Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR DELIVERING A GRINDING MEDIA TO
A GRINDING MILL.
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for delivering a
grinding
media to a grinding mill.
BACKGROUND TO THE INVENTION
Grinding mills are widely used in the grinding of ores and concentrates.
Grinding
mills take the form of ball mills, tower mills," vertical attrition mills,
horizontal
attrition mills, stirred mills as well as other types used to grind materials.
An example
of a grinding mill is the mill sold by Xstrata Technology under the trademark
IsaMillTm
Grinding mills are often operated to grind a slurry containing a liquid
(normally
water), the ore or concentrate and a grinding media. The grinding media may
comprise particulate material, such as sand, ceramic, metal or other material.
In many
grinding mills, a slurry of the ore or concentrate is mixed with the grinding
media.
This mixing may take place either just before entrance to the grinding mill or
within
the grinding mill itself
A number of different arrangements have been utilised to feed the grinding
media to
the grinding mill. The terms "feeding to a grinding mill" or "delivery to a
grinding
mill" are general terms, and in reality, grinding media is fed into a pumpbox
along
with the material to be ground, and this is then pumped into the mill.
Throughout this
specification, the expressions "feeding to a grinding mill", "delivering to a
grinding
mill" or similar expressions are to be taken to include directly feeding to
the mill or
feeding to a pumpbox or an intermediate vessel and thereafter to the mill. The
material to be ground, or other material, may also be fed to the pumpbox or
other
intermediate vessel.
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In some arrangements, augers or screw conveyors are used to transfer the
grinding
media from a hopper to the grinding mill. In other arrangements, pneumatic
conveying may be used to transfer the grinding media from a hopper to the
grinding
mill. Some attempts have also been made to use hydraulic conveying to transfer
grinding media to the grinding mill. However, none of these arrangements are
entirely
satisfactory for use with many grinding media presently in use. For example,
ceramic
grinding media are relatively coarse, dense particulates that are also highly
abrasive.
Existing screw conveyors have difficulty in transferring ceramic grinding
media.
Existing pneumatic and hydraulic conveying apparatus have trouble coping with
the
highly abrasive nature of ceramic grinding media, which causes a short
operational
life for the pneumatic or hydraulic conveying apparatus and necessitates
periods of
downtime to replace that apparatus.
While this invention is suited to ceramic grinding media, it also has
applications with
steel based media.
BRIEF DESCRIPTION OF THE INVENTION
In one aspect, the present invention provides an apparatus for delivering a
grinding
media from a holding vessel or storage vessel to a grinding mill, the vessel
holding a
quantity of the grinding media, the grinding media being in the form of a
particulate
material, the vessel having an outlet at lower end thereof, the apparatus
comprising:
- a housing positioned below the outlet of the vessel, the housing receiving
grinding
media from the vessel,
- a nozzle delivering a liquid to the housing,
- a mixing chamber having an inlet for receiving liquid and grinding media,
the inlet
of the mixing chamber being spaced from an outlet of the nozzle whereby liquid
exiting the nozzle entrains grinding media in the housing and a mixture of
liquid and
grinding media enters the inlet of the mixing chamber and is further mixed in
the
mixing chamber,
- a diffuser having an inlet for receiving the mixture of liquid and grinding
media
from the mixing chamber, the diffuser including a portion defining a generally
divergent flow path therein,
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- the diffuser having an outlet through which the mixture passes for supply to
the
grinding mill.
In one embodiment, the present invention provides an apparatus for delivering
a
= grinding media from a holding vessel or storage vessel to a grinding mill,
the vessel
holding a quantity of the grinding media, the grinding media being in the form
of a
particulate material, the vessel having an outlet at lower end thereof, the
apparatus
comprising:
- a housing positioned below the outlet of the vessel, the housing receiving
grinding
media from the vessel,
- the housing having a first side opening and a second side opening,
- a nozzle connected to the first side opening, the nozzle delivering a liquid
to the
housing,
- a mixing chamber connected to the second side opening, the mixing chamber
having
an inlet for receiving liquid and grinding media, the inlet of the mixing
chamber being
spaced from an outlet of the nozzle whereby liquid exiting the nozzle entrains
grinding media in the housing and a mixture of liquid and grinding media
enters the
inlet of the mixing chamber and is further mixed in the mixing chamber,
- a diffuser having an inlet for receiving the mixture of liquid and grinding
media
from the mixing chamber, the diffuser including a portion defining a generally
divergent flow path therein,
- the diffuser having an outlet through which the mixture passes for supply to
the
grinding mill.
