Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BAcKGRouND OF T~IE INVENTION
1. Field of the Invention:
The present invention relates to processing liquids by passing
the liquids into both ends of the same bed of granular material and flow-
S ing all the liquids from the bed at a position between lts ends. More
specificàlly, the invention relates to filtering liquids by passing them
into the ends of a bed of granular materials which have been classified
into multiple strata which contàct each of the flows of liquids from the
ends of the bed in sequence with a first coarse grade of granular media
and then a second fine grade of granular media to remove particulate
mat~er from the liquids.
2. Description of the Prior Art:
Industrial liquids have long been processed by passing them over
granular material. The most common of the industrial liquids is water and
lS the most common of the granular materials is sand. The mos~ common process
is filtration, i.e., foreign, solid particles of material suspended in
water have been deposited on beds of sand.
The development of sand filters took place in Englana in the
mid 1800's. Beds of sand were used to process municipal waters by re D val
of solid, foreign material suspended in the waters and~~were operated at
very low throughput rates (.04-.12 GPM/sq.ft.).
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At the turn of the century, in America, thase filters were used
in conjunction with coagulants -- thereby enabling the rates to be increased
to 1-4 GPM/sq.ft. The English filters are referred to as "slow sand filters"
or "English ilters." The American version is called "rapid mechanical."
These filters are characterized by downflowing the llquids to~be processed
through a bed of sand which has fine media at the top and progressively
larger media toward the bottom. At low flow rates this gradual grading
supports the finer sands at the top and prevents them from being carried
out ~he bottom with the clean water.
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In the 1940's poro~s underdrains were introduced to replace
the coarse gravel support. This allowed much higher rates to be achieved~.
Since that time flow rates as high as 20-30 GPM/sq.ft. have been used.
This type of unit is called a "High Rate Sand Filter."
Further development of filters has been made. Upflow of the
liguids has proven effective. The underdrain system thus became a distri-
bution system with far less plugging problems with the granular media.
Gratings were extended through the upper part of the bed to hold it in
place during upflow. A hydraulic plug of the liguids above the bed to
hold it in place was also developed.
Different grades, and kinds, of granular media have been
developed in both upflow and downflow patterns. One generalization is
that there are three types of the high rate filter:
1. Upflow with one type of media.
2. Downflow with one type of media.
3. Downflow with multiple types of media.
In all systems, the filter is cleaned by "backwashing" upward
with liquid or liquid and air. With upward flow backwash, the bed of media
is expanded until it fluidizes. The rubbing action between the media
granules, generated by the high velocity backwash liquid, dlslodges~foreign
matter collected on the bed, this material is washed upward and out to t~aste.
Air may be used with the liquid at the start of the backwash cycle to in-
crease the intergranular agitation. The last of the cycle must always be
wi~h the liguid only so that all air is removed from the bed.
It is controversial whether or not alr is useful in providing
effeative agitation during the baokwashing cyole. ~owever, this controversy
is not a subject of this disclosure. ~ ~ -
Although the more common use of beds of granular media is in
filtration, it is underlined from the outset that the prior art has the
broad, standing problem of increasing flow rates through beds for processing
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in general. Greater and greater capacity without proportibnal size
increase in equipment is the standard goal of this art~ Increase in fil-
tration efficiency by multi-media bed arangement is a gooa auxiliary goal,
and pendant, to the first goal.
SUMMARY OF ~HE INVENTION
A principal object of the invention is to greatly increase the
liquid throughput capacity of a bed of granular material as compared to
the capacity with flow into but one end of the bed.
Another object is to classify a multi-media bea to provide
coarse-to-fine filtration for flow into each end of the bed to a common
position between the two inlets.
The present invention is embodied in a liquid filter with a
container supporting a bed of strata of granular particles, the granular
particles being grouped in stràta differing from one another in at least
size and specific gravity. The stratificatlon of the groùps of~granular
particles result in a classification, after backwash, which uill provide
the liquid flow into each end of the bed with coarse-to-fine filtration
to a common outlet.
