Li Luo, Yimin Zhang, Shenxu Bao, Tiejun Chen, "Utilization of Iron Ore Tailings as Raw Material for Portland Cement Clinker Production", Advances in Materials Science and Engineering, vol. 2016, Article ID 1596047, 6 pages, 2016. https://doi.org/10.1155/2016/1596047
The cement industry has for some time been seeking alternative raw material for the Portland cement clinker production. The aim of this research was to investigate the possibility of utilizing iron ore tailings (IOT) to replace clay as alumina-silicate raw material for the production of Portland cement clinker. For this purpose, two kinds of clinkers were prepared: one was prepared by IOT; the other was prepared by clay as a reference. The reactivity and burnability of raw meal, mineralogical composition and physical properties of clinker, and hydration characteristic of cement were studied by burnability analysis, differential thermal analysis, X-ray diffraction, and hydration analysis. The results showed that the raw meal containing IOT had higher reactivity and burnability than the raw meal containing clay, and the use of IOT did not affect the formation of characteristic mineralogical phases of Portland cement clinker. Furthermore, the physical and mechanical performance of two cement clinkers were similar. In addition, the use of IOT was found to improve the grindability of clinker and lower the hydration heat of Portland cement. These findings suggest that IOT can replace the clay as alumina-silicate raw material for the preparation of Portland cement clinker.
IOT are the solid wastes generated during the beneficiation process of iron ore concentration and are one of the main pollution concerns in the mining industry. Continuous development of the iron and steel industry has led to the increasing amount of IOT; there are over 300 million tons of IOT discharged per year, but the comprehensive utilization rate of IOT is still less than 10%; stockpiling is still the most common and cost-effective way in the management of IOT [1, 2]. However, the huge amount of stockpiled IOT brings a series of environmental and social problems. In recent years, IOT as secondary resources have received considerable attention in many countries in the word. At present, the researches about comprehensive utilization of IOT mainly focused on the recycling of useful metal and producing of building materials, among which utilizing IOT to produce the building materials is a more effective solution for resource recovery and management of IOT [3, 4]. Utilization of IOT as raw material for building industry not only consumes large amount of IOT and realizes zero-emission of IOT wastes, but also is beneficial to protecting natural mineral resources.
Portland cement clinker production consumes large amounts of natural resources (limestone, clay, etc.), and clay has been widely used as traditional alumina-silicate raw material for good reasons . Cement industry has undergone a tremendous development in the past decades, but it causes excessive exploitation of clay resource and considerable environmental damage. Now, the cement industry is facing the challenge of the insufficient supply of raw materials and environment protection, so it has for some time been seeking alternative raw materials for Portland cement clinker production. It is well known that various industrial solid wastes have been utilized as alternative raw materials in Portland cement clinker production such as steel slag, waste sludge ash, and ceramic wastes . With the benefit of high content of silica and iron, IOT can be utilized as silicate or iron corrective material during the Portland cement clinker production, but the consumption of IOT is rather low. In addition, the effect of using IOT as raw material on the properties of raw meal and hydration characteristic of Portland cement has also been seldom discussed. Comparing with being used as corrective material, utilizing IOT as alumina-silicate raw material for Portland cement clinker production can consume more IOT and decrease the mining of clay; however, there is little information about IOT replacing clay as alumina-silicate raw material for the preparation of Portland cement clinker so far.
The possibility of utilizing IOT to completely replace clay as alumina-silicate raw material for Portland cement clinker production was investigated in this paper; the properties of raw meal, clinker, and cement were studied by burnability analysis, differential thermal analysis, X-ray diffraction technique, and hydration analysis. On one hand, it can solve the environment problems of IOT and improve the comprehensive utilization rate of IOT. On the other hand it can provide an alternative alumina-silicate raw material for cement industry.
In this study, IOT was obtained from iron ore dressing plant in Henan province. Clay was from a brick plant in Shiyan and iron ore was from Jiugang Group. Limestone and quartz sand were acquired from Huangshi XinHai Trade Co., Ltd., and Jingyou Sand Co., Ltd., respectively. IOT, clay, limestone, quartz sand, and iron ore were used as raw materials for Portland cement clinker production. Two different kinds of alumina-silicate material (clay and IOT) were used in the experiment. The calcareous material was limestone. Quartz sand and iron ore were used as corrective materials to adjust the contents of silicate and iron of raw meal, respectively.
The main chemical composition of raw materials is shown in Table 1. The chemical composition of IOT is shown in the Supplementary Material available online at http://dx.doi.org/10.1155/2016/1596047. The main component of IOT and clay is similar and the aluminum content of IOT is rather high, which belongs to rich-aluminum type. The hazardous substances of IOT are SO3 and Cl, but their contents are very low. The XRD pattern (Figure 1) shows that the major mineral phases of the IOT are ferrotschermakite and anorthite while augite and clinochlore occur as minor phases. However, quartz is not detected in the XRD pattern of IOT, which is a common constituent of IOT. The SiO2 in the amphibole and feldspar is easier to combine with CaO during the sintering process than in the quartz, which means that IOT has relatively high reactivity. Consequently, the IOT appears to be a suitable alternative alumina-silicate raw material for Portland cement clinker production.
Two kinds of samples were prepared; one was prepared by clay as a reference (RM-1) and the other was prepared by IOT (RM-2). The clinker moduli of two samples were both adjusted to the same values (KH = 0.90, SM = 2.50, and IM = 1.50). The blend ratios of raw materials of two samples are shown in Table 2.
The quartz sand passed through a 0.08mm sieve by grinding, because coarse quartz sand has a negative effect on the burnability of raw meal. The raw meals were shaped in small spheres with a diameter of 15mm and then dried in an oven at 105C for 1h. These small spheres were burned at 1450C for 1h. After the sintering process, the produced clinkers were cooled rapidly to room temperature. The produced clinkers were pulverized with 5% gypsum by weight for 2 minutes in a laboratory oscillating mill to produce the Portland cement.
The cement pastes were prepared to study the hydration products of Portland cement clinker. The pastes were prepared with water to solids ratio of 0.3 and cured in standard curing box. At 3 and 28 days, the hydration of pastes was terminated by alcohol and dried at 80C in a vacuum oven for 24h for the further characterization.
The burnability tests of cement raw meal were performed according to Chinese National Standard GB/T 26566-2011. The cement raw meals were fired at 1350C, 1400C, and 1450C for 30min, respectively. The free lime content of clinkers was analyzed by the glycerol-ethanol method.
