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Prof. Grobéty B., Inst. de Minéralogie et Pétrographie, Univ. de Fribourg Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP.

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Presentation on theme: "Prof. Grobéty B., Inst. de Minéralogie et Pétrographie, Univ. de Fribourg Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP."— Presentation transcript:

1 Prof. Grobéty B., Inst. de Minéralogie et Pétrographie, Univ. de Fribourg Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

2 Introduction Cementitous materials Definition: Material, which binds together with solid bodies (aggregates) by hardening from a plastic state. Examples:organic polymers inorganic cements - mixed with water  plastic state - hydration of the components  development of rigidity (setting) - steady increase of strength (hardening) - Examples: Portland cement, gypsum plasters, phosphate cements - when hardening occurs also under water: hydraulic cement - Example: Portland cement Inorganic cements Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

3 Historical background I (www.auburn.edu/academic/architecture/bsc/classes/bsc314/timeline/timeline.htm) 12M BC:Natural production of clinker through the spontaneous combustion of oil shales (Israel) 3000 BC: Egyptians used sulfate and lime based plasters Use of cementitous materials in China (Great Wall) 300 BC:Concrete and mortars based on lime and pozzolanic material (volcanic ashes). Pliny reported a mortar mix of 1 part of lime and 4 part of sand. Examples: 193 BC: Porticu House, Amaelia, 200 AD: Pantheon, Rome (www.romanconcrete.com) Introduction Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

4 Middle ages:Decline of cement and concrete technology 1756:John Smeaton, British Engineer, rediscovered hydraulic cement through repeated testing of mortar in both fresh and salt water 1824:Joseph Aspdin, bricklayer and mason in Leeds, England, patented what he called portland cement, since it resembled the stone quarried on the Isle of Portland off the British coast. Historical background II Introduction Technical Mineralogy Department of Geosciences Portland cement. This was the name given by Joseph Aspdin to the product consisting of limestone and clay, on which he took out a patent in 1824: "Portland", owing to the similarity to the building stone from Portland in England, and "cement" from the Latin caementum, which means chipped stone. Technische Mineralogie ETHZ IMP 2008

5 Cement: definitions Portland cement: Hydraulic cementitous material based on clinker, a material composed of calcium silicates and aluminates, and a small amount of added gypsum/anhydrite. The clinker is made by burning mixtures of limestone and argilaceous rocks (slates). Mortar:Mixture of Portland cement, fine sand and water (used f.ex. for the construction of brick walls) Neat paste:Mixture of Portland cement and water alone (used for filling cracks and sealing small spaces) Concrete:Mixture of Portland cement, coarse and fine aggregates (rock pebbles, sand), water and chemical additives. The mechanical strength can be reinforced by the insertion of steel bars. Introduction Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

6 Cement: chemical notations C = CaOS = SiO 2 A = Al 2 O 3 F = Fe 2 O 3 M = MgOK = K 2 ON = Na 2 OS = SO 3 T = TiO 2 P = P 2 O 5 H = H 2 OC = CO 2 LOI = loss of ignition (≈ H 2 O+CO 2 ) C-S-H = poorly crystallized calcium silicate hydrates HCP = hydrated cement paste PFA = pulverized fuel ash PC = Portland cement OPC = Ordinary Portland cement Chemical notation Introduction Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

7 Portland Cement I Chemical composition The composition of Portland Cements and puzzolanic additives cover a certain range. Introduction Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

8 Portland cement II Name + Chem. Comp Approx. % in OPCProperties Belite C 2 S 20Slow strength gain, responsible for long term strength Alite C 3 S 55 Rapid strength gain, responsible for early strength gain Aluminate C 3 A 12 Quick setting (contr. by gypsum), liable to sulfate attack Ferrite C 4 AF 8 Little contribution to setting or strength, responsible for gray color of OPC Main mineralogical components Introduction Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

9 Portland Cement III Main production steps (http://www.ppc.co.za/Cement/c_cement_manprocess.asp) Quarrying chalk in northern Jutland (Aalborg Cement) Introduction Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

10 Portland Cement IV Chalk slurry tank (Aalborg cement) Main production steps (cont.) Introduction Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

11 Portland Cement V Main production steps (cont.) Preheater, rotary kilns and storage silos Introduction Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

12 Portland Cement VI Main production steps (cont.) Cement silo Shipping by ship Introduction Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