Other objects, advantages and features o~ this inventicn will
~ecome apparent to one skilled in the ark upon consideration cf the
written specification, appended claims, and attached drawlngs, wherein:
The drawing is a somewhat diagrammatic elevatlon, ln section,
of a ~ertical vessel and associated piping with a bed of medla in pIace
embodying the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Filtration in General
Objects of the invention are attained by~adjusting the buoyancy
of the bed media matexial. Fundamentally, after backwash, the media
fluidized grades as it settles acccrding to a combination of~density and
granule size (volume). It is this combination of densit~ and volume which
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is termed buoyancy.
- It follo~s that in a bed of media with uniform density the bed
grading will follow the granule sizing. The smaller size bed granules
will settle toward the upper part of the bed. The larger size bed gran-
ules ~ill settle toward the lower part of the bed.
In using bed media, mixed in size, the buoyancy must be care-
fully selected to grade the bed with the larger size toward the direction
of liquid flow if filtration is the process. If upflow is the desired
flow pattern, the buoyancy should be adjusted to settle the larger bed
granules toward the lower portion of the bed. If downflow is the desired
flow pattern. the buoyancy should be adjusted to settle the larger bed
granules toward the upper portion of the bed.
~ hy is it best to havs the larger granules contacted first?
First, experience shows filtration is better the smnller the bed granule.
~o~ever, bridging of the small passages between the smaller granules, by
the foreign, solid material from the filtered liquids, builds a "caXe"
on the face of the bed into which the filtering liquid is fIowed. The
"loading" capacity of the bed is quickly reached. The pressure drop
across the bed rises quickly.
For example, 310 micron qize garnet removed 95% of the material
from liquids filtered. However, the pressure drop across the bed rapidly
i increases.
On the other hand,-1280 micron size flint sand removed 50% of
the material from liquids filtered. The pressure drop increased very
lit~le.
Of course we are dealing with relative values at this~poi~t.
Ho~ver, these examples are enough on which to construct the~aarapace of ;
expectation that a bad with a first strata of coarse gra~ulea will remove
50% of material suspended in liquids. Then a subsequent strata of eine:
granules will remove 95~ o~ the remaining material. The total removal
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would then b~ 97.5~. Purther the pressure drop across the complete bed
would only gradually increase.
Experience has proven the coarse-to-fine filtration technique.
~;y own laboratory work has confirmed the expected performance. I have
formulated theories of why the filter cake does not develop at the face
of the finer grade of media and the penetration of both grades of media
~ith the suspended material gives a high loading capacity with low
pressure drop. However, this disclosure is shaped to show how the coarse-
to-fine filtration can be obtained in a novel flow pattern of a media bed
The present invention provides a media bed for filtering with a
strata o coarse media above and below a strata of fine media, removing
the iltered liquid from the middle, fine media. Ho~ever, the problem is
how to put together a unified bed wlth fine and coarse media which will
clas_ify into strata as desired after expansion~of the bed into the free-
board during back~7ash. If this problem is solved, effective coarse-to-
fine filtration can be carried out by flowing into each end of the bed
and out the inter~ediate take-off. The resuIt would be to greatly
increase the capacity, or throughput, of a media bed and still have the
effective coarse-to-fine filtration for flow into each end of the bed.
Significant work has been done in combining medià wlth different
particle sizes and specific gravities to produce a filter bed with the
particles classified as desired in the liquid flow path through the bea.
However, no one, to my knowledge, has classified a uni~ied, multi-media
bed to provide the coarse-to-fine filtration from opposite ends of the
bed to an intermediate take-off strata.
Novel Flow Pattern
~Even more fundamentally, putting aslde medln classiflcatlon, no
one to my ~nowledge, has provided a flow pattern rélative to a~media bed
in ~hich the liquid processed i5 flowed into opposite enas of the bed to
an intermediate take-off point. ~gain, the fundamental concept is double-
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end flow of liquid to be processed into a media bed. Whether the liquid
is filtered, or some other process function is brought about, this concept
stretches the capacity of a media bed within the fixed dimensions-of a
container of the bed. It is beneath this ends flow concept that the medla
selection for filtration is disclosed for this specific process. The
media is selected for its density, or specific gravity, and sized to
provide a stratification of the bed which will ~ive coarse-to-fine
filtration as the flow is direoted into each end of the bea.
