Note: Descriptions are shown in the official language in which they were submitted.
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;l This invention is concerned with the manufacture of
granulated slag by quenching molten slag with water.
Molten slag generated in an electric furnac~, a re-
verberatory furnace, a converter, a blast furnace or the
'` 5 like is at a very high temperature. Molten slag discharged
from such a furnace is broken into numerous granules by mix-
' ing large quantities of water thereinto outside the furnace,
-' the water subsequently being removed to form the granulated
slag, which is utilized as a cement material, as sand for
i lO ballast, and in other uses.
;l The preferred method of separating the water from the `
! granulated slag is sedimentation,,but this requires relatively
voluminous tanks for which space is not available near the
furnace. It was common practice prior to this invention to
convey the entire aqueous slag mixture from a quenching con-
tainer adjacent to the furnace to a remote sedimentation zone
by means of a pump capable of withstanding the abrasive effect
of the solids in the mixture.
Suitable slurry pumps are relatively expensive, and
their initial cost, their operating expense, and the costs of
maintaining them increases rapidly with their size~ Pipe
lines capable o~ withstanding the abrasive action of the
pumped slurry are correspondingly expensive. It is an object
of this invention to provide a method which enables these
expenses to be reduced.
According to one aspect of this invention there is
provided a method of thickening a granulated slag slurry which
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comprises slag granules and heated water, the method compri
ing the steps of:
introducing said slurry into a tank; r
precipitating the granulated slag in a lower part of
5 the tank and stirring the precipitated granulated slag by
introducing water into the lower part of the tank;
causing at least a part of the heated water in said slurry
to overflow from the tank; and
removing the thicXened slurry from the lower part of
10 the tank.
According to another aspect of the invention there is pro-
vided a method of making granulated slag comprisi~g the
steps of: -
contacting water with molten ~lag to produce a granu-
15 lated slag slurry which comprises slag gxanules and heated
water;
; introducing said slurry into a quenching tank;
precipitating the granulated slag in a lower part of
the quenching tank and stirring and cooling the precipitated
20 granulated slag by jetting water colder than said heated
water into the lower part of the quenching tank;
causing at least a part of the heated water in said
slurry to overflow from the quenching tank;
pumping the slurry from the lower part of the~quenching
25' tank to a sedimentation zone; and
separating the granules from the water of the pumped
slurry in sai~ zone to produce the granulated slag, :
Preferably the heated water overflowing from the quenching
tank is conveyed to the sedimentation zone and combined with
30 the water separated from the granules of the pumped slurry,
the eombined water then being cooled in said zone and delivered
to the region of the quenching tank to form at least part of
the water with which the molten slag is contacted, and possibly
also the water jetted into the lower part of the quenching
35 tank~
Preferably a substantially constant water level is main-
tained in the tank by continuous overflow of water from the tank.
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The overflow of heated water from the tank not only
substantially reduces the quantity of water in the slurry
removed from the lower part of the tank, so that the removed r
slurry is thickened and there is a reduced quantity to be ' -
handled, but also results in a reduced temperature of this
thickened slurry.
The invention will be further understood from the follow-
ing description with reference to the accompanying drawings,
in which:
Fig. 1 is a schematic illustration, in a plan view,
of apparatus in which an embodiment of the method of this
invention is carried out; and
Fig. 2 is a sectional elevation of part of the apparatus
of Fig. 1.
, 15 Referring initially to ~IG. 1, there is indicated a blast
furnace 1 from which a chute 3 leads obliquely downward into
a quenching tank 2. A conventional array of water jets 4,
not illustrated in detail, is directed toward the material in
the chute 3. Molten slag discharged from the blast furnace
1 to the chute 3 is broken into granules by quickly cooling
it with water supplied by the water jets 4, so that the chute
3 supplies granulated slag and water to the tank 2. A conically
tapering bottom portion o the tank 2 is connected to a remote
primary sedimentation tank 5 by a pipe line 6 including a
main slurry pump Pl. An overflow line 10 for hot water leads
from the tank 2 downwardly to a secondary sedimentation tank
7a which also receives supernatant liquid from the primary
sedimentation tank 5 through a pipe or chute 8 by gravity.
