Use of organic fibre cement as a raw material in the production of cement clinker
09926229 ยท 2018-03-27
Assignee
Inventors
Cpc classification
C04B7/246
CHEMISTRY; METALLURGY
Y02P40/10
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
International classification
Abstract
Fiber cement material, which contains organic fibers, is used as an additional raw material for the production of cement clinker. The cement clinker is produced in a system which comprises a cyclone tower (11) and a rotating drum kiln (15). The cyclone tower (11) comprises cyclones (1-5) and a pre-calciner unit (10) wherein fuel is combusted to feed the cyclone tower with heat. The raw clinker meal is passed through the cyclone tower to preheat it. By the combustion of the fuel in the pre-calciner unit (10) a hot zone is produced in the cyclone tower wherein the raw clinker meal is calcined. In order to be able to add larger amounts of the fiber cement material without causing a too high total organic carbon content of the exhaust gasses and/or without causing depositions of organic matter onto the inner walls of the cyclone tower (11), the organic fiber cement material is added in a dry powdered form in said hot zone, in particular in the pre-calciner unit (10) to be heated in less than 5 seconds to a temperature of at least 800 C.
Claims
1. A method for the production of cement clinker in a system comprising a cyclone tower with cyclones and with a pre-calciner unit wherein fuel is combusted to feed the cyclone tower with heat, a rotating drum kiln which has at least one feed end and which is heated by means of further fuel and a kiln riser duct leading from the kiln to the bottom of the pre-calciner unit, in which method raw clinker meal is passed through said cyclone tower to preheat it, said fuel is combusted in said pre-calciner unit to produce a hot zone in the cyclone tower wherein the raw clinker meal is heated to a temperature of at least 800 C. to calcine it, the heated and calcined raw clinker meal is fed from the cyclone tower via the feed end of the rotating drum kiln into this rotating drum kiln wherein the raw clinker meal is further heated to be molten and the molten raw clinker meal is subsequently cooled to produce the cement clinker, wherein a fibre cement material containing organic fibres is added in an amount of above 2 wt. % based on the total weight of raw clinker meal and fibre cement material to said raw clinker meal by feeding the fibre cement material containing organic fibres directly into the pre-calciner unit or via said kiln riser duct without being preheated in the cyclones of the cyclone tower and is heated in said pre-calciner unit or in said kiln riser duct in less than 5 seconds to a temperature of at least 800 C.
2. A method according to claim 1, wherein the fibre cement is added in a dry powdered form to said raw clinker material.
3. A method according to claim 2, wherein a rising gas stream is generated in the cyclone tower wherein the fibre cement material is dispersed in said dry powdered form.
4. A method according to claim 3, wherein said rising gas stream passes the pre-calciner unit, the gas contained in said rising gas stream having a retention time in the pre-calciner unit of at least 2 seconds.
5. A method according to claim 3, wherein the fibre cement material is removed from the rising gas stream by means of one of said cyclones and is supplied by this cyclone to the feed end of the rotating drum kiln.
6. A method according to claim 1, wherein the fibre cement material is heated up in less than 2 seconds to said temperature of at least 800 C.
7. A method according to claim 1, wherein the fibre cement material has an inorganic material content of at least 80 dry weight % based on the total dry weight of the fibre cement material.
8. A method according to claim 1, wherein the fibre cement material comprises fibre cement sheets, produced by Hatschek technology, which is milled into dry powdery form.
9. A method according to claim 1, wherein said fibre cement material is heated in said pre-calciner unit or in said kiln riser duct to a temperature of at least 900 C.
10. A method according to claim 3, wherein said rising gas stream passes the pre-calciner unit, the gas contained in said rising gas stream having a retention time in the pre-calciner unit of at least 3 seconds.
11. A method according to claim 6, wherein the fibre cement material has an inorganic material content of at 90 dry weight %, based on the total dry weight of the fibre cement material.
12. A method according to claim 1, wherein said fibre cement material is added in an amount of at least 10 wt. %, based on the total weight of raw clinker meal and fibre cement material.
Description
LIST OF FIGURES
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(15) As appears from the above description, the method of the present invention is to be performed in a kiln which comprises a pre-calciner unit creating the hot zone wherein the fibre cement material is to be added to the raw clinker meal. Such kilns are most advantageous from the point of view of energy consumption and enable the most efficient use of the organic fibre cement materials, also in quite large relative amounts thereof.
(16) In practice there are different types of cement clinker installations which comprise a pre-calciner unit, namely In-Line Calciners (ILC) and Separate Line Calciners (SLC). More particularly, the present invention can be applied to so-called pre-heater kilns, air through calciners, inline calciners, inline calciners with burning chamber and air separate calciners. Such installations are well known to the skilled person so that only as an example an in-line calciner will be described shortly hereinafter.
(17) As illustrated schematically in
(18) In the present specification, the term pre-calciner unit 10 has to be understood as including not only the actual pre-calciner vessel but also the riser duct leading towards the last cyclone 5 before the rotating drum kiln 15 since it forms one volume with the cavity of the actual pre-calciner vessel and a same high calcining temperature prevails therein so that the material passing through the pre-calciner vessel is further calcined in the riser duct part of the pre-calciner unit 10. In order to heat this pre-calciner unit 10, and to generate a rising gas stream therein, combustion gases produced by the combustion in the rotating drum kiln 15, i.e. kiln gas which has a temperature of about 1000 C., is guided through the kiln riser duct 17 to the bottom of the pre-calciner unit 10. Moreover, tertiary air, heated in the grate cooler 16 to a temperature of about 750-900 C., is also guided, by a tertiary air duct 18, to the pre-calciner unit 10. This tertiary air enters the pre-calciner unit 10 tangentially to create a moderate swirl ensuring an effective mixing of fuel, raw meal and gas. The temperature in the pre-calciner unit 10 is further controlled by means of a burner supplied with fuel and with primary air. The air for combustion of the fuel in the pre-calciner unit thus consists of kiln gas, tertiary air from the cooler and fuel conveying/atomising air supplied through the pre-calciner burner in the pre-calciner unit as indicated by arrow 20. About 55 to 60% of the fuel is supplied to the pre-calciner burner whilst the remaining amount of fuel (40 to 45%) is supplied to the kiln burner.
