Note: Descriptions are shown in the official language in which they were submitted.
V~L~7
A SUCTION SINTERING METHOD AND APPARATUS THEREFCR
_*_*_
The presen-t invention relates to a method for producing
a charge of high permeability and stable structure on a mobile
suction-sintering grate or in a stationary or mobile suction-
sintering pan, comprising the steps of compacting a moist
material mixture to be sintered, preferably between at least
one pair of pressure-loaded rolls, to form a coherent cake,
the particles forming said cake being held together mainly
by capillary forces, and breaking the cake into pieces of a
size suitable for formning a suction-sinter charge. The in-
vention also relates to apparatus for carrying out the method.
Suction sintering is primarily applied for the purposeof agglomerating finely divided iron-oxide material into a
form suitable for charging to a blast furnace, and represents
a substantial cost in the manufacture of crude iron. Conse-
quently, it is important that as much sinter as possible isproduced per each unit of qrate area, in order to reduce in-
vestment, maintenance, fuel and electrical-energy costsO
With regard to sinteriny capacity, -the most important
factor is the permeability of the charge. The more yas drawn
through the charye per un:it of tirne, the less time required to
e~ect a satisfact~ry sintering operation. The pexmeability
of the charge can be increased in a number of ways. The most
usual method in this respect is to increase the amount of
coarse particulate return-sinter admixed with the charge.
Large quantities of coarse return-sinter, however, increase
the ar,1ount of fuel required per unit of weight of final
sinter, and incur additional handling costs. Furthermore, in
certain instances it is necessary to crush the final sinter,
in order to obtain the requisite amount of return-sinter. An-
other method often used is one in which the charge mixture issubiected to a subsequent rolling process in a drum. Al-though
the perrneabLlity of the charge is increased to a certain
2 ~g~7
extent by this method, it is necessary to control accurate-
ly the amount oE moisture present, and normally the amount of
water needed is more than is justified by the thermal pro-
gress of the sintering operation at the desired low level of
fuel consumption. Nei-ther does rollin~ a mixed charge in a
drum produce a stable charge. Instead, the charge produced
tends to become compacted when subjected to the high
underpressure desirable in suction sintering operations in
respect of high plant capacity, when sin-tering fine, particu-
late material.
In a number of cases attempts have been made to increase
the permeability of the charge by micro-pelletizing one or
more of the iron-oxide products making up the charge. How
ever, this technique requires the provision of additional
and expensive pelletizing apparatus, such as drum or pan
pelletizers. Only extremely fine-grain material can be
micro-pelletized, and normally it is necessary to use a
binder, together with an accurately controlled addition of
water, which may result in bogging in the lower regions of
the charge during the sintering process, i.e. the mutual ad-
hesion of respective particles in the bottom region. Another
drawback is that the charge consit~ents are not mixed together
with a thoroughness suffic:ient to favour desired formation of
slag during the sintering and blast-furnace operations.
In many parts of the world, iron-oxide is highly en-
riched i.n order ~irs-tly to increase -the iron content and
secondly to remove con-taminents, such as phosphorous. In such
working-up processes, prior to being enriched the ore must be
ground down to such a small particle size as to render the
resultant fine concentrate unsuitable or suction sintering.
Examples of such concentrates include the ~id-Swedish and
Northern-Swedish concentrates which have been purified of
phosphorous and which are thus very fine. In order to find
a market for such materials, ~t has been elected to sinter
them to pellet form. Sintered pellets, however, are not ideal
agglomerates for treatment in blast furnaces, neither with
respect to shape nor chemical composition, and in many in-
~9~ 7
s-tances the sinter obtained from suction-sintering processes
is preferred, no-t ieast because it can be made self-fluxing,
i.e. the sinter can be made to include constituents neces-
sary for the blast furnace.
In addition to fine particulate ore concentrates, there
are many fine particulate iron-containing materials which
cannot, at present, be agglomerated by suction sin-tering
techniques. Examples of such concentrates include pyrite
cinders, dust from oxygen-blowing processes, and other very
fine metallurgical intermediate productsO
~ne attempt to find a solution with regard to a fine-
particulate sinter charge is illustrated in Swedish Patent
Specification No. 212 742, according to which a moist charge-
mixture is subjected to high-frequency vibrations, to form
a coherent cake which is placed in -the form of small pieces
on a sinter grate and sintered. The aforementioned pieces are
passed through a screen and classified in a manner so that
the coarser fraction of the charge lies nearest the grate
and the finer fraction lies on top of said coarser fraction.