In one embodiment a small amount of water is added to the media in the holding
vessel or storage vessel above the apparatus to assist in the movement of the
media
into the housing
In one embodiment no water is added to the media in the holding vessel or
storage
vessel above the apparatus. In this embodiment, the media leaving the holding
vessel
or storage vessel is either essentially dry or it may have essentially the
same water
content as the media entering the hopper or vessel or it may have a lower
water
content than the media entering the hopper or vessel (for example, the holding
vessel
Or storage vessel may be provided with dewatering apparatus or drying
apparatus).
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In one embodiment, the nozzle is a replaceable nozzle.
In one embodiment, the mixing chamber is a replaceable mixing chamber.
In one embodiment, the diffuser is a replaceable diffuser.
In one embodiment, a liquid supply system (such as a water supply system) that
includes a liquid supply pump is provided for delivering liquid to the nozzle.
The
liquid supply system may include a non-return facility to prevent the media
flowing
back into the liquid supply system when a liquid delivery pump stops.
In one embodiment a screen or other dewatering technique or apparatus, such as
a
dewatering cyclone, can be used to separate the grinding media from the
delivery
liquid being added to the mill to , minimise delivery fluid from being added
to the
grinding mill. This is preferably positioned on the inlet of the slurry
holding tank or
pumpbox where the media is delivered from the apparatus, the water being
returned
directly to the process or water system. Other dewatering techniques such as
poly-
deck screens, pre-densifiers, or settling devices such as tanks allowing the
water to
bypass the tank, while the media settles in the tank, and exits via an
automated valve
or a pressure sensitive device acting due to the media load such as a "duck
bill" can
also be used.
In one embodiment, the housing includes a water inlet positioned below the
outlet of
the vessel, enabling the grinding media to be wetted. The water inlet is
suitably
positioned so that it wets the media prior to the media contacting the liquid
flow from
the nozzle. It has been found that wetting the media prior to contacting the
media with
the liquid from the nozzle surprisingly increases the media transfer rates.
In one embodiment, the holding vessel or storage vessel has one or more sides
consisting of a portion of screen used to dewater the media that is being
stored in the
housing vessel.
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In some embodiments of the present invention, the housing may include an
opening
having a closure, the closure being removable to gain access to an interior
volume of
the housing. This is advantageous in that any blockages in the housing caused
by the
grinding media can be easily cleared by opening the housing to gain access to
the
5 interior volume of the housing and hence to the site of the blockage.
Clearing of the
blockage may be as simple as poking into the blockage with a rod, or by
removing the
blockage from the housing.
In some embodiments of the present invention, a valve is positioned to control
flow of
grinding material from the outlet of the holding vessel or storage vessel into
the
housing. The valve may be operated so that it is normally partly opened to
allow a
trickle of grinding media to pass therethrough. The valve may be moved to a
fully
opened position in the event that a blockage or bridging occurs in the
grinding media
in the vicinity of the valve. The valve may also be closed fully during
shutdowns for
maintenance of the installation. The valve is suitably a knife gate valve
having a large
opening so that it can be opened wide if bridging of the grinding media in the
vessel
outlet occurs.
The housing may be provided with a viewing port in order to allow an operator
in to
view the interior volume of the housing. The viewing port may be provided by a
transparent portion in a wall of the housing. The viewing port may be provided
in the
form of a window in a wall of the housing.
=
The nozzle may be connected to the housing via any appropriate connection. For
example, the nozzle may be connected to the housing via a flange connection.
For
example, the housing may have a conduit or projection extending from aside
wall, the
conduit or projection having a flange at an outer end thereof, and the nozzle
may also
be provided with a complementary shaped flange for joining to the flange of
the
conduit or projection. Appropriate nuts and bolts may be used to connect the
nozzle to
the flange connection. The nozzle may be fitted by inserting the nozzle
through the
opening in the side wall of the housing such that the nozzle extends into the
interior
volume of the housing and connecting the nozzle to the housing.