(19) In the method of the present invention, organic fibre cement material is added, in a dry powdered form, to the raw clinker meal. The organic cement fibre is added to this raw clinker meal in a hot zone in the cyclone tower where the organic fibre material is heated quickly, in less than 5 seconds, to a temperature of at least 800 C. The organic cement fibre is preferably added in the pre-calciner unit 10, more particularly in the vessel 10a of the pre-calciner unit 10 or in the riser duct 10b of this pre-calciner unit 10 leading from this vessel towards a final cyclone. In this way, it is dispersed in the rising and swirling gas stream in the pre-calciner unit and an instantaneous heat transfer is achieved. Heating is moreover accelerated by the high temperature of the fuel which is combusted in the pre-calciner unit. In fact, the organic fibre material passes the combustion zone of this fuel so that it is heated, in less than 5 seconds or even in less than 2 seconds, to a temperature of at least 900 C.
(20) Instead of feeding the organic fibre cement material directly into the pre-calciner unit 10, it can also be fed therein via the kiln riser duct 17. In fact, by the rising gas stream in this kiln riser duct 17, the organic fibre cement powder is immediately carried along into the pre-calciner unit 17 where it is added, in the hot zone within the pre-calciner unit 10, to the raw clinker meal.
EXPERIMENTAL
1 Materials and Methods
(21) 1.1. Classic Raw Materials (CRM)
(22) As representative CRM, materials are selected that are used at a daily base in three reference clinker factories. These factories are CBR Antoing (CRM/Ant) and CBR Lixhe (CRM/Lxh) in Belgium and ENCI Maastricht (CRM/Maa) in the Netherlands, all belonging to the Heidelberg Benelux group. From each of these three grey Portland clinker factories, four of their most important CRM were collected, more specifically those that act as the main sources of the four critical metal oxides in clinker: CaO, SiO.sub.2, Al.sub.2O.sub.3 and Fe.sub.2O.sub.3. CBR Antoing uses two kinds of limestone: Rich (CFM/Ant/CR) and Poor (CFM/Ant/CP). These act as CaO and SiO.sub.2 sources. CBR Lixhe uses Tufa (CFM/Lxh/Tu) and Loam (CFM/Lxh/Lo), ENCI Maastricht a typical Marl (CFM/Lxh/Ma) and Sabulous Clay (CFM/Lxh/SC) as CaO and SiO.sub.2 source respectively. All 3 factories use Fly Ash (CFM/Ant,Lxh,Maa/FA) as Al.sub.2O.sub.3 source and an artificially produced Fe.sub.2O.sub.3 source (CFM/Ant,Lxh,Maa/IC). All four of the CRM from each clinker factory were sampled at three different instances. To generate representative samples, the separate samples from each factory were homogenised. These representative samples were grinded for 2 minutes in a Siebtechnic disc mill to obtain sufficient fineness to perform analytical testing. The average chemical analysis of the limestones, as measured by XRF is presented in Table 1.
(23) TABLE-US-00001 TABLE 1 Average Chemical analysis of the Limestones of CBR Antoing (Ant), CBR Lixhe (Lxh) and ENCI Maastricht (Maa) in weight %. CRM/ CRM/ CRM/ CRM/ CRM Ant/PL Ant/RL Lxh/Tu Maa/Ma CaO 42.9 50.1 51.8 50.8 SiO.sub.2 15.1 6.4 4.7 7.1 Al.sub.2O.sub.3 2.2 0.9 0.4 0.8 Fe.sub.2O.sub.3 0.9 0.4 0.3 0.4 K.sub.2O 0.68 0.21 0.07 0.13 Na.sub.2O 0.25 0.25 0.02 0.20 SO.sub.3 0.90 0.57 0.09 0.21 MgO 1.1 0.9 0.7 0.8 Cl 0.011 LOI 975 C. (O.sub.2) 35.04 40.18 42.03 40.18
1.2. Alternative Raw Material (ARM): Fibre Cement
(24) The fibre cement materials used for this investigation were taken from four different production lines, corresponding with two roofing products, Corrugated fibre cement Sheets (ARM/CS) and fibre cement Roofing Slates (ARM/RS), and two faade products, Medium Density fibre cement boards (ARM/MD) resp. High Density fibre cement boards (ARM/HD). The roofing products concern air-cured products whereas the faade products are autoclaved. The air-cured products have very similar formulations and contain synthetic reinforcement fibres (Polyvinyl Alcohol and Polypropylene), process fibre (cellulose), Portland cement, pozzolanic and inert filler. The corrugated sheets (ARM/CS) contain twice as much pozzolanic filler as the slates (ARM/RS). The final corrugated sheet density amounts to values between 1.45 and 1.50 g/cm.sup.3. In case of the slates, the density is about 1.85 g/cm.sup.3. The autoclaved products mainly contain cellulose reinforcement and cellulose process fibres, Portland cement, quartz flour and some stabilizing agent. Furthermore, they each contain some product-specific additional functional mineral filler(s). The product's final density amounts to respectively 1.30 and 1.85 g/cm.sup.3 for Medium Density fibre cement boards (ARM/MD) and High Density fibre cement boards (ARM/HD) respectively. For each ARM source, material was recovered at 24 different points of time spread over 6 months after which they were 2 by 2 homogenised. After crushing in a Retsch cutting mill those samples were ground for 1 minute in a Siebtechnic disc mill to obtain sufficient fineness. For each of the 4 types of fibre cement product, the average chemical analysis determined by XRF of the 12 samples is presented in Table 2.
