WO2015181447A1

WO2015181447A1 - Method and apparatus for manufacturing cement

Info

Publication number: WO2015181447A1
Application number: PCT/FI2015/050367
Authority: WO
Inventors: Aino Heikkinen-Mustonen
Original assignee: Fatec Oy
Priority date: 2014-05-28
Filing date: 2015-05-27
Publication date: 2015-12-03
Also published as: EP3148954A1; FI127048B; FI20145489A; EP3148954A4

Abstract

The object of the invention is a method and an apparatus for manufacturing cement, in which method additives and/or agents, such as fly ash, the particles (21) of which are smaller in grain size than the cement particles (22) of the cement powder, are added to ground clinker material. In conjunction with the cement manufacturing process, fly ash precisely graded by grain size is added to the cement powder ground from clinker material after grinding, said fly ash comprising approx. 20-80% essentially round fly ash particles.

Description

METHOD AND APPARATUS FOR MANUFACTURING CEMENT

The object of the present invention is a method as defined in the preamble of claim 1 and an apparatus as defined in the preamble of claim 13 for manufacturing cement.

Ground limestone is used in the manufacture of cement needed for making concrete, into which ground limestone inter alia clay is mixed, and the mixture is burnt in a clinker furnace, where the material sinters into clinker comprising cement minerals. The clinker nodules that are the raw material of cement are ground into cement powder, e.g. in a ball mill, and additives and agents are added to the material in conjunction with the grinding for achieving the desired properties. For example, gypsum is added to the material for regulating the setting time. The rate of strength gain can be adjusted with, inter alia, the grain size of the cement powder. One problem in the manufacture of cement is that it produces a considerable amount of CO₂ emissions .

In this application the designation "cement powder" is used to refer to ground clinker, irrespective of whether it refers to pure clinker powder or to the type of mixture in which additives and agents have been added to the clinker material before grinding or in conjunction with grinding.

Fly ash is already used as an agent in the manufacturing of cement according to prior art, but the results have not necessarily been sufficiently good from the viewpoint of the strength of the concrete to be obtained, because the fly ash has generally been used as it is, without grading it in any way, in which case concrete, in which ungraded fly ash has been used as an additive, has been improved in terms of quality only to some extent or not at all. Cements supplemented with fly ash, in solutions according to prior art, generally contain approx. 15-40% fly ash. The use of untreated fly ash is typically seasonal, the amounts used are limited and, given the strict technical limit values set, the advantage to be gained has been small.

In solutions according to prior art untreated fly ash is added, e.g. along with other agents, to the clinker material used as a raw material in the cement manufacturing process before the grinding of the cement, after which the pulverized and mixed cement powder in the grinding device is conveyed to storage and distribution. One problem, among others, in these solutions is that a cement mixture with a grain size that is not, in all respects, controlled is obtained as the result of grinding. This is because inter alia there are differences between the hardnesses of the clinker material and of the various agents, e.g. the slag used as an agent can be considerably harder or softer than the clinker material. Likewise, the fly ash can have harder particles than the clinker. Thus some harder component is not perhaps ground to be sufficiently small, or a softer component is ground to be too small, in which case the cement powder is not sufficiently homogeneous in terms of its grain size, but is instead indeterminate and the quality of the cement suffers. In addition, in the grinding the round grains, i.e. particles, contained in the fly ash often break, in which case those properties of the fly ash that improve the cement degenerate. One aforementioned solution according to prior art for manufacturing cement is presented in United States patent publication US 2005/0252421 Al . In the solution according to the patent publication, various supplementary materials, such as fly ash, are mixed into the preground Portland cement powder, for inter alia improving the properties of the cement. A great problem in this solution is, however, that the fly ash being taken from the silo is ground before it is mixed into the cement powder. The round fly ash grains are broken in conjunction with the grinding, in which case the properties of the fly ash as a cement- improving additive appreciably deteriorate. After grinding, also, the fly ash is no longer necessarily sufficiently homogeneous, which also detracts from the properties of the fly ash material.

