CA1082890A - Balling process - Google Patents
Balling processInfo
- Publication number
- CA1082890A CA1082890A CA252,884A CA252884A CA1082890A CA 1082890 A CA1082890 A CA 1082890A CA 252884 A CA252884 A CA 252884A CA 1082890 A CA1082890 A CA 1082890A
- Authority
- CA
- Canada
- Prior art keywords
- balls
- balling
- separated
- drum
- discharged
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B1/00—Preliminary treatment of ores or scrap
- C22B1/14—Agglomerating; Briquetting; Binding; Granulating
- C22B1/24—Binding; Briquetting ; Granulating
- C22B1/242—Binding; Briquetting ; Granulating with binders
Abstract
ABSTRACT OF THE DISCLOSURE
In a continuous balling process, which may be the formation of green balls from iron ore, water and a binder in a balling drum as a stage in the pelletizing of iron ore, which includes a balling circuit in which undersized balls are recycled directly together with further raw material, the phenomenon known as surging is reduced by a method which involves including in the process a stage modifying the fundamental direct relationship between discharged undersize balls and those recharged, this unmodified direct relationship being the recurrence of the discharged balls identically as recharged balls after a constant time interval.
In a continuous balling process, which may be the formation of green balls from iron ore, water and a binder in a balling drum as a stage in the pelletizing of iron ore, which includes a balling circuit in which undersized balls are recycled directly together with further raw material, the phenomenon known as surging is reduced by a method which involves including in the process a stage modifying the fundamental direct relationship between discharged undersize balls and those recharged, this unmodified direct relationship being the recurrence of the discharged balls identically as recharged balls after a constant time interval.
Description
108~8~0 This invention relates to a balling process. It is especially suitable for the control of a balling process producing green balls from finely crushed iron ore and water.
Balling is a process which can be applied ~o the p~elletizing of iron ore to form a product suitable as a blast furnace feed material. In a typical pelletizing plant an ore or a mixture of ores is dried and then ground to the required fineness. A very small proportion of a binding additive (e g. bentonite~ is added to improve its adhesion properties. A finely controlled amount of water is added.
The product, now referred to as concentrate, is then charged to several balling drums into which a further small proportion of water is sprayed. In each rotating balling drum the damp materil agglomerates to form green balls.
The product of each drum is screened: undersize and crushed oversize green balls are recirculated, while the acceptable product is charged to a moving grate on which the green balls are dried and preheated before being fired to form the required pellets.
A balling drum rotates about its longitudinal axis which is slightly inclined to the horizontal. The higher end is the charge end, the lower end the discharge end.
A conveyor is provided to return the undersize green balls from the discharge end to the charge end.
The mechanism of balling is complex but two significant stages in green ball growth are the initial formation of small porous stable balls known as seeds and a subsequent growth phase in which balls grow by taking up either raw concentrate or the material of smaller balls.
In the balling process new concentrate at a constant rate and returned undersized green balls are S supplied to the charge end of the balling drum. In the flrst fe~ metres of the drum the existing balls grow and new seeds are formed from the concentrate. In the remainder of the drum the larger balls grow at the expense of the smaller ones. At the discharge end a new distribution of green balls emerges of which the undersized are recycled to the charge end and pass through the drum again.
We have performed a theoretical analysis on the balling drum circuit and have found that the balling -process is essentially a non-linear feedback system, with non-linear components due to the drum and the screens, and an effective linear part consisting of the net loop time dealy. Such loops are a feature ln control systems analysis and, depending upon the nature of the loop components, the system may exhibit a periodic non-linear, limit cycle, oscillation. This behaviour is continuously observed in practice on balling circuits and is known colloquially as 'surging' i.e. a self-sustaining oscillation in product size distribution. If a large number of undersized green balls are discharged and returned to the charge end of the drum they will act as seeds; and during their next pass through the drum they will reduce the number of new seeds formed by initially taking up more of the available raw :' ~ ~0~32890 material and subsequently crushing more of the seeds that do form to grow further. This will result in a small number of undersized balls being discharged, and correspondingly a small number of seeds being recycled. In the next pass of these seed~l through the drum new seed formation will be less inhibited and the product will once again contain a large number of undersized green balls. In the normal operating region to ohtain acceptable ball quality surging is inevitable in the conventional balling circuit.
Surging in the balling drum results in cyclical variations in the number of green balls formed of satisfactory size. These variations must be contained to a small proportion of product throughput to enable satisfactory performance to be achieved in the subsequent stages of the pelletizing process.
We are aware of no practical and economic way which has yet been found to elirninate surging but various control methods have been proposed. These include variation in the binding additive addition and in the water spray addition in the balling drum. Each method has its own disadvantages.
