AU5795000A

AU5795000A - Method for comminuting bulk material or a granulate and a device for carrying out said method

Info

Publication number: AU5795000A
Application number: AU57950/00A
Authority: AU
Inventors: Alfred Edlinger
Original assignee: Holderbank Financiere Glarus AG
Current assignee: Holcim Ltd
Priority date: 1999-07-09
Filing date: 2000-06-30
Publication date: 2001-01-30
Also published as: ATA119999A; EP1121473A1; WO2001004363A1; AT407525B

Description

- 1 Method for Comminuting Bulk Material or Granulated Material and Device for Carrying out said Method The invention relates to a method for comminuting bulk 5 material or granulated material, in which the material to be ground is introduced into a mill together with a propellant. A method for comminuting granulated material has already been known from AT 405 511 B, in which water under pressure is fed 10 to a slag melt and the granulated material is discharged together with at least a portion of the vapor formed. The quenching of the melt flow with- water ensures rapid solidification during which crystallization should be largely avoided, and the production of an amorphous, glassy structure 15 of the granules. Such granulates with a suitable chemical composition of the molten slag may yield valuable raw materials for the production of hydraulic binders, which, as a rule, will imply intensive subsequent comminution and, in particular, grinding. In this connection, AT 405 511 B already 20 proposed to energetically utilize the melt heat of the slag for the energy required for the reduction of size or the increase in surface, thus lowering the overall consumption of energy. To this end, the liquid slag was introduced into a granulation chamber in freeflowing jets, whereupon compressed 25 water jets were directed against the slag jet and the solidified and granulated slag, along with at least a portion of the vapor formed, was conducted over a pneumatic conveying duct and a distributor, whereupon the partial streams were introduced into a grinding chamber via multicomponent jets 30 and, in particular, conically tapering jets. The grinding chamber was operated in the manner of a counterjet mill. The configuration of two-phase jets via which vapor and granulated material were introduced into the grinding chamber, which was indispensable for that mode of operation, however, presupposed 35 relatively expensive jet constructions, such two-phase jet systems having turned out to be relatively prone to wear, anyway.

