specific burning process leads to no or very little change in the reduction of CO2 emissions, but a change from a wet process to a dry process with preheating and precalciner kilns can lead to significant improvements (WBCSD, 2013). The energy used by a wet kiln is estimated to be between 5.9 and 6.7GJ/tonne of clinker, whereas a kiln with preheating and precalciner kilns uses only 2.9 to 3.3GJ/tonne of clinker (reduction by 50%). Shifting the cement production from wet to dry with preheating and precalciner kilns can lead to a reduction of 20% (International Energy Agency, 2010) of the energy needed and 17% in the amount of CO2 emitted per tonne of clinker (Damtoft et al., 2008). It can be seen that the increase in part of the clinker produced by this technology could partially overcome the increase in cement production (WBCSD, 2013). These savings could be increased by the use of more alternative fuels (Nielsen and Glavind, 2007) (to coal, which actually accounts for 60% of the fuel used in cement production).

The use of SCMs in concrete is different from using them to produce blended cements. There is no guarantee on the potential strength achieved by a mixture of cement and SCM because of the great variability in the physicochemical properties of SCM. In order to control the amount used in concrete, use of SCM has been standardised through the k-value concept (Smith, 1967). This concept is based on the potential reactivity of each SCM, which helps in fixing a maximal replacement rate of cement to achieve the same mechanical and durability properties. The k-value for each addition differs depending on the type, on the concrete exposure conditions (frost, salt, sulphate, etc.)and on the local national standards. Depending on the type of SCM, the volume used and the targeted concrete strength, the savings in terms of CO2 emissions can be more than 20% (Table 15.9).

The previous solutions for improving the environmental aspect of concrete are widely used and remain of interest for further development, and some new, challenging solutions are also being studied but will need either breakthrough technology or huge investments in development. So far emissions of CO2 are inherent to cement production, so finding ways to prevent this gas from getting into the atmosphere need to be explored, as illustrated next.

Carbon capture and sequestration (CCS): This process consists basically of capturing the CO2 before it is released into the atmosphere and then compress it and store it underground (in mines, caves, oceans). Unfortunately, currently this process remains quite expensive and energy-consuming. Nevertheless, it is a new technology which can be improved in the future. On the other hand, it can also be argued that far from dealing with the problem, CCS is just a way to avoid the problem and leave it for later. Therefore it is totally in contradiction with sustainable development, which is defined by the Brundtland report (United Nations, 1987) as a development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

Biofuel production: Although this approach is not yet totally explored, some researches have shown that captured carbon can be used in the production of algae that can then be transformed to biofuel, agricultural fertilizer or even animal protein (Potgieter, 2012).

Electrochemical carbon reduction (ECR): This process involves creating a reaction which will transform carbon into formic acid. This product is often used in the pharmaceutical industry. It is usually manufactured with high energy consumption but ERC requires less energy (Potgieter, 2012).

The first approach will be to reduce the volume of CO2 in the production of cement which is emitted into the atmosphere. But the most interesting solution in the short-term will be the development of alternative binders with a lower environmental impact, and some proposed solutions already provide excellent results on a laboratory scale or event in pilot projects (Aldred and Day, 2012; Duxson and Provis, 2008; Owens et al., 2010). Alkali-activated cements are aluminosilicatepozzolana-based materials (glass furnace slag, natural volcanic glass, manmade glass, fly ash, metakaolin). The activation occurs between the alumina-rich pozzolana and a strong alkali base, which dissolves the silicate and aluminate groups to form a cementitious gel to form the structure of the matrix. The so-called geopolymer is proven to have similar mechanical properties as cement-based concrete with a lower environmental impact (Duxson et al., 2007). This solution is already implemented in Australia by using fly ash and slag (Duxson and Provis, 2008). This solution is, however, hindered by some practical aspects, including the robustness of the design of the mix, the heat needed for a proper reaction to occur in a reasonable amount of time, the limited amount of available aluminosilicate compounds, the handling of the alkaline activator on the job site, the cost, and the environmental impact of the activator (Flatt et al., 2012).

Belite-rich cement, with a combination of calcium sulphoaluminate and calcium sulphoferrite, have been tested with success. Compared to ordinary Portland cement, belite-rich cement contains relatively higher belite (C2S) and lower alite (C3S) contents (Chatterjee, 1996). Belite-rich cement produces performances comparable to cement with the production of 2030% less CO2 (Li et al., 2007).

