FR2729587A1 - PROCESS AND INSTALLATION FOR GRINDING OF GRINDING MATERIAL - Google Patents

Abstract

Process and plant for grinding a material to be ground, preferably for fine to very fine grinding of the pre-crushed material, characterized in that after its pre-crushing to a primary grain, having a screening residue (R) of a maximum of 3%, at a mesh width of 500 mum or at a specific surface area measured according to Blaine, of at least 1600 cm**2/g, preferably from 2500 to 4000 cm**2/g, the material to be The pre-crushed crushed material is ground to the final product grinding fineness (19) by friction grinding using an agitator roller mill (16).

Description

The invention relates to a method for grinding a material to be ground,

  preferably for fine to very fine grinding of the pre-crushed material to be crushed and a corresponding installation for the implementation of the latter. Particularly for the grinding of cement clinkers, but also of ores and raw materials for the manufacture of cement, two-stage grinding is used more and more today, partially also a finished grinding with a roller press respectively a high pressure roller mill to significantly reduce the specific consumption

  energetic (ZKG 43 (1990) 7, pages 347-351).

  The theoretically possible economy, achieved by the application of high pressure crushing in a roller press, is unfortunately not obtained in practice as regards the grinding of cement since the characteristic line of the grain size of the product is too stiff, that is to say that there is a very narrow distribution of the grain size classes with relatively little fineness of grain less than 10 a, on the other hand, the shape of the grain is flat and with sharp edges . The consequence is a deterioration of the processing properties, such as the increase in water supply necessary to obtain the standard stiffness, an early start of solidification and, finally, due to the deterioration of the water-cement ratio, in concrete, this also produces a decrease in standard pressure resistances. This negative influence of the properties of cement occurs even when the particle size of a roller press cement (finished grinding) coincides with that of a traditional cement ground in a grinding tube. The cause is that the particles have sharp edges. These must be rounded. Hitherto, a grinding tube has always been used which, however, has the following drawbacks: high energy consumption; - great need for surface and considerable equipment

  - high grinding heat and noise generation.

  It is known that, due to grinding friction in roller agitator mills, the particles are abrasively rounded, the agglomerates are destroyed and in particular, the upper derating is eliminated. True subsequent grinding, i.e. additional crushing of the primary particles is in the finest range, is also only possible in the roller agitator mill at the cost of a large consumption of energy. This implies high rotational speeds on the part of the agitator and high energy dissipation. This would happen if the agitator roller mill was used for finishing grinding without having proceeded

  before a major preliminary crushing.

  The known constructions for roller mills agitators for dry grinding, for example those which have an endless screw acting as a stirring member (EP 0217 977 A2, DD 296 7936), are not suitable for grinding finishing of the cement, only in a restricted manner, since the fluidizing gas is brought in from the bottom of the mill, for example by means of a hollow shaft or also, from the external wall of the container and the finished product is discharged upwards, the bottom of the container being closed. So no particle with edges

  vivid unwanted can not reach the product.

  Other solutions according to which the finished product is discharged in free fall downwards, via a split or perforated plate (DD 275 188, DD 291 707, DE OS 42 02 101), have the drawback that the crushed bodies can be distributed between the openings of the discharge plate and the worm agitator respectively the scraper mounted below. The agitator shaft wears out more, respectively, can become blocked and the cross-section

  transverse discharge is further reduced.

  The object of the invention is to improve the grinding process and the corresponding grinding installation of the type mentioned, using a pre-crusher and a secondary crusher, so as to eliminate or reduce the aforementioned drawbacks of the installation structures.

known.

  This object is achieved in accordance with the invention by the following measures: after pre-crushing to a primary grain, having a screening refusal (R) of a maximum of 3%, at a mesh width of 500 μm or at an area specific measured according to Blaine, of at least 1600 cm2 / g, preferably from 2500 to 4000 cm2 / g, the pre-crushed material to be ground is ground to the fineness of grinding of the finished product by friction grinding using an agitator mill with pebbles; - the material crushed to the fineness of the finished product is discharged into the bottom area of the vertical agitator mill with rollers; - the pre-grinding is carried out in a roller press respectively a high pressure roller mill respectively in a roller mill respectively in an MPS roller pulverizer mill (or Bowl-Mill mill); - the roller agitator mill is operated continuously, in circular motion without air separator, or in circular motion with high power air separator; - in the bottom area of the roller agitator mill, a fluid is preferably blown with air, to

  assist the discharge of matter.