Structural Disclosure
The drawing required to aisclose this class of lnvention need
only be diagrammatic without extensive mechanical detail. After all, a
structural embodiment of the invention is in a simplistic bed of granular
material whose overall function is to process liquids. The bed is sup-
ported within a container 1. Conduits are connected into container 1 to
form inlet and o~tlet means for the Iiquids. This dlsclos~d structure
lacks many details but adequately teaches the invention.
More specifically, the present invention provides a vertlcal
form for container l. It is usually preferred that the container be
cylindrical, for ready fabrication. An inlet is provided fox each ena
of the container. Inlet 2 is through the bottom end of the container.
Inlet 3 is throug~ the top end. The 11quids to be processed are divided
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; i~to two streams and flow into each end of the container through the t~o ~ ;
inlets. The processed liquids are discharged from the side of~the container,
between the two inlets.
The bed 4 of granular material is placed in the~;lower portion
of container 1, filling the lower portion of the container and leavlng
freeboard space 5 in the upper portion of the~container. In this arrange- -
ment, the liqùid to be filtered flows into the opposite~ends of bed 4 at
the same time. Take-off of the processed liquids is through a foraminous
30 member 6 over openings 6a in a section of the container wall. n compart-
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ment 7 is formed over the take-off section of the contalner wall. Outlet
conduit 8 removes the processed liquids from the apparatus through valve 9.
~he-op~nings 6a and screen 6a are disclosed at this time in very
simple form. The problem of providing a screen with openings small enough
to retain the bed media in place can be met in several ways. The support
of the finely meshed screen in a vertical position with strong stxuctural
backing can become complex. ~This partic~lar problem is not a primary
factor of this disclosure.
What is important is that in bed supports of this type, the
processed liquids which are flowed from the bed have an~e~it structure
which does not extend laterally into the bed. In vertical eY~ansion of
th~ bed, the movement of the bed does not have lateral structure upon
~h~ch to exert forces. The bed 4 can move up and down ln container 1 as
a rcciprocating piston and meet no obstruction. The processed liquids
can flow from either, or both, inlets to the outlet of openings 6a and
screèn 6 with uniformity. This sidewise, exit, flow from the bed has
severa~ advantages in both the fabrication to provide it and its function ~ -
in the flow pattern of liquids relative to the b~d.
Although many valves not disclosed here are desirable for the~
overall, continuous and cyclic functions of the system, only the principal
valves are indicated. Valve 9 discloses baslc control of the removal of
11quids which flow from bed 4, through openings~6a and lnto compartment 7.
Valve 10 controls the liqulds flowed from lnlet 2, through inlet 3, and
presents the reversal of this flow during backwash operations. ~Valve 11
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con~rols the flow of backwash liquld from 3 as an outlet.
Full consideration is now given~the~backwash fùnct1on of~tne
system. It is assumed that after the bed 4 has processed li~uids~ the;bed
wlll requlre flushing - cleaning~of deposits on the bed material. The
systems available for backwash ars many snd varied. Whatever the system
of backwash, lt is always to ~s expected that bed ~ will be expanded~into
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freeboard 5.
- To expana bed 4 into freeboard 5, valves 9 and 10 are closea,
valve 11 is opened and the liquid is flowed up throu~h lower inlet 2 at
a rate which will force bed 4 to expand into freeboard 5. The bed
~aterial is agitated by this upward liquid flow and whatever forei~n
matter with which it is loaded is scrubbed from the bed particles and
flushed out inlet 2 and through valve 11 to waste. Return to processing
service is brought about by reversal of the valve settings.
In this structural disclosure of the bed 4 as a processing tool,
I continue to avoid the limitation of filtering as a specific form of
processing. The immediate prospects for use of the bed 4 to remove sus-
pended solid, foreign material, from water are vast. Elowever, this view
of the reduction to practice of the invention could be far shork of all
potential applications of the invention.