13 Introduction Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

14 World cement productions (minerals.usgs.gov/minerals/pubs/commodity/cement World cement production 2000 (thousand of tons): United States (includes Puerto Rico) 92,300 Brazil 41,500 China 576,000 Egypt 23,000 France 24,000 Germany 38,099 India 95,000 Indonesia 27,000 Italy 36,000 Japan 77,500 Korea, Republic of 50,000 Mexico 30,000 Russia 30,000 Spain 30,000 Taiwan 19,000 Thailand 38,000 Turkey 33,000 Other countries (rounded) 450,000 World total (rounded) 1,700,000 Introduction China 576,000 China produces one third of the world cement output! World total (rounded) 1,700,000 Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

15 Swiss cement industry (www.cemsuisse.ch) Cement plants in Switzerland cement plant klinker mills 1 Eclépens 2 Cornaux 3 Reuchenette 4 Wildegg 5 Siggenthal 6 Thayngen 7 Brunnen 8 Untervaz Total production 1987: 4 ’ 478 ’ 000 t 1989: 5 ’ 461 ’ 000 t 2000: 3 ’ 715 ’ 908 t Introduction Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

16 Raw materials Calcareous lime stones: - calcite-rich - low in dolomite Corrective constituents Shales: - clay rich, usually dominated by illite, smectite and kaolinite. Ideal bulk composition ranges: 55-60wt% SiO 2, 15-25wt% Al 2 O 3, 5-10wt% Fe 2 O 3 Main raw materials Sand, flyash:- adjust SiO 2 -content in quartz-poor shales Ironores, bauxite:- adjust Fe resp. Al content Additional reactive constituents, which have to be considered, may be introduced through impurities in the fuel. Up of 30% of ash is produced by the firing of brown coal. Raw materials Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

17 Composition of ordinary Portland cements SiO 2 Al 2 O 3 Fe 2 O 3 CaO MgO K 2 O Na 2 O SO 3 LOI (H 2 O+CO 2 ) Minor components and traces (deleterious) few %: MgO, SrO 2 few tenth of a %: P 2 O 5, CaF 2, alkalis traces: heavy metals Major components The composition of different cements, their minimum mechanical properties and their application is regulated by Norm SIA Norm /002 (http://www.vicem.ch/produits/normes/2_7d.htm) which corresponds to the European Norm ENV 197 (http://www.readymix-beton.de/service/betontechnische_daten/kap_1_1.pdf) Raw materials Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

18 Targets for an ordinary Portland cement (OPC) - Lime saturation factor (LSF) close to 100% - Free lime content under 1.5wt% - Silica ratio (SR module) between 2.0 and Alumina ratio (AR module) between 1.0 and Hydraulic index (IH) ≈ Low concentration of deleterious components Proportioning of raw materials Lime saturation factor The calcium present in the raw materials should be completely bound in the silicate and aluminate phases of the cement clinker. The amount of different oxide components necessary to saturate the amount of lime is given by(in wt%): CaO = 2.8 SiO Al 2 O Fe 2 O 3 Raw materials Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

19 Proportioning of raw materials VII Example (cont.) The proportion p of mix A and 1-p of mix B to get an SR of 3.0 can be obtained through following consideration: The value a can be obtained from S 13.1p (1-p) A+F 7.5p + 2.1(1-p) - SR = = Mix AMixB S A+F S A +F = 3.0 =  p = 0.51 Raw materials Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

20 Klinker phases I 1. Alite Ca 3 SiO 5 = C 3 S Polymorphic transformations: T1T2T3M1M2M3R T: triclinicM: monoclinicR: rhombohedral 620°C 920°C 980°C 990°C 1060°C 1070°C Max. concentration of impurities: 1.0 wt% Al 2 O 3, 1.2% Fe 2 O 3, 1.5 % MgO impurities stabilize the M1 and or M3 in klinkers, rarely T2 is found orthosilicate 0.71nm R- C 3 S projected along the c-axis SiO 4 Ca O Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

21 Klinker phases II 2. Belite Ca 2 SiO 4 = C 2 S Polymorphic transformations: O1(  ) M1(  ) M2(  L  ’ ) O2(  H ’ ) H1(  ) O: orthorhombic M: monoclinicH: hexagonal <500°C 630°C 1160°C 1425° Max. concentration of impurities: wt% Al 2 O 3 + Fe 2 O 3 impurities stabilize the  -phase orthosilicate 0.55nm  - C 2 S proj. down c-axis Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

22 Klinker phases III 3. Aluminates and ferrites Ca 3 Al 2 O 6 = C 3 A (cubic)impurities: up to 4wt% NaO up to 16% Fe 2 O 3 + SiO 2 imputirities stabilize an orthorhombic polymorph Ca 2 Al x Fe 1-x O 10 = C 4 AF x clinker : around 1.0 impurities: up to 10 wt% MgO + TiO 2 + SiO 2 Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

