U.S. patent application number 11/880546 was filed with the patent office on 2008-02-07 for ceramic packing element.
Invention is credited to Stephen L. Dahar, Hassan S. Niknafs, John S. Reid, Richard N. Robinette, Thomas Szymanski.
Application Number | 20080029201 11/880546 |
Document ID | / |
Family ID | 29732287 |
Filed Date | 2008-02-07 |
United States Patent
Application |
20080029201 |
Kind Code |
A1 |
Niknafs; Hassan S. ; et
al. |
February 7, 2008 |
Ceramic packing element
Abstract
The invention provides an improved ceramic packing element (1,
6, 8) suited to use as a bed limiter having a generally uniform
cross-section in the length (l) direction with the basic shape of a
bow-tie and having a plurality of through passages (5) parallel to
the length dimension (L).
Inventors: |
Niknafs; Hassan S.; (Stow,
OH) ; Robinette; Richard N.; (Stow, OH) ;
Dahar; Stephen L.; (Solon, OH) ; Szymanski;
Thomas; (Hudson, OH) ; Reid; John S.;
(Wooster, OH) |
Correspondence
Address: |
Saint-Gobain Ceramics & Plastics, Inc.;Intellectual Property Law
Department
One New Bond Street
P O Box 15138
Worcester
MA
01615-0138
US
|
Family ID: |
29732287 |
Appl. No.: |
11/880546 |
Filed: |
July 23, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10517545 |
Dec 10, 2004 |
7246795 |
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11880546 |
Jul 23, 2007 |
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10167893 |
Jun 12, 2002 |
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10517545 |
Dec 10, 2004 |
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Current U.S.
Class: |
156/87 |
Current CPC
Class: |
B01J 2219/3185 20130101;
B01J 2219/30242 20130101; B01J 2219/30246 20130101; B01J 2219/3183
20130101; B01J 2219/30223 20130101; Y10T 428/24273 20150115; B01J
2219/30296 20130101; B01J 2219/3188 20130101; B01J 2219/30416
20130101; B01J 2219/312 20130101; B01J 2219/30475 20130101; B01J
19/30 20130101; B01J 2219/30203 20130101; Y10S 261/72 20130101;
Y10T 428/24479 20150115 |
Class at
Publication: |
156/087 |
International
Class: |
B29C 65/02 20060101
B29C065/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 9, 2003 |
US |
PCT/US03/17994 |
Claims
1. A method of forming a bed of packing elements comprising:
extruding a mixture comprising one or more ceramic-forming
components; sectioning the extruded mixture to form sections;
firing the sections to form packing elements, wherein each of the
packing elements is characterized by first and second concave
external surfaces at the ends of height and width axes respectively
perpendicular to a length direction, said concave surfaces being
connected by surfaces that are selected from convex surfaces and
convex surfaces connected to the concave surfaces by relatively
short intermediate flat surfaces, a ratio of a width dimension to
the length being from 1.5:1 to 5:1, and the element being provided
with at least three through passages in the length direction, at
least one of the passageways being kidney bean-shaped in
cross-section, the kidney-bean shaped passageway having two
generally parallel arcuate surfaces; and assembling a bed of
packing elements which includes a plurality of the fired packing
elements.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to packing elements of the type that
are often called "random" or "dumped" packings, and will be
described with particular reference thereto. However, it will be
appreciated that the elements have applications in other areas.
[0003] 2. Discussion of the Art
[0004] Random or dumped packings are used to fill towers units in
which mass or heat transfer or any chemical reaction processes
occur. A particularly important application is the use of such
ceramic elements in heat recovery operations where it is necessary
to provide maximum effective contact with hot fluids passing
through the reactor. Another key factor in maximizing efficiency is
the maintenance of as low a pressure difference between top and
bottom of the tower as possible. To ensure this the packing
elements should present the minimum resistance to flow. This is
promoted by very open structures but open structure alone is of
limited use if the elements in the tower nest together such that
parts of one packing element penetrate within the space of a second
element. It is therefore important that the design of the elements
minimize the tendency of the elements to nest together. Another
particularly important application is as a bed topping material
which is intended to keep material within a bed confined with
limited ability to be entrained in a gas flow or to be caused to
move around by such a flow. Such entrainment or abrasion typically
causes significant losses to the material in the bed.
[0005] Ceramic packing elements can be produced by an extrusion or
a dry-pressing process and hence have an essentially uniform
cross-section along one axial direction which provides an axis of
symmetry for the element. Several such shapes have been described
in the art ranging from the very simple to the complex. All are
based on an essentially cylindrical shape and differ basically in
the internal structure within the cylindrical shape. The simplest
structure is a basic cylinder with no internal structure at all.
This type of structure is often called a Raschig ring and has been
known for many years. At the other end of the complexity scale are
the structures described in U.S. Design Pat. 455,029 and U.S. Pat.