According to the present invention, as herein claimed, there is provided a process for balling particulate material com-prising the steps of: improving the adhesion properties of the particulate material by adding water and a binding medium;
balling said particulate material in a balling drum to produce green balls; discharging said balls from said balling drum;
separating balls having a size other than predetermined size from balls having said predetermined size after their discharge from the said balling drum; and continuously returning said separated balls to said balling drum for balllng with adde~
particulate material, in which process the recurrence of dis-charged separated balls identically as those balls recharged to the balling drum after a constant time interval is modified by B
~ ~08Z890 varying the normally constant mass relationship between the discharged separated and recharged balls so as to reduce the system gain.
The recurrence of discharged separated balls identi-call~ as those balls recharged to the balling drum after a constant time interval may be modified by feeding discharged separated balls to a reservoir and recharging separated balls to the balling drum from the reservoir at a more constant rate than that at which they are discharged.
Discharged separated balls of different sizes may be fed to separate reservoirs and balls may be recharged to the balling drum from each reservoir at a more constant rate than ;~
that at which they are fed to that reservoir. The average rate of feeding the separated balls to the or each reservoir may be equal to the average rate of removing the balls from that reservoir.
The separated balls discharged from one balling drum may be recharged to another balling drum. The separated balls discharged from one balling drum may be exchangedwith separated balls of different sizes discharged from another balling drum before being recharged to the balling drums.
Discharged balls under a predetermined size may be separated from those balls discharged from the balling drum.
A predetermined proportion of these discharged under-size balls may be removed from those returned to the balling drum. The balling process may be adapted for the production of green balls from iron ore, water and a binding additive.
The invention is illustrated by way of example in the accompanying drawings which show diagrammatically in Figures 1 to 5 five balling processes in which surging is controlled.
In Figure 1 a source 11 of raw material for the balling process steadily supplies a concentrate of ground iron ..~
- :
:.
ore, water and binding medium to a balling drum 12. Green balls are formed in the balling drum. At the discharge end of the drum is a screen 13 at which correctly sized and oversize green balls are directed towards a grate 14 from which they continue in the pelletizi.ng process, with the pos-sibility that oversize balls are instead crushed and recycled.
Undersize green balls are separated at the screen 13 and conveyed back to a device 15 from which they are fed at a controlled rate back to the charge end of the balling drum together with fresh concentrate from the source 11.
In the process illustrated in Figure 2 a source 21 of concentrate supplies two bslling drums 22a and 22b, having at their discharge ends screens 23a and 23_ feeding correctly sized and oversize green balls to grate 24.
The undersize balls are normally returned to the charge ends of the drums in which they were formed but cross-conveyors 26a and 26b are provided whereby some or all of the undersize green balls from drum 22a and/or 22b can for a period of time be switched to the charge end of the other drum 22b and/or 22_ respectively.
Although only two balling circuits are shown for the sake of simplicity, in practice five or s~ might be interconnected in a similar manner.
In Figure 3 a source of concentrate 31 supplies the charge end of one balling drum 32 which is provided with screen 33 at its discharge end to feed correctly sized and oversize green balls to a grate 34. The undersize green balls separated at the screen pass to a further screen 37 in the return circuit. This screen 37 is selected, and can be changed, to remove from the return circuit balls either greater or smaller than a chosen size. These balls are conveyed to a crusher 38 from which they are recycled and their material in due course recurs in the feed concentrate.
~` 1082890 The remaining balls are returned to the charge end of the balling dru~ as in the previous ex~mples.
It is possible to replace the screen 37 with a simple sampling device to extract randqm green balls from the return circuit at a controllable rate, the extracted balls likewise being crushed before being recycled.
In Figure 4 a source 41 feeds concentrate to a single balling drum 42 provided with a discharge screen 43 feeding a grate 44 as before. The undersize green balls from the screen 43 are conveyed to another screen 47a at which the largest balls are taken out and passed to a surge hopper 45a. The remaining balls pass through the screen 47_ to a further screen 47b at which the larger balls are taken out and passed to a second surge hopper 45_. The smaller balls pass through the screen 47b to a third surge hopper 45c . The three sizes of undersize green balls in the three surge hoppers 45a, 45b and 45c are thence conveyed each at a constant rate to be recharged into the balling drum 42.
In Figure 5 a source 51 feeds concentrate to two balling circuits which respectively have balling drums 52_ and 52_ and discharge screens 53_ and 53b feeding grate 54 in a similar manner to the balling circuits previously described. The undersize green balls from the screens 53_ and 53b go to further screens 57a and 57b to be separated ` into larger and smaller balls. These are normally returned to the charge ends of the drums in which they were formed but ' cross-conveyors 56a and 56b are provided whereby some or all of the smaller or the larger green balls from balling drum 52a and/or 52b can for a period of time be switched to the charge end of the other drum.
