Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention relates to fluid distributors, and -
more particularly to distributors that provide uniform
distribution of either a liquid or a gas throughout a bed of
granular media.
Uniform distribution of fluid in beds of grannular
media is important in many fluid treating systems. For example,
in filters where a liquid being treated flows down through a
bed o~ filter media, such as sand, the bed is usually supported
by a filter bottom that collects the filtered liquid and also
distributes a backwashing liquid that is forced up through the
bed when cleaning is necessary. Uhiformity~ of distribution
of this backwash liquid is extremely important. Nonuniform
distribution can leave parts of the bed contaminated after
backwashing and can disrupt the bed, which reduces the life
of the filter.
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In some filters, a gas such as air is forced through
the bed prior to conventional liquid backwashing, The air
bubbles up through the filter and provides a very thorough
agitation of the media, dislodging acc~ted dirt and/or
gelatinous floc which then can be removed easily by liquid
backwashing. This type of agitation is particularly attractive
for cleaning tertiary filters, in which heavy, sticky deposits
are formed in the media.
With air backwashing, uniform distribution of-both
air and water is important. In addition, in air backwashing it
is desirable to minimize expansion of the air as it passes from
the filter bottom into the bed. If the air expands significantly
at this point, it can disrupt the gravel support layers
frequently used beneath beds of sand filter media. As a result,
many filters that utilize air cleaning either deposit the sand
directly on top ~f the filter bottom or place the air
distri~ution system above the gravel support layer. If the
sand is placed directly on the filter bottom, the passages or
orifices leading from the bottom into the bed must be extremely
small to keep sand out of the filter bottom. This situation
frequently leads to plugging of the underdrain. On the other
hand, placing an air distribution system above the gravel
support layer requires two separate systems and increases the
cost of the installation.
One prior art system that provides extremely uniform
distribution of a liquid backwashing medium is disclosed in
U.S. Patent 3,110,667 to Mark L. Stuppy. This system utilizes
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filter bottom blocks having upper and lower lateral conduits
extending from block to block across the filter. The lower
or primary lateral conduits are connected to a flume, through
which the backwash liquid is supplied. Ports connect the lower
laterals to the upper or sécondary laterals, and additional
ports connect the secondary laterals to the filter bed. Thus~
the backwashing liquid passes from the flume along the lower
or primary laterals, into the secondary laterals, and from there
into the filter bed,
Since the upper or secondary laterals extend from
block to block along the rows, the backwashing liquid can flow
along them to compensate for any inequalities in the flow from
the ~rimary to the secondary laterals. If the primaries are
supplied equal amounts of water, this dual lateral system
provides extremely unifoxm distribution of the backwash li~uld
across the entire filter bottom. However~ if there are
variations in the amount of water supplied to individual
primaries, as might occur due to roughness~ construction
tolerances or the like or if a prima~y was partially blocked,
2Q the flow from the secondaries to the bed will vary in a similar
manner. Also, the system has no provision for air backwashing,
which would ~e desirable in many installations.
SUMMARY OF T~E IN~'ENTION
An object of this invention is to provide a
distributor that distributes either a liquid or a gas uniformly
throughout a bed of granular media,
The invention uses a distributor which, like the
system disclosed in the Stuppy patent, is divided into primary
and secondary lateral conduits that extend parallel to each
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other. However, in this invention the secondary and primary
conduits are placed side by side and separated from each other
by inclined walls. Gas metering orifices at an intermediate
level in these inclined walls control the flow of gas from the
primary to the secondary laterals, and liquid metering orifices,
positioned beneath and separated from the gas metering orifice~
in the inclined walls, control the flow of liquid from the
primary to the secondary laterals. Thus, this system provides
the compensatory liquid flow in the secondaries provided by the
system shown in the Stuppy patent and also provides means for
distributing gas uniformly.
Another object of this invention is to provide a
distributor that introduces a gas into a bed of granular media
with minimal expansion of the gas as it enters the bed. This is
~accomplished by making the total cross-sectional area of the gas
metering orifices in the above-mentioned inclined walls
substantially smaller than the total cross-sectional area of the
dispersion orifices that connect the secondary lateral conduits
to the bed. Thus, most of the expansion of the air occurs
within the distributor as it passes from the primary to the
secondary laterals, where it cannot disrupt the bed. The gas
forms a low pressure blanket at the top of the secondary conduits,
and passes up through the dispersion orifices into the bed with
minimal expansion. As a result, gravel support layers can be
placed on filter bottoms using this invention without being
disrupted.