  Other advantageous configurations of the invention are also characterized by the following facts: a) the grinding installation, comprising a grinding device, the discharged product of which is ground to the fineness of grinding of the finished product in a secondary mill, characterized by the fact that the mill is designed as a roller mill, known per se, equipped with a single or multiple pitch worm agitator, which is arranged, on the bottom side, on a discharge plate respectively of wear, provided with discharge openings, preferably discharge slots, the discharge openings being arranged in the region of the periphery of the worm pitches of the worm agitator and of the internal wall of the container, b) using grinding rollers, the diameter of which is greater than 15 mm, the discharge openings are distributed in the discharge plate over the entire cross section, c) openings, widening outward, preferably conically, are arranged, in the form of discharge slots, in the internal wall of the container, just above the discharge plate, d) a distributor tube is arranged in the lower zone of the agitator mill. rollers, in order to ensure the supply of the fluidizing air, e) the worm agitator is associated, on the bottom side, with one or more agitating elements whose distance from the discharge plate is at least twice as large as the maximum diameter of the grinding body and in that there is a small gap between the outer edge of the agitator element and the inner wall of the container, f) the shaft of the screw agitator without end is housed, twice, overhang on the side of the drive when the latter is placed at the top, or is housed additionally on the bottom side, in which case the agitator shaft is connected, by the through an elastic coupling, when driving the agitator, g) the drive is arranged on the bottom side and the agitator shaft is housed downstream of the discharge plate, h) downstream of the discharge plate, is disposed an discharge hatch or a rotary mucking wheel which is driven separately or which is connected to the agitator shaft, i) the internal wall of the container is coated with wear plates, preferably in wear-resistant molded steel or ceramic and the wear plates are provided with 'a bead which forms, in the peripheral direction of the inner wall of the container, a closed ring. In the grinding process, according to the invention, the principle, known per se, of friction crushing in a roller agitator mill, is applied for the secondary grinding of cement clinkers or of another product having edges alive or having already suffered

significant preliminary grinding.

  The method, in accordance with the invention, provides for bringing the material to be ground, preferably cement clinkers, after its pre-crushing to a primary grain, having a screening refusal (R) of a maximum of 3%, at a mesh width of 500 µm, or a pre-crushed and pre-graded loading material to a specific surface of at least 1600 cm2 / g, preferably 2500 to 4000 cm2 / g (measured according to Blaine), to a grinder roller agitator for crushing by friction and discharging the material, crushed to the fineness of the finished product, in the bottom zone of the mill, so that the advantages of the principle of agitation, such as rapid dispersion, abrasion fast, high energy density, due to the high filling of the grinding vessel (approximately 80% of the

  filling of the material to be ground), are exploited.

  In particular, high pressure crushing provides particles, having microcracks, which can be destroyed, advantageously from an energy point of view, in the roller agitator mill,

  until the primary grains are obtained (without cracking).

  The grinding installation according to the invention consists of a pre-crushing device, such as a roller press or a roller mill, which is placed downstream of a roller agitator mill. The roller agitator mill is equipped with a single or multiple pitch worm screw agitator, and on the bottom side, a discharge wear plate respectively. The discharge plate has, in the peripheral zone of the threads of the worm agitator and of the internal wall of the container, discharge openings in the form of slots. The advantage of the invention resides in the fact that, in the case of a two-stage grinding which uses a roller press respectively a high-pressure roller mill as the first grinding stage and a roller agitator mill as a second grinding stage, a finished product which has the fineness and

  the desired grain shape of the finished product.

  Various other features of the invention

  appear moreover from the detailed description which

  follows. Embodiments of the subject of the invention are shown, by way of nonlimiting examples, in

attached drawings.

  Figure 1 is a diagram of the assembly, according to

  the invention, a grinding installation.

  Figure 2 is a variant of the assembly, according to

  the invention, a grinding installation.

  FIG. 3 is the design, in accordance with the invention,

  of the second grinding stage in cross section.

