Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS FOR AND PROCESS OF WATER
GRANULATING MATTE OR SLAG
BACKGROUND OF THE INVENTION
This invention relates to water granulation. In one aspect, this invention
relates to
an apparatus useful for the water granulation of molten matte or slag while in
another
aspect, this invention relates to a method of water granulating matte or slag.
In yet
another aspect this invention relates to an apparatus and method of water
granulating
matte or slag in an environmentally safe manner and with minimal, if any,
phreatic
explosions.
In the various pyrometallurgical processes, particularly nonferrous processes,
1 S molten matte and slag are generated as intermediate product and by-
product, respectively.
Efficient handling of these materials favors their reduction to a flowable,
particulate state.
Many methods are known for making this reduction, and these include water
granulation,
air granulation, grinding, rotary atomization (as described in USP 5,409,521
which is
incorporated herein by reference) and the like. For reasons of convenience,
safety and
cost, water granulation is often a preferred method of size reducing matte and
slag. One
representative water granulation method is described in USP 5,468,279 which is
incorporated herein by reference.
While all of the above techniques are effective to one degree or another, all
are
2S subject to improvement, particularly with respect to environmental and
safety
considerations. With respect to water granulation in particular, improvements
in gas
emission capture and reduction in phreatic explosions are the targets of a
constant quest.
SUMMARY OF THE INVENTION
According to this invention, molten matte or slag is water granulated by
feeding
molten matte or slag through a launder to a granulator tank. The tank
comprises sloping
walls, and it is equipped with one or more baffles which divides it into an
active
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granulation zone and a quiescent settling zone. The tank is
also equipped with adjustable overflow weirs and a
multiplicity of spray nozzles. These nozzles are positioned
such that the water that they emit impacts on all or
substantially all of the molten matte or slag that is fed to
the granulator tank. The granulation tank is optionally
coated with a polymeric material to reduce the potential for
phreatic explosions. The granulator is also optionally
equipped with a gas offtake which can be connected directly
to a quench tower which in turn can be connected to an
induced ventilation system.
The granulator tank is also equipped with a bucket
elevator for removing granulated material. Water overflow
from the granulator is transferred to a thickener/clarifier
to recover solids. The recovered granulation water from the
thickener/clarifier is cooled and recycled, and the pH of
this water is controlled to maximize the efficiency of
removing pollutants from the granulator ventilation gas.
An aspect of the invention provides an apparatus
for granulating molten material, the apparatus comprising:
A. means for conveying a molten material from a source of
molten material to a sloping wall granulator tank having a
freeboard area, the granulator tank equipped with (i) water
overflow weirs, the weirs isolated from the freeboard area
by at least one partition that extends into the granulator
tank, (ii) a baffle to divide the granulator tank into a
settling zone and a granulation zone, (iii) means for
diverting material spills away from the granulation zone,
and (iv) means to impede the discharge of solid material
from the granulator tank to the means for conveying;
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B. means for projecting water onto the molten material as
the molten material is discharged from the means for
conveying into the granulation zone of the granulator tank
such that the molten material is converted into a granulated
material and then collects in the settling zone of the
granulator tank; C. means for removing the granulated
material from the settling zone of the granulator tank; and
D. means for capturing gas emissions from the granulator
tank.
Another aspect of the invention provides an
apparatus for granulating molten material, the apparatus
comprising: A. means for conveying a molten material from a
source of molten material to a sloping wall granulator tank
having a freeboard area, the granulator tank equipped with
(i) water overflow weirs, the weirs isolated from the
freeboard area by at least one partition that extends into
the granulator tank, the weirs are adjustably positioned in
the granulator tank, (ii) a baffle to divide the granulator
tank into a settling zone and a granulation zone, (iii) a
polymeric coating, (iv) means for diverting material spills
away from the granulation zone, and (v) means to impede a
discharge of solid material from the granulator tank to the
means for conveying; B. means for projecting pH neutral or
slightly basic water onto the molten material as the molten
material is discharged from the means for conveying into the
granulation zone of the granulator tank such that the molten
material is converted into a granulated material and then
collects in the settling zone of the granulator tank;
C. means for removing the granulated material from the
settling zone of the granulator tank comprising a bucket
2a
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elevator, the bucket elevator being adjustably positioned in
relation to the bottom of the granulator tank; D. means for
capturing gas emissions from the granulator tank; and E.
means for recycling the water from the granulator tank back
to the means for projecting.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic flow diagram of one
embodiment of a matte granulation process from matte
launders to two granulators to a granulated matte conveyor
belt.