- 2 AT 405 512 B likewise describes a method for granulating and comminuting granulated material, in which water is provided in a first, pressure-tight reaction chamber, said reaction 5 chamber being set under a vapor pressure of more than 5 bars and granulation being carried out in that pressure chamber. In order to maintain a pressure of more than 2.5 bars, the decisive measure in that known method was to impede the degasification of hydrogen sulphide and bond it in the 10 glassily solidifying granulates in high amounts. The granulates were then decanted and transferred into a jet mill, which jet mill was again operable by the vapor formed during the solidification of the melt. In that configuration, it was feasible to do without complex and expensive jets prone to 15 high wear, since the granulated material could be directly introduced into a fluidized-bed counterjet mill and the injection of vapor could be effected through separate jets. The granulated material was discharged from the reaction chamber via pressure sluices and decanted, wherein also in 20 that case the decanted granulates, above all, were nozzled into the fluidized-bed jet mill using vapor as a propellant, whereby nozzling of the slag granulates into the fluidized bed could be effected accelerated in the manner of a solids injector. 25 The invention aims to provide a method which enables the use of structurally substantially simpler devices for its realization and which ensures a particularly high grinding efficiency as well as a high comminution performance while 30 obviating complex multicomponent jets. To solve this object, the method according to the invention essentially consists in that grinding elements, in particular balls, are held within the mill in a fixed bed or in a fluidized bed, whereby the propellant loaded with bulk material or granulated material is 35 expanded and/or evaporated into the space filled with grinding elements, whereupon the ground material is drawn off the mill via a screening means. The presence of grinding elements in - 3 the grinding chamber causes hollow spaces to remain between the grinding elements and become active within the fixed bed or the fluidized bed in the manner of a plurality of individual jets. Thus, no complex two-component jets are 5 required to introduce the granulated material along with the propellant, and the jet-like hollow spaces formed in the interspaces between the grinding elements cause large-scale turbulent flows in the interspaces between the grinding elements and hence particularly intensive comminution. The 10 grinding elements, which may be designed, in particular, as grinding balls, may have different diameters such that a ball radius gradient results within a fluidized bed, into which expands the flow of the propellant under pressure along with the bulk material. The same holds for the jet-like hollow 15 spaces between balls in a fixed bed. In order to comminute melts, in particular slag melts, the method according to the invention in a particularly advantageous manner may be carried out such that the liquid melts are granulated in water under a superatmospheric pressure and that the granulated material is 20 introduced into the mill together with the wet vapor which is under a superatmospheric pressure. Wet vapor is used to denote mixtures of liquid and gaseous phases, which may also be referred to as mist. At temperatures of above 100 0 C and pressures of above 1 bar, vapor is in equilibrium with water, 25 whereby pressure and temperature in any event are to be chosen such that superheated, i.e., dry vapor is formed at a pressure decrease within the mill, or during expansion, respectively, so that materials that tend to hydration or losing their hydraulic properties on account of water will not be 30 destroyed. Due to the fact that only wet vapor is conveyed along with the granulated material, the only thing required is a pressure-tight duct, and separate jets for expanding the wet vapor into the grinding elements or into the fluidized bed of the grinding chamber may be obviated. The wet vapor itself, as 35 a rule, has a temperature of above 150 0 C and may be introduced into the grinding chamber at a pressure of above 5 bars, whereby the expansion under vapor formation leads to an - 4 approximately 1500-fold volume increase and superheated water vapor is formed within the layer filled with grinding elements or grinding balls such that the fine material forming will not be hydrated. The slag granulates are ground within the 5 grinding element bed at a high efficiency, wherein the grinding element bed may contain different grinding elements and, for instance, also grinding additives acting as grinding elements such as, for instance, clinkers and puzzolans. In the main, comminution to a dmax <75pm is feasible with such a mode 10 of procedure, screening being subsequently feasible according to conventional techniques. The quality of the water used for graAulation is not critical in terms of purity, either, it being even possible to dispose 15 of slightly loaded waste water. The supply of slag melt into the granulation chamber may be effected discontinuously via slag ladles or continuously via slag chutes and pressure sluices. 20 During vapor condensation, energy may be recovered so as to increase the efficiency by approximately 20%. Yet, in the first place, the two-phase jet systems which are extremely prone to wear and were required for the injection of vapor along with granulated material are omitted due to the 25 expansion of wet vapor with slag granulates directly into the grinding element bed. Overall, between 0.57kg water/kg slag and 2.25kg water/kg slag are used. For instance, at an addition of 1 kg water/l kg 30 slag, wet vapor consisting of 0.6kg vapor and 0.4kg water per kg slag is formed in the pressure granulator at a pressure of 5 bars and a temperature of 150 0 C. The expansion into the grinding chamber, in which a pressure of, for instance, 0.2 bar prevails, causes the formation of slightly superheated 35 vapor. In this example, approximately 750 1 (0.75 m 3 ) vapor would form per kg slag during the expansion in the ball grinding chamber.

