Glass flour generation method and glass flour generation device

Abstract

The invention relates to a glass flour production process for producing glass flour with a particle size < 40 µm, comprising the following steps: feeding a fine mill (1) with glass shards and dry grinding the glass shards in the fine mill (1), feeding the ground glass shards into an air classifier (2) and air classifying the ground glass shards into a fine fraction and a coarse fraction, wherein the separation limit of the air classifier (2) is set to a particle size < 40 µm, discharging the coarse fraction from the air classifier (2), and removing the fine fraction as the final product, the glass flour.The invention further relates to a glass flour production device for producing glass flour with a particle size < 40 µm, comprising a fine mill (1) for dry grinding of glass shards with an upstream glass shard feeder (7) for feeding the fine mill (1) with the glass shards, an air classifier (2) for separating the ground glass shards into a fine fraction and a coarse fraction, with a separation limit at a particle size < 40 µm, a feed device (2a) arranged between the air classifier (2) and the fine mill (1) for feeding the glass shards ground on the fine mill (1) into the air classifier (2), a coarse discharge device (2c) for discharging the coarse fraction from the air classifier (2), and a removal device (2b, 14, 15, 16) arranged downstream of the air classifier (2) for removing the fine fraction as the end product, the glass flour.

Description

[0001] The invention relates to a glass flour production process and a glass flour production device.

[0002] In light of the increased infrastructure investments required in industrialized nations in recent years, it has become apparent that modern concrete structures often wear out after relatively short periods, whereas, for example, the ancient Pantheon in Rome has survived for millennia. Therefore, efforts are being made to give modern concrete and cement pozzolanic properties, as the ancient Romans did.

[0003] Fly ash is frequently used as a pozzolan, serving as an additive for concrete or cement. Fly ash consists of spherical particles that favorably influence the grain size distribution in concrete, improving workability. Its pozzolanic properties also result in additional, slow-release compaction of the hardening concrete structure, thus giving the concrete long-lasting durability. Fly ash is a combustion residue from coal-fired power plants and, therefore, will be available in less quantity in the future than it is today, reflecting the energy transition.

[0004] Recent trials have shown that finely ground glass powder can be used as a substitute for pozzolan in fly ash. The fineness of the glass powder not only improves the workability of concrete but also results in higher strength at a lower weight and better flowability for filling cavities. However, currently available glass powder has a relatively coarse structure. Furthermore, grinding the glass in wet ball mills—typically rotating drums loaded with metal balls—results in high rejection rates of coarse particles. These particles must be laboriously separated from the final product and disposed of after grinding. While this is feasible under laboratory conditions, it makes large-scale implementation difficult.

[0005] Starting from this, it is therefore an object of the present invention to provide a glass flour production process and a glass flour production device with which a glass flour of fine grain size can be produced with high efficiency.

[0006] This problem is solved with respect to the glass flour production process by the features of claim 1, and with respect to the glass flour production device by the features of claim 9.

[0007] According to the invention, a glass flour production process and an apparatus for carrying out this process are proposed, with which glass flour with a particle size < 40 µm or even 15 µm to 25 µm, preferably < 20 µm, is produced. It has been shown that, despite the highly abrasive nature of the glass shards to be processed, dry grinding can be carried out on a fine mill, producing a high proportion of fine particles in the ground glass shards. This offers the additional advantage that the classification of the ground glass shards into a fine fraction, serving as the end product glass flour, and a coarse fraction to be separated from the end product can be carried out on a downstream air classifier. A jet mill, an impact plate mill, or, as has been found, a vortex mill, can be used as the fine mill to be fed with the glass shards, on which the dry grinding of the glass shards then takes place.

[0008] Impact disc mills have two almost vertically positioned grinding discs rotating around a horizontal axis, between which the material to be ground is placed and, after grinding, extracted from the grinding chamber.

[0009] In jet mills, particles are ground in a gas stream without the use of mechanical tools such as high-speed rotors. The particles are reduced in size by the energy supplied by the milling gas. A cyclone separator is typically installed downstream of the mill to separate the milling gas from the mill dust. In jet mills, or fluidized bed counter-jet mills (a subtype of jet mill), the bulk material to be ground is fed into a feed hopper and enters a grinding zone surrounded by compressed air nozzles. The jets of compressed air capture the fed bulk material particles and accelerate them concentrically, causing them to collide and be ground.