Yet another object of this invention is to provide a
distributor that compensates for variations in the amount of
liquids supplied to the primary conduits of a dual lateral system, This
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is accomplished by connecting at least some of the secondary
conduits to at least two primary conduits. Thus, backwashing
liquid can flow from one primary conduit across a secondary
conduit to another primary to compensate for variation in the
amount of fluid supplied to or flowing along the primaries.
In one particular aspect the present invention
provides in a system for distributing a liquid uniformly through-
out a bed of granular media, including: a distributor positioned
beneath and supporting said media, said distributor being divided
into primary horizontal conduits and secondary horizontal conduits
that extend parallel to said primary horizontal conduits and
containing liquid metering orifices that connect said primary
conduits to said secondary conduits and dispersion orifices that
connect said secondary conduits to said bed of granular media;
a flume extending transverse to said primary conduits and
connected to each of said primary conduits; and means for
supplying a liquid to said flume, whereby said liquid flows from
- said flume to said primary conduits, through said liquid metering
orlfices into said secondary conduits, and through said
dispersion orifices into said bed; the improvement comprising:
a plurality of inclined walls separating said primary conduits
from said secondary conduits, whereby said secondary conduits
are positioned beside said primary conduits; gas metering orifices
located at an intermediate level in said inclined walls; said
liquid metering orifices being positioned beneath and separated
from said gas metering orifices in said inclined walls; and
means for supplying a gas to said primary conduits, whereby said
gas passes through said gas metering orifices into said secondary
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conduits and through said dispersion orifices into said bed.
-~ Other ob;ects and advantages of this invention will be
apparent from the following detailed description.
DRAWINGS:
Figure 1 is a partially cut away plan view of a filter
embodying this invention.
Figure 2 is a cross-sectional elevation view along lines
2-2 of Pigure 1.
Figure 3 is a fragmentary cross-sectional elevation view
along lines 3-3 of Figure 1.
- Pigures 4 and 5 are oblique pro;ections of individual
filter blocks of the type used to straddle a flume through which
' - backwash liquid and gas are introduced.
Figure 6 is a fragmentàry cross-sectional view, taken
along lines 6-6 of Figure 1, of a filter block of the type placed
end to end to form parallel adjacent rows of blocks extending
from the flume blocks to the other side of the filter.
Pigure 7 is a detailed view taken along lines 7-7 of
Figure 6.
Pigure 8 is a fragmentary plan view of another embodiment
of this invention.
Figure 9 is a cross-sectional elevation view along lines
9-9 of Figure 8.
Figure 10 is a cross-sectional elevation view, taken from
the same vantage point as Figures 2 and 9, of yet another
embodiment of this invention.
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Figure 11 is a cross-sectional elevation view along
lines 11-11 of Figure 10.
DETAILED DESCRIPTION:
Referring to Figures 1-3, the illustrated filter has
a bed of sand 11 or similar filter media and a layer of a
support media such as gravel 12 resting on a filter bottom or
distributor 14, which consists of filter blocks 15, 16, 17, 18
assembled in a plurality of parallel adjacent rows. Water or
other liquid being filtered passes down through the sand and
gravel, into the filter bottom, and from there into a flume 21,
The water leaves the flume through outlet pipe 22, which also
supplies backwashing fluid, usually water, to the filter, The
flume also contains a gas manifold 25, connected to a gas supply
line 26, that supplies air or other gas during backwashing.
As may be seen in Figures 3-6, each block is divided
by inclined planar walls 30 into primary lateral conduits 31
and secondary lateral conduits 32. The secondary conduits 32
are placed beside the primary conduits 31, instead of above
them as in the blocks shown in the Stuppy patent, so that the
blocks will accomodate a gas such as air during backwashing as
well as liquid. However, since both the primary and the
secondary lateral conduits have substantially triangular cross-
sections, with the sides of the secondary laterals being defined
by the tops 34 of the filter blocks 15, 16, 17, 18 and the
inclined interior walls 30 or the side walls 35 of the blocks,
almost all of the upper surface of the filter bottom is adjacent
to a secondary conduit, and either gas or liquid can be
dispensed evenly throughout the bed during backwashing.
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The ends of these blocks are open, and the blocks
are placed end to end in parallel adjacent rows so that each
primary and each secondary conduit extends from block to block
along the row, or from the end of the filter next to the flume
21 to the opposite end of the filter. Thus, backwashing liquid
can flow along the secondary conduits to compensate for
inequalities in flow from the primaries to the secondaries in
the same manner as in the system shown in the Stuppy patent.