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In some embodiments, the nozzle may include a nozzle insert. The nozzle insert
may
extend through a nozzle housing that is connected to the housing.
The mixing chamber may be connected to the housing via any appropriate
connection.
For example, the mixing housing may be connected to the housing via a flange
connection. In one embodiment, the housing may have a conduit or projection
extending from the sidewall, the conduit or projection having a flange at an
outer end
thereof, and the mixing chamber may also be provided with a complementary
shaped
flange for joining to the flange of the conduit or projection. Appropriate
nuts and bolts
may be used to connect the mixing chamber to the flange connection. The mixing
chamber may be fitted by inserting the mixing chamber through the opening in
the
side wall of the housing such that the mixing chamber extends at. least partly
into the
interior volume of the housing and connecting the mixing chamber to the
housing.
The mixing chamber may include a mixing chamber insert. The mixing chamber
insert may extend through a mixing chamber housing that is connected to the
housing.
The diffuser may be connected to the mixing chamber or to the housing. For
example,
the diffuser may be connected to the mixing chamber or to the housing via a
flange
connection. It will be understood that the diffuser is positioned such that
the mixture
of grinding media and liquid leaving the mixing chamber passes into the
diffuser.
In some embodiments, the diffuser is connected to an upwardly extending pipe
will
conduit that forms part of the delivery piping or conduits for delivering the
mixture of
liquid and grinding media to the grinding mill. It has been found that having
the pipe
or conduit extending from the diffuser in an upwardly direction minimises or
avoids
settling of the grinding media in that pipe or conduit.
The supply of liquid to the nozzle should be sufficiently high to ensure an
adequate
transfer of grinding media. The actual flow rate of water may depend upon
nozzle size
and the amount or rate of grinding media to be transferred. A pump may be used
to
supply delivery liquid to the nozzle. Use of a pump ensures that a stable flow
and
pressure of delivery liquid can be provided. Although addition of process
water
through a pipe may be adequate to provide delivery liquid, the flow of process
water
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might vary due to variations in ,pressure in other parts of the overall
process water
circuit.
The nozzle used in the present invention may have a ratio of outlet diameter
to inlet
diameter of from 10% to 50%, more preferably from 15% to 35%, even more
preferably from 20% to 30%.
In some embodiments of the present invention, the mixing chamber may have a
ratio
of diameter to length of from 5% to 30%, more preferably from 10% to 20%, even
more preferably from 10% to 15%. These ratios have been found to provide
sufficient
length in the mixing chamber to produce good mixing between the liquid and the
grinding media.
The diffusor may have a ratio of inlet diameter to outlet diameter that falls
within the
range of up to 75%, preferably from 30% to 75%, more preferably from 40% to
60%.
Use of a divergent diffuser is likely to minimise the likelihood of blockages
in the
grinding media delivery system
In some embodiments, it may be possible to omit the diffuser. Accordingly, in
another
aspect, the present invention provides an apparatus for delivering a grinding
media
from a holding vessel or storage vessel to a grinding mill, the vessel holding
a
quantity of the grinding media, the grinding media being in the form of a
particulate
material, the vessel having an outlet at lower end thereof, the apparatus
comprising:
a housing positioned below the outlet of the vessel, the housing receiving
grinding
media from the vessel,
a nozzle delivering a liquid to the housing, and
a mixing chamber having an inlet for receiving liquid and grinding media, the
inlet of
the mixing chamber being spaced from an outlet of the nozzle whereby liquid
exiting
the nozzle entrains grinding media in the housing and a mixture of liquid and
grinding
media enters the inlet of the mixing chamber and is further mixed in the
mixing
chamber, the mixing chamber having an outlet through which the mixture passes
for
supply to the grinding mill.
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In one embodiment of this aspect of the present invention, the apparatus
comprises:
- a housing positioned below the outlet of the vessel, the housing receiving
grinding
media from the. vessel,
- the housing having a first side opening and a second side opening,
- a nozzle connected to the first side opening, the nozzle delivering a liquid
to the
housing,
- a mixing chamber connected to the second side opening, the mixing chamber
having
an inlet for receiving liquid and grinding media, the inlet of the mixing
chamber being
spaced from an outlet of the nozzle whereby liquid exiting the nozzle entrains
grinding media in the housing and a mixture of liquid and grinding media
enters the
inlet of the mixing chamber and is further mixed in the mixing chamber, the
mixing
chamber having an outlet through which the mixture passes for supply to the
grinding
mill.