Sediment formed in the tank 7a is returned to the primary
sedimentation tank 5 by an auxiliary slurry pump P3 while
water substantially free from solid matt~r is conveyed from
the secondary sedimentation -tank 7a to a cooling tower 7b.
The cooled water is collected in a reservoir 7 where it is
also replenished for evaporation and drag-out losses in a
manner not specifically illustrated, and from where it is
pumped to the water jets 4 by a pump P2 through a line 9. A
distributor valve V permits a portion of the water to be
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diverted to be jetted directly into the quenching tank 2
through a branch line 9a.
~ s is shown in greater detail in FIG. 2, the quenching
tank 2 is covered by a hood 13 from which steam is conducted
into a stack 14, only partly shown. The rim about the open top
of the tank carries an upright, cylindrical wire screen 11.
An annular trough 12 extends about the rim of the tank to catch
liquid passing through the screen 11 and to lead the
; liquid into the overflow line 10.
The branch line 9a includes an annular distributor
section about the conically tapering bottom part of the
tank 2. Radial injection nozzles 15 extend from the distri-
butor section into the tank 2 and terminate near the bottom
wall of the tank. The intake line 16 o the main slurry
pump Pl enters the bottom portion of the tank 2 and has an
enlarged end 16a directed downwardly toward the bottom wall
of the tank and the nozzles 15.
In the above described apparatus, granulated slag mixed
with large quantities of hot water is supplied to the tank 2
via the chute 3. Most or part of the hot water overflows
through the screen 11 to the trough 12 and overflow line 10,
and the granulated sla~ precipitates to the bottom ~art of
the tank 2.
Cold water injected as needed into the tank 2 through
the nozzles 15 not only reduces the water temperature in the
tank 2, but also stirs the contents of the tank to prevent a
solid cake of slag particles from being formed in the tank
bottom, and maintains a uniform distribution of solids in the
granulated slag slurry which is pumped from the tank 2 via the
line 16. Because the intake orifice 16a is located near the
bottom wall o~ the tank and the injection nozzles 15, solid
slag particles generally move downwardly through -the tank
2 while there is very little corresponding movement of water.
Most of the hot water entering the tank 2 with the freshly
granulated slag is discharged into the trough 12 in a con-
tinuous stream and is replaced in the pumped slurry by the
cooler injected water.
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The granulated slag slurry which is pumped from the tank
2 is in a thickened state because the hot water introduced
via the chute 3 is caused to overflow and the quantity of
water contained in the slurry is reduced to this extent.
When a need to stir the precipitated granulated slag in the
tank 2 arises, water is jetted into the precipitated granulated
slag from the nozzles 15, and the quantity of water in the tank
2 increases. There is an overall reduction of the quantity
of water in the slurry, increasing the concentration of the
granulated slag slurry to be transferred.
The overflow arrangement on the quenching tank 2 does
not significantly increase the space required by the tank, but
the transfer of a substantial portion of the process water
from the tank 2 to the remote sedimentation zone by gravity
through the overfLow li~ne 10 materially decreases the burden
on the primary slurry pump Pl. The method of the invention
thus may be performed with a slurry pump and associated equip-
ment of smaller capacity, and thus at lower cost than an other-
wise comparable conventional method of making granulated slag.
The overflow arrangement, in cooperation with the nozzles 15,
maintains a practically uniform liquid level in the quenching
tank 2, virtually independent of variations in the rate
of slag delivery into the tank. The power demand of the
pump Pl is thereby held near a constant value, and the driving
electric motor, not illustrated, may be chosen accordingly to
operate at highest efficiency. A practically uniform flow
rate is maintained readily in the pipe line 6 even at varying
rates of slag delivery to the quenching tank sothat clogging
of the line by settling slag particles is avoided or minimized.
In addition, the effective internal volume of the sedi-
mentation tank 5 and the diameter of the pipe line 6 can be
reduced, and the sedimentation time can be shortened, thereby
enhancing operating efficiency. Since the construction costs
and the maintenance and operating costs for the whole slag
granulation apparatus are reduced in comparison to the prior
art, the costs of the granulated slag product can be lowered.
