METHOD FOR THE PRODUCE OF FINEST PARTICLES AND BLASTING MILL FOR THIS PUMP, AS WELL AS AIR SISTENS AND OPERATING METHOD THEREOF THEREOF

Description

[0001] The present invention relates to a method for producing finest particles by means of a jet mill with an integrated dynamic air classifier and a jet mill with such an air classifier, as well as an air classifier and an operating method thereof according to the preambles of the independent claims.

[0002] The material to be classified or ground consists of coarser and finer particles carried in an airflow, forming the product stream that is introduced into the housing of an air classifier in the jet mill. The product stream flows radially into a classifier wheel of the air classifier. In the classifier wheel, the coarser particles are separated from the airflow, and the airflow, containing the fine particles, exits the classifier wheel axially through an outlet pipe. The airflow containing the fine particles to be filtered out or produced can then be fed into a filter, where a fluid, such as air, and the fine particles are separated.

[0003] From DE 198 24 062 A1, such a jet mill is known, in whose grinding chamber at least one high-energy grinding jet of superheated steam with high flow energy is introduced, wherein the grinding chamber, in addition to the inlet device for the at least one grinding jet, has an inlet for the material to be ground and an outlet for the product, and wherein, in the area of ​​contact between the material to be ground and at least one grinding jet of superheated steam, the material to be ground and the material to be ground have at least approximately the same temperature. Further examples are disclosed in JP2002126560 and EP1080786.

[0004] Furthermore, a suitable air classifier, particularly for a jet mill, is known, for example, from EP 0 472 930 B1. This air classifier and its operating procedures are fundamentally very satisfactory.

[0005] The present invention therefore aims to further optimize a method for producing the finest particles using a jet mill and a jet mill with an integrated air classifier.

[0006] This objective is achieved with a method for producing finest particles according to claim 1 and a jet mill according to claim 9.

[0007] Accordingly, a generic method for producing the finest particles by means of a jet mill with an integrated dynamic air classifier, which includes a classifier wheel and a classifier wheel shaft as well as a classifier housing, wherein a classifier gap is formed between the classifier wheel and the classifier housing and a shaft passage is formed between the classifier wheel shaft and the classifier housing, characterized in that a gap flushing of the classifier gap and / or shaft passage with compressed gases of low energy content is carried out, and that grinding jet inlets, such as grinding nozzles or grinding nozzles contained therein, are provided which are supplied with energy-rich superheated steam.

[0008] The purge gas is intended to be used at a pressure of no more than approximately 0.4 bar, preferably no more than approximately 0.3 bar, and in particular no more than approximately 0.2 bar above the internal mill pressure. The internal mill pressure can be in the range of approximately 0.1 bar to 0.5 bar.

[0009] Furthermore, it is preferred if the purge gas is used at a temperature of approximately 80 °C to approximately 120 °C, in particular approximately 100 °C, and / or if low-energy compressed air, in particular at approximately 0.3 bar to approximately 0.4 bar, is used as the purge gas.

[0010] Preferably, the superheated steam has a pressure of at least approximately 12 bar, preferably at least approximately 25 bar and further preferably at least approximately 40 bar, and / or the temperature of the superheated steam is selected so that it is dry at the end of the process.

[0011] In a jet mill according to the invention with an integrated dynamic air classifier for producing the finest particles, the air classifier comprising a classifier wheel and a classifier wheel shaft as well as a classifier housing, wherein a classifier gap is formed between the classifier wheel and the classifier housing and a shaft passage is formed between the classifier wheel shaft and the classifier housing, flushing devices are further provided by means of which a gap flushing of the classifier gap and / or shaft passage with compressed gases of low energy content is carried out, and it is further provided that grinding jet inlets, such as grinding nozzles or grinding nozzles contained therein, are provided which are supplied with energy-rich superheated steam.

[0012] The purging devices are designed to introduce purging gas at a pressure of no more than approximately 0.4 bar, preferably no more than approximately 0.3 bar, and in particular no more than approximately 0.2 bar above the internal mill pressure. It is even more preferred if the internal mill pressure is at least approximately in the range of 0.1 bar to 0.5 bar.

[0013] Other further developments are characterized by the fact that the purge gas is used at a temperature of approximately 80 °C to approximately 120 °C, in particular approximately 100 °C, and / or that low-energy compressed air, in particular at approximately 0.3 bar to approximately 0.4 bar, is used as the purge gas.

[0014] Another preferred embodiment of the jet mill consists in the fact that the superheated steam has a pressure of at least approximately 12 bar, preferably at least approximately 25 bar and further preferably at least approximately 40 bar, and / or that the temperature of the superheated steam is selected so that it is dry at the end of the process, and / or that a source, such as a tank for the superheated steam, is included or assigned as an operating resource.

[0015] The jet mill can also be further developed by being a fluidized bed jet mill or a dense bed jet mill.

[0016] Another preferred embodiment consists in the provision of grinding nozzles connected to a steam supply line, such as piping systems, which is equipped with expansion joints. It is further preferable that the steam supply line is connected to a steam source.

[0017] Furthermore, the jet mill may be designed to have the smallest possible surface area.

[0018] Another preferred embodiment consists in the screening rotor or screening wheel having an increasing clear height with decreasing radius. It is further preferred if the flow area through the screening rotor or wheel is at least approximately constant.

[0019] It may also be preferable to provide that the classifier rotor or classifier wheel has a replaceable, co-rotating immersion tube, and / or that a fines discharge chamber is provided which has a cross-sectional expansion in the direction of flow.

[0020] It is further preferred if the flow paths are at least largely free of protrusions, and / or if the components of the jet mill are designed to prevent mass accumulation. In other preferred embodiments, the components of the jet mill are designed to prevent condensation and / or include devices for preventing condensation.

[0021] Furthermore, the jet mill according to the invention can advantageously include, in particular, an air classifier which incorporates individual features or combinations of features of the air classifier according to EP 0 472 930 B1. In particular, the air classifier can include means for reducing the circumferential components of the flow according to EP 0 472 930 B1. It can be provided, in particular, that an outlet nozzle associated with the classifier wheel of the air classifier, which is designed as a dip tube, has a cross-sectional expansion in the flow direction, preferably rounded to prevent vortex formation.

[0022] The invention further provides a dynamic air classifier comprising a classifier wheel, a classifier shaft, and a classifier housing, wherein a classifier gap is formed between the classifier wheel and the classifier housing, and a shaft passage is formed between the classifier shaft and the classifier housing. The invention also provides purging devices by means of which a gap purging of the classifier gap and / or shaft passage with compressed gases of low energy content is carried out. The purging devices are designed to apply the purging gas at a pressure of no more than approximately 0.4 bar, preferably no more than approximately 0.3 bar, and in particular no more than approximately 0.2 bar above the internal mill pressure. Alternatively or additionally, the internal mill pressure can be approximately in the range of 0.1 bar to 0.5 bar.

[0023] It is further preferred if the purge gas is used at a temperature of approximately 80 °C to approximately 120 °C, in particular approximately 100 °C, and / or if low-energy compressed air, in particular at approximately 0.3 bar to approximately 0.4 bar, is used as the purge gas.

[0024] Another preferred embodiment consists in the provision of grinding nozzles that are supplied with high-energy superheated steam. It is further preferable that the superheated steam has a pressure of at least approximately 12 bar, preferably at least approximately 25 bar, and more preferably at least approximately 40 bar, and / or that the temperature of the superheated steam is selected such that it is dry at the end of the process.

[0025] Furthermore, it is preferred that a source, such as a tank, for the superheated steam as an operating medium is included or assigned.

[0026] Another preferred embodiment includes a screening rotor or screening wheel with an increasing clear height as the radius decreases. In particular, the flow area through the screening rotor or wheel can be at least approximately constant.