Some specially designed concretes have been developed with the eco-efficiency of products at a structural level in mind. This is particularly the case of HPC, including SCC (Hossain et al., 2013; Sonebi and Bartos, 1999, 2002). First, SCC will not act directly on the environmental aspect of sustainability, but rather on economical and societal aspects. When properly designed from the beginning, a construction made of SCC brings economic benefits by increasing the productivity because of the higher casting rate and the reduction in manpower which results in the elimination of vibration. This latter aspect also has a major societal aspect because it reduces the noise at construction sites and concrete factories and removes the risk of injury to workers related to crowded construction sites and vibration (Nielsen, 2007). The use of SCC in concrete factories (Yahia et al., 2011) can also be a solution for increasing mould service life and saving energy. In the case of concrete pipes, this reduction can be about 1.0GWh (De Schutter et al., 2010). Note also the reduced need for post-treatment of a surface by plaster, which accounts for 0.57kg of equivalent CO2 per m2, or by paint because of the better finish of concrete surfaces (Witkowski, 2015). This latter aspect can also increase the CO2 uptake by concrete carbonation because the concrete surface has no applied post-treatment. The major issue of SCC is that proportioning of a mix involves a significant amount of cementitious material in order to improve the workability of the concrete. This problem can be overcome with the development of high-performance chemical admixtures, use of high SCM content (Diederich et al., 2013), and an adequate selection of the granular skeleton of solid particles to achieve proper rheological properties of concrete. The latter approach has allowed the production of Eco-SCC with 40% fewer CO2 emissions than standard vibrated concrete, along with a 150-year service life (Mansour et al., 2013).

The development of high-strength concrete and high-strength, fibre-reinforced concrete is also a new approach to sustainability in construction materials. These concrete types are designed with a relatively greater amount of binder (cement and SCM) and chemical admixture, which achieves better performance than conventional concrete, including 316 times more compressive strength, 10 times more flexural strength and 10100 times more durability than conventional concrete does (Wang et al., 2015). These high performances allow a reduction in the size of elements for similar structural performance, therefore leading to a lower volume of concrete for the same structure. This reduction in volume can lead to a reduction of 65% in raw materials consumed, 51% in the primary energy used, and 47% in CO2 emissions (Batoz and Rivallain, 2009).

Currently in the United Kingdom, concrete debris is not sent to landfills but is treated so it can have a second life in the construction sector. Indeed, concrete is a material that can be fully recycled. In 2011 recycled and secondary aggregates represented about 5.3% of all aggregates used in concrete (Concrete Centre, 2011). This material is used mainly in road construction, but recycled concrete aggregates (RCA) can count for up to 30% of the aggregates in a concrete mix. In the United Kingdom recycled and secondary materials represent 28% of the total aggregates used in the marketplace, the highest in the Europe. The precast concrete industry provides greater opportunities for using recycled aggregates over to 20% (Concrete Centre, 2011). However, the following issues need to be considered when using RCA:

CO2 emissions from cement production are incurred through the consumption of fossil fuels, the use of electricity, and the chemical decomposition of limestone during clinkerization, which can take place at around 1400C. The decarbonation of limestone to give the calcium required to form silicates and aluminates in clinker releases roughly 0.53t CO2 per ton of clinker [8]. In 2005, cement production (total cementitious sales including ordinary Portland cement (OPC) and OPC blends) had an average emission intensity of 0.89 with a range of 0.650.92t CO2 per ton of cement binder [133]. Therefore, the decarbonation of limestone contributes about 60% of the carbon emissions of Portland cement, with the remaining 40% attributed to energy consumption, most of which is related to clinker kiln operations; the WWF-Lafarge Conservation Partnership [6] estimated that the production of clinker is responsible for over 90% of total cement production emissions.

In view of the fact that the requirement for decarbonation of limestone presents a lower limit on CO2 emissions in clinker production, and that there exist technical issues associated with the addition of supplementary cementitious materials (SCMs, including fly ash and ground granulated blast furnace slag), which restrict the viability of direct Portland cement supplementation by SCM above certain limits, the possibility to reduce CO2 emissions using Portland chemistry is limited. The WWF-Lafarge Conservation Partnership [6] expects that the emissions intensity of cement, including SCM, could be reduced to 0.70t CO2 per ton of cement by 2030, which still amounts to around 2 billion tons of CO2 per annum worldwide, even if cement production does not increase from its current level.

Fig. 10.6 shows the CO2 emissions of various binder designs as a function of Portland cement content. There have been a limited number of life-cycle analyses (LCA) of geopolymer technology. One reasonably extensive research program carried out in Germany [134] has provided information regarding the selection of precursors and mix designs for a range of geopolymer-based materials. However, geographic specificity plays a significant role in a full LCA, so there is the need for further studies considering different locations in addition to a wider range of mix designs spanning the broader spectrum of geopolymers. The main carbon-intensive and also the most expensive ingredient in geopolymer cement is the alkali activator, which should be minimized in mix design. McLellan et al. [135] provided further detail, while Habert et al. [136] concluded that geopolymer cement does not offer any reduction in carbon emissions; such a conclusion needs to be drawn with caution.