Difficulties were encountered, however, when trying to put
this method into practice. A relatively high moisture content
was required in order -to obtain a plasticity suitable to
form a cake. When the particulate material was vibrd-ted, the
surfaces Oe the ca]ce became moist, which resulted in adhe-
~5 sion to the surface supporting said cake. In addition, it was
diEficult to achieve high-frequency vibration of sufficient
penetration depth.
An object of the present invention is to provide a novel
and advantageous method for producing a highly permeable suc-
tion-sinter charge of stable structure, by which the dis-
advantages discussed above can be at least substantially over-
come.
To this end there i5 provided a method of the kind
stated in the introduction, which is further characterized by
adjusting the wa-ter content of -the material mixture to a
level at which substantially the minimum of fuel is con-
~I
sumed at the sintering temperature intended; and by so ad-
justing the com~action pressure in relation to the set
water content, corresponding substantially to the minimum
fuel consumption, that the pore volume of the resultant
cake is not totally filled by the water present in said
mixture~ In this way, the aforementioned disadvantages
are overcome in a simple manner. In suction-sintering a mate-
rial bed formed in accordance with the invention, there is
formed, when the bed is ignited at the upper surface thereof
a combustion layer which is thin relative to the thickness
of the bed and which moves downwardly through the entire bed
while air is drawn by suction through said bed. Air which
has been heated by cooling the already heated overlying part
of the bed is charge~ to said layer, while gas from the com-
bustion layer dries and heats the nearest underlying bedlayer. In this respect, the water content is of great signi-
ficance to the course taken by the sintering operation, since
with the amount of air charged per unit oE time constant, the
water content determines the speed at which the front of the
combustion layer moves down through the bed. On the other hand,
the speed of the cooling layer following the combustion layer,
and in which cooling layer the sintered charge material is
cooled by the incoming air, is deterrnined by the highest
temperature reached in the hed and the amount of air drawn
therethrough, the speed of said combustion layer being constant
when a constant amount of air is supplied and with a cons-tant
highest temperature. The combus-tion layer and the cooling
layer, however, will only move at mutually the same speed
when the water content is that utilized in the method ac-
cording to the invention, whereat, as before mentioned,there is obtained a desired thin combust:ion layer, which af-
fords substantially minimum fuel consumption at desired
sintering temperature. If the water content is reduced, the
speed at which the combustion layer moves will increase but
not the speed of the cooling layer, whereat the fronts of
the two layers will move apart and there will be obtained a
thick combustion la~er, requiring more fuel to be added in
order to reach the desired combustion temperature. The
reason why, in this case, a reduced water content results
in an increased fuel consumption is that the sinter contains
more residual heat when the combustion layer reaches the
grate. If the water content is, instead, increased above the
value at which the combustion and cooling layers move at the
same speed, the speed at which the front of the combustion
layer moves will decrease. The speed at which the colling
layer movesr howeverf is unchanged. Besause of this, the
sintering temperature will gradually fall, and may even fall
to a level at which the charge will be extinguished, and hence
the higher water content must be compensated fGr by increasing
the amount of fuel supplied. Thus, at every given sintering
temperature there is a determinable water content, which is
adjusted in the method according to the invention so as to ob-
tain the lowest possible fuel consumption. The cake formed by
compacting the material in accordance with the invention may
not, however, contain free moisture on the surfaces thereof,
since otherwise the cake pieces become sticky and bake together
in the charge placed on he grate, and when producing the cake
by rolling, cause the rolls to slip against the cake, and a
mechanicall~ weak cake is obtained. If the pores of the formed
cake are unable to accomrnodate the amount of water necessary
-to provide for the lowest possible fuel consumption, so that
surface water occurs when pressing the rnaterial to cake form,
it would seem an obvious thing to decrease the amount of water.
This would mean that more fuel must be charged, nowever. Thus,
it has been found in accordance with the invention necessary
to adjust the pore volume of the cake by regulating the com-
paction pressure such that the cake is able to accornmodate therequisite amount of water. The extent to which the pores are
filled, however, must not be extensively low, since, to a
large extent, it is capillary forces which hold the cake to-
gether. In this respect, it has been found that the pores ofthe pressed cake should be filled to at least 60 %, pre~erably
~0 - 90 ~,.