FIGURE 2 is a schematic depiction of the two
granulators of FIGURE 1.
FIGURE 3 is a schematic depiction of the bucket
excavator of FIGURES 1 and 2:
DESCRIPTION OF THE PREFERRED EMBODIMENT
The water granulation apparatus of this invention
is capable of granulating either molten matte or slag or a
combination of both. Typical matte and slag compositions
include those generated in copper smelting processes as
those described in USP 5,449,395; 4,416,690; 5,217,427 and
5,007,959. Representative mattes and stags generated from a
nickel smelting process are described in USP 5,215,571.
Like numerals are employed to designate like parts
throughout the drawings. Various items of equipment, such
as valves, fittings, heaters and the like, are omitted so
2b
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as to simplify the description of the invention but those skilled in the art
will recognize
that such conventional equipment can be, and is, employed as desired.
One typical embodiment of the process of this invention is depicted in FIGURE
1.
Molten matte (e.g. copper or nickel) or slag. in this case matte. is conveyed
by launders
l0a and l Ob from one or more smelters or other pyrometallurgical furnaces
(not shown)
to granulation tanks 1 I a and 11 b. The molten matte is contacted with water
within these
tanks, and it is converted to granulated matte which collects at the bottom of
the tanks.
Bucket excavators 12a and 12b remove the granulated matte on a continuous or
batch
basis from the bottom of the granulation tanks to conveyor 13 or similar
transport
equipment which transports the granulated matte to a storage or shipping
facility or to
another station for further processing (none of which are shown in the
Figures).
FIGURE 2 depicts one embodiment of the granulator of this invention. Typically
the granulator (here described in terms of granulator 11 b) includes an
enclosed and
ventilated tower 14b connected to a ventilation duct 15. Tower 14b is joined
to steam
hood 16b which covers granulation zone 17b. The granulation zone is equipped
with an
intermediate ladle (e.g. ladle 18a shown in the cutaway section of granulation
zone 17a)
positioned relative to one or more water nozzles (e.g. 19a and 19b) such that
molten matte
discharged from the intermediate ladle (which was received from launder l0a or
l Ob,
respectively) comes into immediate and substantially complete contact with
water
discharged from the nozzles.
The contact of molten matte with water generates steam which is captured by
the
steam hood and vented through the tower to the ventilation duct. Typically and
preferably, the intermediate ladle is located above the nozzle, and the nozzle
is operated
in such a manner that it ejects a spray or cascade of water. The molten matte
discharged
from the ladle thus passes or falls through the water spray or cascade.
Upon contact with water, the molten matte is granulated and collected at the
bottom of the granulation tank, i.e. in settling zone 20b. Granulation zone
17b is
separated from settling zone 20b by baffle 21 b which is typically one or more
concrete or
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steel structures extending from the inner walls of the granulation tank.
Settling zone 20b
is also equipped with granulation water overflow weir 22b which will capture
and divert
from the settling zone the granulation water. The granulated matte is
eventually removed
from the settling zone by excavation buckets 23b which are depicted in greaser
detail in
FIGURE 3.
The granulation tank is also equipped with provisions (e.g. emergency launder
24b and emergency pot 25b) to control and direct any molten material spills
that may
occur on occasion away from the granulation area.
The granulator tank consists of reinforced concrete or other suitable
construction
material, e.g. steel, and comprises sloping walls (as depicted in FIGURE 3) to
direct the
granulated material to the bucket elevator. The overflow weirs are located
along the side
of the tank to allow controlled withdrawal of water, and preferably these
weirs are
1 ~ adjustable. The weirs are isolated from the free-board in the granulator
and the turbulent
water by metal partitions 26a and b which extend into the water as shown in
FIGURE 2.
