Method and Installation Configuration for Preparing and Activating a Raw Material

Abstract

The invention relates to a method for preparing and activating a raw material, wherein the raw material is comminuted by means of grinding rollers in a mill-classifier combination, and wherein the mill-classifier combination is set and operated to produce a ground product with a fineness of between D50=3 m and D50=12 m. Here, a part of the grinding product is comminuted by means of the mill-classifier combination to a diameter of <5 m. Subsequently the ground product is subjected to a further classification in an ultrafine grain classifier unit which has a separation threshold in order to separate ultrafine grain with a fineness of <D50=6 m. The invention further relates to an installation configuration for carrying out the method according to the invention.

Claims

1. Method for preparing and activating a raw material which has latently hydraulic, hydraulic, inert or pozzolanic properties, wherein the raw material is comminuted by means of grinding rollers (24) of a mill-classifier combination (20), wherein the mill-classifier combination (20) has a classifier (22) and a vertical mill (21) with a grinding pan (25) and with the grinding rollers (24), wherein the mill-classifier combination (20) is set and operated to produce a ground product with a fineness of between D50=3 m, and D50=12 m, and wherein in a first classification raw material comminuted at least once by means of the grinding rollers (24) in a first classification is fed from the classifier (22) of the mill-classifier combination (20) as rejected coarse material back to the grinding pan (25) of the vertical mill (21) for further comminution by means of the grinding rollers (24), characterised in that a part of the grinding product is comminuted by means of the grinding rollers (24) to a diameter of less than 5 m, wherein in the case of a raw material with potentially reactive properties, existing pozzolanic, latently hydraulic or hydraulically active phases are released, the grinding product is subjected to a further classification into fine and ultrafine grain in an ultrafine grain classifier unit (30), the ultrafine grain classifier unit (30) is operated and set with a separation threshold in order to separate ultrafine grain with a fineness of less than D50=6 m, the fine grain is removed from the preparation process and supplied for a building materials application, the ultrafine grain is fed to a filter (40), wherein a process air flow is guided from the mill-classifier combination (20) via the ultrafine grain classifier unit (30) to the filter (40) and the ultrafine grain is separated from the process air flow by means of the filter (40) and fed for a use as composite material in cement, wherein in the ultrafine grain in the case of a raw material with potentially reactive properties at least a part of the pozzolanic, latently hydraulic or hydraulically active phases is activated by the release and/or an increased overall reactivity is achieved by the significantly increased particle surface area.

2. Method according to claim 1, characterised in that the ultrafine grain classifier unit (30) is operated and set with a separation threshold in order to separate, after the filter (40), 10% to 20% of the mass of the raw material as ultrafine grain from the process air flow.

3. Method according to claim 1 or 2, characterised in that cyclone arrangements such as multi-cyclones (35) or cyclone packs or a plurality of ultrafine classifiers connected in parallel, are used as an ultrafine grain classifier unit (30).

4. Method according to claims 1 to 3, characterised in that LD slags, fly ash or granulated slags are used as raw material.

5. Method according to one of claims 1 to 4, characterised in that grinding aids, in particular amine-containing grinding aids with or without a small proportion of chloride-containing salts, are added into the mill-classifier combination (20).

6. Method according to one of claims 1 to 5, characterised in that the fine grain is removed from the ultrafine grain classifier unit (30) via a means which at least limits a false air entry into the process air flow.

7. Method according to one of claims 1 to 6, characterised in that when using cyclone arrangements to increase the fineness of the ultrafine grain the flow speed in the cyclones (36) of the cyclone arrangements is increased.

8. Method according to claim 7, characterised in that the flow speed is increased by increasing the amount of process air flow and/or reducing the number of the active cyclones (36) of the cyclone arrangements.

9. Method according to claim 7, characterised in that the amount of process air flow is increased in the region of the cyclone arrangements by recirculating a part of the process air from downstream of the filter (40) and feeding the part of the process air to upstream of the cyclone arrangements.

10. Method according to one of claims 1 to 9, characterised in that when using cyclone arrangements to reduce the fineness of the ultrafine grain the flow speed in the cyclones (36) of the cyclone arrangements is reduced.

11. Method according to claim 10, characterised in that the flow speed is reduced by reducing the amount of process air flow, increasing the number of the active cyclones (36) of the cyclone arrangements, feeding funnel air into the cyclone (36) of the cyclone arrangements and/or by removing a part of the process air from upstream of the cyclone arrangements and feeding the part of the process air downstream of the cyclone arrangements.