D ~ ~0~7
In the conventional preparation of a sinter charge it
has been found necessary, in many cases, to add more water
than required from the thermal aspect, in order to obtain a
permeable charge, which means that more fuel is consumed.
S This is not necessary when preparing a sinter charge in
accordance with the method of the invention proposed here,
which constitutes a highly important advantage.
If the pressed cake is too thick, there is a risk of
the fuel, normally fine coke particles, being entrapped so
as to delay the ignition of the fuel. Because of this, the
cake thickness should not exceed 12 rnm, and should not be
smaller than 4 mm, since otherwise the cake will be too weak
to enable it to be broken up in a predeterminable manner into
pieces having a size suitable to form a suction-sinter charqe.
Furthermore, in order to obtain yood gas distribution and
heat transfer between gas and goods in the sinter charge,
the compacted cake should be broken up into pieces having a
largest dimension of at most 20 rnm, preferably of at most
15 mm.
The resistance to suction of a mixture of two particle
sizes is greater than the total suction resistance of the
two particle classifications per se. ~ecause of this it has
been found to be of advantage when the compacted cake, sub~
sequent to being broken up, is classified in a screening
apparatus to form a relatively coarse particulate material
fraction, which is placed nearest the grate, and a fine
particulate material fraction, which is placed upon the coarse
fraction. In this respect, it is to particular advantage when
the classifying process is adapted so that the major part of
the material, preferably about 2/3rds thereof, is present in
the coarse material fraction lying neares-t the grateO The
fact that the upper layer of the charge comprises the finer
particles, rnakes it easier to ignite the charge. This also
improves the transfer oE heat between goods and gas at that
stage of the sintering process where stabilization of the
front of the combustion layer is desirable. In addition, fuel
can be saved by mixing fine, particulate additional fuei
with the finer particulate fraction, since less fuel can
then be used for the remainder of the charge.
As before mentioned, the invention also relates to an
apparatus for producing on a mobile suction-sintering grate
or in a stationary or mobile suction-sintering pan a highly
permeable charge of stable structure, said apparatus com-
prising means for compac-ting a stream of moist material-
mixture to be sintered, to form a coherent cake, which is
then broken up into pieces of a size suitable to form a suc-
tion-sinter charge, said apparatus further including in ac-
cordance with the invenkion means for so adjusting the com-
paction pressure in relation to the water content of the
material mixture that the pore volume of the cake formed is
not completely filled by the water present in the material
mixture. This arrangement enables the object of the invention
to be realized with the use of means of simple construction.
Further charac-terizing features of the apparatus and
advantages afforded thereby are disclosed in the following
claims and illustrated hereinafter.
The invention will now be described in more detail with
reference to the accompanying drawings, in which
Figure 1 illustrates schematically a first embodiment of
the invention,
Figure 2 illustrates schema-tically a second embodi}nent of
the invention, and
Figure 3 illus-trates schematically a third embodiment of
the invention, in which bed layers are formed, one upon the
other, by means of roll pairs arranged back-to-back in one
and the same frame structure.
In Figure 1 the reference 10 identifies a mobile suc-
tion-sintering grate, which is only partially shown, the bot-
tom of the underlying suction box 11 being shown at 12.
Located on the grate 10 is a hearth layer 13 which comprises
a coarse particulate material and which is intended to pre
vent overheating of the grate 10 during a suction-sintering
operatlon~ It '~7ill be seen from the drawings that as the
grate moves slowly forwards in the direction of arrow 15,
there is gradually formed on the grate 10 a bed 14 of mate-
rial to be suction-sintered.
Arranged above the grate are means for compacting a
moist material mixture 18 arriving on a conveyor 17 to form
a coherent cake 19, said means in the illustrated embodiment
having the form of a rolling mill identified generally at 16.
The moist material mixture may, for example, comprise a fine
particulate iron-ore concentrate, fine particulate, iron-
.10 -containing metallurgical intermediate products, coke dust
and slag formers, whereat the fuel and water content are ad-
justed with respect to one another so that substantially the
minimum of fuel is consumed at the requisite sintering tempera-
ture. The conveyor 17 is provided with a weighing device 20
and is driven at a speed such as to supply a constant amount of
material to the rolling mill 16 per unit of tir.e. The string of
material passing to the rolling mill is smoothed out or level-
led by means of a scraper device 21, so that said string or
stream of material has a uniform thickness along that part of
the rolls 22 and 23 of the rolling mill active in compacting
the material.
