METHOD FOR GRINDING CEMENT CLINKER

Abstract

Method of grinding cement clinkers comprising at least two kinds of clinker phases with differing grindability.

Claims

1-12. (canceled)

13. Method of manufacturing a cement from a cement clinker comprising at least two kinds of clinker phases with differing grindability, comprising the steps: feeding the cement clinker to a first milling stage grinding the cement clinker in the first milling stage with a setting of grinding power and grinding time that allows grinding an easier to grind phase to a predetermined maximum particle size while a harder to grind phase maintains a particle size larger than the predetermined maximum particle size transferring the output from the first milling stage to a first separator dividing the output into a first fraction with the predetermined maximum particle size and a second fraction with a larger particle size transferring the second fraction with a larger particle size to a second milling stage and grinding the second fraction with a larger particle size in the second milling stage to a final maximum particle size smaller than the predetermined maximum particle size combining the first fraction with the predetermined maximum particle size, optionally after grinding in a third mill, with the second fraction with a larger particle size after the first milling stage and ground to a final maximum particle size below the predetermined maximum particle size in the second milling stage, wherein the or a harder to grind phase(s) has(have) a higher fineness than the or an easier to grind phase.

14. Method according to claim 13, wherein a second separator is included in the second milling stage, the output from a mill of the second milling stage is transferred to the second separator and divided into a fraction with the final desired fineness and a fraction with coarser particles which is recycled into the second mill.

15. Method according to claim 13, wherein a roller press, a ball mill or a vertical mill is used as mill in the first milling stage.

16. Method according to claim 13, wherein a ball mill or a vertical roller mill is used as mill in the second milling stage.

17. Method according to claim 13, wherein the first separator is a sifter, an air classifier, a VRM separator or a dynamic separator of the 1.sup.st, 2.sup.nd or 3.sup.rd generation.

18. Method according to claim 14, wherein the second separator is a sifter, an air classifier, a VRM separator or a dynamic separator of the 1.sup.st, 2.sup.nd, or 3.sup.rd generation.

19. Method according to claim 13, wherein a disagglomerator is used to disagglomerate the output from the first milling stage and/or the second milling stage.

20. Method according to claim 13, wherein the first fraction with the predetermined maximum particle size is transferred to a third milling stage and ground to a desired fineness.

21. Method according to claim 13, wherein the clinker is a belite-calciumsulfoaluminate clinker or a belite-calciumsulfoaluminate-ternesite clinker.

22. Method according to claim 13, wherein one or more additional component(s) are added before, during or after grinding.

23. Method according to claim 13, wherein the additional component(s) is(are) chosen from the group consisting of sulfate carrier, fillers, preferably limestone, and supplementary cementitious materials, and mixtures of two or more of them.

24. Method according to claim 23, wherein the supplementary cementitious material is and/or ashes.

25. Method according to claim 24, wherein the slag is ground granulated blast furnace slag and/or the ash is fly ash.

26. Method according to claim 14, wherein a roller press, a vertical roller mill or a crusher is used as mill in the first milling stage.

27. Method according to claim 14, wherein a ball mill or a vertical roller mill is used as mill in the second milling stage.

28. Method according to claim 15, wherein a ball mill or a vertical roller mill is used as mill in the second milling stage.

29. Method according to claim 17, wherein a roller press, a vertical roller mill or a crusher is used as mill in the first milling stage and a ball mill or a vertical roller mill is used as mill in the second milling stage.

30. Method according to claim 29, wherein a disagglomerator is used to disagglomerate the output from the first milling stage and/or the second milling stage.

31. Method according to claim 29, wherein the first fraction with the predetermined maximum particle size is transferred to a third milling stage and ground to a desired fineness.

32. Method according to claim 14, wherein the clinker is a belite-calciumsulfoaluminate clinker or a belite-calciumsulfoaluminate-ternesite clinker.

33. Method according to claim 17, wherein the clinker is a belite-calciumsulfoaluminate clinker or a belite-calciumsulfoaluminate-ternesite clinker.

34. Method according to claim 20, wherein the clinker is a belite-calciumsulfoaluminate clinker or a belite-calciumsulfoaluminate-ternesite clinker.

35. Method according to claim 29, wherein the clinker is a belite-calciumsulfoaluminate clinker or a belite-calciumsulfoaluminate-ternesite clinker.

36. Method according to claim 30, wherein the clinker is a belite-calciumsulfoaluminate clinker or a belite-calciumsulfoaluminate-ternesite clinker.

Description

[0033] In the figures:

[0034] FIG. 1 shows a grinding method according to CN 1410379 A

[0035] FIG. 2 shows a grinding process according to DE 195 14 971

[0036] FIG. 3 shows a grinding process according to the invention

[0037] FIG. 4 shows a second grinding process according to the invention

[0038] FIG. 5 shows a third grinding process according to the invention

[0039] The process of the prior art illustrated in FIG. 1 optimizes the grinding by using two mills which are serial connected. For each mill a sifter is provided that separates the material ground to the fineness desired in that stage from the still coarser material. The coarser material is recycled into the preceding milling stage, the finer material is transferred to the following milling stage. With this approach a clinker comprising a phase easier to grind than at least one other phase of the clinker will lead to a cement in which the easier to grind phase is finer than the harder to grind phase. Energy consumption is high, since typically high amounts of finer than necessary material are present in the second stage.