The reactivity of raw meal is defined by the reaction rate of the raw materials and is related to its mineral characteristic. The reactivity of raw meal was studied by DSC analysis. The DSC heating curves of two samples are presented in Figure 2. During the sintering process, the formation of clinker minerals is companied with endothermic and exothermic reactions. Endothermic peak at about 830C is attributed to thermal decomposition of the limestone. Exothermic peak between 1230C and 1260C is attributed to solid state reactions, which means the progressive formation of C3A, C4AF, and C2S . Endothermic peaks at about 1330C are attributed to the sintering of liquid phase and the formation of C3S. It can be seen from Figure 2 that the solid state reactions temperature of RM-2 can be up to 30C lower than RM-1, but the decomposition temperature of limestone and the sintering temperature of liquid phase in two samples are almost the same. The results of DSC analysis indicate that using IOT as alumina-silicate material promotes the solid state reactions and improves the reactivity of raw meal while it has little effect on the processes of limestone decomposition and reducing the formation temperature of C3S. The chemical composition of IOT that is in the Supplementary Material shows that IOT contains trace elements (CuO, TiO2, MnO, etc.), which can promote the solid state reaction .
The burnability of raw meal describes the degree of difficulty of clinker formation during sintering process and is evaluated by the content of free lime in clinker. The lower the content of free lime in clinker is, the higher the raw meal burnability is. The results of burnability tests are given in Figure 3. The content of free lime in RM-2 is lower at all sintering temperatures, and the reaction of sintering process after 1350C is mainly the formation of C3S. The results of burnability analysis suggest that the use of IOT has improved the burnability of raw meal and promoted the formation of C3S during the sintering process. The improvement of burnability can be attributed to the existence of trace elements and particular mineral composition of IOT.
The results of reactivity and burnability analyses show that RM-2 has higher reactivity and burnability. Comparing with clay, utilizing IOT as alumina-silicate raw material for Portland cement clinker production can lower the sintering temperature or reduce sintering time during sintering process, which can lower the production costs of cement industry.
The XRD analysis of two produced Portland cement clinkers is given in Figure 4. In both clinkers, the main mineral phases of two produced clinkers were C3S, C2S, C3A, and C4AF, which were in accord with the characteristic minerals of a typical Portland cement clinker . However, there is a small difference between the two clinkers that RM-2 contains less amount of C2S, which is related to the promotion of sintering process. Free lime content is very low in both clinkers, so it cannot be detected in the XRD pattern. The results of XRD analyses indicate that the use of IOT does not affect the formation of characteristic mineralogical phases of Portland cement clinker.
Table 3 presents the physical and mechanical properties of two produced Portland cement clinkers. The results of physical tests show that the use of IOT only slightly affected the setting times of produced Portland cement. However, RM-2 cement presents greater specific surface and water demand. The greater specific surface represents better grindability and leads to the greater water demand. The differences in mineralogical composition of clinkers significantly impact the grindability of clinkers; C2S is known to be the most prominent strength giving components in all clinker minerals . The grindability of RM-2 clinker increases as the amount of C2S decreases.
Portland cement sample was made by grinding the 95wt% of clinker with 5wt% of gypsum, and the mechanical properties of produced Portland cement sample were tested for strengths after curing for 3 and 28 days. Both mortars gave quite similar bending and compressive strengths in the same days, and the mechanical performances of two Portland cement clinkers were in agreement with those of Portland cement of 42.5MPa strength grade, which confirmed the probability of utilizing IOT as alternative raw materials for Portland cement clinker production.
The XRD patterns of two pastes, hydrated for 3 and 28 days, are given in Figure 5. In both pastes, the hydration products of two cement clinkers are Ca(OH)2 and ettringite. No calcium silicate hydrate (C-S-H) was detected during the whole hydration process, presumably due to the amorphous characteristic of the calcium silicate hydrate itself . The diffraction peaks of C3S and C2S are higher in RM-2 paste at 3 days, which indicates that the hydration velocity of calcium silicate of RM-2 cement is slower. With increasing hydration time, the peaks of C3S, C2S, and C4AF decrease at 28 days.
The rate of heat liberation and hydration heat of two cement clinkers for 3 days is shown in Figure 6. In both cases, the heat liberation is quite intense in the first few minutes of the preinduction period. Soon thereafter, the hydration process is delayed and the rate of heat liberation decreases rapidly in the induction period. Then, a second main exothermic peak appears as a result of the formation of ettringite and hydration of C3S . And finally, the rate of heat liberation decreases gradually in the following period. It can be seen from Figure 6 that the end times of induction period of two cement clinkers are almost the same, the end times of induction period are related to the setting times of cement, and the analysis results of induction period are in good agreement with the results of physical tests. RM-2 has a weaker exothermic peak; however, the formation process of ettringite of two cement clinkers could be similar according to the results of setting time of two cement clinkers, so the weaker exothermic peak was due to the lower hydration rate of calcium silicate. The XRD analysis of two pastes also has the same results.
The hydration heat of RM-2 cement is lower in the early hydration period, which is due to the higher hydration liberation rate of RM-2 cement. The greater specific surface of RM-2 cement promotes the hydration process of cement in the initial hydration period and leads to higher hydration liberation rate of cement. As the heat liberation rate of RM-2 cement decreases faster in the following period, the hydration heat of RM-1 exceeds RM-2 after about 10h and the gap of hydration heat of two cement clinkers gradually enlarges in the later period.
Chemical and mineralogical analysis of IOT has shown that it can be considered as a ready alumina-silicate raw material due to its high content of alumina and relatively high reactivity. Furthermore, the similar mineralogical, physical, and mechanical properties of two produced Portland cement clinkers have confirmed that IOT can completely replace clay as an alternative alumina-silicate raw material for the production of Portland cement clinker. However, the use of IOT is found to improve the reactivity and burnability of raw meal and promote the sintering process. In addition, the Portland cement clinker prepared by IOT presents better grindability and the hydration heat of Portland cement is lower. The availability and low cost of IOT make it attractive to replace clay as alumina-silicate raw material for the production of Portland cement clinker. This will be beneficial for the management of IOT, alleviating the raw materials supply problem of the cement industry and allowing the reduction in processing costs of raw materials.
Description of the Supplementary MaterialIOT contains various trace elements such as TiO2, MnO, CuO, etc. Althoug the contents of trace elements were low, they can promote the sintering process of clinker.
Copyright 2016 Li Luo et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The raw cement ingredients needed for cement production are limestone (calcium), sand and clay (silicon, aluminum, iron), shale, fly ash, mill scale and bauxite. The ore rocks are quarried and crushed to smaller pieces of about 6 inches. Secondary crushers or hammer mills then reduce them to even smaller size of 3 inches. After that, the ingredients are prepared for pyroprocessing.
The crushed raw ingredients are made ready for the cement making process in the kiln by combining them with additives and grinding them to ensure a fine homogenous mixture. The composition of cement is proportioned here depending on the desired properties of the cement. Generally, limestone is 80% and remaining 20% is the clay. In the cement plant, the raw mix is dried (moisture content reduced to less than 1%); heavy wheel type rollers and rotating tables blend the raw mix and then the roller crushes it to a fine powder to be stored in silos and fed to the kiln.