(25) TABLE-US-00002 TABLE 2 Average chemical analysis of the fibre cement materials in weight % Corrugated Fibre Autoclaved Autoclaved Fibre cement High Medium Density cement Roofing Density Fibre Fibre cement Sheets Slates cement Boards Boards ARM ARM/CS ARM/RS ARM/HD ARM/MD CaO 51.24 52.14 28.55 25.01 SiO.sub.2 18.85 18.42 44.2 51.06 Al.sub.2O.sub.3 2.80 3.55 5.95 4.95 Fe.sub.2O.sub.3 2.52 3.15 2.37 1.74 K.sub.2O 0.37 0.28 0.22 0.15 Na.sub.2O 0.20 0.17 0.06 0.12 SO.sub.3 1.87 1.35 0.69 0.61 MgO 1.38 1.57 0.59 0.71 TiO.sub.2 0.25 0.43 0.34 0.38 P.sub.2O.sub.5 0.44 0.31 0.16 0.18 Cl 0.03 0.01 0.01 0.01 LOI 19.65 18.11 16.13 14.83 975 C. (O.sub.2) C.sub.total 3.94 4.10 3.66 3.44 S.sub.total 0.86 0.66 0.33 0.31
(26) The mutual relationship between the CaO and the SiO.sub.2 content is graphically illustrated in
(27) 1.3. Testing of Raw Materials, Clinker and Cement Properties
(28) To prepare the different CCM compositions, all raw materials were crushed in advance in a Siebtechnic Disc mill. The calculated dosage to achieve 500 g of CCM were brought together in a vessel used for the analysis of the micro-Deval abrasion resistance. This procedure was used to homogenise as good as possible the raw meal before it was thermally treated in a kiln. Before sintering, the different CCM compositions were first granulated on granulation plates (5 mm holes). The sintering was performed in an electric high temperature static kiln (Carbolite BLF1800) to 1450 C. at a constant heating rate (10 C./min). The Hot Clinker Meals (HCM) were maintained for 1 h at 1450 C. after which they were immediately air-cooled to room temperature by open air to form the final clinker. XRF analyses were performed on a Philips PW2404 in accordance with EN 197-2 to chemically characterise the classic (CRM) and alternative raw materials (ARM), all cold clinker meals (CCM) and final clinkers. For the analysis of the total C and S, a Leco CS230 was used. A Netzsch STA 449F3 was used to evaluate by TGA/DTA measurement all the CRM and selected ARM as well as all the CCM compositions on their thermal decomposition mechanism as also on the energy required during their heating up to 1450 C. and were performed in an atmosphere of 5 V % O.sub.2 and 95 V % N.sub.2 which corresponds with the typical V % O.sub.2 in the atmosphere of a clinker kiln. A Mettler Toledo Star TGA/DTA was used to evaluate the same materials in a pure N.sub.2 gas atmosphere, as also to evaluate by TGA/DTA the cement pastes described in Paragraph 3.2 in an atmosphere of 5 V % O.sub.2 and 95 V % N.sub.2. As heating rate, 10 C./min was chosen for both devices which gave the best resolution for evaluation of the graphs. Of course, an industrial clinker process will exhibit a much higher heating rate, e.g. 600 C./min in a cyclone tower, most probably resulting in other reaction products for heating rate sensitive compounds like the organic fibres in the ARM. XRD analyses were performed on a Bruker D8 ADVANCE refined by Rietveld method to mineralogically characterise all the final clinkers. These analyses were only performed on the Final Clinkers. An IKA calorimeter system C7000 was used to measure the gross calorific values of the CCM and the selected fibre cement ARM in accordance with ISO 1928. A Mettler Toledo Star DSC was used to determine the required energy for the liberation of chemically bound H.sub.2O on the cement pastes described in Paragraph 3.2. Four pastes were made out of 450 g CEM I type cement and W/C ratios of 0.25, 0.30, and 0.35. To obtain the paste with the lowest W/C ratio (0.18), a paste with a W/C ratio of 0.21 was made, which was subsequently filtered off in view of obtaining a still lower W/C ratio. The pastes were stored for 28 days at 201 C. hermetically wrapped in plastic and were afterwards dried at 105 C. at the respective curing times that had been selected. For the analysis of the formed volatiles after thermal degradation of the organic fibres in fibre cement ARM, a Varian GC (3900)-MS (Saturn 2100T) was used and for the formed gases, a MS Balzers Quadstar 422.
2 Theory/Calculation
(29) 2.1. Chemical and Mineralogical Limitations of Each Reference Clinker and Clinker Kiln
(30) For each clinker factory, the chemical and mineralogical data of the clinkers produced in the first 6 months of 2011, was used to define the reference clinker of each clinker factory (Table 3).
(31) TABLE-US-00003 TABLE 3 The average chemical composition of the reference clinker of each clinker factory in weight % Antoing Lixhe Maastricht Clinker Average Average Average CaO 65.90 65.87 64.92 SiO.sub.2 21.42 21.42 20.40 Al.sub.2O.sub.3 4.44 4.84 5.01 Fe.sub.2O.sub.3 2.61 3.65 3.52 K.sub.2O 0.74 0.57 0.47 Na.sub.2O 0.21 0.30 0.34 SO.sub.3 1.21 0.51 0.92 MgO 1.70 2.01 2.08 Cl 0.068 0.017 0.020 CaO free 1.46 0.55 2.33 LSF_MgO 98.24 98.19 98.20 C3A 7.35 6.65 7.33 LiqSimple 19.18 22.73 22.97
(32) To prevent undesirable effects on both the clinker production process as well as on the clinker quality and to remain within the framework of the cement standards, chemical and mineralogical limits specific for each clinker factory were defined and used to evaluate the feasibility of applying fibre cement as an alternative raw material (Table 4).
(33) TABLE-US-00004 TABLE 4 Chemical and mineralogical limitations on the final clinker in weight % Clinker Antoing Lixhe Maastricht Cl x < 0.08 x < 0.08 x < 0.08 SO.sub.3 x < 1.4 x < 1.2 x < 1.1 Na.sub.2Oeq x < 1.2 x < 1.2 x < 1.2 MgO x < 4.0 x < 4.0 x < 4.0 DoS-level 80.0 < x < 120.0 80.0 < x < 120.0 80.0 < x < 120.0 LSF_MgO 98.5 < x < 98.5 98.5 < x < 98.5 98.5 < x < 98.5 C.sub.3A 7.4 < x < 7.4 6.7 < x < 6.7 7.3 < x < 7.3 LiqSimple 19.2 < x < 19.2 22.7 < x < 22.7 23.0 < x < 23.0
(34) One of possible problems in a clinker kiln concerns clogging of material on the sides of the kiln, by which the smooth operation of the clinker kiln can be disturbed. This explains why the SO.sub.3, Na.sub.2Oeq and Cl contents of the clinkers produced in the three reference clinker factories have to meet even stricter limits than those required in order to be in line with the cement standards.
