Method for operating a multi-cyclone for the separation of fine and very fine grain as well as a multi-cyclone

Abstract

The invention relates to a multi-cyclone and to a method for operating such a multi-cyclone for separating fine material and very fine material. In this context, a multi-cyclone according to the invention has multiple individual cyclones which are of essentially identical construction and which are housed in a housing that has an upper and a lower chamber. Via a supply into the lower chamber it is possible to introduce in a targeted manner cyclone regulating air which can be used to set the quantity, the fineness and/or the purity of the material separated by means of the multi-cyclone.

Claims

1. A method for operating a multi-cyclone for separating fine and very fine particles comprising: utilizing a multi-cyclone that comprises: two or more individual cyclones, each of which comprises a carrier gas inlet opening, a carrier gas outlet opening and a grit discharge opening, whereby the two or more individual cyclones are housed together in a low-infiltrated-air housing, in which an upper and a lower chamber is designed, whereby the carrier gas outlet openings of the two or more individual cyclones are open towards an upper chamber, whereby the upper chamber has a carrier gas overall outlet opening to discharge carrier gas which enters the upper chamber from the respective carrier gas outlet openings of the two or more individual cyclones, via the carrier gas overall outlet opening from a housing of the multi-cyclone, whereby the grit discharge openings are each designed open towards the lower chamber, whereby the lower chamber has a device for the low-infiltrated-air extraction of cyclone grits introduced through the grit discharge openings, enabling an extraction largely free from infiltrated air, whereby a common cyclone control air supply is provided to the lower chamber, wherein: the carrier gas inlet openings are each supplied from outside the housing with a carrier gas flow of equal volume with the fine and very fine particles to be separated, in the individual cyclones, an at least partial separation of fine and very fine particles is carried out, the fine particles enter the lower chamber as cyclone grit via the grit discharge openings and are discharged from there out of the housing via the device for low-infiltrated-air extraction, whereby the very fine particles are passed as cyclone fines through the upper chamber and the carrier gas overall outlet opening out of the multi-cyclone by means of the carrier gas flow, and the method comprising controlling a quantity per unit of time of cyclone control air fed into the lower chamber by the cyclone control air supply to adjust one or more of a quantity, a fineness, and a purity of the very fine particles fed from the multi-cyclone.

2. The method according to claim 1, wherein a volume per unit of time of carrier gas flows of equal volume to the individual cyclones is adjusted depending on the geometry of the individual cyclones in order to separate approximately 99% of the fine and very fine particles being in carrier gas flows as cyclone grit when the cyclone control air supply is closed.

3. The method according to claim 1, wherein a load of carrier gas flows of equal volume to the individual cyclones with fine and very fine particles is adjusted depending on the geometry of the individual cyclones, in order to separate approximately 99% of the fine and very fine particles being in carrier gas flows as cyclone grit when the cyclone control air supply is closed.

4. The method according to claim 1, wherein: a pressure difference between the upper and lower chamber is set during operation, and the pressure in the upper chamber is lower than the pressure in the lower chamber.

5. The method according to claim 1, wherein a pressure in the upper chamber and in the lower chamber is set lower than an ambient pressure.

6. The method according to claim 1, wherein the fine and very fine particles to be separated are fed to a dispersing unit, before a feed, in the multi-cyclone and from there transported to the multi-cyclone by means of the carrier gas flow.

7. The method according to claim 1, wherein: the carrier gas flow with the very fine particles from the carrier gas overall outlet opening is fed to a filter for separating the very fine particles from the carrier gas flow.