A pre-heating chamber consists of a series of cyclones that utilizes the hot gases produced from the kiln in order to reduce energy consumption and make the cement making process more environment-friendly. The raw materials are passed through here and turned into oxides to be burned in the kiln.
The kiln phase is the principal stage of the cement production process. Here, clinker is produced from the raw mix through a series of chemical reactions between calcium and silicon dioxide compounds. Though the process is complex, the events of the clinker production can be written in the following sequence:
The kiln is angled by 3 degrees to the horizontal to allow the material to pass through it, over a period of 20 to 30 minutes. By the time the raw-mix reaches the lower part of the kiln, clinker forms and comes out of the kiln in marble-sized nodules.
After exiting the kiln, the clinker is rapidly cooled down from 2000C to 100C-200C by passing air over it. At this stage, different additives are combined with the clinker to be ground in order to produce the final product, cement. Gypsum, added to and ground with clinker, regulates the setting time and gives the most important property of cement, compressive strength. It also prevents agglomeration and coating of the powder at the surface of balls and mill wall. Some organic substances, such as Triethanolamine (used at 0.1 wt.%), are added as grinding aids to avoid powder agglomeration. Other additives sometimes used are ethylene glycol, oleic acid and dodecyl-benzene sulphonate.
The heat produced by the clinker is circulated back to the kiln to save energy. The last stage of making cement is the final grinding process. In the cement plant, there are rotating drums fitted with steel balls. Clinker, after being cooled, is transferred to these rotating drums and ground into such a fine powder that each pound of it contains 150 billion grains. This powder is the final product, cement.
Cement is conveyed from grinding mills to silos (large storage tanks) where it is packed in 20-40 kg bags. Most of the product is shipped in bulk quantities by trucks, trains or ships, and only a small amount is packed for customers who need small quantities.
Please note that the information in Civiltoday.com is designed to provide general information on the topics presented. The information provided should not be used as a substitute for professional services.
Blast furnaces came under scrutiny in 1904 when the Pennsylvania Supreme Court reversed a lower court ruling and perpetually enjoined Jones & Laughlin from such operation of its blast furnaces, which had caused dust to be distributed upon adjoining property (Anonymous 1904).
Blast furnace gas is produced during the iron oxide reduction in blast furnace iron making in which iron ore, coke and limestone are heated and melted in a blast furnace and is an indigenous process gas of the steelworks industry (Pugh etal., 2013). Blast furnace gas has a high carbon monoxide (CO) content and a low heating value, typical 3900MJ/m3 (International Energy Agency, 2007). The five primary components of blast furnace gas are N2, CO, CO2, H2O and H2. The typical blast furnace gas composition in volume is N2=55.19%, CO=20.78%, CO2=21.27% and H2=2.76% (Hou etal., 2011). The water content is removed by demisters following the cleaning process. This gas is used for the furnace mills, in gas engines and for electricity and steam generation. Often, in the steel industry, blast furnace gas is used as an accessional to natural gas (Bojic and Mourdoukountas, 2000). Blast furnace gas deposits adhere firmly; therefore, boilers using these type of fuel should be frequently cleaned.
Blast furnaces have grown considerably in size during the twentieth century. In the early days of the twentieth century, blast furnaces had a hearth diameter of 45m and were producing around 100,000THM per year, mostly from lump ore and coke. At the end of the twentieth century the biggest blast furnaces had between 14 and 15m in hearth diameter, and were producing 34milliontons of hot metal per year . A typical development of blast furnaces is illustrated in Figure 1.1.8, showing the evolution of shape and dimensions of the ironmaking blast furnaces, from 1860s to 1980s. Since mid-1980s, the size of blast furnace remained more or less the same, at its optimal level (30005000m3) .
Presently, very big furnaces reach production levels of 12,000tpd or more. For instance, the Oita No. 2 blast furnace (NSC) has a hearth diameter of 15.6m and a production capacity of 13,500tpd hot metal. The Thyssen-Krupp Schwelgern No. 2 blast furnace has hearth diameter of 14.9m and a production capacity of 12,000tpd hot metal .
Blast furnaces are the largest consumers of materials and energy in the iron and steel-making process. They are relatively flexible in their ability to use different metal charges, such as pellets, sinter, or scrap, with little change in performance. Other inputs include coke to produce carbon monoxide for the reduction of iron ore to iron, and other energy sources for various stages of the production process, such as preheating of air up to 1100C for injection into blast furnaces. Since blast furnaces require significant quantities of coke, they are often operated in close conjunction with coke ovens, creating opportunities for joint use of byproducts, such as coke oven gas as well (Fig. 3).
The main outputs of blast furnaces includes pig iron and slag, which is formed by combination of limestone with sulfur and other impurities. Pig iron is typically tapped every 3 to 5hours in quantities of 300 to 600tons. After tapping, the pig iron is transported, typically in liquid form, to steel-making operations.
Other outputs from blast furnaces include blast furnace gas, an off-gas with a heating value of 3MJperm3, which is approximately one-tenth of the energy content of natural gas. This heating value has been dropping as a result of reduced coke rates and better burden preparation. The gas quality is insufficient to allow high-efficiency conversion to electricity in gas turbines. To increase heating values, blast furnace gas is often mixed with other gases such as coke oven gas and natural gas, which have higher energy content. This mixture can be converted into electricity with efficiencies of 41 to 42% in combined cycle plants. Much of that conversion takes place onsite at steel plants for electricity used in steel making and in some instances for sale into the electricity grid. A portion of the off-gas is consumed in boilers that produce compressed air via steam-powered or electric blowers. Funneling that air through hot blast stoves provides the heat required in the blast.
With the price of coke rising, steel makers have sought to reduce their dependence on coke, for example, by installing pulverized coal injection into their blast furnaces as a partial substitute for coke. A few use natural gas for the same purpose. The need for greater efficiency in blast furnaces has also focused attention on the efficiency of oxygen use so that combining coal injection and large amounts of oxygen can further diminish the need for coke.
Integrated coal-fueled steel mills accounted for 60% of the 1.4Gt of global steel produced in 2008, consuming 1518GJ per t-steel produced and emitting a global average of 1.4 t-CO2 per t-steel produced. In the first stage of the steelmaking process, high-grade coal (anthracite) is used to fuel a blast furnace in which iron is extracted by reduction from the ore hematite (Fe2O3), using carbon monoxide as the reducing agent. The key reactions taking place in the furnace are as follows. Coal is combusted with oxygen to produce carbon dioxide and heat, while limestone, introduced as a fluxing agent to remove impurities from the iron, is calcined to produce CaO plus CO2 via the same reaction as in cement production (Equation 5.1). The CO2 product from these two reactions then reacts with more carbon, producing carbon monoxide:
In the second stage of the steelmaking process, known as basic oxygen steelmaking (BOS), the carbon content of pig iron is reduced from a typical 45% to 0.11% in an oxygen-fired furnace. The excess carbon is oxidized to carbon monoxide, which can be recycled as a fuel gas or used as the reducing agent. At the same time other impurities, such as phosphorus and sulfur, are oxidized to form acidic oxides, neutralized by the addition of lime, and recovered as a slag that has a variety of recycling uses (see, for example, cement production, earlier, and mineral carbonation, in Section 10.3.1). Alloying elements such as chromium, manganese, nickel, and vanadium are also added at this stage to achieve the required steel composition and properties.