The aim of the present invention is to eliminate the aforementioned drawbacks and to achieve an inexpensive and reliable method and apparatus for manufacturing high- quality cement. In this case one aim, among others, is to endeavor to manufacture a cement giving strength properties and workability to the concrete made from it that are better than solutions presently known in the art. In addition, one aim is to endeavor to manufacture a cement enabling less concrete made from said cement to be used in the finished product than current grades of concrete. The method according to the invention is characterized by what is disclosed in the characterization part of claim 1. Correspondingly the apparatus according to the invention is characterized by what is disclosed in the characterization part of claim 13. Other embodiments of the invention are characterized by what is disclosed in the other claims.

A great advantage, among others, of the solution according to the invention is a reduction in the CO₂ emissions produced by the manufacture of cement, because less clinker is needed for the manufacture of cement when some of the clinker is replaced with fly ash precisely graded to a certain grain size. Replacing clinker material with fly ash does not, however, succeed so well with ungraded fly ash. Concrete products made from cement manufactured with the method and apparatus according to the invention are of homogeneous quality and technically reliable, in which case the usage amount needed in the manufacture of concrete is smaller than in concrete products made from conventional cement. In this case raw material costs, transport costs and energy costs can be reduced, in which case the ecological footprint is smaller than with concrete products manufactured from conventional cement. Yet a further advantage is that the cement particles and fly ash particles are mixed together optimally when the fly ash particles are of a controlled round shape and suitably smaller than the cement particles in which case the reaction surface area binding the particles in the mixture and boosting strength increases, and at the same time the amount of water needed decreases. The result is improved consistency and strength of the concrete after a certain hardening time.

In the following, the invention will be described in greater detail by the aid of some embodiments and by referring to the attached simplified drawings, wherein

Fig. 1 presents a simplified and diagrammatic side view of one method and apparatus according to prior art,

Fig. 2 presents a simplified and diagrammatic side view of one method and apparatus according to the invention,

Fig. 3 presents a diagrammatic and simplified sample of recently mixed fresh concrete, and

Fig. 4 presents the sampling point presented with dot- and-dash lines in Fig. 3, significantly magnified and in diagrammatic form. In the method and apparatus according to prior art that are presented in Fig. 1, in other words, more briefly, in the solution, clinker, which is the main raw material of cement, is stored in a storage container 101, from where the amount of clinker material needed at any one time is conveyed by means of conveying apparatus 102 into the clinker proportioning containers 103, from where the clinker is conveyed onwards with a conveyor apparatus 105 to the grinding apparatus 106 for grinding. In connection with the proportioning apparatus, agents, such as gypsum, slag and e.g. ungraded fly ash, that are in the agent containers 104 are also added to the clinker material, which agents are transported with the conveyor apparatus 105 to the grinding apparatus 106, where both the clinker and the agents are ground together. After grinding the ground and mixed cement powder is transported by means of a conveying apparatus 107 to the storage & dispensing containers 108 for cement, from which containers the finished cement powder is dispensed for distribution, e.g. into delivery vehicles 109 or distribution containers 110.

In one method and apparatus according to the invention presented in Fig. 2, in other words, more briefly, in the solution, clinker, which is the main raw material of cement, is stored in a storage container 1, from where the amount of clinker material needed at any one time is conveyed by means of conveying apparatus 2 into the clinker proportioning containers 3, from where the clinker is transported onwards with a conveying apparatus 6 to the grinding apparatus 7 for grinding. In connection with a proportioning apparatus comprising one or more proportioning containers 3, also the agents in one or more agent containers, such as gypsum, slag and e.g. the graded fly ash that is essentially rough in terms of its grain size in agent container 4, are also added to the clinker material, which agents are transported with the aforementioned conveying apparatus 6 together with the clinker mass to the grinding apparatus 7, where both the clinker and the agents are ground together in a manner that is known in the art. The average fineness (D50) of the graded rough fly ash is essentially approx. 40-60 μπι. After grinding the ground and mixed cement powder is transported by means of a conveyor apparatus 8 to the storage & dispensing containers 9, from which the finished cement powder is dispensed for distribution, e.g. into delivery vehicles 15 or distribution containers 16.