Connecting to the outfeed si.de of the roll palr 22, 23
is a slide plate haviny a flat bottom 24, which forms a down-
wardly inclined support plate for receiving and yuiding the
cake 19 forrned by the rolls 22, 23, to a location directly above
the grate 10. As the cake 19 passes over the lower edge 25 of
the plate 24, the cake is broken, by the action of gravity,
into pieces having a size suitable to form a suction-sinter
charge. The size of the pieces obtained can be varied by suit-
able adjustment between, inter alia, the amount of materialmixture 18 supplied per unit of time and the roll pressure,
which parameters determine the cak~e thickness and the mechani-
cal strength of the ca~se, at least to a certain extent. The
plate 24 may be arranged so as to enable it to be adjusted to
different anyles relative to the horizontal. The angle at
which the plate is inclin~d to the horizontal, howeverr shall
be small enough to ensure that the friction generated between
the plate and the cake 19 will prevent the cake from being
broken upon the plate by gra~itational forces acting on said
cake, before the cake reaches the edge 25, o~er which the
cake is broken.
The rolls 22, 23 are driven synchronously by means of a
respective motor (not shown) or a common motor, and are
journalled in a rolling stand, which in the illustrated
embodiment is supported by the ceiling of the building housing
the suction-sintering plant, a part of said ceiling being
shown at 26. Only one rolling stand, identified by reference
27, is illustrated in Figure 1. The other rolling stand has
substantially the same design. The lower roll 23 is journal-
led in a part 28 of each rolling stand, while each end o~ the
other roll 22 is journalled in one arm 29 of a double-arm
lever pivotally mounted at 30 in the associated rolling stand
27, che other arm of said lever being identified by reference
31. Acting against the other arm 31 is a hydraulic piston-
cylinder device 32, which endea~ours to swing the lever in a
direction in which the ro l 22 is urged towards the roll 23.
A double-arm lever with associated piston-cylinder device is
provided for each end o~ the roll 22. The levers ma~, to ad-
vantage, be rigidLy connected -toyether, so tha-t they are swung
synchronously. Further, the arrangement is such that the plane
cont~inin~J the axes of the rolls 22, 23 is substantially per~
pendicuJar to the plate 24, so that the cake 19 is supported
by the plate 24 immediately it leaves the roll pair 22, 23l
thereby eliminating the risk of unintentional, pr~mature dis-
integration of the cake.
~ guide plate 33 which slopes downwardly rom the plate
24 connects with 'che lower edge 25 of the plate 24~ over which
edge 25 the cake 19 is caused to disintegrate, said plate 33
beinq arranged to guide 'che cake pieces tc a screening appa-
ratus 34, where they are divided into a relatively coars~
particulate fraction, which is placed nearest che grate 10 on
top of the hearth layer 13 to form a lower layer 35 of the
1 ~
charge bed 14, and a relatively fine particulate fraction,
which is placed on top of the layer 35, to form an upper
layer 36 of the bed 14. In this way, screening oE the cake
pieces is adapted so that the layer 35 will contain approxi-
mately 2/3rds or more of the total amount of material in thebed.
In the illustrated embodiment, the screening apparatus
34 has the form of a drum comprising an outer casing of po1y-
gonal cross-sectional shape provided with screen openings.
Extending along the whole of the length of the drum are out-
wardly projecting, substantially radial ~lades 37. The screen-
ing openings ma~ comprise slots which pass through the drum
casing and extend peripherally thereof between mutually ad~
jacent blades 37. The width of the slots may, to advantage,
be in the order of 10 mm. The drum is rotated clockwise by
means of a motor (not shown), whereat coarse cake-pieces fall-
ing onto the drum from the guide plate 33 will not pass through
the screening openings, but will be moved to -the right, as seen
in Figure 1, by the blades 37 and fall down onto the grate 10,
as indicated at 38, to form the bed layer 35. The smaller cake-
pieces will enter the drum through the screening openings and
pass straight through said drum, to form a stream 39 of rela-
tively fine particulate material, said finer pieces ~eing chargecl.