[0027] It may also be preferable to include a classifier rotor or classifier wheel with a replaceable, co-rotating immersion tube, and / or a fines discharge chamber with a cross-sectional expansion in the flow direction. Alternatively or additionally, it may be provided that the flow paths are at least largely free of protrusions.

[0028] In an operating method for an air classifier with a classifier rotor or wheel, a classifier wheel shaft and a classifier housing, wherein a classifier gap is formed between the classifier wheel and the classifier housing and a shaft passage is formed between the classifier wheel shaft and the classifier housing, it is provided according to the invention that a gap flushing of the classifier gap and / or shaft passage with compressed gases of low energy content is carried out, and that grinding jet inlets, such as in particular grinding nozzles or grinding nozzles contained therein, are provided which are supplied with energy-rich superheated steam.

[0029] This can be further developed by using the purge gas at a pressure of no more than approximately 0.4 bar, preferably no more than approximately 0.3 bar, and in particular no more than approximately 0.2 bar above the internal mill pressure. It is preferably provided that the internal mill pressure is at least approximately in the range of 0.1 bar to 0.5 bar.

[0030] Another preferred variant involves using a purge gas with a temperature of approximately 80 °C to approximately 120 °C, particularly approximately 100 °C. Alternatively or additionally, low-energy compressed air, particularly at a pressure of approximately 0.3 bar to approximately 0.4 bar, may be used as the purge gas.

[0031] Furthermore, the superheated steam can have a pressure of at least approximately 12 bar, preferably at least approximately 25 bar and more preferably at least approximately 40 bar, and / or the temperature of the superheated steam can be selected so that it is dry at the end of the process.

[0032] In general and in specific embodiments, the process is carried out in a grinding system (grinding apparatus), preferably in a grinding system comprising a jet mill, and particularly preferably comprising a counter-jet mill. For this purpose, the feed material to be ground is accelerated in expanding gas jets at high velocity and comminuted by particle-particle collisions. Fluidized bed counter-jet mills, dense bed jet mills, or spiral jet mills are particularly preferred as jet mills. In the case of the particularly preferred fluidized bed counter-jet mill, two or more grinding jet inlets, preferably in the form of grinding nozzles, are located in the lower third of the grinding chamber, preferably in a horizontal plane. The grinding jet inlets are particularly preferably arranged around the circumference of the preferably round mill container such that the grinding jets all converge at a single point inside the mill container.Preferably, the grinding jet inlets are evenly distributed around the circumference of the grinding container. In the case of three grinding jet inlets, the distance between them would thus be 120°.

[0033] In a particular embodiment of the method according to the invention, the grinding system (grinding apparatus) comprises a classifier, preferably a dynamic classifier, particularly preferably a dynamic paddle wheel classifier or a classifier according to the Fig. 2 and 3 . This dynamic air classifier comprises a classifier wheel and a classifier wheel shaft as well as a classifier housing, wherein a classifier gap is formed between the classifier wheel and the classifier housing and a shaft passage is formed between the classifier wheel shaft and the classifier housing, and is characterized in that a gap flushing of the classifier gap and / or shaft passage with compressed gases of low energy takes place.

[0034] By using a classifier in combination with the jet mill operated under the conditions according to the invention, the upper particle size is limited, whereby the product particles rising together with the relaxed gas jets from the center of the grinding chamber are guided through the classifier, and subsequently the product that has a sufficiently fineness is discharged from the classifier and from the mill. Particles that are too coarse are returned to the grinding zone and subjected to further comminution.

[0035] In the grinding system, a classifier can be installed as a separate unit downstream of the mill, but an integrated classifier is preferred.

[0036] Another possible feature of the method according to the invention is that a heating phase precedes the actual grinding step. This heating phase ensures that the grinding chamber, and preferably all essential components of the mill and / or grinding system on which water and / or steam could condense, are heated to a temperature above the dew point of the steam. In principle, any heating method can be used. However, it is preferably achieved by passing hot gas through the mill and / or the entire grinding system so that the temperature of the gas at the mill outlet is higher than the dew point of the steam. Particular care is taken to ensure that the hot gas sufficiently heats all essential components of the mill and / or the entire grinding system that come into contact with the steam.

[0037] In principle, any gas and / or gas mixture can be used as the heating gas; however, hot air and / or combustion gases and / or inert gases are preferred. The temperature of the hot gas is preferably above the dew point of water vapor. The hot gas can, in principle, be introduced into the grinding chamber at any point. Preferably, inlets or nozzles are provided in the grinding chamber for this purpose. These inlets or nozzles can be the same inlets or nozzles through which the grinding jets are directed during the grinding phase (grinding nozzles). However, it is also possible for separate inlets or nozzles (heating nozzles) to be provided in the grinding chamber through which the hot gas and / or gas mixture can be introduced. In a preferred embodiment, the heating gas or heating gas mixture is introduced through at least two, preferably three or more, inlets or nozzles arranged in a single plane.Nozzles are inserted and arranged around the circumference of the preferably round mill container such that the jets all converge at a single point inside the mill container. Preferably, the inlets or nozzles are evenly distributed around the circumference of the mill container.

[0038] During grinding, a gas and / or steam, preferably water vapor and / or a gas / water vapor mixture, is expanded through the grinding jet inlets, preferably in the form of grinding nozzles. This operating medium typically has a significantly higher speed of sound than air (343 m / s), preferably at least 450 m / s. Advantageously, the operating medium comprises water vapor and / or hydrogen gas and / or argon and / or helium. Superheated water vapor is particularly preferred. To achieve a very fine grind, it has proven particularly advantageous for the operating medium to be expanded into the mill at a pressure of 15 to 250 bar, particularly preferably 20 to 150 bar, most preferably 30 to 70 bar, and most preferably 40 to 65 bar. The operating equipment also preferably has a temperature of 200 to 800 °C, particularly preferably 250 to 600 °C and particularly 300 to 400 °C.

[0039] Further preferred and / or advantageous embodiments of the invention will become apparent from the claims and their combinations as well as from the entire application documents presented here.

[0040] The invention is explained in more detail below by way of example embodiments with reference to the drawings, in which Fig. 1 shows a diagrammatic embodiment of a jet mill in a partially cutaway schematic drawing, Fig. 2 shows an embodiment of an air classifier of a jet mill in a vertical arrangement and as a schematic mid-longitudinal section, wherein the discharge pipe for the mixture of classifying air and solid particles is assigned to the classifier wheel, and Fig. 3 shows a classifier wheel of an air classifier in a schematic representation and as a vertical section.

[0041] The invention is explained in more detail by way of example using the embodiments and applications described below and illustrated in the drawings; that is, it is not limited to these embodiments and applications or to the respective combinations of features within individual embodiments and applications. Method and device features can also be derived analogously from device and method descriptions.

[0042] Individual features that are specified and / or illustrated in connection with specific embodiments are not limited to these embodiments or their combination with the other features of these embodiments, but can be combined, within the limits of what is technically possible, with any other variants, even if they are not specifically addressed in the present documentation.

[0043] Identical reference numerals in the individual figures and illustrations of the drawings denote identical or similar components, or components with the same or similar effects. The representations in the drawing also clearly indicate features that are not marked with reference numerals, regardless of whether such features are described subsequently or not. Conversely, features included in this description but not visible or depicted in the drawing are readily understandable to a person skilled in the art.

[0044] In the Fig. 1Figure 1 shows an embodiment of a jet mill 1 with a cylindrical housing 2 enclosing a grinding chamber 3, a material feed 4 located approximately halfway up the grinding chamber 3, at least one jet inlet 5 in the lower region of the grinding chamber 3, and a product outlet 6 in the upper region of the grinding chamber 3. An air classifier 7 with a rotatable classifying wheel 8 is arranged there, which classifies the material to be ground (not shown) in order to discharge only material below a certain particle size from the grinding chamber 3 through the product outlet 6 and to feed material with a particle size above the selected value to a further grinding process.