Filtration S~ecifically
For only the moment, I will shift the gears of disclosure into
the filter mode. In the description of the~prior art it~was basically
established that, relative to the size of the granular mater1al of the
bedj liquids to be filtered should first flow through the more coarse
media and then the finer media. This coarse-to-fine sequence is required
to obtain the efficient filtration for a lQng period of ti~e before back-
washing is required. This-stratification is not~difficult to obtain with
upflow patterns of filtration and backwash. }~owever, it is not so easy
to establish on downflow. It is an even greater problem to obtain with
simultaneous upflow and downflow into the ends of the same~bed. Th1s-is~
a precise problem solved by the present invention. It is vith this solu-
tion of the problem that a large advance is made in the throughput capacity
of filters.~ Coarse-to-fine filtration is provided for both upflow ànd
downflow. Further,.the same d1ameter of fllter bed which provided a first
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rate of downflow, or upflow, now provides a signi~icantly greater rate of ~ ~
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filtration flow by simultaneously flowing into each end of the bed and out
its middle.
In the drawing, the bed 4, a~ a filter, is disclosed as comprising
three strata of granular material. The finer grade of material at 12 is
opposite the foraminous mem~er 6. Above and below the strata 12 are
relatively coarse strata 13 and l4. Therefore, both flows of liquids to
be filtered pass through one of the coarse strata and then the finer strata.
When backwash liquid is flowed up through strata 12, 13 and 14
of bed 4 agitation takes place. Of course there is mixing across each
interface sho~Yn as the bed is expanded;into freeboard 5. Because of
the selection of size and specific gravity for each of the three strata
of granular media, resetting of the bed after stopping backwash is toward
the original stratification disclosed in the drawing. It is not expected
that the.precise, sharp interfaces of the drawing be regained. Stili a
~15 satisfactory degree of restratification is obtained. Filtration is again
through coarse-to-fine media in both upflow and downflow to the common
outlet.
Filtration Bed
~ The invention-was first reduced to practice with laboratory-
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sized cons~ruction. Plastic was used for container 1 so the processing(filtration) and backwash functioD could be directly vlewed. The results
were dramatic and confirmed all the advantages I sought with the invention.
Strata 14 of granular media ~as formed with garnet w1th an -
average mesh of 25. Strata 12 was formed of 60-80 mesh garnet. Strata
13 was formed with coal at about 25 mesh. With the~coal~having a specific
qravity of about 1.7 and the garnet at about 4.2,~the strata classified
after bac~wash as depiated in the drawin~. As indicated previously the
interface is not actually as sharp as shown in the draw.ing.~ As a matter
of fact, the lower interfaae might be improved w1th sand havlng a
specific gravity of ?.~ With this mesh size and specifio;gravity for;
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the granules of the media the bed 4 will reclassi~y into the three strata
12, 13, 14 as disclosed in the drawing.
Flow of liquids with suspena~d particulate foreign material is
directed into each end of bed 4. One flow stream is directed upwara,
through inlet 2. The other flow stream is directed downward, through
inlet 3. Both flow streams combine to flow out through foraminous
member 6, into compartment ~ and out conduit 8. In moving through the
bed 4 the liquids~have their suspended particulate foreign material re-
tained by the granules of the bed. The filtered tprocessed) liquids flow
from the unit through outlet 8.
It has been established that as the mixture of particulate
material and liquids flow down throush strata 13 and into strata 12, the
material will distribute down through the bed of 25.mesh, 1.7 specific
gravity coal. Not all the matter will be filtered from the liquids. The
60-80 mesh, 4.2 specific gravity garnet will remove material. However,
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the large burden of-filtration will be borne by the coarse coal and the
fine garnet will polisb the liquids. This coarse-to-fine flltration has
several advantages.
With the coarse coal ~unctioning to distribute the particulate
material filtered from the liquids, a filter cake of this material does
not form. Therefore, a larger load of matter is filtered from the liquids
than is filtered with a uniform bed of 60-80 mesh garnet.
~lso, the distribution down through the coarse media militates
against differential pressure buildup. Of course there~ls bulldup,~ but
the time over which the buildup ta~es place is greatly lengthened.
