Note: Descriptions are shown in the official language in which they were submitted.
P4696 ~32~6
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Title of the Invention
Exhaust gas filter
Background of the lnvention
1. Field of the Invention:
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The present invention relates generally to the
art of preventing environmental pollution` attributable to
exhaust gas of internal combustion engines. Particularly,
it is concerned with filter for removing particulates
such as soot, which is inevitably contained in the
exhaust gas of diesel engine due to the gas component~
Such soot has recently been reported to be carcinogenic
and is extremely harmul to human health.
A legislative regulation on emission of such
particulates is now being contemplated in order to fight
against the air pollution.
2. Descri~tion of_the Prior Axt:
Although considerable improvement has been made
on the engine or other combustion apparatus itself, the
very source, which emits such particulates, has hitherto
been made and is still in progress, for the present time,
it is considered to be the best way for preventing the
environment from pullution to trap the particulates by
a filter thereon and then to burn the particulates-carryir.g
filter to oxidize the particulates into carbon dioxide. And
a variety of concrete systems for accomplishing this object
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have been proposed.
The known proposals include the use of metal
mesh or ceramic fiber packed and sealed in a container,
and that of a porous~ceramic foam or a monolithic ceramic
honey comb structure. An apparatus of the container
wherein the metal mesh or ceramic fiber is randomly filled
to be sealed is not suited for the purpose because the
filter may frequently offset during the service to create
channels of too large size for the particulates-containing
~xhaust gas and there occurs a blow-off phenomenon for
the soot or an attrition phenomenon of the fiber. The
metal mesh may encounter a problem of melting-down during
a process for reyenerating the filtering function wherein
the trapped particulates should be burn-t. The ceramic
foa~ and monolithic ceramic structured body have insuf-
ficient heat shock resistant property to cause a crack
during the regeneration process. Particularly, the mono-
lithic ceramic structural body has another drawback that
it has an insufficient gas permeability which amounts to
a large pressure drop, because it cannot be structured
to have a large porosity.
Summar~ of the Invention
~he present invention has for its object the
provision of an exhaust gas filter which obviates the
drawbacks inherent to the above described known filters
almost completely. The exhaust gas filter built in
accordance witb the present invention can treat large
quantities of exhaust gas containing particulates with a
high particulates collection efficiency, a small initial
5- pressure drop and a small increasing rate of the pressure
drop~
The present inventors have found that a sintered board
of ceramic fiber composite, which is made of the ceramic
fiber and a binding agent of fire clay of silica~alumina
is excellent for the filter element and able to be embodied
in a structure of a large filtering area by being put
together in a container to have a corrugated s~ape of
accordion pleats cross-section and completed the present
in~ention.
Namely, according to the present invention, there is
provided an exhaust gas filter to be placed in a path for
the exhaust gas containing particulates which comprises:
a container having a side wall partitioned by a filter
element into first and second compartments; the Eirst
compartment forming an inlet compartment having an inlet
conduit for introducing the exhaust gas therein, and the
second compartment forming an outlet compartment having
an outlet conduit Eor withdrawing the treated exhaust gas
therefrom, wherein said filter element has a generally
corrugated cross-section and an edge, and is made of
sintered ceramic fiber composite board of heat-resistant
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ceramic fiber and a binding agent of fire clay o~ alumina-
silica the entire edge of said container is supported by
the side wall of said container, said sintered ceramic
fiber composite board having numerous minute pores in the
direction of its thickness for permitting passage of gas
component of the inflowing exhaust gas therethrough and
for trapping solid component of the inElowing exhaust gas
therein, to filter the exhaust gas which is introduced
into the inlet compartment ~hrough the inlet conduit and
is to be withdrawn from the outlet compartment through the
outlet conduit.
The structural and functional features of the filter
element is that; numerous minute pores are provided
therein in the direction of its thickness for permitting
passage of gas component of the inflowing exhaust gas
there~hrough and for trapping solid component of the
inflowing exhaust gas therein, so that the exhaust gas
introduced into the inlet compartment through the inlet
conduit is withdrawn from the outlet compartment through
the outlet conduit after said gas is removed of its
particulates.-
Although novel features which are believed to be char-
acteristic of the present invention are pointed out in the
appended claims, the invention itsel:E, as to its objects
and advantages, and the manner in which it may be carried
out, may be better understood by reference to the follow--
ing detailed description taken in connection with the
acco!npanying drawings.
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Brief Exp].anat on of the Drawin~
FIG. 1 is a schematic iLlustration representing a
scanning electron microphotograph of the ceramic fiber
composite to be used as the filter element of the exhaust
gas filter of the present invention.
FIG. 2~a) is a persepctive view of one embodiment of
the exhaust gas filter.
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FIG. 2(b) is a cross-section of the e~bodiment
shown in FIG. 2ta).
FIG. 3 is a graph showing a curve which repre-
sents pressure drop/operating time characteristics of
the embodiment.
Description of the Preferred ~mbodiments
The filter element to be used in the exhaust
gas filter of the present invention is preferably a
sintered ceramic fiber composite board made of the
~0 ceramic fibe~ and a fire clay of silica-alumina as the
binding agent. The ceramic fiber is at least one selected
from the group consisting of alumina fiber, alumina-silica
fiber and silica fiber.