[0045] The classifier wheel 8 can be a classifier wheel commonly used in air classifiers, whose blades (see later, e.g., in connection with the Fig. 3) radially extending blade channels, at the outer ends of which the classifying air enters and carries particles of smaller grain size or mass to the central outlet and to the product outlet 6, while larger particles or particles of greater mass are rejected under the influence of centrifugal force. In particular, the air classifier 7 and / or at least its classifying wheel 8 are equipped with at least one design feature according to EP 0 472 930 B1.

[0046] Only one grinding jet inlet 5, e.g., consisting of a single, radially directed inlet opening or inlet nozzle 9, can be provided to impinge a single grinding jet 10 with high energy on the material particles entering the grinding jet 10 from the material feed 4, thus breaking the material particles into smaller subparticles. These subparticles are drawn in by the classifier wheel 8 and, provided they are of a sufficiently small size or mass, conveyed to the outside through the product outlet 6. However, a better effect is achieved with pairs of diametrically opposed grinding jet inlets 5, forming two colliding grinding jets 10. This results in more intensive particle fragmentation than is possible with only one grinding jet 10, especially when several pairs of grinding jets are generated.

[0047] Preferably, two or more grinding jet inlets, preferably grinding nozzles, in particular 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 grinding jet inlets, are used, which are located in the lower third of the preferably cylindrical housing of the grinding chamber. These grinding jet inlets are ideally arranged in a single plane and evenly distributed around the circumference of the grinding chamber, so that the grinding jets all converge at a single point inside the grinding chamber. It is further preferred that the inlets or nozzles are evenly distributed around the circumference of the grinding chamber. With three grinding jets, this would result in an angle of 120° between the respective inlets or nozzles. Generally speaking, the larger the grinding chamber, the more inlets or grinding nozzles are used.

[0048] In a preferred embodiment of the method according to the invention, the grinding chamber can, in addition to the grinding jet inlets, contain 5 heating openings, preferably in the form of heating nozzles, through which hot gas can be introduced into the mill during the heating phase. These nozzles or openings can be arranged – as previously described – in the same plane as the grinding openings or nozzles 5. One, but preferably also several, particularly preferably 2, 3, 4, 5, 6, 7 or 8 heating openings or nozzles can be included.

[0049] In a particularly preferred embodiment, the mill contains two heating nozzles or openings and three grinding nozzles or openings.

[0050] Furthermore, the processing temperature can be influenced, for example, by using an internal heating source 11 between the material feed 4 and the area of ​​the grinding jets 10, or a corresponding heating source 12 in the area outside the material feed 4, or by processing particles of an already warm material that enters the material feed 4 while avoiding heat loss, for which purpose a feed pipe 13 is surrounded by a temperature-insulating jacket 14. The heating source 11 or 12, if used, can essentially be any type and therefore be selected according to its intended use and market availability, so that further explanation is not necessary.

[0051] The temperature of the grinding jet or jets 10 is particularly relevant for the temperature, and the temperature of the material being ground should at least approximately correspond to this grinding jet temperature.

[0052] In the present embodiment, superheated steam is used to generate the grinding jets 10 introduced into the grinding chamber 3 through grinding jet inlets 5. It can be assumed that the heat content of the steam after the inlet nozzle 9 of the respective grinding jet inlet 5 is not significantly lower than before this inlet nozzle 9. Because the energy required for impact grinding is primarily intended to be available as flow energy, the pressure drop between the inlet 15 of the inlet nozzle 9 and its outlet 16 will be considerable (the pressure energy will be largely converted into flow energy), and the temperature drop will also be significant.In particular, this temperature drop should be compensated by the heating of the material being ground to such an extent that the material being ground and the grinding jet 10 have the same temperature in the area of ​​the center 17 of the grinding chamber 3 when at least two grinding jets 10 meet or a multiple of two grinding jets 10 meet.

[0053] For the design and implementation of the preparation of the grinding jet 10 from hot steam, in particular in the form of a closed system, reference is made to DE 198 24 062 A1.

[0054] For example, a closed system makes it possible to grind hot slag as grinding material with optimal efficiency.

[0055] In the illustration of the present embodiment of the jet mill 1, a reservoir or generating device 18, such as a tank 18a, is shown as a representative of any supply of an operating resource or operating medium B, from which the operating resource or operating medium B is conveyed via piping devices 19 to the grinding jet inlet 5 or grinding jet inlets 5 to form the grinding jet 10 or grinding jets 10.

[0056] When using hot steam as operating medium B, it is advantageous to provide piping devices 19 equipped with expansion loops (not shown), which can then also be referred to as steam supply lines, to the inlet or grinding nozzles 9, preferably when the steam supply line is connected to a steam source as a reservoir or generating device 18.

[0057] Another advantageous aspect of using steam as operating medium B is to provide the jet mill 1 with the smallest possible surface area, or in other words, to optimize the jet mill 1 with regard to minimizing its surface area. Especially in connection with steam as operating medium B, it is particularly advantageous to avoid heat exchange or heat loss, and thus energy loss, in the system. The further alternative or additional design measure also serves this purpose, namely to design or optimize the components of the jet mill 1 to avoid mass accumulation. This can be achieved, for example, by using the thinnest possible flanges in and for connecting the piping devices 19.

[0058] Energy loss and other flow-related impairments can be further reduced or avoided if the components of the jet mill 1 are designed or optimized to prevent condensation. For this purpose, special condensation prevention devices (not shown) can even be included. Furthermore, it is advantageous if the flow paths are largely free of protrusions or optimized accordingly. In other words, these design variants, individually or in any combination, implement the principle of avoiding as much or everything as possible that can cool down and thus where condensation can occur.

[0059] Furthermore, it is advantageous and therefore preferred if the screening rotor has a clear height that increases with decreasing radius, i.e., towards its axis, whereby in particular the flow area through the screening rotor is at least approximately constant. Additionally or alternatively, a fines discharge chamber can be provided, which has a cross-sectional expansion in the flow direction.

[0060] A particularly preferred embodiment of the jet mill 1 consists in the fact that the classifier rotor 8 has an interchangeable, co-rotating immersion tube 20.

[0061] For the sole purpose of clarification and to deepen the overall understanding, the particles to be produced from the material preferably being processed will be discussed below. These include, for example, amorphous SiO₂ or other amorphous chemical products that are comminuted using a jet mill. Other materials include silicic acids, silica gels, or silicates.

[0062] In general, the method according to the invention and the devices to be used and designed according to the invention relate to powdered amorphous or crystalline solids with a very small mean particle size and a narrow particle size distribution, a method for their production, and their use.

[0063] Fine-particle, amorphous silica and silicates have been produced industrially for decades. It is known that the achievable particle diameter is proportional to the square root of the reciprocal of the particle impact velocity. The impact velocity, in turn, is determined by the jet velocity of the expanding gas jets of the respective grinding medium from the nozzles used. For this reason, superheated steam can be used preferentially to generate very small particle sizes, since the acceleration potential of steam is approximately 50% greater than that of air. However, the use of steam has the disadvantage that condensation can occur throughout the entire grinding system, particularly during mill start-up, which generally results in the formation of agglomerates and crusts during the grinding process.

[0064] The mean particle diameters d 50 achieved when using conventional jet mills for grinding amorphous silica, silicates or silica gels were therefore previously significantly above 1 µ m.

[0065] Furthermore, after treatment with previous methods and devices according to the state of the art, the particles exhibit a broad particle size distribution with particle diameters, for example, from 0.1 to 5.5 mm. µ m and a proportion of particles > 2 µ m of 15 to 20%. A high proportion of large particles, i.e., > 2 µ m, is disadvantageous for applications in coating systems, as it prevents the production of thin layers with a smooth surface. In contrast, with the method according to the invention and the corresponding devices, it is possible to reduce solids to an average particle size d 50 of less than 1.5 µto grind and also to achieve a very narrow particle size distribution. In particular, amorphous or crystalline solids with a mean particle size d 50 < 1.5 are thus suitable. µ m and / or a d90 value < 2 µ m and / or a d99 value < 2 µ m.