As in the case of the system illustrated in Figure 2, more than two balllng circuits may well be interconnected in a similar manner.
It will be appreciated that other control methods and combinations of control methods will be possible to modify the fundamental direct relationship between discharged -undersize balls and those recharged to the balling operation to reduce surging.
In the above examples reference is made to passing oversize green balls to the grate. This may be a tolerable practice when, as is often the case, such balls form only about five per cent of the product,
Balling is a process which can be applied ~o the p~elletizing of iron ore to form a product suitable as a blast furnace feed material. In a typical pelletizing plant an ore or a mixture of ores is dried and then ground to the required fineness. A very small proportion of a binding additive (e g. bentonite~ is added to improve its adhesion properties. A finely controlled amount of water is added.
The product, now referred to as concentrate, is then charged to several balling drums into which a further small proportion of water is sprayed. In each rotating balling drum the damp materil agglomerates to form green balls.
The product of each drum is screened: undersize and crushed oversize green balls are recirculated, while the acceptable product is charged to a moving grate on which the green balls are dried and preheated before being fired to form the required pellets.
A balling drum rotates about its longitudinal axis which is slightly inclined to the horizontal. The higher end is the charge end, the lower end the discharge end.
A conveyor is provided to return the undersize green balls from the discharge end to the charge end.
The mechanism of balling is complex but two significant stages in green ball growth are the initial formation of small porous stable balls known as seeds and a subsequent growth phase in which balls grow by taking up either raw concentrate or the material of smaller balls.
In the balling process new concentrate at a constant rate and returned undersized green balls are S supplied to the charge end of the balling drum. In the flrst fe~ metres of the drum the existing balls grow and new seeds are formed from the concentrate. In the remainder of the drum the larger balls grow at the expense of the smaller ones. At the discharge end a new distribution of green balls emerges of which the undersized are recycled to the charge end and pass through the drum again.
We have performed a theoretical analysis on the balling drum circuit and have found that the balling -process is essentially a non-linear feedback system, with non-linear components due to the drum and the screens, and an effective linear part consisting of the net loop time dealy. Such loops are a feature ln control systems analysis and, depending upon the nature of the loop components, the system may exhibit a periodic non-linear, limit cycle, oscillation. This behaviour is continuously observed in practice on balling circuits and is known colloquially as 'surging' i.e. a self-sustaining oscillation in product size distribution. If a large number of undersized green balls are discharged and returned to the charge end of the drum they will act as seeds; and during their next pass through the drum they will reduce the number of new seeds formed by initially taking up more of the available raw :' ~ ~0~32890 material and subsequently crushing more of the seeds that do form to grow further. This will result in a small number of undersized balls being discharged, and correspondingly a small number of seeds being recycled. In the next pass of these seed~l through the drum new seed formation will be less inhibited and the product will once again contain a large number of undersized green balls. In the normal operating region to ohtain acceptable ball quality surging is inevitable in the conventional balling circuit.
Surging in the balling drum results in cyclical variations in the number of green balls formed of satisfactory size. These variations must be contained to a small proportion of product throughput to enable satisfactory performance to be achieved in the subsequent stages of the pelletizing process.
We are aware of no practical and economic way which has yet been found to elirninate surging but various control methods have been proposed. These include variation in the binding additive addition and in the water spray addition in the balling drum. Each method has its own disadvantages.
According to the present invention, as herein claimed, there is provided a process for balling particulate material com-prising the steps of: improving the adhesion properties of the particulate material by adding water and a binding medium;
balling said particulate material in a balling drum to produce green balls; discharging said balls from said balling drum;
separating balls having a size other than predetermined size from balls having said predetermined size after their discharge from the said balling drum; and continuously returning said separated balls to said balling drum for balllng with adde~
particulate material, in which process the recurrence of dis-charged separated balls identically as those balls recharged to the balling drum after a constant time interval is modified by B
~ ~08Z890 varying the normally constant mass relationship between the discharged separated and recharged balls so as to reduce the system gain.
The recurrence of discharged separated balls identi-call~ as those balls recharged to the balling drum after a constant time interval may be modified by feeding discharged separated balls to a reservoir and recharging separated balls to the balling drum from the reservoir at a more constant rate than that at which they are discharged.
Discharged separated balls of different sizes may be fed to separate reservoirs and balls may be recharged to the balling drum from each reservoir at a more constant rate than ;~
that at which they are fed to that reservoir. The average rate of feeding the separated balls to the or each reservoir may be equal to the average rate of removing the balls from that reservoir.