12. Installation configuration (10) for preparing and activating a raw material which has latently hydraulic, hydraulic, inert or pozzolanic properties, having a mill-classifier combination (20) which has a classifier (22) and a vertical mill (21) with a grinding pan (25) and grinding rollers (24), wherein the mill-classifier combination (20) is designed to comminute the raw material to a fineness of between D50=3 m and D50=12 m as a grinding product by means of the grinding rollers (24), wherein the mill-classifier combination (20) is designed in order to feed raw material comminuted at least once by means of the grinding rollers (24) in a first classification as rejected coarse material back to the grinding pan (25) of the vertical mill (21) for further comminution by means of the grinding rollers (24), characterised in that the mill-classifier combination (20) is designed to comminute a part of the grinding product to a diameter of <5 m, wherein in the case of a raw material with potentially reactive properties, existing pozzolanic, latently hydraulic or hydraulically active phases are released, an ultrafine grain classifier unit (30) and a filter (40) are provided, a guided process air flow is provided from the mill-classifier combination (20) via the ultrafine grain classifier unit (30) to the filter (40) which is designed to transport the raw material comminuted in the mill-classifier combination (20), the ultrafine grain classifier unit (30) is designed to classify the grinding product in a further classification into fine and ultrafine grain, the ultrafine grain classifier unit (30) can be set and operated at a separation threshold in order to separate ultrafine grain with a fineness of less than D50=6 m, and the filter (40) is designed to separate ultrafine grain from the process air flow coming from the ultrafine grain classifier unit.

13. Installation configuration according to claim 12, characterised in that cyclone arrangements such as multi-cyclones (35) or cyclone packs or a plurality of ultrafine classifiers connected in parallel are used as an ultrafine grain classifier unit (30).

14. Installation configuration according to claim 12 or 13, characterised in that the ultrafine grain classifier unit (30) has a means for removing the separated fine grain which at least limits a false air entry into the process air flow.

15. Installation configuration according to one of claims 12 to 14, characterised in that a controllable process gas recirculation line (52) is provided from downstream of the filter (40) to upstream of the cyclone arrangements.

Description

[0058] The invention will be described in greater detail below using a schematic exemplary embodiment by reference to the further figures, in which:

[0059] FIG. 1 shows a schematic flowchart of an installation configuration according to the invention;

[0060] FIG. 2 shows a simplified grain size distribution after a mill-classifier combination;

[0061] FIG. 3 shows a simplified grain size distribution after an ultrafine grain classifier unit;

[0062] FIG. 4 shows a diagram for strength studies of ultrafine ground LD slag; and

[0063] FIG. 5 shows a diagram for strength studies of ultrafine ground granulated slag.

[0064] FIG. 1 shows a flowchart of an installation configuration 10 according to the invention in a schematic form. The installation configuration 10 has as essential elements a mill-classifier combination 20, an ultrafine grain classifier unit 30 and also a filter 40.

[0065] The mill-classifier combination 20 consists of a vertical mill 21 and a classifier 22. The vertical mill 21 has a driven grinding pan 23 and a plurality of grinding rollers 24 which are arranged to be stationary and designed to be rotatable. During the grinding process, a grinding bed is formed on the grinding pan 23 by means of the grinding material supplied, on which grinding bed the grinding rollers 24 roll and thus comminute the grinding material.

[0066] Subsequently the comminuted grinding material is conveyed by means of an air flow to the classifier 22. A classification of the grinding material into coarse and fine grain takes place in said classifier 22. Coarse material is rejected by the classifier 22 and conveyed back to the grinding pan 23 of the vertical mill 21 for a further overgrinding.

[0067] Here, the mill-classifier combination 20 can in principle be operated both as an overflow mill and also as an air-swept mill. In the embodiment shown here, the mill-classifier combination 20 is configured as an air-swept mill.

[0068] To transport the comminuted grinding material, which can also be described as grinding product, different pipelines are provided. A first pipeline 71 leads from the mill-classifier combination 20 to the ultrafine grain classifier unit 30. From there, a second pipe line 72 leads to the filter 40. A further pipeline 73 leads to a T junction, which leads on the one hand to a flue 63 and on the other hand to a fourth pipeline 74. The fourth pipeline 74 leads to a hot gas generator 60 which is used to heat process gas in order to also carry out drying during the grinding. The process gas heated by the hot gas generator 60 is conveyed via a fifth pipeline 75 back to the mill-classifier combination 20.