[0010] Vortex mills are known, for example, from patent EP 0 787 528 B1 and feature a defined grinding gap between a stator and a rotor. Vortex mills operate on the principle of an impact mill with a vertically arranged rotor and a stator radially surrounding the rotor. The stator typically has a frustoconical grinding track with inwardly directed, axially (i.e., vertically) ribbing, which is usually mounted in a housing of the vortex mill. On the other side of the grinding gap, the rotor, which can be driven at high speed, is located inside. This rotor is equipped along the axial direction with one or, more commonly, several grinding rings, on which grinding tools are mounted.If the rotor now rotates at high speed in the stator, with the axis of rotation running in a vertical direction, and material to be ground is fed from above and centrifuged outwards in a gap between the rotor and a cover of the housing and from there into the grinding gap, this material to be ground is crushed between the grooves of the grinding track and the grinding tools, in which the individual particles, depending on the material density and grain size, are flung back and forth more or less often between the grinding track and the grinding tools and are broken or shattered upon impact.

[0011] Air classifiers are described, for example, in German patent DE 3 303 078 C1 and German patent application DE 10 2005 001 542 A1 and serve to separate coarse material from fine material in a heterogeneous mixture of different particle sizes. For this purpose, air classifiers have one or more classifier wheels arranged above a classifying chamber. The particles of the material to be classified are carried along in the classifying chamber by an upward airflow or, if the particle is too heavy, are not carried along. Of the lighter particles that reach the classifier wheel, only those particles smaller than the upper particle size limit defined by the classifier wheel can pass through it. The others fall back.

[0012] According to the invention, a fine mill, and preferably an eddy current mill, is combined with a downstream air classifier to produce glass powder with the specified particle size. The relatively imprecise cutoff point of air classifiers must be taken into account, so that a particle size of < 20 µm cannot be interpreted as accurate to one µm.

[0013] It should be noted that such eddy current mill-air classifier combinations are already known in themselves, see German patent DE 10 2013 002 237 B3. However, it is surprising that the use of such an eddy current mill-air classifier combination as a glass powder production device for carrying out the glass powder production process according to the invention yields significantly larger fine fractions compared to glass grinding on wet ball mills, especially for the particularly sought-after glass particles with grain sizes below 20 µm.

[0014] The further dependent claims relate to advantageous further developments of the glass flour production process according to the invention, or of the glass flour production device according to the invention.

[0015] It is particularly advantageous to feed the discharged coarse fraction back into the fine mill and subject it again to the milling process and subsequent air classification, resulting in a significantly smaller residue that cannot be milled to the desired particle size. However, it has been found that returning the coarse fraction to the fine mill in the state it enters the air classifier results in a long process time and thus a milling and classification process for glass powder production that could be further improved from an efficiency standpoint. Therefore, it is particularly advantageous to prepare the coarse fraction for re-feeding into the fine mill. In this context, preparation can mean further milling, low-temperature embrittlement, the removal of particularly large particles, or similar processes.

[0016] It has proven particularly advantageous to process the coarse fraction by wet grinding it on a wet mill, such as a wet ball mill, followed by drying the wet-ground coarse fraction before feeding it back into the fine mill. This has been shown to result in not only complete or near-complete utilization of the broken glass for the production of fine-grained glass powder, but also an extremely efficient grinding process in terms of time and energy consumption.

[0017] This is particularly surprising in terms of energy consumption, because drying the wet-ground coarse material is relatively energy-intensive. According to a beneficial further development, a hot gas stream is generated for this purpose, which dries the wet-ground coarse material fraction and, to prevent contamination, also the added broken glass before it is fed into the vortex mill or fine mill. However, this hot gas stream can be generated in a virtually CO2-neutral and cost-effective manner using a wood powder burner or a modified oil burner for burning wood flour, provided that the wood powder burner is preceded by another fine mill, in particular another vortex mill, which serves to grind wood waste into wood flour.

[0018] Further developments and advantages of the invention are explained in more detail with reference to the embodiment shown in the accompanying figure.

[0019] The figure shows a schematic diagram of a glass flour production device according to a preferred embodiment of the invention.