[0066] Amorphous solids can be gels or have other structures, such as particles from agglomerates and / or aggregates. Preferably, they are solids containing or consisting of at least one metal and / or at least one metal oxide, particularly amorphous oxides of metals from groups 3 and 4 of the periodic table. This applies to both gels and other amorphous solids, especially those containing particles from agglomerates and / or aggregates. Precipitated silicas, pyrogenic silicas, silicates, and silica gels are particularly preferred, with silica gels including hydrogels, aerogels, and xerogels. Such amorphous solids generally have a mean particle size d50 < 1.5 µ m and / or a d90 value < 2 µ m and / or a d99 value < 2 µ m are used, for example, in surface coating systems.

[0067] The process according to the invention has the advantage over prior art methods, particularly wet milling, that it is a dry milling process which directly yields powdered products with a very small average particle size, which can also advantageously exhibit high porosity. The problem of reagglomeration during drying is eliminated, since no drying step is required after milling. A further advantage of the process according to the invention in one of its preferred embodiments is that milling can be carried out simultaneously with drying, so that, for example, a filter cake can be processed directly. This eliminates an additional drying step and simultaneously increases the space-time yield.In its preferred embodiments, the method according to the invention also has the advantage that no or only very small amounts of condensate form in the grinding system, particularly in the mill, during startup. Dried gas can be used during cooling. This prevents condensate from forming in the grinding system during cooling and significantly shortens the cooling phase. Effective machine operating times can thus be increased. Finally, because little or no condensate forms in the grinding system during startup, it prevents already dried material from becoming wet again, thereby preventing the formation of agglomerates and crusts during the grinding process.

[0068] The amorphous powdered solids produced by the process according to the invention exhibit particularly good properties for use in surface coating systems, e.g., as rheology aids, in paper coatings, and in paints or varnishes, due to their very specific and unique mean particle sizes and particle size distributions. The products obtained in this way allow, for example, the production of very thin coatings due to their very small mean particle size and, in particular, their low d90 and d99 values.

[0069] The terms powder and powdered solids are used synonymously within the scope of the present invention and each refers to finely granulated, solid substances consisting of small, dry particles, where "dry particles" means that the particles are externally dry. While these particles generally contain water, this water is so tightly bound to the particles or within their capillaries that it is not released at room temperature and atmospheric pressure. In other words, these are particulate substances perceptible by optical methods and not suspensions or dispersions. Furthermore, these can be either surface-modified or non-surface-modified solids. Surface modification is preferably achieved with carbon-containing coating agents and can be carried out either before or after milling.

[0070] The solids according to the invention can be in the form of a gel or as particle-containing agglomerates and / or aggregates. A gel means that the solids are composed of a stable, three-dimensional, preferably homogeneous network of primary particles. Examples include silica gels.

[0071] Particles containing aggregates and / or agglomerates as defined in the present invention do not have a three-dimensional network, or at least not a network of primary particles extending over the entire particle. Instead, they exhibit aggregates and agglomerates of primary particles. Examples include precipitated silicas and pyrogenic silicas.

[0072] A description of the structural difference between silica gels and precipitated SiO2 can be found in Iler RK, "The Chemistry of Silica", 1979, ISBN 0-471-02404-X, Chapter 5, page 462, and therein in Figure 3.25. The contents of this printed document are hereby expressly included in the description of this invention.

[0073] With the technology according to the invention, any particles, in particular amorphous particles, can be ground in such a way that powdered solids with a mean particle size d 50 < 1.5 are obtained. µ m and / or a d90 value < 2 µ m and / or a d99 value < 2 µ These particle sizes and particle size distributions can be obtained. In particular, it is possible to achieve these particle sizes or particle size distributions via dry milling.

[0074] Such amorphous solids, in particular, are characterized by having a mean particle size (TEM) d 50 < 1.5 µ m, preferably d 50 < 1 µ m, especially preferably d 50 from 0.01 to 1 µ m, especially preferred d 50 from 0.05 to 0.9 µ m, in particular preferably d 50 from 0.05 to 0.8 µ m, especially preferred from 0.05 to 0.5µ m and especially preferred from 0.08 to 0.25 µ m, and / or a d90 value < 2 µ m, preferably d 90 < 1.8 µ m, especially preferably d 90 from 0.1 to 1.5 µ m, especially preferred d90 from 0.1 to 1.0 µ m and especially preferably d 90 from 0.1 to 0.5 µ m, and / or a d99 value < 2 µ m, preferably d 99 < 1.8 µ m, especially preferred d 99 < 1.5 µ m, especially preferred d 99 from 0.1 to 1.0 µ m and especially preferably d 99 from 0.25 to 1.0 µ exhibiting m. All previously mentioned particle sizes refer to particle size determination using TEM analysis and image evaluation.

[0075] These solids can be gels or other types of amorphous or crystalline solids. Preferably, they are solids containing or consisting of at least one metal and / or metal oxide, in particular amorphous oxides of metals from groups 3 and 4 of the periodic table. This applies to both gels and amorphous or crystalline solids with other structures. Precipitated silicas, pyrogenic silicas, silicates, and silica gels are particularly preferred, with silica gels including hydrogels, aerogels, and xerogels.

[0076] The first specific embodiments of the solids concerned are particulate solids containing aggregates and / or agglomerates, in particular precipitated silicas and / or pyrogenic silicas and / or silicates and / or mixtures thereof, with a mean particle size d 50 < 1.5 µ m, preferably d 50 < 1µ m, especially preferably d 50 from 0.01 to 1 µ m, especially preferred d 50 from 0.05 to 0.9 µ m, in particular preferably d 50 from 0.05 to 0.8 µ m, especially preferred from 0.05 to 0.5 µ m and especially preferred from 0.1 to 0.25 µ m, and / or a d90 value < 2 µ m, preferably d 90 < 1.8 µ m, especially preferably d 90 from 0.1 to 1.5 µ m, especially preferred d 90 from 0.1 to 1.0 µ m, in particular preferably d 90 from 0.1 to 0.5 µ m and especially preferred d 90 from 0.2 to 0.4 µ m, and / or a d99 value < 2 µ m, preferably d 99 < 1.8 µ m, especially preferred d 99 < 1.5 µ m, especially preferred d 99 from 0.1 to 1.0 µ m, in particular preferably d 99 from 0.25 to 1.0 µm and especially preferably d 99 from 0.25 to 0.8. Precipitated silicas are particularly preferred, as they are significantly less expensive than pyrogenic silicas. All particle sizes mentioned above refer to particle size determination by TEM (transmission electron microscopy) analysis and image evaluation.

[0077] In a second special embodiment, the solids are gels, preferably silica gels, in particular xerogels or aerogels, with a mean particle size d 50 < 1.5 µ m, preferably d 50 < 1 µ m, especially preferably d 50 from 0.01 to 1 µ m, especially preferred d 50 from 0.05 to 0.9 µ m, in particular preferably d 50 from 0.05 to 0.8 µ m, especially preferred from 0.05 to 0.5 µ m and especially preferred from 0.1 to 0.25 µ m, and / or a d90 value < 2 µ m, preferably d 90 0.05 to 1.8µ m, especially preferably d 90 from 0.1 to 1.5 µ m, especially preferred d 90 from 0.1 to 1.0 µ m, in particular preferably d 90 from 0.1 to 0.5 µ m and especially preferred d 90 from 0.2 to 0.4 µ m, and / or a d99 value < 2 µ m, preferably d 99 < 1.8 µ m, especially preferred d 99 0.05 to 1.5 µ m, especially preferred d 99 from 0.1 to 1.0 µ m, in particular preferably d 99 from 0.25 to 1.0 µ m and especially preferably d 99 from 0.25 to 0.8. All previously mentioned particle sizes refer to particle size determination by means of TEM analysis and image evaluation.