The separated balls discharged from one balling drum may be recharged to another balling drum. The separated balls discharged from one balling drum may be exchangedwith separated balls of different sizes discharged from another balling drum before being recharged to the balling drums.
Discharged balls under a predetermined size may be separated from those balls discharged from the balling drum.
A predetermined proportion of these discharged under-size balls may be removed from those returned to the balling drum. The balling process may be adapted for the production of green balls from iron ore, water and a binding additive.
The invention is illustrated by way of example in the accompanying drawings which show diagrammatically in Figures 1 to 5 five balling processes in which surging is controlled.
In Figure 1 a source 11 of raw material for the balling process steadily supplies a concentrate of ground iron ..~
- :
:.
ore, water and binding medium to a balling drum 12. Green balls are formed in the balling drum. At the discharge end of the drum is a screen 13 at which correctly sized and oversize green balls are directed towards a grate 14 from which they continue in the pelletizi.ng process, with the pos-sibility that oversize balls are instead crushed and recycled.
Undersize green balls are separated at the screen 13 and conveyed back to a device 15 from which they are fed at a controlled rate back to the charge end of the balling drum together with fresh concentrate from the source 11.
In the process illustrated in Figure 2 a source 21 of concentrate supplies two bslling drums 22a and 22b, having at their discharge ends screens 23a and 23_ feeding correctly sized and oversize green balls to grate 24.
The undersize balls are normally returned to the charge ends of the drums in which they were formed but cross-conveyors 26a and 26b are provided whereby some or all of the undersize green balls from drum 22a and/or 22b can for a period of time be switched to the charge end of the other drum 22b and/or 22_ respectively.
Although only two balling circuits are shown for the sake of simplicity, in practice five or s~ might be interconnected in a similar manner.
In Figure 3 a source of concentrate 31 supplies the charge end of one balling drum 32 which is provided with screen 33 at its discharge end to feed correctly sized and oversize green balls to a grate 34. The undersize green balls separated at the screen pass to a further screen 37 in the return circuit. This screen 37 is selected, and can be changed, to remove from the return circuit balls either greater or smaller than a chosen size. These balls are conveyed to a crusher 38 from which they are recycled and their material in due course recurs in the feed concentrate.
~` 1082890 The remaining balls are returned to the charge end of the balling dru~ as in the previous ex~mples.
It is possible to replace the screen 37 with a simple sampling device to extract randqm green balls from the return circuit at a controllable rate, the extracted balls likewise being crushed before being recycled.
In Figure 4 a source 41 feeds concentrate to a single balling drum 42 provided with a discharge screen 43 feeding a grate 44 as before. The undersize green balls from the screen 43 are conveyed to another screen 47a at which the largest balls are taken out and passed to a surge hopper 45a. The remaining balls pass through the screen 47_ to a further screen 47b at which the larger balls are taken out and passed to a second surge hopper 45_. The smaller balls pass through the screen 47b to a third surge hopper 45c . The three sizes of undersize green balls in the three surge hoppers 45a, 45b and 45c are thence conveyed each at a constant rate to be recharged into the balling drum 42.
In Figure 5 a source 51 feeds concentrate to two balling circuits which respectively have balling drums 52_ and 52_ and discharge screens 53_ and 53b feeding grate 54 in a similar manner to the balling circuits previously described. The undersize green balls from the screens 53_ and 53b go to further screens 57a and 57b to be separated ` into larger and smaller balls. These are normally returned to the charge ends of the drums in which they were formed but ' cross-conveyors 56a and 56b are provided whereby some or all of the smaller or the larger green balls from balling drum 52a and/or 52b can for a period of time be switched to the charge end of the other drum.
As in the case of the system illustrated in Figure 2, more than two balllng circuits may well be interconnected in a similar manner.
It will be appreciated that other control methods and combinations of control methods will be possible to modify the fundamental direct relationship between discharged -undersize balls and those recharged to the balling operation to reduce surging.
