Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02452594 2003-12-08
TITLE OF THE INVENTION
Method and Apparatus for stabilizing and supplying feed to multiple froth
flotation
vessels that use feed slurry aeration as the primary means of bubble to
particle
collection.
FIELD OF THE INVENTION
This invention relates to both a method and apparatus for controlling and
stabilizing
the feed slurry consisting of minerals and water to a froth flotation vessel
that uses
feed slurry aeration as it's primary means of bubble to particle collection.
In
particular the invention relates to a new and useful method for:
1 ) controlling feed surges to multiple flotation vessels that use Feed Slurry
Aeration for primary particle-bubble contact and formation of bubble particle
aggregates,
2) providing a steady feed to the flotation vessel and its air/slurry
contacting
chamber,
3) facilitating easy and streamlined engineering layout/arrangement of the
Feed
Slurry Aeration flotation vessels.
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BACKGROUND OF THE INVENTION
In the mining and mineral processing industries froth flotation has long been
used
as a means to separate or concentrate valuable or desirable minerals from
waste
materials or gangue. In flotation, finely ground particles of an ore are
typically
added to water to produce a slurry that is then treated with a reagent to make
the
surface of one or more mineral components sufficiently hydrophobic such that
the
mineral surface will preferentially adhere to an air bubble rather than remain
wetted. The remainder of the ore is preferably made or kept sufficiently
hydrophilic
to enable the hydrophobic and hydrophilic components to be separated from each
other when placed in an aerated volume of water. That is, when immersed in
water
and subjected to an injected stream of air, small bubbles attache to the
hydrophobic
mineral components causing them to float to the surface where they can be
collected and removed for further processing. The remaining hydrophilic
components tend to settle at the bottom of the volume of water and can be
extracted
therefrom using a variety of mechanical methods. To aid in the separation of
the
mineral components a further chemical may be added to produce a controllable
froth. Depending upon the nature of the minerals contained within an oxe, the
component sought to be concentrated may be the hydrophobic component that is
separated with the froth or, in other cases, the desired component may be
hydrophilic and may remain immersed in the water.
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For separation to be achieved in a flotation system, air bubbles must come
into
contact with hydrophobic particles prior to or within the flotation cell or
the phase
separation vessel. The invention described within this document is designed to
assist the operation of a flotation vessel that uses a pipe, or similar type
chamber, as
the mechanism where the bubbles come into contact with the slurry prior to
being
released into the flotation tank or separation vessel. These type of flotation
machines are often referred to as using Feed Slurry Aeration flotation as the
means
for bubble-particle contact and collection, as opposed to using an agitating
mechanism within the flotation cell to generate the bubble-particle contact.
One
particular Feed Slurry Aeration Machine developed by MinnovEX is comprised of
the steps of delivering a pressurized stream of feed slurry and a pressurized
stream
of air to a pipe or chamber external or internal to the separation vessel to
provide an
environment where the slurry and air come into contact to create the bubble-
particle
contact, said feed slurry including a mixture of oil or hydrophobic
minerals/materials and water; causing said feed slurry and said stream of
pressurized air to intermix within the chamber or contactor to allow for the
attachment of air bubbles to said particles of oil or hydrophobic
minerals/materials
forming bubble aggregates; and, discharging the contents of said chamber or
contactor into a separation vessel where said particle-bubble aggregates form
a froth
for removal as a concentrate.
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S Now the froth flotation machines that use Feed Slurry Aeration as the
primary
method to form the particle-bubble aggregates are operationally sensitive to
unsteady feed rates and sudden surges in feed rates, a trait that can cause
these
flotation machines to under perform with respect to the quality and quantity
of the
product they produce. Also, in a processing plant or facility that separates
minerals
from ground up rock, the feed slurry stream to the flotation process is rarely
steady.
This new invention solves the majority of the inefficiencies of Feed Slurry
Aeration
flotation machines that are due to feed surges or unsteady feed.
The invention is a continuous or series of continuous sumps (continuous being
more
1 S than one sump combined into one) that has particular features that allow
it to
stabilize feed, control feed surges and enhance/simplify layoutlarrangement of
the
flotation vessels. A sump, as defined in the mining industry, is generally
identified
as a square, rectangular or round vessel that receives feed slurry or
discharge
(tailings) slurry from single or multiple unit operations such as a flotation
2Q machine(s). The sump provides volume or capacity, typically about 45
seconds of
residence time which is the time a slurry resides in the sump, and this slurry
is
discharged from the sump via a pumps) which send the slurry to another unit
operation.