to the layer 35 already Eormed on the grate, to form the upper
charye layer 36. As illustrated in Figure 1, desirable, fine
additlves, such as fine, particulate additional fuel, can be
homogenously mixed into the upper layer 36. To this end there
is provided a conveyor 40 on which the fine particulate addi-
tive material 41 is conveyed to the screening apparatus 34,
through which said additive material is caused to pass whilst
being admixed with the finer fraction of the material arriving
from the guide plate 33. As shown at 42, the conveyor 40 is
arranyed to co-ac-t with a weighing device, to enable correct
metering of the additive material to the drum, and with a
scraper device 43 for levelling out the stream of additive
material passing to the screening apparatus ~4, so that said
stream of additive material is of uniform thickness over the
1 1
whole of its width.
For the purpose of obtaining, by rolling, a cake 19
having the correct properties there is provided a control
means, generally referenced 44, by means of which the roll
5 pressure can be automa-tically adjusted and monitored so l:hat
the cake 19 obtains the correct porosity relative to the amount
of moisture present in the mixture 18, preferably so that the
pores of the cake 19 are filled with water to a given percent-
age within the range of 60 - 90 ~ by volume, within which
10 range the cake obtains the desired mechanical strength. The
control means includes a pump 45, the suction side of which is
connected to a hydraulic liquid sump 46 and the pressure side
of which is connected to each hydraulic piston cylinder device
32, via a line 47. A return line 48 extends from the line 47
15 back to the sump 46, there being arranged in the return line
48 a regulatable throttle valve 49, the degree to which the
valve 49 is throttled determinin~ the pressure exerted by each
piston-cylinder device 32 on the arm 31, and therewith the roll
pressure. The val~7e 49 is controlled from a known comparison
20 circuit 51, via a control line 50, said circui-t being arranged
to receive on an input line 52 a signal which corresponds to a
selected set-point value of the thickness of the cake 19. The
comparison circuit 51 receives, via a line 53, an input signal.
sent by a -transducer 54 arranged to sense the thickness of the
25 cake 19, sa:id input slynal corresponding to the instantaneous
cake thickness, whereat the comparison circuit 51 compares the
signals from the lines 52 and 53 and when the signal obtained
on line 53 deviates from the value corresponding to the set-
point value of the thickness of said cake 19, adjusts the out-
30 put signal on the line 50 so as to increase or decreasethe throttling effect exerted by the valve, thereby to change
the roll pressure to a magnitude at which the desired cake
thickness will be obtained.
As will be understood, the screening apparatus 34 and
35 the conveyor 40 can be omitted from the apparatus illustrated
in Figure 1 when classification of the pieces obtained when
12
disintegrating the cake 19, and the supply of additive material
41 is unnecessary. Further, it is, of course, possible to
control the manufacturing process of the sinter charge in a
different way to that illustrated and described. It will
also be understood that the sintering grate 10 may be sta~
tionary and the apparatus producing the sinter charge arranged
form movement along the grate.
In order to improve -the accuracy at which the material
fraction 39 of finer particle size is placed on the grate
when fractioning the material by means of the screening ap-
paratus 34, there is arranged inside the screening drum a guide
plate 55 which is journalled on the shaft 57 of the screening
drum via end pieces 56, and the angle of inclination of
which guide plate can be adjusted by rotation about said
shaft 57.
Coinciding or substantially coinciding elementq in
Figures 1, 2 and 3 are identified with the same reference nume-
rals and will not be described in detail in the following de-
scription of Figures 2 and 3, which illustrate a first and a
second modifi.cation of the apparatus shown in Figure 1.
In the Figure 2 embodiment there is arranged above the
support plate 24 adjacent the lower end thereof a d.riveable
spiked roller 58, which :i.s pre~erably a variable-speed roller
and which is intended to Eorrn f:ractural impressions in the
cake l9 or to completely disintegrate the cake, the slze of the
cake pieces being determined by the distance between -the
spikes and the peripheral speed of the roller. For the sake of
clarity, the motor driving the spiked roller 58 and the means
supporting said roller have not been shown in Figure 2. The
cake pieces obtained fall from the lower edge of the plate 24
in a stream 59, which forms an upper layer 60 of the bed 14 on
top of a bed layer 61 previously placed on the grate 10 and the
hearth layer 13. The bed layer 61 may be formed with the aid
of a further roll pair (not shown) located to the righ-t, as
seen in Fiyure 2, of the illustrated roll pair, and the mate-
ri~l of the layer 61 may have a different composition or a dif-
ferent r~lean particle size to the material of the layer 60.
