Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Frost 9-,6, 17 7 1, 4 One
PARTICULATE FILTER AND MATERIEL FOR PRODUCING TOE SAME
Removal of solid particulate from fluids - gazes
and/or liquids - in which the particulate are suspended is
commonly done by use of filters. Generally filters are made
of porous solid materials in the form of articles or masses
with a plurality of pores extending there through (which may
be interconnected) and hove small cross-sectional size or
minimum diameter such that the filters are: if) permeable
to the fluids, which flow through the filters from their
inlet surface to their outlet surface, and (2) capable of
restraining most or all of the particulate, as desired,
from passing completely through the filters with the fluid.
Such pores constitute what is termed "open porosity" or
"accessible porosity". The restrained particulate are
collected on the inlet surface and/or within the pores of
the f titer while the fluid continue to pass through those
collected particulate and the filter. The minimum cross-
sectional size of each of some or all of the pores can be
larger than the size of some or all of the particulate, but
only to the extent that significant or desired amounts of
the particulate become restrained or collected on and/or
within the filters during filtration of the fluids flowing
through the filters. As the mass of collected particulate
increases, the flow rate of the fluid through the filter
usually decreases to an undesirable level. At that point,
the filter is either discarded as a disposable/replaceable
element or regenerated by suitably removing the collected
particles off Andre out of the filter so that it can be
reused.
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.
Four general main considerations for useful filters
are:
(1) filter efficiency: the amount of suspended portico-
fates of concern in a given volume of fluid thaw are removed
from what volume of fluid as it passes through the jilter
(usually expressed as a weight percentage of the total
particles of concern originally in that given volume of
fluid prior to passing into the filter,
(2) flow rate: the volume of the fluid per unit of
10 time that passes through the filter and collected portico-
fates or, in a closed continuous feed system, the back
pressure or increased pressure created in such system
upstream from the filter by the presence of the filter and
- particulate collected thereon in comparison to what the
pressure therein would have been in the absence of the
filter,
(3) continuous operating tome: the cumulative time
of continued service of the filter before filter efficiency
and/or flow rate/back pressure become unacceptable so as to
necessitate replacement and/or regeneration of the filter;
and
I compact structure: smallest space~sa~ing volume
and configuration of the filter for attaining the best
combination of filter efficiency, flow ratetback pressure
and continuous operating time.
or filtration of fluids at elevated temperatures,
consideration must also be given to the filters having
adequate mechanical and chemical durability under the pro-
veiling conditions of temperature within the filter and
chemical reactivity of the fluids and suspended particulate
coming into contact with the filter.
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The considerations noted above, especially the four
general main ones, appear to be accommodated in varying
degrees, but in less than fully satisfactory ways, by the
following examples of prior art filters or incomplete
filter suggestions:
US. Patents 2,884,0~1, 2,952,333 and 3,242,649 thus-
irate filters of the type made of pleated thin porous sheets
of filter material whose layers are interleaved with corrugated
or crimped spacers with the parallel corrugations or crisps
thereof extending substantially perpendicular to the folds
of the pleated sheets. In essence, fluid enters a complete
layer or column of cells defined by a spacer and then passes
- through only the filter sheets on each side thereof (but not
through corrugation or crimp segments of a spacer separating
adjacent cells in that spacer) to effect filtration. More
over, the corrugations involve cell-like passages whose
transverse cross-sections have sinusoidal geometric shapes
having smell interior angle "ccrnersi' of substantially less than 30.
British Patent Specification 848,129 shows another form
of thy pleated-type filters wherein, instead of being
interleaved with corrugated spacers, the thin porous sheets
of filter aerial are Impressed with spacer dimples to
maintain spacing between the pleats.
US. Patent 3,346,121 discloses thin porous-walled
honeycomb filters ox corrugated layer structure having
crosswise oppositely indented portions that block end
portions of the channels or passages in an alternating
pattern within each layer (but not necessarily from layer
to layer to cause fluid therein to pass through the porous
walls to effect filtration of the fluid. The corrugation
pattern is such that the channels or cells have transverse,
SLY
cro~s-sectional, geometric shapes with numerous instances of
corners formed by small interior angles substantially less than 30
Moreover, the layered structure involves numerous portions,
where the layers adjoin each other, which are of double and
sometimes triple layer or wall thickness.
US. Patent 3,533,753 describes catalyst bodies with
layered networks of intersecting "capillary" channels which
can function as a filter body for combustion exhaust gas
dust or sediment Ed particles, which can be diesel engine
exhaust soot or particulate as noted in US. Patent 4,054,417.
US. Patent 3,637,353 discloses a tubular packed bed of
granular catalyst with fluid-flow interstices for filtering
- particulate from exhaust gases generated by diesel engines.
: US. Patent 4,054,417 also suggests making the disk
closed diesel exhaust filters of known materials used in
heat exchangers for turbine engines or in monolith catalytic
converters for automotive vehicles ego. as disclosed in
I- US. Patent 3,112,184 as a corrugated structure and in US.
Patent 3,790,654 as an extruded structure) as alternatives
to and in a manner similar to the material in US. Patent
3,533,753 it with fluid flow passing into r through and
out of Avery channel.
Research report EPA-600t~;77-056 of the U~5O Environ-
mental Protection Agency suggests thaw several commercially
available thin-porous-walled ceramic monoliths of honeycomb
appearance, Roth corrugated and extruded, are potential
filters for diesel exhaust particulate. However, the only
illustrated arrangement given Hereford is the alternate
layer cross-flcw design of a corrugatedl~nolith, with small mterior corner
angles less to 30 in transverse cross section, wherein
the exhaust gas passes through only those thin walls between
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layers of cells or passages. This report Allah suggests the
suitability of porous bonded mycosis of ceramic fibers for
filters of diesel exhaust particu].ates.
British Patent Specification 1,440,184 discloses that
porous bonded sheets of refractory metal oxide fibers can be
formed into corrugated or embossed honeycomb structures for
use in filtration of hot waste gases containing particulate
matter and of molten metal prior to casting. As in cases
noted above, the transverse cross-section of the corrugated
embossed or structures contain numerous small interior angle
corners much less than 30.
US. Patents 3,893,~17 and 3,962,081 describe ceramic
. foam filters for removing entrained solids or inclusion
particulate from molten metals as whose metals pass through
the foam structure.
US. Patents 4,041,591 and 4,041,592 disclose thin-
walled, honeycombed, multiple-fluid-flow-path bodies with
all cells or passages parallel such that fluid entering each
of the passages can continue through and pass out of the
open exit end thereon without passing through any cell wall.
Alternate selected columns or layers of cells have their
ends sealed for advantageous separate manifolding to fluid
-- conduits. An optional use indicated for these bodies is in
filtration and osmosis when porous materials are used to
form thy honeycombed body so that some of the fluid flowing
in a first set of cell can past into an adjacent alternate
set of cells through the thin porous walls between them
while a remaining portion of the fluid with a hither concern-
traction of an undesirable or separable constituent can
continue through and pass out of the open exit end of the
first set of cells. Examples of the latter use are reverse
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AL
osmosis filtration and ultrafiltration of saline or Impure
water to produce potable or purified water, in which cases
the surfaces of the porous walls de~ininy the first jet of
cells are lined with suitable selectively permeable membranes.