[0078] In a further, even more specific embodiment, the xerogel is a narrow-pored material which, in addition to the d50, d90, and d99 values ​​already described in the preceding embodiments, has a pore volume of 0.2 to 0.7 ml / g, preferably 0.3 to 0.4 ml / g. In a further alternative embodiment, the xerogel has a pore volume of 0.8 to 1.4 ml / g, preferably 0.9 to 1.2 ml / g, in addition to the d50, d90, and d99 values ​​already described in connection with the second type of embodiment. Another alternative within the second group of embodiments described above is a xerogel which, in addition to the d 50, d 90 and d 99 values ​​already given, also has a pore volume of 1.5 to 2.1 ml / g, preferably 1.7 to 1.9 ml / g.

[0079] The following are, with reference to the Fig. 2 and 3Further details and variants of exemplary designs of the jet mill 1 and its components are explained.

[0080] The jet mill 1 contains, as shown in the schematic diagram in the Fig. 2 As can be seen, an integrated air classifier 7 is used, which, for example, in the case of designs of the jet mill 1 as a fluidized bed jet mill or as a dense bed jet mill, is a dynamic air classifier 7 that is advantageously arranged in the center of the grinding chamber 3 of the jet mill 1. The desired fineness of the ground material can be influenced depending on the grinding gas volume flow rate and the classifier speed.

[0081] At the air classifier 7 of the jet mill 1 according to the Fig. 2The entire vertical air classifier 7 is enclosed by a classifier housing 21, which essentially consists of the upper housing part 22 and the lower housing part 23. The upper housing part 22 and the lower housing part 23 are each provided with an outwardly directed circumferential flange 24 and 25, respectively, at their upper and lower edges. In the installed or operating state of the air classifier 8, the two circumferential flanges 24 and 25 are in contact with each other and are fixed against each other by suitable means. Suitable fixing means include, for example, screw connections (not shown). Clamps (not shown) or similar fasteners can also be used as releasable fastening means.

[0082] At virtually any point on the flange circumference, both circumferential flanges 24 and 25 are connected to each other by a hinge 26 such that, after the flange connections are released, the upper housing part 22 can be pivoted upwards relative to the lower housing part 23 in the direction of arrow 27, allowing access to the upper housing part 22 from below and the lower housing part 23 from above. The lower housing part 23 itself is designed in two parts and essentially consists of the cylindrical inspection chamber housing 28 with the circumferential flange 25 at its upper open end and a discharge cone 29 that tapers conically downwards. The discharge cone 29 and the viewing chamber housing 28 are located at the upper and lower ends respectively with flanges 30, 31 on top of each other, and the two flanges 30, 31 of discharge cone 29 and viewing chamber housing 28 are connected to each other by detachable fastening means (not shown), as are the circumferential flanges 24, 25.The classifier housing 21 assembled in this way is suspended in or on support arms 28a, several of which are distributed as evenly spaced as possible around the circumference of the classifier or compressor housing 21 of the air classifier 7 of the jet mill 1 and engage the cylindrical classifier chamber housing 28.

[0083] A key component of the housing internals of the air classifier 7 is the classifier wheel 8, comprising an upper cover plate 32, a lower downstream cover plate 33 axially spaced from it, and blades 34 with a suitable contour arranged between the outer edges of the two cover plates 32 and 33. These blades are rigidly connected to the cover plates and evenly distributed around the circumference of the classifier wheel 8. In this air classifier 7, the drive of the classifier wheel 8 is effected via the upper cover plate 32, while the lower cover plate 33 is the downstream cover plate. The bearing of the classifier wheel 8 includes a suitably positively driven classifier wheel shaft 35, the upper end of which extends out of the classifier housing 21 and, at its lower end, supports the classifier wheel 8 in a cantilevered bearing within the classifier housing 21, preventing rotation.The classifier wheel shaft 35 exits the classifier housing 21 via a pair of machined plates 36, 37. These plates close off the classifier housing 21 at the upper end of a truncated conical housing end section 38, guide the classifier wheel shaft 35, and seal this shaft passage without impeding the rotational movement of the classifier wheel shaft 35. Advantageously, the upper plate 36 can be fixedly connected to the classifier wheel shaft 35 as a flange and rotatably supported on the lower plate 37, which in turn is connected to a housing end section 38, by means of rotary bearings 35a. The underside of the downstream cover plate 33 lies in the common plane between the circumferential flanges 24 and 25, so that the classifier wheel 8 is entirely located within the hinged upper housing section 22.In the area of ​​the conical housing end section 38, the housing upper part 22 also has a tubular product feed nozzle 39 for the grinding material feed 4, the longitudinal axis of which runs parallel to the axis of rotation 40 of the classifier wheel 8 and its drive or classifier wheel shaft 35 and which is arranged radially outside the housing upper part 22 as far as possible from this axis of rotation 40 of the classifier wheel 8 and its drive or classifier wheel shaft 35.

[0084] Furthermore, the integrated dynamic air classifier 7 of the jet mill 1 includes a classifier wheel 8 and a classifier wheel shaft 35, as well as a classifier housing 21, as already explained. A classifier gap 8a is defined between the classifier wheel 8 and the classifier housing 21, and a shaft passage 35b is formed between the classifier wheel shaft 35 and the classifier housing 21 (see [reference]). Fig. 2 and 3In particular, starting from a jet mill 1 equipped with such an air classifier 7, the embodiments described herein being intended only as examples and not as limiting, a process for producing ultrafine particles is carried out with this jet mill 1 with an integrated dynamic air classifier 7. The innovation compared to conventional jet mills lies in the fact that the classifier gap 8a and / or shaft passage 35b are flushed with compressed gases of low energy content. The special feature of this design is precisely the combination with the fact that grinding jet inlets 5, such as grinding nozzles or grinding nozzles contained therein, are provided with high-energy superheated steam. Thus, high-energy and low-energy media are used simultaneously.

[0085] The classifier housing 21 accommodates the tubular outlet nozzle 20, which is arranged axially concurrently with the classifier wheel 8. The upper end of the outlet nozzle is located just below the downstream cover plate 33 of the classifier wheel 8, but is not connected to it. An outlet chamber 41, also tubular, is attached axially to the lower end of the tubular outlet nozzle 20. However, the diameter of the outlet chamber 41 is significantly larger than that of the outlet nozzle 20 and, in the present embodiment, at least twice its diameter. Thus, there is a distinct change in diameter at the transition between the outlet nozzle 20 and the outlet chamber 41. The outlet nozzle 20 is inserted into an upper cover plate 42 of the outlet chamber 41. The outlet chamber 41 is closed at the bottom by a removable cover 43.The assembly consisting of outlet nozzle 20 and outlet chamber 41 is held in several support arms 44, which are evenly distributed around the circumference of the assembly in a star shape, are firmly connected to the assembly with their inner ends in the area of ​​the outlet nozzle 20 and are attached to the classifier housing 21 with their outer ends.

[0086] The outlet nozzle 20 is surrounded by a conical ring housing 45, the lower, larger outer diameter of which corresponds at least approximately to the diameter of the outlet chamber 41 and the upper, smaller outer diameter of which corresponds at least approximately to the diameter of the sight wheel 8. The support arms 44 terminate at the conical wall of the ring housing 45 and are firmly connected to this wall, which in turn is part of the assembly consisting of the outlet nozzle 20 and the outlet chamber 41.

[0087] The support arms 44 and the ring housing 45 are components of a purge air system (not shown), wherein the purge air prevents the ingress of material from the interior of the classifier housing 21 into the gap between the classifier wheel 8, or more precisely its lower cover plate 3, and the outlet nozzle 20. To allow this purge air to enter the ring housing 45 and from there into the gap to be kept clear, the support arms 44 are designed as tubes, with their outer end sections passing through the wall of the classifier housing 21 and connected via an intake filter 46 to a purge air source (not shown). The ring housing 45 is closed at the top by a perforated plate 47, and the gap itself can be adjusted by an axially adjustable ring disc in the area between the perforated plate 47 and the lower cover plate 33 of the classifier wheel 8.