Each row of blocks contains one block 15, 16 positioned
over the flume 21. These blocks contain cut-outs or ports 38,
best seen in Figures 4 and 5, through which the filtered water
can pass from the primary conduits into the flume and through
which backwashing water and air can pass from the flume into
the primary laterals. The blocks 17, 18 that are placed end
to end with the flume blocks 15, 16 and with each other to
form the parallel adjacent rows extending across the filter
do not contain the flume cut-outs or ports 38 In all other
respects these blocks are the same as the flume blocks.
The inclined walls 30 that separate the primary and
secondary lateral conduits contain gas metering orifices 41,
located at an intermediate level in the walls, and liquid
metering orifices 32 positioned below the gas metering orifices.
The gas metering orifices control the rate at which the
backwashing gas, usually air, passes from the primary to the
secondary laterals. The liquid metering orifices, and to a
lesser extent the gas metering orifices, control the flow rate
of the liquid backwashing medium,
As may be seen in Figures 1, 4 and 5, two different
widths of block are used in the filter. The blocks 15, 17 in
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the central portion of the filter are relatively wide, whereas
narrower blocks 16, 18 are used at the sides of the filter to
achieve the desired overall width. The wider blocks are used
in the central portion so that each block can contain several
primary lateral conduits. The liquid metering orifices in these
wider blocXs are arranged so that at least some of the secondary
lateral conduits are each fed from two primary conduits through
orifices 42 that are aligned with each other. This allows the
backwashing liquid to flow from one primary conduit to another
across an intervening secondary to compensate for inequalities
G~ flow to the individual primaries, such as might occur i~ one
primary were partia~,ly blocked or through roughness at the
entrance to the primaries, construction tolerances or the like.
This system can be used with liquid backwashing or
with gas and liquid backwashing. When both types are used, the
filter is usually backwashed first with air in order to
thoroughly agitate the filter media and dislodge accumulated
dirt and gelatinous floc. The filter is then backwashed with
water to remove the loosened impurities.
During gas backwashing, the air or other gas is
supplied through pipe 26, passes through gas distribution
orifices 27 in the manifold 25 that extends along flume 21, and
bubbles up through the flume ports 38 into the primary lateral
conduits 31. As is best shown in Figure 6, the air collects in
pockets at the top of the primary laterals and depresses the
liquid level in these laterals below the gas metering orifices
41. Air then passes through these orifices and forms thin
blankets 44 at the top of the secondary lateral conduits 32.
From there it passes through secondary dispersion orifices 43
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into the filter bed.
The rate at which air is supplied to the secondary
laterals is controlled by the effective air pressure in the
primary laterals 31, which in turn is controlled by the level
of the air/water interface in these laterals. The control
provided by changes in the heighth of this interface enables
this system to handle widely varying flow rates. With proper
sizing of the orifices, the illustrated system can distribute
air uniformly throughout the filter bed at rates varying from
less than 0.5 to more than 5 standard cubic feet per minute
(SCFM) per square foot of filter area. This range is
considerably larger than the range provided by most currently
available air distribution systems.
Preferably, the gas metering orifices are sized so
that the air/water interface in the primary laterals will be
depressed at least 1/2 inch below the gas orifices at the lowest
flow rate the system is designed for. This ensures that all of
the gas orifices will be exposed even if the filter blocks are
slightly out of level. Ribs 47 extending transversely across
the top of each secondary lateral, which may be seen in Figures
6 and 7, prevent air from migrating to the high point in the
secondary laterals if the blocks are installed slightly out
of level. The ribs do not extend to the bottom of the air
blankets 44 at the top of the secondary laterals; thus, air
can flow along the secondaries to compensate for inequalities
in the flow of air from the primary to the secondary laterals.
Adequate depression of the air/water interface may be
achieved at a flow rate of 0.5 SCFM per square foot of filter
surface, with the illustrated system, by uslng four 3/16 inch
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diameter gas metering orifices per square foot of filter
surface. ~ith this arrangement, the liquid metering orifices
42 are preferably placed about 3 1/2 inches below the gas metering
orifices to insure that the air/water interface is not depressed
enough to expose any of the liquid metering orifices at air
flows up to 5 SCFM per square foot of filter surface.
This arrangement of gas orifices also makes the total
cross-sectional area of these orifices much smaller than the
total cross-sectional area of the secondary dispersion orifices.
