Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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IN-CHANNEL SCREENING WITH A DRUM SCREEN
SPECIFICATION
Background of the Invention
This invention concerns screening of objects from a water
flow using a drum screen, and more particularly is concerned
with an efficient flow pattern and arrangement of components
in a drum screen system. The invention applies to wastewater
treatment plants and other situations as well.
There are a number of situations in which a flow of
water, especially water containing impurities, must be
screened to remove relatively large particles or items prior
to further steps. For example, in a wastewater treatment
plant the first process applied to incoming wastewater
typically involves screening. Refractory items, including
plastics, and paper and other materials larger than the screen
opening size are separated out since these materials typically
cannot be digested. A typical range of screen size for
wastewater plants is 0.5 mm to 10 mm. Screen types have
included belt screens, spiral screens and drum screens, all of
which include some means for removing the screened out items.
Drum screens in such applications are typically large,
with diameters of 15 feet or 18 feet or even larger, such as
36 feet or greater. Large wastewater treatment plants, e.g.
handling 150 million gallons per day, have employed drum
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screens of 36 feet diameter or greater. Many smaller
have screened using drum screens in the range of about 14 feet
to 26 feet diameter.
These typical drum screen systems the drums, which
receive water from the side, have been positioned with the
rotation axis parallel to the direction of flow in the
channel. Thus, water enters the drum on a direct path axially
into the drum, typically flowing into the lower half of the
drum, flows through the screen and then continues in the same
flow direction. Debris is trapped on the screen and removed
out one side of the drum.
Such drum screen systems require special water flow
channels, wide enough to contain the diameter of the drum. In
many cases of existing plants that might advantageously be
retrofitted with drum screens to replace another type of
screen, the channels simply are not wide enough to accept
drums of a large enough size to handle the flow. Even in a
newly constructed plant or screening subsystem, considerable
space is required for drum screens of adequate size, with the
typical axial inflow pattern conventionally used. A more
efficient drum screen system is needed.
Patent No. 5,407,563 describes screening panel
constructions for use in band screens and drum screens.
Figure 3 of that patent shows a schematic indication of a
double-entry drum screen, the drum being of T-frame
construction. The subject matter of the patent is the
particular screen panel construction, and little description
is given for Figure 3, but the drawing has some relevance to
the present invention.
Summary of the Invention
The invention is a new and more efficient flow
arrangement that allows a drum screen to be more easily
retrofitted into existing channels and requires less space in
new construction. The invention places a reduced width drum
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screen in an orientation such that the shaft of the dr
perpendicular to the flow of the water. The drum diameter is
approximately twice the depth of the channel with the drum
shaft attached at deck level. The width of the drum may be
approximately half the width of the channel in which the drum
is placed (or about 45% to 55% of the channel width). The
water flow will travel down the channel toward the drum where
a diverter plate or "S" plate will direct water around and
into the drum from the side. The plate, or a channel barrier
connected to the plate, may also have a simple automatic
bypass gate or bypass weir to let excess flow bypass the
screen in case of screen blinding. This will keep the channel
from overflowing.
In smaller drum screens it is difficult to completely
remove the screening from the screening panels because of the
short time the panels are in the spray wash system. To
overcome this, the invention employs a high pressure, multi-
nozzle water spray system to remove the drum screenings into
the removal trough.
Drum screens of the invention are preferably less than
ten feet in diameter, and may be five feet, six feet, eight
feet, etc. Such a drum screen is applicable particularly to
wastewater plants of smaller capacity, e.g. under 10 million
gallons per day (mgd), more preferably about 4 to 6 mgd.
However, the efficient arrangement of the drum screen in the
channel can also apply to larger plants with larger-diameter
drum screens.
The invention enables a drum screen to be installed
efficiently in a channel for new construction, and also for
retrofitting an existing channel in the plant, where a screen
is to be replaced. The installation requires no complex
concrete geometry. The preferred small size of the drum
screens allows them to be fully fabricated before shipping,
rather than requiring assembly and welding in the field, which
is typical of normal, much larger drum screens.
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The drum screens of the invention are simple, wit
two moving parts, bearings and pinion gear. A drum
installation of the invention can be placed in a pumped flow
system as well as other gravity flow channels. No submerged
maintenance is required. The drum screen can produce a
capture ratio of over 90%. The installation may include an
automatic bypass or overflow gate.
The drum screen system of the invention is economical,
simple in construction with few moving parts, adaptable to
almost any existing channel, and can be an ideal screening
solution for many applications requiring screening.