The preparing process of the sintered board
of ceramic fiber composite generally includes the follow~
ing steps. Firstly, the ceramic fiber (mean diameter:
2 ~m) such as alumina fiber, alumina-silica fiber or
silica fiber is cut by a chopper into short yarns (or
staple) of 0.1 mm - 10 mm lengthes, and the chopped fiber
is dispersed in water. Then, powdery clay prepared by
blending a fire clay of silica-alumina, such as ball clay
or china clay, with coarse particle powder material such as
petalite, is added to the dispersion at a ratio ranging
from 4 to ~0 w-t ~ of the total weight to give a slurry.
After being stirred well, the slurry is combined
with an aqueous solution of starch to be ayylu-ti.nated,
and then placed in a forming die, where it is dehydrated
and molded. A paper mill may suitabl~ be used to give
a sheet-like material. Af-ter being dried, the molded
material is baked at a temperature of 900C or above to
give a sintered ceramic fiber composite board, as illus-
trated in FIG. 1.
In general, the larger the effective filtering
surface of a filter becomes, the smaller become the
initial pressure drop as well as its increasing rate.
Accordingl~, the disclosed corrugated ~accordion-pleats
shaped) arrangement of the multiplicity of the ceramic
fiber composite boards means a filteriny surface area
of as large as possible.
Furthermore, the V-shape cross-section of the
flow paths formed between the ceramic fiber composite boards
makes inflowing or withdrawing pressure drop small.
The ceramic fiber composite board used in the filter
of the present invention has a thickness of 2 mrn, a
pressure drop of below 20 cm Aq at flow path velocity of
room temperature air of 10 cm/sec and a heat shock
resisti~ity of 1000C or above.
Furthermore, it is found that the very small increasiny
rate of pressure drop is attributable to its ability of
taking the dust therein, as is the case of a fibrous
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filter of container packed with metal mesh or ceramic
fiber.
The improved performance of the filter is also
attributable to its manner of partitioning the container
whereby both of the inlet compartment and the outlet
compartment have gradually widening cross-sections toward
their inlet and outlet openings, respectively.
Example
1. Preparation of the filter element:
Ceramic fiber of alumina-silica (500 g) which
has a mean diameter of approximately 2 ~m was cut by a
chopper into short yarns (staple) of 0.1 - 10 mm lengthes
and the chopped fiber was dispersed in water (about 50 ~)
together with a small quantity of a surfactant. The
dispersion, after being added with 150 g of a fire clay
of silica~alumina, prepared by blending ball clay and
china clay in 1:3 ratio, was moderately stirred to give
an intimate admixture. Then an aqueous solution of starch
was added to the admixture of ceramic fiber/clay system
to be agglutinated. This was~ poured into another
100 ~ of water to be diluted to give a slurry
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and was formed into a sheet of 1 m2 area and 2 mm thick-
ness by a paper mill equipped with a screen of 60 mesh.
After being dried in the air at 120C for abou-t
30 minu-tes, the sheet was baked in an electric furnace
at 1200C in the presence of air to give a sintered ceramic
fiber composi-te board, which is illustrated by EIG. 1.
2. Assembly of the fi]ter:
The ceramic fiber composite board was cut into 90
rectangular boards of 120 mm width and 90 mm length.
The rectangular boards were arranged in a corrugated
shape of 90 accordion-pleats cross-section with 4 mm
intervals as a filter element 1 in the container 2 and
abutting edges of the boards were bonded by a known
ceramic bonding agent, so that they form a multiplicity
of flow pathes of V-shaped cross-section by being supported
and sealed by the side walls of the container 2 at their
respective side edges. As a modified example, the
accordior~shaped filter is made by molding the belt-
shaped material of half-dried sheet of the filter material
in a mold of accordion form. The upper side surfaces of
the multiplicity o~ the filter elements 1 face an inlet
gas chamber 3 which is connected to an inlet conduit 4,
and the lower side surfaces face an outlet gas chamber
5 which is connected to an outle-t conduit 6. Accordingly,
the multiplicity of upper flow pathes form an inflowincJ
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path 7 and those of the lower flow pathes form a withdra~
ing path. The effec-tive surface area of the composite
ceramic board of this embodiment, throuyh which the
exhaust gas passes and on which the particulates
contained in the exhaust gas is trapped, amounts to 0.86 m2.
In FIG. 2(b), an arrow ~1 designates the direction of
the exhaust gas inflow through the inlet conduit 4, arroT"s
31 represent the manner whereby the gas inflow is intro-
duced into the multiplicity of the flow pathes 7.
Arrows 91 represent the manner whereby the gas removed of
its particulates is withdrawn from the flow
pathes 8 through the filter element, and an arrow 61
designates the direction of the exhaust gas out~low
through the outlet conduit 6.
FIG. 3 is a graph showing a curve which represents
the pressure drop/operating time characteristics obtained
as a result of experiment wherein the filter constructed
as described above was connected to a diesel engine which
emits an exhaust gas containing particulates at
0.1 g/m3 at a rate of 3.1 m3/min. In this experiment, the
particulate collection efficiency E defined in SAE standard as:
quantity of soot in the exhaust gas~
~- 1 (after beinq trapped by -the filter
rwhole quantity of soot exhausted
lwith being trapped
the value E is approximately 75 %.