Blast furnace gases contain close to 30% CO2, after full combustion of the CO fraction, while the overall flue gas stream from an integrated steel mill is 15% CO2. The same CO2 capture options introduced above for power-generation plant can therefore also be applied to a steel mill:
Recycling of scrap steel, using electric-powered arc or induction furnaces, accounts for 35% of overall shipped steel volume worldwide, with production of 500 Mt-steel reported from this type of process in 2008. Recycled steel is significantly more energy-efficient than new-steel production, requiring only 25% of the energy input per unit of steel shipped. A mini-mill typically consumes 4.06.5GJ per tonne of steel produced, reducing CO2 emissions by 80% to 0.3 t-CO2 per t-steel. In this case the reduction of related CO2 emissions reverts to the discussion of CCS in the power-generation sector.
Larger blast furnace, use of better prepared burden, recovery of waste energy, and maximum recovery of slag characterize the iron making technology proposed for VSP. The largest blast furnace in India at that time was of 2000m3. Compared to this, elsewhere furnaces up to 5070m3 had been built. Considering the plant capacity of VSP and the necessity of installing at least two furnaces, installation of 5000m3 furnaces were precluded. Therefore, the selection of the furnace size and number gets limited to the alternatives of three 2000m3 furnaces or two 3200m3 furnaces. It was found that the later option was more economical and hence installation of two 3200m3 blast furnaces was proposed for VSP.
Integrated coal-fueled steel mills accounted for ~65% of the 1.5Gt of global steel produced in 2016, consuming ~19GJ/t-steel produced and emitting a global average of ~1.8t-CO2/t-steel produced. In the first stage of the steelmaking process, high-grade coal (anthracite) is used to fuel a blast furnace in which iron is extracted by reduction from the ore hematite (Fe2O3), using carbon monoxide as the reducing agent. The key reactions taking place in the furnace are as follows. Coal is combusted with oxygen to produce carbon dioxide and heat, while limestone, introduced as a fluxing agent to remove impurities from the iron, is calcined to produce CaO plus CO2 via the same reaction as in cement production (Reaction (5.1)). The CO2 product from these two reactions then reacts with more carbon, producing carbon monoxide:
In the second stage of the steelmaking process, known as basic oxygen steelmaking (BOS), the carbon content of pig iron is reduced from a typical 4%5% to 0.1%1% in an oxygen-fired furnace. The excess carbon is oxidized to carbon monoxide, which can be recycled as a fuel gas or used as the reducing agent. At the same time other impurities, such as phosphorus and sulfur, are oxidized to form acidic oxides, neutralized by the addition of lime, and recovered as a slag that has a variety of recycling uses (see, for example, cement production in the previous section, and mineral carbonation in Section 10.3.1). Alloying elements such as chromium, manganese, nickel, and vanadium are also added at this stage to achieve the required steel composition and properties.
Blast furnace gases contain close to 30% CO2, after full combustion of the CO fraction, while the overall flue gas stream from an integrated steel mill is ~15% CO2. The same CO2 capture options introduced above for power-generation plant can therefore also be applied to a steel mill:
The oxygen-fired blast furnace option is interesting in that it can reduce CO2 emissions from an integrated steel mill by 40%, even without CCS, due to the reduced coke consumption in the blast furnace.
One pre-combustion option that has been developed in the EU-funded CACHET and CAESAR projects is the application of sorption-enhanced water-gas shift reaction to convert blast furnace gas to hydrogen, with CO2 captured in a potassium carbonate hydrotalcite-based sorbent from which it is recovered by a pressure swing. The technology is being further developed under the EU STEPWISE project (see Section 7.2).
As an alternative to iron production in a blast furnace, direct-reduced iron (DRI) is produced by reducing iron ore using a mixture of hydrogen and carbon monoxide (Reaction (5.7) and (5.9)) at temperatures of 8001000C. The first commercial CCS project at a steel plant began operating in November 2016 at the Emirates Steel DRI plant in Mussafah, Abu Dhabi. The plant produces syngas (H2+CO) for the direct reduction reactions by steam reforming locally abundant natural gas, and the DRI plant off-gas, containing 98% CO2, in dehydrated, compressed to scCO2 and transported 43km for EOR at the ADNC operated BAB and Rumaitha oil fields. The project will capture 800kt-CO2/year when fully operational.
Recycling of scrap steel, using electric-powered arc or induction furnaces, accounts for ~35% of overall shipped steel volume worldwide, with production of c. 550Mt-steel reported from this type of process in 2016. Recycled steel is significantly more energy-efficient than new steel production, requiring only ~25% of the energy input per unit of steel shipped. A mini-mill typically consumes 4.06.5GJ/t-steel produced, reducing CO2 emissions by ~80% to ~0.3t-CO2/t-steel. Since energy input is in the form of electrical power, the reduction of related CO2 emissions reverts to the discussion of CCS in the power-generation sector.
BFG is a by-product of the chemical reduction of iron ore in blast furnaces. It typically contains about 2030% carbon monoxide (CO) and about 26% hydrogen (H2) as combustible components, and a significant amount of inert gases with about 4560% nitrogen (N2), and 2025% carbon dioxide (CO2) (see Table 14.1). Due to the high inert gas content and the already relatively low heating value of the main combustible component CO, it has a low heating value in the range of 34MJ/m3. As a consequence of the low heating value and the low reactivity of the main combustible component CO, the reactivity of BFG is very low and special care has to be taken that lean-flame blow-off stability and burn out are sufficiently achieved by the combustion system.
Corex gas is a by-product of the upcoming cost-efficient and environmentally friendly Corex iron-generation process, which is based on a smelting reduction process without requiring coke but directly applying coal. The residual gas of this process, called Corex export gas, typically contains about 4247% carbon monoxide (CO), about 20% hydrogen (H2) and about 2% methane (CH2) as combustible components, and about 30% carbon dioxide (CO2). The heating value is about 8MJ/m3. Composition and heating value are nearer to typical raw syngases in comparison to BFG. Consequently, similar requirements are valid as for syngas application.
Coke oven gas is the by-product of the pyrolysis of coal, which is the basic process for coke production for the blast furnace process. It typically contains about 5% carbon monoxide (CO), about 55% hydrogen (H2), about 25% methane (CH4) and about 3% higher hydrocarbons as combustible components. Furthermore, it contains about 1012% nitrogen (N2) and about 2% carbon dioxide (CO2) as well as contaminants (H2S, HCN, CS2, HG, Cd, etc.). Due to its relatively high hydrogen (H2) and methane (CH4) content, it has a higher heating value and Wobbe index compared to BFG and Corex gas, but below the level of standard natural gases (E, H or L). The reactivity is in the range of typical syngases and above the reactivity of natural gas. Depending on the combustion system specifics it potentially requires dilution.