8. A multi-cyclone comprising: two or more individual cyclones, each of which comprises a carrier gas inlet opening, a carrier gas outlet opening and a grit discharge opening, whereby the individual cyclones are housed together in a low-infiltrated-air housing, in which an upper chamber and a lower chamber is designed, whereby the carrier gas outlet openings of the individual cyclones are designed open towards the upper chamber, whereby the upper chamber has a carrier gas overall outlet opening to discharge carrier gas which enters the upper chamber from the respective carrier gas outlet openings of the individual cyclones, via the carrier gas overall outlet opening from a housing of the multi-cyclone, whereby the grit discharge openings in each of the individual cyclones are designed open towards the lower chamber, whereby the lower chamber has a device for the low-infiltrated-air extraction of grits introduced through the grit discharge openings, enabling an extraction largely free from infiltrated air, whereby the carrier gas inlet openings are each designed to be supplied from outside the housing with a carrier gas flow of equal volume, which contains fine and very fine particles to be separated, whereby a common cyclone control air supply is provided to the lower chamber, via which control air is operable to be directed into the lower chamber, whereby a control and regulating device is provided to adjust a quantity, a fineness, and/or a purity of the very fine particles directed from the multi-cyclone by means of a quantity of the cyclone control air per unit of time, and whereby fine particles are operable to be separated as cyclone grit.

9. The multi-cyclone according to claim 8, wherein the individual cyclones are provided in the housing in parallel, flow-wise.

10. The multi-cyclone according to claim 8, wherein the upper chambers and the lower chambers are designed to be airtight to each other, whereby an air exchange between the upper chamber and the lower chamber only takes place via the individual cyclones.

11. A very fine particle separator for separating fine and very fine particles from a preliminary or an intermediate product comprising at least one multi-cyclone comprising: two or more individual cyclones, each of which comprises a carrier gas inlet opening, a carrier gas outlet opening and a grit discharge opening, whereby the individual cyclones are housed together in a low-infiltrated-air housing, in which an upper chamber and a lower chamber is designed, whereby the carrier gas outlet openings of the individual cyclones are designed open towards the upper chamber, whereby the upper chamber has a carrier gas overall outlet opening to discharge carrier gas which enters the upper chamber from the respective carrier gas outlet openings of the individual cyclones, via the carrier gas overall outlet opening) from a housing of the multi-cyclone, whereby the grit discharge openings in each of the individual cyclones are designed open towards the lower chamber, whereby the lower chamber has a device for the low-infiltrated-air extraction of grits introduced through the grit discharge openings, enabling an extraction largely free from infiltrated air, whereby the carrier gas inlet openings are each designed to be supplied from outside the housing with a carrier gas flow of equal volume, which contains fine and very fine particles to be separated, whereby a common cyclone control air supply is provided to the lower chamber, via which control air is operable to be directed into the lower chamber, whereby a control and regulating device is provided to adjust a quantity, a fineness, and/or a purity of the very fine particles directed from the multi-cyclone by means of a quantity of the cyclone control air per unit of time, and whereby fine particles are operable to be separated as cyclone grit, and a filter, whereby: the preliminary or the intermediate product is operable to be supplied to the at least one multi-cyclone by means of carrier gas flow, the fine particles are operable to be separated on the multi-cyclone, and by means of carrier gas the very fine particles can be further directed to the filter and separated there.

12. The very fine particle separator according to claim 11, wherein: two or more multi-cyclones are provided in series, flow-wise, one after another upstream of the filter, and the individual cyclones of the multiple multi-cyclones each feature a smaller diameter in a flow direction of the carrier gas flow.

13. The very fine particle separator according to claim 11, further comprising a storage hopper for the preliminary and intermediate product and a dispersing unit, whereby the preliminary or intermediate product to be separated is fed from the storage hopper via the dispersing unit to the very fine particle separator by means of the carrier gas flow.

14. A grinding plant to produce fine and very fine particles from a raw material with a mill-sifter combination, which features a sifter and a mill, and further comprising: a very fine particle separator comprising: two or more individual cyclones, each of which comprises a carrier gas inlet opening, a carrier gas outlet opening and a grit discharge opening, whereby the individual cyclones are housed together in a low-infiltrated-air housing, in which an upper chamber and a lower chamber is designed, whereby the carrier gas outlet openings of the individual cyclones are designed open towards the upper chamber, whereby the upper chamber has a carrier gas overall outlet opening to discharge carrier gas which enters the upper chamber from the respective carrier gas outlet openings of the individual cyclones, via the carrier gas overall outlet opening) from a housing of the multi-cyclone, whereby the grit discharge openings in each of the individual cyclones are designed open towards the lower chamber, whereby the lower chamber has a device for the low-infiltrated-air extraction of grits introduced through the grit discharge openings, enabling an extraction largely free from infiltrated air, whereby the carrier gas inlet openings are each designed to be supplied from outside the housing with a carrier gas flow of equal volume, which contains fine and very fine particles to be separated, whereby a common cyclone control air supply is provided to the lower chamber, via which control air is operable to be directed into the lower chamber, whereby a control and regulating device is provided to adjust a quantity, a fineness, and/or a purity of the very fine particles directed from the multi-cyclone by means of a quantity of the cyclone control air per unit of time, and whereby fine particles are operable to be separated as cyclone grit, and a filter, whereby: the preliminary or the intermediate product is operable to be supplied to the at least one multi-cyclone by means of carrier gas flow, the fine particles are operable to be separated on the multi-cyclone, and by means of carrier gas the very fine particles can be further directed to the filter and separated there whereby the mill-sifter combination is designed to feed raw material ground at least once during an initial sifting from the sifter of the mill-sifter combination back again to the mill as rejected coarse material for further grinding, with a grinding plant filter, whereby by means of a grinding plant carrier gas flow, ground material not rejected by the sifter of the mill-sifter combination is operable to be transported to the grinding plant filter, and there it is separated from the grinding plant carrier gas flow, wherein: whereby at least a part of a ground product separated on the grinding plant filter can be fed to the very fine particle separator as preliminary or intermediate product for the separation of fine and very fine particles.

15. The grinding plant according to claim 14, wherein the mill of the mill-sifter combination is a vertical mill with a grinding table and grinding rollers.

Description

(1) The invention is explained below using examples with schematic figures.

(2) FIG. 1 shows a sketch of a multi-cyclone according to the invention;

(3) FIG. 2 shows a schematic flow diagram of a very fine particle separator according to the invention with dispersing unit and storage hopper;

(4) FIG. 3 shows a schematic flow diagram of a grinding plant with very fine particle separator according to the invention, and

(5) FIG. 4 shows a combined schematic diagram to illustrate the cyclone control air quantity and the dust load of the carrier gas in relation to the fineness.

(6) FIG. 1 shows a schematic diagram of a multi-cyclone 1 according to the invention. In the multi-cyclone 1, several individual cyclones 10 of identical design are arranged in a housing 3, in the design example shown here, six by six, i.e. 36. In FIG. 1 only six individual cyclones 10 are visible. The further individual cyclones 10 are located in the depth directions of the sketch. The individual cyclones 10 are preferably used in a square arrangement.

(7) The individual cyclones 10 are essentially of identical design and each have a carrier gas inlet opening 11, a carrier gas outlet opening 12, and a grit discharge opening 13. The housing 3 is divided into an upper chamber 5 and a lower chamber 6 by means of a separation 15.

(8) Each of the individual cyclones 10 are arranged between the upper chamber 5 and the lower chamber 6. The carrier gas inlet openings 11 of the individual cyclones 10 are designed so that they can be operated with a carrier gas flow from outside the housing 3. The carrier gas is fed into the carrier gas inlet openings 11 of the individual cyclones 10 directly from outside the housing 3, so that the carrier gas does not first penetrate into the upper chamber 5 or lower chamber 6.

(9) Each individual cyclone 10 is connected flow-wise to the upper chamber 5 via its carrier gas outlet opening 12. In the same way, each individual cyclone 10 is connected flow-wise to the lower chamber 6 via its grit discharge opening 13. The upper chamber 5 has a carrier gas overall outlet opening 7 through which carrier gas, which enters the upper chamber 5 from the carrier gas outlet openings 12 of the individual cyclones 10, can exit.

(10) The lower chamber 6 is equipped with a device for low-false-air or low-infiltrated-air extraction of cyclone grits. This device can be designed as a rotary valve 8, for example, so that the cyclone grits can be discharged from the lower chamber 6 without larger quantities of air entering the lower chamber 6.

(11) In addition, a cyclone control air supply 9 is provided in the lower chamber 6. Air or gas can be selectively directed into the lower chamber 6 via this cyclone control air supply 9. For this purpose, a volume flow measurement 62 and a control valve 61 are mounted in front of the cyclone control air supply 9, with which the volume or the quantity of cyclone control air introduced into the lower chamber 6 can be varied and adjusted.

(12) In the following, the operation and function of the multi-cyclone 1 according to the invention will be explained in more detail.

(13) According to the invention, the multi-cyclone 1 is not used for removing particles from an air or gas flow as is customary, but as a targeted separation unit for particles present within a carrier gas flow. For this purpose, a carrier gas flow is fed into the individual cyclones 10, each of which is arranged in parallel flow-wise, i.e. side by side and in a row, with a corresponding particle load.

(14) In the context of the invention, reference is made in this respect to fine and very fine particles, whereby a separation between fine and very fine particles is to be carried out. The carrier gas loaded with particles is divided among the individual cyclones 10 with an equal volume per unit of time and an equal particle loading, so that the individual cyclones 10 have separation characteristics that are as identical as possible. Due to the geometry of the inlet cylinder and the cone of the individual cyclones 10, it is possible to separate the particles from the carrier gas flow in a familiar manner. The separated particles are transferred via the grit discharge opening 13 as cyclone grits into the lower chamber 6 or fall into this. The carrier gas, essentially cleaned of the particles, can then penetrate in the upper chamber 5 via the carrier gas outlet opening 12 from the individual cyclones 10 and in turn leave this via the carrier gas overall outlet opening 7.

(15) In individual cyclone 10, the particles are separated essentially by the fact that the carrier gas with the particles being on a circular path is further accelerated through the geometry of the cyclone, so that the particles leave the accelerated carrier gas flow due to centrifugal force and gravity and fall out downwards via the grit discharge opening 13. The carrier gas cleaned in this way can then escape from the individual cyclone 10 via a provided immersion tube, as already described, and via the carrier gas outlet opening 12.

(16) The flow conditions that occur within an individual cyclone 10 are also known as the vortex sink. If this vortex sink is disturbed, for example by cyclone control air flowing into the individual cyclone 10 via the grit discharge openings 13, the flow velocity of the carrier gas in the individual cyclone 10 changes so that even lighter particles, which are referred to here as very fine particles, can exit the individual cyclone 10 via the immersion tube and are separated not as cyclone grit via the grit discharge opening 13.

(17) The invention makes use of this knowledge by specifically feeding cyclone control air into the lower chamber 6 of the multi-cyclone 1 via the cyclone control air supply 9. It is essential to ensure that the supplied cyclone control air flows through the individual cyclones 10 and influences the vortex sink. This can be done, for example, by providing a suction fan downstream of the carrier gas overall outlet opening 7, which sucks the carrier gas through the multi-cyclone 1. In this way, the static pressure in the upper chamber 5 is lower than in the lower chamber 6, where in turn the pressure there is lower than the ambient pressure. In this way, the cyclone control air can be supplied to the lower chamber 6 by opening and closing the control valve 62.

(18) To achieve an effective operation of the multi-cyclone 1 according to the invention, it has proven to be advantageous to adjust the quantity of the carrier gas and the loading of this with particles in such a way to achieve a 99% or even better separation of the particles in the individual cyclones 10 with cyclone control air supply 9 closed. If cyclone control air is now purposefully supplied, the separation rate can be changed so that a part of the particles can be discharged as very fine particles via the carrier gas overall flow exiting from the multi-cyclone 1 and can later be separated from this.

(19) In other words, by means of the cyclone control air can be used to adjust the mass flow distribution between very fine particles, which are discharged from the multi-cyclone, and fine particles, which are separated as cyclone grit in the multi-cyclone. This means that with a completely open cyclone control air supply 9 almost 100% of the particles present in the carrier gas flow are removed from the multi-cyclone 1 via the overall carrier gas outlet opening 7. In contrast, almost 100%, more precisely approximately 99%, of the particles in the carrier gas flow are separated as cyclone grit in multi-cyclone 1 when the cyclone control air supply 9 is completely closed.

(20) For example, it is possible when inputting particles to be separated with 5000 Blaine, i.e. approx. D50=8 m, and using individual cyclones with a diameter of 150 mm, to separate very fine particles with a fineness of D50<6 m with a correspondingly adjusted cyclone control air quantity. In principle, it can be stated that the area of the optimum separation is essentially also defined by the geometry, in particular the diameter of the individual cyclones. This can also be called as selectivity of an individual cyclone. In connection with the cyclone control air, the fineness of the fine particles can be defined and readjusted in this way within a certain band range.

(21) The D50 value describes the particle size distribution in a particle distribution where 50 wt. % is larger and 50 wt. % is smaller than the specified diameter of the limit particle. It has transpired, especially with the finenesses shown here, that this size is better suited than the usual specific surface according to Blaine.

(22) FIG. 2 shows the multi-cyclone 1 according to the invention in the context of a very fine particle separator 40. As essential elements, the very fine particle separator 40 has a storage hopper 42 for a preliminary or intermediate product to be separated.

(23) Furthermore, a dispersing unit 20 is provided to be able to distribute the preliminary or intermediate product to be separated as homogeneously as possible in a carrier air flow. This is followed by a multi-cyclone 1 according to the invention, followed downstream by a filter 30, which is preferably designed as a bag filter.

(24) In the following, the design of the very fine particle separator 40 will be discussed in more detail, including a description of its function and mode of operation.

(25) The preliminary or intermediate product stored in hopper 42 is fed via a rotary valve 43 to a speed-controlled screw conveyor 44, which feeds the preliminary or intermediate product to the dispersing unit 20. In principle, the discharge from the hopper and the feeding to the dispersing unit 20 can also be achieved by other means.

(26) As already explained, the dispersing unit 20 serves to distribute the product to be separated as homogeneously as possible in a carrier gas flow. The dispersing unit 20 shown schematically in FIG. 2 is described as an example, whereby differently designed dispersing units can also be used.

(27) To generate the carrier gas flow into which the preliminary and intermediate product is introduced, a fan 45 with corresponding control is provided downstream of the filter 30. This fan 45 sucks the carrier gas through the filter 30, the multi-cyclone 1, and the dispersing unit 20.

(28) For this purpose, air intake openings 23 are provided in the dispersing unit 20. The dispersing unit 20 itself has a distributor plate 22, a blade ring 24, turbulence fixtures 25, and a displacement body 26. The preliminary or intermediate product fed to the dispersing unit 20 via the screw conveyor 44 falls onto the distributor plate 22. The distributor plate 22 rotates, so that the fed preliminary or intermediate product slides off at the side of the distributor plate 22 or is flung onto a wall of the dispersing unit 20. It is thus mechanically torn apart and distributed over a larger flow cross-section. Due to the carrier gas already described above, which flows through the air intake openings 23 and is additionally swirled by means of the blade ring 24, which is arranged at the edge of the distributor plate 22, the preliminary or intermediate product to be separated is swept along by the carrier gas flow. The rapidly entering carrier gas causes the preliminary or intermediate product to be torn apart again, in this case pneumatically.

(29) To achieve an even better dispersion, turbulence installations 25 are provided in the flow direction of the carrier gas, which achieve an additional turbulence and thus better dispersion of the preliminary and intermediate product to be separated. The turbulence installations 25 can, for example, be designed using static mixing elements or bluff bodies. However, in addition to or as an alternative to these embodiments, it is also possible to use a dynamic rotor, which further improves the mixing and dispersion of the preliminary or intermediate product. This is additionally improved by the displacement body 26, which can be designed so as to be height-adjustable.

(30) After the dispersing unit 20, the preliminary or intermediate product to be separated is directed to the multi-cyclone 1 according to the invention by means of the carrier gas flow. This is regulated, as already explained in relation to FIG. 1, by operating it in the basic state with regard to the loading of the carrier gas flow, which is adjusted by means of the supply from hopper 42, and the volume per unit of time of the carrier gas flow, which is adjusted via the fan 45, in such a way that in the initial state an almost complete separation of the fine and very fine particles in the multi-cyclone 1 is possible. By supplying cyclone control air via the cyclone control air supply 9, a poorer separation is then achieved, which means that the fine particles in the carrier gas flow are not separated as cyclone grit but are directed further towards filter 30 with the carrier gas flow.

(31) In this filter 30, the very fine particles are also separated and can be discharged from filter 30, for example via a rotary valve 31. The carrier gas flow thus cleaned can be partially fed back into the process or blown out into the environment.

(32) The advantage of the very fine particle separator 40 described here is that it can always be operated in the range of an optimum operating point, irrespective of upstream processes that produce the preliminary or intermediate product, since both the loading and the volume per unit of time of the carrier gas are only defined by the properties of the individual assemblies of the very fine particle separator 40 and do not have to take into account further upstream or downstream processes.

(33) This is further clarified in the following with reference to FIG. 3. FIG. 3 shows a grinding plant 50 with a mill-sifter combination 51. The mill-sifter combination has a mill 52 and a sifter 53. The ground material comminuted in the mill-sifter combination 51 is transported to a grinding plant filter 55 by means of a grinding plant carrier gas flow, which is adjusted by the mill fan 56. The grinding plant carrier gas flow can be returned again in part via a hot gas generator 57, which, for example, enables a grind drying in the mill-sifter combination.

(34) In the grinding plant filter 55, particles located in the carrier gas flow of the grinding plant are separated. These particles are then fed to the very fine particle separator 40 with a multi-cyclone 1 according to the invention.

(35) This figure shows that by the design of the very fine particle separator 40 accordng to the invention allows it to be operated essentially decoupled from the grinding plant circuit. As a result, both the grinding plant 50 itself and the very fine particle separator 40 each can be operated at optimum operating points, which also depend on the loading of the carrier gas flows with material to be ground or separated and the volume per unit of time of the carrier gas.

(36) For example, conventional grinding plants 50, as shown in FIG. 3 as an example, usually have a carrier gas load in the range of 30 g/m.sup.3 to 50 g/m.sup.3 with a fineness of up to 6000 cm.sup.2/g at their optimum operating point. On the other hand, a multi-cyclone 1 according to the invention and thus also the very fine particle separator 40 can be operated with a load in the range between 200 g/m.sup.3 and 300 g/m.sup.3. By decoupling, it is thus possible to dimension the very fine particle separator 40 smaller or to provide only one very fine particle separator 40 for several grinding plants 50. This reduces the required plant size and thus minimizes investment costs.

(37) FIG. 4 shows a combined schematic diagram illustrating the relationship between the cyclone control air quantity and the dust load of the carrier gas in relation to the fineness of the very fine particles.

(38) Here, the fineness in cm.sup.2/g of the very fine particles is provided on the ordinate. The cyclone control air quantity in m.sup.3/h is shown on the left side of the abscissa and the load of the carrier gas in g/m.sup.3 on the right side.

(39) As can be seen from the diagram, the fineness of the very fine particles decreases with increasing cyclone control air quantity. In contrast, for the fineness an optimum dust load or particle load of the carrier gas flow before the multi-cyclone is formed.

(40) From this it can be concluded that, as already described above, there is an optimum operating point for operating a multi-cyclone according to the invention in relation to the loading of the carrier air flow. The fineness of the very fine particles can then be influenced according to a control system using the cyclone control air.

(41) The multi-cyclone according to the invention and its operating method for separating fine and very fine particles thus enable simple and efficient separation of fine and very fine particles as well as a decoupled operation from upstream process plants.