[0088] The outlet from the discharge chamber 41 is formed by a fines discharge pipe 48, which is led into the classifier housing 21 from the outside and connected to the discharge chamber 41 in a tangential arrangement. The fines discharge pipe 48 is part of the product outlet 6. A deflector cone 49 serves to cover the opening of the fines discharge pipe 48 to the discharge chamber 41.

[0089] At the lower end of the conical housing end section 38, a screening air inlet spiral 50 and a coarse material discharge 51 are arranged horizontally. The direction of rotation of the screening air inlet spiral 50 is opposite to the direction of rotation of the screening wheel 8. The coarse material discharge 51 is detachably attached to the housing end section 38, with a flange 52 being attached to the lower end of the housing end section 38 and a flange 53 to the upper end of the coarse material discharge 51. Both flanges 52 and 53 are detachably connected to each other by known means when the air classifier 7 is ready for operation.

[0090] The dispersion zone to be laid out is designated 54. Flanges machined (chamfered) on the inner edge for clean flow guidance and easy lining are designated 55.

[0091] Finally, a replaceable protective tube 56 is attached to the inner wall of the outlet nozzle 20 as a wear part, and a corresponding replaceable protective tube 57 can be attached to the inner wall of the outlet chamber 41.

[0092] At the start of operation of the air classifier 7 in the illustrated operating state, classifying air is introduced into the air classifier 7 via the classifying air inlet spiral 50 under a pressure gradient and at an appropriately selected inlet velocity. As a result of the introduction of the classifying air via a spiral, particularly in conjunction with the conicity of the housing end section 38, the classifying air rises spirally upwards into the area of ​​the classifier wheel 8. Simultaneously, the "product" consisting of solid particles of varying mass is fed into the classifier housing 21 via the product feed nozzle 39. From this product, the coarse material, i.e., the particle fraction with greater mass, flows against the classifying air into the coarse material discharge area 51 and is made available for further processing. The fine material, i.e.,The particle fraction with lower mass is mixed with the classifying air, passes radially from the outside in through the classifying wheel 8 into the outlet nozzle 20, into the outlet chamber 41, and finally via a fines outlet pipe 48 into a fines outlet 58, and from there into a filter where the operating medium, in the form of a fluid such as air, and the fines are separated. Larger fine particles are radially ejected from the classifying wheel 8 and mixed with the coarse material to exit the classifier housing 21 with the coarse material or to circulate within the classifier housing 21 until they have become fines of such a particle size that they are discharged with the classifying air.

[0093] As a result of the abrupt widening of the cross-sectional area from the outlet nozzle 20 to the outlet chamber 41, a significant reduction in the flow velocity of the fines-air mixture occurs there. This mixture will therefore pass through the outlet chamber 41 via the fines outlet pipe 48 into the fines outlet 58 at a very low flow velocity and will only generate minimal abrasion on the wall of the outlet chamber 41. For this reason, the protective tube 57 is only a highly precautionary measure. The high flow velocity in the classifier wheel 8, necessary for effective separation, still prevails in the discharge nozzle 20, which is why the protective tube 56 is more important than the protective tube 57. The change in diameter, with its widening at the transition from the outlet nozzle 20 to the outlet chamber 41, is particularly significant.

[0094] Furthermore, the air classifier 7 can be easily maintained by subdividing the classifier housing 21 in the manner described and assigning the classifier components to the individual sub-housings, and damaged components can be replaced with relatively little effort and within short maintenance times.

[0095] While in the schematic representation of the Fig. 2 The sight wheel 8 with the two cover plates 32 and 33 and the blade ring 59 with the blades 34 arranged between them is still shown in a known, usual form with parallel and parallel-surface cover plates 32 and 33, is shown in Fig. 3 The classifier wheel 8 is shown for a further embodiment of the air classifier 7 of an advantageous further development.

[0096] This sight wheel 8 according to the Fig. 3In addition to the blade ring 59 with the blades 34, the classifier 8 includes the upper cover plate 32 and the lower, downstream cover plate 33, which is axially spaced from it, and is rotatable about the axis of rotation 40, and thus the longitudinal axis of the classifier 7. The diametrical extension of the classifier 8 is perpendicular to the axis of rotation 40, i.e., to the longitudinal axis of the classifier 7, regardless of whether the axis of rotation 40, and thus the aforementioned longitudinal axis, is vertical or horizontal. The lower, downstream cover plate 33 concentrically surrounds the outlet nozzle 20. The blades 34 are connected to both cover plates 33 and 32. In contrast to the prior art, the two cover plates 32 and 33 are now conically shaped and preferably such that the distance of the upper cover plate 32 from the downstream cover plate 33 is inwards from the blade ring 59.towards the axis of rotation 40, the area increases, preferably continuously, for example linearly or non-linearly, and further preferably such that the area of ​​the cylinder shell through which the fluid flows remains at least approximately constant for every radius between the blade exit edges and the outlet nozzle 20. The outflow velocity, which decreases with the decreasing radius in known solutions, remains at least approximately constant in this solution.

[0097] Apart from the above and in the Fig. 3 In the explained variant of the design of the upper cover plate 32 and the lower cover plate 33, it is also possible that only one of these two cover plates 32 or 33 is conically shaped in the explained manner and the other cover plate 33 or 32 is flat, as is the case in connection with the embodiment according to the Fig. 2This is the case for both cover plates 32 and 33. In particular, the shape of the non-parallel cover plate can be such that the area of ​​the flow-through cylinder shell remains constant for every radius between the blade exit edges and the outlet nozzle 20.

[0098] The following examples serve to illustrate and further explain the invention, but do not limit it in any way. Raw materials: Silica 1:

[0099] The starting material to be ground was precipitated silica, which was prepared as follows: The water glass and sulfuric acid used at various points in the following procedure for the preparation of Silica 1 are characterized as follows: Water glass: Density 1.348 kg / l, 27.0 wt.% SiO2, 8.05 wt.% Na2O Sulfuric acid: Density 1.83 kg / l, 94 wt.%

[0100] In a 150 m³ precipitation tank with a sloping bottom, MIG inclined-blade agitator system, and Ekato fluid shear turbine, 117 m³ of water are pre-charged and 2.7 m³ of water glass are added. The ratio of water glass to water is adjusted to achieve an alkali number of 7. The tank is then heated to 90 °C. Once this temperature is reached, water glass is added simultaneously at a rate of 10.2 m³ / h and sulfuric acid at a rate of 1.55 m³ / h for 75 minutes while stirring. Afterward, water glass is added simultaneously at a rate of 18.8 m³ / h and sulfuric acid at a rate of 1.55 m³ / h for another 75 minutes while stirring at 90 °C. Throughout the entire addition period, the dosage rate of sulfuric acid is adjusted as needed to maintain an alkali number of 7 during this time.

[0101] The water glass dosing is then switched off. Subsequently, sulfuric acid is added over 15 minutes until a pH of 8.5 is reached. At this pH, the suspension is stirred (aged) for 30 minutes. Then, the pH of the suspension is adjusted to 3.8 by adding more sulfuric acid over approximately 12 minutes. During precipitation, aging, and acidification, the temperature of the precipitated suspension is maintained at 90 °C. The resulting suspension is filtered using a membrane filter press, and the filter cake is washed with deionized water until the conductivity of the wash water is less than 10 mS / cm. The filter cake then has a solids content of less than 25%. The filter cake is dried in a spin-flash dryer.