Summary of the Invention
A new filter body has now been conceived for removing
solid particulate from suspension in fluids and which is
believed to provide a superior combination of satisfaction,
especially with regard to all four main considerations noted
above. When fabricated of inorganic (especially ceramic)
material having incipient melting point above the elevated
temperature of fluids to be filtered, the superior combination
of satisfaction includes regard to adequate mechanical and
chemical durability under the prevailing filtration conditions
with such hot fluids
The new filter body is based on a thin-porous-walled
honeycomb structure with its cells or passages being mutually
parallel and extending longitudinally there through between
inlet and outlet end faces. It is uniquely characterized by
the entirety of all cell walls constituting effective filters
directly between adjacent inlet and outlet cells such that
there are no small interior angle ~30) corners in the transverse
cross-sectior.~l geometric shapes of the culls that inhibit
- full effective access to such filters by the fluid due to
fluid flow patterns and particulate accumulation patterns
effected by such shapes with small angle corners. When
viewed from each of the inlet and outlet end faces of the
filter, alternate groups of cell ends are open and close
in a checkered or checkerboard pattern, with the outlet end
face pattern being the opposite of the inlet end face pattern
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In particular, the invention it an apparatus for
filtering solid particulate from suspension in fluid
streams (e.g. hot gases or liquids) and which comprises a
filter of honeycomb structure having a matrix of thin
porous walls defining a plurality of cells extending long-
tudinally and mutually parallel there through between inlet
and outlet end faces of the structure. Generally, the walls
are not greater than about 1.5 mm (preferably maximum ox
about 0.635 mm) thick. The walls contain substantially
uniform randomly interconnected open porosity of a volume
and size sufficient to enable the fluid to flow completely
through the walls and to restrain most or all of the part-
curates from passing completely through the walls. Generally
the open porosity is at least about 25~ (preferably at least
about 35%) by volume formed by pores with a mean pore diameter
determined by conventional mercury-intrusion porosimetry)
of at least about lam preferably at least about 3.5~m)~
The transverse cross-sectional shapes of the cells form a
- substantially uniformly repeating pattern of geometric shapes
without interior angles of less than 30 (preferably less than
45). Thy inlet group of the cells is open at the inlet end
face and closed adjacent to the outlet end face. The outlet
- group of the cells it closed to adjacent the inlet end face
and open at the outlet end face. Each cell ox the inlet
group shares cell walls only with cells of the outlet
group. Each cell of the outlet group shares cell walls only
with cells of the inlet group.
The walls within each of a plurality of transverse
sectors (e.g. annular or pie/wedge shaped) of the structure
or throughout the structure should beneficially have sub-
staunchly uniform thickness for substantially uniform
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filtration within the entirety respectively of such sectors
or whole structure to maximize continuous operating time.
Transverse cross-sectional cell density within the
structure should be generally at least about 1.5 cells/cm2
(preferably at least about 7.75 cells/cm2) for maximizing
filter surface area within a compact structure.
According to a further embodiment of the present
invention, the volume of interconnected open porosity in
the walls and the mean pore diameter of the pores forming
the open porosity lie uniquely within the area defined by
- the boundary line connecting points 1 2-3-4 in FIG. 8 (and
preferably connecting points 1-5-6-4 in that same figure).
; Such porosity and pore diameters are determined by convent
tonal mercury-intrusion porosimetry.
The walls within each of a plurality of transverse
sectors (e.g. annular or pie/wedge shaped) of top structure
or throughout the structure should beneficially have sub-
staunchly uniform thickness for substantially uniform
filtration within the entirety respectively of such sectors
or whole structure to maximize continuous operating time.
Transverse cross-sectional cell density within the
- structure should be generally at least about 1.5 cells/cm2
- (preferably at least about 7.75 cells/cm2) for maximizing
filter surface area within a compact structure.
As a material for making these products, it has been
found that sistered products characterized by full density,
having a cordierite crystal structure and low thermal
expansion coefficients, can be formed of manganese-containing
mineral batch compositions which comprise narrower compost-
tonal ranges than that disclosed in US. Patent 3,885,977.
It has further been discovered that the impervious
I
manganese-containing cordierite centrical product can be more
economically and more desirably manufactured where prereacted
cordierite material comprise at least 50 White (especially
50-95 White) of the ceramic batch materials.
This material provides an impervious, unglazed, sistered
manganese-containing ceramic product having its major and
primary crystal phase being cordierite crystal structure,
having a analytical molar composition ox about 1.7-2.4
ROW 1.9-2.4 AWOKE 4.5-5.2 Sue and made of mineral batch
composition selected from:
(a) wholly raw ceramic material wherein ROW comprises,
as mole. % of ROW about 55-95% Moo and 5-45% Moo, and
(by at least about 50 White prereacted cordierite
material and the balance whereof being raw ceramic material,
and wherein ROW comprises, as mole % of ROW about 5-40% Moo
and 60-95% Moo.
In toe case of invention products made of wholly raw
ceramic material, the more desirable products have ROW
proportioned as about 74-90. mole % Moo and 10-26 mole Moo.
In the case of invention products made of mixtures of
raw ceramic material and prereacted cordierite material,- the
more desirable products have ROW proportioned as about 6-15
mole. % Moo and 85-94 mole % Moo Moreover, it is preferable
to have to prereacted cordierite material be about 80-90
wt.% of the mineral batch composition.
For the most preferred Norm of the invention, its molar
composition is about 1.9-2~1 ROW o 1.9-2.1 Aye o 4.9-5 1 Sue.
When desired, Moo on the above formulations can be
partially replaced my other oxide such as No, Coo Leo
and/or Chihuahuas in toe manner described in US. Patent 3,885,977
(column. 2, Lyons. Accordingly, recital herein of Moo
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is intended to include such optional partial substitutions
in the present invention.
The products of this invention not only stinter to
impervious condition, but exhibit typical low coefficient
of thermal expansion (CUTE) on the order of about 15-20 x
10-7/C (25-1000C). They are particularly applicable to
the production of honeycomb structures by the methods of
US. Patents 3,790,654, 3,899,326, 3,900,546 and 3,919,384,
and to the manufac~llxe of ceramic cements for bonding or
plugging of cordierite honeycomb structures with similar low
Cues. In particular, the products of this invention in the
form of honeycomb structures are useful in constructing
industrial heat recovery wheels.
As a further aspect of this invention, a cement is
provided for bonding the aforedescribed products.
It was found that a formable particulate ceramic
cement capable of forming a sistered cordierite foamed
ceramic mass can be made by seeding ceramic base material
of controlled composition with cordierite grog of another
2C controlled composition and adding thereto a foaming agent
in an effective amount to effect foaming of the cement upon
firing to produce the foamed ceramic mass.
This cement consists essentially, by weight, of 1-40%
cordierite grog, 9q-60% ceramic base material and foaming
agent. The vase material Lo raw ceramic material that has
an analytical molar composition consisting essentially of
about 1.7-2.4 MO 1.2-2.4 Aye 4.5-5.4 Sue wherein MO
comprises, as mole % of MO, bout 0-55% Moo and at least
45% Noah The grog is ceramic material that has been
previously fired and commented, and thaw has an analytical
molar composition consisting essentially of about 1.7-2.4
10--
Skye
ROW 1.9-2.4 Aye 4.5-5.2 Sue wherein ROW comprises, as
mole of ROW Moo in an amount of I up to a mole % that
is about 20 mole % lower than the mole ox MO that it Moo
and the balance it substantially Moo. Minor portions ox
Moo it either or both of MO and ROW can be replaced by equal
molar amounts of other oxides such as No, Coo Foe and Shea
as noted in USE Patent 3,885,977~
Foaming agent can be selected from a
variety of substances that decompose to give of gas at
about the foaming temperature of the cement, i.e. the
temperature at which the grog and base material axe in
- a softened condition adequate to be foamed by the gas.