This invention (new form of sump) is totally unique in a number of ways,
namely:
25 1 ) The sump is a continuous or series of continuous sump segments used to
feed
the Feed Slurry Aeration flotation machines and accept the flotation cell
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4 '
underflow or discharge (usually referred to as tailings unless a reverse
flotation process is used at which time the underflow is referred to as
concentrate). While existing style sumps can receive multiple feed streams,
these sumps are never combined into a continuous or series of continuous
sumps with one continuous level for each continuous sump fox controlling
slurry flow that feeds flotation vessels.
2) The sump has partitions and baffles which control circulating streams, sump
level and movement of coarse particles at the bottom of the sump,
3) The residence time in each sump section (generally about 10 seconds or
less)
is typically much lower than a stand alone sump which normally has 30 to 45
seconds,
4) There is freeboard or a continuous length of extra capacity at the top of
the
continuous, or series of continuous, sumps connected together by this
freeboard, which is sized to allow any slurry surge feeding the flotation
circuit
to pass through the top of the continuous or series of continuous sumps
without significantly disturbing the feed to the Feed Slurry Aeration
flotation
vessel and contacting chamber.
5) The sump internal baffling is located to allow the underflow from the
flotation
vessel (inlet} and the pump suction (outlet) from the same segment of the
sump, to be located anywhere within that sump segment as long as the baffle
remains between the inlet and outlet to limit short-circuiting of material to
a
calculated amount. This facilitates and optimizes flotation vessel layout. The
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sump segment partitions can be adjusted to make each segment larger or
smaller to further facilitate and optimize flotation vessel layout.
6) The partitions do not continue the whole height of the sump. There is an
open
area at the bottom of the partition to allow part of the slurry to flow along
the
sump bottom from one sump segment to another. This prevents sanding by
coarse particles and minimizes the height and cross sectional area of the
freeboard required at the top of the sump to handle surging. The open area of
the bottom of the partition is designed to maintain the appropriate level in
the
sump at low feed flows to the sump while still preventing sanding and
minimizing freeboard cross sectional area. The top of the segment partitions
in conjunction with a control valve at the bottom of the last sump segment
control the level in the sump during the times when slurry surging is not
occurring. By maintaining a constant level during times of no surging, there
is
a constant head of pressure on the pump inlet and therefore a constant/steady
feed flow from the pump to the froth flotation machine.
7) During times of feed slurry surging, the freeboard allows the surge to flow
down the length of the top of the sump and pass through to waste (tailings).
The only minor change the flotation vessel would see in the feed rate would
be a slight increase in feed rate for a short period of time while the surge
passes over the top of the sump. The slight increase in feed rate would be due
to the slight increase in head pressure on the pump inlet due to the height of
the surge.
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Each segment of the sump will take the discharge from one flotation vessel
through
the sump segment inlet, and provide feed to the next flotation vessel
downstream
through the sump segment outlet feeding a pump. The feed flow to each Feed
Slurry Aeration Cell will be set at approximately the maximum flow that the
plant is
expected to receive. When feed flow is less than the maximum (normal), a
portion
of the tailings (underflow) from a flotation cell will make up the required
pumping
slurry flow. The baffle for each sump segment will minimize short circuiting
of
underflow slurry to the new feed or upstream side of the baffle, to the amount
necessary to allow the pump to operate at full flow.
Since the Feed Slurry Aeration Cells are fed by fixed speed pumps running off
a
constant feed head, the flow rate to each cell will be virtually constant.
Variable
speed pumps can be used but are not required. When feed rate changes, the
recycle
quantity changes. This means that the flotation cells will be operated with an
extremely steady feed rate, even when flotation feed (cyclone overflow) varies
dramatically. When a large feed surge hits the flotation circuit the surge
will be
carried out of the circuit via the sump; the feed slurry aeration cells will
continue to
operate as normal.