(35) SO.sub.3 [weight %] is the general form to describe all SO.sub.4.sup.2 [weight %] present in clinker or cement. SO.sub.4.sup.2 can occur mineralogically in Portland clinker in different forms with their own specific solubility and will be particularly present in the alite (C.sub.3S) and belite (C.sub.2S) phases. SO.sub.3 will generally be formed after oxidation of S compounds in a clinker kiln. High concentrations of S are often present in pet coke fuel where contents up to 3 to 6 weight % are commonly found. When taking into account their respective dosages in the raw meal mixture, also limestone, clay or blast furnace slag, used as raw materials, can bring significant levels of S or SO.sub.3 in clinker, like can be noted in Table 1. In an alkali-rich environment, mainly installed by Na and K from the raw materials, these sulphates can be found particularly in the form of alkali sulphates. If no sufficient SO.sub.3 content is available to combine all Na and K into sulphates, the majority of the free alkali will be built into the Belite phase. The free alkali will increase viscosity of the melt and decrease the formation of Alite. Also an excess of alkali emitted to the gas phase of a clinker kiln by its high volatility, will make that clogging phenomena will appear faster. This could lead to faster wear of the refractory bricks. However when the amount of SO.sub.3 strongly exceeds the amount that can be bound by the alkali, CaSO.sub.4 will be formed, whereas in the case of a moderate excess of SO.sub.3 several other forms of alkali sulphates will dominate like arcanite, aphihitalite, thenardite and calcium langbeinite. In addition an imbalance between alkali and SO.sub.3 could damage the furnace process and have negative influences on the clinker quality and by that on the final cement hydration. Like described above, a stoichiometric balance is imposed, expressed as the so called DoS value calculated by equation (1) using the chemical analysis of the final clinker.
DoS=77.41.Math.SO.sub.3/(Na.sub.2O+K.sub.2O.Math.0.658)(1)
(36) DoS levels between 80 to 120 weight % are recommended and therefore implemented in the three factories. For this reason these DoS levels will be retained in all simulations presented in this work. Increasing levels of Cl as well as SO.sub.3 have increasing levels in the gas phase of a clinker kiln increase clogging and therefore disturbed process. As shown in
[X].sub.HCM=[X].sub.CCM+.sub.X.Math.[X].sub.HCM.sub.X.Math..sub.X.Math.[X].sub.HCM=[X].sub.CCM/[1.sub.X.Math.(1.sub.X)] (2) (X=Cl, SO.sub.3, K.sub.2O or Na.sub.2O)
(37) Based on this assumption, limits on Cl and SO.sub.3 can be set for the Final Clinker. If exceeded, this will result in disturbances in the function of the kiln. The introduction of fibre cement materials will not markedly change the Cl content of the kiln feed because the Cl content of fibre cement ARM is very low and in line with the other CRM. Actually, Cl is especially brought in by fuel materials such as waste oils, tires, plastics, animal meals, etc. In the present investigation the fuel mix is not adapted. So instead of putting a limitation on a parameter in that SO.sub.3 and Cl are taken into account, the requirement by which safe combinations of SO.sub.3 and Cl contents are guaranteed can be simplified to a SO.sub.3 limitation (max) on the raw meal as listed for each clinker factory in Table 4. These SO.sub.3 limitations were derived from
LSF_MgO=100.Math.(CaOCaO.sub.free+0.75.Math.MgO)/(2.8.Math.SiO.sub.2+1.18.Math.Al.sub.2O.sub.3+0.65.Math.Fe.sub.2O.sub.3)(3)
(38) The approximative calculation of the C.sub.3A content is done by a commonly known Bogue calculation described in equation (4).
C.sub.3A=(2.650.Math.Al.sub.2O.sub.31.692.Math.Fe.sub.2O.sub.3)(4)
(39) The composition of the liquid at 1450 C. is to a high extent governed by the ratio of Al.sub.2O.sub.3 to Fe.sub.2O.sub.3. In the simulations of the present study the combined influence of these 2 components is expressed by means of a parameter defined by the simplified equation (5).
LiqSimple=(3.Math.Al.sub.2O.sub.3+2.25.Math.Fe.sub.2O.sub.3)(5)
(40) By limiting the-three above parameters for the final clinker, the 4 metal oxides are sufficiently anchored within a safe zone for each factory. Actually, in the present study, the 3 parameters were each given fixed, but factory dependent, values as displayed in Table 4. Also MgO has to be monitored because of its limitation within the cement standards. Though this parameter was not critical in this investigation as levels were very low.
(41) 2.2. Emissions and Energy Consumption
(42) The diversity of compounds that the organic materials of fibre cement can liberate by heating them up to 1450 C. makes it almost impossible to quantify these compounds completely. With thermogravimetric analysis (TGA)/differential thermal analysis (DTA), gas chromatography-mass spectrometry (GC-MS) and mass spectrometry (MS) measurements, an effort is made to analyse the organic compounds formed after thermal degradation at specific temperatures. A specific test setup was designed to heat the selected fibre cement samples as fast as possible up to a specific temperature. The selection of the temperatures considered for these tests resulted from the evaluation of the TGA/DTA analyses and the literature study on the decomposition of the organic fibres present in the fibre cement ARM. In this specific test a quartz reactor is loaded with 400 mg of sample under a gas flow of 95 V % He and 5 V % O.sub.2 connected to a GC-MS to measure the volatiles with a high molecular weight and to a MS to measure the gases with a low molecular weight. The recipient was preheated to heat up the sample as fast as possible to the selected temperature after which, over a period of 5 minutes, all gases and volatiles generated, were measured. The heating rate as well as the V % O.sub.2 in the surrounding gas flow was set to be comparable with those present in a real clinker kiln. The knowledge of the amount as well as the nature of these volatiles and gases is important in view of the determination of the ideal point of introduction of the fibre cement ARM in the clinker kiln. Because organic compounds are present in the fibre cement ARM and an additional energetic benefit is expected from the reduced endothermic decarbonation part, it is interesting to comparatively evaluate the energy necessary to heat the classic cold clinker meal up to 1450 C., with that necessary for doing the same but with alternative cold clinker meal. TGA/DTA and calorimetric measurements were performed to give an idea of this possible energetic gain. On the other hand, the presence of chemically bound H.sub.2O in the fibre cement ARM also implies loss of energy while heating. The energy required to liberate the chemically bound H.sub.2O is not so easy to quantify because of a variety of hydration products that are generated upon the hydration of cement. By performing DSC analyses on cement pastes with different W/C ratios like those described in paragraph 1.3., an effort is made to estimate the required energy to liberate the chemically bound H.sub.2O. The pastes are made with the OEM I cement presently used at the fibre cement plant from that the fibre cement production waste for this study was taken to produce fibre cement.