Among such substances are compounds such as carbides,
- carbonates, sulfates, etc., preferably of cations that
are in the grog and/or base material. Silicon carbide
it the preferred foaming agent and can be employed in any
effective amount (usually at least 0.25 White) up to a
; practical amount of about 5% my weight of grog plus base
material. Larger amounts can be employed without additional
benefit, but they dilute the amount of ceramic in the foamed
mass. Generally 1-2 wt.% tic (by weight of grog plus base
material) is preferred.
To insure thorough cordierite crystallization in the
foamed ceramic masses, it is advantageous for the grog in
the cement to be at least 5 White and correspondingly for
the base material to not exceed 95 White. Preferred pro-
portions are 5-20 wt.% grog and 95-80 wt.% base material.
While the invention can broadly utilize base combo-
sessions within the aforesaid molar composition range
embracing both the stoichiometric cordierite area and the
nonstoichrometric eutectic cordierite area, it is preferred
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to use base compositions of the generally stoichiometric
type having an analytical molar composition consisting
essentially of about 1.7-2.4 MO 1.9-2.4 Aye 4.5-5.2
Sue wherein MO is as previously stated. Most preferably,
such molar composition is about 1.8-2.1 MO 1.9-2.1 Aye
4.9-5.2 Sue and MO is wholly Moo.
The requisite minimum difference of about 20 mole for
Moo in MO and ROW provides the grog with adequately higher
melting point vise a vise melting point of the base material
so as to insure proper cordierite crystallization seeding
effect by the grog at foaming temperature. To enhance such
effect, it is preferred to have MO of the base composition
comprise not more than about 15 mole % Moo.
`- The most preferable grog has an analytical composition
of about 1.8-2.1 ROW 1.9-2.1 Aye 4.9~5.2 Sue, and JO
comprises 8-12 mole % Moo and the balance go.
If desired, optional customary fluxes may be included
; in the cement in minor amounts up to 5 wt.% or so of the
: .
: grog plus assay material. Such fluxes are illustratively
disclosed in US. Patents 3,189,512 and 3,634tlll.
- The present invention also encompasses ceramic structures
embodying the novel sistered cordierite foamed ceramic mass
and the method providing suck mass in the structures. The
structure broadly comprises at least two closely spaced
cordierit~ ceramic surfaces hazing the mass in the space
between and bonded to those surfaces. In the method, the
cement it disposed between such surfaces, then the structure
with the cement so disposed is fired to foaming temperature
in the range of about 1160-1325C and thereafter cooled with
to cement converted to the foamed ceramic mass. Preferably
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the foaming temperature is in the range ox 1170-1250C,
especially for attaining foamed ceramic mass that it sub Stan-
tidally impervious to fluids. Lower temperatures Hall to
develop an adequate foaming of the cement. Also, it it
desirable to fire to the foaming temperature at an average
fate of at least about 100C per hour (preferably at least
about 200C per hour) to avoid the possible adverse effect
of much slower (e.g. cry.) heating rates that may cause
loss of foaming agent gas before the ceramic constituents
lo of the cement are soft enough to be foamed.
grief Description of Drawn s
FIG. 1 is a partially broken away, oblique view of a
- preferred embodiment of a filter body according to the
present invention.
FIG. 2 is a sectional view taken in each plane India
acted by each of the line and arrows A-A and the line and
arrows B-B of FIG. 1.
- FIGS. 3-6 inclusive are views of the end faces of four
alternative embodiments of filter bodies according to the
present invention, which bodies have different transverse
cross-sectional cell geometries ox shapes.
FIG. 7 is a longitudinal sectional view through a
filter apparatus according to the present invention for
filtration of particulate from diesel engine exhaust gas.
FIG. 8 is a graphical representation of the combined
open porosity and mean pore size of filters according to the
present invention. It includes, as the best mode of carrying
out the present generic invention with respect to filters in
diesel engine exhaust conduits or systems, an indication of
unique combinations of open porosity and mean pore size
I
I
FOE 9 is a longitudinal sectional view through a
; filter chamber according to the present invention for
filtration of particulate or entrained solids from molten
metals.
IT. 10 is a schematic illustration of a rotatable
heat exchanger or heat recovery wheel assembly with filter
structure according to the present invention.
'-'
: Detailed Description
. .
The filter body 1 shown in FIG. 1 comprises a cellular
or honeycomb structure (monolith) which has a matrix of
intersecting, uniformly thin walls 2 defining a plurality of
cells 3. The Silas extend longitudinally and mutually
parallel through thy body 1 between the inlet end face 4
- and the outlet end face 5. Ordinarily the body 1 also has
a peripheral wall or skin 6.. An inlet group of alternate
cells 7 are open at the inlet end face 4 and are closed,
: sealed or plugged with closure means 8 adjacent outlet end
- face 5. Means 8 can be a seal nut or cement mass adhering to
walls 2 and extending from face 5 a short distance inwardly
Jo end face 2 of means 8. The other alternate cells 10 form
an outlet group and are open at outlet end face S, but they
are similarly closed adjacent inlet end face 4 by closure
means 11, which likewise extend inwardly a short distance
from face 4 to end face I of means 11. Thus, as viewed at
14-
I
end races 4 and 5, the alternating open and closed cells are
in a checkered or checkerboard patkernO
Body 1, including means 8 and 11, can be mode ox any
suitable materials such that walls 2 have the requisite
interconnected open porosity therein and means 8, 11 are
generally Impermeable to fluids. Such materials may include
ceramics (generally crystalline), glass-ceramics, glasses,
- metals, cermets, resins or organic polymers, papers or
textile fabrics. (with or without fillers, etc. and come
binations thereof. For walls 2 and skin 6, it is preferred
to fabricate them from plastically formable and sinterable
finely divided particles and/or short length fibers of
substances that yield a porous sistered material after being
fired to effect sistering thereof, especially ceramics,
glass-ceramics, glasses, metals and/or swarms. As desired
(besides volatizable plasticizers/binders for the formable
particle batch or mixture, any suitable or conventional
fugitive or combustible urinate additive can be dispersed
within the formable and sinterable mixture so as to provide
appropriate and adequate open porosity in the sistered
material of walls 2. Moreover, the requisite open porosity
can also be designed into walls 2 by raw material selection
. as described in US. Potent.
The Cody 1 can be fabricated by any suitable technique.
It (without plugs 8 and 11~ is made preferably by extrusion
of a sînterable mixture in the manner as disclosed in US.
Patents, 3,919,384 and 4,008,033. Such extruded
green honeycomb body is then fired for effecting the sistered
condition thereof in the manner as disclosed in US. Patent
30 3,8~9,3~6.
Plug means 8,11 can then ye formed in the sistered
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I
monolith 1 by injecting a sinterable or other suitable
sealant mixture into the appropriate ends of the cells 3.
For example such mixture can be injected by moans ox a
pressurized air actuated sealant gun whose nozzle can be
positioned at the proper cell openings on the end faces 4,5
so as to extrude the mixture Unto and to plug the end
portions of the cells. An appropriate assembly and post-
toning of an array of sealant nozzles of such gun(s) can he
used to inject the plug mixture simultaneously in a plurality
or all of the alternate cells at Mach face 4,5 for efficient
production. Upon subsequent f irking of the body 1 after
-; having teen plugged with a sinterable or other heat-setting
mixture, there results rigid if ted closure masses 8,11 which
are adherently bonded to adjacent portions of walls 2.
These plugs 8,11 are substantially nonpermeable to the fluid
to be pasted through filter 1.