23 Klinker phases IV Polymorphs and composition of phases present in clinker C 3 Apolymorphs is coupled with substitution. Clinker aluminate phases are cubic (fine grained) or orthorhombic (lath shapedand twinned) 13% to 20% of substituting elements: Mg, Al, Fe, Si C 3 S early crystallized small crystals rich in substitutes: M3 late crystallized large crystals: M2 (single twins), rarely T1 (polysynthetic twins) 3-4% of substituting elements, mainly Mg, Al and Fe C 2 S usually only in the M1(  ) polymorph with parallel twin lamellae M2(  L  ’ ) has typical crossed twin lamellae. The transformation M2(  )  M(  ) sho

24 Klinker phases V Etched microstructures of the different klinker polymorphs Alite crystals with both single and polysynthetic twins Klinker production Belite crystals with complex twin lamellae (M2(  L  ’ ) polymorph) Belite crystals with paralllel twin lamellae (M(  ) polymorph) Belite crystals with crack formation along lamellae boundaries (M(  )  (M(  ) transf.) Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

25 Rotary kiln Without preheater/precalciner the kiln aspect ratio is about 30 Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

26 Klinker reactions below 1300°C Decomposition of calcite (calcining): °C free lime (CaO) Decomposition of phyllosilicates: °C dehydroxilated, amorphous material Temp. rangeproducts Formation of first clinker phases: > 800°C belite, aluminate (different phases), ferrite Formation of first melt phases: > 1000°C Drying 100°C free water evaporates °C release of adsorbed and crystal water Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

27 Decomposition of carbonate phases I Decomposition reaction:CaCO 3 = CaO + CO 2 Equilibrium constant Rate of decarbonation is influenced by: - gas temperature (heat transfer) - material temperature (=> K) - external partial pressure of CO 2 - size and purity of the calcite particles Klinker production Calcite decomposition temperature As function of CO 2 partial pressure  C T(  C) P(CO 2 ) Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

28 Decomposition of carbonate phases II Reaction mecanism: Possible rate determining steps 2. reaction at the calcite surface 1. heat and mass transport (CO 2 ) through the product layer formation of a lime layer around calcite Activation energy: 196kJ/mol (Khraisha et al, 1992)  reaction controlled ? a t reaction progress a Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

29 Belite formation 1. Formation of belite through solid state reaction quartz amorphous material belite 2. Transformation of the belite shells to belite crystal clusters lime Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

30 Appearance of first melts 2. C-S-A melts: lowest eutecticum 1170° 1. Alkali and sulfate melts Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

31 P: typical bulk composition of Portland cement klinkers First melt appearance: 1455°C Phase diagram Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

32 Klinker reactions between 1300°C and 1450°C 1. Melting reactions - Melting of ferrite and aluminate phases - Melting of part of the early formed belite 2. Formation of new phases Reaction of melt, free lime, unreacted silica and remaining belite to alite 3. Polymorphic transformation of belite 4. Recrystallization of alite and belite 5. Nodulization (clinkering) Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

33 Amount and composition melts II At 1450°C and above the liquid content depends on the silica modulus Klinker production SM Liquid phase (wt%) 3.5 Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

34 Formation and recrystallization of alite amorphous material lime belite alite 1. Formation of melt around lime crystals 2. Crystallization of alite walls at the contacts between belite cluster and lime 3. Recrystallized and new formed alite replaces lime crystals Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

35 Microtextures I (all pictures FL Smidth review 25) 0.05mm Alite wall separating CaO and a belite cluster alite melt phase (aluminates,ferrites) belite lime Belite clusters replacing previous quartz grains. 0.1mm Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

36 Alite crystallizing at the expense of lime and belite 0.3mm Microtextures II lime belite alite Well crystallized, homogeneous clinker. The raw mix contained few quartz grains and a well controlled carbonate grain size. pores 0.2mm Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

37 Klinker reactions during cooling 1. Crystallization of the restitic melt. Products: aluminates (C 3 A) and ferrites (C 4 AF) 2. Polymorphic transformations of alite and belite 3. Backreaction of alite to belite + lime 4. Recrystallization aluminates and ferrites If cooling is too slow Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

38 Microtextures III Backreaction of alite rims to belite plus lime in a belite poor clinker (fast cooling). 0.04mm belite rims Etched thin section showing the transformation twins in belite. 0.02mm Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