[0102] The data for Silica 1 are given in Table 1. Hydrogel - Production

[0103] A silica gel (hydrogel) is produced from water glass (density 1.348 kg / l, 27.0 wt% SiO₂, 8.05 wt% Na₂O) and 45% sulfuric acid. For this, 45 wt% sulfuric acid and sodium silicate are thoroughly mixed until a reactant ratio corresponding to an excess of acid (0.25 N) and an SiO₂ concentration of 18.5 wt% is achieved. The resulting hydrogel is stored overnight (approx. 12 h) and then broken down to a particle size of approximately 1 cm. It is washed with deionized water at 30–50 °C until the conductivity of the wash water is below 5 mS / cm. Silica 2 (Hydrogel)

[0104] The hydrogel, prepared as described above, is aged for 10–12 hours at pH 9 and 80 °C with the addition of ammonia, and then adjusted to pH 3 with 45 wt% sulfuric acid. The hydrogel then has a solids content of 34–35%. It is subsequently milled to a particle size of approximately 150 mm on a pin mill (Alpine type 160Z). µ The material is coarsely ground. The hydrogel has a residual moisture content of 67%.

[0105] The data for Silica 2 are given in Table 1. Silica 3a:

[0106] Silica 2 is dried using a spinflash dryer (Anhydro A / S, APV, type SFD47, Tein = 350 °C, Taus = 130 °C) so that it has a final moisture content of approximately 2% after drying.

[0107] The data for Silica 3a are given in Table 1. Silica 3b:

[0108] The hydrogel produced as described above is washed further at approximately 80 °C until the conductivity of the wash water is below 2 mS / cm and then dried in a circulating air drying oven (Fresenberger POH 1600.200) at 160 °C to a residual moisture content of < 5%. To achieve more uniform dosing behavior and a more consistent grinding result, the xerogel is reduced to a particle size of < 100 µ m pre-crushed (Alpine AFG 200).

[0109] The data for Silica 3b are given in Table 1. Silica 3c:

[0110] The hydrogel produced as described above is aged for 4 hours at pH 9 and 80°C with the addition of ammonia, then adjusted to approximately pH 3 with 45 wt% sulfuric acid and dried in a forced-air drying oven (Fresenberger POH 1600.200) at 160°C to a residual moisture content of < 5%. To achieve more uniform dosing behavior and a more consistent milling result, the xerogel is reduced to a particle size of < 100 µ m pre-crushed (Alpine AFG 200).

[0111] The data for Silica 3c are given in Table 1. Table 1 - Physicochemical data of the unmilled starting materials Silica 1 Silica 2 Silica 3a Silica 3b Silica 3c Particle size distribution using laser diffraction (Horiba LA 920) d 50 [µm] 22,3 nb nb nb nb d 99 [µm] 85,1 nb nb nb nb d 10 [µm] 8,8 nb nb nb nb Particle size distribution by sieve analysis > 250 µm % nb nb nb 0,0 0,2 > 125 µm % nb nb nb 1,06 2,8 > 63 µm % nb nb nb 43,6 57,8 > 45 µm % nb nb nb 44,0 36,0 < 45 µm % nb nb nb 10,8 2,9 Humidity % 4, 8 67 < 3 < 5 < 5% PH value 6, 7 nb nb nb nb nb = not determined Examples 1 - 3: Grinding according to the invention

[0112] To prepare for the actual milling with superheated steam, a fluidized bed counterjet mill is used according to Figure 1 , 2 and 3 First, the material is heated via two heating nozzles, which are pressurized with compressed air at 10 bar and 160°C, until the mill outlet temperature reaches approximately 105°C.

[0113] A filter system is installed downstream of the mill to separate the ground material (not in Figure 1(shown), whose filter housing in the lower third is indirectly heated by 6 bar saturated steam via attached heating coils to prevent condensation. All apparatus surfaces in the area of ​​the mill, the separator filter, and the supply lines for steam and hot compressed air are specially insulated.

[0114] Once the desired heating temperature is reached, the supply of hot compressed air to the heating nozzles is stopped and the application of superheated steam (38 bar(abs), 330°C) to the three grinding nozzles is started.

[0115] To protect the filter medium used in the separator filter and to adjust a specific residual water content of the milled material of preferably 2 to 6%, water is injected into the milling chamber during the start-up phase and during milling via a compressed air-operated two-component nozzle, depending on the mill outlet temperature.

[0116] Product feeding begins when the relevant process parameters (see Table 2) are constant. The feed rate is controlled based on the classifier flow rate. The classifier flow rate regulates the feed rate so that approximately 70% of the nominal flow rate cannot be exceeded.

[0117] The feed mechanism consists of a speed-controlled rotary valve, which doses the feed material from a feed container into the pressurized grinding chamber via a metering gate that serves as a barometric seal.

[0118] The coarse material is crushed in the expanding steam jets (grinding gas). Together with the expanded grinding gas, the product particles rise in the center of the mill hopper to the classifier wheel. Depending on the set classifier speed and grinding steam quantity (see Table 1), particles of sufficient fineness are carried by the grinding steam to the fines outlet and from there into the downstream separation system, while particles that are too coarse are returned to the grinding zone and subjected to further crushing. The discharge of the separated fines from the separator filter into the subsequent ensiling and packaging process is accomplished via a rotary valve.

[0119] The grinding pressure of the grinding gas prevailing at the grinding nozzles, or the resulting quantity of grinding gas in conjunction with the rotational speed of the dynamic paddle wheel classifier, determine the fineness of the grain distribution function as well as the upper grain limit.

[0120] The relevant process parameters can be found in Table 2, and the product parameters in Table 3: Table 2 Example 1 Example 2 Example 3a Example 3b Example 3c Source material: Silica 1 Silica 2 Silica 3a Silica 3b Silica 3c Nozzle diameter [mm] : 2,5 2,5 2,5 2,5 2,5 Nozzle type: Laval Laval Laval Laval Laval Quantity [pieces]: 3 3 3 3 3 Mill internal pressure [bar abs.]: 1,306 1,305 1,305 1,304 1,305 Inlet pressure [bar abs.]: 37,9 37,5 36,9 37,0 37,0 Inlet temperature [°C]: 325 284 327 324 326 Mill outlet temperature [°C]: 149,8 117 140,3 140,1 139,7 Classifier speed [min -1< ] : 5619 5500 5491 5497 5516 Classifier current [A%]: 54,5 53,9 60,2 56,0 56,5 Immersion tube diameter [mm]: 100 100 100 100 100 Table 3 Example 1 Example 2 Example 3a Example 3b Example 3c d 50 1)< 125 106 136 140 89 d 90 1)< 275 175 275 250 200 d 99 1)< 525 300 575 850 625 BET surface area m² / g: 122 354 345 539 421 N2 pore volume ml / g: nb 1,51 1,77 0,36 0,93 Average pore size (nm): nb 17,21 20,5 2,7 8,8 DBP (anhydrous) g / 100g: 235 293 306 124 202 Tapped density g / l: 42 39 36 224 96 Drying loss %: 4,4 6,1 5,5 6,3 6,4 1)< Determination of particle size distribution using transmission electron microscopy (TEM) and image analysis, and values ​​given in nm. Reference symbol list

[0121] 1 Jet mill 2 Cylindrical housing 3 Grinding chamber 4 Material feed 5 Grinding jet inlet 6 Product outlet 7 Air classifier 8 Classifying wheel 8a Classifier gap 9 Inlet opening or inlet nozzle 10 Grinding jet 11 Heat source 12 Heat source 13 Feed pipe 14 Temperature insulating jacket 15 Inlet 16 Outlet 17 Center of grinding chamber 18 Reservoir or generating unit 19 Piping equipment 20 Outlet nozzle 21 Classifier housing 22 Upper housing 23 Lower housing 24 Circumferential flange 25 Circumferential flange 26 Joint 27 Arrow 28 Classifying chamber housing 28a Support arms 29 Discharge cone 30 Flange 31 Flange 32 Cover plate 33 Cover plate 34 Blade 35 Classifying wheel shaft 35a Swivel bearing 35b Shaft feedthrough 36 Upper machined plates 37 Lower machined plate 38 Housing end section 39 Product feed nozzle 40 Rotary axis 41 Discharge chamber 42 Upper cover plate 43 Removable cover 44 Support arms 45 Conical ring housing 46 Intake filter 47 Perforated plate 48 Fine material discharge pipe 49 Deflector cone 50 Air inlet spiral 51 Coarse material discharge 52 Flange 53 Flange54 Dispersion zone 55 Flanges and lining machined (chamfered) on the inner edge 56 Replaceable protective tube 57 Replaceable protective tube 58 Fine material outlet / discharge 59 Blade ring