In the above examples reference is made to passing oversize green balls to the grate. This may be a tolerable practice when, as is often the case, such balls form only about five per cent of the product,
Claims (9)
1. A process for balling particulate material compri-sing the steps of:
improving the adhesion properties of said particulate material by the addition of water and a binding medium;
balling said particulate material in a balling drum to produce green halls;
discharging said balls from said balling drum;
separating balls having a size other than predetermined size from balls having said predetermined size after their discharge from the said balling drum; and continuously returning said separated balls to said balling drum for balling with added particulate material, in which process the recurrence of discharged separated balls identically as those balls recharged to the balling drum after a constant time interval is modified by varying the normally constant mass relationship between the dis-charged separated and recharged balls so as to reduce the system gain.
improving the adhesion properties of said particulate material by the addition of water and a binding medium;
balling said particulate material in a balling drum to produce green halls;
discharging said balls from said balling drum;
separating balls having a size other than predetermined size from balls having said predetermined size after their discharge from the said balling drum; and continuously returning said separated balls to said balling drum for balling with added particulate material, in which process the recurrence of discharged separated balls identically as those balls recharged to the balling drum after a constant time interval is modified by varying the normally constant mass relationship between the dis-charged separated and recharged balls so as to reduce the system gain.
2. A process as claimed in claim 1 in which the recurrence of discharged separated balls identically as those balls recharged to the balling drum after a constant time interval is modified by feeding discharged separated balls to a reservoir and recharging separated balls to the balling drum from the reservoir at a more constant rate than that at which they are discharged.
3. A process as claimed in claim 2 wherein discharged separated balls of different sizes are fed to separate reser-voirs and separated balls are recharged to the balling drum from each reservoir at a more constant rate that that at which they are fed to that reservoir.
4. A process as claimed in claim 2 or claim 3 wherein the average rate of feeding the separated balls to the or each reservoir is equal to the average rate of removing the balls from that reservoir.
5. A process as claimed in claim 1 wherein the separated balls discharged from one balling drum are recharged to another balling drum.
6. A process as claimed in claim 5 wherein separated balls discharged from one balling drum are exchanged with separated balls of different sizes discharged from another bal-ling drum before being recharged to the balling drums.
7. A process as claimed in claim 1, wherein balls under a predetermined size are separated from those balls dis-charged from the balling drum.
8. A process as claimed in claim 7 wherein a predeter-mined proportion of the discharged undersize balls are removed from those returned to the balling drum.
9. A process as claimed in claims 1, 2 or 5, wherein the balling process is a process for the production of green balls from iron ore, water and a binding additive.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB21630/75A GB1550623A (en) | 1975-05-20 | 1975-05-20 | Balling process |
| GB21630/75 | 1975-05-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1082890A true CA1082890A (en) | 1980-08-05 |
Family
ID=10166165
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA252,884A Expired CA1082890A (en) | 1975-05-20 | 1976-05-19 | Balling process |
Country Status (12)
| Country | Link |
|---|---|
| JP (1) | JPS527302A (en) |
| AU (1) | AU501957B2 (en) |
| BE (1) | BE842003A (en) |
| BR (1) | BR7603128A (en) |
| CA (1) | CA1082890A (en) |
| DE (1) | DE2622348A1 (en) |
| FR (1) | FR2311855A1 (en) |
| GB (1) | GB1550623A (en) |
| NL (1) | NL7605425A (en) |
| NO (1) | NO761684L (en) |
| OA (1) | OA05328A (en) |
| SE (1) | SE7605667L (en) |
-
1975
- 1975-05-20 GB GB21630/75A patent/GB1550623A/en not_active Expired
-
1976
- 1976-05-14 NO NO761684A patent/NO761684L/no unknown
- 1976-05-17 AU AU14001/76A patent/AU501957B2/en not_active Expired
- 1976-05-18 BR BR3128/76A patent/BR7603128A/en unknown
- 1976-05-19 DE DE19762622348 patent/DE2622348A1/en not_active Withdrawn
- 1976-05-19 BE BE167171A patent/BE842003A/en unknown
- 1976-05-19 CA CA252,884A patent/CA1082890A/en not_active Expired
- 1976-05-19 SE SE7605667A patent/SE7605667L/en not_active Application Discontinuation
- 1976-05-19 OA OA55825A patent/OA05328A/en unknown
- 1976-05-20 NL NL7605425A patent/NL7605425A/en not_active Application Discontinuation
- 1976-05-20 FR FR7615251A patent/FR2311855A1/en not_active Withdrawn
- 1976-05-20 JP JP51058471A patent/JPS527302A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE2622348A1 (en) | 1976-12-02 |
| AU1400176A (en) | 1977-11-24 |
| FR2311855A1 (en) | 1976-12-17 |
| GB1550623A (en) | 1979-08-15 |
| BR7603128A (en) | 1977-01-25 |
| NL7605425A (en) | 1976-11-23 |
| JPS527302A (en) | 1977-01-20 |
| BE842003A (en) | 1976-09-16 |
| SE7605667L (en) | 1976-11-21 |
| NO761684L (en) | 1976-11-23 |
| AU501957B2 (en) | 1979-07-05 |
| OA05328A (en) | 1981-02-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |