Blending flowable solid materials

An apparatus and method are disclosed for blending flowable solid materials. These are conveyed in turn, conveniently over a belt weigher, to a tripper mounted above a hopper so as to build up a first charge consisting of a plurality of inclined contiguous bands each of a different material. A paddle feeder removes material in a series of passes along the bottom of the first charge, the material removed being conveyed again to the tripper for discharge into a second hopper adjacent the first, thereby to build up a second charge also consisting of a plurality of inclined contiguous bands each of a different material. A second paddle feeder then removes material in a series of passes along the second charge to form the final blend.

This invention relates to a method of and apparatus suitable for blending 
flowable solid materials. 
Flowable solid materials require to be blended on a large scale in a number 
of industries, for example the metallurgical, fertilizer and cement 
industries. 
In the metallurgical industry, for example, a metallurgical furnace such as 
a copper smelter is usually designed to operate on a feed charge having 
metal contents and impurity levels lying within specified ranges. However 
actual batches of ore may vary quite widely in metal content and/or 
impurity level and often it is found that these values for a particular 
batch lie outside the specified design ranges. Thus it is common practice 
to blend ore from different batches, which, although nominally of the same 
composition, may differ in metal content and/or in impurity level because, 
for example, they originate from different locations. In this way 
differences between different batches of metal content or of impurity 
level may be balanced so as to make up a feed charge batch of the 
appropriate composition. Any necessary additives such as fluxes can be 
blended in during the making up of the feed charge batch or can be added 
separately to the copper smelter or other furnace. 
In blast furnace operations it is a common practice to pre-mix the iron 
ore, coke, limestone and any other desired additives, e.g. slag-forming 
additives, prior to charging to the blast furnace at a rate of perhaps 
several thousand tons per hour. However such blending is usually on a much 
larger scale, involving preparation of a feed charge batch of many 
thousands of tons, compared with copper smelter operations where feed 
rates of the order of 40 tons per hour are not uncommon, corresponding to 
a feed batch size requirement of 320 tons for a 8-hour working shift. 
In large scale operations, such as blast furnace operations, blending can 
be carried out by feeding the solid materials to be blended continuously 
in turn to a blending area. Using a stacker comprising a belt conveyor and 
a belt tripper or other suitable feeder device an elongate pile is built 
up in which the various batches of materials to be blended from discrete 
layers. When the pile is complete an automated reclaiming machine arranged 
to feed a belt feed conveyor leading to the furnace area is traversed 
slowly along the pile. In this way the materials fed to the belt feed 
conveyor are blended automatically. The scale of the equipment has of 
course to be massive and, since it is usual to build a pile for the next 
feed batch whilst reclaiming a previously built pile, duplication of at 
least most of the equipment is necessary. 
Proposals have previously been made for blending smaller batches of 
material involving a few hundred tons for smaller scale operations such 
as, for example, in copper smelter operations. One proposal involves 
transferring the materials to be blended from their respective stockpiles 
to individual feed bins or hoppers by front end loaders. Each feed bin or 
hopper, of which there may be, for example 6 or 8, has an adjustable 
throat arranged to discharge on to a respective belt weigher. All of the 
belt weighers discharge continuously into a main feed charge batch hopper. 
High and low level warning devices are fitted to each feed bin or hopper 
and the drivers of the front end loaders have to ensure that the 
individual feed bins or hoppers are kept supplied with the individual 
components of the blend throughout the blending operation. 
A disadvantage of this arrangement is that the use of a plurality of belt 
weighers is involved. Also, it will usually be necessary to have more than 
one front end loader and driver available throughout the blending 
operation to ensure that all feed bins are kept filled. Although belt 
weighers can be calibrated with an accuracy of perhaps 1/2% at full load, 
frequent maintenance and calibration is necessary if this accuracy is to 
be maintained. Furthermore the make-up of a particular feed blend batch 
may require that one or more of the belt weighers operates at low load 
with a consequent reduction of accuracy and with an increased danger of 
"bridges" forming in the corresponding feed bin or hopper and of 
consequent interruption of the flow of that particular material to the 
blend batch hopper. The operation of such a blending installation requires 
careful monitoring by the operating personnel, therefore, if satisfactory 
operating is to be achieved. 