39 Slowly cooled clinker with corroded alite phase and recrystallized belite grains. 0.05mm Microtextures IV Fast cooled clinker with euhedral alite and rounded belite crystals. 0.05mm Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

40 Normative mineralogy of clinker I Klinker production Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

41 Normative mineralogy of clinker II Klinker production Minor elements in the main klinker phases in cements of different cement factories. Most cements contain 5wt% and more minor elements which introduces considerable errors when using Bogues original formula, Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

42 Normative mineralogy of clinker III Klinker production Corrected Bogue equation 0.05mm C 3 S corr = C 3 S bogue MgO clinker K 2 O clinker C 2 S corr = C 2 S bogue MgO clinker K 2 O clinker C 3 A corr = C 3 A bogue Na 2 O AR S 3 O C 4 AF corr = C 4 AF bogue Na 2 O AR Mn 2 O Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

43 Normative mineralogy of clinker IV Klinker production 0.05mm Difference in calculated alite and belite content using the original(top) and the corrected (bottom) Bogue formula Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

44 Energy balance in clinker production Temp range °C wet 100°C ca. 450°C °C ca. 900°C °C ca. 1300°C °C °C °C Process Heating of the material Evaporation of free H 2 O Removal of H 2 O from clay heating of the material Dissociation of calcite Crystallisation of dehydrated clay Heating of the decarbonated material Heat of formation of clinker minerals Melting of liquid phases Cooling of clinker Cooling of CO 2 Cooling of H 2 O Total Heat exchange kJ/kg clinker 710 (1800) Klinker production Institut de Minéralogie et Pétrographie Université de Fribourg Technische Mineralogie ETHZ IMP 2008

45 Energy costs of cement production Process Quarry Crushers Prehomoginizing and transport Raw mill Raw meal silo Kiln feeder Kiln and cooler Coal mill Cement mill Packing plant Other total FuelElectricity Cost($/day) kcal/kg cementkwh/ton cement Klinker production Dry process cement plant 5000t/day Institut de Minéralogie et Pétrographie Université de Fribourg Technische Mineralogie ETHZ IMP 2008

46 - use of alternative raw materials - increasing the burning rate - lowering the melting point of the system. - use of alternative raw materials - increasing the burning rate Mineralized cement Improvements in klinker manufacturing 1. Energy savings through: - better insulation, improved heat exchanger etc. 2. Reduction of CO 2,SO 3 NO x etc output through: Technische Mineralogie ETHZ IMP 2008 Institut de Minéralogie et Pétrographie Université de Fribourg

47 - use of alternative raw materials - increasing the burning rate - lowering the melting point of the system. - use of alternative raw materials - increasing the burning rate Mineralized cement Improvements in klinker manufacturing 1. Energy savings through: - better insulation, improved heat exchanger etc. 2. Reduction of CO 2,SO 3 NO x etc output through: Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

48 Bulk composition and mineralogy of mineralized clinkers M (wt%) in clinker M(wt%) in silicates F 3.0 Partitioning of SO 3 and F between silicates and other phases SO 3 SiO 2 Al 2 O 3 Fe 2 O 3 CaO MgO SO 3 F K 2 O Na 2 O C 2 S C 3 S C 3 A C 4 AF produced in 3500tpd precalciner kiln. (Herfort et al., 1997, Shen et al., 1995) normal PC mineralized Mineralized cement Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

49 Mineralizer used in klinker manufacturing: FluoriteCaF 2 = CF GypsumCaSO 4. 2H 2 O = CS Mineralizer Effects of mineralizers:- Lowering of the eutectic temperature of the CaO-SiO 2 -Al 2 O 3 -FeO system - Enhancing the crystallization of reactant phases Energy savings: kJ/kg = % Mineralized cement Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

50 Effect of mineralizer concentration on clinker mineralogy clinker mineral (wt%) SO 3 (wt%) clinker mineral (wt%) alite belite F (wt%) Herford et al (contained < 0.2wt%F) Shen et al., 1995 (contained 2wt% SO 3 ) Mineralized cement Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

51 The system Ca 2 SiO 5 - CaO - CaF 2 first melt appearance: 1113°C Mineralized cement Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

52 0.05mm Mineralized klinker with langbeinite filling interstitial space Microstructures I Mineralized klinker rich in alite which remained in the hexagonal modification Mineralized cement Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

53 Mechanisms enhancing clinker formation I With the addition of gypsum and fluorite intermediate fluor-ellestadite (Ca 10 Si 3 O 32 (SO 4 ) 3 F 2 is formed, which decomposes to belite and liquid at 1113°C. Mineralized cement Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

