Note: Descriptions are shown in the official language in which they were submitted.
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DEWATERING TANK
Technical Field
A dewatering tank is disclosed. In particular, although not exclusively, a
dewatering
tank is disclosed for receiving water containing particulates produced from
one or more
dewatering processes, wherein the dewatering tank is configured to retain
particulates,
such as fines, in suspension.
Background
Dewatering is the removal or drainage of groundwater or surface water from
surface or
sub-surface excavation, earthworks, caissons or mine shafts. Typically, this
frequently
involves the use of submersible pumps, centrifugal pumps, positive
displacement
pumps, eductors and, less frequently, the application of vacuum to remove and
transport the water via conduits to one or more storage locations.
In sub-surface operations, there may be several dewatering pumps operating at
appropriate locations underground interconnected by a network of conduits.
Prior to
pumping the water above ground, it may be more efficient and productive for
water
from one or more dewatering operations to be collected and stored in a
dewatering
tank. The pump to transport the water to the surface can be operated
intermittently
when the dewatering tank reaches or approaches capacity, rather than on a
continuous basis.
Water produced from de-watering processes typically contains particulates of
varying
size range. Generally, it is advisable to separate larger particulates (>2-
3mm), such as
gravel from the water to protect the pump from damage prior to pumping the
water to
the surface. However, the water may still contain a considerable amount of
particulate
material including fines which may settle in the dewatering tank over time (in
between
pumping operations).
The build-up of sedimentation in the dewatering tank may occur very quickly
and it is
not unusual for the dewatering tank to fill up with sedimentation within 24
hours,
thereby reducing the capacity of the dewatering tank to store water.
Consequently, the
dewatering tank may need to be manually flushed on a daily basis, an operation
that
takes about 30-60 minutes. In some underground operations, there may be up to
20
dewatering tanks which need to be manually flushed on a daily basis.
Consequently, a
considerable amount of labour is consumed by this particular task. It would be
beneficial to reduce the frequency at which a dewatering tank needs to be
manually
flushed.
Furthermore, the build-up of sedimentation in the dewatering tank may also
result in
slug flow of fines into the pump, causing pump blockages and/or high wear of
the
pump internals.
The holding capacity of most dewatering tanks is between 3 kilolitres (kL) to
9 kL. The
magnitude of the problems discussed above appears to increase as the holding
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capacity of the dewatering tank increases.
The above references to background art do not constitute an admission that the
art
forms a part of the common general knowledge of a person of ordinary skill in
the art.
The above references are also not intended to limit the application of the
tank as
disclosed herein.
Summary of the Invention
Generally, a dewatering tank is disclosed. In particular, although not
exclusively, a
dewatering tank is disclosed for receiving water containing particulates
produced from
one or more dewatering processes, wherein the dewatering tank is configured to
retain
particulates, such as fines, in suspension. In this way, the water containing
particulates may be discharged from the dewatering tank and pumped to another
location, thereby reducing the build-up of particulate sedimentation in the
dewatering
tank and consequently reducing maintenance and down time associated with
manually
flushing particulate sedimentation from the dewatering tank.
The present invention provides in a first aspect a dewatering tank configured
to retain
fines in suspension, the tank comprising a floor portion that has a downward
inclination, the tank further comprising a sump that is located such that the
floor portion
inclines towards the sump, the tank having an inlet for admission of water
containing
the fines and an outlet that is adapted for connection with a pump to
discharge the
water containing the fines from the tank and that is located in the sump,
wherein the tank is arranged such that the water flows from the inlet to the
outlet and wherein the tank comprises a wall or cover portion that is
positioned to divert
a flow of the water in a manner such that turbulences are induced and fines
that may
otherwise settle in the sump and on the floor portion are suspended.
The sump may be partially covered by a cover portion that constricts flow of
water into
the sump and is configured such that the water containing the fines changes
direction
when flowing into the sump whereby turbulences are induced.
The outlet may be a single outlet through which in use the water with
suspended fines
flows.
The cover portion of the sump may be a baffle that is spaced apart from a wall
portion
of the tank such that a gap is formed for inflow of the water into the sump.