According to the present invention there is provided a method of blending 
flowable solid materials which comprises establishing an elongate first 
charge of the materials to be blended of substantially uniform height 
comprising a plurality of contiguous transverse first bands, each 
extending from top to bottom of the first charge and each being composed 
of a different flowable solid material from that of the or each adjacent 
first band; removing material from each first band in turn in a plurality 
of first passes made lengthwise of the first charge, the quantity of 
material removed from the first charge in each first pass being small in 
comparison with the initial volume of the first charge; establishing an 
elongate second charge of substantially uniform height comprising a 
plurality of contiguous transverse second bands, each extending from top 
to bottom of the second charge and each being substantially composed of 
material removed from a corresponding first band; and removing material 
from each second band in turn in a plurality of second passes made 
lengthwise of the second charge, the quantity of material removed from the 
second charge in each second pass being small in comparison with the 
initial volume of the second charge. 
Preferably the step of establishing the elongate first charge comprises 
supplying the materials to be blended continuously in turn to a first 
storage location provided with an upwardly extending first end surface at 
one end thereof, and building up the first charge to the desired height 
against the first end surface. According to one procedure the step of 
building up the first charge comprises feeding the materials to be blended 
continuously in turn to a delivery point above the first storage location, 
sensing the height of material deposited at the first storage location in 
the region of the delivery point, and moving the delivery point 
longitudinally of the first storage location away from the one end thereof 
in dependence on the sensed height. 
In a similar manner the step of establishing the elongate second charge 
preferably comprises supplying the material removed from the first charge 
continuously to a delivery point above a second storage location provided 
with an upwardly extending second end surface at one end thereof, and 
building up the second charge to the desired height against the second end 
surface. 
Conveniently the step of establishing the second charge comprises feeding 
the material removed from the first charge continuously to a delivery 
point above the second location, sensing the height of material deposited 
at the second storage location in the region of the delivery point, and 
moving the delivery point longitudinally of the second storage location 
away from the one end thereof in dependence on the sensed height. 
In the method of the invention it is preferred to remove material from the 
first and/or second charge from the bottom of the respective charge in 
each of a plurality of first and/or second passes, as the case may be. 
The invention further provides apparatus for blending flowable solid 
materials comprising means defining a first storage location; feed means 
for feeding the flowable solid materials continuously in turn to the first 
storage location so as to establish at the first storage location an 
elongate first charge of the materials to be blended of substantially 
uniform height comprising a plurality of contiguous transverse first 
bands, each extending from top to bottom of the first charge and each 
being composed of a different flowable solid material from that of the or 
each adjacent first band; first extractor means longitudinally traversable 
with respect to the first storage location for removing material from the 
first charge; means for traversing the first extractor means 
longitudinally of the first charge in a plurality of first passes and 
arranged to remove material from each first band in turn in each first 
pass, the quantity of material removed from the first charge in each first 
pass being small in comparison to the initial volume of the first charge; 
means defining a second storage location; conveying means for conveying to 
the second storage location material removed from the first charge and 
arranged so as to establish at the second storage location an elongate 
second charge of substantially uniform height comprising a plurality of 
contiguous transverse second bands, each extending from top to bottom of 
the second charge and each being composed substantially of material 
removed from a corresponding first band; second extractor means 
traversable with respect to the second storage location for removing 
material from the second charge; and means for traversing the second 
extractor means longitudinally of the second charge in a plurality of 
second passes and arranged so as to remove material from each second band 
in turn during each second pass, the quantity of material removed from the 
second charge on each second pass being small in comparison to the initial 
volume of the second charge. 
Conveniently the first and second storage locations comprise respective 
first and second hoppers, which are preferably disposed adjacent one to 
another. Each hopper may be of the slot discharge type having an elongate 
opening at its lower end arranged a predetermined height above a support 
surface whereby, in use, at least some of the material charged to the 
hopper emerges from the opening to form an elongate pile on the support 
surface below the opening of the hopper. In this case at least one of the 
first and second extractor means comprises a paddle feeder. 