These and other objects, advantages and features of the
invention will be apparent from the following description of a
preferred embodiment, considered along with the accompanying
drawings.
Description of the Drawings
Figure 1 is a perspective view showing one example of
installation of a single entry drum screen system in
accordance with the invention.
Figure 1A is a perspective view showing another example
of the single entry drum screen arrangement of the invention.
Figure 2 is another perspective view, showing the Figure
1A installation at its outlet end.
Figure 3 is a plan view of the same installation.
Figure 4 is a sectional view as seen along the line 4-4
in Figure 3.
Figure 5 is a detail view in section, with an enlargement
of the region identified as 5 in Figure 4.
Description of Preferred Embodiments
In Figure 1 a drum screen installation of the invention
is shown at 10. In this example the system is shown mounted
on and elevated above a concrete floor 12, for connection to a
flow of water, e.g. wastewater input to a treatment plant,
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from what would be the left end of the drawing in Figi.
The drum screen is shown at 14, being a relatively small
drum screen no greater than about ten feet in diameter. The
diameter may be about six feet. Panels of the drum screen are
shown at 16, and these can have opening size in the range of
about 0.5 mm to 10 mm, with 0.5 mm to about 2 mm typically
used in polishing steps. The drum is supported on a
rotational shaft 18, which is supported on bearings 20, one at
each side. The direction of revolution of the drum in this
particular installation is in the clockwise direction as
viewed in this drawing, i.e. as shown by the directional arrow
22. The bottom of the drum screen thus moves against the
direction of general flow through the installation. In this
pumped-inflow system (as opposed to a concrete channel), an
outflow fitting downstream of the drum screen is shown at 24,
for connection to a pipe, and with an inlet fitting at the
inlet end, not seen in Figure 1.
This is a single entry drum screen, the drum being open
at the side opposite the gearing shown at 25 on the near side
of the drawing. Influent flow is Indicated at 26, into a
channel 28 that feeds the water into the far side of the drum
screen 14. Typically water level entering the drum screen is
just below the rotation shaft 18. The outlet 24 could be at a
different position, such as in line with the drum screen, if
desired. Also the inlet flow then could be in line with the
drum screen but diverted left just upstream of the drum to
facilitate drum entry.
The single-entry drum screen, as is typical, has all
structural drum support at the near side as viewed in Figure
1, without spokes or other radial obstructions at the opposite
side. This allows intrusion of a debris catcher or discharge
hopper from the far side into the drum interior, not seen in
Figure 1. The hopper feeds the debris to a wash water trough
34 which carries the debris away. Spray equipment 40 drives
debris off the drum and into the hopper.
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The drum 14 is a cup drum, with a series of lifti
elevators (not shown in Figure 1) on the inner side of the
screen to help move debris up toward the discharge hopper.
The water and debris enter pushing generally in the direction
of flow. Much of the debris is caught near the bottom, and
the debris rotates in the clockwise direction as seen in
Figure 1, up to a position near the top where it is sprayed
from outside the screen with pressurized wash water at 40,
preferably with high-velocity nozzles, to release it into the
debris hopper.
The arrangement according to the invention shown in
Figures 1 through 5 provides a compact assembly especially
since the drum screen 14 is essentially parallel to the water
or wastewater flow, rotatable on an axis that is perpendicular
to that flow. Prior drum screen installations have usually
had the rotational axis parallel to flow, so that influent
liquid travels axially into one side of the drum in a single-
entry system. Typically these drums are very large, thus
requiring a custom-built system of liquid channels that will
accommodate that large diameter. In a system of the invention
the drum screen preferably is ten feet or less in diameter,
with a maximum width to diameter ratio usually about 5:8, more
typically about 1:2. As seen in these drawings, the total
channel width can be quite narrow, requiring a parallel flow
offset to the side of the drum screen's width, with flow then
directed into an open side of the single-entry drum.
Figures lA through 5 show a single entry drum screen
installation 42, with a drum screen 44 positioned in a channel
46, typically a concrete channel. This can be a retrofit in a
channel which had been equipped with a different type of
screening. The channel 46 is defined by concrete walls 48 and
floor 50.
In this case the direction of rotation of the drum screen
44 is different from that of Figure 1, with the drum screen's
bottom moving in the general direction of water flow through
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the channel. This is preferable in a straight channel
the debris being carried toward the outlet of the flow. The
drum screen is positioned at one side of the channel,
supported on a shaft 18 via bearings 20 as described above.
The remaining channel width receives the full water flow.