In one embodiment, water enters the granulation pit or tank through a plate
(not
shown), typically made of stainless steel, which is fitted with a multiplicity
of spray
nozzles. The number, diameter (size) and positioning of the nozzles can vary
to
convenience, the exact size, number and positioning of the nozzles a function
of the
molten material, the parameters of the granulating operation, the desired
final particle size
of the granulated product, and similar factors. The combination of all these
factors
ultimately determines the number and size of phreatic explosions.
Optionally, the granulation pit is coated with a polymeric material, e.g. a
coal tar
epoxy, to reduce the potential for molten material explosions. While not
wanting to be
bound by theory, organic materials are believed to prevent metal-water
explosions by
interfering with the onset of nucleate boiling at the interface between the
molten material
and the granulation tank.
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The water flow rate to the granulator tank will vary with the design of the
tank,
the nature and amount of molten material, water temperature and other
variables, but
typically varies between about 30 and about 10 tons of water per ton of
material,
preferably between about 2~ and 1 ~ tons water per ton of material. Depending
upon the
various design and operating variables of the water granulation system,
typical systems
can routinely process 60 tons per hour (tph) of molten material, e.g. copper
matte, often in
excess of 85 tph, and some system designs and operations can process in excess
of 200,
even 300, tph molten material without damaging explosions.
Water pressure is typically between about 6~ and 120 psig, preferably between
about 85 and 105 psig, to promote explosion-free granulation. Some small
"bangs" are
typical and useful to assure the operators that the system is operating
normally. The
water temperature is typically in excess or 90 F, preferably between about 120
to 140 F.
Preferably, the granulators are fitted with an explosion relief opening 27b
consisting of durable, e.g. stainless steel, channels 28b set at a spacing to
reduce the
possibility of solid material being expelled from the granulation area closest
to the molten
material inlet launder. Here too, preferably the explosion relief opening is
covered with a
polymeric material 29b, e.g. a polymer coated fabric, and retained by elastic
cords to
prevent release of steam during normal operation but allowing relief of
pressurized gases
in the event of an explosion (thus preventing structural damage to the
granulator tank and
associated equipment).
The granulator is preferably equipped with a gas offtake which connects
directly
to quench tower (scrubber) 14b and then to an induced ventilation system (e.g.
ventilation
duct 15). The quench tower can be operated with a side-stream of the main
granulation
water to effect the scrubbing of pollutants such as sulfur dioxide or
particulate matter.
The quench tower effluent can flow directly into the granulation tank.
Alternatively the
granulator can be ventilated through a remotely located scrubber (not shown).
In another
alternative, the granulator can be tightly sealed to prevent any gas escape
with the
exception of gases into the ventilated launder enclosure.
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The bucket elevator is used to remove material from the granulation tank, and
it is
equipped with rollers, guides and a lifting hoist so it can be partially
removed from the
granulation tank for servicing or to effect a controlled removal of material
from the tank.
This latter procedure allows the tank to be "mined" should it be overfilled
with granulated
material.
The water overflow from the granulator is directed to a thickener/clarifier
(not
shown) to recover any solids that are entrained in the granulation water. The
underflow
from the thickener can optionally be fed into slotted granulation excavator
buckets to
effect filtration and recovery of the material. Alternatively, the underflow
can be directed
to a filtration apparatus.
The granulation water pH is controlled by addition of a basic compound, such
as
NaOH, to maintain the pH at about neutral to slightly basic. In one
embodiment, the
1 S controlled pH water is used to scrub pollutants from the granulator
ventilation gas.
The granulation water can be cooled in a conventional cooling tower, and then
recycled to the granulation system. Preferably, a backup water supply system
is provided
to assure water flow to the granulation heads even in the event of an
electrical power
failure that shuts down the main granulation pumps.
Although this invention has been described in considerable detail by reference
to
the drawings and the various embodiments detailed above, this description is
for the
purpose of illustration and is not to be construed as a limitation upon the
invention as
described in the appended claims.
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