In a preferred form of apparatus the first storage location is provided at 
one end thereof with an upwardly extending first end surface, and the feed 
means comprises means for continuously feeding the materials to be blended 
in turn to a delivery point above the first storage location, first sensor 
means for sensing the height of material deposited at the first storage 
location in the region of the delivery point, and means for moving the 
delivery point along the first storage location away from the first end 
surface in dependence on the height sensed by the first sensor means. The 
feed means may comprise an endless belt feed conveyor incorporating a 
tripper. 
It is preferred that the feed means comprises an endless belt feed 
conveyor, a reception hopper for the flowable solid materials to be 
blended for supplying the endless belt feed conveyor, and a belt weigher 
for weighing materials carried by the endless belt feed conveyor. 
The second storage location may be provided at one end with an upwardly 
extending second end surface, in which case the conveying means 
conveniently comprises means for continuously feeding material removed 
from the first charge to a delivery point above the second storage 
location, second sensor means for sensing the height of material deposited 
at the second storage location in the region of the delivery point, and 
means for moving the delivery point along the second storage location away 
from the second end surface in dependence on the height sensed by the 
second sensor means. 
Desirable economies of equipment can be achieved if the material removed 
from the first charge is conveyed to the second storage location along a 
pathway which coincides partly with the pathway followed by the materials 
to be blended in their passage to the first storage location. Thus it is 
preferred that the feed means comprises an endless belt feed conveyor 
incorporating a tripper and selective discharge means for selectively 
discharging material from the tripper to a chosen one of the first and 
second storage locations, the conveying means including an endless belt 
transfer conveyor arranged to transfer material extracted from the first 
charge to the endless belt feed conveyor upstream from the tripper. In a 
convenient arrangement the tripper comprises a chute device having first 
and second exit openings communicating with the first and second storage 
locations respectively, the selective discharge means comprising a flopper 
for diverting material discharged from the feed conveyor to a chosen one 
of the two exit openings.

Referring to the drawings, and in particular to FIG. 1, the flowable solid 
materials to be blended are each drawn from a respective stockpile 1, 2, 3 
or 4 by means of a front end loader 5 for conveyal to a reception hopper 
6. Each of the materials in the stockpiles 1, 2, 3 and 4 has preferably 
been subjected to a suitable grinding or other comminuting operation 
and/or graded so that each material has substantially the same angle of 
repose as the others. In other words on forming a sample of each material 
into a pile, the angle of slope of each pile will be approximately equal 
to the corresponding angle for the piles of all the other materials. The 
degree of comminution of the materials is not critical so long as they are 
all readily flowable and all have substantially the same angle of repose. 
Preferably the materials are all -16 mesh (British Standard Sieve) and 
they will usually be comminuted to at least -100 mesh. Typically all of 
the materials are -200 mesh, for example. 
FIG. 1 shows four stockpiles 1 to 4; the invention is however not limited 
to the blending of any particular number of materials. In some cases more 
than four materials may be required to be blended, e.g. 5, 6, 8 or 10 or 
more, and in other cases it may be desired to blend only 2 or 3 materials. 
Reception hopper 6 is arranged to discharge onto a feed conveyor 7 driven 
by a suitable motor 8 and fitted with a belt weigher 9. Feed conveyor 7 is 
provided with a conventional belt tensioning arrangement (not shown) and 
is arranged to discharge into an elongate hopper assembly 10 via a tripper 
11 fitted with a flopper 12 (which is shown in FIG. 2 but, for the sake of 
simplicity is omitted from the other Figures). Hopper assembly 10 is 
divided longitudinally by a vertical wall 13 into first and second hoppers 
14 and 15. Material from feed conveyor 7 can be diverted into a chosen one 
of the two hoppers 14 and 15 depending on the position of the flopper 12. 
In the full line position of the flopper 12 shown in FIG. 2, material will 
be diverted into first hopper 14, whereas in the position 12' shown in 
broken lines the flopper 12 will divert material from feed conveyor 7 into 
second hopper 15. Each of the hoppers 14 and 15 is of the slot discharge 
type, and is open at its lower end, being arranged to discharge onto a 
horizontal shelf 16. Vertical wall 13 extends down to shelf 16. Materials 
flowing out of hoppers 14 and 15 can form respective piles on shelf 16. 