Sodium carbonate is the usual Na source for the production of sodium silicate. The different processes for conversion of Na2CO3 (or NaOH) and SiO2 to sodium silicate, via either furnace or hydrothermal routes, differ by a factor of 23 in CO2 emissions, and up to a factor of 800 in other emissions categories [137]. It is therefore essential to state which of these processes is used as the basis of any LCA. Moreover, the best available data for emissions due to sodium silicate production were published in the mid-1990s [137], so improvements in emissions since that time have not been considered. Sodium carbonate itself can be produced via two main routes, which vary greatly in terms of CO2 emissions. The Solvay process, which converts CaCO3 and NaCl to Na2CO3 and CaCl2, has emissions between 2 and 4t CO2 per ton of Na2CO3, depending on the energy source used. Conversely, the mining and thermal treatment of trona for conversion to Na2CO3 has emissions of around 0.14t CO2 per ton of Na2CO3 produced plus a similar level of emissions attributed to the electricity used. This indicates an overall factor of 510 difference in emissions between the two sources of Na2CO3 [138].

A commercial LCA was conducted by the NetBalance Foundation, Australia, on Zeobonds E-Crete geopolymer cement, as reported in the Factor Five report published by the Club of Rome [139]. This LCA compared the geopolymer binder to the standard Portland blended cement available in Australia in 2007 on the basis of both binder-to-binder comparison and concrete-to-concrete comparison. The binder-to-binder comparison showed an 80% reduction in CO2 emissions, whereas the comparison on a concrete-to-concrete basis showed slightly greater than 60% savings, as the energy cost of aggregate production and transport was identical for the two materials. However, this study was again specific to a single location and a specific product, and it will be necessary to conduct further analyses of new products as they reach development and marketing stages internationally. Fig. 10.6 shows a comparison of the CO2 emissions of four different E-Crete products against the Business as Usual, Best Practice 2011, and a Stretch/Aspirational target for OPC blends. It is noted that in some parts of the world (particularly Europe), some of the blends shown here in the Stretch/Aspirational category are in relatively common use for specific applications, particularly CEM III-type Portland cement/slag blends, but this is neither achievable on a routine scale worldwide at present, nor across the full range of applications in which Portland cement is used in large volumes.

Environmental impact of cement production is calculated based on the data provided by Ecoinvent (2012). Detailed information on the production process and on all inputs can be taken from Knniger et al. (2001). The functional unit is the production of 1kg of Portland cement strength class 42.5 (CEM I 42.5 R). Average fuel for clinker production is composed of 6.81103MJ natural gas (high pressure), 3.74104kg light fuel oil, 2.55102kg heavy fuel oil, 3.54102kg hard coal and 3.91103kg petroleum coke. In addition 5.80102 kWh electricity (medium voltage) is considered. Besides 0.912kg of Portland cement clinker, an input of 0.063kg gypsum (not balanced, origin from flue gas desulphurization), 0.025kg additional milling substances (not balanced as it is taken as waste without environmental burdens, e.g. dust from the cement rotary kiln, fly ash, silica dust, limestone) and 3.50104kg ethylene glycol (process material for grinding) is taken into account. A total energy for grinding and packing of 4.85102 kWh (electricity, medium voltage) as well as transport processes corresponding to 4.40103 tkm (lorry, 16t) is necessary. The production of 1kg Portland cement CEM I 42.5R yields an environmental impact of 0.833kg CO2-eq. (GWP100), 2.241108kg CFC-11-eq (ODP), 4.211105kg C2H4-eq. (POCP), 1.138103kg SO2-eq (AP) and 1.702104kg PO43-eq. (NP).

the cement manufacturing process

Different minerals need to be mined in order to make cement. Limestone (containing the mineral calcite), clay, and gypsum make up most of it. The US Geological Survey notes that cement raw materials, especially limestone, are geologically widespread and (luckily) abundant. Domestic cement production has been increasing steadily, from 66.4 million tons in 2010 to about 80.5 million tons of Portland cement in 2014 according to the U.S. Geological Survey 2015 Cement Mineral Commodity Summary. The overall value of sales of cement was about $8.9 billion, most of which was used to make an estimated $48 billion worth of concrete. Most construction projects involve some form of concrete.

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 1450C in a cement kiln. In this process, the chemical bonds of the raw materials are broken down and then they are recombined into new compounds.The result is called clinker, which are rounded nodules between 1mm and 25mm across. The clinker is ground to a fine powder in a cement mill and mixed with gypsum to create cement.The powdered cement is then mixed with water and aggregates to form concrete that is used in construction.

Clinker quality depends on raw material composition, which has to be closely monitored to ensure the quality of the cement. Excess free lime, for example, results in undesirable effects such as volume expansion, increased setting time or reduced strength. Several laboratory and online systems can be employed to ensure process control in each step of the cement manufacturing process, including clinker formation.