- 5 The energy involved in the volume change to vapor of the water contained in the wet vapor to a large extent is converted into comminution energy, thus yielding high energetic advantages as 5 compared to conventional systems. Advantageously, the method according to the invention is carried out such that the grinding elements are recirculated and subjected to a temperature change. The grinding fineness 10 may thus be further enhanced by effecting an energy transfer from the grinding elements to the material to be ground, which is particularly beneficial to the grinding procedure from an energetic point of view, it being advantageous to heat the grinding elements to temperatures of >6000C and introduce 15 CaCO3 into the grinding chamber. The introduction of CaCO3 into the grinding chamber causes calcination and, at the same time, cleavage into CaO and C02, which, on the one hand, brings about an improvement in the hydraulic properties of the material to be ground and, on the other hand, results in an 20 additional volume increase and hence a better comminution of the material to be ground. Moreover, the recirculation of the grinding elements causes the grinding elements to be efficiently cleaned. 25 In an advantageous manner, the grinding elements may be used in a manner coated with catalysts such as, e.g., Ni or Ni oxide. Thus, the mechanical grinding procedure may be overlaid also by chemical reactions. The grinding elements also may be subjected to a cooling process within the circulatory system, 30 thus facilitating the grinding of heat-sensitive products. Advantageously, the method according to the invention is carried out in a manner that metal balls or ceramic balls are used as grinding elements, wherein it is proceeded in any 35 event such that the grinding chamber is kept at a lower pressure than the granulation chamber. Such a pressure difference between the grinding chamber and the granulation - 6 chamber may be regulated in a particularly simple manner, it merely will do to arrange in the pressure duct an accordingly adjustable control valve which safeguards both the respective amount of water required in the granulation space and the 5 appropriate expansion into the fluidized bed filled with grinding elements. Advantageously, the method according to the invention is realized such that the propellant is introduced into the mill 10 in a pulsed manner. This causes the fluidized bed formed by the grinding elements to be periodically built up and broken down such that an additional grinding effect is provided in that balls which are located further pup, under the effect of gravity during the collapse of the fluidized bed, come to lie 15 on grinding elements located therebelow, thus comminuting the grinding material present between them. Cold pressurized water having a pressure of about 100 bars may, for instance, be chosen as a propellant for hydration-insensitive grinding material such as, e.g., puzzolans. In that case, pulsation may 20 be reached in a particularly simple manner by slowly running high-pressure piston pumps. The device according to the invention for carrying out the method described is essentially characterized by a grinding 25 chamber which is at least partially filled with grinding elements and to which are connected at least one connection means or a pressure-tight duct to introduce the material to be ground and the propellant as well as at least one duct to draw off the ground material. In the main, relatively simple 30 structural components may, thus, be used such that the apparative expenditure involved in the realization of the method according to the invention is relatively low. A device of this type is suitable, in particular, for the grinding of lime, mica, clays, oxidation-sensitive products or organic 35 color pigments, superheated water vapor or inert gases (N2, Ar), for instance, being used as propellants in those cases. In order to comminute melts and, in particular, slag melts, - 7 the device is, furthermore, characterized by two chambers which are interconnected by means of a pressure-tight duct, wherein the first chamber is designed as a pressure-tight granulation chamber including a charging means for liquid slag 5 and is at least partially filled with water and the second chamber is designed as a grinding chamber including a discharge means for the ground material and is at least partially filled with grinding elements, the pressure-tight duct running from the water-filled space of the granulation 10 chamber into the space of the grinding chamber filled with grinding elements. In this case, the configuration advantageously is devised such that the pressure-tight duct is connected to the grinding chamber belor the grinding elements, the pressure-tight duct advantageously comprising at least one 15 control or check valve to adjust the water level required in the granulation space and the desired expansion into the grinding chamber. The grinding elements and, in particular, grinding balls 20 present in the interior of the grinding chamber may be brought into the appropriate fluidized form already prior to the first-time expansion of hot wet vapor loaded with granulated material, to which end vapor or compressed air may, for instance, be used. In this case, the configuration according 25 to the invention is devised such that the grinding chamber comprises a grate or mesh bottom plates to support the grinding elements such that the geometry desired in the interior of the grinding chamber can be readily observed. Advantageously, the grinding elements for the formation of a 30 fluidized layer have diameters of less than 10 mm and, preferably, less than 5 mm in order to enable the maintenance of an appropriate fluidized bed without any additional measures. Grinding elements for use in a fixed bed may have accordingly larger diameters, balls being geometrically 35 preferred because of the formation of jet-like interspaces within the bed. The grinding effect in this case is obtained by an acceleration of the particle flow in the jet-like - 8 interspaces and impact of the granulated material on the grinding elements contained in the fixed bed. The separation of fine material may be effected in a 5 conventional manner in that a screening means, in particular a cyclone, is connected to the discharge openings for the ground material and that coarse material separated in the screening means is returned to the grinding chamber. In order to further enhance the grinding effect, the device advantageously is 10 configured in a manner that a discharge means for the grinding elements is connected to the chamber filled with grinding elements in order to recirculate the grinding elements into the grinding chamber via a heat exchanger. In the heat exchanger, the grinding elements may be heated or cooled, 15 depending on the properties of the product to be ground. Furthermore, the device may be designed such that at least one further duct for water under pressure, reducing gases and/or gases decomposable while increasing in volume is connected to the grinding chamber. 