.'15 In a third aspect, the present invention provides a method for
delivering grinding
media to a grinding mill, the method comprising the steps of supplying
grinding
media from a vessel into a housing, the housing being provided with a nozzle
for
providing a transverse flow of liquid through the housing such that the
transverse flow
of liquid entrains grinding media in the housing and forms a mixture of liquid
and
20' grinding media, the mixture of liquid and grinding media entering a
mixing chamber
and passing through the mixing chamber into a diffuser, causing the mixture of
liquid
and grinding media to pass through a flow path having a divergent portion in
the
diffuser and subsequently delivering the mixture of liquid and grinding media
to a
grinding mill.
In a fourth aspect, the present invention provides a method for delivering
grinding
media to a grinding mill, the method comprising the steps of supplying
grinding
media from a vessel into a housing, the housing being provided with a nozzle
for
providing a transverse flow of liquid through the housing such that the
transverse flow
of liquid entrains grinding media in the housing and forms a mixture of liquid
and
grinding media, the mixture of liquid and grinding media entering a mixing
chamber.
and passing through the mixing and subsequently delivering the mixture of
liquid and
grinding media to a grinding mill.
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In one embodiment of the Method of the present invention, the step of
delivering the
mixture of liquid and grinding media to a grinding mill comprises passing the
mixture
of liquid and = grinding media along an upwardly extending conduit or pipe.
The
upwardly extending conduit or pipe may be connected to the diffuser. It has
been
found that settling of the grinding media is minimised or avoided into the
upwardly
extending conduit or pipe.
The upwardly extending conduit or pipe may extend upwardly at an angle to the
vertical.
In some embodiments, the method comprises wetting the media prior to mixing
with
the liquid from the nozzle. For example, a water inlet may be provided in or
just
below the outlet to the vessel so that a small amount of water is added to the
media
flowing through the outlet or exiting the outlet to thereby wet the media. The
wetted
media then comes into contact with the delivery liquid. It has been
surprisingly found
that this can increase the rate of delivery of the media. The water inlet may
alternatively be provided in an upper part of the housing.
In some embodiments of the method of the present invention, the method further
comprises providing a valve to control the flow of grinding media from the
vessel to
the housing, the valve being normally operated in a partly open condition to
allow a
trickle of grinding media to flow therethrough, the valve being opened more
fully in
the event that bridging of the grinding media or a blockage in the grinding
media in
the vicinity of the valve occurs.
In the method of the present invention; a liquid (which will typically be
water) is
provided under pressure to the nozzle. This establishes a transverse flow of
liquid in
the housing. The housing is suitably arranged such that it is positioned below
the
vessel such that the grinding media drops through an outlet of the vessel into
the
housing. The grinding media that is in the housing becomes entrained by the
flow of
liquid leaving the nozzle. The liquid leaving the nozzle suitably flows in a
transverse
direction through the housing. The nozzle has an outlet that is suitably
positioned near
but spaced from an inlet of the mixing chamber. The outlet of the nozzle and
the inlet
of the mixing chamber are both suitably within an interior volume of the
housing. The
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mixture of liquid and grinding media that enters the housing flows along and
through
the housing. This assists in forming a more homogenous mixture of liquid and
grinding media. The mixture then passes into the diffuser where it moves along
a
divergent flow path. The mixture leaving the diffuser is then passed into the
grinding
5 mill.
Advantageously, in embodiments of the present invention, one or more of the
nozzle,
mixing chamber and diffuser are replaceable components. In this manner, if
those
components wear, for example due to the abrasive nature of the grinding media
being
10 transported, it is a simple matter to shut down the apparatus for a
short period of time,
remove the replaceable component that needs replacing and replace that
component
with a new or reconditioned component. Replacement of both the nozzle and the
mixing chamber may be further simplified in embodiments where the nozzle or
the
mixing chamber comprise a nozzle insert or a mixing chamber insert.