One difference to solutions according to prior art is now, however, that a dispensing apparatus 12 of fly ash pregraded to the desired grain and comprising a lot of essentially round fly ash grains has been added into connection with ordinary cement manufacturing apparatus, by means of which dispensing apparatus special cements that are extremely homogeneous in composition can be made, in addition to conventional cement, with the same cement manufacturing apparatus, the concrete made with which special cements is e.g. extremely strong and very workable, or the concrete made in this way has other desired properties, such as the slow or fast development of strength.

The proportioning apparatus 12 of fly ash comprises a weighing unit 12a and a mixing unit 12b, in which the components weighed with the weighing unit 12a are mixed together and conveyed with a conveyor apparatus 13 into the storage & dispensing containers 14 for special cement, from which the finished special cement powder is dispensed for distribution, e.g. into delivery vehicles 15 or distribution containers 16. The apparatus according to the invention comprises one or more additional agent containers 5, 5a, which container (s) is/are connected by means of a conveyor apparatus 10 to the weighing unit 12a of the proportioning apparatus 12. In the solution according to the embodiment there are two additional agent containers, but there can be only one or more than two, e.g. 3, 4, 5 or 6. In the first additional agent container 5 is pregraded fly ash of very fine grain size, having an average fineness (D50) of e.g. between 1-8 μπι. Correspondingly, in the second additional agent container 5a can be pregraded fly ash of a rougher grain size, having an average fineness (D50) of e.g. between 8-16 μπι, in the third additional agent container can be pregraded fly ash of even rougher grain size, having an average fineness (D50) of e.g. between 17-40 μπι, et cetera. In addition to a precisely selected grain size, it is advantageous that the graded fly ash particles are essentially round in shape, in which case the amount of water needed when making concrete decreases, from which follows also an increase in the strength of the concrete. A large amount of essentially round fly ash particles is ensured, inter alia, by all, or at least some, of the additive containers 5, 5a containing fly ash that is unground, and therefore only graded by grain size. The fly ash material in each additive container 5, 5a contains, in terms of percentage by weight, between approx. 20-80%, suitably approx, 30-70%, preferably approx. 40-60%, and e.g. roughly approx. 50% essentially round particles. The pregraded, preferably unground, fly ash from additional agent container 5 or 5a, et cetera, said fly ash still containing a sufficient proportion of round particles, is conveyed by means of conveyor apparatus 10 directly to the weighing unit 12a for weighing and onwards after weighing to the mixing unit 12b, to which cement powder ground with grinding apparatus 7 is also brought, said cement powder being either completely pure clinker powder or clinker powder in which the necessary amount of possible other additives and agents has been mixed. The aforementioned ground cement powder is brought either directly with the grinding apparatus 7 or is separated, e.g. by means of the distribution device 8a in connection with the conveyor apparatus 8, from the material going into the storage & dispensing containers 9 and is conducted via the conveyor apparatus 11 to the weighing unit 12a of the proportioning apparatus 12 for weighing and after weighing to the mixing unit 12b. Cement powder can also be brought directly from a storage silo or from some other storage location, in which case the cement powder is preground to the finished grain size and other necessary additives are possibly already added to it.

According to the invention essentially unground graded fly ash of very small grain size and containing suitably round fly ash particles is mixed in suitable proportion in the mixing unit 12b into preground cement powder, in which case the strength properties and workability of the concrete made from cement powder enhanced in this way improve compared to cement according to prior art. In this case the cement powder, into which the aforementioned fine fly ash is added, can contain just ground clinker, or mixed in with the clinker there can be small amounts of additives or other agents, such as gypsum. Additionally, in some cases, in addition to or instead of the aforementioned additives and agents, slag and/or fly ash that is rougher than the aforementioned fine fly ash and that is e.g. ground together with the clinker in the grinding apparatus 7 can be mixed in with the clinker. Table 1 presents an extract from one test result, in which fly ash was graded with a test device for the use of the method and of the apparatus according to the invention. In it, Product 1 is essentially ungraded coarse source material and Product 5 is the most fine-grained material of all. Four different percentage by volume values are presented in the vertical columns: D10, which corresponds to 10%; D50, which corresponds to 50%; D97, which corresponds to 97%; and D100, which corresponds to 100%. The decimal figures presented in the columns are the grain sizes of the fly ash material in micrometers (μπι) .