In order to handle the flow of water during liquid backwa~hing,
which may range from about 10 to about 25 GPM per square foot
of filter surface, the total cross-sectional area of the
secondary dispersion orifices is preferably about 1.2 square
inches per square foot of filter surface, which can be provided
with t~nty-four 1/4 inch diameter orifices per square foot of
surface. This is more than 10 times the total cross-sectional
area of the foregoing arrangement of gas metering orifices,
which have a total cross-sectional area of about ~.11 square
inches per square foot of filter surface. With this
combination of cross-sectional areas, most of the expansion of
the air occurs across the gas metering orifices~ and very little
occurs as the air passes through the secondary dispersion
orifices. In fact, the pressure drop across the secondary
dispersion or fices is so small that it is believed that the
flow of air through these orifices is controlled by the surface
tension OL the water in or above the orifices. This surface
tension apparently creates just enough back pressure in the
secondary laterals to form a low pressure blanket of air at
the top of these laterals, which insures uniform distribution
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of the backwash air throughout the filter,
Since there is no violent expansion of air entering
the bed, gravel support layers can be used with these blocks.
This in turn means that the secondary orifices do not have to
be small enough to keep sand from passing through the orifices
into the filter bottom, The large orifices permitted by this
invention greatly reduce the probability of plugging.
As may be seen in Figure 7, the secondary dispersion
orifices preferably open into slots 47 in the tops of the filter
blocks. These slots prevent complete plugging of a secondary
dispersion orifice by the gravel resting upon it. If the
secondary dispersion orifices were flush with the top surface
of the block, a large piece of gravel could be positioned
directly over the orifice, completely plugging it. Recessing
the orifices by means of the slot allows backwash liquid or gas
to pass under any gravel blockage.
With the foregoing combination of cross-sectional
areas, the illustrated system can supply about 5 SCFM of air
per square foot of filter surface with a total head loss from
the primary laterals to the bed of about three inches of water,
which is considerably less than the head loss required by most
other air distribution systems. Other air distribution systems
generally depend upon the pressure drop across dispersion
orifices to achieve good distribution. In the illustrated
system, flow along the secondary laterals compensates for any
inequalities in the air flow from the primaries and reduces the
total pressure drop required to achieve good distribution,
which provides an additional safeguard against explosive
expansion of air.
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While the foregoing arrangement is believed
preferable, other combinations of orifices may be used. It is
believed that most combinations wherein the total cross-
sectional area of the secondary dispersion orifices is at least
twice the total cross-sectional area of the air metering
orifices will prevent explosive expansion of the air as it
passes into the filter bed.
The gas metering orifices are positioned far enough
down on the inclined walls 30 that separate the primary and
secondary laterals so that the cross-sectional area of the
primary laterals above the orifices is large enough to handle
the desired flow rate of gas along the laterals. With the
illustrated system, the preferred location is about 4 inches
below the top of the blocks. Of course, the preferred position
of these orifices can change with the length of the lateral
conduit, the desired air flow rates, and the internal
configuration of the blocks.
Since this system prevents explosive expansion of
air, the gravel layer 12 above the filter bottom can be generally
the same as gravel support layers used with standard liquid
backwash systems; i.e., a layer of coarse gravel immediately
above the filter bottom followed by layers of progressively
smaller gravel. However, air backwashing can create eddy
currents in the sand filter media, which can erode the top
surface of the gravel. In order to prevent this erosion, it
may be desirable to place a layer of relatively large gravel
next to the sand
After air backwashing, the flow or air to gas supply
line 26 is shut off and backwash liquid is supplied through pipe
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22 This backwash liquid passes along flume 21 and up through
the flume ports 38 into the primary lateral conduits 31. The
incoming backwash water raises the air/water interface in the
primary laterals at least to the level of the gas metering
orifices, passes through both the liquid metering orifices
42 and gas metering orifices 41 into the secondary lateral
conduit, and from there passes through the secondary dispersion
orifices 43 into the filter bed. The air/water interface in
the primary laterals will usually be raised somewhat above
the gas metering orifices during liquid backwashing because
the pressure drop in the primary laterals to the filter bed
will usually be somewhat higher during liquid backwashing
Thus, the air at the top of the primary laterals is compressed
by the backwash water, This air may be left in the primary
laterals during liquid backwashing to provide a cushion that
protects against water hammer in the blocks; or i~t may be bled
out to provide additional cross-sectional area for liquid flow
along the primary laterals~ In most applications, it is
believed that it will be preferable to leave the air in the
primary laterals.