[0069] Through the process gas flow, which flows through the mill-classifier combination 20, the grinding product not rejected by the classifier 22 is conveyed via the first pipe 71 to the ultrafine grain classifier unit 30. The structure of the ultrafine grain classifier unit 30 is in principle arbitrary. In the embodiment shown schematically here, it is designed as a multi-cyclone 35 with a plurality of cyclones 36 arranged one after the other. Instead of a multi-cyclone 35, at this point a classifier especially suited for this task or a plurality of smaller ultrafine classifiers connected in parallel can also be used.

[0070] A further classification takes place in the multi-cyclone 35. Here, fine grain is separated from the ultrafine grain. The fine grain separated in the multi-cyclone 35 can subsequently be removed via rotary air locks 37 from the installation configuration 10 and supplied for use as a building material.

[0071] The ultrafine grain not separated in the multi-cyclone 35 is transported by means of the process air flow via the second pipeline 72 further to the filter 40. This can for example be a bag filter. The use of filter assemblies with a plurality of filters arranged one after the other is also possible.

[0072] In the filter 40 the ultrafine grain still in the process air flow is separated from this. The ultrafine grain can now be removed via an air lock 41 from the installation configuration 10.

[0073] The process air flow is guided from the filter 40 via the fourth pipeline 74 to the mill fan 26. By means of this mill fan 26 the flow speed of the process air flow can be adjusted. Subsequently to the mill fan 26, it is possible to expel a part of the process air flow via the flue 63. For this, a flue valve 64 is provided. Another part can be fed via a fourth pipeline 74 to the previously described hot gas generator 60, in which the process air of the process air flow is heated again. This heated process air is then fed via a fifth pipeline 75 back to the mill-classifier combination 20.

[0074] Further details will be set out below in relation to the fundamental recognition of the invention by reference to FIGS. 2 and 3. FIG. 2 shows a schematic grain size distribution after the mill-classifier combination 20 in the region of the first pipeline 71. FIG. 3 shows the grain size distribution of the ultrafine grain and the fine grain after the multi-cyclone 35. Both figures show greatly simplified, idealised grain size distributions.

[0075] Corresponding to the invention it has been recognised that when using a mill-classifier combination 20 which has a vertical mill 21 operated for example in order to produce a ground product with a fineness of between D50=3 m and D50=12 m, a grain size distribution as shown in FIG. 2 is present.

[0076] In the diagram in FIGS. 2 and 3 the diameter of a grain of the grinding product is recorded on the abscissa. The mass of the respective grain fraction in mass % is recorded on the ordinate.

[0077] As shown in FIG. 2, in the case of a fineness of D50=8 m, 50% of the total mass of the ground product has a grain with a diameter of over 8 m and 50% of the total mass of the grinding product has a grain size with a diameter of over 8 m.

[0078] A grinding product with this particle size distribution is subsequently conveyed further for a second classification in the ultrafine grain classifier unit 30. In FIG. 3, the particle size distribution for the ultrafine grain is shown on the left side of the diagram and the particle size distribution for the fine grain on the right side of the diagram after the ultrafine grain classifier unit. As shown, here also, in dependence upon construction, there is no distinct separation between fine grain and ultrafine grain, but a smooth transition is present to a certain extent. The thus produced and classified ultrafine grain has in this example a fineness of D50=3 m and the fine grain a fineness of D50=10 m.

[0079] Through the second classification by means of an ultrafine grain classifier unit 30, which can for example be a cyclone pack, it is thus possible, in a normal grinding process with a mill-classifier combination 20, to also produce ultrafine grain without additional energy having to be expended for this for a particularly fine grinding.

[0080] As also follows from FIG. 3, the ratio between ultrafine grain and fine grain is approximately 10 to 20 mass % to 90 to 80 mass %.

[0081] When using multi-cyclones or a cyclone pack for the ultrafine grain classifier unit 30 there are different possibilities for setting the separation grain threshold. These are explained below in greater detail by reference to FIG. 1.

[0082] The separation grain threshold in the multi-cyclone 35 is determined substantially by the dimensions of the design of the individual cyclones of the multi-cyclone 36. However, it can be influenced in operation by the volume flow of the process air flow through each individual cyclone 36. The grain separation threshold is displaced in the direction of ultrafine grain if the flow speed is increased in the individual cyclones 36. There are different possibilities for this.

[0083] On the one hand the total amount of process air flow per time unit can be increased in the whole installation configuration 10. For this, it is possible to correspondingly control the mill fan 26.

[0084] On the other hand it is possible to increase the total amount of process air flow per time unit only in the region of the multi-cyclone 35. For this, a return gas line 52 can be provided which begins downstream of the filter 40 and ends upstream of the multi-cyclone 35. In addition, a control valve 55 is provided in the return gas line. By means of the return gas line 52 it is possible to convey process gas from behind the filter 40 or from behind the mill fan 26 to in front of the multi-cyclone 35 and thus to increase the amount of process gas air per time unit in the multi-cyclone 35. By means of the valve 54 the recirculated amount of process air can be regulated.

[0085] It is also possible to reduce the number of the active cyclones 36 in the multi-cyclone 35. As the amount of process air gas per time unit is not hereby changed, the flow speed within the active cyclone 36 increases. This in turn leads to a displacement of the separation threshold in the direction of ultrafine grain.

[0086] Similarly the separation threshold of the multi-cyclone 35 can also be displaced in the direction of the fine grain. For this, as previously similarly explained, by means of the mill fan 26 the amount of process air flow per time unit can be reduced. Another possibility is to activate or use more cyclones 36 of the multi-cyclone 35. Since this occurs with the same amount of process air per time unit, the respective flow speed in each cyclone 36 decreases.

[0087] Furthermore there is also the possibility of conveying funnel air via a regulating valve 38 into the individual cyclones 36. The flow speed also decreases here within the cyclone 36.

[0088] A further possibility is to provide a bypass line 51. This leads from upstream of the multi-cyclone 35 to directly downstream of the multi-cyclone 35. In addition a regulating valve 54 is provided. By means of the bypass line 51 it is possible to convey process gas from in front of the multi-cyclone 35 to behind the multi-cyclone 35 and thus reduce the amount of process gas per time unit in the multi-cyclone 35. By means of the valve 54 the amount of process air can be regulated.

[0089] In particular in the preparation of a potentially reactive raw material such as LD slag the method according to the invention has a further advantage. Conventionally LD slag could not be used as composite material in cement, as it does not contribute, or at least does not significantly contribute, to the strength.

[0090] Corresponding to the invention, however, it was recognised that clinker phases such as alite or belite in the range of from, in total, 20 mass % to 30 mass % and glass phase in the range of from 5 mass % to 40 mass % are present in LD slag. However, these phases are overgrown and are not freely accessible in the case of conventional grinding with a fineness of coarser than D50=8 m.

[0091] Through the method according to the invention these phases are released in the ultrafine grain so that they can make a contribution to the strength when used in composite cement. For this, corresponding strength studies according to DIN EN 196 were carried out on standard prisms. The corresponding results are shown in FIG. 4.

[0092] The base cement or reference cement was CEM I 42.5 R. By way of reference specimen, 70 mass % reference cement was mixed with 30 mass % quartz sand and studied. The quartz sand is used as a non-reactive inert stone grain. In the third, fourth and fifth specimens, a mixture of 70 mass % reference cement with 30 mass % ultrafine grain from LD slag was studied. During the grinding of the specimen 3, no grinding aid was used. For the specimen 4, MasterCem ES 2168 was used as a grinding aid and for the specimen 5 MasterCem LS 3116 was used as a grinding aid, respectively of BASF.

[0093] As shown in FIG. 4, it follows from the studies that at the latest with effect from the seventh day the strength level of the specimens 3, 4 and 5 lies significantly above that of the reference specimen. It can be concluded from this that the LD slag provides its own contribution to strength in mixed cement at the latest after seven days.

[0094] Similarly, strength studies were also carried out for ultrafine ground granulated slag. In turn, CEM I 42.5 R was used as base cement. In the second specimen, in this case a 50:50 mixture of base cement and ultrafine ground granulated slag was studied.

[0095] The studies were carried out in turn corresponding to DIN EN 196 on standard mortar. As shown in FIG. 5, the studied mixture of base cement and ultrafine ground granulated slag in specimen 2 reaches a higher strength than the base cement already after the seventh day.

[0096] In summary, it can be stated that it is possible with the method according to the invention and the installation configuration according to the invention to produce composite material for use in cement without having to take substantially increased energy costs into account. Through the ultrafine grinding, even potentially reactive raw materials can be activated which have not been suited as cement composite material up to now.