13
As will be understood from the aforegoing, when prac-
ticing the invention according to the embodiment illustrated
in and described with reference to Figure 2, two separate
roll pairs 22, 23 and ancillary equipment, arranged at some
distance apart, are required to build the bed layers 60, 61
on the grate 10. While such an arrangement may be perfectly
adequate, it requires a relatively large amount of space and
equipment. Figure 3 illustrates an embodiment of the invention
where the space required has been cut down by combining the
two pairs of rolls in a common, compact unit.
Thus, Figure 3 illuskrates a mobile suction-sintering
grate 10, on which the bed layers 60, 61 are formed by means
of the two roll pairs 22, 23, and 22',23' arranged in one and
the same open-frame structure 62, thereby obviating the need
to provide two mutually spaced, separate layer-forming sta-
tions and reducing the amount of space required. As shown in
the Fig~lre, the open-frame structure comprises mutually spaced
vertical members 63l top horizontal members 64 attached to
ceiling 26 and bottom horizontal members 65, only one such top
and bottom horizontal member being shown.
In the Figure 3 em~odiment, the roll pairs 22, 23 and 22',
23' are arranged back-to-back, so that the infeed sides of re-
sp~c~ve roll pairs face one another. ~s will be seen from
Figure 3, the infeed sides of respective roll pairs lie in a
common storage vessel 66, into which material to be sintered
is poured from a single conveyor 17. As with the previously
described embodiments, -the conveyor 17 is arranged to co-act
with a doctor on scraper means 21, for smoothing the material
18 conveyed by the conveyor 17. Connecting with the outfeed
side of respective roll pairs 22, 23 and 22'/ 23' is a sup-
port plate 24, which is inclined at an angle at which, while
allowing a cake string to be moved down the plate 24 by the
forces exerted thereon by the part of the cake issuing from
the roll nip is not sufficiently large to cause the cake to
slide down the plate under the influence of gravity at a
speed liable to cause premature disintegra~ion of the cake.
As shown in Figure 3, each of the slide plates 24 has
arranyed in the vicinity of the end thereof remote from re-
spective roll pairs a spiked roll 58 mounted fox rotation on
a bracket 67 carried by a respective vertical member 63.
5 Similar to the Figure 2 embodiment, the spiked rolls 58 are
intended to break the coherent cakes on plates 24 into pieces
of given size, said size being dependent on the spacing of
the spikes on said rolls and on the peripheral speed thereof.
The roll pairs 22, 23 and 22', 23' of the Figure 3
embodiment are arranged in a manner resembling the mounting
of the roll pairs 22, 23 of the Figure 1 and Figure 2 embodi-
ments. Thus, the upper roll 22 or 22' of the roll stand shown
to the left of the Figure is journalled for rotation in a
fi~ed stand part 28, while the lower roll 23 or 23' of said
roll pair is journalled on one arm 29 of a rotatable double-
arrn lever journalled at 30 to the fixed stand part 28. The
other arm 31 of respective double-arm levers is pivotally at-
tached to the piston of a piston-cylinder device 32, which
endeavours to swing the lever in a direction in which the rolls
20 23, 23' are urged towards the rolls 22, 22'. As with the roll
pair of the emboaiments previously described, the arrangement
is such that the planes containing the axes of th~ rolls 22~
23 and 22', 23' are substantially perpendicular to respective
sli.de plates 24.
~lthouyh not ShOWIl in Figure 3 ea~h of the roll pairs
is yoverned hy a control rneans 44 similar to that described
with reference to Figure 1.