Again, as for other low-LHV gases in general, and also for BFG, Corex gas and COG, the reduced heating value compared to standard fuels leads to increased fuel mass flows and the requirement for a larger fuel system. Due to the poisonous CO content, special care has to be taken concerning fuel system tightness and detection of potential leakages (see Section 14.3.1 (d) Syngas).
A blast furnace is a large structure in which iron ore is heated under pressure so that it melts and pure iron metal separates out and can be collected (Collins Dictionary). The heritage value of blast furnaces built before 1900 has been recognized already for a long time, and most preserved installations from the 19th century are now museums or are anyhow open to visitors. However, the recognition of more recent mass production blast furnaces as industrial heritage is relatively recent. Until recently it has been pretty normal to demolish blast furnaces after their deactivation and either replace them with newer models, or to clear the entire site for redevelopment. The first modern blast furnace not to be dismantled is situated at Starachowice, Poland (shut down in 1968), followed by the last blast furnace of Yahata Steel Works at Yahatahigashi-ku, Kitakysh, Japan (shut down in 1972) and the Carrie Furnaces at Homestead, PA, USA [shut down in 1978 (Abandoned America, 2018)]. One of the two blast furnaces at Neunkirchen, Germany (shut down in 1982) was the first blast furnace to be not only preserved as-is, but refurbished for the purposes of preservation.
The installations built in the last century were normally part of large industrial compounds where multiple blast furnaces were in operation side by side to improve efficiency. Raw materials were delivered to the site by freight trains and loaded into the furnaces by external elevating mechanisms; the trains carried off the smelted pig iron in ladles.
In many cases, the preserved sites have been despoiled to minimize maintenance costs; besides, many blast furnaces have been dismantled. The policy was to keep only one or two furnaces and related installations at each site: this was deemed enough to explain the mechanical and chemical processes to visitors. Currently, most preserved furnaces are used as museums. Typically, colorful light installations brighten these furnaces at night. A comprehensive description of the redevelopment of a blast furnace site is given in ICOMOS (2007).
Working height is a distance between the tuyere level and the stockline (more exactly 1m below the rotating chute in vertical position in the case of bell-less-type charging system, right in Figure 17.1, or 1 m below the large bell in low position in the case of bell-type charging system, left). Corresponding furnace volume is working volume. Inner or useful height is a distance from the hot metal taphole level to the stockline. Total height is a distance from the hearth bottom to the stockline. Above definitions are used in the EU countries.
The real BF lining wear profile, whose formation and stabilization depend on the operating conditions and constructive features such as a cooling system (see next sections), differs from the designed profile presented above.
It is considered that the BF was evolved in fourteenth century from the bloomery furnace. Figure 17.2 shows examples of inner shape for two German blast furnaces at the end of eighteenth to the beginning of the nineteenth centuries.
Figure 17.3 and Table 17.1 show evolution of blast furnace dimensions from 1860. Between the years 1860 and 1960, the diameter of the furnace hearth increased from 0.9 to 89m with production of 25 and 15002000tons of hot metal per day, respectively. From the 1960s to the 1980s, the hearth diameters have almost doubled, and the furnace volume and the productivity increased about 2.5- and 5-fold, respectively (Babich et al., 2008a).
Large blast furnaces with an inner volume of about 5000m3 and more have a full height (including charging and off-gas systems; see Section 17.2) of about 100130m and production capacity approximately 11,00013,000tons of hot metal a day.
Two worldwide largest blast furnaces are BF 1, Shagang Group, China, with inner volume of 5800m3 and BF 1, Gwangyang, POSCO, South Korea, with inner volume of 6000m3 and hearth diameter of 16.1m (Anon, 2013).
The BF is covered with a shell of steel plate and internally lined with refractories. The refractory structure is cooled by water-cooled metal components (the so-called staves), which are located between the shell and the refractories. Advanced refractory materials and effective furnace shell cooling along with technological advances in operation and maintenance enable campaign life of modern BFs over 15 years (Kawasaki Steel, 1997).
An ore storage yard (or an ore dock) serves to unload rail hoppers or ships with ore burden and flux raw materials. These materials and coke (from conveyor belts or rail hoppers) are transferred to the stockhouse. Each type of material (ore, pellet, sinter, coke, limestone, etc.) is dumped into separate bins. The raw materials are weighed by discharging from bins and transported to the furnace top by a belt conveyor or skip cars. Modern large blast furnaces are equipped with the conveyor belt.
Aside from the bell-less or no-bell charging systems such as shown in Figure 17.5, the raw materials can enter the furnace using bell-type charging equipment. A charging apparatus should also enable an appropriate distribution of the raw materials at the BF top.
The shaft, belly, and bosh are usually lined with chamotte bricks and silicon carbide bricks, and the hearth is lined with carbon bricks. Different cooling techniques can be applied in different BF zones to assist the lining to resist the specific deterioration factors, to maintain stability of the refractories, and to protect the furnace shell.
Depending on the size of the furnace, the side wall of the hearth is radially fitted with some 1442 of water-cooled copper tuyeres, which are used to inject the hot blast into the furnace from the hot stoves through the hot-blast bustle main and blowpipes (Figure 17.5). A tuyere apparatus of a modern BF is fitted with special lances for the injection of auxiliary reducing agents and other additives (Babich et al., 2008a).
Tapholes for discontinued discharging hot metal and slag are also installed in the hearth. Modern large BFs have three to four tapholes (Figure 17.6). A taphole drill is used to bore a hole through the taphole clay into the hearth for tapping. A mud gun is used to close the taphole after the tapping with clay or with special high-temperature refractory compounds. Trough and runner systems serve to separate the hot metal and slag and to convey them to the torpedo and slag ladles.
Hot stoves serve for heating the blast. It is a type of heat exchanger, in which the heat produced by combustion of the BF gas usually mixed with natural gas (NG) or coke oven gas (COG) is stored in the checkerwork chamber, after which cold air is blown through the hot checkerwork to produce the preheated hot air blast to the furnace. Three to four stoves are operated on alternate cycles, providing a continuous source of hot blast to the BF.
The blast furnace, a vertical shaft kiln, is the oldest industrial furnace. Reactant enters in the top of the shaft and falls down through a preheating section, a calcinating section, past oil, gas, or pulverized coal burners, through a cooling section, with the product ash falling through a discharge gate.
The blast furnace operates continuously although the individual particles see a batch mode of reaction. The actual reaction conditions must be based on the batch reactor sequence for the particles since complete conversion is desired. This requires control of the mass throughput in the furnace, but primarily it requires accurate temperature control. Control of the solids is maintained at the bottom discharge port. Gas flow rate is controlled by blowers or by a stack discharge fan.
Raw mill is made up of feeder part ,discharging part ,rotating part ,transmission part(reducer,samll transmission gear ,motor,electric control) etc. It's a key equipment for grinding materials, widely used in powder-making production line such as cement, silicate sand, new-type building material, ore dressing of ferrous metal and non-ferrous metal, etc. Do your know how does the raw mill work in the cement plant? This paper mainly introduces the raw mill in cement plant.
In order to achieve the desired setting qualities in the finished product, a quantity (2-8%, but typically 5%) of calcium sulfate (usually gypsum or anhydrite) is added to the clinker and the mixture is finely ground to form the finished cement powder. This is achieved in a cement raw mill. The grinding process is controlled to obtain a powder with a broad particle size range, in which typically 15% by mass consists of particles below 5 m diameter, and 5% of particles above 45 m. The measure of fineness usually used is the "specific surface area", which is the total particle surface area of a unit mass of cement. The rate of initial reaction (up to 24 hours) of the cement on addition of water is directly proportional to the specific surface area.
The cement is conveyed by belt or powder pump to a silo for storage. Cement plants normally have sufficient silo space for 120 weeks production, depending upon local demand cycles. The cement is delivered to end-users either in bags or as bulk powder blown from a pressure vehicle into the customer's silo. In industrial countries, 80% or more of cement is delivered in bulk.
Our raw mill has been widely used in the cement making plant. In a large number of customer feedback, we received a lot of enthusiasm and positive reaction. They speak very highly of our machines. According to a lot of customers' response, this plant generally have the following four advantages.
Raw mill is generally called cement raw mill, raw mill in cement plant, it refers to a common type of cement equipment in the cement plant. In the cement manufacturing process, raw mill in cement plant grind cement raw materials into the raw mix, and the raw mix is sent to the cement kiln to make cement clinker, next, clinker and other admixtures will be ground into finished cement by cement mill.
As for the type of raw mill, there are two types including cement ball mill and vertical cement mill. In the traditional cement raw mill system, the cement ball mill system is more typical. After technology modification, the vertical cement mill has obvious advantages compared with the cement ball mill, and it is suitable for the large cement production line.
AGICO CEMENT is a raw mill manufacturer from china who has the ability to manufacture cement ball mill and vertical cement mill. As a leading and trusted manufacturer, we had exported many projects of cement raw mill and cement equipment to the countries or regions around the world. Why AGICO CEMENT is popular?
Vertica raw mill, also known as vertical roller mill, in the 1920s, the first vertical raw mill in cement plant is designed in German. It is widely used in cement, electric power, metallurgy, chemical industry, and other industries.
Low investment: the vertical raw mill set crushing, drying, grinding, grading transportation in one, simple system, compact layout, less space, it also can be arranged in the open air, save a lot of investment costs.Low operation cost: small energy consumption and less damage reduce the running cost.Environment protection and clean: small vibration, low noise, and good sealing, the system works under negative pressure, no dust overflow.Stable quality of raw mix: because the material stays in the raw mill for a short time, it is easy to detect and control the product size and chemical composition, reduce repeated grinding, and stabilize the product quality.
The main motor drives a millstone by rotational speed reducer, at the same time the wind enters into the raw mill from the air inlet, material through the screw feeder fell in the middle of the raw mill, under the action of centrifugal force, the raw materials move uniformly from central to the edge of the millstone, the materials will be ground by the roller when it passes through the grinding roller way, large materials are directly crushed. Crushed material continues to move to mill edge, until being taken away by the wind ring in strong turbulence, and larger particles material again fell to the mill to continue to crush, the flow of materials through the upper part of the separator, in the effect of separator blade, coarse particle back to the grinding mill, qualified fine powder with airflow is out of the raw mill, and collected by the powder collection.
The cement ball mill usually can be applied to raw meal grinding or cement grinding. Besides, the cement ball mill also can be used for metallurgical, chemical, electric power, other mining powder grinding, and other grindable materials.
Safe and reliable system: the maintenance of the reduction gear and gear is more convenient, firm and wear-resistant, and also reduces the downtime, maintenance time and the labor intensity of the operators.
Good wear resistance and long service life: Cement ball mill adopts the high-quality wear-resisting material, and the lining can be removed, therefore the service life of the equipment or vulnerable part is all longer.
The main working part of cement ball mill occurred in the low-speed rotary cylinder, when the cylinder is drove to rotary, grinding medium is attached on the liner to rotary together due to the effect of inertial centrifugal force, and taken to a certain height, freely fall because of gravity, grinding medium break the materials in the cylinder body, at the same time the grinding body in the rotary raw mill have circular motion, also can produce sliding and rolling, which result in grinding among the grinding medium, liner, and materials. When the material is crushed and ground by impact, the material flows slowly from the feeding end to the discharging end to finish the grinding operation.
The raw mill is a kind of necessary cement equipment in the cement plant. In the real working condition, but the large configuration will produce a bad effect on the cement plant, so it is very important to set a reasonable configuration of the raw mill. There are five reasons why we control the configuration of the raw mill in cement plant:
Composition fluctuation of the raw meal: The frequently start-stop of a raw mill will bring different degrees of influence on the quality, whether it is the cement ball mill, the vertical cement mill or the cement roller press system.
Raw meal grinding is a vital link in the cement raw material preparation process. After the cement raw material is crushed, it will be sent into the raw mill for further grinding until a certain degree of fineness is reached, and then enter the clinker calcination process. From the production experience of many cement plants, the selection of cement equipment, especially raw mill, will directly affect the project investment, production schedule and economic benefits. At present, in order to adapt to the process characteristics of the new dry method cement production line and make full use of the exhaust gas residual heat of the kiln tail preheating decomposition system, we usually adopt the grinding system that merges drying and pulverizing into a single.
AGICO is an experienced Chinese cement equipment manufacturer. We have been in the cement industry for almost 20 years, specializing in cement EPC project exporting and cement making machines exporting, such as cement production line, cement kiln, cement crusher, cement mill cement raw mill, etc. According to the different properties of materials, there are mainly two kinds of grinding systems used in our cement plant.
The cement ball mill manufactured by AGICO can complete the drying and grinding of raw materials at the same time. After entering the ball mill, materials directly contact with the gas with high temperature, so the heat exchange and the water evaporation is fast. Under normal conditions, we usually divide the cement ball mill grinding system into an intermediate discharge circulating grinding system and tail discharge circulating grinding system.
Intermediate discharge circulating grinding system is a drying form in the cement ball mill. In terms of drying function, this system is the product of the combination of wind swept mill and tail discharge circulating grinding mill. In terms of grinding function, it is equivalent to a secondary closed-circuit grinding system. After classified by the powder concentrator, most of the raw meal will go back to the fine grinding chamber and a small part to the coarse grinding chamber. This is better for the hardness and granularity adaptability of raw materials.