Table 1

For example, if looking at the lowermost Product 5, it is seen that in the grading 100% of all the material has gone through the screen, the aperture size of which is 4 μπι, i.e. in the graded product the largest grain size is 4 μπι. Generally, however, a more important criterion is considered to be a grain size with the value D97, which in most cases is sufficient instead of D100, and the product is usually evaluated with the value D50, with which the average fineness of the grain size of the product is determined. From Table 1 it is seen that the average fineness D50 of Product 5 is thus 1.46 μπι and more than 10% of the product is of material having a grain size of below 1 μπι, i.e. some of the product already belongs to the nanometer scale in terms of its grain size.

The processing and grading of fly ash into products of exactly a certain size in terms of their grain size enables the inexpensive and appropriate productive use of these products in different applications. For example, fly ash that is selected according to exactly the correct grain size, that is unground and that contains an abundance of round fly ash particles, as an additive to cement used in concrete, among other things, improves the quality and strength of the concrete and also lowers the price of concrete and reduces the consumption of clinker needed in the concrete, in which case also the ecological footprint improves .

Table 2 presents an extract from one test result, in which the development of the compression strength of concrete of strength grade K40 was tested. The products compared were concrete manufactured with cement according to prior art and concrete manufactured with special cement according to the invention in which very fine fly ash graded by grain size had been added to the ground clinker material.

Table 2 The baseline for comparison was therefore concrete manufactured from cement according to prior art (Prior Art), in the manufacture of which 300 kg of cement was used, in which cement there was no fly ash as an agent. Full compression strength developed gradually in such a way that after the first day (24-hour period) the compression strength was 15 MPa and after 28 days 45 MPa. Correspondingly, only 225 kg of cement and 15 kg of very fine fly ash graded by grain size was needed for the concrete manufactured with the special cement according to the invention (Invention) for achieving the same strength properties, the fly ash being mixed into the cement powder after grinding of the clinker. The missing volume could be replaced with nature's own material, i.e. sand. An amount (225 kg) of cement according to the invention that was 25% smaller with respect to the original amount of cement (300 kg) was sufficient for achieving the same final result when 15 kg of fly ash was added to the cement as an agent, which amount is 5% of the original amount of cement needed. In this context, whenever percentages are presented they refer to percentages by weight. Since the amount of cement could be reduced for achieving the same final result and the manufacture of cement stresses the environment a lot with its CO₂ emissions, the cement mixture manufactured with the solution according to the invention is, in addition to its other advantages, also a lot more environmentally friendly than cement according to prior art.

When fly ash that is graded into precisely the correct grain size and that contains a suitable abundance of essentially round fly ash particles is used as an additive to the cement needed in the manufacture of concrete, also less fly ash can be used than in solutions according to prior art for achieving the same end result, i.e. instead of 15-40% fly ash, only approx. 2-25% of the amount of other cement material is needed in the solution according to the invention. In this case the grain size of the fly ash is e.g. as follows: D50 is between 1-8 μπι, D97 is between 2-60 μπι and D100 is between 3-80 μπι. Correspondingly D10 is between 0.5-2 μπι.

Table 3 presents an extract from another test result, in which the development of the compression strength of concrete was tested. The products compared were concrete manufactured with cement according to prior art, in which fly ash had been added to the clinker material before the grinding of the clinker, and three concretes manufactured with special cement according to the invention, in which different percentages of very fine fly ash graded by grain size had been added to the ground clinker material, said fly ash having a grain size that was smaller than the grain size of the ground clinker material.

Table 3 The column Prior Art (20-25%) of Table 3 presents the compression strengths of concrete made from a cement mixture according to prior art 1, 7, 28 and 91 days after the placement of the concrete. In this case a percentage of approx. 20-25% by weight of ungraded, or very roughly graded, fly ash has been added to the clinker material before the grinding of the clinker material.