Tripper 11 is arranged in conventional fashion so as to run on rails (not 
shown in the drawings for the sake of clarity) which extend along the top 
of the hopper assembly and some distance to the left of it, as shown in 
FIG. 3, so as to permit it to move from the position shown in full lines 
to the position 11' shown in broken lines. Adjustable limit switches 18 
and 19 indicated in FIGS. 1 and 3 are used to limit the movement of 
tripper 11 along its rails. Movement of tripper 11 along its rails is 
controlled by a pair of sensors 20 and 21 as will be described hereafter. 
The height of the lower end 22 of the outer side wall of each of hoppers 14 
and 15 above the shelf 16 can be adjusted in a conventional manner. In 
this way it can be ensured that, within a certain predetermined range of 
particle size, and hence of the corresponding angle of repose, a pile of 
material from the corresponding hopper can be formed on the shelf 16 on 
each side of vertical wall 13 without overflowing over the lateral edge of 
the shelf 16. By suitable adjustment of the lower ends 22, the apparatus 
can be adapted for use with a wide variety of flowable solid materials of 
differing average particle size. 
A paddle feeder 23 is traversable longitudinally of the hopper assembly 10 
and is arranged to feed a return conveyor 24 with material from hopper 14 
that has fallen onto shelf 16. Return conveyor 24 discharges into a hopper 
25 from which material can be returned to hopper assembly 10 by feed 
conveyor 7. Reference numeral 26 indicates a motor for return conveyor 24 
and reference numerals 27 show the rails on which paddle feeder 23 is 
arranged to run. 
The paddle of paddle feeder 23 is shown at 28 and is driven by a motor 29. 
The arrangement for driving paddle feeder 23 along its rails 27 is 
conventional. Movement of the paddle feeder 23 is controlled in a 
conventional manner by appropriate limit switches (not shown in FIG. 1 for 
the sake of simplicity). 
A second paddle feeder 30 is traversable longitudinally of hopper assembly 
10 for feeding material falling from second hopper 15 onto shelf 16 to a 
further endless belt conveyor 31 which serves to convey the blended 
materials away to a storage area, to a furnace or to some other desired 
location. As with feed conveyor 7, conveyor 31 and return conveyor 24 are 
provided with a conventional belt tensioning arrangement (not shown). As 
before, the paddle 32 of paddle feeder 30 is driven by a motor 33 and 
rails 34 are provided on which paddle feeder 30 is arranged to run. As 
with paddle feeder 23 the arrangement for driving paddle feeder 30 along 
rails 34 is conventional. Adjustable limit switches 35 and 36 are used to 
control movement of paddle feeder 30 along its rails 34. (The limit 
switches for controlling movement of paddle feeder 23 are similar). 
As shown in FIGS. 1 and 3, the load conveying run of feed conveyor 7 passes 
around reversing rollers 37 and 38 mounted on a tripper 11. Material from 
reception hopper 6 is conveyed on feed conveyor 7 as far as reversing 
roller 37 whereupon it is discharged into the throat 39 of tripper 11 as 
shown by arrow 42 in FIG. 1 to fall down one or other of chutes 40 and 41 
depending on the position of flopper 12. 
In use, in order to blend a number of flowable solid materials by the 
method of the invention the make-up of the blend to be made is first 
decided and then the flopper 12 is put in the full line position of FIG. 2 
and the materials to be blended are fed batchwise in turn via reception 
hopper 6 to feed conveyor 7. The front end loader driver or drivers 
continue to feed a particular material from one of the stockpiles 1, 2, 3, 
4 etc. to the hopper 6 until belt weigher 9 indicates that the desired 
quantity has been delivered. Thereupon the driver or drivers switch to 
another of the stockpiles and feed another material, repeating the 
procedure for each component of the blend. Since all of the components are 
weighed by the same belt weigher 9 they will be delivered in the correct 
proportions despite any calibration error of belt weigher 9. No 
supervision of the reception hopper 6 or feed conveyor 7 by operating 
personnel is required. 