The main difference between the tail discharge circulating grinding system and the air swept mill is that materials in the tail discharge grinding system will first pass through a drying chamber before reaching the grinding chamber. Besides, this system adopts the mechanically discharging method. The hot air will be transferred from the head to the tail, and then discharged into the atmosphere after dedusting by the dust collector.
Cement vertical mill, also called roller mill, is another raw mill commonly used in cement plants. Compared with the cement ball mill, it has a great difference in structure, grinding principle, process layout, automatic control, and energy consumption, which play an important role in the modern cement industry.
AGICO Group is an integrative enterprise group. It is a Chinese company that specialized in manufacturing and exporting cement plants and cement equipment, providing the turnkey project from project design, equipment installation and equipment commissioning to equipment maintenance.
According to the Bank of Tanzania (BoT), the growth in the construction sector was attributed to growing public investments (construction of standard gauge railway, bridges, airports, and roads, expansion of ports), as well as on-going rehabilitation of metre-gauge railway.
The manufacturing sector in Tanzania consists mainly of food processing (24%), textiles and clothing (10%), chemicals (8.5%), and others, including beverages, leather and leather products, paper and paper products, publishing and printing, and plastics.
In line with the 2025 Vision of the Ministry of Agriculture, Food and Cooperatives of Tanzania, there should be at least two new products developed from each of the staple crops, horticultural crops, livestock, and fisheries by that year.
The Tanzania Portland Cement Company (TPCC) is the leading company in Tanzanias cement industry, holding 36% of the market share. The companys production of cement stands at 2 million tonnes per year as a result of the construction of a new Cement Mill (CM5), completed in 2014.
Africas leading cement producer, Dangote Cement, commissioned the largest cement factory in Tanzania (the Mtwara plant) in December 2015. The Tanzanian plant is part of Dangotes regional plan to shift Africa from cement importer to producer, raising the yearly production by 25 million tonnes per annum.
The Government of Tanzania introduced its Sustainable Industrial Development Policy (SIDP) in 1996 to phase itself out of investing directly in productive activities and let the private sector take that role.
In 2002 Tanzania established its Export Processing Zones (EPZ) scheme, to provide for the establishment of export-oriented investments within the designated zones with the views of creating international competitiveness for export-led economic growth.
In addition, in 2006 the Special Economic Zones (SEZ) scheme was introduced, to promote quick and significant progress in economic growth, export earnings, and employment creation as well as attracting private investment in the form of both Foreign Direct Investments (FDI) and Domestic Direct Investment (DDI) from all productive and service sectors.
Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website. These cookies do not store any personal information.
Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies. It is mandatory to procure user consent prior to running these cookies on your website.
Howden products are used throughout the cement production process. Our blowers are used to move the iron ore, calcium carbonate, silica and alumina immediately after extraction and continue to be used throughout the process and once the end product is generated and needs transported.
Once the raw materials have been crushed into raw meal, they are transported to the kiln and Howden fans play an important role in super heating the meal into the cement clinker and then to cool the clinker. The clinker then has gypsum added and is moved into the cement mill to be ground into the final product.
As the ever increasing demand for cement puts pressure on plant capacity and efficiency, our extensive experience in the industry allows us to revamp and upgrade fans and blowers, and increase cement manufacturers output.
We supply all the fans for a complete cement plant. These include the process critical fans, mainly centrifugal, for the pre-heater exhaust, kiln induced draught, raw mill exhaust, final exhaust, cooler forced draught and cement mill exhaust applications. We also supply all the other associated centrifugal and axial fans. We supply rotary positive displacement (Roots) blowers for cement conveying systems. Our experience in the cement industry goes back many years and we have supplied equipment in many parts of the world.
In preparing raw meal, raw materials like limestone, clay and iron ore are proportioned and fed to raw mill, where these raw materials are ground and well mixed. However, this mixing is not enough to produce clinker of uniform quality. For stable kiln operation and to obtain uniform quality of clinker it is necessary to keep the variation in kiln feed in LSF 0.5, in SM 0.03 and in AM 0.03 measured as a standard deviation.
A specific blending operation is therefore necessary to produce kiln feed of quality that is consistently uniform in chemical composition and also particle size distribution. For cement plants of small capacities where preblending by staking-reclaiming was not a necessity, batch type blending (Air merge-turbulent blending) to achieve a blending ratio of 10-1 was enough to produce a consistent kiln feed. However, as the plant capacities grew bigger and bigger, Batch type silos to contain a buffer stock of 2-3 days (kiln feed) became unfeasible and the concept of continuous controlled silos of capacities as high as 15k-20k metric tons started to evolve. Modern designed controlled flow silos yielding a blending ratio of 3-5. Controlled flow silos may have multiple discharge points, or an inverted cone over a center discharge within which the raw meal is fluidised. In controlled flow silos, blending is achieved by differential rates of material descent within the silo by sequenced light aeration of segments of air-pads. Moreover, it is recommended to have a preblending system (staking-reclaiming) and a regular analysis of from raw mill feed or product by XRF to augment blending of raw meal to consistent kiln feed for good quality clinker formation and stable kiln operation
Caution: Blending silos are very prone to internal build-up of dead material, particularly if feed material is moist or if segment aeration is defective. Re-circulation provision is always available in silos to recirculate raw meal during kiln shut-down or any inactive period to avoid internal build-ups. Therefore, it is recommended to do periodic (1-2 years) internal inspections and maintenance.
What is Portland cement? Portland cement derives its name from Portland, England, in many cases, also called silicate cement. It is a kind of hydraulic cementing material made of calcium silicate cement clinker, limestone or blast furnace slag (less than 5%), and an appropriate amount of gypsum. At present, Portland cement has been widely used in residential construction, traffic construction, large-scale water conservancy construction, and civil engineering, etc.
For different applications, Portland cement is classified into various types. The ordinary Portland cement (OPC) refers to Portland cement containing 5 ~ 20% of active mixing material. The Portland cement with a higher proportion of admixture (more than 20%) usually named by the admixture, such as the Portland pozzolan cement, Portland fly-ash cement, Portland slag cement, etc.
The main components of Portland cement include calcium oxide (CaO), silicon dioxide (SiO2), aluminum oxide (Al2O3), and iron oxide (Fe2O3). They account for more than 95% of the total cement composition. In addition, there are other oxides like magnesium oxide (MgO), sulfur trioxide (SO3), titanium dioxide (TiO2), phosphorus pentoxide (P2O5), potassium oxide (K2O), sodium oxide (Na2O), etc., accounting for less than 5% of the total amount. These components that make up raw materials react at high temperatures and finally form compounds tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium aluminoferrite. The tricalcium silicate and dicalcium silicate determine the strength of Portland cement, in which the tricalcium silicate mostly affects the early strength. Tricalcium aluminate causes the initial setting of Portland cement.
