Note: Descriptions are shown in the official language in which they were submitted.
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VA~UUM ~K~ lN~ DIAPHRAGM FILTER PRESS PLATES
~R~-RO~ND OF THE lNV~N LlON
DESCRIPTION
TECHNICAL FIELD
ThiR in~ention relates generally to filter pres_
plates, and more Rpeclfically to an impro~ed vacuum drying
~;aph~agm-type filter press plate.
R~ ROUND ART
There are many manufacturers of recessed filter
plates and ~;arhragm filter plates on the market.
StAn~rd diap_ragm plate~ are m_nufactured by placing an
ela_tomer co~er o~er a solid pla~tic core. The _olid
pla~tic core contain_ the indi~idual drain channels and
the corner drain piping. The elastomer covers the
filtration area of the plate and i8 inflated with a fluid
introduced through a pipe fitting in t_e core of the
plate. The advantagee of a ~;~rhTagm plate are: shortened
cycle timeR, better cake w~h;ng, and the ability of the
press to take vari_ble feed 10A~;ng.
Disad~antages of current ~iArhTagm plates are
many. The main reason ~;Aphragm plates are not used
exclu~ively in the filter press market iB cost. The
current method of mPn~fActure i~ very expen~i~e and
requires a large capital cost for equipment. A diaphragm
plate will usually cost four timee that of a stan~ard
recessed plate. In addition to the initlal cost the two
piece construction (elastomer ~;Arhragm and ~olid plate
body) will have higher failure rate due to ~eparation of
the pieces. Failure of the elastomer ~;ap~Tagm itself can
alRo occur.
At lea_t one manufacturer of diaphragm plates
ha~ suggested that a hot or cold liquid can be pumped into
the core area. Thi~ is prim_rily used to preheat or
precool the plate and diaphragm to stay within the
material temperature limitations of the part, and not to
actually transfer heat to or from the material being
filtered.
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A non~ phragm teflon plate with steam coils in
the plate has also been proposed. Thi~ was to heat and
dry the cake solids after the filtration cycle was
complete. This approach is problematic because after any
initial drying the fllter cake loses volume and creates a
gap between the cake and the filter press plate. This gap
insulates the cake, and heat transfer and drying are
limited only to applications where the cake remains in
contact with the hot plate surface. Another manufacturer
has tried to rotationally mold an outer shell and foam
fill the inner section. HO.I_VeL, it is difficult to
manufacture a continuous outer shell out of crosslink
polyethylene, and incorporate drain ports from the filter
area to the drain link6.
DISC~OSURE OF lNV .llON
The filter press plate of this invention can be
distinguished from any other commercial filter plate in
physical differ-nces and in functional differences. As
oppo~ed to a stan~d diaphragm plate that has an exposed
core with an ela~tomer ~;ap~agm covering the filtration
area, the inventive plate is rotationally molded in one
sealed hollow piece. The shell is placed in a second mold
and urethane foamed under pressure. This results in a
solid core inside the shell that can ~upport the pressures
from the press closure and the filtration pressures.
Because no other plate is rotationally molded,
no other plate is made from cross linked polyethylene.
The crosslinked other shell allows the plate to handle
much higher temperatures than the propylene plastic plates
currently available.
The inventive plate also has multiple pipe
fittings molded into the shell. The pipe fittings allow
the hot or cold fluid to be pumped into the core area to
heat the shell.
The filter press plate functions like no other
available plate. This is primarily due to its one piece
cross link polyethylene shell and urethane core. As a
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conventional ~;aph~agm plate, the one piece outer shell
cannot separate in the f~ltration area because there is no
joint or connection point. The cross linked polyethylene
i~ not an ela~tomer and i~ much tougher and allows higher
filtration temperatures.
Because the shell iR a thin sealed crosslinked
piece, this allows heat tran~fer from any fluid pumped
into the core to the filter cake. The heating fluid
inflates the diaphragm and maintains contact with the cake
as the cake loses ~olume during the drying process under
vacuum.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 ie a perspective view of a complete
rotomolded filter press plate of thi~ invention, without
cloths.
Fig. 2 is a cutaway perspective view of a filter
press plate of this invention.
Fig. 3 is a side elevation cross-sectional view
of a filter press plate of this invention, showing the
foamed core and outer shell.
Fig. 4 is an elevation view of a pipe fitting
molded into the crosslinked shell, used to introduce or
remove fluids form the core area.
BEST MODE FOR CARRYING O~T THE lNv~r.~lON
Fig. 1 i6 a perspective view of a complete
rotomolded filter press plate 10 of this invention,
without cloths. Filtration area 12 of the plate i6 ribbed
to allow filtrate to flow to the four corner drain ports.
This i8 also the area that delaminate~ from the core when
core pressure is applied and diaphragms out. Heat
transfer to the cake occur~ in this area. Drain porting
14 allow~ filtrate to leave each plate and flow to the
fixed end of the pre~s to exit. Sludge is pumped to each
plate cavity through feed port 16, and is cont~;ne~ by
sealing edge 18 of the plate. Molded in pipe fittings 20
allow fluids to be introduced or removed from the plate
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core (bottom connections not shown). Molded in drain
pa~sages 22 allow filtrate to get to the drain ports.
Fig. 2 is a cutaway perspective view of a filter
press plate 10 of this invention, illustrating the solid
foam core 24 of the plate, drain passages 22, and molded
in pipe fittings 20.
~ ig. 3 is a side elevation cross-sectional view
of filter press plate 10 of this invention, showing the
foam core 24 and outer shell 26.
Fig. 4 is an elevation view of a pipe fitting 20
molded into the crosslinked shell 26, used to introduce or
remove fluids form the core area.