Correspondingly, the column Invention 1 (20%) presents the compression strengths of concrete made from one cement mixture according to the invention 1, 7, 28 and 91 days after the placement of the concrete. In this case an amount of 20% by weight of fly ash graded according to the invention that is smaller in grain size than the grain size of the ground clinker has been added to essentially pure cement powder that is approx. 95% pure and mixed only with conventional agents, such as gypsum, but not with fly ash. In this case, therefore, the fly ash is added only after the grinding of the clinker. The column Invention 2 (25%) presents the compression strengths of concrete made from a second cement mixture according to the invention 1, 7, 28 and 91 days after the placement of the concrete. In this case fly ash is added in the same way as in the previous column, but now to a percentage by weight of 25% of the amount of ground clinker. And the column Invention 3 (5%) presents the compression strengths of concrete made from a third cement mixture according to the invention 1, 28 and 91 days after the placement of the concrete. In this case also fly ash is added in the same way as in the previous two columns, but now to a percentage by weight of only 5% of the amount of ground clinker.

It is clearly seen from the test results of Table 3 that the compression strength of concrete made from cement mixtures (Invention 1-3) according to the invention is substantially greater than the compression strength of concrete made from cement (Prior Art) according to prior art mixed with fly ash. For example, the cement mixture Invention 3 reaches a compression strength of 15 MPa already 24 hours after placement, i.e. a compression strength that is two times greater than concrete made from the Prior Art cement mixture.

The conclusion can also be drawn from the test results of Table 3 that if it is desired to give priority to a good initial strength, less fly ash graded according to the invention is mixed as an additive into the ground cement powder to be used in the manufacturing of concrete than in cases where it would be desired to give priority to a good final strength. For example, the compression strength of the cement mixture Invention 3 is still greater 28 days after placement of the concrete than that of the other cement mixtures Invention 1 and Invention 2 that were in the test, whereas the compression strength of these is greater than that of cement mixture Invention 3 only 91 days after placement of the concrete. Final strength thus improves when more than 5% but less than 25% fly ash, graded according to the invention, is mixed as an additive into the ground cement powder. The exact percentages were not, however, ascertained in the tests.

What can, however, be specified is e.g. that when raising the initial strength of the manufactured concrete, fly ash, graded according to the invention, to the amount of approx. N% by weight of the amount of cement powder is added to the ground cement powder, where N is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14 or fractions of these integers. Correspondingly, when raising the final strength of the manufactured concrete, fly ash, graded according to the invention, to the amount of approx. N% by weight of the amount of cement powder is added to the ground cement powder, where N is 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26...40 or fractions of these integers. Figure 3 presents a diagrammatic and simplified sample of recently mixed fresh concrete, in which is both small stones 18 and larger stones 19 as a reinforcement in a mixture of cement gel 17, presented with diagonal lines, that is the binder agent. In addition, there can be metal reinforcements and other reinforcements in the concrete, but they are not presented in the figures. The sampling point 20, presented with dot-and-dash lines, and which is presented in much greater magnification in Fig. 4, is also added in Fig. 3.

The sample of concrete according to Fig. 4 is diagrammatic and simplified and it only presents how the particles, i.e. grains 21, of fly ash graded according to the invention are situated between cement particles, i.e. cement grains 22, larger than them, condensing the structure of the cement mass functioning as a binder agent. Without fly ash grains 21 smaller in size than the cement grains 22, an unnecessary abundance of empty space, e.g. approx. 2-15%, would remain between the cement grains 22, which empty space weakens the structure. Fly ash that is smaller- grained than the cement grains 22 and that is correctly selected by grain size for the intended use and is used as an additive to the cement thus physically increases the reaction surface area of the particles of the mixture and thereby the strength of the cement and in this way strengthens concrete manufactured from cement to which the fly ash has been added, and the concrete becomes more workable and placeable. In addition, particles of small grain size replace the amount of water and cement to be used, because the empty spaces of the cement grains 22 would otherwise be filed with a cement-water mixture. This property also helps to save cement as a raw material. Likewise, among other things, drying cracks decrease and frost resistance improves when using small fly ash particles 21 that are pregraded by grain size mixed in with the cement particles 22.