Claims

1. A method for generating finest particles by means of a jet mill (1) with an integrated dynamic air classifier (7) including a classifying wheel (8) and a classifying wheel shaft (35) as well as a classifier housing (21), wherein between the classifying wheel (8) and the classifier housing (21) a classifier gap (8a) and between the classifying wheel shaft (35) and the classifier housing (21) a shaft passage (35b) are formed, a gap flushing of classifier gap (8a) and / or shaft passage (35b) is carried out with compressed gases of low energy content, and grinding jet inlets (5) are present which are supplied with energy-rich superheated steam, characterized in that the flushing gas is used at a pressure of no more than approximately 0.4 bar above the mill internal pressure.

2. Method according to claim 1, characterized in that the flushing gas with a pressure of not more than approximately 0.3 bar and especially not more than approximately 0.2 bar above the mill internal pressure is used.

3. Method according to claim 2, characterized in that the mill internal pressure lies at least approximately in the range of 0.1 bar to 0.5 bar.

4. Method according to one of the preceding claims, characterized in that the flushing gas is used with a temperature from approximately 80 °C to approximately 120 °C, especially approximately 100 °C.

5. Method according to one of the preceding claims, characterized in that as flushing gas low energy pressurized air especially with approximately 0.3 bar to approximately 0.4 bar is used.

6. Method according to one of the preceding claims, characterized in that the grinding jet inlets (5) comprise grinding nozzles.

7. Method according to one of the preceding claims, characterized in that the superheated steam exhibits a pressure of at least approximately 12 bar, preferably at least approximately 25 bar and further preferred at least approximately 40 bar.

8. Method according to one of the preceding claims, characterized in that the temperature of the superheated steam is chosen such that it is provided dry at the end of the process.

9. Jet mill (1) with an integrated dynamic air classifier (7) for generating finest particles, which air classifier (7) comprises a classifying wheel (8) and a classifying wheel shaft (35) as well as a classifier housing (21), wherein between the classifying wheel (8) and the classifier housing (21) a classifier gap (8a) and between the classifying wheel shaft (35) and the classifier housing (21) a shaft passage (35b) are formed, flushing means are provided by means of which a gap flushing of classifier gap (8a) and / or shaft passage (35b) is carried out with compressed gases of low energy content, and wherein grinding jet inlets (5) are present which are supplied with energy-rich superheated steam, characterized in that the flushing means are adapted to apply the flushing gas at a pressure of no more than approximately 0.4 bar above the mill internal pressure.

10. Jet mill (1) according to claim 9, characterized in that the flushing means are adapted to apply the flushing gas with a pressure of not more than approximately 0.3 bar and especially not more than approximately 0.2 bar above the mill internal pressure.

11. Jet mill (1) according to claim 10, characterized in that the mill internal pressure lies at least approximately in the range of 0.1 bar to 0.5 bar.

12. Jet mill (1) according to one of claims 9 to 11, characterized in that the flushing gas is used with a temperature from approximately 80 °C to approximately 120 °C, especially approximately 100 °C.

13. Jet mill (1) according to one of claims 9 to 12, characterized in that as flushing gas low energy pressurized air especially with approximately 0.3 bar to approximately 0.4 bar is used.

14. Jet mill (1) according to one of claims 9 to 13, characterized in that the grinding jet inlets (5) comprise grinding nozzles.

15. Jet mill (1) according to one of claims 9 to 14, characterized in that the superheated steam exhibits a pressure of at least approximately 12 bar, preferably at least approximately 25 bar and further preferred at least approximately 40 bar.

16. Jet mill (1) according to one of claims 9 to 15, characterized in that the temperature of the superheated steam is chosen such that it is provided dry at the end of the process.

17. Jet mill (1) according to one of claims 9 to 16, characterized in that a tank (18a) as source for the superheated steam as operating means (B) is comprised or assigned.

18. Jet mill (1) according to one of claims 9 to 17, characterized in that it is a fluid bed jet mill or a dense bed jet mill.

19. Jet mill (1) according to one of claims 9 to 18, characterized in that grinding nozzles (9) are provided which are connected to piping means (19) as a steam supply line which is equipped with expansion bends.

20. Jet mill (1) according to claim 19, characterized in that that the piping means (19) as a steam supply line is connected to a tank (18a) as a water vapor source.

21. Jet mill (1) according to one of claims 9 to 20, characterized in that its surface area has a value as small as possible.

22. Jet mill (1) according to one of claims 9 to 21, characterized in that that the classifying rotor or the classifying wheel (8) has a clear height that increases with decreasing radius.

23. Jet mill (1) according to claim 22, characterized in that the flow through area of the classifying rotor or wheel (8) is at least approximately constant.

24. Jet mill (1) according to one of claims 9 to 23, characterized in that the classifying rotor or the classifying wheel (8) has a replaceable, co-rotating dip tube (20).

25. Jet mill (1) according to one of claims 9 to 24, characterized in that a fines discharge chamber (41) is provided which has a cross-sectional expansion in the direction of flow.

26. Jet mill (1) according to one of claims 9 to 25, characterized in that the flow paths are at least largely free of protrusions.

27. Jet mill (1) according to one of claims 9 to 26, characterized in that the components of the jet mill (1) are designed to avoid mass accumulation.

28. Jet mill (1) according to one of claims 9 to 27, characterized in that the components of the jet mill (1) are designed to avoid condensation.

29. Jet mill (1) according to one of claims 9 to 28, characterized in that means to avoid condensation are comprised.

30. Dynamic air classifier (7) with a classifying wheel (8) and a classifying wheel shaft (35) as well as a classifier housing (21), wherein between the classifying wheel (8) and an outlet connection (20) received by the classifier housing (21) a classifier gap (8a) and between the classifying wheel shaft (35) and the classifier housing (21) a shaft passage (35b) are formed, and flushing means are provided by means of which a gap flushing of classifier gap (8a) and / or shaft passage (35b) is carried out with compressed gases of low energy content, characterized in that the flushing means are adapted to apply the flushing gas at a pressure of no more than approximately 0.4 bar above the mill internal pressure.

31. Dynamic air classifier (7) according to claim 30, characterized in that the flushing gas is used with a temperature from approximately 80 °C to approximately 120 °C, especially approximately 100 °C.

32. Dynamic air classifier (7) according to claim 30 or 31, characterized in that as flushing gas low energy pressurized air especially with approximately 0.3 bar to approximately 0.4 bar is used.

33. Dynamic air classifier (7) according to one of claims 30 to 32, characterized in that a classifying rotor or classifying wheel (8) is comprised which has a clear height that increases with decreasing radius.

34. Dynamic air classifier (7) according to claim 33, characterized in that the flow through area of the classifying rotor or wheel (8) is at least approximately constant.

35. Dynamic air classifier (7) according to one of claims 30 to 34, characterized in that a classifying rotor or classifying wheel (8) is comprised which has a replaceable, co-rotating dip tube (20).

36. Dynamic air classifier (7) according to one of claims 30 to 35, characterized in that a fines discharge chamber (41) is provided which has a cross-sectional expansion in the direction of flow.

37. Dynamic air classifier (7) according to one of claims 30 to 36, characterized in that the flow paths are at least largely free of protrusions.