20 In the following, the invention will be explained in more detail by way of devices used for carrying out the method, which are schematically illustrated in the drawing. Therein, Fig. 1 shows a first embodiment of a device suitable for 25 carrying out the method according to the invention and Fig. 2 illustrates an alternative configuration. In the drawing, a first pressure-tight chamber which is designed as a granulation chamber is denoted by 1. The chamber 30 1 comprises a lid 2 which is pressure-tightly connected with the wall 3 of the granulation chamber, water 4 being present in the interior of the granulation space. The water level is indicated by 5. Liquid slag charging is schematically indicated by way of a pivotable slag ladle 6, wherein other 35 charging means such as, for instance, slag chutes or appropriate sluices may be provided alternatively. In the interior of the pressure granulator, water is in equilibrium - 9 with the vapor volume while slag granulates 7 are forming, which are drawn off along with the hot wet vapor via a duct 8. The wet vapor has a temperature of about 150 0 C, the vapor pressure adjusting at approximately 5 bars. The wet vapor 5 granulate flow via an adjustable check valve 9 gets to the bottom 10 of a grinding chamber 11. A grate 12 supporting a grinding element bulk 13 is provided in the interior of the grinding chamber 11. With accordingly small-dimensioned grinding elements, a fluidized bed may be adjusted by an 10 appropriate flow, the grinding effect thus being promoted by the movement of the grinding elements. With accordingly large dimensioned grinding elements, also a fixed bed may yet be present, whereby appropriate jet-like' interspaces are formed in the interspaces between the grinding elements 13, in which 15 the expanding vapor along with the particle flow is accelerated and the particles are again rapidly braked while being disintegrated, by impinging on the grinding elements. Through a charging means 14, further grinding aids and grinding additives may be introduced into the space filled 20 with grinding elements and, in particular, balls, it being feasible to additionally charge already solidified slag or CaCO 3 . The pressure prevailing in the interior of the grinding chamber 11 is altogether lower than the pressure prevailing within the pressure granulator such that the wet vapor will 25 get from the pressure granulator into the grinding chamber without additional pumps. To the grinding chamber 11 is connected a discharge duct 15 via which the grinding elements are supplied to a heat exchanger 16, whereupon the grinding elements, which are subjected to a temperature change, are 30 recycled to the grinding chamber 11. The ground material is drawn off the grinding chamber via a duct 17 and supplied to a screening means 18. Coarse material is drawn off via a duct 19 and a cellular wheel sluice 20 and at least partially may be recycled into the grinding chamber 11 via a duct 21. The 35 remaining fine material leaving the screening means reaches a filter 22 and there is discharged via a cellular wheel sluice 23 and a duct 24. The vapor drawn off through duct 25 - 10 subsequently may be condensed and recharged into the pressure granulator in the form of water. Water under pressure, reducing gases and/or gases decomposable while increasing in volume may be fed to the grinding chamber 11 via a duct 26. 5 Fig. 2 depicts an alternative configuration of a device suitable for carrying out the method according to the invention. By 27 is denoted a slag tundish in which liquid slag 28 is maintained at the appropriate temperature. A 10 throttle pipe 29 which is adjustable in height in the sense of double arrow 30 is immersed in the slag bath 28 so as to leave a throttle gap between the lower edge of the throttle pipe 29 and the slag exit opening 31 of the slag tundish 27, via which gap a tubular slag jet is formed. A vapor jet tube 32, via 15 which vapor may be injected, opens into the interior of the throttle pipe 29. The slag exit opening 31 is designed as a cooled annular chamber through which cooling water flows. The extremely fine slag droplets thus ejected are contacted by 20 quenching water emerging from an annular jet 33, whereupon the slag droplets get into the region of a radiation cooler 34 which is designed as a radiation steam boiler. The radiation steam boiler is fed with high-pressure feed water having a maximum pressure of 10 bars, whereby forced flows stream 25 through the cooling chambers and high-pressure vapor may be withdrawn. On the point of impact of the quenching water on the slag droplets the temperature amounts to about 950 0 C, whereas the particles on the lower end of the radiation cooler have temperatures of about 400 0 C. An excess pressure of a 30 maximum of 2.5 bars prevails on that site, the particle diameters ranging between 50 and 200pm. After this, the particles impinge on a fixed bed comprised of jet grinding balls having diameters of more than 10mm, preferably at least 30 to 40mm. In the interspaces between the grinding balls 35 35 are formed suitable jet-like interspaces in which the vapor along with the particle flow is accelerated and the particles are again rapidly braked while being disintegrated, by - 11 impinging on the grinding elements. The thus obtained granulates ground to the finest degree are drawn off via a duct 36 and a filter 37 as well as a cellular wheel sluice 38. The comminuted powder has a grain size of between 5 and 45pm. 5 The steam emerging from the radiation steam boiler 34 may be drawn off via a steam collecting drum 39 and optionally be reused as a propellant for the disintegration of the slag upon interposition of a superheater 40.