When manufacturing cement according to prior art, fly ash that is ungraded by grain size is added to the clinker material before the grinding of the clinker material. In this case, however, it is not necessarily possible to obtain fly ash of the correct size in terms of grain size with respect to the properties of the cement grade being manufactured at that particular time. According to the invention, fly ash that is of precisely the correct grain size, that is preferably unground and that contains a suitable abundance of round fly ash grains is added to clinker material, in which are small amounts of additives and agents possibly needed, only after grinding of the material, in which case the grain size of the fly ash to be used depends on the intended use of the cement to be manufactured. Thus larger-grained fly ash in terms of grain size is added to cement containing large cement grains 22 and smaller-grained fly ash in terms of grain size is added to cement containing smaller cement grains 22. In this way cement mixtures of good quality are obtained for different applications. Average grain size (D50) is used in the definition of the grain size of both the fly ash and the cement powder.

According to the invention fly ash grains 21 smaller than the cement grains 22 are mixed into cement made for the manufacture of concrete to fill the empty spaces between the cement grains 22. In this case the solution according to the invention comprises at least one extra agent container 5 of fly ash, the container containing fly ash that is graded by grain size, is preferably unground and contains a sufficient abundance of essentially round fly ash particles, the grain size of the particles 21 of which fly ash are, in terms of their average fineness (D50), between approx. ( 0.1...0.8 ) *grain size of the particles 22 of clinker material, suitably approx. ( 0.2...0.7 ) *grain size of the particles 22 of clinker material, preferably approx. ( 0.3...0.6 ) *grain size of the particles 22 of clinker material, and most suitably approx. ( 0.4...0.5 ) *grain size of the particles 22 of clinker material. The grain sizes of particles stated above are defined according to the average grain size (D50) of the fly ash particles 21 and of the clinker material particles 22.

Suitable fly ash from the additional agent container 5, 5a, et cetera, is added to the grade of cement being manufactured at the time in such a way that essentially unground fly ash pregraded by grain size is added to the clinker material after the grinding of the clinker material, said fly ash containing a percentage by weight of essentially round fly ash particles of approx. 20-80%, suitably approx. 30-70%, preferably approx. 40-60% or e.g. roughly approx. 50%. The grain size of the aforementioned fly ash particles 21 are, in terms of their average fineness (D50), smaller than the ground clinker material of the cement mixture being manufactured at any given time, i.e. smaller than the corresponding grain size according to the average particle size (D50) of the particles 22 of the cement powder .

In this case, according to the grade of cement desired, fly ash that is precisely pregraded and selected by grain size, and also preferably unground, is mixed with the grinding apparatus 7 into the ground clinker material, i.e. into cement powder containing approx. 0-4% of possibly necessary additives and agents, to a percentage by weight of e.g. either approx. 2-40% of the amount of the material, or only approx. 2-25% of the amount of the material, or e.g. 3-14%, suitably e.g. approx. 4-10% and preferably e.g. approx. 5-

8% or whatever suitable percentage whatsoever of the ranges presented above, i.e. approx. 4, 6, 7, 9, 11, 12 or 13 percent or parts thereof. For example, when the ground clinker material, i.e. cement powder with possible additives and agents, is 100 kg, at a 3-12% mixing ratio 3- 12 kg of fly ash is mixed into the cement powder. The fly ash to be mixed is taken e.g. from additional agent container 5, transported to the proportioning unit 12 by means of conveyor apparatus 10 and weighed and also mixed, by means of proportioning unit 12, into the clinker material, i.e. into the cement powder, that came from the grinding apparatus 7, which cement powder is conducted to the proportioning unit 12 by means of conveyor apparatus 11.

In this way the amount of fly ash to be used in the manufacturing of cement can thus, owing to the precise grain size grading, also be a lot smaller than the approx. 15-40% of the amount of the clinker material that is used according to prior art, although more savings in the amount of clinker are achieved with a larger percentage. In addition, a larger percentage of graded fly ash added after the grinding of the clinker enables greater compression strength of the concrete after hardening of the concrete has progressed further, i.e. greater final strength of the concrete .

One essential difference in the solution according to the invention compared to prior art is that unground fly ash pregraded to a certain grain size and comprising a lot of essentially round fly ash grains is mixed into the cement powder, after which the mixture is not ground again, because in the grinding at least some of the round fly ash grains would break. In the embodiment presented in the application the cement powder is taken directly from the material flow ground with the grinding apparatus 7 of clinker material, but the cement powder to be mixed can just as well be already finished, e.g. in a storage silo, as is presented in the solution according to patent publication no. US 2005/0252421 Al presented at the beginning of the present application .

