AU5682600A

AU5682600A - Method for the preparation of fine grain ores

Info

Publication number: AU5682600A
Application number: AU56826/00A
Authority: AU
Inventors: Konstantin Milionis; Johannes Schenk; Gero Tessmer; Johann Zirngast
Original assignee: Voest Alpine Industrienlagenbau GmbH
Current assignee: Primetals Technologies Austria GmbH
Priority date: 1999-07-27
Filing date: 2000-06-16
Publication date: 2001-02-13
Also published as: KR20020016918A; EP1204773A1; AT407346B; JP2003505240A; CA2378956A1; ATA130099A; WO2001007670A1; MXPA02000629A

Description

Process for the beneficiation of fine-grained ore The present invention relates to a process for the beneficiation of fine-grained ore, the ore being 5 subjected to gas classification by means of a gas, in which classification two fractions are formed, namely a coarse fraction and a first fine fraction, the coarse fraction being separated out and the first fine fraction being entrained with the gas, then separated 10 out of the gas and at least as far as possible being fed for processing together with the coarse fraction, and to an installation for carrying out the process. In fluidized-bed processes, for example those used for 15 the direct reduction of fine-grained ore, cyclones are used to separate out and recycle the material which is discharged with the fluidizing gas. The separation capacity, i.e. the efficiency and the separation grain size of the cyclones, is adversely affected by the 20 formation of caking and adhesion in the cyclone, with the result that more material is discharged from the fluidized-bed reactor together with the fluidizing gas. In the case of direct reduction of fine-grained ore, for example iron ore, it is primarily at least 25 partially reduced fine ore dust which causes this caking and adhesion. The resulting increased discharge of material either has to be recorded as a loss or, in the case of multistage processes carried out in downstream fluidized-bed reactors, causes problems by 30 blocking the holes in the distributor bases of these fluidized-bed reactors. The fine dust which causes these problems is formed firstly through mechanical abrasion of the material 35 which is to be reduced in the fluidized-bed process and secondly by being introduced with the charge material. Particularly when using fine iron ores, the proportion of so-called adhesion and fine grains presents a problem. On the one hand, this material is involved in -2 the formation of caking and adhesion, and secondly it is discharged from the system and lost. To dry fine iron ores, it is the state of the art to 5 use fluidized-bed dryers by means of which the charge material is simultaneously separated into a coarse fraction and a fine fraction. These material flows are used to set the charge grain size in a controlled way. 10 A process of this type is known, for example, from AT-B-400 578. In this known process, fine ore is dried with the aid of a hot drying gas which flows around the ore particles of the fine ore, and the drying gas, after it has flowed around the ore particles, is 15 cleaned, with entrained ore dust particles being removed. The ore dust particles are collected and are admixed with the dried fine ore. The drying takes place at the same time as gas classification of the fine ore in the fluidized-bed process, the drying gas being 20 passed through the fine ore to form a fluidized bed, and the velocity of the drying gas being set at a level at which ore dust particles which are smaller than a preselected size are entrained. The ore dust particles entrained by the drying gas are separated out, 25 collected and admixed to the dried fine ore in metered quantities. When using the ore which has been treated in this way in a fluidized-bed direct reduction process, the fine ore may under certain circumstances cause problems by, in an at least partially reduced 30 state, leading to caking and adhesion in the fluidized bed reactor. US-A-3 917 480 has disclosed a process for the beneficiation of particulate material for use in 35 fluidized-bed reactors, in which, in a first process step, 20-70% of the fine fraction of the material is separated out and the remaining fraction is introduced into a fluidized bed, a further fine fraction being separated out in the fluidized bed, discharged and - 3 admixed with the fine fraction obtained in the first process step. The fine fractions are pelletized and added to the fluidized bed. A drawback of this process is that at least a not inconsiderable fine fraction 5 enters the fluidized bed, where it can cause the above mentioned problems, such as adhesion and caking. DE-A-197 11 629 shows a process for the pretreatment of fine ores having a wide grain size range for direct 10 reduction as known, in which the fine ores belonging to the grain size fraction of less than 6.3 mm and preferably less than 3 mm are dried by means of a hot air or flue-gas flow during a pneumatic conveying operation, if appropriate with the moist material being 15 recycled, the 6.3 mm or 3 mm down to approx. 0.04 mm fraction being screened out of the dried fine ore and being fed for direct reduction. The fine ore fraction of a size which is smaller than approx. 0.04 mm and is discharged from the cyclone connected downstream of the 20 dryer together with the drying air or the flue gas, passes for ultrafine separation into a multicyclone. The fine ore which is separated out there is fed to a pelletizing device and is shaped into pellets, with water and binder being supplied, these pellets 25 ultimately being added to the dryer via a delivery device. The multicyclone which is provided for the ultrafine separation is an extremely complex apparatus. The present invention is based on the object of 30 providing a process for the beneficiation of fine grained ore and an installation for carrying out the process, according to which the ore is beneficiated in such a manner that, when the ore is subsequently used in a fluidized-bed reactor, the abovementioned 35 problems, such as caking and adhesion in a cyclone and a fluidized-bed reactor, are avoided. The process should in particular be easy to carry out without major outlay on equipment.