  According to FIG. 1, the material to be loaded, preferably cement clinckers, with or without sulphated carrier substrate as well as with or without grinding additive, is brought to the pre-crusher 14 which is already able to produce fineness of very high grinding. The choice of a common loading with the sulfated substrate respectively with the grinding additives depends on the particle size and the grinding capacity of these substances. REA gypsum, the defined particle size of which is less than 30 μm, could for example be added by dosing in the second grinding stage, that is to say

  in the roller agitator mill 16.

  The preliminary classifier 15, as a rule a basket-separator with bars, equipped with a deagglomerator, or an electric separator (V-shaped separator), ensures that no derating greater than 2 mm, but preferably greater than about 400 μm, does not reach the roller agitator mill 16. The gravel 18, separated in the preclassifier 15, is brought back to the

first grinding stage.

  Roller presses or roller mills mounted in a partial finished grinding unit, for grinding cement with the aforementioned separator, allow

  to produce an intermediate product up to 4000 cm2 / g.

  It is thus guaranteed that a material to be ground, which is pre-crushed to a specific surface of at least 1600 cm2 / g, preferably 2500 to 4000 cm2 / g, is brought to the roller agitator mill 16 to be ground with the

fineness of the finished product.

  The particles of this finished product from the first crushing stage include, due to the multiple stress at high pressure, a large number of microcracks. This product is therefore particularly well suited to the pursuit of crushing by friction in the roller agitator mill 16. A significant increase in temperature in the roller agitator mill 16 is not to be feared, unlike traditional mill tubes. Therefore, there are no negative effects on the properties of the sulfated substrate. We can do without an additional cooling system. In the extremely high pre-shredding described above, the roller agitator mill 16 can be operated continuously. Due to the return of a partial current (grinding in circular motion without separator), the distribution of the particle size can

  be influenced as needed.

  The circular circuit of the roller agitator mill 16, according to FIG. 2, with a finished product classifier 20 (high power separator) allows rapid adjustment without problem of the desired fineness of the finished product. To decouple the two control circuits for the flow rate of the pre-crusher and the roller agitator mill 16, it is recommended to use intermediate storage of the finished product 21 of the first stage for circular movement mounting with a high-voltage separator. crushing. In this case, grinding additives 22, already pre-ground, respectively REA fine gypsum 23 can be added by metering in the roller agitator mill 16 so that the circuit

  of the roller press is relieved.

  FIG. 3 shows the roller agitator mill, designed in accordance with the invention, which acts as a second crushing stage. According to the invention, the aforementioned drawbacks of the known devices are eliminated, by loading the material to be ground from above and by discharging it, bottom side, by means of a wear plate respectively of discharge 1 provided with slots. which are located only between the periphery of the threads of the worm agitator 2 and the internal wall 3 of the container, and by means of lateral discharge slots 4 which are arranged in the container wall. Thus, jams between the agitator respectively the scraper 5, bottom side, are avoided as long as a minimum gap is maintained

  between the smooth discharge plate 1 and the scraper 5.

  The discharge speed can be adjusted by means of the fluidizing air which is preferably supplied by a distributor tube 6 located in the internal wall of the container. Large grinding rollers 7 of about 15 mm are used, so the discharge slots can be evenly distributed over the entire cross section of the discharge plate 1, so that no jamming occurs even in the case as small a distance as possible between

  the scraper 5 and the discharge plate 1.

  An additional agitator element 8, which has a minimum distance from the discharge plate which is twice the maximum diameter of the grinding rollers and which extends almost to the internal wall 3 of the container, ensures free discharge by the lateral slots 4, located in the container wall, and

  through the external slots of the discharge plate 1.

  The elimination of the discharge slots, in the center of the discharge plate 1, allows centering of the agitator shaft by means of a centering cone 9 which is housed by means of an axial bearing 10, on the bottom side. This additional bearing ensures a smooth running of the agitator shaft while having a high revolution accuracy. Since the agitator drives constantly have two bearings and are designed for cantilever mounting, the coupling 11 is elastic when the agitator shaft is centered. The discharge of the mill can be carried out in free fall by discharge hatches (not shown) or a clearing wheel 12. The clearing wheel 12 can be driven separately or by means of

  the agitator shaft, as shown in fig. 3.