If so desired, the monolith 1 need not necessarily be
fired or sistered before injecting sealant mixture, especially
ceramic cement, into the ends of the cells 3. For example,
monolith 1 can be made of ceramic material having a firing
- temperature thaw is substantially the same as or closely
similar to the firing or foaming temperature of an appropri-
lately selected ceramic cement. In that case, the cement can
be injected into the cell ends while the monolith is in the
- unfired or groaner state. Thereafter the green monolith
with green cement plugs is fired to suitable temperature or
temperatures within the appropriate range to effect sistering
of toe monolith and of the cement (including foaming thereof
if that it a characteristic of it
JIG. 2 shows the pattern of fluid flow through filter
1 in Roth a vertical column ox cells 3 (in plane A-A of FIG.
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1) and a horizontal column ox cells 3 (in plane B-B ox FIG.
1). Fluid flow is indicated by the lines 13 with arrows.
Thus, fluid 13 passes into inlet cells 7 from inlet end race
I, but because of the blocking effect of end faces 9 of
plugs 8, the fluid under some pressure then passes through
the pores or open porosity in cell walls 2 at top, bottom
and both sides of the cells 7 so as to respectively enter
outlet cells 10 above, below and on Roth sides of each cell
7. While fluid 13 passes through the entirety of all cell
walls 2, their porosity is such as to restrain particulate
therein and thereon as a porous accumulation which may even
fill up all of cells 7 before replacement of the filter 1).
,
It can be seen that the entirety of all cell walls 2 act as
filters for unique superior filter capability. The fluid
13 passing into cells 10 then flows out of these cells at
the outlet end face 5, since the end faces 12 of plugs 11
adjacent the inlet end face 4 prevents the fluid from
reversing direction. Also, plugs 11 prevent fluid 13 from
directly entering cells I without first going into cells
7 and through walls 2.
While it is preferred to make the transverse cross-
sectional geometry of the cells 3 to be squares as shown in
FIG. 1, any other suite to geometries Jay be employed.
Examples of such other geometries are shown in FIGS. 3-6~ In
FIG. 3, cells pa are in the transverse geometrical form of
equilateral triangle, but they could also have the form of
right triangles. FIG. 4 shows cells 3b with transverse
cross-sectional geometry of rhomboids, which could optionally
be made as rhombuses. Similarly, rectangles can form the
transverse cell geometry instead of squares. A less easily
manufactured transverse cell geometry is shown in FIG. 5,
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Sue
which constitutes a repeating pattern of quadrilateral of
cells 3c. In each of these polygonal shapes, intersecting
walls 2 preferably form include angles what are not less
than 60 to avoid the nonuniform accumulation of particulate
in smaller angle corners and to enable proper complete
plugging of the alternate cells adjacent end faces 4,5.
Also, it may be desirable for enhanced mechanical strength
of the honeycomb filter bodies that the cell corners be
filleted or slightly filled in with the same or similar
material as forms cell walls 2. what latter concept can be
extended to a presently lesser desirable form as shown in
FIG. 6, wherein cell Ed have a circular transverse geometry.
. The walls 2 have a substantially uniform thickness throughout
- in that they substantially uniformly vary from their thinnest
. portions pa to their thicker (or maximum filleted) portions
2b. Another alternative to the latter one would be elliptical
transverse cell geometry. If it is desired for certain
purposes, the filter Cody can be made with a plurality of
transverse sectors (eye. annular or pie/wedge shaped) whereby
the transverse cell cross-sectional axes are larger in a
sector or sectors than such areas are in another sectcx or
other sectors. It is even conceivable that repeating patterns
.-. of different transverse geometric cell shapes can be employed
in different transverse sectors.
In all variations of the filter body with respect to
transverse cell geometry, alternate cells are plugged
adjacent each end face in a checkered style pattern such
that those cells plugged at the inlet end face are open at
toe outlet end face and vice versa. Also, the transverse
cross-sectional areas of such cells are desirably sized to
provide transverse cell densities in the range of about 2-93
-18-
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cells/cm2. Correspondingly, it it desirable to make the
thin walls with thickness in the range of about 0.05-1.27 mm.
One embodiment of the present invention is a filter
apparatus for removing carbonaceous particulate from
diesel engine exhaust gas so as to avoid air pollution by
such paxticulates, which individually can tango in size from
about 5 micrometers down to and below 0.05 micrometer. FIG.
7 shows an exemplary form of such apparatus, which comprises
the filter body 1 held within a container or can 20. Body 1
10 is the same as. that shown in FIG. 1, with skin 6, inlet
cells 7 extending from inlet end face 4 and blocked by plugs
8, and outlet cells 10 open at outlet end face 5. Can 20
is similar to a conventional type of can (see US. Patent
3,441,381) employed for mounting catalytic converter honey-
- comb substrates in exhaust systems of internal combustion
engines. The can 20 comprises two parts 21,22 respectively
formed of filter-holding portions 23,24, conduit-connectors
- 25,26, conical portions 27,28, respectively joining connectors
~5,26 to portions 23,24, and mating flanges 29,30 which are
- 20 mechanically fastened together ego. by bolts and nuts not
shown to keep the can properly assembled for use and so as
to capahle.of being unfastened in order to open the can
20 for replacement ox filter body 1. Internal annular
mounting mummers ox L shaped cross-section are respect
lively fastened to portions 23,24 so as to respectively abut
against faces 4,5 and. hold body 1 in its proper fixed axial
position within can 20. To cushion body 1 against mechanical
shock and vibration, it is ordinarily desirable to surround
body 1 with a wrapping or mat 33 ox metal mesh, refractory
fiber and thy like, which may fill the annular space between
body 1 and portions 23,24. To minimize heat loss from body
--19--
~Z?d~8~
1 and excessive heating of portions 23,24, a layer of
insulating material 34, such as glass or mineral wool mat,
may also be wrapped around body 1.
Connectors 25,26 are suitably fastened (e.g. by welding
or casketed mechanical coupling) to exhaust gas conduit of a
diesel engine. While can 20 can be located in and form part
of the exhaust gas conduit some distance downstream for the
. engine exhaust manifold, it can desirably be located near or
at the exit from the exhaust manifold. The latter arrangement
facilitates regeneration of filter body 1 by utilizing the
. higher temperature of the exhaust gas upon exiting the
- exhaust manifold to cause, with excess air in the gas, the
.: combustion of carbonaceous particulate restrained in body 1
to form further gaseous combustion products that can then
pass on through and out of body 1 for emission through
connector 25 to the tailpipe (not shown) fastened to connector
26. If desirable (especially when can 20 is located downstream
along the exhaust conduit some distance from the exhaust
- manifold, a combustion ignition device may be positioned in
I 20 can 20, such as a glow plug in conical portion I or an
electric heater within the central axis ox body 1 (similar
to the device of US. Potent), and secondary air
may be injected into can 20 upstream from body 1 to assist
in regeneration of Cody 1 without removing it from can 20.
Additionally, catalyst substance can be placed on and in
walls 2 ox Cody 1 (similar to catalytic converter honeycomb
substrates) to facilitate regeneration of combustion in body 1.
In ordinary usage, frequent higher speed or rum of the
diesel engine can contribute sufficient heat (e.g. 400-500C
or higher) to cause repetitive regeneration combustion of
body 1 without rewiring the can 20 to be opened often for
-20-
I
replacement of body 1. Nevertheless;, removed bodies 1 can
be reverse flushed with air to how much of the particulate
out of it into a collector bag and when fully regenerated by
high temperature air passed through it before reinstalling
in can 20.