(43) 2.3. Different Clinker Feed Calculations and Preparations
(44) Of each factory, a simulation program based on linear equations calculated raw meal compositions (CCM/Ant,Lxh,Maa/Ref) in line with the chemical and mineralogical requirements listed in Table 4. These compositions indicated as Classic cold Clinker Meals (CCM) are very close to the compositions actually used in these factories. The composition of the raw materials was merely adjusted to obtain the mineralogical settings, but without taking into account the ashes of the fuels that will actually be used to heat up the clinker meal. The compositions of these classic Cold Clinker Meals are presented in Table 5.
(45) TABLE-US-00005 TABLE 5 Compositions of the different clinkers made to be fed to the StaticKiln. Quantity Quantity Quantity CRM + ARM (weight %) CRM + ARM (weight %) CRM + ARM (weight %) CCM/Ant/Ref CRM/Ant/CP 55.25 CCM/Lxh/Ref CRM/Lxh/Tu 79.44 CCM/Maa/Ref CRM/Maa/Ma 84.38 CRM/Ant/CR 37.50 CRM/Lxh/Li 6.63 CRM/Maa/SC 2.90 CRM/Ant/FA 6.38 CRM/Lxg/FA 12.34 CRM/Maa/FA 11.02 CRM/Ant/IC 0.87 CRM/Lxh/IC 1.59 CRM/Maa/IC 1.70 ARM/HD/S8 0.00 ARM/RS/S7 0.00 ARM/MD/S5 0.00 Sum 100.00 Sum 100.00 Sum 100.00 CCM/Ant/FC CRM/Ant/CP 0.00 CCM/Lxh/FC CRM/Lxh/Tu 38.52 CCM/Maa/FC CRM/Maa/Ma 81.89 CRM/Ant/CR 79.08 CRM/Lxh/Li 0.00 CRM/Maa/SC 0.00 CRM/Ant/FA 7.03 CRM/Lxh/FA 9.32 CRM/Maa/FA 10.33 CRM/Ant/IC 0.61 CRM/Lxh/IC 0.53 CRM/Maa/IC 1.77 ARM/HD/S8 13.28 ARM/RS/S7 51.63 ARM/MD/S5 6.01 Sum 100.00 Sum 100.00 Sum 100.00
(46) Furthermore alternative compositions were calculated with the same program and limits, aiming at the maximisation of the use of the fibre cement ARM. These alternative Cold Clinker Meals compositions are also presented in Table 5. The chemical analyses of the limestone in Table 1 show that the limestone of Antoing have a high SO.sub.3 content, by which that kiln already operates close to the SO.sub.3-limit (Table 4) in the routine condition. Therefore it's not realistic to increase the SO.sub.3-content of the Hot Clinker Meal (HCM) of Antoing any further. After simulation, it is clear that the introduction of Air-cured ARM increases the SO.sub.3-content of the Hot Clinker Meal (HCM) because of its higher level of SO.sub.3 compared with that of the CRM of CBR Antoing. Unlike Air-cured ARM, the use of Autoclaved ARM lowers the SO.sub.3 in the HCM since its SO.sub.3 content is lower than that of the two types of limestone used by CBR Antoing. Clogging phenomena should logically decrease by the lower SO.sub.3 content of the HCM. Therefore, it was chosen to maximise the Autoclaved ARM with the highest CaO [weight %] namely Autoclaved High Density Fibre cement Boards (ARM/HD) in the CCM/Ant/FC as presented in Table 5. The limestone used by CBR Lixhe has a S content that is much lower than the limestone of Antoing. Also the S feed by the fuel mix is limited. Therefore the SO.sub.3-content of the HCM is not as critical as the one of CBR Antoing. An increase of the SO.sub.3 [weight %] could therefore be accepted. By maximisation of the air-cured ARM in the CCM/Lxh/FC, the SO.sub.3 [weight %] of the simulated final clinker was increased to 0.73 weight % which was still below the maximum of 1.2 weight % (Table 4) that is allowed for and in line with the limits set for the DoS factor. It should be noted that in the simulated final clinker, the fuel mix was not taken in account. Performed simulations with the typical fuel mix of CBR Lixhe showed an SO.sub.3 increase of about 0.25 weight % which still is sufficiently below the maximum limit. The limestone or marl used by ENCI Maastricht contains a higher S content than the limestone or tufa used by CBR Lixhe. Also the used fuel mix brings more S to the HCM compared to the fuel mix of CBR Lixhe. All this results in a higher SO.sub.3 [weight %] in the reference clinker of ENCI Maastricht compared to the reference Clinker of CBR Lixhe (Table 3). Also the maximum allowed SO.sub.3 [weight %] is lower than that of CBR Antoing. The SO.sub.3 [weight %] could therefore not be changed significantly what automatically suggests the use of Autoclaved ARM. In the case of ENCI Maastricht, the Autoclaved ARM are still quite high in SO.sub.3 [weight %] compared to the used limestone or marl. This differentiates the use of autoclaved ARM in this plant from that in the CBR Antoing. Because the Autoclaved ARM from Autoclaved Medium Density Fibre cement Boards (ARM/MD) were the lowest in SO.sub.3 [weight %], they were maximised in the CCM/Maa/FC like presented in Table 5.
3 Results and Discussion
(47) 3.1. Chemical Analysis
(48) The Chemical analyses of the CRM, ARM and CCM are presented in Tables 1, 2 and 6, that of the final Clinkers in Table 10.