In some embodiments of the present invention, the nozzle insert is made from a
wear
resistant material. Similarly, in some embodiments of the present invention,
the
mixing chamber insert is made from a wear resistant material. Examples of
suitable
material from which the nozzle insert and the mixing chamber insert may be
made
include polyurethane, ceramic material, hardened steel or other wear resistant
materials. This list should not be considered to be limiting and the person
skilled in
the art would be able to readily identify other wear resistant materials
suitable for use.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a side elevation of an apparatus for delivering a grinding
media to a
grinding mill in accordance with an embodiment of the present invention;
Figure 2 shows a similar view of the apparatus shown in figure 1, but with
internal
details of the apparatus shown in dashed outline;
Figure 3 is an isometric view of the apparatus shown in figure 1;
=
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Figure 4 is an isometric view of a nozzle suitable for use in the apparatus
shown in
figure 1;
Figure 5 is a side elevation view of the nozzle shown in figure 4, with
internal details
shown in dashed outline;
Figure 6 is an isometric view of a mixing chamber suitable for use in the
apparatus
shown in figure 1;
Figure 7 is a side elevation view of the mixing chamber shown in figure 6,
with
internal details shown in dashed outline;
Figure 8 is an isometric view of a diffuser suitable for use in the apparatus
shown in
figure 1; and
Figure 9 is a side elevation cross sectional view of the diffuser shown in
figure 8.
DETAILED DESCRIPTION OF THE DRAWINGS
The person skilled in the art will appreciate that the drawings have been
provided for
the purposes of illustrating preferred embodiments of the present invention.
Therefore, it will be understood that the present invention should not be
considered to
be limited solely to the features as described and shown with reference to the
accompanying drawings.
Figures 1 to 3 show various views of an apparatus in accordance with an
embodiment
of the present invention. The apparatus 10 includes a housing 12. Housing 12
includes
an inlet 14. Inlet 14 is placed into alignment with an outlet of a vessel that
holds or
stores the grinding media. In order to secure the housing 12 to the outlet of
the vessel,
a flange 16 having a plurality of openings, some of which are numbered at 18
in
figure 3, is bolted.to a similar flange on the outlet of the vessel.
The housing 12 includes a lower outlet 20 that is closed by a movable closure
22.
Movable closure 22 may be hinged at hinge 24 to the housing 12. This enables
the
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closure 22 to be selectively opened and closed. The closure 22 may need to be
opened
for maintenance of the housing or for emptying a buildup of grinding media in
the
lower part of the housing 12. A flange 26 may be provided around the outlet 20
of the
housing 12 in order to enable a closure base plate 28 to be mounted to the
outlet 20.
The base plate 28 carries the hinge 24. It may also carry a U-shaped member 30
that
can receive a projecting member 32 in order to retain the closure 22 in the
closed
position. A chain 34 may be used to avoid the possibility of loss of the
projecting
member 32.
The housing 12 also includes an inspection plate 36 that is bolted to a flange
38 (see
figure 3) on the front of the housing 12. The inspection plate 36 can be
removed for
maintenance.
The housing 12 also includes a first side opening 40 and a second side opening
42.
, 15 First side opening 40 has a flange 44. Second side opening 42 has a
flange 46.
Side opening 40 is positioned at the end of a lateral extension 48 of housing
12.
Similarly, opening 42 is positioned at the end of a lateral extension 50 of
housing 12.
Lateral extensions 48, 50 may be formed by welding or otherwise joining pipes
to the
main body of housing 12.
The apparatus 10 shown in figures 1 to 3 includes a delivery water supply, a
nozzle, a
mixing chamber and a diffuser. Each of these features will now be described.
The delivery water supply 52 is positioned to the left of flange 44 in the
views shown
in figures 1 and 2. The delivery water supply 52 includes a water inlet 54.
Water inlet
54 is joined to a water supply. system (not shown). The water supply system
will
typically include a pump for providing a controllable delivery flow rate and
pressure.
A non-return valve or non-return system may be provided between the pump and
the
housing 12 to prevent the back flow of grinding media into the water supply
system or
the pump when the pump is turned off. The water inlet 54 forms an inlet to
supply
water spool 56. A flange 60 extends around inlet 54 and the spool 56 includes
a first
end that is closed by plug 62. Plug 62 is joined via plug flange 64 to spool
flange 66.