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BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, and to show more clearly
how it
may be carried into effect, reference will now be made, by way of example, to
the
accompanying drawings which show the preferred embodiments of the present
invention in which:
Figure 1 is a schematic top view, side sectional view and end view of an
apparatus
for controlling feed flow to multiple Feed Slurry Aeration vessels
(controlling 5
vessels in this example although the invention can be applied to 1 or more
cells)
according to a preferred embodiment of the present invention;
Figure 2 consists of a front view, side view and end view describing how the
five
segment version of a sump in Figure 1 could be connected to five Feed Slurry
Aeration froth flotation vessels.
Figure 3 consists of a top view and side view of two continuous sumps
connected
together on different levels while still maintaining the ability to transport
a feed
slurry surge across the top of the sump segments and move slurry flow and
coarse
material along the bottom,
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DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention may be embodied in a number of different forms. However,
the specification and drawings that follow describe and disclose only some of
the
specific forms of the invention and are not intended to limit the scope of the
invention as defined in the claims section. It is important to note that the
sump
length, width and height will change to accept the flow rates, and number of
flotation cells that the sump will be feeding and receiving underflow from. In
addition, the baffles and segment partitions can also be located to facilitate
layout or
arrangement of the flotation vessels. However, the baffles must always be
located
between the new feed inlet or pipe and the tailings or underflow pipe.
The sump can also consist of a series of circular vessels connected through
overflow sluices or transport launders, and through a pipes) or a rectangular
transport box near the bottom of one segment to the bottom of the end of
another
segment in order to move coarse material and some of the flow (same as per a
rectangular sump). The series of continuous segments can be on one level or on
several levels. If the sump consists of circular vessels on the same level
than the
level will be set by a weir on the last circular segment plus a control valve
at the
bottom outlet of the last circular segment. The overflow launder will still
provide
the freeboard to carry the feed surge along the top of the continuous or
series of
continuous sumps. If a series of continuous sumps are positioned at different
levels
than there would be one sump level for each continuous sump but the transport
launder and bottom transport pipe or box are still required for transporting
the feed
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surges along the top and a share of the slurry flow through the bottom end of
one
segment to anotb:er.
The single sump in Figure 1 is divided into five segments, each feeding one
pump.
The tailings flow from a Feed Slurry Aeration Cell will flow back to the
segment of
the sump from which it is being fed (on the side of a divider furthest from
the pump
suction). The sump has an overflow weir at the discharge, thus maintaining a
constant slurry head throughout the sump. There is a wall/partition between
each of
the five sump segments, and each segment has an internal baffle or divider (to
separate new feed from tailings recycle slurry). As with the baffles, there is
an open
1 S space at the bottom of each segment partition or wall to allow some slurry
to flow
underneath the partition; approximately 50-70% of the slurry would flow over
the
top of the wall and 30-SO % below the wall.
An example of a start-up and shut down procedure for the version of the sump
shown in Figure 1 is as follows:
Startup and Shutdown Procedures
A. Start-up procedure
- Switch all level controls to auto.
- Open all air valves - switch on control
- With exit knife gate on sump No 5 closed, fill sump with water on auto (uses
level
control on sump 1 linked to water addition)
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- Ensure feed flow from grinding section is sufFcient (>0.2m3/s?) on flow
indicator
- Start No. 1 cell feed pump on auto (i.e. level in sump is >50% and feed flow
sufficient)
- Start No. 2 cell feed pump on auto when No.l cell is <O.Sm from top.
- Start No. 3 cell feed pump on auto when No.2 cell is <O.Sm from top.
- Start No. 4 cell feed pump on auto when No.3 cell is <O.Sm from top
- Start No. 5 cell feed pump on auto when No.4 cell is <O.Sm from top
- Open exit knife gate valve on auto when No.S cell is <O.Sm from top.
B. Shut-down procedure
- Stop feed flow from grinding section
- No. l cell feed pump stops on auto
- No. l cell drains to >Sm from top and No. 2 cell feed pump stops on auto
- No.2 cell drains to >Sm from top and No. 3 cell feed pump stops on auto
No.3 cell drains to >Sm from top and No. 4 cell feed pump stops on auto
- No.4 cell drains to >Sm from top and No. 5 cell feed pump stops on auto
No. 5 cell drains to >Sm from top and exit knife gate valve closes on auto
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