In order to ensure that the particulate material
18 in the vessel 66 is sufficiently friable to enable it to
be picked up by the rolls of each roll pair, there is provided
means for agitating the heap of material contained by the
vessel 66, either constantly or at given periods. In the il-
lustrated embodiment, the agitating means comprises at least
one piston cylinder device having on the distal end of the
piston roa 68 of said device a bar 69 which is parallel with
the roll axes and i5 arranged to be moved into and out of the
15 ~ 7
heap of ma-terial 18 con-tained by the vessel 66. The bar 69 is
provided with surfaces of such shape and size as to ensure
that the material is stirred as the bar enters and leaves
said heap, thereby to prevent bogging and to ensure a fri-
able mass. As shown in the Figure, the cylinder 70 of the
piston-cylinder device is secured to the frame structure 62
via a bracket 71. In operation, material 18 is fed to the
vessel 66 by means of the conveyor 17, and is kept in a fri-
10 able state in said vessel by means of the reciprocatingly
movable bar 69. The material 18 is then picked up by the roll
pairs 22, 23, and 22', 23' and compacted therebetween to
form a coherent cake having the porosity desired, said
porosity being controlled by said control means, as with the
15 Figure 1 embodiment. Each cake is moved down its respective
support plate 24 to a spiked roll 58, which disintegrates the
cake into pieces of given si~e. The pieces then fall onto the
grate 10, forming either the layer 60 or the layer 61, depend-
ing on the pOSitiGn of the plate 24 from which said pieces
20 fall, relative to the movement path of the grate 10, as clear-
ly shown in the Figure. In order to provide a bed layer 61
of comparatively coarse material, the spikes of the spiked
roll 58 associated with rolls 22', 23' may have a wider spacing
than the spikes of the other roll 5~.
As will be understood, further modiEications of the
apparatus accordiny to the inven-tion are possible within the
scope of the invention. Thus, the pair or pairs of rolls may
be arranged obliquely to the lonyitudinal direction of the
grate or -the rolling equipment may be separate from the suc-
30 tion-sinter:ing grate, whereat the finished sinter-charge
material is delivered to the grate by means of suitable con-
veying means, optionally via a charging or storage bunker.
The favourable effects which can be obtained by means
of the invention will be evident from the fo:llowing examples,
35 in which a]l contents are given in percent by weight.
34~7
16
EXAMPLE 1
A material mixture comprising about 60 ~ Grangesberg
concentrate GAC (fine particulate concentrate having a high
iron content and a specific surface area of 550 cm2/g), about
32 % of anokher concentrate having a ]ower iron content, and
about 8 % slag former, of which 4 ~ was burnt lime, was ad-
mixed with 5 ~ coke dust, 8 % limestone and about 25 % returnsinter having a particle size beneath 6 mm, to form a suction-
sinter charge mixture. This mixture, which was composed to
provide a highly basic sinter, was moistened to a water con-
tent o~ 7 %. The moist mixture was rolled to form a cake
whose pores were filled with water to about 85 ~ by volume
and which was then disinte~rated and screened in the manner
described with reference to Figure 1 and illustrated in said
Figure, there being used rolls having a diame-ter of 350 mm
and a roll pressure of about 400 kp per cm of effective roll
length. The screening slots in the screening drum had a width
of 10 mm, whereat about 30 % of the material passed through
the screening drum to form the ~in~r upper layer of the
charye bed, the height of which reached to about 320 mm above
the hearth layer, which was 20 mm high. Sintering was effected
with an underpressure of 1500 mm water column. The sintering
time was about 10 minutes (including a standard addition of
2 minutes), -there being obtained a production of about 42.5
ton~ per rn2 grate area and 24 hours. When subjected to a
tumbler ~est, the resultant sinter, which was hard-burnt, had
a value of about 60 ~. The aforegoing represents the result
of a number of sintering tests subsequent to obtaining the
stated approximate 25 % balance between input and output re-
turn sinter. (For the tumbler test there was used a tumbler
drum having a length of 900 mm and a diameter of 990 mm. The
charge comprised 20 kg sintered material having a particle
si~e of 20 - 40 mm, and the drum was rotated 200 revolutions
during 8 minutes. Percentage by weight of tumbled material
having a particle size exceeding 6 mm was measured.)
A charge of the same composition but prepared in a con--
17 ~ ~ ~ V ~ ~ ~
ventional manner, without rolling, gave with all other sinter-
ing conditions equal a production of about 33 tons per m2
grate area and 24 hours, i.e. a production which was almost
30 % lower than the production obtained when practicing the
method according to the invention.