(49) TABLE-US-00006 TABLE 6 Chemical analysis of the Cold Clinker Meals (CCM) fed to the static kiln in weight % CCM CCM/Ant/Ref CCM/Ant/FC CCM/Lxh/Ref CCM/Lxh/FC CCM/Maa/Ref CCM/Maa/FC CaO 43.48 44.63 45.26 47.92 44.79 44.85 SiO.sub.2 14.00 13.56 12.01 14.03 12.83 12.71 Al.sub.2O.sub.3 2.89 2.72 2.90 3.35 3.09 3.05 Fe.sub.2O.sub.3 1.84 1.80 2.72 2.65 2.42 2.40 K.sub.2O 0.59 0.33 0.41 0.32 0.39 0.34 Na.sub.2O 0.11 0.10 0.13 0.12 0.13 0.13 SO.sub.3 0.48 0.41 0.24 0.81 0.28 0.29 MgO 1.10 0.94 0.88 1.18 0.97 0.96 TiO.sub.2 0.16 0.26 0.21 0.29 0.20 0.21 P.sub.2O.sub.5 0.12 0.12 0.15 0.23 0.09 0.10 Cl 0.02 0.02 0.04 0.04 LOI 975 C.(O.sub.2) 34.89 34.79 34.75 28.61 34.51 34.68 C.sub.total 8.98 8.89 8.82 6.66 8.79 8.76 S.sub.total 0.36 0.25 0.09 0.36 0.15 0.16
(50) TABLE-US-00007 TABLE 10 Chemical analysis and Bogue calculations of the Final Clinkers produced in a static kiln Clinker Cl/Ant/Ref Cl/Ant/FC Cl/Lxh/Ref Cl/Lxh/FC Cl/Maa/Ref Cl/Maa/FC CaO (weight %) 65.90 66.71 66.28 65.61 66.18 66.44 SiO.sub.2 (weight %) 22.27 22.72 21.93 21.53 21.39 21.56 Al.sub.2O.sub.3 (weight %) 4.14 3.97 4.40 4.77 4.54 4.45 Fe.sub.2O.sub.3 (weight %) 3.02 2.79 4.21 3.81 3.98 3.99 K.sub.2O (weight %) 0.59 0.24 0.21 0.25 0.33 0.29 Na.sub.2O (weight %) 0.17 0.14 0.20 0.20 0.21 0.19 SO.sub.3 (weight %) 0.89 0.44 0.12 0.58 0.36 0.29 MgO (weight %) 1.73 1.48 1.28 1.7 1.52 1.44 TiO.sub.2 (weight %) 0.25 0.39 0.30 0.40 0.30 0.3 P.sub.2O.sub.5 (weight %) 0.21 0.20 0.24 0.33 0.17 0.16 Cl (weight %) n.a. n.a. n.a. n.a. n.a. n.a. LOI 975 C.(O.sub.2) (weight %) 0.48 0.39 0.39 0.33 0.48 0.45 DoS-factor 123.42 114.33 27.47 123.18 65.24 58.95 Alite (C.sub.3S) 66.84 68.19 67.52 65.92 70.61 70.97 Belite (C.sub.2S) 13.44 13.71 11.95 12.01 8.07 8.29 Aluminate (C.sub.3A) 5.86 5.80 4.54 6.20 5.30 5.04 Ferrite (C.sub.4AF) 9.19 8.49 12.81 11.59 12.11 12.14
(51) The average analyses of the CRM were as expected and were therefore directly used in the simulation program. The analyses of the ARM were evaluated by sorting them by source and plotting them in
(52) 3.2. TGA/DTA Analysis
(53) TGA/DTA analyses of the CRM are quite straightforward. The Limestone, Tufa and Marl have an endothermal decarbonation area between 700 and 900 C. which is quantified in Table 7.
(54) TABLE-US-00008 TABLE 7 TGA/DTA evaluation of all the used Classic Raw Materials (CRM) of CBR Antoing, CBR Lixhe and ENCI Maastricht CRM Total Total Decarb Inorg CO.sub.2 Organic + CaO MgO Intrinsic Decarb E E TGA H.sub.2O CaCO.sub.3 XRF XRF [CaMg]CO.sub.3 CaCO.sub.3 J/g Mat Meas TGA Meas TGA Der Meas Meas XRF Der Vs/mg TGA (weight %) (weight %) (weight %) (weight %) (weight %) (weight %) Mat DTA Der CRM/Ant/RL 39.9 1.0 90.8 50.09 0.9 90.8 226.2 1618 CRM/Ant/PL 34.9 1.2 79.4 42.87 1.1 78.9 219.4 1415 CRM/Ant/IC 4.8 4.0 11.0 6.20 0.3 11.7 28.5 196 CRM/Ant/FA 0.0 4.7 0.0 6.20 1.6 13.5 0.0 0 CRM/Lxh/Tu 39.5 3.4 89.8 51.75 0.7 92.2 251.8 1601 CRM/Lxh/Li 4.2 3.1 9.6 5.63 0.8 11.6 37.8 171 CRM/Lxh/IC 6.2 3.1 14.2 10.70 1.1 20.7 31.2 252 CRM/Lxh/FA 0.0 6.0 0.0 10.65 1.4 20.0 0.0 0 CRM/Maa/Ma 40.0 1.1 91.0 50.78 0.8 91.7 255.1 1622 CRM/Maa/SC 1.1 1.99 2.6 2.70 0.3 5.3 12.2 46 CRM/Maa/IC 4.1 1.1 9.4 18.40 1.4 32.0 6.6 167 CRM/Maa/FA 0.0 4.0 0.0 18.38 1.8 31.4 0.0 0
(55) A good match is found between XRF analysis and the CO.sub.2 loss by TGA/DTA by comparing the CaCO.sub.3 [weight %] derived from TGA analysis and the intrinsic [Ca,Mg]CO.sub.3 [weight %] derived from XRF analysis. This indicates that Ca is almost completely present as CaCO.sub.3. The decarbonation energy (Decarb E) of CaCO.sub.3 can be derived from the known reaction enthalpy of 1782 kJ/kg for CaCO.sub.3 and CaCO.sub.3 [weight %] derived from TGA analysis. As can be noted in Table 7, the calculated decarbonation energies derived from the TGA relate in the same way as the decarbonation energies (Vs/mg) measured by DTA. A gain of mass is measured at about 1280 C. indicating oxidation of sulphides. Loam and sabulous clay also show a small but distinct quantifiable decarbonation area between 650 and 800 C. (Table 7). Here, a deviation between the CaCO.sub.3 [weight %] derived from TGA analysis and [Ca,Mg]CO.sub.3 [weight %] derived from XRF analysis is seen, indicating that not all Ca and Mg are present in a carbonated form. Whereas the Decarb E of CaCO.sub.3 can be derived from the TGA/DTA analysis rather easily, the quantification of the loss of H.sub.2O (i.e. the amount of chemically bound water) is less easy. Assuming that there is no or only negligible amount of organic material present in loam or sabulous clay, the changes registered in the TGA which are normally attributed to the combined loss of organics and H.sub.2O, may be considered to