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The supply water spool 56 includes an outlet having a flange 68 extending
therearound. Flange 68 is joined to flange 70 of rodding spool 72. Rodding
spool 72
effectively provides a communication conduit between the supply water spool 56
and
the housing 12. Appropriate flanges that are shown in figures 1 to 3 but not
numbered
enable the rodding spool to be connected to the housing 12.
The apparatus 10 also includes a nozzle 80. Nozzle 80 shown in figures 4 and
5.
Nozzle 80 is designed to be inserted through the first side opening 40 of the
housing
12. Nozzle 80 includes nozzle housing 82, which will typically be made from
steel. A
nozzle insert 84, which is made from a wear resistant material, such as
polyurethane,
hardened steel or a ceramic material, is fitted inside nozzle housing 82.
Nozzle insert
84 is removable from the nozzle housing 82. This is advantageous in that the
internal
parts of the nozzle 80 are subject to wear and if the nozzle insert 84 becomes
worn, it
is a relatively simple matter to remove the nozzle 80 from the apparatus 10,
replace
the worn nozzle insert 84 with a new or reconditioned nozzle insert and then
replace
the repaired nozzle back into the apparatus 10.
The nozzle housing 82 includes a generally cylindrical portion 86 that has a
flange 88
extending at one end. A jacking ring 90 is provided adjacent to flange 88. The
flange
88 and jacking ring 90 are used to connect the nozzle 82 to the flange 44 of
the first
side opening 40 of the housing 12.
The nozzle 80 includes an inlet opening 92. Inlet opening 92 receives delivery
water
from the delivery water system. The nozzle 80 also includes a nozzle outlet
94. The
nozzle also includes a nozzle chamber 96 that has a converging portion 98 (see
figure
5). As a result of the converging portion 98, the nozzle outlet 94 has a
smaller
diameter than the nozzle in 92. In some embodiments of the present invention,
the
ratio of the nozzle outlet to the nozzle inlet' diameters may be up to about
50%. In
some embodiments, the ratio of nozzle outlet to the nozzle inlet diameters
falls within
the range of 20 to 30%. In some embodiments, the diameter of the feed inlet of
nozzle
may be about 66mm, and the outlet of the nozzle may have a diameter of between
15and 20mm, giving =a ratio of outlet to inlet of 22% to 30% in that specific
embodiment. It will be appreciated that the nozzle dimensions should not be
considered to be limited to these particular dimensions.
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The use of the nozzle 80 causes the delivery water that is supplied to the
housing to
increase in velocity as it flows through the nozzle and into the housing. This
assists in
the delivery water entraining the grinding media in the housing.
As best shown in figure 2, the nozzle 80 is positionea sucn mat me outlet 94
is
positioned quite close to the centre line 100 of housing 12.
The apparatus 10 also includes a mixing chamber 110. The mixing chamber 110 is
best shown in figures 6 and 7. The mixing chamber 110 includes a mixing
chamber
housing 112 and a mixing chamber insert 114. Mixing chamber insert 114 is a
removable insert made from a hard wearing material, such as polyurethane,
ceramic
or hardened steel. It will be appreciated that a mixture of grinding media and
water
flows through mixing chamber 110. This mixture can be quite abrasive and as a
result
the mixing chamber 110 can be subject to high wear conditions. Using a mixing
chamber insert 114 of a hard wearing material means that the life of the
mixing
chamber insert 114 is maximised. Further, when the mixing chamber insert 114
has
reached the end of its usable life, it can be removed and replaced with a new
or
reconditioned mixing chamber insert.
The mixing chamber housing 112 includes a flange 116 that may also be fitted
with a.
jacking ring 118. Flange 116 and jacking ring 118 may be used to connect the
mixing
chamber 110 to the second side opening 42 of housing 12.
The mixing chamber 110 includes a mixing chamber outlet 120 and a mixing
chamber
inlet 122. As can be seen from figure 7, the mixing chamber inlet 122 is
defined by
radiussed, outwardly divergent walls 124.
As can best be seen from figure 2, the mixing chamber inlet 122 is positioned
close to
the centre line 100 of housing 12. Therefore, as can also be seen from figure
2, the
outlet 94 of the nozzle 80 is spaced only a relatively short distance away
from the
inlet 122 of the mixing chamber 110.