The special cement manufactured with the method and apparatus according to the invention is extremely well suited for manufacturing strong concrete, e.g. in conjunction with the manufacturing of cement producing normal concrete strength.

It is obvious to the person skilled in the art that different embodiments of the invention are not only limited to the examples described above, but that they may be varied within the scope of the claims presented below. What is essential is that an additive product, such as fly ash, graded by grain size according to the intended use, is used, in which case the grain size of the aforementioned additive product is essentially precisely known, and that the additive product is added to the cement mixture after the grinding of the clinker material. It is also important that, after grinding, the fly ash mixed into the cement powder comprises an essentially large amount of essentially round fly ash particles, which improve the properties of the cement powder. In this case it is advantageous to use for this purpose unground fly ash, because grinding easily breaks the round fly ash particles.

Claims

1. Method for manufacturing cement, in which method additives and/or agents, such as fly ash, the particles (21) of which are smaller in grain size than the cement particles (22) of the cement powder, are added to ground clinker material, characterized in that fly ash graded by grain size is added to the cement powder ground from clinker material, said fly ash comprising approx. 20-80% essentially round fly ash particles.

2. Method according to claim 1, characterized in that unground fly ash precisely graded by grain size is added to the cement powder ground from clinker material.

3. Method according to claim 1 or 2, characterized in that, in conjunction with the cement manufacturing process, fly ash precisely graded by grain size is added to the cement powder ground from clinker material after the grinding, the percentage of said fly ash being 2-40% by weight of the amount of cement powder.

4. Method according to claim 1, 2 or 3, characterized in that, in conjunction with the cement manufacturing process, fly ash precisely graded by grain size and having an average fineness of between 1-8 μπι is added to the cement powder ground from clinker material, the percentage of said fly ash being e.g. approx. 2-25%, or approx. 3-14%, suitably 4-10% and preferably approx. 5-8% by weight of the amount of ground clinker material.

5. Method according to any of the preceding claims, characterized in that fine fly ash in terms of its grain size is added to the clinker material ground with the grinding apparatus (7) after the grinding by guiding the clinker material coming from the grinding apparatus (7) into the proportioning apparatus (12) that is in connection with the apparatus, into which proportioning apparatus the fly ash to be added, that is graded by grain size and in the additional agent container (5, 5a) for fly ash, is also guided, and by weighing the amounts of material in the weighing unit (12a) of the proportioning apparatus (12) and by mixing the weighed amounts of material in the mixing unit (12b) of the proportioning apparatus (12) and by conveying the special cement mixed in this way into the storage & dispensing containers (14) .

6. Method according to any of claims 1-4 above, characterized in that fine fly ash in terms of its grain size is added to the clinker material ground with the grinding apparatus (7) after the grinding by conveying some of the clinker material coming from the grinding apparatus (7) into the proportioning apparatus (12), into which also fly ash to be added, that is graded by grain size, is also conveyed, and by weighing the amounts of material in the weighing unit (12a) of the proportioning apparatus (12) and by mixing the weighed amounts of material in the mixing unit (12b) of the proportioning apparatus (12) and by conveying the special cement mixed in this way into the storage & dispensing containers (14) .

7. Method according to any of the preceding claims, characterized in that, the reaction surface area of the particles of the cement mixture is increased by adding to the cement powder fly ash particles (21) that are of smaller grain size than the grain size of the particles placed in the empty spaces between cement particles (22) by mixing .

8. Method according to any of the preceding claims, characterized in that the fly ash to be added to the clinker material after grinding comprises e.g. approx. 30- 70%, suitably approx. 40-60% and preferably approx. 50% essentially round fly ash particles.