  It is also possible to drive the roller agitator mill from the bottom. In this case, the agitator shaft is guided through the discharge plate 1 and is protected from dust by blocking air (not shown). The agitator shaft is housed downstream of the discharge plate 1 or is provided by the gear to be used. This variant of the drive is advantageous in the case of low construction height and for large drive powers.

greater than 400 kW.

  The internal wall 3 of the grinding container is protected by wear plates 13 made of steel, of wear-resistant cast steel or of ceramic. These wear plates 13 are provided with a bead which forms, in the direction of the periphery, a closed ring so that the material to be ground, flowing downward along the internal wall 3 of the grinding container , is compressed to

  the interior and this together with the grinding rollers.

  In this way, short-circuit currents are avoided directly against the internal wall 3 of the

grinding vessel.

Claims (11)

Claims:   1 - Method for grinding a material to be ground, preferably for fine to very fine grinding of the pre-crushed material, characterized in that after its pre-crushing to a primary grain, having a screening refusal (R) of a maximum of 3%, at a mesh width of 500 un or a specific surface area measured according to Blaine, of at least 1600 cm2 / g, preferably from 2500 to 4000 cm2 / g, the pre-crushed material to be crushed is fineness of grinding of the finished product (19) by friction grinding by means of an agitator mill rollers (16).   2 - Method according to claim 1, characterized in that the material ground to the fineness of the finished product is discharged into the region of the bottom of the agitator mill vertical with rollers.   3 - Method according to one of claims 1 and 2,   characterized in that the pre-grinding is carried out in a roller press respectively a high pressure roller mill respectively in a roller mill respectively in a pulverizing pulverizer MPS rollers (or Bowl-Mill).   4 - Method according to one of claims 1 to 3,   characterized in that the roller agitator mill is operated continuously, in circular motion without air separator, or in circular motion with   high power air separator.   - Method according to one of claims 1 to 4,   characterized in that in the bottom area of the roller agitator mill, a fluid is preferably blown with air to assist the discharge of the material. 6 - Grinding installation, comprising a grinding device, the discharged product of which is ground to the fineness of grinding of the finished product in a secondary mill, characterized in that the mill is designed as a roller agitator mill known per se equipped with a worm agitator (2) with single or multiple pitch, which is arranged, on the bottom side, on a discharge plate (1) respectively of wear provided with discharge openings, preferably discharge slots, the openings discharge being arranged in the region of the periphery of the worm pitches of the worm agitator (2) and the inner wall (3) of the container.  7 - Grinding installation according to claim 6, characterized in that by using grinding rollers, the diameter of which is greater than 15 mm, the discharge openings are distributed in the plate   discharge (1) over the entire cross section.   8 - Grinding installation according to one of the   claims 6 and 7, characterized in that   openings, widening towards the outside preferably conically, are arranged, in the form of discharge slots (4), in the internal wall (3) of the container,   just above the discharge plate (1).   9 - Grinding installation according to one of the   Claims 6 to 8, characterized in that a tube   distributor (6) is arranged in the lower zone of the roller agitator mill, so as to ensure   the supply of the fluidizing air.   - Grinding installation according to one of the   Claims 6 to 9, characterized in that the agitator   worm screw (2) is associated, on the bottom side, with one or more agitating elements (8) whose distance from the discharge plate (1) is at least twice greater than the maximum diameter of the grinding body and in that there is a small gap between the outer edge of the agitator element (8) and the wall internal (3) of the container.   11 - Molding installation according to one of the   Claims 6 to 10, characterized in that the tree of   the worm agitator (2) is cantilevered twice over the drive side when the latter is placed at the top, or is additionally housed on the bottom side, in which case the shaft of the agitator is connected, via an elastic coupling (11), to agitator training.   12 - Grinding installation according to one of the   Claims 6 to 10, characterized in that   the drive is arranged on the bottom side and the shaft   agitator is housed downstream of the discharge plate (1).   13 - Grinding installation according to one of the   Claims 6 to 12, characterized in that downstream of   the discharge plate (1) is arranged a discharge hatch or a rotary clearing wheel (12) which is driven separately or which is connected to the shaft stirrer.   14 - Grinding installation according to one of claims 6 to 13, characterized in that the internal wall (3) of the container is coated with wear plates (13), preferably in molded steel resistant to wear or made of ceramic and in that the wear plates (13) are provided with a bead which forms, in the peripheral direction of the internal wall (3) of the container, a closed ring.