The invention provides a one piece outer shell,
~l~phragm recessed filter press plate. The outer shell i6
rotationally molded out of cross linked polyethylene. The
inner cavity is filled with a structural polyurethane
foam. The outer shell and the inner core foam delaminate
80 that in the filtration area the shell can be expanded
out by pressurizing the inner core with a fluid. This
eYr~nA;ng of the outer shell makes the plate a diaphragm
filter press plate. Conventional diaphragm plates utilize
an elastomer diaphragm fitted to a solid plastic core.
This design is not one piece and fail6 when the diaphragm
separates from the core.
In the rotomolding of the ehell, internal drain
passages are molded into the shell with pin inserts that
are removed prior to opening the mold. Thi6 leaves molded
in drain pipes that do not compromise the sealed shell of
the part.
This invention provides the ability to pump hot
or cold fluids into the core area of the plate. Metal
pipe inserts are molded into the outer edge of the one
piece shell during the manufacturing proce~s. Fluids
pumped into the ~ealed core area heat or cool the shell of
the plate. This in turn heat6 or c0016 the filter cake
held inside each plate cavity. In the case of heating,
hot fluid is pumped through the shell under pressure.
While the filter press is still in the closed position, a
.
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vacuum is pulled on the filter cake through the filtrate
drain lines. Under reduced pressure moisture or other
volatile materials will ~aporize out of the cake. The
heat of vaporization is supplied by the heat trans$er from
the hot fluid through the shell. The vacuum allows drying
and heat transfer at a temperature compatible with the
plastic materiale used in the part. The pressure to
~Yp~r~A the ~;~pl~ragm~ i~ suppliQd by the heating fluid.
As the $ilter cake driee it lo~ee volume and could loose
contact with the plate shell thus stopping heat transfer.
The ~ap~agm operation of the plate allows the heat
transfer ~urface to eY~n~ as the cake shrinks. This
maintains good heat transfer through out the drying cycle.
The inventi~e process vacuum dries by
tran~ferring heat to the filter cake to supply the heat of
vaporization through the membrane or diaphragm part of the
plate from the circulating hot water. Vacuum is supplied
to the filter cake side of the press plate through the
filtrate drain lines to lower the boiling point of the
liquids in the cake ~o that there will be enough of a
temperature differential between the hot water in the
diaphragm area and the cake to get sufficient heat
transfer for drying.
Each plate i8 ported with molded in fittings to
allow the hot water to be circulated through the inside of
the plate. The internal flow path i8 between the core of
the plate and the ~i~p~ragm. The circulation rate is
sufficiently high to create turbulence for uniform
heating. An external water tank is heated and pumped to a
manifold along the bottom of the press. This manifold is
hosed to each plate to ~upply hot water. The top of each
~ plate i6 ho~ed to a return manifold that returns the hot
water to the tank. Back pres~ure iB maint:-;neA on the
return manifold to inflate the diaphragms and maintain
contact with the cake.
After cake i~ made and filtrate is no longer
exiting the press, the drain lines are connected to the
~acuum source. For example, ~acuum can be supplied by a
~rB
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liguid eductor, wherein water is circulated through a
liquid eductor that pulls a vacuum on the filter prees.
Vaporized liquids can be con~n~ed by direct contact in
the eductor, or in an ~Ych~nger prior to the eductor.
~acuum is maint~; ne~ by cooling the circulating water
etream. Vacuum can be supplied through any one of many
meane.
Hot water can be manifolded ae above, or can be
~upplied through internal plate porting ae are feed and
drain lines. Vacuum can be eupplied by any means. The
heating medium could be any fluid. Other core and
diaphragm materials could be utilized that could withstand
live steam or some other hot fluid.
Wa~te~ can be dried beyond what can normally
achieved with sta~rd dewattering devices. Liquids in
the void spacee between ~olid particles in the cake can be
removed through vaporization, thus reducing the weight and
volume of the waste to be di~posed of. In some case6
other contaminates can be removed with the primary liquid
stream that will help in the disposal options. An example
of thi~ is the benzene in A.P.I. wastes that limit land
fill options. The low level benzene will azeatroph with
the water in the drying process.
Products that need to be supplied in a dry form
for sale or for further procee~ing can be dried in the
filter preee. This would include things like pigments,
metals and metal salts, foods and pharmaceuticals.
~ecauee the drying ie done under vacuum temperature
degradation will not occur.
Sewer sludge dispoeal i~ limited by the level of
pathogens and by the level of moisture in it. St~n~rd
dewatering method~ cannot meet either requirement with out
further treatment. The inventive proces~ can meet 503
regulations for pathogen kill and solids content. The
pathogen kill ie accompllehed by heating the cake with the
circulating hot water in the ~;~rhragms without the
vacuum. The cake could also be heated by introducing a
hot fluid into the cake area. After the temperature and
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time reguirement~ are met, the vacuum is turned on and the
cake iB dried to meet the percent solid~ requirementE~.
The inventive process can also be used if the sludge is
being incineratod, becauRe enough water i~ removed to make
the sludge a po~itive heat value.
In an alternate embodiment, in~tead of the hot
fluid circulation and Reparate ~acuum eystem to dry the
filter cake, a vapor recompression internal heat pump
system could be u~ed. After cake is made in the press, a
~racuum pump/compressor i8 used to pull a ~racuum on the
cake side of the press. The~e vapors are recompressed to
a pressure high enough to inflate the ~;ap~agm~ of the
plate~ and are introduced to the core area of the plate to
supply the heat of vaporization to ~aporize more liquid
from the cake. In order not to exceed the temperature
limitation~ of the plate, a non-con~enQahle gas is
introduced in the recompre_sed gas stream to lower the dew
point of con~nRing temperature of the ~tream.