In a further embodiment of the invention, the volume of
interconnected open porosity and the mean diameter of the
pores forming the open porosity lie within the area defined
by the boundary lines connecting points 1-2-3-4 in FIG. 8 of
the drawings..
. In a preferred embodiment, the walls are not more than
about 1.5 mm thick, the volume of interconnected open porosity
and the mean diameter of the pores forming the open porosity
lie within the area defined by the boundary lines connecting
point 1-5-6-4 in FIG. 8 of the drawings, and the structure
for a transverse cross-sectional cell density of at least
about 1.5 cells/cm2.
In further advantageous embodiments, the walls are not
less than about 0.3 mm thick, even more preferably not more
than about 0.635 mm thick, and the cell density is at least
about 7.75 cells/cm2.
Dense cordierite swineherd structures for these and other
I- products are achieved my the partial substitution of Moo for
Moo in the cordierite crystal structure within controlled
-. amounts. That substitution greatly increases the sinterability
of thy cordierite watch materials my lowering and widening
the sistering temperature range at which full density can be
achieved. In general, the sistering of mineral batch come
positions comprise of wholly raw ceramic materials to lull
density occurred at about 1200-1300C, whereas mineral batch
compositions containing prereacted cordierite material
-21-
I
sistered to impervious conditions at about 1250-1410C.
Also, when prereacted cordierite material is included in the
mineral batch composition, the minimum weight percent manganese
oxide necessary to form the impervious product is about 0.6
wt.%, as compared to a minimum of about 12.6 White for the
mineral batch composition with wholly raw ceramic materials.
Therefore, the benefits of utilizing the mineral batch
compositions containing prereacted cordierite material are
that a more refractory product is produced (similar to
regular cordierite without manganese oxide) and that lesser
amounts of m nganese oxide are required to effect full
density. Furthermore, less firing shrinkage is generally
experienced with the mineral batch compositions containing
prereacted cordierite material.
Full density either is unattainable or cannot be
reliably attained with mineral batch compositions which
either have wholly raw batch material and too little molar
proportion of Moo (i.e. less than 55 mote % of ROW), or which
contain prereacted cordierite material in amounts which are
too small it less than 50 wt.% of the mineral batch
composition, or which contain at least about 50 White
prereacted cordierite material while having a mole proper-
lion of Moo outside the range of 5-40% of ROW The mineral
batch composition of wholly prereacted cordierite material
can be fired to full density at about 1410C, but it requires
extra expense of thoroughly fine grinding of such batch
material prior to shaping and firing it into impervious product.
Impervious sistered products of the invention may
contain minor amounts of phases other than the primary
cordierite phase as may occur within the molar compositional
limits defined avow.
I
As used in the foregoing description of the tense
cordierite ceramic of the present invention:
(a) "full density" and "impervious" mean the condition
of a ceramic body whereby it exhibits leer than 1% by volume
of open porosity as determined either by the conventional
mercury porosimetry test or by the toiling water test for
apparent porosity generally as defined in ASTM Designation
C20-7Q effective January 22, 19~0, both of which give Essex-
tidally the same results for products of the invention stated
herein;
(b) "raw" means the condition of ceramic batch material
which is not prereacted with another batch ingredient, but
- which may have been individually calcined or fired without
melting thereof or otherwise is unfired;
(c) "prereacted" means the condition of ceramic batch
material which has been formed by reaction between two or
more raw ,~aterïals with, at most, melting of only minor
portions thereof; and
(do "mineral batch composition" means a ceramic batch
composition in which all of the ceramic material is raw
and/or prereacted.
Examples
Cordierite ceramic materials of the type disclosed in
US. Patent 3,885,~77 and Alec are generally preferred
for diesel particulate trap filters because, as was earlier
found for their use as catalyst substrates in internal
combustion engine exhaust systems, these material have
properties that enable them to withstand and be durable
under the thermal, chemical and physical conditions to which
they are subjected in such systems including those of diesel
-23-
~LZ~78~1
engines. A series of filter honeycomb samples with square
cross-section cells were extruded of cordierite batch come
; positions as set forth in TALE 1. Those samples were then
dried and fired generally in accordance with the following
typical firing schedule:
-24
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80C to 1425C within about 60 hours.
told about 10 hours at 1~25C.
Cool 1425~C to room temperature within
about 24 hours.
The walls of the as-fired samples had typical open porosity
and mean pore diameters as set forth in TABLE 2, which
varied among the samples with particular relation to vane-
lion in the graphite (as burn-out material) and talc used
in the batch compositions.
TABLE 2
Open Porosity Mean Pore Diameter
Samples volume % micrometers
. A 35 4
B 44.5 9
C 41.3 10
D 48.0 11
- E 48.5 13
F 47~7 13
G 46.8 12
H 6~.6 11
I 65.8 15
: J 3~.8 35
X 37.2 35
L 36.7 23
M 44.7 22
N 54.6 6
Plugs were formed in the end portions of alternate
cells, as previously descried, of the sistered samples by
injecting a plastically formable ceramic cement into such
cell ends with an air-operated sealant gun. The amount of
I
I I
plugging cement injected into the cell ends was controlled
by measuring the time that operative air pressure was applied
to the sealant gun. By this means, the cement plugs were
generally made with a depth or length into the cell from
- an end face thereof in the range of about 9.5-13 mm.
A preferred plugging cement employed with the foregoing
samples was the manganese-magnesium cordierite foam type of
this invention. In particular, the preferred foam cement
used in the above-noted samples had the batch composition
lo in accordance with Sample 6 of TARE lo further below. The
previously fired samples with the injected cement plugs
; were then fired generally in accordance with the following.
- The Mn-Mg cordierite grog in the cement batch was the dense
cordierite containing manganese in accordance with the
present invention In particular, the grog was made of the
following batch composition (in weight of the total
ceramic raw materials:
Sample A grog L-2Qo mesh 84.48
Georgia-Kaolin Xaopaque lo clay ZAPS 10) Lowe
ED Baker MnCO3 power 4~15
- Penn. Glass Sand Mainsail silica UPS 5) 0.78
` Pfizer MY ~6~28 talc UPS 20~ 0.59
Methyl cellulose ~inder/plasticizer4.0
Alkali Stewart extrusion aid 0.5
Distilled water plasticizer 26.0
This Mn-Mg cordierite grog was fired generally in accordance
with the same firing schedule as for Sample A, except that
the maximum temperature was 1405C instead of 1425C.
The previously fired samples with the injected cement
plugs, as noted above, were fired generally in accordance
with the following typical firing schedule:
-27-
~Z7~
Room temperature to 1210C within about 6 hours.
Hold about 30 minutes at 1210C.
Cool 1210C to room t~perature within about 18 hours.
The cement foamed during firing to develop good sealing to
the cell walls and generally fluid impervious plugs. The
foaming action counteracts normal drying and firing shrink-
age of an otherwise non foaming ceramic cement.
While the previously mentioned foam cement is preferred
for worming the plug, other suitable foaming and nonoaming
ceramic cements may be used. Even non ceramic cements or
sealants may be used if they are capable of being durable
under exhaust system conditions of heat as well as chemical
and physical abuse.
The filter samples made as described above, and having
- various cell densities, wall thicknesses and external
dimensions (diameter and length), were tested in the exhaust
- system of a 1980 Oldsmobile 350 CID (cubic inch displacement)
diesel V-8 engine operated with a water brake dynamometers at
-- constant conditions ox spend and load. A dri~eshaft speed
of lOOOrpm was used, which was equivalent to a vehicle road
speed of 40mph ~64 km per ho A load of 100 ills
(approx. 136 joylessly torque was used, which was equivalent
to higher than basic vehicle road load at steady 40 mph
(64 km per ho speed on a horizontally level road surface.