Laboratory X-Ray Fluorescence (XRF) systems are used by cement QC laboratories to determine major and minor oxides in clinker, cement and raw materials such as limestone, sand and bauxite. Read Analysis of Clinker and Cement with Thermo Scientific ARL OPTIMX WDXRF Sequential Spectrometer to learn why XRF is the technique of choice for elemental analysis in cement industry. Combination X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) systems accomplish both chemical phase analysis for a more complete characterization of the sample. Clinker phase analysis ensures consistent clinker quality. Such instrumentation can be fitted with several XRF monochromators for major oxides analysis and a compact diffraction (XRD) system which has the capability of measuring quartz in raw meal, free lime (CaO) and clinker phases as well as calcite (CaCO3) in cement.

Cross Belt Analyzers based on Prompt Gamma Neutron Activation Analysis (PGNAA) technology are installed directly on the conveyor belt to measure the entire material stream continuously and in real time to troubleshoot issues in pre-blending stockpile control and quarry management, raw mix proportioning control, and material sorting. Read PGNAA Improves Process and Quality Control in Cement Production to learn what makes PGNAA particularly suited for cement analysis.

Accurate cement production also depends on belt scale systems to monitor output and inventory or regulate product loadout, as well as tramp metal detectors to protect equipment and keep the operation running smoothly. The Cement Manufacturing Process flow chart sums up where in the process each type of technology is making a difference.

Need a Belt scale system for your bulk material handling? To help you decide which belt scale system is best for your mining operation, weve outlined the options in an easy-to-read belt scale system selection guide so you can decide which belt scale system is right for you. Click on the image, take a look at the chart, and see if it helps you decide.

re: natural gas vs. coal (above) The cost of natural gas is still around 3$ per million btu, while coal is 2$. So for a process like this that just needs heating value coal would be much preferred, and worth the cost for back end pollution control. Gas is becoming preferred for electric generation because a combined cycle plant has around 65% cycle efficiency, vs. 38% for coal-fired.

advanced concrete technology textbook by civilenggforall free download pdf

Concrete is a manmade building material that looks like stone. The word concrete is derived from the Latin concretus, meaning to grow together. Concrete is a composite material composed of coarse granular material (the aggregate or filler) embedded in a hard matrix of material (the cement or binder) that fills the space among the aggregate particles and glues them together. Alternatively, we can say that concrete is a composite material that consists essentially of a binding medium in which are embedded particles or fragments of aggregates. The simplest definition of concrete can be written as

Depending on what kind of binder is used, concrete can be named in different ways. For instance, if a concrete in made with non-hydraulic cement, it is called non-hydraulic cement concrete; if a concrete made of hydraulic cement, it is called hydraulic cement concrete; if a concrete is made of asphalt, it is called asphalt concrete; if a concrete is made of polymer, it is called polymer concrete. Both non-hydraulic and hydraulic cement need water to mix in and react. They differ here in the ability to gain strength in water. Non-hydraulic cement cannot gain strength in water, while hydraulic cement does.

Nonhydraulic cement concretes are the oldest used in human history. As early as around 6500 bc, nonhydraulic cement concretes were used by the Syrians and spread through Egypt, the Middle East, Crete, Cyprus, and ancient Greece. However, it was the Romans who refined the mixtures use. The nonhydraulic cements used at that time were gypsum and lime. The Romans used a primal mix for their concrete. It consisted of small pieces of gravel and coarse sand mixed with hot lime and water, and sometimes even animal blood. The Romans were known to have made wide usage of concrete for building roads. It is interesting to learn that they built some 5300 miles of roads using concrete. Concrete is a very strong building material. Historical evidence also points out that the Romans used pozzolana, animal fat, milk, and blood as admixtures for building concrete. To trim down shrinkage, they were known to have used horsehair. Historical evidence shows that the Assyrians and Babylonians used clay as the bonding material. Lime was obtained by calcining limestone with a reaction of

(a) Economical: Concrete is the most inexpensive and the most readily available material in the world. The cost of production of concrete is low compared with other engineered construction materials. The three major components in concrete are water, aggregate, and cement. Compared with steels, plastics, and polymers, these components are the most inexpensive, and are available in every corner of the world. This enables concrete to be produced worldwide at very low cost for local markets, thus avoiding the transport expenses necessary for most other materials.

(b) Ambient temperature-hardened material: Because cement is a low-temperature bonded inorganic material and its reaction occurs at room temperature, concrete can gain its strength at ambient temperature. No high temperature is needed.

(c) Ability to be cast: Fresh concrete is flowable like a liquid and hence can be poured into various formworks to form different desired shapes and sizes right on a construction site. Hence, concrete can be cast into many different configurations. One good example to show concrete castability is the BahaI Temple located in Wilmette, Illinois, USA. The very complex configurations of the different shapes of flowers in the wall and roof are all cast by concrete.

(d) Energy efficient: Compared with steel, the energy consumption of concrete production is low. The energy required to produce plain concrete is only 450750 kWh/ton and that of reinforced concrete is 8003200 kWh/ton, while structural steel requires 8000 kWh/ton or more to make.