Alternatively,
the cover portion of the sump may be a baffle that comprises one or more
through
holes, gaps or perforations that are located at or near an edge or end-portion
of the
baffle for inflow of the water into the sump.
The dewatering tank may comprise at least one member that is shaped and
positioned
such that turbulences are induced as water flows along the floor portion that
extends in
a downward inclination. The at least one member may be a screen member
extending
between wall portions of the tank.
In one embodiment the at least one member is a substantially vertical baffle.
The at
least one substantially vertical baffle may take the form of a plate member or
a screen
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member extending between the front and rear longitudinal walls of the tank.
In one embodiment, the tank comprises a first wall portion and an opposite
second wall
portion and the sump is positioned at or near the second wall portion. The
floor portion
that has a downward inclination may extend substantially from the first wall
portion
along at least the majority of a length of the tank towards the sump.
In an alternative embodiment, the tank comprises a first wall portion and the
floor
portion that extends in a downward inclination is one of at least two floor
portions that
each extend along a portion of a length of the tank in a downward inclination.
In this
embodiment the sump is positioned between two adjacent floor portions that
incline
towards the sump with the outlet.
In some embodiments, the at least one substantially vertical baffle is spaced
above the
floor of the tank to induce turbulence in the flow of water passing thereunder
Can
underflow). Alternatively, the at least one substantially vertical baffle may
extend from
the floor and be spaced below a water line in the tank to induce turbulence in
the flow
of water passing thereover Can overflow).
In one embodiment, the tank comprises a plurality of substantially vertical
baffles
spaced relative to the floor of the tank or the water line in the tank in an
arrangement
whereby the vertical baffles direct the flow of water in alternate underflows
and
overflows.
In one embodiment, the at least one substantially vertical baffle is disposed
proximal to
the sump in the floor of the tank.
In one embodiment, the at least one substantially vertical baffle comprises an
opening
therein to define a constricted flowpath therethrough. Alternatively, or
additionally, the
at least one substantially vertical baffle may be configured to direct the
flow of water
through the constricted flowpath. For example, the at least one substantially
vertical
baffle may have a generally truncated V-shaped cross section, wherein the
opening is
provided in an apex of the truncated V-shaped cross section.
In one embodiment, the sump comprises a stepped floor portion. In an
alternative form
the sump comprises a steeply inclined floor portion.
The present invention provides in a second aspect a dewatering tank configured
to
retain fines in suspension, the tank comprising a floor portion that has a
downward
inclination, the tank further comprising a sump that is located such that the
floor portion
inclines towards the sump, the tank having an inlet for admission of water
containing
the fines and an outlet that is adapted for connection with a pump to
discharge the
water containing the fines from the tank and that is located in the sump,
wherein the tank is arranged such that the water flows from the inlet to the
outlet and wherein sump is at least partially covered by a cover portion that
constricts
flow of water into the sump and is configured such that the water containing
the fines
changes direction when flowing into the sump whereby turbulences are induced
and
fines that may otherwise settle in the sump and on the floor portion are
suspended.
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The present invention provides in a third aspect a dewatering system
comprising:
the dewatering tank of the first or second aspect of the present invention;
and
a dewatering pump positioned at the outlet in the sump of the dewatering tank;
wherein a cover portion partially covers the sump at a position over the
outlet of
the dewatering tank such that, when the dewatering pump is not in use and the
water
is stationary, fines settle on the cover portion whereby the cover portion
reduces the
likelihood of blockage of the pump by the fines.
Description of the Figures
Notwithstanding any other forms which may fall within the scope of the
dewatering tank
as set forth in the Summary, specific embodiments will now be described, by
way of
example only, with reference to the accompanying drawings in which:
Figure 1 is a schematic representation of a perspective view of a dewatering
tank in accordance with the disclosure;
Figure 2 is a perspective view of the dewatering tank shown in Figure 1
indicating internal detail in phantom;
Figure 3 is a plan view of the dewatering tank shown in the preceding Figures;
Figure 4 is a front view of the dewatering tank shown in the preceding Figures
indicating internal detail in phantom;
Figures 5a and 5b are respective opposing side views of the dewatering tank
shown in the preceding Figures; and,
Figure 6 is a perspective view of the dewatering tank, as shown in the
preceding Figures, shown in use with a dewatering pump and gravel screen.