This higher than basic road load provided more realistic
exhaust particulate volume per unit time with respect to
the fact that actual or commonly experienced road loads are
ordinarily higher than basic road loads because of phlox- -
lions in acceleration and variations in road surfaces from
toe revel condition. Thy engine was warmed up to normal
operating temperature before beginning the tests of the
-28-
~.2Z~
filter samples.
The filter cans were located about 2.1 meter downstream
from the engine exhaust manifold. Exhaust gas flow rate
through each filter placed in the can (from only four
engine cylinders) was approximately constant in the range
of about 1.0-l.l cubic meters per minute. Back pressures
callused by or pressure drops across) the filter samples were
measured by water manometer and were monitored during the
tests from an initial level up to the time they rose to 140
cm of water, at which time the test were discontinued
because higher back pressure has been determined by the
engine manufacturer to ye unacceptable for proper engine
operation. Thus, when the pressure drop across the filter
retches 14Q cm of water, the filter has attained its maximum
effective filter capacity in a single operation in the noted
system. The total time from the beginning of the test (with
the exhaust gas started through the filter) until the filter
Jack pressure becomes 140 cm of water is referred to as the
Operating Tome of the filter.
- 20 Exhaust gas samples were taken downstream of the
filter can. Without any filter in the can, the amount of
part~culates in the total unfiltered exhaust gas (in terms
of grams per mile or g~mi.~ were calculated from the amount
of partlculates measured in an unfiltered gas sample. This
amount of particulate - called the Baseline Particulate -
was found to haze negligible variation over a range of back
pressures exerted on the system up to 14~ cm of water. The
Baseline Partïculates ranged between 0.17 gamin and 0.24
gamin in the various tests. With a filter in the can, the
amount ox Residual Particulate in the total filtered exhaust
gas (it terms of g~mi.~ were calculated from the amount
--2g--
` ~2;~'78~
of particulate measured in a filtered gas sample. The
difference between the Baseline Particulate and the
Residual Particulate as a percent of the Baseline Portico-
fates is referred to as the calculated Filter Efficiency.
Incidentally, the Filter Efficiency in terms of the weight
gain of the filter during a test (i.e. the gain over the
initial untested filter weight) as a percent of the Baseline
Particulate for the same test agreed closely with the
above-noted calculated Filter Efficiency.
TABLE 3 sets forth the initial pressure drop, Operating
Time and Filter Efficiency for a series of tested filter
samples having a square cell density of 15.5 cells/cm2,
external dimensions of about 9.3 cm diameter and 30.5 cm
length, and wall thickness as indicated in that table. In
most cases for a given wall thickness, two filters of the
same sample honeycomb body were tested.
. .
-30-
:
TABLE 3
Wall
Thickness 0.432 0.635
.
',
Sample B 30.2/14.2 35.0/34.5 39.8/34.5
Sample D 29.4/24.8 28.2 40.5/29.7
Sample H 24.6/20.9 20.0/16.. 3 30.1
Sample I - 11.6/10.0
Sample J 6.2/7.3 - 15.7/16.8
Sample K 8.1/8.0 9,5/9.9 17.4/17.6
Sample L 12.7 19.0/17.2 24.0/21.3
Sample M ho 0/11~ 7 29.0/23.7 23.4/21.7
Sample N 20.8/23.7 - 28.6/27.9
Operating Time (hours)
-
Sample C 2.01/2.20 2.39/2.04 1.18/1.48
Sample-D 3.40/3.8 3.17 1.89/2.3
Sample H 3.60/5.0 3,20/4.30 3.30
Smut I 4,50/4,90
Sample J 18.0~/16.6 - 5.90/4.30
Sample K 8.80/11.3 5.40/5.70 2.17/3.00
Sample 6.00 1.80/2.16 1.32/1.5;
Sample M 7.80/8.50 2.67/3.00 1.39/1.78
Sample N 3.5~/3060 3~00/3.30 2.40/2.60
-31
I
Filter Efficie~y (~)
Sample B - 91.3/95.0
Sample C 95.9/~6.0 95.8/97.8 97.0/~8.2
Sample D 94.6/95.3 96.0 94.6/95.0
Sample H 84~3/80.9 86.8/89.0 87.0
Sample I - 69.7/60.1
Sample J 51.2/41.~ 64.0/6Z.6
Sample K 57.5/46.4 66.8/62.3 78.1/77.6
: 10 Sample L 67.8 85.8/86.1 85.3/89.4
Sample M 66.8/70.3 87.0/84.9 88.4/87.6
Sample N ~6.3/96.2 98.0~97.0 98.3/98.8
-............... Preferred as the most practical filters, based on the
foregoing tests, are those which have an average Filter
Efficiency of at least 75% and a minimum average Operating
Tome of three hours. The data of TABLE 3 show samples D, H.
and N to fit this preferred category, which is more generally
defined in FIG. 8 by the area 1234 and by the most preferred
area 1564 (represented my the undoer lines connecting
those numbered points with coordinate values as follows):
.
: Coordinates
Point pen Porosity mean Pore Dime or us
1 58.5
2 33.Q 20
3 5~-5 20
4 9Q.0
3~.5 15
62.Q 15
32-
~2~7~
Thus, the preferred category of filters or diesel exhaust
systems have an optimum balance of open porosity and mean
pore diameter.
The preceding test data also show a tendency for
reduced Operat~lg Time when maximiz1n~ Filter Efficiency
in filters of a given external size and cell density.
However, it has been found that Operating Time is directly
proportional to the filter surface area. To avoid come
promise of Filter Efficiency, Operating Tome can be increased
10 by increasing cell density and/or external size.
- The test data of TABLE 4 (derived from the same test
previously described) illustrate the effect of increasing
cell density and of increasing external size on Operating
Time of the filters with wall thickness of 0.305 mm and a
- diameter of about 9.3 cm. Typical initial Jack pressures of
those filters with square cell densities of 31 and 46.5
cells/cm2 were respectively 14.1/lQ.5 and 15.7 cm of
water. Live Sample D, Samples E and F also are within the
preferred category of filters indicated by FIG. 8. While
- I no actual test data was obtained for a Sample F filter with
- more than 1 my of filter surface aria, it is evlden~ from
the presented data that such larger Sample F filter would
- have an Operating Time in excess of three hours.
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--34--
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A further illustration of larger filter suffice area
providing greater Operating Time I the test results with a
Sample D filter having a square cell density of 15.5 cells/cm
a diameter of about 14.4 cm, a length of about 30.5 cm and
wall thickness of about 0.432 mm. Its jilter surface area
was 3.03 my. The filter had an initial back pressure of 3~0
cm of water. It exhibited a Filter Efficiency of 79~ and
an Operating Time of 23.1 hours.
The tested filter samples were examined for the con-
10 diction of accumulated particulate that generally completely
filled such filters. No significant differences in the
amount of particulate were seen with respect to varying
radial and axially positions in the filters These results
are believed to be in significant part due to lack of lower
angle corners in the geometric transverse square shapes of
- the cell in those filter samples. Further, the packed
densities of the accumulated particulate were estimated to
be relatively constant throughout the filter samples -
- being in the range of Owe g/cm3 for samples with about
20 9.3 cm diameter and 30.5 cm length and about Owe g/cm3 for
the sample with about 14.4 cm diameter and 30.5 cm length.