9. Method according to any of the preceding claims, characterized in that fly ash graded by grain size is added to ground clinker material, the grain size of the particles (21) of which fly ash are, in terms of their average fineness (D50), between approx. ( 0.1...0.8 ) *grain size according to average fineness (D50) of the particles (22) of clinker material, suitably approx. ( 0.2...0.7 ) *grain size according to average fineness (D50) of the particles (22) of clinker material, preferably approx. ( 0.3...0.6 ) *grain size according to average fineness (D50) of the particles (22) of clinker material, and most suitably approx. ( 0.4...0.5 ) *grain size according to average fineness (D50) of the particles (22) of clinker material.

10. Method according to any of the preceding claims, characterized in that the grain sizes of fly ash to be added to ground clinker material are e.g. one or more of the following: D10 is between 0.5-2 ym; D50 is between 1-8 μπι; D97 is between 2-40 μπι and D100 is between 3-80 μπι. 11. Method according to any of the preceding claims, characterized in that, for raising the initial strength, fly ash to the amount of approx. N% by weight of the amount of cement powder is mixed as an additive into the cement powder to be used in manufacturing concrete, where N is 2, 3, 4, 5, 6, 7, 8, 9, 10,

11, 12, 13 or 14 or fractions of these integers.

12. Method according to any of the preceding claims, characterized in that, for raising the final strength, fly ash to the amount of approx. N% by weight of the amount of cement powder is mixed into the cement powder to be used in manufacturing concrete, where N is 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26...40 or fractions of these integers.

13. Apparatus for manufacturing cement, which apparatus comprises at least a plurality of proportioning containers (3), a conveying path formed from a plurality of conveying apparatuses and handling apparatuses (6, 8) for conducting the material to be handled from one location to another as a material flow, and also a grinding apparatus (7) and one or more additional agent containers (5, 5a) containing fly ash as well as a plurality of storage & dispensing containers (9, 14) of the finished cement, characterized in that the apparatus comprises at least a proportioning apparatus (12) provided with a mixing unit (12b), which proportioning apparatus is connected by means of a first conveyor apparatus (10) to one or more additional agent containers (5, 5a) containing fly ash that is graded by grain size, by means of a second conveyor apparatus (8, 11) to the material flow of cement powder ground from clinker, and by means of a third conveyor apparatus (13) to the storage & dispensing container (14) of cement mixed from the aforementioned fly ash and from the aforementioned cement powder.

14. Apparatus according to claim 13, characterized in that the grinding apparatus (7) is connected by means of a conveyor apparatus (8, 11) to a proportioning apparatus (12) for transferring cement powder ground with the grinding apparatus (7) from the grinding apparatus (7) directly to the proportioning apparatus (12) .

15. Apparatus according to claim 13 or 14, characterized in that in connection with the first end of the conveyor apparatus (11) is a distribution device (8a), with which one part of the cement powder being received from the grinding apparatus (7) is separated for conveying to the proportioning apparatus (12) and a second part of the aforementioned cement powder is conducted for conveying to the storage & dispensing container (9) .

16. Apparatus according to claim 13, 14 or 15, characterized in that the apparatus comprises a weighing unit (12a) for weighing the mixture amounts of the cement powder being received from the grinding apparatus (7) and the fine-grained fly ash to be mixed into the cement powder before the mixing of the aforementioned components in the mixing unit (12b) .

17. Apparatus according to any of the preceding claims 13- 16, characterized in that the apparatus comprises at least one or more additional agent containers (5, 5a) of fly ash that is graded by grain size, is preferably unground and contains approx. 20-80% essentially round fly ash particles, which container (s) is/are connected by means of a conveyor apparatus (10) to a proportioning apparatus (12) for transporting pregraded fly ash to the proportioning apparatus (12) .

18. Apparatus according to any of the preceding claims 13- 17, characterized in that at least one additional agent container (5) of fly ash is arranged to contain fly ash graded by grain size, wherein the grain size of the particles (21) of the fly ash are, in terms of average fineness (D50), between approx. ( 0.1...0.8 ) *grain size according to average fineness (D50) of the particles (22) of clinker material, suitably approx. ( 0.2...0.7 ) *grain size according to average fineness (D50) of the particles (22) of clinker material, preferably approx. ( 0.3...0.6 ) *grain size according to average fineness (D50) of the particles (22) of clinker material, and most suitably approx. ( 0.4...0.5 ) *grain size according to average fineness (D50) of the particles (22) of clinker material.