Portland cement has a high setting and hardening speed, high strength, especially its early strength growth rate. It is suitable for high strength concrete structures, prestressed concrete engineering, and projects with high early strength requirements.
The rich content of carbon disulfide in Portland cement leads to its high heat release, high release speed, and high strength in the early stage. If it is used in winter construction, freezing damage can be avoided.
Portland cement has the characteristic of strong alkalinity, high density, and strong carbonation resistance. When the steel bar is buried in an alkaline environment, a layer of gray passivation film will be formed on the surface, which can keep the steel bar from rusting for decades. Therefore, Portland cement is especially suitable for important reinforced concrete structures and prestressed concrete works.
A large amount of calcium silicate hydrate will be produced during the hardening process of Portland cement. As a result, cement stone has high density, less free moisture, and is not easy to produce dry shrinkage cracks. Therefore, Portland cement can be used in concrete engineering in a dry environment.
Portland cement mixture is not easy to bleed, and the density of hardened cement stone is large, so the frost resistance is better than other general cement. It is suitable for concrete engineering under repeated freeze-thaw action in severe cold areas.
Portland cement manufacturing process can be divided into 6 steps: raw material crushing, pre-homogenization, fine grinding, clinker production, cement grinding, cement packing, etc. In these processes, we need the assistance of different kinds of cement equipment, such as cement kilns, cement mills, and cement crushers. The specific manufacturing processes are as follow:
After cement raw materials are mined, most of them should be crushed into small particle sizes. Coal, the main fuel for cement production, also needs to be broken in advance. In this step, all of them should be crushed by special crushing mills and then be transported to the pre-homogenization yard by belt conveyor.
The pre-homogenization refers to the preliminary homogenization of cement raw materials and fuel raw materials through the application of scientific stacking and reclaiming technology in the process of material storing and taking. In this step, the stacker is applied to pre-homogenize and stack raw materials in layers. Then the scraper reclaimer takes out raw materials and sends them to the batching station helped by the belt conveyor.
After the raw material batching is completed, cement raw meals (calcareous raw materials, clayey raw materials, and a small amount of corrective materials) need to be further ground by raw mills to realize a certain fineness, appropriate chemical composition, and uniform structure so that they can meet the calcination requirements of various cement kilns. The frequently used raw mills include cement ball mill, cement vertical mill, Raymond mill, etc. The air-swept coal mill is used for coal grinding.
Clinker production is the most critical stage in the cement manufacturing process. At present, the new dry process clinker production technology is the most advanced clinker production method. It has the advantages of high efficiency, energy-saving, and high production quality. By this production method, the raw meal powder will be pre decomposed in cyclone preheater and calciner firstly, and then enter cement kiln to be calcined under high temperature. After that, the calcined clinker will be cooled by the grate cooler and stored in the clinker warehouse.
After calcination, the clinker needs to be mixed with gypsum and additives to meet the requirements of different properties. Then, they will be ground by cement mills to appropriate particle size, forming a certain particle gradation, which increases the hydration area and accelerates the hydration speed.
Cement packing is the last step in the cement manufacturing process. After the cement powder is discharged from the unloading system at the bottom of cement silos, they will be sent into the cement packaging machine by the bucket elevator. In the packing machine, they are packaged into bags and then be transported to different sales markets.
AGICO Group is an integrative enterprise group. It is a Chinese company that specialized in manufacturing and exporting cement plants and cement equipment, providing the turnkey project from project design, equipment installation and equipment commissioning to equipment maintenance.
What is Portland pozzolana cement? The hydraulic cementitious materials made of Portland cement clinker, pozzolanic material, and a proper amount of gypsum are all called Portland pozzolana cement (PPC cement). It is a kind of blended cement which is manufactured by mixing and fine-grinding silicate cement clinker, pozzolanic material, and gypsum.
Pozzolanic materials contain active silica and aluminum and usually do not have any cementitious properties. But when they are mixed with water and lime at ambient temperatures, they will react with calcium hydroxide to form compounds possessing cementitious properties. The commonly used pozzolanic materials can be classified as natural or artificial:
Portland pozzolana cement shall be manufactured by mixing and inter-grinding Portland cement clinker, pozzolanic materials, and gypsum. The manufacturing process is approximately the same as ordinary Portland cement, which can be divided into four processes: raw material crushing, raw material grinding, clinker calcination, and cement grinding.
Limestone and clay are the main material for Portland cement production. After mining, these raw material stones are unloaded by trucks and sent into crushers for reducing particle size. Then they are piled in a pre-homogenization yard waiting for processing.
Fine particle size raw materials are fed into the raw mill in a desired proportion for further particle size reduction, then they are stored in silos, meanwhile completing the material blending and homogenization process.
Cement raw meals are sent into a cement rotary kiln to be calcined under a high temperature. After several chemical reactions are produced, some spherical gray particles, what we called clinker, are formed. In cement cooler, these hot clinkers will be cooled to a normal temperature.
After cooling, the clinker is mixed with pozzolanic materials and gypsum in a required proportion and then sent to the cement mill for final grinding. The cement powder is usually stored in cement silos, then bagged and stored in the warehouse.
In the Portland pozzolana cement manufacturing process, we need a variety of cement equipment. AGICO, as a cement plant supplier in China, offers different cement solutions and cement manufacturing equipment.
Portland pozzolana cement, portland slag cement, and portland fly ash cement are all made by adding active admixture and an appropriate amount of gypsum based on Portland cement clinker. They are similar in nature and scope of application, so they can be used interchangeably in most cases. However, the physical properties and characteristics of the active admixture are different, which makes the three types of cement have their unique characteristics.
Slow setting and hardening, low early strength, and high late strength. The clinker content of the three kinds of cement is small, and the secondary hydration reaction is slow, while their later strength exceeds the ordinary Portland cement of the same grade.
Sensitive to temperature and humidity, suitable for high-temperature curing. When the three types of cement are cured at high temperatures, the hydration of the active mixture and clinker will be accelerated, and the early strength is improved without affecting the development of the later strength. Ordinary Portland cement, although the use of high-temperature curing can improve the early strength, the development of later strength will be affected.
Good corrosion resistance. They have good corrosion resistance and are suitable for the environment containing sulfate, magnesium salt, soft water, etc. However, when the corrosion resistance requirements are high, it is not suitable for the application.
Poor frost resistance. Slag and fly ash are easy to bleed to form connected pores. As to pozzolana, it has a large water storage capacity, which will increase the internal pore number. Therefore, the frost resistance of the three types of cement is poor.
Composite Portland cement: the early strength of composite Portland cement is higher than slag (or pozzolana, fly ash) cement, closes to ordinary Portland cement. It has low hydration heat, good corrosion resistance, impermeability, and frost resistance.
AGICO Group is an integrative enterprise group. It is a Chinese company that specialized in manufacturing and exporting cement plants and cement equipment, providing the turnkey project from project design, equipment installation and equipment commissioning to equipment maintenance.Get in Touch with Mechanic