(e) Excellent resistance to water: Unlike wood (timber) and steel, concrete can be hardened in water and can withstand the action of water without serious deterioration, which makes concrete an ideal material for building structures to control, store, and transport water, such as pipelines, dams, and submarine structures. A typical example of a pipeline application is the Central Arizona Project, which provides water from the Colorado river to central Arizona. The system contains 1560 pipe sections, each 6.7 m long, 7.5 m outside diameter, and 6.4 m inside diameter. Contrary to popular belief, water is not deleterious to concrete, even to reinforced concrete; it is the chemicals dissolved in water, such as chlorides, sulphates, and carbon dioxide, that cause deterioration of concrete structures.

(f) High-temperature resistance: Concrete conducts heat slowly and is able to store considerable quantities of heat from the environment. Moreover, the main hydrate that provides binding to aggregates in concrete, calcium silicate hydrate (CSH), will not be completely dehydrated until 910 Degrees Celsius. Thus, concrete can withstand high temperatures much better than wood and steel. Even in a fire, a concrete structure can withstand heat for 26 hours, leaving sufficient time for people to be rescued. This is why concrete is frequently used to build up protective layers for a steel structure.

(g) Ability to consume waste: With the development of industry, more and more by-products or waste has been generated, causing a serious environmental pollution problem. To solve the problem, people have to find a way to consume such wastes. It has been found that many industrial wastes can be recycled as a substitute (replacement) for cement or aggregate, such as fly ash, slag (GGBFS = ground granulated blast-furnaces slag), waste glass, and ground vehicle tires in concrete. Production of concrete with the incorporation of industrial waste not only provides an effective way to protect our environment, but also leads to better performance of a concrete structure. Due to the large amount of concrete produced annually, it is possible to completely consume most of industry waste in the world, provided that suitable techniques for individual waste incorporation are available.

(h) Ability to work with reinforcing steel: Concrete has a similar value to steel for the coefficient of thermal expansion (steel 1.2 105; concrete 1.01.5 105). Concrete produces a good protection to steel due to existence of CH and other alkalis (this is for normal conditions). Therefore, while steel bars provide the necessary tensile strength, concrete provides a perfect environment for the steel, acting as a physical barrier to the ingress of aggressive species and giving chemical protection in a highly alkaline environment (pH value is about 13.5), in which black steel is readily passivated.

(i) Less maintenance required: Under normal conditions, concrete structures do not need coating or painting as protection for weathering, while for a steel or wooden structure, it is necessary. Moreover, the coatings and paintings have to be replaced few years. Thus, the maintenance cost for concrete structures is much lower than that for steel or wooden structures.

(a) Quasi-brittle failure mode: The failure mode of materials can be classified into three categories: Brittle failure, quasi-brittle failure, and ductile failure. Glass is a typical brittle material. It will break as soon as its tension strength is reached. Materials exhibiting a strain-softening behaviour are called quasi-brittle materials. Both brittle and quasi-brittle materials fail suddenly without giving a large deformation as a warning sign. Ductile failure is a failure with a large deformation that serves as a warning before collapse, such as low-carbon steel. Concrete is a type of quasi-brittle material with low fracture toughness. Usually, concrete has to be used with steel bars to form so-called reinforced concrete, in which steel bars are used to carry tension and the concrete compression loads. Moreover, concrete can provide a structure with excellent stability. Reinforced concrete is realized as the second generation of concrete.

(b) Low tensile strength: Concrete has different values in compression and tension strength. Its tension strength is only about 1/10 of its compressive strength for normal-strength concrete, or lower for high-strength concrete. To improve the tensile strength of concrete, fibre-reinforced concrete and polymer concrete have been developed.

(c) Low toughness (ductility): Toughness is usually defined as the ability of a material to consume energy. Toughness can be evaluated by the area of a loaddisplacement curve. Compared to steel, concrete has very low toughness, with a value only about 1/50 to 1/100 of that of steel. Adding fibers is a good way to improve the toughness of concrete.

(d) Low specific strength (strength/density ratio): For normal-strength concrete, the specific strength is less than 20, while for steel it is about 40. There are two ways to increase concrete specific strength: one is to reduce its density and the other is to increase its strength. Hence, lightweight concrete and high-strength concrete have been developed.

(e) Formwork is needed: Fresh concrete is in a liquid state and needs formwork to hold its shape and to support its weight. Formwork can be made of steel or wood. The formwork is expensive because it is labor intensive and time-consuming. To improve efficiency, precast techniques have been developed.

(f) Long curing time: The design index for concrete strength is the 28-day compressive strength. Hence, full strength development needs a month at ambient temperature. The improvement measure to reduce the curing period is steam curing or microwave curing.