be mainly due to the evaporation of chemically bound H.sub.2O. The Fe.sub.2O.sub.3 sources are more difficult to evaluate due to the fact that they mostly concern artificially made raw materials, derived from waste. In inert atmosphere, the loss of mass is 2 times bigger than in the presence of 5v % O.sub.2 what indicates that the Fe.sub.2O.sub.3 sources perform oxidation reactions while heating. Comparison of the TGA/DTA curves under inert and oxidative atmosphere also indicates the areas were oxidation takes place: a first time between 700 and 900 C. and a second time between 1200 and 1300 C. Also nicely visible is the exothermal oxidation of FeO to Fe.sub.2O.sub.3 starting from about 280 C. because FeO is thermodynamically unstable below 575 C. TGA/DTA curves of the CRM/Lxh/IC and CRM/Maa/IC show small decarbonation reactions that can be quantified in the same way as for the other CRM (Table 7). The fly ashes have an opposite behaviour in the two atmospheres, with a bigger loss of mass in oxidative than in inert atmosphere indicating the presence of organic material. The mass loss in inert atmosphere indicates the formation of organic volatiles in absence of O.sub.2. Because fly ash is a material which has had already a thermal treatment at high temperatures, no decarbonation-related mass losses are detected (Table 7). Because there is a loss of organic volatiles and CO.sub.2 visible in the whole temperature range between 400 C. and 1450 C. under inert and oxidative atmosphere, the presence of char is indicated. TGA/DTA analyses of the fibre cement materials (Table 8) give a lot of information on their raw materials and how they will behave when thermally degraded up to 1450 C.
(56) TABLE-US-00009 TABLE 8 TGA/DTA evaluation of all the used Alternative Raw Materials (ARM) coming from fibre cement. ARM Decarb Anorg Total Total E CO.sub.2 Organic + CaO MgO Intrinsic CaCO.sub.3 Decarb E TGA H.sub.2O CaCO.sub.3 XRF XRF [CaMg]CO.sub.3 Vs/mg CaCO.sub.3 Meas TGA Meas TGA Der Meas Meas XRF Der Mat J/g Mat (weight %) (weight %) (weight %) (weight %) (weight %) (weight %) DTA TGA Der ARM/CS/S2 7.1 11.1 16.1 52.09 1.54 70.99 14.6 287 ARM/CS/S3 9.6 12.7 21.9 49.99 1.36 70.22 22.5 389 ARM/CS/S5 10.0 13.5 22.7 50.86 1.64 71.53 41.5 405 ARM/RS/S3 7.7 9.8 17.5 52.55 1.62 71.81 26.9 312 ARM/RS/S7 8.2 11.0 18.7 51.89 1.52 71.41 33.6 334 ARM/RS/S9 7.9 11.6 17.9 52.20 1.56 71.53 32.9 319 ARM/HDB/S8 0.6 16.1 1.4 28.20 0.67 42.32 5.3 25 ARM/HDB/S9 0.5 16.8 1.1 28.62 0.59 42.67 9.7 20 ARM/HDB/S11 0.5 15.8 1.2 28.53 0.67 42.68 8.6 21 ARM/MDB/S5 0.3 14.3 0.6 24.83 0.79 38.28 4.8 11 ARM/MDB/S6 0.3 14.5 0.6 25.24 0.75 38.73 5.2 10 ARM/MDB/S11 0.2 16.6 0.6 25.12 0.59 38.35 4.2 10
(57) The TGA peaks of the autoclaved ARM show the absence of limestone filler which is present for maximum 15 weight % in the air-cured materials. This makes it possible to quantify the CO.sub.2 part coming from the limestone filler of the air-cured products. Nicely visible is also the two-step degradation starting at 480 C. of PVA, present at about 1.7-1.9 weight % in the air-cured materials in
(58) TABLE-US-00010 TABLE 9 TGA/DTA evaluation of the Reference Cold Clinker Meals of CBR Antoing, CBR Lixhe and ENCI Maastricht CCM Decarb Decarb Decarb Decarb E E Anorg Organic + Anorg CaCO.sub.3 E E CaCO.sub.3 CaCO.sub.3 CO.sub.2 H.sub.2O CaCO.sub.3 CO.sub.2 Der Der CaCO.sub.3 CaCO.sub.3 Der Der Mat TGA TGA Vs/mg Vs/mg J/g J/g Mat Meas Meas TGA Der TGA TGA Meas Mat Mat DTA Mat TGA (weight %) (weight %) (weight %) Meas (weight %) DTA FM TGA FM CCM/Ant/Ref 34.0 0.6 77.3 34.3 78.0 213.4 206.3 1378 1390 CCM/Ant/FC 29.7 4.8 67.6 31.7 72.1 190.5 179.7 1205 1284 CCM/Lxh/Ref 32.5 0.5 73.9 31.8 72.2 189.3 203.0 1318 1287 CCM/Lxh/FC 16.9 9.3 38.4 19.5 44.3 105.9 115.3 685 800 CCM/Maa/Ref 34.2 0.0 77.7 33.9 77.0 219.3 215.7 1385 1373 CCM/Maa/FC 33.3 1.2 75.8 32.9 74.7 199.7 209.3 1350 1332
(59) This is done by calculating the decarbonation energies of CaCO.sub.3 out of the TGA/DTA analysis of the CCM and calculating the decarbonation energies derived of the TGA/DTA analysis of the raw materials taking in account the calculated compositions of Table 5. The fact that these two totally separated calculations gave a comparable result, proofs that the interpretation of the TGA/DTA analyses were objective as well as correct and could therefore be used to evaluate the CO.sub.2 reduction as well as the gain in Decarb E by the use of the ARM.
(60) 3.3. XRD Analysis
(61) The XRD analyses of the final clinkers are presented in Table 11 and show different weight percentages than those calculated by Bogue equations out of the chemical analysis of the final Clinker presented in Table 10.