EXAMPLE 2
A material mixture comprising about 60 ~ Grangesberg
concentrate GPC (pellet-sinter concentrate having a high iron
content and a specific surface area of 1600 cm /g), about
32 ~ of another concentrate having a lower iron content and
about 8 ~ slag former, o~ which 4 ~ was burnt lime, was ad-
mixed, for the purpose o~ forming a suction-sinter.charge
mixture, with 4 % coke dust, 8 % limestone and about 22 %
return sinter ~6 mm). This mixture was moistened to a water
content of 7 % and was ro~ed in accordance with Example 1
above to form a cake, t.he pores of which were filled with
water to about 80 % by volume, whereafter the cake was dis-
integrated by means of a spiked roller in accordance with
Figure 2 and layed on a sinter grate, without being screened,
to form a bed havin~ a height of about 350 mm over the hearth
layer which was 20 mm high.
Subsequent to being dried, a sample of the mater.ial
disintegrated by rneans of the spiked roller had the following
particle ~ize distribution:
Particle size (mm)Percentage (~I
> 8 12.2
8 - 6 26.2
6 - 4 16.5
4 - 2 16.3
2 - 1 11.9
1 - 0,2 10.8
~ 0.2 ~.1
The sintering operation was carried out in complete
accordance with Example 1 above, and requi.red a time of 13
minutes (inclusive of the aforementioned two standard addi-
tional rninutes) to carry out, there being obtained, subse-
18
quent to reaching the return balance of about 22 %, a produc-
tion of about 42 tons per m2 grate area and 24 hours. A
tumbler test as specified in Example 1 gave a result of about
65 ~.
It will be understood that such a fine concentrate as
Grangesberg GPC could only be incorporated in extremely small
quantities, when preparing suction-sinter charges in a conven-
tional manner~
EX~MPLE 3
A material mixture comprising about 60 % Malmberget
concentrate MPC 3 (pellet sinter concentrate having a high
iron content and a fineness appro~imately the same as Granges-
berg concentrate GPC), about 32 % of another concentrate having
a lower iron content, and ahout 8 ~ slag former, of which 4 %
was burnt lime, was admixed, for the purpose of forming a
suction-sinter charge mixture, with 4 % coke dust, 8 % lime-
stone and about 23 % return sinter (<6mm). The mixture was
moistened to a water content oE 7 % and rolled in accordance
with Example 1 to form a cake, the pores of which ~ere filled
with water to about ~0 ~ by volume, whereafter the cake was
disintegrated by means of a spiked roller a~cording to Figure
2, and then placed on a sinter grate, without being screened,
to Eorm a bed having a heiyht o~ about 350 mm above the hear-th
layer, which was 20 mm high.
Sintering was effected in complete accordance with
Example 1 above, and required a time o~ 13.5 minutes (inclusive
of the 2 minute standard additional time), there being obtained,
after reaching the return balance of about 23 %, a production
o~ about 39.5 tons per m grate area and 24 hours. The tumbler
test as specified in Example 1 gave a result of about 63 %.
It will be seen that such a fine concentrate as Malm-
berget concentrate ~PC 3 could only be incorporated in an
extremely small quantity, when preparing suction-sinter
charges in a conventional rnanner.
1 9
It will readily be seen from the above description and
~xamples that the present invention provides a novel method
and a novel arrangement of apparatus, capable of af~ording the
following advantages:
1. Increased charge permeability, and therewith an in-
crease in production per unit of grate area can be achieved,
irrespective of the particle size of the input material.
2. The moisture content of the charge mixture can be
held at the low level required for an optimal thermal sequence,
~0 thereby saving fuel.
3. When sintering, a small underpressure can be main-
tained while achieving, at the same time, a high production,
thereby reducing the amount of energy required to drive the
fans.
4. The charge remains stable and will not compact during
a sintering operation.
5. Sintering can be effected without admixing the charge
with any other return material than return sinter.
6. ~ low level of ignition fuel and fuel admixed with
the sinter charge can be maintained by employing a large charge-
bed height.
7. Extremely fine particulate material, such as dus-t
from steel manufacturing processes, ash from coal combusting
process0s etc., can be sintered.
2~ ~. When cornpressing the charge mixture between rolls,
only a low roll pressure is re~uired, for example a linear
pressure of 150 - 1000 kp, preferably 200 ~ 800 kp, per cm of
roll length, thereby greatly reducing the wear on the rolls.