[0020] Reference numeral 1 denotes a fine mill, specifically an eddy current mill, upstream of which are a coarse crushing device 7 (which simultaneously serves as the glass breakage feeder), a washing unit 5 for the fed and coarsely crushed glass breakage, and a dryer 6 for the coarsely crushed and washed glass breakage. The coarse crushing device can be, for example, a hammer mill or the like. The dryer, on the other hand, can be designed as a rotating drum through which a (hot) airflow flows.

[0021] From the vortex mill 1, the ground material is conveyed via a feed line 2a into an air classifier 2, where it is separated into a fines fraction and a coarses fraction. The feed line 2a could also include a conveying fan or similar equipment, if necessary. The fines fraction passing through the classifier wheel of the air classifier 2 is conveyed via a further airflow line 2b into a filter system 14, for example, a cyclone separator or vapor filter, with an attached exhaust fan 15 and a rotary valve 16 for residual particle discharge.The line 2b, the filter system 14, the extraction blower 15 and the rotary valve 16 thus form a withdrawal device 2b, 14, 15, 16 for the withdrawal of the fine fraction, which simultaneously represents the end product produced by the glass flour production process or the glass flour production device according to the preferred embodiment of the invention, namely the glass flour with a particle size of < 40 µm, in particular < 15 µm to 25 µm and preferably < 20 µm.

[0022] The coarse material separated in air classifier 2 is conveyed via the coarse material discharge rotary valve of air classifier 2, or a similar mechanism such as a coarse material discharge screw and a downpipe 2c, which together form a coarse material discharge unit 2c for removing the coarse material from air classifier 2, into a wet mill, in this case a wet ball mill 3. There, the coarse material fraction discharged from air classifier 2 is wet-milled and then fed to a drying system designed as a spray drying tower 4, and from there back into the vortex mill 1. The wet ball mill 3 and the spray drying tower 4 thus form a coarse material processing unit 3, 4 for processing the coarse material fraction before it is fed back into the vortex mill 1.

[0023] A fluid line 3b leads from the outlet of the wet ball mill 3 to an upper inlet on the spray drying tower 4. The slurry, consisting of the wet-ground coarse material fraction, is conveyed from the wet ball mill 3 to the spray drying tower 4 via this line by means of a feed pump 3a or similar device. A downpipe 1b connects to the lower outlet of the spray drying tower 4 and leads into an inlet downpipe 1a at the inlet of the vortex mill 1. The input material, namely the broken glass, is also fed into the vortex mill 1 through this downpipe. The feed pump 3a, the conveying line 3b, and the downpipe 1b thus form a refeeding device 3a, 3b, 1b for feeding the processed, i.e., wet-ground and dried, coarse material fraction back into the vortex mill 1.

[0024] The drying of the wet-milled coarse material fraction in the spray drying tower 4 is achieved by means of a hot air stream introduced in the lower section of the spray drying tower 4, which flows upwards to an air outlet in the upper section of the spray drying tower 4. The slurry coming from the wet ball mill 3 is injected into this hot air stream via a nozzle arrangement provided at the upper inlet of the spray drying tower 4. As it falls against the hot air stream, it dries towards the lower outlet of the spray drying tower 4.The hot air stream loaded with water vapor is then fed via a vapor line 9c connected to the air outlet of the spray drying tower 4 to a vapor filter 11, which is extracted by means of an extraction blower 12, whereby the residual glass particles separated in the vapor filter can optionally also be returned to the vortex mill 1 via a rotary valve on the underside and a connecting line connected to the downpipe 1b.

[0025] To generate the hot air or gas flow supplied to the spray drying tower 4, a hot gas flow generation device designated as 8 is provided, which includes a wood powder burner 9, which is supplied with wood powder by a further fine mill 10, which the further fine mill 10, designed as a vortex mill, grinds from wood waste, plywood or the like.

[0026] A hot gas line 9a serves as the hot gas inlet device 9a for introducing the hot gas stream generated at the wood burner 9 into the spray drying tower 4 and the dryer 6. This line leads from the wood burner 9 to the air inlet of the spray drying tower 4 and has a branch that connects to the dryer 6. On the air outlet side, the dryer 6 is connected to the vapor filter 11 via a further vapor line 9b.

[0027] Variations and modifications of the embodiment shown are possible without leaving the scope of the invention.

[0028] For example, it would be conceivable to use the still warm air extracted at the vapor filter 11 by means of the extraction blower 12 to preheat the air supply to the wood burner.