(62) TABLE-US-00011 TABLE 11 Mineralogical analysis by XRD of the Final Clinkers produced in a static kiln in weight % Clinker Cl/Ant/Ref Cl/Ant/FC Cl/Lxh/Ref Cl/Lxh/FC Cl/Maa/Ref Cl/Maa/FC Alite (C.sub.3S) 64.52 64.50 65.04 62.72 71.33 70.58 Belite (C.sub.2S) 19.73 20.61 14.93 17.61 8.56 9.79 Aluminate 1.79 2.58 3.68 1.56 4.64 4.22 Ferrite (C.sub.4AF) 12.86 11.23 15.87 17.61 14.89 14.53 Free Lime 0.23 0.51 0.23 0.28 0.35 0.75 Periclase 0.39 0.19 0.18 0.22 0.23 0.13 Arcanite 0.32 0.20 0.07
(63) Like stated in paragraph 3.1, the chemical analyses were in the line of the expected and in the line of the average values of the clinkers produced in the first 6 months of 2011 on the 3 factory sites like presented in Table 3. The difference between the C.sub.3A and the C.sub.4AF measured with XRD and the corresponding values calculated with the Bogue equations stems from the method itself. The Bogue equations indeed are merely estimations which describe the phases formed when perfect clinker production conditions could be achieved. The XRD analysis indicates the actual mineralogical composition as it appears in the real clinker itself. Though, in view of the evaluation of the possible influence of the ARM on the mineralogy of the clinkers a reliable and objective comparison of the Classic Clinkers with the Alternative Clinkers can be done by any of these methods. For the kilns of CBR Antoing and ENCI Maastricht, it can be noted that the 13.28 weight % dosed Autoclaved High Density Fibre cement Boards ARM (Antoing) or the 6.01 weight % dosed Autoclaved Medium Density Fibre cement Boards ARM (Maastricht) had no significant influence on the mineralogy of the clinker (Tables 10 and 11). In case of the CBR Lixhe kiln, it can be noted that the alite [weight %] of the alternative clinker (Cl/Lxh/FC) is lower compared to the classic clinker (Cl/Lxh/Ref) for XRD analyses and Bogue calculations. Because the difference in alite [weight %] between Cl/Lxh/Ref and Cl/Lxh/FC is bigger by XRD analysis (2.32 weight %) than by Bogue calculation (1.6 weight %), it may be concluded that the difference in alite [weight %] doesn't originate from a small difference in the chemical composition of both clinkers only. In fact, this difference indicates that most probably, for equal chemistry, there still would be an influence of the air-cured ARM on the mineralogy of the alternative clinker. From Table 10, it can be noted that the alternative clinkers of CBR Lixhe were quite high in SO.sub.3 compared to the reference clinker, but lower than calculated with the simulation program (Table 4). The same can be remarked for the clinkers of CBR Antoing where both the reference as well as the alternative clinkers were high in SO.sub.3 but lower than calculated. Also the alkali contents of all clinkers were lower than simulated. It can be noted that some of the DoS-factors (1) were out of equilibrium: both clinkers of CBR Antoing were still between the limits as also the alternative clinkers of CBR Lixhe but all clinkers of ENCI Maastricht and especially the classic clinker of CBR Lixhe had a DoS-factor that was too low. Like described in paragraph 2.1., an excess of alkali will decrease the viscosity of the melt by which the alite formation is increased. The reason for these deviations lies in the fact that the static kiln has other enrichment factors (2) than the real clinker kilns that were simulated by the simulation program like described in paragraph 2.1. In fact, the enrichment factors of a static kiln will be much lower than those of the real clinker kilns. There is no gas stream flowing in the opposite direction of the hot clinker meal (HCM) stream towards colder regions in the clinker kiln allowing alkali and SO.sub.3 to return to the HCM flow like described in
(64) 3.4. Estimation of the Influence on Enemy Consumption: Calorimetric Evaluation
(65) As indicated in paragraph 3.2, the decarbonation energies were calculated and presented in Tables 8 and 9. These decarbonation energies together with the different gross calorific values of the CCM (paragraph 1.3.) and the selected fibre cement ARM determined by calorimetric analysis, were plotted in
(66) 3.5. GC-MS and MS Analyses
(67) Two of the selected fibre cement ARM, ARM/RS/S7 and ARM/HD/S8 were heated up in three separated tests from room temperature to 390 C., 500 C. and 800 C. These temperatures were reached within a period of 3 minutes. The generated volatiles and gases were collected for 5 minutes from the moment the samples were being heated up after which they were inserted in a GC-MS and a MS for analysis. By comparing the integral calculation of the CO and CO.sub.2 measurement graphs coming from the MS presented in
4 Conclusions
(68) As could be noted in the different paragraphs, fibre cement recycled materials is an interesting alternative raw material for Portland clinker production. It was shown that compared to a situation where pure limestone is used in the cold clinker meal, an inorganic CO.sub.2 emission reduction as well as a decarbonation energy gain is possible. Furthermore, it was demonstrated that the chemistry and mineralogy of the final clinkers were not influenced significantly by the use of the fibre cement materials. Because of its compositional constancy, and by that its chemical stability, fibre cement is a valid raw material. However, when used in practice, these materials should be introduced at a hot point in the process, e.g. using a pre-calciner unit or a pre-heater unit, to ensure full thermal degradation of the organic fibres for physical and chemical reasons, like to avoid clogging of the filter system and exceeding organic volatile emissions levels. The potential energy loss by skipping the cyclone tower as energetically most profitable way of heating, should be minimal because the biggest energy consuming reaction in these cyclones, the decarbonation of CaCO.sub.3, will almost not be present in fibre cement ARM. The possible energy gain for use of fibre cement versus limestone, coming from the exothermal degradation of organic compounds as also coming from the lowered decarbonation energy, were quantified. Together with the estimated energy consumption needed for the liberation of chemically bound H.sub.2O, it was shown that using fibre cement as raw material for clinker production lowers the total required energy compared to the use of classic raw materials, without compromising neither on physical, chemical nor mineralogical properties. It should, together with the already available alternative fuels and raw materials, be considered as a way to get in line with the Cement Sustainability Initiative.