Detailed Description of Specific Embodiments of the Invention
An embodiment of a dewatering tank configured to hold water containing
particulates
and retain fines in suspension will now be described by way of example only.
Referring to the figures, there is shown a dewatering tank. The dewatering
tank
includes a generally rectangular-box shaped tank 10 having a front
longitudinal wall 12,
a rear longitudinal wall panel 14, a pair of opposing side walls 16a, 16b
interconnecting
the front and rear longitudinal walls 12, 14 and a floor 18 that slopes
downwardly from
opposing side wall 16a to opposing side wall 16b.
The tank 10 may be open, as shown in the Figures. Alternatively, the tank 10
may be
partially or fully closed, for example with a cover or screen as will be
described later.
The tank 10 has an inlet 20 for admission of water containing particulates and
an outlet
22 adapted for connection with a pump 100 (as shown in Figure 6) to discharge
said
water from the tank 10. Typically, the pump 100 may be a positive displacement
pump, such as a helical rotor pump, that pumps the water containing fine
particulates
from outlet 22 of the tank at a flow rate of about 10-40 litres/second (L/s).
The floor 18 may be provided with a sump 24 proximal to opposing side wall
16b. In
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the embodiment shown in the Figures, the sump 24 comprises a stepped floor
portion.
However, it will be appreciated that the sump 24 may take alternative forms.
For
example, in an alternative embodiment, the sump 24 may comprise a steeply
inclined
floor portion.
5
A horizontal baffle 26 is arranged above the sump 24 and spaced apart from the
front
and rear longitudinal walls 12, 14 of the tank 10 to define two openings 25
into which a
constricted flow of water may enter the sump 24. The horizontal baffle 26 may
take the
form of a plate member. The horizontal baffle 26 may be removable from the
tank 10
to enable access to the sump 24 for maintenance and cleaning purposes.
The arrangement of the horizontal baffle 26 above the sump 24 induces
turbulence in
the flow of water into the sump 24. Advantageously, in the event that some
settling of
fine particulates in the sump 24 occurs over time, it is thought that the
turbulent water
flow into the sump 24 will re-suspend at least some of the fine particulates
in the water.
In this way, the build-up of fine particulate sedimentation in the tank 10
will, at least in
part, be reduced.
Generally, the inlet 20 is located or defined by an opening in the tank 10
proximal to
the opposing side wall 16a of the tank 10. It will be appreciated that the
inlet 20 is
positioned proximal to opposing side wall 16a so that water admitted into the
tank 10
through the inlet 20 will flow under gravity along the downwardly inclined
floor 18
towards the outlet 22. The outlet 22 may be configured in a lower end 28 of
the
opposing side wall 16b adjacent to the sump 24.
The inlet 20 may be provided with a screen 200 (as shown in Figure 6) to
prevent
larger size particulates (<2-3 mm), such as gravel, from entering the tank 10.
A chute
for gravel having a discharge port 32 may be provided on the front
longitudinal wall
12 of the tank 10 to collect and discharge the gravel separated by the screen
200.
30 Alternatively, the chute 30 may be provided on the rear longitudinal
wall 14 of the tank
10.
The tank 10 also includes vertical baffles 34a, 34b configured to induce
turbulence in
the flow of water to the outlet 22. The vertical baffles 34a, 34b may be
positioned
and/or configured to constrain the flow of water in the tank 10.
Vertical baffle 34a may comprise a plate member 36 extending between the front
and
rear longitudinal walls 12, 14 having an upper edge 38 and a lower edge 40.
The plate
member 36 may be spaced apart from and disposed in parallel alignment with the
opposing side walls 16a, 16b.
The plate member 36 may be positioned in the tank 10 so that the lower edge 40
is
spaced above the floor 18 of the tank 10. In this orientation, the plate
member 36
defines the inlet 20 of the tank 10 as comprising the space between the
opposing side
wall 16a and the plate member 36. Furthermore, in this orientation, the plate
member
36 constrains the flow of water to pass through an opening defined by the
opposing
side panels 16a, 16b, the floor 18 and the lower edge 40 of the plate member
36,
thereby creating an `underflow' and turbulence in the water. The inventor
opines that
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creating the underflow assists in scouring sedimentation of fine particulates
from the
floor 18 and re-suspending them in the water flow.