(g) Working with cracks: Even for reinforced concrete structure members, the tension side has a concrete cover to protect the steel bars. Due to the low tensile strength, the concrete cover cracks. To solve the crack problem, prestressed concrete is developed, and it is also realized as a third-generation concrete. Most reinforced concrete structures have existing cracks on their tension sides while carrying the service load.

how the cement industry is trying to mitigate its emissions

On a scorching July morning at a testing facility outside of Paris, a cadre of scientists, engineers, and architects wearing hard hats and safety goggles watched through protective glass as a machine molded a soupy, grey mixture into batches of brick-size blocks. Further along the line, a forklift operator carefully loaded the blocks into a curing chamber like loaves of bread in a bakery.

What they were witnessing was a trial run of a new concrete-making process developed by Solidia Technologies, one that the New Jersey-based company hopes will dramatically reshape the way this building material is made. By tweaking the chemistry of one of concretes essential ingredientscementand altering its curing process, the company says it can make concrete cheaper than the traditional process, while at the same time drastically cutting the carbon emissions associated with cement production.

Cement is one of the global economys most carbon-polluting industries. Responsible for about 8%of global carbon dioxide (CO2) emissions in 2015, if it were ranked with individual countries, the cement industry would be the third-largest greenhouse-gas emitter in the world behind only China and the United States. And this already outsized footprint is only projected to grow in the coming decades as economic development and rapid urbanization continue across Southeast Asia and sub-Saharan Africa. According to the International Energy Agency and the Cement Sustainability Initiative, by 2050, cement production could increase by as much as 23%.

This poses a significant challenge for combating climate change. One 2018 study estimated that cement-related emissions will have to fall by at least 16% by 2030, and by far more after that, if nations are to meet the 2015 Paris Climate Accord target of staying below two degrees Celsius of warming this century.

According to industry experts, reductions on that scale will require the widespread adoption of less carbon-intensive cement alternatives now under development in labs around the world. But in a market ruled by a handful of major producers wary of making changes to their existing business models, an absence of strong policies incentivizing greener technologies, and a construction industry reasonably cautious about novel building materials, the prospects for such a radical shift are far from certain.

The concrete industrys staggering carbon footprint is mainly due to the sheer scale of the materials use. A mundane combination of sand and gravel glued together by cement, this man-made stone is so ubiquitous that it is part of nearly every structure of our modern built environment.

Todays society would not have been possible without concrete, says Robert Courland, author of the book Concrete Planet. Its the most abundant synthetic material in existence, and according to the Cement Industry Federation, an Australian trade group, if you divvied up all of the concrete used around the world each year, three tons of concrete would go to every person on the planet, making it the worlds second most-consumed resource after water.

With its abundance, concrete takes a mammoth toll on the environment. The process for making Portland cement, the most common form used to produce concrete, for example, is one of the most carbon-intensive manufacturing processes in existence; manufacturing just one ton yields upwards of 1,000 pounds of carbon dioxide.

The process begins with crushed limestone, which is mixed with other raw materials and then fed into a large, rotating, cylindrical kiln heated to more than 2,600 degrees Fahrenheit. The kiln is inclined at a slight angle, and materials are poured into the raised end. As they move toward the roaring blast of flame at the kilns lower end, some components are burned off as gases, while the remaining elements unite to produce gray balls known as clinker. The lumps of materialabout the size of marblesare cooled and then ground into a fine powder to form the key binding element that allows concrete to harden when cured with water.

This process, which has barely changed since it was invented nearly two centuries ago, produces carbon emissions in two ways. First, fossil fuels are typically burned to heat the kiln to the high temperatures required to break the materials down, emitting carbon in the process. In addition, the thermal decomposition process itself results in emissions, as carbon trapped in the limestone combines with oxygen in the air to create carbon dioxide as a byproduct.

As much as two-thirds of cement-related carbon emissions arise from this reaction, which is why cement making is considered such a particularly difficult process to decarbonize, says Gaurav Sant, a professor of civil and environmental engineering at the University of California, Los Angeles (UCLA). Since carbon dioxide emissions are a part of the chemical process itself, he says, even a complete switch to low- or zero-carbon energy sources for heating the kilns would solve only part of the problem.

Cement producers have already taken steps to reduce emissions. Thanks to improvements in energy-efficiency and tweaks to concrete mixtures, the average carbon dioxide intensity of cement production has decreased by 18% globally over the past 20 years. Some companies have also installed technology to prevent carbon dioxide emissions from ever entering the atmosphere, though such systems can only capture so much and may not prove to be feasible on the scale required to make a significant impact.

While industry leaders have recently pledged even further decreases, Sant warns that existing technologies can only deliver a part of the carbon dioxide savings needed to achieve the Paris goals. What the industry really needs to do is plow money and efforts into producing new or alternative types of cement that require less to no clinker, he says. Its the only way they can address the issue of upstream CO2 emissions from cement production.

Companies are trying different methods to reduce or eliminate the amount of clinker required to make concrete. North Carolina-based bioMASON, for example, employs naturally occurring bacteria as a binder to make concrete bricks, while CO2Concrete, a spin-off from UCLA, has developed a technology that takes carbon dioxide directly from the flues of power plants to produce solid mineral carbonates that can then be used to replace traditional Portland cement. Others, like banah in the United Kingdom and Zeobond in Australia, are focused on using byproducts from other industrial processes to create so-called geopolymers to replace clinker in making cement.