54 Mineralizer lower the melting point. Even early belite formation happens in the present of a liquid phase. Transport of matter is by fast diffusion through the liquid phase. The reactions producing belite and too a smaller extent alite in an ordinary PC klinker composition occur in the solid state. Matter is tranported by slow, solid state diffusion Mechanisms enhancing clinker formation II Consequences: - increased number of belite nuclei - faster growth kinetic of belite - in presence of fluorine, faster reaction rates for the transformation belite -> alite Mineralized cement Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

55 Problems with mineralized cement I High gaseous alkali- and sulfate species can condensate in towards the outlet. Klinker particle coalesce on the wet kiln surface and lead to ring formation. Fine grained belite and alite lead to excessive dusting in the kiln 0. 2mm Mineralized cement Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

56 Problems with mineralized cement II Anhydrite inclusions in belite crystals. (6.4 wt% total SO 3 ) Activation of sulfur dissolved in silicates or present as sulfate inclusions: Late ettringite formation causing deterioration of mechanical properties. Mineralized cement Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

57 Pro and cons of mineralized klinker - lowering of burning temperature - increase of alite content - formation of the rhombohedral, hydraulic more active polymorph of alite - stabilization of the hydraulic more active  phase of belite Pro: - Ring formation and excessive dusting in the kiln - with too low fluorine content: increase in belite content - Presence of phases deletrious to mechanical properties Cons: Mineralized cement Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

58 Rapid burning Consequences of steep temperature ramps: - Decomposition and new phase formation occur simultaneously - New phases are formed through metastable reactions having larger reaction free energies - Decomposition products are much smaller and have a higher surface activity Rapid burning Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

59 Grain size of decomposition products diameter (Å) t (min) °C/min 5 °C/min T(max): 1300°C CaO Rapid burning Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

60 Rapid burning Free energy of formation for C 2 S and C 3 S  G (KJ/mol) t (min) CaCO 3 +SiO 2 = Ca 3 SiO 5 + 3CO 2 2CaCO 3 +SiO 2 = Ca 2 SiO 4 + 2CO 2 3CaO +SiO 2 = Ca 3 SiO 5 2CaO +SiO 2 = Ca 2 SiO 4 Above 1100° the direct reactions of calcite with silica to form CS-phases have more negative  G f and are favoured over the reaction involving lime. Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

61 Batch production of PC klinker Rotary kiln - continous process - steady speed Batch production - heating and cooling speeds can be enhanced and adapted Burning technique: - Batches of raw meal is fed into a furnace with circulating air at reaction temperature such as to form a gaseous suspension. - Reaction occurs at contact points between suspended particles Feeder Collector Rapid burning Cours bloc 2006Institut de Minéralogie et Pétrographie Université de Fribourg

62 Proportioning of raw materials II Lime saturation factor (cont.) The actual lime saturation of a raw material mix is given by the ratio CaO 2.8 SiO Al 2 O Fe 2 O 3 The LSF is in the ideal case 1.0, but often the reaction time in the kiln is not sufficient to bind all the CaO. Free lime The free lime is the leftover CaO which did not react to form silicates. An acceptable free lime content is more important than an LSF of 1.0. LSF = Raw materials Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

63 Proportioning of raw materials III Silica and alumina ratios The silica and alumina ratios are defined as SiO 2 Al 2 O 3 Al 2 O 3 + Fe 2 O 3 Fe 2 O 3 Hydraulic index SR = AR = Raw materials IH = CaO + MgO SiO 2 + Al 2 O 3 + Fe 2 O 3 Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

64 Proportioning of raw materials IV Example Raw materials Chalk wt% Clay wt% Loam wt% Ash wt% S A F C Res From trials we know that to keep the free lime at an acceptable value the LSF must not be higher than The lime required to saturate the oxides to this level is: CaO = 0.96 (2.8 SiO Al 2 O Fe 2 O 3 ) Raw materials Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

65 Proportioning of raw materials V Example (cont.) 1. lime required to saturate acidic oxide in chalk: lime required to saturate acidic oxides in clay: lime available in chalk lime available in clay net lime required for clay = net lime available from chalk = 46.6 To get the right mix A, clay and chalk have to be mixed at the ratio chalk 46.6 clay162.4 = = 3.49 Raw materials Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

66 Proportioning of raw materials VI Example (cont.) The SR of this mix is however too low and has to be adjusted using a mix B between chalk and loam with an LSF of The final mix C, with an LSF of 0.96 and a SR of 3.0 can be obtained by blending mix A and B together. Mixes Mix A wt% Mix B wt% Mix C wt% S A F C Res Raw materials Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008


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