[0040] The improved prior art method illustrated in FIG. 2 optimizes the energy demand and substantially avoids grinding to more than the desired fineness. The energy efficient production of fine material from cement clinker (13), comprises the steps: (a) adjusting the output (14) of a pre-grinding stage (2) to a maximum permissible particle size in a pre-grinding circuit (30, 32); (b) mixing the material with the output (16) of a fine grinding stage (6); (c) feeding the mixture into an air classification stage (7) to separate coarse (17) and fine (10) fractions; (d) delivering the coarse fraction (17) for post-grinding in the fine grinding stage (6); and (e) discharging the fine fraction (10) as the finished product. However, this means a lot of material to handle for the air classifier and it still does not allow to individually adjust the fineness of clinker phases with different grindability.

[0041] The method according to the invention illustrated in FIG. 3 uses analogous devices in principle, however, the material streams are different. The clinker 100 is fed to the first mill 101. The output from the first mill 101 is fed to a first separator 102, which divides the output into material 103 with a particle size as desired after mill 101 and a material 200 with a particle size above that desired for the output of mill 101. The fine material 103 contains substantially most of the easier to grind phase(s) and is transferred to a reservoir or mixing stage 105. The coarse material 200 contains substantially most of the harder to grind phase(s) and is fed into the second mill 201. There it is ground to the desired fineness, which is finer than that of material 103. Typically, a second separator 202 is assigned to the second mill 201, so that output of the second mill 201 can be divided into fine enough material 203 and material 204 recycled into the second mill 201. It would of course be possible to operate the second mill 201 without a separator 202 when the mill 201 provides the desired particle size distribution. The fine enough material 203 from the second mill 201 is combined with the fine material 103 from the first mill 101 in the reservoir or mixing stage 105 to provide the cement 106 comprising the easier to grind phase(s) with a lower fineness than the harder to grind phase(s).

[0042] The variant shown in FIG. 4 uses an additional separate fine milling stage with third mill 301, separator 302, material 304 returned to the mill 301 and output 303 for the easy to grind phase 103 separated off after the first grinding stage. In other respects, the method does not differ from the one shown in FIG. 3. This is for example useful when the easier to grind phase(s) have to be ground to a desired final particle size above the maximum particle size in the first milling stage to ensure good separation of the phases.

[0043] A further variant illustrated in FIG. 5 uses a separate milling stage for the separate grinding of other cement constituents 400, such as supplementary cementitious materials (e.g. fly ash, blast furnace slag, pozzolanic materials, etc.) and/or limestone or other fillers and/or sulfate carrier. The material 400 ground in mill 401 is fed to separator 402, where the fine enough material 403 is separated from the coarser material 404 and conveyed to the finished product 106 and the still coarse material 404 is recycled into mill 401. It would of course be possible to operate mill 401 without a separator 402 when the mill provides the desired particle size distribution.

[0044] The method illustrated in FIGS. 3, 4, and 5 also allows the addition of e.g. gypsum or other set regulators or cement constituents in any or more than one mill or separator among 101, 102, 201, 202, 301, 302, 401, and 402 in dependence of the fineness and grindability of the material added and its desired fineness.

[0045] The benefit of the method according to the invention is demonstrated with a belite-calcium sulfoaluminate clinker. This clinker contains two main phases, belite and ye'elimite or C.sub.2S and C.sub.4A.sub.3$ in cement chemists notation abbreviating oxides as follows: HH.sub.2O, CCaO, AAl.sub.2O.sub.3, FFe.sub.2O.sub.3, MMgO, SSiO.sub.2 and $SO.sub.3. Of course, all the phases can contain varying amounts of foreign ions, e.g. aluminum A can be partly (or even predominantly) replaced by iron F, as is usual in technical products. In a cement obtained by grinding such a clinker the belite C.sub.2S mostly contributes to final strength and the ye'elimite C.sub.4A.sub.3$ plus added sulfate is responsible for the early hydration and strength development reactions. Those phases differ considerably with respect to grindability. Belite is harder to grind than ye'elimite but needs a higher fineness to provide adequate strength development and if applicable enough lime to properly activate/react with added supplementary cementitious materials.

[0046] Grinding the clinker with a method as illustrated in FIG. 3, wherein the first mill 101 is a roller press, a ball mill or a vertical mill provides substantially all or most of the ye'elimite as phase 103 and substantially all or most of the belite as phase 200. Belite is then ground to the desired higher fineness in mill 201. Mixing phases 103 and 203 provides the cement containing a finely ground and highly reactive belite and a ye'elimite that is coarser so that it does not impair workability.

LIST OF REFERENCE NUMBERS

FIG. 1

[0047] 1 first sifter [0048] 2 first mill [0049] 3 second sifter [0050] 4 second mill

FIG. 2

[0051] 1 reservoir for clinker [0052] 2 pre-grinding mill [0053] 3 transport means [0054] 4 temporary storage [0055] 5 bucket conveyor [0056] 6 fine-grinding mill [0057] 7 sifter [0058] 10 fine fraction [0059] 13 clinker [0060] 14 output from pre-grinding mill [0061] 15 volumetric dosage discharge means [0062] 16 output from fine-grinding mill [0063] 17 coarse fraction [0064] 30 sieving station [0065] 32 recycling means

FIGS. 3, 4 and 5

[0066] 100 clinker [0067] 101 first mill [0068] 102 first separator [0069] 103 fine material from output from first mill (easy to grind phase(s)) [0070] 105 reservoir or mixing [0071] 106 cement [0072] 200 coarse material from output from first mill [0073] 201 second mill [0074] 202 second separator [0075] 203 fine material from output of second mill (hard to grind phase(s)) [0076] 204 coarse material from output from second mill [0077] 301 third mill [0078] 302 third separator [0079] 303 fine material from third mill [0080] 304 coarse material from third mill [0081] 401 fourth mill [0082] 402 fourth separator [0083] 403 fine material from fourth mill [0084] 404 coarse material from fourth mill