Experts say Solidia, the New Jersey company that was put through its paces in France over the summer, is one of the most promising. Its process, which was first developed in 2008 at Rutgers University, involves manipulating the cement chemistry to significantly lower the kiln temperature required to produce the clinker, and then curing the concrete made with their cement with waste carbon dioxide instead of water.

Those technologies combined garner a carbon footprint reduction up to 70% compared to ordinary Portland cement-based concreteand for a lower cost, says Tom Schuler, president and CEO of Solidia, which has gathered financial support from well-known venture capital firms Kleiner Perkins and Bright Capital, oil giant BP, and Switzerland-based LafargeHolcim, the largest cement producer in the world.

Another company working on alternative cement solutions is CarbonCure, headquartered in Halifax, Nova Scotia. The brainchild of civil engineer Rob Niven, CarbonCure has developed a system where liquefied carbon dioxide is pumped into wet concrete as its being mixed. As the concrete hardens, the carbon from the carbon dioxide reacts with the concrete to become a mineral, effectively reducing the need for cement without compromising the concretes strength or price.

On any given building or infrastructure project, this CO2 mineralization process reduces as much carbon as hundreds, if not thousands of acres of trees would absorb in the course of a year, says Christie Gamble, CarbonCures director of sustainability. Worldwide deployment, she says, could reduce about 550 million tons of carbon dioxide each year, the equivalent of taking 150 million cars off the road.

For now, CarbonCures technology, which requires a small retrofit consisting of a computer system, a tank to store the carbon dioxide, and a tube to pump it into the concrete mix, is now installed in nearly 150 concrete plants across North America. The company says its also expanding into Southeast Asia and Europe.

A real-world demonstration of their product is taking shape in Georgia at a multistory commercial office building under construction in one of Atlantas hippest neighborhoods. Set to be completed by the end of the year, the building will be the first large-scale development to use concrete made with CarbonCure throughout the entire structure. According to Gamble, this project alone will prevent more than 750 tons of carbon dioxide from being released into the atmosphere, an amount equivalent to 800 acres of forestland sequestering carbon dioxide for a year.

Although companies like Solidia and CarbonCure are starting to make headway, they still have a long way to go before capturing even a small share of the market. Schuler says a major hurdle is the building sectors widespread conservatism. The industrys general attitude is to see it to believe it, Schuler says. The company has spent around $100 million on research and development and trials like the one in France to convince commercial clients.

Reluctance to adopt newer technologies is understandable. When it comes to ensuring life safety in structures, you have to be sure that what youre doing will work, Sant says. But he also argued that todays safety regulations are not capable of evaluating the novel processes for producing concrete that will be required to significantly cut the industrys carbon emissions.

The problem is that we have relied too long on prescriptive codes and standards that tell us to make concrete a certain way, rather than using performance-based criteria that would spur sectoral innovation, he says.

Another major issue is cost. Though novel solutions do not always cost more than conventional solutions, in cases where they do, there is limited willingness to pay for the additional cost, says Jeremy Gregory, executive director at MITs Concrete Sustainability Hub, a research group focused on sustainable concrete production and use. A 2015 study found that geopolymer-based cements, for example, can cost triple what traditional ones do.

Policies to offset those higher costs and encourage investment in climate-friendly cements are also lacking, Gamble says, suggesting, technological advancement cannot on its own drive cement emissions down. Whats needed, she says, are measures such as emission caps and penalties to send market signals and encourage the widespread adoption of greener technologies.

In the end, she conceded that low-carbon cement is still quite far from reaching wide-scale adoption. Yet she remains positive: Perhaps it will take 20, 30 years, maybe more. But we are starting to see the first glimmers of that path.

Given the monumental scale of its carbon footprint, cement alone could make or break efforts to slow global warming. For Gregory, the only way forward is to keep pushing the whole industry to accelerate its efforts.

oxygen enrichment technologyan innovation for improved solid fuel combustion and sustainable environment | springerlink

There is an absolute need to adopt innovative technologies to improve energy efficiency with minimum possible environment emission and conservation of natural resources. Oxygen-enriched combustion is one of the latest technologies that may improve combustion efficiency depending on the exhaust gas temperature and percentage of oxygen in the combustion air. Cement industry is responsible for approximately 8% of the global anthropogenic CO2 emissions (IPCC, 2006) and the cement market is expected to grow with increased industrialization and urbanization. In typical cement manufacturing process, 60% of CO2 emissions are due to the transformation of limestone to lime (the calcination process) and rest 40% is due to fuel combustion in pyro processing. The air is used as an oxidizing agent content in industrial combustion processes that has maximum nitrogen component (7879%) by volume. The chemically inert nitrogen dilutes the reactive oxygen and carries away some of the energy in the hot combustion exhaust gas during the air-fuel combustion process. An increase in oxygen in the combustion air can reduce the energy loss in the exhaust gases and increase the fuel combustion efficiency. Oxygen enrichment is helpful in curbing gaseous emission. By increasing oxygen content in air, N2 content is limited that leads to less NOx in exhaust gases. In this condition exhaust gases are more CO2 rich that are partially recirculate along with combustion air. In CO2 rich exhaust gases, water vapour is removed though condensation process and remaining CO2 is captured through CCS technology.