In an alternative embodiment, the vertical baffle 34a may take the form of a
screen
member. In this particular embodiment, the screen member may advantageously
retain coarse particulates, preventing them from flowing toward the sump 24
and outlet
22 of the tank 10.
Alternatively, or additionally, the plate member 36 may be positioned in the
tank 10 so
that the upper edge 38 thereof is spaced below the water line of the tank 10
and the
lower edge 40 abuts, or is integral with, the floor 18 of the tank 10. In this
arrangement, the plate member 36 constrains the flow of water to pass through
a
limited flow path defined by the opposing side walls 16a, 16b, and the upper
edge 38
of the plate member 36, thereby creating an 'overflow' and turbulence in the
water.
In one embodiment, a plurality of plate members 36 may be spaced relative to
the floor
of the tank or the water line in the tank as described above in an arrangement
as
whereby the plate members 36 direct the flow in alternate underflows and the
overflows.
Vertical baffle 34b includes a pair of plate members 42a, 42b, plate members
42a, 42b
projecting inwardly, respectively, from the front and rear longitudinal walls
12, 14 at an
angle towards one another. Respective lower edges 44 of the plate members 42a,
42b
abut, or are integral with, the floor 18 of the tank 10. Respective upper
edges 46 of the
plate members 42a, 42b may be spaced below the water line.
Vertical baffle 34b further includes a plate member 48 interconnecting the
pair of plate
members 42a, 42b, thereby defining a truncated V-shaped cross-section (as
shown in
Figure 3). The plate member 48 is disposed in parallel alignment with the
opposing
side walls 16a, 16b. An upper edge 50 thereof is flush with the upper edges 46
of the
plate members 42a, 42b. A lower edge 52 thereof is spaced above the floor 18
of the
tank 10, thereby defining an opening 53 in the vertical baffle 34b.
In this particular form, the baffle 34b thus defines both an overflow above
the upper
edges 46, 50 of the plate members 42a, 42b, 48 and an underflow through the
opening
in the vertical baffle 34b. Furthermore, the angled orientation of plate
members 42a,
42b defines a channel for water to flow through the opening in the vertical
baffle 34b
which also reduces sedimentation of fine particles on the floor 18 proximal to
the
vertical baffle 34b.
In the embodiment shown in the Figures, the vertical baffle 34b is disposed
adjacent
the sump 24. In this particular arrangement, the overflow and underflow
created by
this particular baffle 34b assists in scouring sedimentation of fine
particulates which
may have settled on the horizontal baffle 26 and/or in the sump 24 and re-
suspending
them in the water flow.
It will be appreciated that alternative baffle designs may be used to restrain
flow within
the tank 10 and induce turbulence in the water sufficient to retain, at least
in part, fine
particulates in suspension.
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The floor 18 of the tank 10 may be further provided with one or more drain
holes 52 to
drain the tank 10 for maintenance and cleaning purposes. The one or more drain
holes 52 may be disposed in the floor 18 and/or the sump 24.
The tank 10 may also be provided with an overflow pipe 54 having an upper end
56
and a lower end 58 passing through the floor 18 of the tank 10. The overflow
pipe 54
is arranged, in use, to drain excess water from the tank 10 through the floor
18 when
the water line in the tank 10 rises above the upper end 56 of the overflow
pipe 54. In
the embodiment shown in the Figures, the overflow pipe 54 is spaced
approximately
midway along the floor 18.
The tank 10 may be supported on a plurality of leg members 60 disposed at
opposing
side walls 16a, 16b thereof. The leg members 60 may be interconnected by
reinforcing members 62 in the form of braces or struts. In this particular
embodiment,
each leg member 60 may be provided with a foot plate 64 for engaging the
ground.
The tank 10 may also be provided with a plurality of pad-eyes 66 as lifting
points to
enable the tank 10 to be lifted and transported to a desired location.