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In one specific embodiment, the mixing chamber had a length of 300nun and, a
diameter of 40mm for the majority of the length of the chamber. ( the feed end
of the
mixing chamber is curved to the outer edge). The ratio of diameter to length
for the
mixing chamber of this specific embodiment is about 13%. It will be
appreciated that
5 the dimensions of the mixing chamber should not be considered to be
limited to these
specific dimensions.
In operation of the apparatus 10, grinding media drops down through inlet 14
of
housing 12. A fast flowing flow of water passes through the outlet 94 of the
nozzle 80
10 and into the inlet 122 of the mixing chamber 110. This fast flowing flow
of water
entrains grinding media and carries grinding media with the flow of water into
the
mixing chamber 110. As the flow of water and entrained grinding media flow
through
the mixing chamber 110, they become relatively homogenously mixed.
15 The apparatus 10 shown in figure 1 also includes 'a diffuser 130. The
diffuser 130 is
best shown in figures 8 and 9. The diffuser 130 includes a diffuser housing
132
having a flange 134. A jacking ring 136 may be fitted next to flange 134. The
diffuser
housing 132 will typically be made from steel.
The diffuser 130 is also fitted with a diffuser insert 138. Diffuser insert
138 may be
made from a hard wearing material, such as polyurethanes, a ceramic or
hardened
steel. It will be appreciated that a mixture of water and grinding media flows
through
the diffuser 130. This mixture is very abrasive. Therefore, manufacturing the
diffuser
insert 138 from a hard wearing material maximises the effective working life
of the
insert. When the diffuser insert 138 becomes worn, it can be removed from the
diffuser housing 132 and replaced with a new or reconditioned diffuser insert.
This
allows for simple maintenance and reconditioning of the diffuser 130.
As can be seen from figure 9, the. diffuser includes a diffuser inlet 140, a
diverging
portion 142 and a diffuser outlet 144. As the diameter, of the diffuser outlet
144 is
larger than the diameter of the diffuser inlet 140, the velocity of the flow
of water and
grinding media passing out through the diffuser outlet 144 is lower than the
velocity
of the mixture of flowing into the diffuser inlet 140. It will be understood
that the high
flow conditions at the inlet occurred because the high water flow rate leaving
the
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nozzle 80 is required in order to pick up and entrain grinding media within
the
housing 12. However, once the grinding media has been properly taken up into
and
entrained by the delivery water, the very high rates of flow may not be
required to
convey the entrained grinding media to the mill or to the pump box. Therefore,
it is
desirable to slow down that flow in order to minimise wear and abrasion in
piping
located downstream of the apparatus 10. The diffuser 130 allows this to occur.
The diffuser 130 is connected via the flange 134 to the flange 46 of the
second side
opening 42.
Figure 10 shows a schematic flow diagram of the apparatus 10 shown in figures
1 to 3
being located in a feed flow sheet for feeding grinding media to a pumpbox and
then
to a grinding mill. The apparatus 10 is mounted to a hopper or storage vessel
200 that
holds or stores the grinding media. A water pump 202 provides water to water
inlet
54. A mixture of water and grinding media exit the apparatus 10 through outlet
144.
The mixture of grinding media and conveying water passes along pipe, which
shown
schematically at 204 and into the slurry pumpbox 208. A slurry stream 210,
which
may comprise a slurry containing ore or concentrate, is mixed with the
grinding media
in the slurry punipbox 208. The mixture of grinding media and slurry exit
slurry
pumpbox 208 through outlet 212 and is transferred via slurry pump 214 into
grinding
mill 216.
In some embodiments, the pipe 204 may include a portion that is angled
upwardly
from the outlet 144 of apparatus 10. It is believed that having an upwardly
angled part
in this pipe that extends from the outlet 144 assists in avoiding settling of
the grinding
media in the pipe 204.
=
Also shown in figure 10 is water stream 220 that can be added to the hopper or
storage vessel 200. It has been found that adding water to the grinding media
into the
hopper or storage Vessel can assist in transferring grinding media via the
apparatus 10
into the slurry pump box 208. The water stream 220 may be added at any part of
the
storage hopper. For example, the water stream 220 may add water to the
grinding
media at a point just above the outlet of the hopper or storage vessel 200
into the
apparatus 10. Alternatively, the water stream 220 may be added to any other
part of
=
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the storage vessel. As a further alternative, the additional water may be
added to the
grinding media at a point just above the mixing chamber of apparatus 10.