Combustion is a chemical process in which a substance reacts rapidly with oxygen and releases heat as product. The original substance is called the fuel and the source of oxygen is called the oxidizer (Mathieu 2006).

Oxygen is required for any combustion process and ambient air is the most common source of oxygen that contains about 79% Nitrogen by volume. N2 is inert gas and does not contribute in heat released through combustion reaction (Oates 1998). The nitrogen contained in air actually inhibits fuel from reacting with oxygen. This results in a flame temperature below that attainable with pure oxygen (Schorcht et al. 2013). Oxygen enrichment which is known as increased O2% in combustion air. This improves the overall combustion process and the resulting heat transfer increases flame temperature and the amount of available heat (Eriksson 2015). Oxygen enrichment process enhances burning zone control and improves kiln stability in the industrial furnace or rotary kiln (Eriksson et al. 2014). We get more consistent kiln operation, better clinker quality, and increased production or alternative fuel substitution rate among all possible positive results (Liu et al. 2015). Oxygen is added to combustion air to increase specific fuel rates in kg fuel/kg air (supplemental enrichment) or reduce overall air volume (equivalent enrichment) (Sharma et al. 2017). Overall gas flow rates are reduced and thermal efficiency increases by substituting pure oxygen either for a portion or total combustion air(Gao et al. 2017). For an example 21m3/h of pure oxygen can replace 100m3/h of air, thereby reducing the total flue gas volume by 79m3/h. The benefits of oxygen enrichment can be achieved even at very low levels of enrichment (Hokfors 2014).

The volumetric reduction in exhaust gases is easily illustrated by comparing the combustion reactions of air/methane (2.1) and oxygen/methane (2.2). Similar reductions in combustion products occur for all fuels due to the elimination or reduction of nitrogen contained in air.

On the above, it can be easily understood that for the air/methane reaction, there are 10.5 volumes of combustion products, compared to only three volumes of combustion products for the oxygen/methane flame. The adiabatic flame temperature of the oxygen/methane flame is roughly 800C higher than the air/methane flame due to the elimination of nitrogen.

Lime (calcium oxide, CaO) is produced by calcination of limestone, containing a high concentration of calcium carbonate (CaCO3) better known as Limestone. Limestone is an abundant natural raw material where lime is used for environmental purposes like waste neutralization or flue gas desulphurization. Limestone is also widely used in many industrial processes like in formation of metallurgical Slags or for production of paper pigments. The method used is based on multi-component chemical equilibrium calculations to predict process conditions.

The calcination starts between 800 and 900C and the operational solid temperature usually reaches 10001200C. The calcination temperature is dependent on the partial pressure of carbon dioxide in the kiln.

The two main oxygen enrichment methods for the kiln burner are either by general enrichment or focused enrichment. General enrichment is a method of adding the oxygen to combustion air piping (typically primary air) to increase the percentage of oxygen above 21%. This method is simple to retrofit and is an inexpensive way to obtain some of the benefits of oxygen enrichment.

Second method is focused enrichment of the kiln burner. This is accomplished by adding lance(s), rather within the burner or adjacent to the burner for injecting oxygen into the flame. This method of enrichment provides the most effective use of oxygen for increasing production or alternative fuel utilization. This is related with modifying the flame heat release profile. Special attention must be given to burner flame shape to maximize performance and to avoid degradation of the protective coating on the kiln refractory. Often various techniques can be used to allow the producer to adjust the flame length and heat release pattern to optimize the overall performance, economics and emissions. Proper lance design along with the evaluation of burner primary airflow is essential to ensure successful implementation.

It may be clearly noticed from figures that the highest temperature zone around the core of the flame has been increased while the temperature at the walls of the kiln has remained similar to the conventional air combustion flame case. This can translate into increased production, increased alternative fuel usage and reduced emissions.

There is less smoke production with reduction in dust pollution and environmental pollution. The successful application of oxygen-enriched combustion technology in the rotary kiln cement production industry will bring huge economic and social benefit aspects.

The oxy-fuel combustion process involves burning of pulverized coal in an oxygen enriched atmosphere that consists of pure O2 that is mixed with recycled flue gas. This process differs from the conventional fuel combustion process where ambient air serves as the only oxidant. This entails specific conditions regarding thermo-physical properties, which affect both combustion characteristics and heat transfer.

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