-4 According to the invention, this object is achieved, in a process of the type described in the introduction, by the fact that the first fine fraction is subjected to a further gas classification by means of a gas, in which 5 a second fine fraction and an ultrafine fraction are formed, and the second fine fraction is fed for processing together with the coarse fraction and the ultrafine fraction is entrained with the gas and is then separated out of the gas. 10 The invention is based on the discovery that the ultrafine fraction of the ore, in the at least partially reduced state, is principally responsible for caking and adhesion in fluidized-bed reactors. 15 Furthermore, it has been discovered that this ultrafine fraction adheres to the first fine fraction, which is separated from the charge material by means of the first gas classification. After reduction, i.e. in the at least partially reduced state, during the processing 20 of the second fine fraction together with the coarse fraction, the ultrafine fraction, as is known, for example, from the abovementioned AT-B-400 578, causes the abovementioned problems in the fluidized-bed reactor. According to the invention, this is avoided by 25 separating the ultrafine fraction out of the first fine fraction. Preferably, the ultrafine fraction which has been separated out of the gas is admixed with a binder, 30 granulated and fed for processing or discharged. In the case of granulation and further processing, the ultrafine fraction is advantageously not lost to further processes. 35 Expediently, granules which are formed from the ultrafine fraction are processed further together with the coarse fraction and the second fine fraction. By way of example, the further processing involves direct reduction downstream of the ore beneficiation.

- 5 However, according to a further preferred embodiment, granules which are formed from the ultrafine fraction can also be admixed with the fine-grained ore which is to be subjected to the first gas classification. 5 Expediently, gas from which the entrained ultrafine fraction has been removed is subjected to further cleaning, in which an extremely ultrafine fraction is separated out, and this fraction, preferably together 10 with the ultrafine fraction, is granulated and fed for processing or discharged. As a result, it is also possible to substantially utilize the dust fractions which are still present in the gas after the ultrafine fraction has been separated out. 15 According to a preferred embodiment, at least a partial quantity of the second fine fraction is likewise granulated, preferably together with the ultrafine fraction and/or extremely ultrafine fraction. In this 20 way, problems with caking and adhesion of ore in dust form in subsequent processes are particularly reliably avoided. In the process according to the invention, the first 25 fine fraction is separated out of the fine-grained ore by means of the first gas classification preferably with a particle size of up to 150 pm, and the ultrafine fraction is separated out of the first fine fraction with a particle size of up to 20 pm by means of the 30 further gas classification. According to a preferred embodiment of the process according to the invention, a drying gas is used at least in the first gas classification. In this case, 35 drying takes place at the same time as the gas classification of the charge material. The binder used for the granulation is advantageously calcined lime or bentonite.