-I Moreover, it was observed that the accumulation of
- particulate in the filter samples has a restage effect
on filter pressure drop. The first stage involves a fairly
substantial steady rise in pressure drop. It is hollowed
by a second stage during which the pressure drop rises at a
much lower rate. Finally in a third stage (apparently when
fluid flow paths through the accumulated particulate are
being fully blocked), the rise in pressure drop accelerates
30 again to a much higher rate. All three stages can usually
be observed in toe larger samples with 14.4 em diameter and
-35-
~LZ2~
.
30.5 cm length. however, the smaller samples often showed
only either the first and second stages or the first stage
before the pressure drop reached 140 cm of water.
The effects of lower cell density were demonstrated
with Samples G of filters having square cell density of
about 7.75 cells/cm2 and wall thickness of about 0.635 mm.
Their approximate external dimensions and jest results are
set forth in TABLE 5. Those results show that lower cell
density tends to decrease Operating Time because of lower
filter surface area, but that such tendency can be offset by
employing larger external dimensions As indicated in FIG.
8, Sample G is also within the preferred category of filters.
..'
TUBULE
Diameter Length Filter Operating
cm cm Effic eons Time-hours
go 30.5 95.0 1.35
- 9.3 30.5 96.~ 1.73
14.4 I 93.3 14.7
A Sample A filter was also made with cell density of
about 7.75 cells/cm2, wall thickness of about 0.635 mm,
diameter of about 14.9 cm and length of about OWE cm. It
had a fairly high initial pressure drop indicative of pro-
voiding too little Operating Time. However, improved Operating
Time could be obtained with Sample A filters by increasing
cell density Andre external dimensions.
MOLTEN METAL FILTERS
Another embodiment of the present invention is a
filter apparatus for removing entrained solid particulate
from molten metal ego. aluminum prior to casting it into
-36-
~227~
a solid body or ingot and so as to avoid defects in the cast
metal products caused by such particulate trapped herein.
Such particulate can be of the individual size order of
10-20 micrometers. FIG. 9 shows an exemplary form of such
apparatus, which comprises the filter body 40 (of the type
shown in FIGS. 1 and 21 held within a molten metal filtration
chamber 41 (of the type discussed in US. Patent 4,024,056).
Chamber 41
comprises an inlet portion 42 and an outlet portion 43
separated by an intermediate refractory wall 44. Allah 44
- joins with a base portion 45 connected to and forming part
of floor 46 of inlet portion 42. Portion 45 contains an
aperture 47 for passage of molten metal from the inlet
portion 42 into outlet portion 43. Filter 40 is interposed
across aperture 47 such that the inlet face 48 of jilter 40
(which corresponds to inlet face end 4 of filter body 1 in
FIGS . 1 and 2 ) faces upstream of the molten metal flow path
- through aperture 47, viz. into inlet portion 42. Outlet
portion 43 has a floor I which is lower than inlet floor 46
20 to facilitate flow of molten metal through aperture 47 via
the filter 40. Conventional staling means 50 replaceable
holds and seals filter 4Q within aperture 47 so that all of
the molten metal passes through filter 40 from inlet portion
42 to outlet portion 43 and that, when it becomes substantially
filled and clogged wit entrained solids, filter 40 can be
readily replaced with a new like filter. Thus, unfiltered
molten metal enters inlet portion 42 via pouring spout 51
and the filtered metal exits from filter 40 into outlet
portion 43. Filter I has plugs 52 and 53 in alternate cell
ends respectively adjacent to the inlet and outlet faces of
the filter in the same manner as shown in FIGS . 1 and 2.
-37-
2~7~
As an example ox this embodiment of the present invent
lion, a molten aluminum filtration chamber is employed in a
modified form from that described above to contain a filter,
between inlet and outlet portions of the modified chamber,
which has a diameter of about 14.6 cm and a length of about
15.2 cm. The filter is like that of Sample C with square
cell density of about 7.75 cells/cm and wall thickness of
about 0.635 mm. Upon completion of a casting run, this
filter is removed and discarded, and then replaced with a
lo n w like filter.
Preferably the above-described filter is made of
thermal shock resistant, micro cracked type of ceramics
having good corrosion/erosion resistance to molten aluminum
- in addition to the requisite porosity in the walls of the
; filter. Such ceramics include zirconia-spinel ceramics,
aluminum titan ate based ceramics, etc., with a particularly
desirable one being, by weight, 60% zircon phase and
40% magnesium acuminate spinet phase.
HEAT RECOVERY WISE
A further embodiment of the present invention is a
heat exchange assembly involving a rotatable honeycomb heat
recovery (or exchange wheel for absorbing heat from one
fluid stream and Imparting such heat to another fluid
stream. According to the present invention, the coven
tonal heat recovery wheel is modified to additionally act
as a filter ox particulate suspended in such fluids. FIG.
10 schematically shows the conventional assembly with the
heat recovery wheel 60 in modified form (similar to filter
Cody l of PHASE 1 and 21 Jo function as a filter as previously
discord Wheel I rotates within and across two fluid
-38-
I
flow paths within a heat exchange chamber and separated by
conventional robing seal and duct structure 62. As shown,
a first fluid passes sequentially through a pair of ducts
- (as indicated by arrows) with the wheel 60 interposed between
those ducts and their fluid flow paths. The cooler first
fluid passes from one duct into the slowly rotating honeycomb
wheel 60, absorbs heat from the wheel as it passes through
. it and then continues as heated first fluid flowing through
the second duct downstream of the wheel 60. A second fluid
passes sequentially trough another pair of ducts (as India
acted by arrows with the wheel 60 interposed between those
ducts and their fluid flow paths. The hotter second fluid
passes from one duct into the slowly rotating honeycomb wheel
60, gives up heat to the wheel as it passes through it and
then continues as cooled second fluid flowing through the
second duct downstream of the wheel 60. Thus, each of the
faces 63 and 64 of wheel 60 alternately function as inlet
and outlet faces as wheel 60 rotates between the first and
second fluid' flow paths, which faces 63 and 64 are facing
the fluid flow directions from and to the ducts. Wheel 60
- also constitutes the filter with thin cell walls 65 defining
Jo two sets of alternate cells - cells 66 open at face 63 and
the other cells closed adjacent face 63 by plugs 67. A
: reverse arrangement exists at and adjacent face 64.
eat recovery wheel 60 is typically employed for risque
lying heat from a second fluid which is an exhaust gas of a
combustion system, such as an internal combustion engine
system or an industrial furnace system. By the last men-
toned embodiment of the present invention, the filter heat
recovery wheel 60 will remove particulate entrained in the
second fluid. Then, as the wheel 60 rotates a sector of the
-39-
~L227~
wheel from the second fluid flow path to the first fluid
flow path, air for the combustion system passes through the
same sector of wheel 60, but in a direction opposite of the
second fluid, to pick up heat from it (thereby becoming
preheated air) and to blow the particulate collected in
such sector of wheel 60 back through the combustion system
to ye oxidized into gaseous species or a smaller particulate
form. Moreover, the filter wheel 60 may also serve to
filter particulate from incoming air and to exhaust such
accumulated particulate with cooled exhaust gas from the
combustion system.
; Although the impervious products of the invention can
- be fabricated into a variety of forms by any of the usual
or known ceramic forming techniques, a series of samples of
the invention as noted in TABLES 6 and 8 were made in the
preferred form of honeycomb structures by the previously
noted method of extrusion and firing. The batch ceramic
- materials were dry blended with (as White of the total ceramic
materials therein) 4.Q~ methyl cellulose plasticizer/
winder and 0.5~ alkali Stewart extrusion aid. Those
mixtures were plasticized with the water in a mix-muller,
and further plasticized and desired by pre-extrusion into
spaghetti-like masses. Then the fully plasticized and
compacted batches were extruded in honeycomb green shapes,
dried and fired.