Alternatively no water at all is added at all to any part of the hopper or
storage vessel,
or just above the mixing chamber so that the media leaving the holding vessel
or
storage vessel is either essentially dry or has essentially the same water
content as
media entering the hopper or storage vessel or has a water content lower than
the
media entering the hopper or vessel. The hopper or vessel may be provided with
dewatering apparatus, such as a screen or screens in a side or a wall or
floor, to lower
the water content of the media entering the hopper or vessel prior to
discharge of the
'media from the hopper or vessel.
Figure 11 shows a flow sheet of a slightly modified version of the flow sheet
shown in
figure 10. For convenience, features in figure 11 that are common with the
features
shown in figure 10 are denoted by the same reference numerals. The apparatus
shown
in figure 11 also includes a dewatering device 222. Dewatering device 222 may
comprise, for example, a screen. Other dewatering devices may also be used,
such as
poly-deck screens, pre-densifiers, or settling devices such as tanks allowing
the water
to pass through the tank, while the media settles in the tank, and exits via a
automated
valve or a pressure sensitive device acting due to the media load such as a
"duck bill".
The dewatering device. transfers dewatered media 224 to the slurry pump box
208.
Water 230 that is removed from the mixture of water and grinding media leaving
pipe
204 by the dewatering device may be returned as a water feed to pump 202.
Alternatively, the water stream 230 may be reused in other parts of the plant
or as
process water.
The embodiment of Figure 11 does not add water to the media leaving the
holding
vessel or storage vessel 200. Indeed, holding vessel or storage vessel 200 may
have a
screen 201 in a wall or floor portion to allow for dewatering of the media in
the
holding vessel or storage vessel 200 so that the media leaving the holding
vessel or
storage vessel 200 has a lower water content than the media entering the
hopper or
storage vessel 200. Other dewatering devices or drying apparatus may be used.
It will
also be appreciated that, in an alternative embodiment, the media being
returned to the
holding vessel or storage vessel 200 may be dewatered to a desired water
content
prior to being returned to the holding vessel or storage vessel 200.
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Example.
A test rig instructed similar to the apparatus shown in figures 1 to 3 was
used to
conduct some experimental runs to measure the transfer of grinding media from
a
hopper. The results are shown in Table 1 below. The results show that
satisfactory
transfer of grinding media can be achieved when the grinding media exiting the
holding vessel is dry. However, the results also show that by adding water
(and not a
lot) to the system just above the nozzle/mixing chamber, the transfer of media
increased 3 fold. This is assuming that the media in theholding vessel is de-
watered
but still damp (in table 1, the notation "dry" refers to grinding media that
has been
dewatered but is still damp).
Table 1
Flowrate 15mm Nozzle 20mm Nozzle
Tonnes per Hour Wet Dry Wet Dry
Run 1 19.49 8.50 22.52 7.99
Run 2 18.93 7.93 22.08 8.06
AVERAGE 19.21 8.22 22.30 8.03
The testwork has indicated the flowrate when using dry media with different
nozzles
has negligiable effect on the flowrate. However when the media is wetted the
flowrate
did increase from a 19.21tph average to a 22.30 tph average using a larger
nozzle
diameter.
Wetting of the media was achieved in having a water addition inlet on the
mixing
chamber. For the current set up this was a 2" (50 mm) water inlet.
Without wishing to be bound by theory, the improvement in the flowrate with a
wet
system compared to a dry system, is thought to be due to the water allowing
the media
to "slip" easier down into the mixing chamber, while when the system is dry,
the
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increased friction between the particles prevents free movement of the media
downwards into the mixing chamber.
This allows the invention to be used in two modes. The first in a wetted mode,
which
allows higher flowrates of media to be delivered to an empty mill after a
shutdown,
which minimizes the time required to get up to working power. The second mode
is
when the media is dry, and can be used for media addition while the mill is
operating,
when small addition rates are required for mill power control rather than
large
addition rated which can cause unsteady mill operation.
Alternatively the media is added dry to allow media to be delivered to an
empty mill
after a shutdown as well as while the mill is operating.
The scope of the claims should not be limited by the preferred embodiments set
forth
in the examples, but should be given the broadest interpretation consistent
with the
description as a whole.