Claims

1. Glass powder production process for producing glass powder with a grain size of < 40 µm, in particular < 15 µm to 25 µm, preferably < 20 µm, with the following steps: feeding a fine mill (1), namely a jet mill, impact disc mill, or preferably a whirlpool mill, with glass cullet and dry grinding the glass cullet in the fine mill (1), feeding the ground glass cullet into an air classifier (2) and air classifying the ground glass cullet into a fine material fraction and a coarse material fraction, wherein the separation limit of the air classifier (2) is predetermined to a grain size of < 40 µm, in particular a grain size of < 15 µm to 25 µm, preferably < 20 µm, discharging the coarse material fraction from the air classifier (2), removing the fine material fraction as the end product, the glass powder.

2. Glass powder production process according to claim 1, with the additional step of: refeeding the coarse material fraction into the fine mill (1).

3. Glass powder production process according to claim 2, with the additional step of: processing the coarse material fraction for refeeding into the fine mill (1).

4. Glass powder production process according to claim 3, wherein the processing of the coarse material fraction is carried out by wet grinding the coarse material fraction and subsequent drying of the wet-ground coarse material fraction before the coarse material fraction is fed back into the fine mill (1).

5. Glass powder production process according to claim 4, wherein the drying of the wet-ground coarse material fraction takes place in a spray-drying tower (4) in which the wet-ground coarse material fraction is injected into an air or gas stream coming from below in the upper region and then exits in the lower region.

6. Glass powder production process according to one of the preceding claims, wherein the glass cullet is washed and dried before being fed to the fine mill (1).

7. Glass powder production process according to claim 4, 5 or 6, wherein a hot gas stream is generated with which the wet-ground coarse material fraction and / or the washed glass cullet is dried.

8. Glass powder production process according to claim 7, wherein the hot gas stream is generated by means of a wood powder burner (9) which is preceded by a further fine mill (10), in particular a further eddy current mill for grinding wood waste into wood powder.

9. Glass powder production device for producing glass powder with a grain size of < 40 µm, in particular < 15 µm to 25 µm, preferably < 20 µm, with a fine mill (1) for dry grinding glass cullet, namely a jet mill, impact disc mill, or preferably a whirlwind mill, with an upstream glass cullet feed (7) for feeding the fine mill (1) with glass cullet, an air classifier (2) for classifying the ground glass cullet into a fine fraction and a coarse fraction, with a separation limit at a grain size of < 40 µm, in particular at a grain size of < 15 µm to 25 µm, preferably < 20 µm, a feed device (2a) arranged between the air classifier (2) and the fine mill (1) for feeding the glass cullet ground on the fine mill (1) into the air classifier (2), a coarse material discharge device (2c) for discharging the coarse material fraction from the air classifier (2), and a removal device (2b, 14, 15,16) for the extraction of the fine fraction as the final product, the glass powder.

10. Glass powder production device according to claim 9, with a refeed device (3a, 3b, 1b) for refeeding the coarse material fraction into the fine mill (1).

11. Glass powder production device according to claim 10, with a coarse material processing device (3, 4) for processing the coarse material fraction for refeeding into the fine mill (1).

12. Glass powder production device according to claim 11, wherein the coarse material processing device (3, 4) comprises a wet mill (3), in particular a wet ball mill, for wet grinding the coarse material fraction, and a downstream drying system (4) for drying the wet-ground coarse material fraction before refeeding it into the fine mill (1).

13. Glass powder production device according to claim 12, wherein the drying plant comprises a spray drying tower (4) with a nozzle arrangement for injecting the wet-ground coarse material fraction in the upper region, an air inlet arrangement in the lower region so that the wet-ground coarse material fraction is injected into the air or gas stream coming from below, and with a dry material outlet in the lower region for the dried, wet-ground coarse material fraction.

14. Glass powder production device according to one of claims 9 to 13, with a washing system (5) for washing the glass cullet and a dryer (6) for drying the washed glass cullet before feeding the fine mill (1) with the washed and dried glass cullet.

15. Glass powder production device according to claim 13 or 14, which comprises a hot gas stream generation device (8) which generates a hot gas stream, and a hot gas introduction device (9a) for introducing the hot gas stream into the spray drying tower (4) and / or the dryer (6), wherein the hot gas stream generation device (8) preferably comprises a wood powder burner (9) which is preceded by a further fine mill (10), in particular a whirlwind mill for grinding wood waste into wood powder.

Images