Granted, these are simple relative descriptions linking functions of the~
present bed and the prior art. However, the advantages of coarse-to-fine
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filtration begins to shine through. And when this~coarse-to-~ine filtra-
tion is rendered possible from both ends of bed ~, the advantages over
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The prior art has provided a liquid pressure in freeboard'
space 5 to keep a bed in place. But the prior art did not provide
the stratified bed confi~uration now disclosed'together with flow into
both ends of the ked. The increase of volume in filtered liquids over the
prior art arrangements is now apparent. The simultaneous advantage o
coarse-to-fine filtration in both directions of flow is a cumulative
advantage over the prior art.~ '
Coalescence Bed
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Processing liquids by the invention is not limited to filtr~-
t.ion. Flowin~ the liquids-to be processed through ~ed 4 from two direc-
tions is an art advance in utiliæation of bed 4. This ad~ance is separate
rom the specific processing yiven the liquids by the bed material.
Bed 4 can be made up with granular materlal which will provide
the mechanism with which to coalesce one liquid which has been finèly
dispersed in a second liquld with which it is immiscible.~ It 1: not
'necessary to discuss the coalescing mechanism of the bed media.~ Whether
electrical forces or preferential wettlng characteristics are involved
is a non sequitur. This disclosure i: not a forum for dev:loping and
e~pounding these theories.
In the present disclosure, the view~is advance~ that bed 4 can ~ '~
coale:ce one liquid from another. Contact of the bed wlth the liquids i5
brought about by the invention -- with all o'f its advantagesO The con-
' clusion here emphasized is~that the invention finds application in fields
beyond that of filtration.
- 25 Ion Exchange Bed
So there will be no que:tion about th: utility'~of"th: invention
with all forms of bed material, that material used in ion exchange is ~`'
:tipulated. With respect to the invention ln the flo~pattern,~bed :trat~
ification and removal system, an ion exchange hed` is simply made up of
granular~material. A~ain, this~is only~to emphasize~that the invention
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finds application in fields beyond that of filtration.
CONCLUS ION
- The basic concept of the inver.tion is embodied in a container in
which a bed of granular material is placed in the lower portion of the con-
S tainer so a freeboard space will remain in the container and above the bed.
Inlet means are connected into the container above and below the bed. L~quids
to be processed are then flowed into the bed from opposite directions. ~n
outlet ~or the processed liquids is then provided at some point between the
ends of the bed. To backwash the bed the inlet above the bed must aIso be
arranged to flow backwash from the bed which is expandéd by the backwash into ' '
the freeboard space. ' "
Another concept of the invention, within the basic concept, is a
bed of selected materials. The materlals ara basically selected for buoyancy
and so they will stratify into three layers. me stràta will reform, relative
to the two inlets and outlet, after backwash has expanded the bed into the
' freeboard space. Within this second concept the mvention provides the center
- strata with relatively a fine mesh of granules and the strata on each side of '
the center strata with relatively coarse mesh of granules. ~herefore, each'
st~eam o the liquids processed (filtered~ ~will be provided with coarse-to-fine
iltration.
Still another concept wh1ch I deslre to exphasiz~ i6 r~ducèd to
practice in the take~off, or withdrawal, system for liquids at the middle of
tho bed. In this concèpt the liquids are passed through holes in the containex'
. o~er which a screen structure is placed. The~screen is'fine enough~to retain
the bed granules in position yet permeable to the-liqulds which have passed
through their~portion of the bed.' This side opèning provlslon'for the
container leaves the cross-section~of the ccntàiner ~ree~of structure which
would encumber the bed expansion and reclassi~ication into strata. A simple ~-~
container on the outside of the container, over the holes through the contalner
wall collects the discharged liquids-lfor controlled exit~through a ccnnected
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conduit.
From the foregoin~, it will be seen that this invention is one well
adapted to attain all of the ends and objects hereinabove set forth, together
with other advantages which are obvious and inherent to the apparatus.
S It will be understood that certain features and subcombinations
are of utility and may be employed without reference to other features and
subcombinations. This is contemplated by and is within the scope of the
invention.
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As many possible embodiments may be made of the invention without
departing from the scope thèreof, it is to be understood that all ma~ter herein
set forth;or shown in the accompanying drawings is to be interpreted in an
illustrative and not in a limiting sense.
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