In Figure lA a debris hopper can be partially seen at 52,
at or near the highest point of drum travel, and spray
equipment is shown at 40, outside the drum and positioned to
dislodge debris down into the hopper. A wash water trough is
shown at 34, as above.
Water flowing into the inlet end of the installation,
indicated by the arrow 54, is diverted to the right side of
the channel by a diverter plate 56 (which can be referred to
as an "S" plate due to its shape). Preferably this angled
plate is connected to or integral with a seal plate 58 that
seals against the side of the drum screen 44 as it rotates.
The plate will also guide heavy debris into the drum from the
channel floor.
A large essentially semi-circular or open U-shaped
opening 60 is defined by the seal plate 58 so that the water
is diverted into the open side of the drum screen. A barrier
is provided at 62, connected to or sealed against the seal
plate 58 at right angles, to prevent water from bypassing the
drum screen. Figures 2 to 5 show these features from
different view points. The barrier 62 can act as a safety
overflow weir.
A drum drive gear is shown at 64. A motor and gearing in
driving engagement with the drum gear 64 are shown at 66 in
Figure 2. Support structure is shown at 68 in Figures 1A, 2
and 3, to support the debris trough 52, spray equipment 40,
wash water trough 34 and water deflecting side plates 70 which
can be on the concrete walls 48. The side plates 70, which
can be hanging sheets of Neoprene, deflect and contain water
from the spray nozzles.
In the plan view of Figure 3, the flow of water through
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the installation is clearly depicted. The water enter
alignment with the channel, as shown at the arrow 54, and is
shifted to the right side of the channel 46 by the flow
diverter plate 56. The water enters the side of the drum
screen 44, thus being shifted back to the left side of the
channel 46. The barrier 62 closes the right side of the
channel at or near the downstream end of the drum screen as
shown, being connected to the drum seal plate 58. At the
outlet end of the installation, the flow exiting the drum
screen again fills the width of the channel 46 as indicated.
Figures 4 and 5 show further details of the invention.
The sectional view of Figure 4 is taken through the rotation
shaft 18, looking toward the inlet end of the system. The
debris hopper 52 is visible in Figure 4, extending into the
interior of the cup drum screen 44. The water deflecting side
plates 70 are provided on each side, with the side plate on
the left in Figure 4 open for movement of collected debris
exiting from the hopper 52. Lift plates or elevators 72 are
indicated on the interior of the drum screen, secured at
spaced positions along the screen for moving debris up the
drum to be collected in the hopper. Shown at the top of the
drum screen in the position of Figure 4 is a flexible,
preferably Neoprene wiper 73 that engages the hopper 52 once
per revolution. The wiper 73 contacts the top edge of the
hopper, deflects and wipes debris such as fabric items off the
hopper lip.
The spray equipment is shown at 40, above the hopper 52,
with high pressure, high velocity nozzles to reliably dislodge
debris off the screen and into the hopper. The high velocity,
multi-nozzle spray can compensate for the relatively small
diameter of the drum, which would otherwise make debris
removal difficult. In a preferred embodiment the nozzle
pressure is about 45 to 90 psi, more preferably about 60 psi.
The sealing around the drum screen inlet opening 60 (see
Figure 1A), via the seal plate 58, is an important feature of
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the invention. Figure 4 shows a contact seal 74 secur
the rotating drum screen around a full circumference,
deflected essentially 90 via pressure against the seal plate,
to maintain a water seal. This is better seen in the enlarged
detail of Figure 5. The full-circumference seal 74, which can
be of an elastomeric material such as Neoprene, is retained to
the drum screen by fasteners such as bolts 76 passing through
a plate 78 that extends around the circumference of the drum.
The seal 74, which may be planar in its undeflected state, has
a deflected arm 80 that bears against and slides along the
seal plate 58 as shown. Since the seal 74 is allowed to
partially return toward the undeflected state as it moves
above the seal plate 58, the seal plate can have, as seen in
Figure 1A, an angled guide 82 fixed to the seal plate to
transition the seal back into its deflected position as it
descends to again engage in a deflected configuration the seal
plate. Note that in Figure 5 the sectioned portion of the
seal plate 58 is at the bottom center of the drum, whereas
above that sectioned region is the opening for flow into the
drum. And thus, the edge of the seal plate 58 defining the
opening is seen above the sectioned region.
The above described preferred embodiments are intended to
illustrate the principles of the invention, but not to limit
its scope. Other embodiments and variations to these
preferred embodiments will be apparent to those skilled in the
art and may be made without departing from the spirit and
scope of the invention as defined in the following claims.
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