At the start of a blending operation tripper 11 is withdrawn to one end of 
the hopper (i.e. the left-hand end as shown in FIGS. 1, 3 and 4). This 
position is indicated in broken lines at 11' in FIG. 3. (It will be 
appreciated that in FIG. 1 feed conveyor 7 is not drawn precisely to 
scale; in particular a longer horizontal run immediately to the left of 
hopper assembly 10 would be needed in practice in order to allow tripper 
11 to move far enough to the left). Material falling from feed conveyor 7 
at reversing roller 37 will fall into throat 39 and down chute 40 into 
hopper 14 to form a heap therein whose right-hand slope will have the 
characteristic angle of repose of the particular material. When sensor 20 
senses that the heap formed in hopper 14 below chute 40 has reached a 
predetermined level, motor 17 is automatically actuated and tripper 11 is 
shifted a predetermined short distance along the hopper assembly 10 (to 
the right as illustrated in FIGS. 1, 3 and 4). In this way an elongate 
charge of substantially constant height is gradually built up in hopper 14 
consisting of a plurality of first bands 43, 44, 45, 46, each consisting 
of a different material. For example, when copper ores are being blended, 
each first band 43, 44, 45, 46 may comprise ore mined at a different 
location, each nominally perhaps of the same mineral, but differing from 
the others in its copper content and/or impurity levels. Reference numeral 
47 indicates a region of "dead material" which is allowed to build up in 
the hopper 14 on its first filling and is thereafter not disturbed. 
When the elongate charge has been built up, paddle feeder 23 is traversed 
in a first pass along the hopper 14 so as to dislodge material from shelf 
16 onto return conveyor 24. In this way paddle feeder 23 removes material 
in turn from first bands 43, 44, 45 and 46. Its controlling limit switches 
are set so that it does not remove any of the "dead material" 47. At the 
end of each pass of paddle feeder 23 along the charge in hopper 14 its 
direction of movement is reversed for a fresh pass. In this way the 
material of the charge is gradually removed in a plurality of passes of 
the paddle feeder 23. The speed of traversing of paddle feeder 23 along 
hopper 14 is set so that the quantity of material removed in any one pass 
of paddle feeder 23 is small in comparison to the initial volume of the 
charge formed by the first bands 43, 44, 45 and 46 in the hopper 14. 
Before initiating the traversing movement of the paddle feeder 23 the 
tripper 11 is returned to its start position 11' and flopper 12 is moved 
to the position 12' of FIG. 2. The material removed from hopper 14 is 
thereby fed via conveyor 24 and then as shown by arrow 48 into 
intermediate hopper 25. From intermediate hopper 25 the material returns 
via feed conveyor 7 to tripper 11 and down chute 41 into hopper 15. The 
second height sensor 21 senses the height of the pile of material in 
hopper 15 below chute 41 and is used to control movement of tripper 11 
along hopper assembly 10 in a manner analogous to that by which sensor 20 
controls the movement of tripper 11 along hopper 14. In this way an 
elongate charge of substantially constant height is built up in hopper 15. 
This charge consists of a large number of thin second bands 49, 50, 51, 
52, 53, 54 etc., each extending from top to bottom of the charge and each 
consisting of material removed by paddle feeder 23 in one of its passes 
from a corresponding one of the first bands 43, 44, 45, 46. Calling the 
materials of first bands 43, 44, 45 and 46 by the reference letters A, B, 
C and D respectively then second bands 49, 50, 51, 52 consist of portions 
of materials A, B, C and D respectively removed in the first pass of 
paddle feeder 23 whilst second bands 53, 54 etc. are comprised of material 
C, B, etc. removed in the second and subsequent passes of paddle feeder 
23. In this way the second charge in hopper 15 consists of a plurality of 
second bands of material each stretching from top to bottom of the charge 
in the order ABCDCBABCDC . . . etc. In FIG. 3 all the bands of the second 
charge will have a thickness similar to that of second bands 49, 50, 51 
etc., but for the sake of clarity only a few such thin bands are shown. 