~6 Preferably, gas which is used in the first gas classification and from which the first fine fraction has been removed is used for the further gas 5 classification. An installation for carrying out the process according to the invention, having a first gas classifier, provided with a feed for fine-grained ore, a gas feed 10 line, an outlet line for a coarse fraction and an outlet line for gas and a first fine fraction entrained with the gas, and having a first gas-cleaning device which is connected downstream of the first gas classifier and separates the first fine fraction out of 15 the gas, is characterized in that an outlet line for the first fine fraction leading out of the first gas cleaning device has a line connection to a further gas classifier, which has a gas feed line, an outlet line for a second fine fraction and an outlet line for gas 20 and an ultrafine fraction entrained with the gas, and in that a second gas-cleaning device, which separates the ultrafine fraction out of the gas, is connected downstream of the further gas classifier. 25 Preferably, an outlet line for the ultrafine fraction leading out of the second gas-cleaning device has a line connection to a granulation apparatus, a feed line for a binder opening into the granulation apparatus. 30 According to a further preferred embodiment, the granulation apparatus has a line connection to the feed for feeding fine-grained ore to the first gas classifier. 35 Advantageously, a common discharge apparatus is provided for the coarse fraction, the second fine fraction and the ultrafine fraction which is subjected to granulation.

- 7 The gas-cleaning devices are expediently designed as cyclones. Preferably, a further gas-cleaning device for 5 separating out an extremely ultrafine fraction, which is entrained with the gas, is connected downstream of the second gas-cleaning device, an outlet line for the extremely ultrafine fraction leading out of the further gas-cleaning device having a line connection to a 10 granulation apparatus. According to a further preferred embodiment of the installation according to the invention, the outlet line for the second fine fraction leading out of the 15 further gas classifier has a line connection to a granulation apparatus. Expediently, at least the first gas classifier is designed as a dryer, a feed line for drying gas opening 20 into the gas classifier. Advantageously, a gas outlet line leading out of the first gas-cleaning device has a line connection to the gas feed line leading to the further gas classifier. 25 The invention is explained in more detail below with reference to the drawing and on the basis of an exemplary embodiment. The figure diagrammatically depicts a flow diagram for a preferred embodiment of 30 the invention. The figure illustrates a gas classifier 1, which is designed as a fluidized-bed unit and into which fine grained ore 2 is introduced via a feed 3. The fine 35 grained ore 2, which forms a bed 4 in the gas classifier 1, is fluidized and subjected to gas classification by means of a gas supplied via a feed line 5. In the process, it is separated into a coarse fraction 6, which is discharged via an outlet line 7, -8 and a first fine fraction 8, which is entrained with the gas. In the exemplary embodiment shown, the fine-grained 5 ore 2 used has a grain size of from 0 to 12 mm. It is separated into the coarse fraction 6, with a grain size of from 0.15 to 12 mm, and the first fine fraction 8, with a grain size of from 0 to 0.15 mm, by gas classification. The gas used is a drying gas, the fine 10 grained ore 2 being subjected to drying as well as gas classification. The coarse fraction 6 which is discharged via the outlet line 7 is applied to a discharge apparatus, 15 which is designed as a conveyor belt 9, and is fed for further processing, for example direct reduction. The first fine fraction 8 is discharged from the gas classifier 1 together with the gas via an outlet line 10 and is separated out of the gas. An impingement 20 separator 11 and a cyclone 12 are used for this purpose. The fine fraction 8 which has been separated out passes into a storage hopper 13 and, from there, via a line 14, into a further gas classifier 15, which is likewise designed as a fluidized-bed unit. In the 25 further gas classifier 15, the first fine fraction 8 forms a bed 16. The gas used is gas from which the first fine fraction 8 has been removed by means of the cyclone 12 and which is supplied via a feed line 17. 30 In the further gas classifier 15, the first fine fraction 8, with a grain size of from 0 to 0.15 mm, is separated into a second fine fraction 18, with a grain size of from 20 to 150 sm, and an ultrafine fraction 19, with a grain size of from 0 to 20 pm. The 35 second fine fraction 18 is discharged from the further gas classifier 15 via an outlet line 20, is applied to the conveyor belt 9 and is fed for further processing together with the coarse fraction 6.