TABLES 6 and 8 also set forth the analytical molar
compositions as calculated from the batch ceramic materials.
TALE 7 sets forth the sistering temperatures, firing
shrinkages and Cues for the Samples 1-4 of TABLE 6 made of
mineral batch compositions with wholly raw ceramic materials
and exiting less than 1% by volume of open porosity.
-40-
ZOO
Such temperatures were the approx~late lowest temperatures
for full density.
-41-
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TABLE 7
Sistering FiringCTE x 10-7/C
Sample Temperature C Shrunk C_
1 1285 13.2 17.5
2 1300 19.7 19.7
3 1200 12.0 16.4
4 1200 19.4 18.4
In contrast to Samples 1-4, other similarly prepared
samples with wholly raw ceramic materials, but not within
this invention because of having molar proportions of Moo
that were 50 mole % or less of ROW failed to develop full
density at sinteriny temperatures that did not cause over-
firing. For example, a sample with the analytical molar
composition of about 0.8 Moo lo 2 Moo AYE 5 Sue
(wherein Moo is 40 mole of ROW exhibited 47% by volume
of open porosity after hying fired at sistering tempera-
lure of 124QC.
-43-
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The Samples 5~9 in Table 8 illustrate the mineral batch
compositions of the invention containing prereact~d cordierite
material. Prereacted cordierite material #l is essentially
the same as fired composition F in US. Patent 3,885,977,
but in crushed and ground particulate form. Prereacted
cordierite material #2 is essentially the same as fired
Composition 804 in US. Patent 4,001,028, but in crushed and
ground particulate form.
Table q sets forth the sistering temperatures, firing
shrinkages and Cues for the Samples 5-9 of Table 8 exhibiting
less than 1% by volume of open porosity. Such temperatures
were the approximate lowest temperatures for full density.
..''
TABLE 9
Sistering Firing CUTE x 10-7/C
Sample Temperature CShrinkage 25-1000C
1250 15.4 17.1
6 139Q 14.6 17.8
7 1400 16-18 16.7
8 1400 16-18 18.0
9 141~ 17.0 17.0
Other samples with either less than 50 wt.% prereacted
cordierite or having Moo substantially outside the range of
5-40 mole % of ROW while also having at least 50 wt.% pro-
- reacted cordierite cannot be reliably made with full density.
A series of formable particulate ceramic cement samples
according to this invention were prepared by thoroughly
mixing the watch materials as shown in Table 10 to form
pastes of those samples.
The analytical molar composition of the combined raw
base materials of clay, silica and MnCO for Samples 1-4
-45-
~22~
and 6 was 1. 84 Moo 2. 04 Aye 5.11 Sue. Such combo-
session for Sample 5 was 2. 36 Moo 1. 29 Aye 5 . 35 Sue .
--46~
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The Mn-Mg cordierite grog in the cement batches in
Table 10 was a dense cordierite containing manganese of
- the present invention. In particular, the grog was made
of the following batch composition yin weight % of the
total ceramic batch materials):
My Cordierite grog (95~-200 mesh) 84.48
Georgia-Kaolin Kapok 10 clay ZAPS 10) 10.00
waker reagent MnCO3 powder 4.15
Penn. Glass Sand Mainsail silica ZAPS 5) 0.78
- 10 Pfizer Jo ~6-28 talc ZAPS 20) 0.59
Methyl cellulose binder/plasticizer4.0
. i-
Alkali Stewart extrusion aid 0.5
Distilled water plasticizer ~6.0
This Mn-Mg cordierite grog was fired generally in accord-
ante with the following firing schedule:
- 80C to 1405C within about 60 hours.
Hold about 10 hours at 1405C.
Cool 1405C to room temperature within about 24 hours.
The My cordierite grog (in the batch for the My My
cordierite grog) was made of the following batch composition
yin weight % ox the total ceramic batch materials):
Georgia-Raslin ~ydrite MY clay UPS 9.7~ 25.15
George a-Kaolin Glomax LO clay UPS 1.9) 21.17
Pfizer MY 96-28 talc UPS 20~ 40.21
Alcoa A-2 alumina UPS 5.8~ 13.47
-Methyl cellulose binder/plasticizer4.0
Allele Stewart extrusion aid 0.5
Distilled water plasticizer 32.5
This My cordierite grog was fired generally in accordance
with the same fifing schedule as for the Mug cordierite
grog, except that the maximum temperature was 1425C.
-48-
- ~27~8~L
The analytical molar composition of Mn-Mg cordierite
grog was 2.03 ROW 20.4 Aye 4.92 Sue wherein ROW con-
sited of 9.7 mole 5 Moo and 90.3 mole % Moo.
Pieces of ceramic honeycomb monolith wore extruded in
accordance with US. Patents 3,79Q,654 and 3,919,384 from
the same batch composition as described for the Mn-Mg
cordierite grog. Those extruded green honeycomb bodies
w no then fused in the manner as disclosed in US. Patent
3,89~,326 and in accordance with the same firing schedule
as described for the Mn-Mg cordierite grog. A series of
pairs of these honeycomb pieces were cemented together by
- applying the sample pastes described in TABLE 10 to the
cordierite surfaces of these pieces that were to be joined
and then pressing those paste-coated surfaces together. These
assembled pairs of cemented pieces were dried in air at
least 22-75C, then fired at about cry. to the foaming
-I temperature set forth in TABLE 1, held at the foaming tempera-
- lure for about one hour and thereafter cooled at furnace rate
to at least 2~QC, at which time the foam cemented pieces
were removed from the furnace for further cooling in ambient
- air atmosphere. The coefficients of thermal expansion (CUTE)
ox the foamed cement samples are set forth in TABLE 10, which
- are closely similar to the typical CUTE of 18 x 10 icky
(awoke for the pieces except the CUTE of Sample 5.
- All of those sistered foamed cement samples had a
substantially wholly cordierite crystal structure.
Upon subjecting the foam cemented pieces to a cycling
thermal shock test of SO cycles of heating from 250C to
800C in 3 minutes and then cooling back to 250C in 3
30 minutes, the foam cemented pieces with cement Samples 1-4
and 6 showed good resistance to thermal shock whereas the
I
~L227~
.
foam cemented pieces with cement Sample 5 showed moderate
resistance to thermal shock. However, cement Sample 5
should serve well with pieces having CUTE more closely similar
to the CUTE of roamed Sample 5 so as to exhibit good nests-
lance to thermal shock.
~oamahle cement Sample 6 has also been used to plug the
end portions of cells in extruded ceramic honeycomb bodies
made of the same and similar compositions and fired in the
same manner as the My cordierite grog previously described.
In those cases, the Mn-Mg cordierite grog was US wt. % - 325
mesh, and the cement batch was formed with 2.0 woo % methyl
cellulose and 70.0 White water to provide a paste that was
injected into the cell ends, between the surfaces of opposed
cell walls, by means of an air pressure operated sealant or
caulking gun with an appropriately shaped nozzle. Those
bodies with the green plugs were then fired generally in
accordance with the following typical firing schedule:
Room temperature to 1210C within about 6 hours.
told about 30 minutes at 1210C.
Cool 1210~C to room temperature within about 18 hours.
The cement foamed during firing to develop a sistered
cordite mass having good sealing to the cell walls and
. . .
belong generally impervious to fluid.
The particle sizes of cordierite grog and Six or other
; foaming agent in the cement can be varied as desired. For
example, the grog may be as coarse as -20 mesh. All mesh
sizes herein are according to the US. Standard Sieve series.
-50-