The precise thickness of second bands 49, 50, 51 etc. will depend on the 
number of bands in the first charge, their thickness and the speed of 
traversing of paddle feeder 23. However the total quantity of material in 
any one second band 49, 50, 51 etc. will be small in comparison to the 
overall size of the second charge. 
When the charge has been wholly transferred from hopper 14 to hopper 15, 
paddle feeder 30 is traversed longitudinally of hopper 15, again in a 
plurality of passes controlled by the limit switches 35 and 36. In this 
way material from hopper 15 is dislodged from shelf 16 into conveyor 31. 
Since second bands 49, 50, 51 etc. are very thin by comparison with first 
bands 43, 44, 45 and 46 the material fed to conveyor 31 is essentially a 
homogeneous blend of materials A, B, C and D. 
Reference numeral 55 indicates a body of "dead material" in hopper 15. As 
with hopper 14 the limit switches 35 and 36 are set so that paddle feeder 
30 does not encroach into this "dead material". 
As illustrated, hoppers 14 and 15 are provided with vertical end walls 56 
and 57. If desired hoppers 14 and 15 can be provided at their left-hand 
end with inclined end walls at an angle corresponding to the angle of 
repose of the materials to be blended. In this case the bodies of "dead 
material" 47 and 55 can be entirely eliminated. 
In the drawings hoppers 14 and 15 are shown to be of equal length. However 
it will usually be desirable to make hopper 15 longer than hopper 14. In 
this way, an "overlap" of feed charge material can be built up in the 
hopper 15 for use in case of any interruption of operation of the 
illustrated blending apparatus. 
The materials of stockpiles 1, 2, 3, 4 etc. may be batches of the same ore 
or of compatible ores and may include one or more fluxes and any other 
requisite materials for the smelting or other process to be effected. For 
example, the materials to be blended may comprise copper-containing ores, 
each of nominally the same type but containing differing copper contents 
and/or impurity levels and possibly mined at differing locations. 
In other applications of the invention the materials of stockpiles 1, 2, 3, 
4 etc. comprise compound fertilizer raw ingredients or cement raw 
materials. 
As illustrated in the accompanying drawings the hoppers 14 and 15 are each 
provided with a slot discharge apparatus including a respective paddle 
feeder 23 or 30. It will however be appreciated by those skilled in the 
art that the invention can equally well be practised using hoppers with 
other forms of slot discharge apparatus having, for example, a plough or 
similar device in place of a paddle feeder. Such a plough or similar 
device can be rail-mounted like the paddle feeders 23 and 30 so as to be 
reciprocably traversable along the length of the hopper assembly 10. In 
place of the rotatable paddles 28 and 32, however, such ploughs each 
comprise fixed member or members each having a face appropriately inclined 
with respect to the shelf so that the plough acts to displace material 
from shelf 16 on to the appropriate conveyor 24 or 31 as the plough is 
traversed along the hopper assembly 10. It will be further appreciated 
that hopper 14 should preferably not be filled beyond the point shown in 
FIG. 1. Clearly if the material of band 46 is allowed to build up against 
end wall 58 of hopper 14 the amount of material removed from band 46 upon 
each pass of paddle feeder 23 may change as the hopper 14 empties. 
Furthermore, although the first bands 43, 44, 45 and 46 are shown for 
convenience as being of approximately equal thickness they can be of any 
desired thickness depending on the composition of the desired blend. 
Although as described, best blending is achieved by maintaining a body of 
"dead" material 47 in hopper 14 and a similar body 55 in hopper 15, in 
some instances, particularly when the length of each of the hoppers 14 and 
15 is considerably greater than its depth or width so that the volume of 
"dead" material is small in comparison to the total volume of the first or 
second charge, adequately good uniformity of blending can be achieved by 
extending each pass to extend as far as the wall 56 or 57 as the case may 
be so that the hopper 14 or 15 is essentially completely emptied. 
Similarly filling the hopper 14 or 15 beyond the position shown in the 
drawings may not be critical and adequate uniformity of blending can be 
achieved provided the empty space (e.g. that shown in FIG. 1 to the right 
of band 46) in the hopper is small in comparison to the overall volume of 
the charge.