- 9 The gas and the ultrafine fraction 19 which is entrained with the gas are discharged from the further gas classifier 15 via an outlet line 21. The gas is cleaned by means of a cyclone 22, in which the 5 ultrafine fraction 19 is separated out. The ultrafine fraction 19 passes into a storage hopper 23 and, from there, to a granulation apparatus 24. A feed line 25 for a binder 26 for 10 granulating the ultrafine fraction 19 opens into the granulation apparatus 24. The binder 26 used in the exemplary embodiment shown is calcined lime or bentonite. 15 The ultrafine fraction 19 is granulated to form granules 27 with a grain size of from 0.5 to 4 mmn, and the granules 27 are likewise applied to the conveyor belt 9. They are fed for further processing together with the coarse fraction 6 and the second fine 20 fraction 18. However, it is also possible for the granules 27 to be fed to the first gas classifier 1 via a line (not shown in more detail in the figure) and to be introduced into 25 this classifier together with the fine-grained ore 2. According to a further preferred embodiment, the ultrafine fraction 19 is not fed to the granulation apparatus 24 but rather, as indicated by dashed line 28 30 in the figure, is discharged and fed, for example, for landfill. The advantage of this variant is that the step of granulating the ultrafine fraction 19, which in quantitative terms forms a relatively small proportion of the overall charge of fine-grained ore 2, is 35 dispensed with, yet at the same time the ultrafine fraction 19 is prevented from causing disruption in subsequent processing steps, in particular from causing caking and adhesion. The small quantity of charge material lost is of only subordinate importance if ore - 10 prices are low. In the exemplary embodiment shown, the gas which has been cleaned by means of the cyclone 22 is fed to a 5 further gas-cleaning device 29 which may, for example, be an electrostatic filter. By means of the further gas-cleaning device 29, an extremely ultrafine fraction 30, which is still entrained following cleaning in the cyclone 22, is separated out of the gas 10 and is likewise fed to the granulation apparatus 24 and granulated together with the ultrafine fraction 19. However, it is also equally possible for the extremely ultrafine fraction 30 to be discharged and landfilled, as indicated by dashed line 28 in the figure. 15 The second fine fraction 18 which is discharged from the second gas classifier 15 and is not entrained with the gas can at least in part be fed, via a line 31 which is indicated in dashed lines in the figure, to 20 the granulation apparatus 24, where it is granulated together with the ultrafine fraction 19 and the extremely ultrafine fraction 30 and is fed for further processing. 25 The invention is to be explained in even more detail on the basis of the following exemplary embodiment: Fine-grained ore 2 with a grain size of from 0 to 12 mm, which represents 100% of the charge material, is 30 introduced into the first gas classifier 1 and is separated into a coarse fraction 6, with a grain size of from 0.15 to 12 mm, and a first fine fraction 8, with a grain size of from 0 to 0.15 mm. The coarse fraction 6 makes up 67% of the charge. 35 The first fine fraction, which makes up 33% of the charge, is introduced into the further gas classifier 15 and is separated into a second fine fraction 18, with a grain size of from 20 to 150 [ym, - 11 and an ultrafine fraction 19, with a grain size of from 0 to 20 gm. The second fine fraction 18 makes up 29% of the fine-grained ore 2 which is used, and the ultrafine fraction 19 makes up 4% of the charge material. 5 Electrostatic filters are used to separate an extremely ultrafine fraction 30 with a grain size of up to 1 gm out of the gas from which the ultrafine fraction 19 has been removed. 10 The invention is not restricted to the exemplary embodiment given above. Naturally, there is considerable scope for variations with regard to the grain size of the material used and with regard to the grain size of the fractions which are separated out and 15 their quantitative proportions in the material used.

Claims

1. A process for the beneficiation of fine-grained ore (2), the ore (2) being subjected to gas 5 classification by means of a gas, in which classification two fractions (6, 8) are formed, namely a coarse fraction (6) and a first fine fraction (8), the coarse fraction (6) being separated out and the first fine fraction (8) 10 being entrained with the gas, then separated out of the gas and at least as far as possible being fed for processing together with the coarse fraction (6), characterized in that the first fine fraction (8) is subjected to a further gas 15 classification by means of a gas, in which a second fine fraction (18) and an ultrafine fraction (19) are formed, and the second fine fraction (18) is fed for processing together with the coarse fraction (6) and the ultrafine fraction 20 (19) is entrained with the gas and is then separated out of the gas.

2. The process as claimed in claim 1, characterized in that the ultrafine fraction (19) which has been 25 separated out of the gas is admixed with a binder (26), granulated and fed for processing or discharged.

3. The process as claimed in claim 2, characterized 30 in that granules (27) which are formed from the ultrafine fraction (19) are processed further together with the coarse fraction (6) and the second fine fraction (18). 35

4. The process as claimed in claim 2, characterized in that granules (27) which are formed from the ultrafine fraction (19) are admixed with the fine grained ore (2) which is to be subjected to the first gas classification. - 13

5. The process as claimed in one of claims 1 to 4, characterized in that gas from which the entrained ultrafine fraction (19) has been removed is 5 subjected to further cleaning, in which an extremely ultrafine fraction (30) is separated out, and this fraction, preferably together with the ultrafine fraction (19), is granulated and fed for processing or discharged. 10

6. The process as claimed in one of claims 1 to 5, characterized in that at least a partial quantity of the second fine fraction (18) is likewise granulated, preferably together with the ultrafine 15 fraction (19) and/or extremely ultrafine fraction (30).

7. The process as claimed in one of claims 1 to 6, characterized in that the first fine fraction (8) 20 is separated out of the fine-grained ore (2) by means of the first gas classification with a particle size of up to 150 gm, and the ultrafine fraction (19) is separated out of the first fine fraction (8) with a particle size of up to 20 gm 25 by means of the further gas classification.

8. The process as claimed in one of claims 1 to 7, characterized in that a drying gas is used at least in the first gas classification. 30

9. The process as claimed in one of claims 2 to 8, characterized in that calcined lime or bentonite is used as binder (26) for the granulation. 35

10. The process as claimed in one of claims 1 to 9, characterized in that gas which is used in the first gas classification and from which the first fine fraction (8) has been removed is used for the further gas classification. - 14

11. An installation for carrying out the process as claimed in one of claims 1 to 10, having a first gas classifier (1), provided with a feed (3) for 5 fine-grained ore (2), a gas feed line (5), an outlet line (7) for a coarse fraction (6) and an outlet line (10) for gas and a first fine fraction (8) entrained with the gas, and having a first gas-cleaning device (11, 12) which is connected 10 downstream of the first gas classifier (1) and separates the first fine fraction (8) out of the gas, characterized in that an outlet line (14) for the first fine fraction (8) leading out of the first gas-cleaning device (11, 12) has a line 15 connection to a further gas classifier (15), which has a gas feed line (17), an outlet line (20) for a second fine fraction (18) and an outlet line for gas and an ultrafine fraction (19) entrained with the gas, and in that a second gas-cleaning device 20 (22), which separates the ultrafine fraction (19) out of the gas, is connected downstream of the further gas classifier (15).

12. The installation as claimed in claim 11, 25 characterized in that an outlet line for the ultrafine fraction (19) leading out of the second gas-cleaning device (22) has a line connection to a granulation apparatus (24), a feed line (25) for a binder (26) opening into the granulation 30 apparatus (24).

13. The installation as claimed in claim 12, characterized in that the granulation apparatus (24) has a line connection to the feed (3) for 35 feeding fine-grained ore (2) to the first gas classifier (1).

14. The installation as claimed in claim 12 or 13, characterized in that a common discharge apparatus - 15 (9) is provided for the coarse fraction (6), the second fine fraction (18) and the ultrafine fraction (18) which is subjected to granulation. 5

15. The installation as claimed in one of claims 11 to 14, characterized in that the gas-cleaning devices are designed as cyclones (12, 22).

16. The installation as claimed in one of claims 11 to 10 15, characterized in that a further gas-cleaning device (29) for separating out an extremely ultrafine fraction (30), which is entrained with the gas, is connected downstream the second gas cleaning device (22), an outlet line for the 15 extremely ultrafine fraction (30) leading out of the further gas-cleaning device (29) having a line connection to a granulation apparatus (24).

17. The installation as claimed in one of claims 11 to 20 16, characterized in that the outlet line (20) for the second fine fraction (18) leading out of the further gas classifier (15) has a line connection (31) to a granulation apparatus (24). 25

18. The installation as claimed in one of claims 11 to 17, characterized in that at least the first gas classifier (1) is designed as a dryer, a feed line (5) for drying gas opening into the gas classifier (1). 30

19. The installation as claimed in one of claims 11 to 18, characterized in that a gas outlet line leading out of the first gas-cleaning device (11, 12) has a line connection to the gas feed 35 line (17) leading to the further gas classifier (15).