Embodiments of the dewatering tank 10 may be fabricated from metal such as
aluminium or steel, or alloys thereof, and may comprise polymeric components
such as
injection moulded plastic materials. The capacity of the dewatering tank 10
may
generally vary from 2 kilolitres (kL) to 10 kL, although it will be
appreciated that some
embodiments of the dewatering tank 10 may be configured to have a capacity
outside
of this range.
In one embodiment, the inlet 20 may be adapted for admission of water
containing
particulates from one or more conduits for transporting water produced from
dewatering processes used underground in mines or civil engineering works. The
screen 200 covering the inlet 20 separates larger particulates, such as
gravel, which
collect in the gravel chute 30 and are discharged through discharge port 32
into an
underlying bin or skip.
The screened water entering the tank 10 through inlet 20 still contains
particulates
including fine particulates (<2-3 mm). The screened water falls under gravity
onto the
inclined floor 18 of the tank 10 proximal to the opposing side wall 16a and
flows along
the downwardly inclined floor 18 towards the outlet 22 located in the opposing
side wall
16b.
The flow of water within the tank 10 is first constrained to an underflow of
water by
vertical baffle 34a and subsequently to both an underflow and an overflow of
water by
baffle 34b proximal to the sump 24 in the floor 18 of the tank 10, thereby
inducing
turbulence in the water. Any fine particulate which may have settled or begun
to settle
on the floor 18, on an upper surface of the horizontal baffle 26, or the sump
24 in the
floor of the tank 10 may be disturbed by the turbulence and re-suspended in
the water.
Additionally, the flow of water into the sump 24 is restricted by the pair of
openings 25
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defined by the horizontal baffle 26 and the front and rear longitudinal walls
12, 14. The
horizontal baffle 26 significantly changes the direction of the flow of water
from a
longitudinal flow path relative to the floor 18 to a substantially
perpendicular flow path
with respect to the front and rear longitudinal walls 12, 14 of the tank 10.
Furthermore,
the provision of the two openings 25 defined by the horizontal baffle 26 above
the
sump 24 effectively 'splits' the flow of water into the sump 24 into a pair of
opposing
streams. The two streams generally increase turbulence in the sump 24 and
provide a
scouring action to re-suspend particulate fines which may have settled in the
sump 24.
The pump 100 attached to the outlet 22 of the tank 10 may be used continuously
to
withdraw water containing fine particulates from the tank 10. Alternatively,
the pump
100 may be used intermittently, for example, only when the tank 10 has
reached, or is
approaching, capacity. Pumping water from the tank 10 will also create a flow
of water
toward the outlet 22 but the flow will be interrupted and constrained by the
vertical
baffles 34a, 34b and the horizontal baffle 26 as described above, thereby
inducing
turbulence in the flow. Therefore, any fine particulate which may have settled
or begun
to settle on the floor 18, the horizontal baffle 26 or the sump 24 may be
disturbed by
the turbulence and re-suspended in the water prior to discharge from the
outlet 22.
it will be appreciated from the above description that sedimentation of fine
particulates
in the dewatering tank 10 is likely to be reduced. Consequently, the inventor
anticipates that the frequency with which the dewatering tank 10 must be
flushed
manually to remove build-up of settled fine particles is likely to be
substantially
reduced, potentially to the extent where manual flushing could become
redundant.
Numerous variations and modifications will suggest themselves to persons
skilled in
the relevant art, in addition to those already described, without departing
from the
disclosure. All such variations and modifications are to be considered within
the scope
of the disclosure. For example, it will be appreciated that the tank may not
have a
generally rectangular shape, but may have any suitable shape, such as an oval
or
round shape. Further, the inclined floor portion of the tank may be one of two
inclined
floor portions and the outlet may for example be positioned between the two
inclined
floor portions.
In the claims which follow, and in the preceding description, except where the
context
requires otherwise due to express language or necessary implication, the word
"comprise" and variations such as "comprises" or "comprising" are used in an
inclusive
sense, i.e. to specify the presence of the stated features but not to preclude
the
presence or addition of further features in various embodiments of the
apparatus and
method as disclosed herein.