A conventional plant for producing granulated slag
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was modified by installing a screened overflow on its
quenahing tank substantially as shown in FIG. 2 so that the
water supplied by the jets 4 and the nozzles 15 was partly
removed by gravity. The solids content of the slurry pumped
from the bottom of the quenching tank under a wide range of
operating conditions was determined both before and after the
modification. It ranged from 8.41% to 13037% by volume prior
to the modification, and from 17.64% to 26.47% after the modi-
fication, indicating that approximately one half of the total
water entering the quenching tank was removed before it
reached the main slurry pump Pl. There was still enough water
left in the slurry for pumping, but the dwell time of the
slurry in the primary sedimentation tank 5 could be consider-
ably reduced.
It should be understood, of course, that the foregoing
disclosure relates only to a preferred embodiment of the
invention, and that variations and modifications may be made
thereto without departing from the scope of the appended claims.
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SUPPLEMENTARY DISCLOSURE
FIG. 3 of the accompanying drawings schematically
illustrates the sedimentation devices of the apparatus o
FIG. 1 in elevation and partly in section, but rearranged for
simpler pictorial representation.
In operation, the mixture of slag particles and hot water
at almost 100C dropped from the chute 3 into the tank 2 is
mixed with enough water discharged at approximately 40C from
the nozzles 15 to reduce the temperature of the pumped slurry
to about 70C, and thereby to prevent cavitation in the slurry
pump Pl. The co~bined rate at which water enters the tank 2
from the chute 3 and the nozzles 15 is controlled by means of
the valve V to exceed the capacity of the slurry pump Pl. The
water level in the tank Z thus rises above the tank rim and
water flows through the screen 11. When the tank is first
operated, the overflowing water carries slag pa~ticles with it.
However, the size of the coarsest slag particles is approxi-
mately 7 ~m, and a filter cake impervious to all but the smallest
slag particles, but readily premeable to water, is built up
on the inner surface of the screen 11, whose openings have
an approximate size of 5 mm. Only a minor fraction of the
solids entering the tank 2, much less than 10% by weight of the
granules leaves the tank through the screen 11, and does
not interfere with gravity flow of the water from the trough
12 through the line 10. More than half of the hot water
introduced into the tank 2 with the granulated slag is removed
via the line 10 and consequently is not pumped by the pump Pl.
Referring to Fig. 3, the primary sedimentatlQn tank 5
has an upright cylindrical top portion 5a made of wire screen
and a coaxial, conical bottom portion or hopper 5b whose
top rim supports the screen portion 5a ~nd an annular overflow
trough 5c about the lowermost part of the screen portion.
The pipe 8 leads downwardly from the trough 5c into the open,
wide top of the conical secondary sedimentation tank 7a which
also receives the discharge end of the overflow line 10. The
intake pipe of the auxiliary slurry pump P3 has its orifice near
the bottom end of the tank 7a, and its discharge pipe terminates
in the top of the primary sedimentation tank 5. A screened
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overflow opening 17 near the top of the tank 7a leads into a
storage compartment 18 from which water may be transferred to
the top of the cooling tower 7b by a pump 19. The cooling
tower is mounted atop the reservoir 7 from which the pump
P2 pumps water to the lines 9 and 9a. Fresh water may be
added to the contents of the reservoir 7 by means not
illustrated. A cap 20 is removed from time to time from
the bottom of the hopper 5b of the tank 5 to empty the same
of granulated slag carrying only a minimal amoun-t of water.
The water conveyed by the pump P2 is virtually free of suspended
solids.
The coarse particles in the slurry entering the tank
5 through the pipe line 6 drop into the hopper 5b. A cake
building up on the inner face of the screen portion 5a in the ~ -
manner described with reference to the screen 11 also retains
finer particles which ultimately settle in the hopper 5b. A
small amount of fines is collected on the bottom of the
secondary sedimentation tank 7a together with fines out
of the hot water overflowing from the quenching tank 2 and
is transferred to the primary sedimentation tank by the small
auxiliary slurry pump P3. The supernatant water from the
secondary sedimentation tank 7a, after being further filtered
through the screen in the opening 17 and any cake that may
build up on the screen, is cooled to about 40C in the tower
7b for return from the reservoir 7 to the quenching tank 2
by the pump P2.
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