Claims

1. A method for comminuting bulk material or granulated material, in which the material to be ground is introduced 5 into a mill together with a propellant, characterized in that grinding elements, in particular balls, are held within the mill in a fixed bed or in a fluidized bed, whereby the propellant loaded with bulk material or granulated material is expanded and/or evaporated into the space filled with grinding 10 elements, whereupon the ground material is drawn off the mill via a screening means.

2. A method according to claim 1 for comminuting melts and, in particular, slag melts, characterized in that the liquid melts 15 are granulated in water under a superatmospheric pressure and the granulated- material is introduced into the mill together with the wet vapor which is under a superatmospheric pressure.

3. A method according to claim 1 or 2, characterized in that 20 the grinding elements are recirculated and subjected to a temperature change.

4. A method according to claim 1, 2 or 3, characterized in that the grinding elements are heated to temperatures of 25 >600 0 C and CaCO3 is introduced into the grinding or ball chamber.

5. A method according to any one of claims 1 to 4, characterized in that the grinding elements are used in a 30 manner coated with catalysts such as, e.g., Ni or Ni oxide.

6. A method according to any one of claims 1 to 5, characterized in that metal balls or ceramic balls are used as said grinding elements. 35 - 13

7. A method according to any one of claims 1 to 6, characterized in that the grinding chamber is maintained under a lower pressure than the granulation chamber. 5

8. A method according to any one of claims 1 to 7, characterized in that the propellant is introduced into the mill in a pulsed manner.

9. A device for carrying out the method according to any one 10 of claims 1 to 8, characterized by a grinding chamber (11) which is at least partially filled with grinding elements (13) and to which are connected at least one connection means or a pressure-tight duct (8) to introduce the material to be ground and the propellant as well as at least one duct (17) to draw 15 off the ground material.

10. A device according to claim 9, characterized in that the connection means is designed as an outlet of a slag tundish (27) into which a propellant duct (32) opens. 20

11. A device for carrying out the method according to any one of claims 2 to 8, characterized by two chambers which are interconnected by means of a pressure-tight duct (8), whereby the first chamber (1) is designed as a pressure-tight 25 granulation chamber including a charging means (6) for liquid slag and is at least partially filled with water (4) and the second chamber (11) is designed as a grinding chamber including a discharge means (17) for the ground material and is at least partially filled with grinding elements (13), the 30 pressure-tight duct (8) running from the water-filled space of the granulation chamber (1) into the space of the grinding chamber (11) filled with grinding elements (13).

12. A device according to claim 9 or 11, characterized in that 35 the pressure-tight duct (8) is connected to the grinding chamber (11) below the grinding elements (13). - 14

13. A device according to claim 9, 11 or 12, characterized in that the pressure-tight duct (8) comprises at least one check valve (9). 5

14. A device according to any one of claims 9 to 13, characterized in that the grinding chamber (11) comprises a grate (12) or mesh bottom plates to support the grinding elements (13). 10

15. A device according to any one of claims 9 to 14, characterized in that the grinding elements (13) have diameters of less than 10 mm and, preferably, less than 5 mm.

16. A device according to any one of claims 9 to 15, 15 characterized in that a screening means (18), in particular a cyclone, is connected to the discharge openings for the ground material and coarse material separated in the screening means (18) is returned to the grinding chamber (11). 20

17. A device according to any one of claims 9 to 16, characterized in that a discharge means (15) for the grinding elements (13) is connected to the chamber (11) filled with grinding elements (13) to recirculate the grinding elements into the grinding chamber (11) via a heat exchanger (16). 25

18. A device according to any one of claims 9 to 17, characterized in that at least one further duct (26) for compressed water under pressure, reducing gases and/or gases decomposable while increasing in volume is connected to the 30 grinding chamber (11).