Additional flow area for liquid, or gas, can also be
provided by modifying the internal configuration of the blocks.
For example, the liquid flow area can be increased by using
"Y" shaped internal walls, so that the secondary laterals do
not extend to the bottom of the blocks The liquid or gas
flow areas can also be increased by using curved interior walls
in place of the illustrated planar walls 30~ Various other
modifications will be apparent to those skilled in the art.
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With the illustrated system, the cross-sectional
areas of the various orifices are preferably sized so that
about two-thirds of the pressure drop from the primary laterals
to the filter bed during liquid backwashing occurs as the liquid
passes from the primaries to the secondaries and about one
third takes place across the secondary dispersion orifices.
Since most of the backwash water flows through the liquid
metering orifices 42, the pressure drop ratio will depend
chiefly upon the sizing of the liquid metering orifices and
the secondary dispersion orifices. However, the gas metering
orifices will have a slight affect.
With the arrangement of gas metering orifices and
liquid metering orifices described above, the preferred ratio
of pressure drops can be achieved with two 3/4 inch diameter
liquid metering orifices per square foot of filter area, which
yields a total cross-sectional area for the liquid metering
orifices of 0.9 square inches per square foot of surface area.
This arrangement of orifices will supply backwash
water to the filter bed with considerably less head loss than
most filter bottoms. Other designs usually depend upon the head
loss across the dispersion orifices to distribute the water
throughout the bed. In the filter blocks of this in~Jention, ;
as in the system shown in the Stuppy patent, uniform distribution
of the backwash water is achieved by compensating flow of the
liquid along the secondary laterals. Thus, better distribution
of water is achieved with less pressure drop. Since the pressure
drop is less, air remaining in the secondary laterals after
air backwashing, or air that accumulates in the secondaries
through other causes, will not expand explosively as it enters
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the filter bed Thus, disru~tion of the gravel support layer
is avoided.
Figures 8 and 9 illustrates an alternative version of
this invention. In this version, the gas is supplied to the
primaries by individual pipes 57 connected to an air manifold
55 located outside the filter bed, One of the pipes 57 extends
into each primary lateral, preferably near the top of the
lateral. This facilitates bleeding at least some of the air
out of the laterals to provide additonal area for liquid flow
during liquid backwashing if this is desired. In all other
respects, this version is the same as the one illustrated in
~igures 1-7.
~ igures 10 and 11 illustrate another alternative
version. In this system, the flume 61 is positioned beside the
filter, at one end of the primary conduits, instead of beneath
the conduits as in the filters shown in Figures 1-9. The
primary laterals 31 are connected to the flume by short
triangular shaped connectors or wall-sleeves 66 that extend
from the flume 61 through the wall of the filter bed into the
primary laterals.
Filtered water is discharged from the flume, and
backwash water supplied, through an outlet pipe 62 connected to
one end of the flume 61. Air for backwashing is supplied through
line 63, also connected to one end of the flume. Line 63
contains a three way valve 67, which alternately connects the
line to a gas supply line 68 and to a vent line 69.
During air backwashing, the air supplied through line
63 depresses the water level in the primary laterals, and in
flume 61, below the level of the gas metering orifices 41 that
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feed the air to the secondary laterals. At the end of the air
backwashing cycle, the air is bled out of the primary laterals
and the flume to provide room for the flow of backwash water.
All three of the foregoing embodiments provide
mechanically simple systems that distribute either liquid or gas
backwashing agents uniformly throughout the filter bed.
Furthermore, the low pressure drops required to achieve this
uniform distribution minimize the danger of explosive expansion
of air entering the filter bed. Thus, the filter bottoms of
this invention can be used with gravel support layers, which
simplify construction and installation of the systems and
minimize plugging of the filter bottom.
Of course, it will be understood that the system
described above is merely illustrative and that many changes
may be made by those skilled in the art. For example, the
filter bottom may be constructed of formed sheets and plates,
instead of the illustrated blocks, Similarly, although the
invention has been described in connection with the air bac~-
washing of a sand filter, it is equally applica~le in many other
situations where a liquid or a liquid and a gas must be
distributed throughout a bed of granular media, such as ozone
treatment of tertiary filters, granular carbon adsorption
systems, which may be operated either upflow or downflow and
typically require periodic contact with an oxygen containing
gas to prevent septicity, sludge drying beds, and ion exchange
systems. These and may other modifications may be made within
the scope of this invention, which is defined by the following
claims.
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