No. 6,007,915. Between the extremes there are simple wagon-wheel
shapes such as are described in U.S. Pat. Nos. 3,907,710 and
4,510,263. Others show deformed cylindrical structures, such as
those described in U.S. Pat. No. 5,304,423. BE 481 212 discloses a
packing element for use in heat exchangers, distillation towers,
catalyst supports, and the like having four through passages and an
indented exterior surface. DE 24 25 058 discloses a ceramic filling
material with a cylindrical or hexagonal shape and multiple through
passages. U.S. Pat. No. 2,172,714 discloses a stackable block for
regenerators.
[0006] For certain applications, such as bed limiters, the pressure
drop is less important since the thickness of the bed limiter layer
is relatively small. It is far more important that the packing
elements do not nest together and still allow free passage of gases
while being heavier that the elements comprising the bed on which
the packing elements rest and whose extent is thereby limited.
SUMMARY OF THE INVENTION
[0007] In accordance with one aspect of the present invention, a
ceramic packing element is provided. The element has an essentially
uniform cross-section along an axis passing through a center of the
element and about which the element is symmetrical defining a
length of the element. A ratio of a width to the length is from
1.5:1 to 5:1. First and second concave external surfaces are
provided at the ends of height and width axes respectively,
perpendicular to the length direction. The concave surfaces are
connected by surfaces that are selected from (i) convex surfaces
and (ii) convex surfaces connected to the concave surfaces by
relatively short intermediate flat surfaces. The element is
provided with at least three through passages in the length
direction. At least one of the passageways is kidney bean-shaped in
cross-section. The kidney-bean shaped passageway has two generally
parallel arcuate surfaces.
[0008] In accordance with another aspect of the invention, a method
of forming a bed of packing elements is provided. The method
includes extruding a mixture comprising one or more ceramic-forming
components, sectioning the extruded mixture to form sections,
firing the sections to form packing elements. Each of the packing
elements has first and second concave external surfaces at the ends
of height and width axes respectively perpendicular to a length
direction. The concave surfaces are connected by surfaces that are
selected from convex surfaces and convex surfaces connected to the
concave surfaces by relatively short intermediate flat surfaces.
The element is provided with at least three through passages in the
length direction. At least one of the passageways is kidney
bean-shaped in cross-section. The kidney-bean shaped passageway has
two generally parallel arcuate surfaces. The method further
includes assembling a bed of packing elements including a plurality
of the fired packing elements.
[0009] In accordance with yet another aspect of the present
invention, a ceramic packing element is provided. The element has
first and second opposed generally planar surfaces. First and
second concave external surfaces are provided at the ends of height
and width axes, respectively, of the planar surfaces. The concave
surfaces are connected by surfaces that are selected from (i)
convex surfaces and (ii) convex surfaces connected to the concave
surfaces by relatively short intermediate flat surfaces. The
element is provided with a plurality of through passages in a
length direction, at least one of the through passages having a
cross section defined by a first arcuate surface and a second
arcuate surface, the second arcuate surface being longer than the
first arcuate surface and located generally parallel thereto.
[0010] The advantages of the present invention will be readily
apparent to those skilled in the art, upon a reading of the
following disclosure and a review of the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a cross-section of a bed limiter packing element
of the invention;
[0012] FIG. 2 is a side view of the packing element of FIG. 1;
[0013] FIG. 3 is a cross-section of a second embodiment of a bed
limiter packing element of the invention similar to that shown in
FIG. 1 except for the provision of flat exterior portions
connecting the convex and concave portions;
[0014] FIG. 4 (a to d) shows four different side views illustrating
possible end configurations of the element;
[0015] FIG. 5 is a top plan view of a third embodiment of a bed
limiter packing element of the invention; and
[0016] FIG. 6 is a perspective view of the embodiment of FIG.
5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] A solid ceramic packing element is provided having an
essentially uniform cross-section along an axis of symmetry in the
direction of extrusion defining the length of the element. The
element has first and second concave external surfaces at the ends
of height and width axes respectively perpendicular to the length
direction. The concave surfaces are connected by convex surfaces.
The element is provided with a plurality of through passages in the
length direction.
[0018] The invention is now more particularly described with
reference to the embodiment illustrated in FIG. 1. This is not
intended to imply any necessary limitations in the scope of the
invention because it will be readily appreciated that many minor
variations could be made without departing from the essential
spirit of the invention.
[0019] In FIG. 1 a bed limiter packing element 1 is shown in
cross-section along the length dimension. The element has a width
dimension W, parallel to the width axis w, and a height dimension
H, parallel to the height axis h, the width W being greater than or
equal to the height H. At either end of the height dimension are
first concave surfaces 2 and at either end of the width dimension
are second concave surfaces 3. These first and second concave
surfaces 2, 3 are connected by convex surfaces 4.
[0020] The provision of an essentially uniform cross-section along
the direction defining the length L of the element (FIG. 2) does
not preclude the provision of ends to the element that are not
perpendicular to the length direction. Indeed it is sometimes
preferred that the ends be cut at an angle to the length direction
since this is found to reduce the incidence of "nesting" or
alignment of the elements in a manner that increases the pressure
drop across a reactor containing the elements. The ends can also be
cut to have concave, convex, or dentate appearances in
cross-section.
[0021] The element of any of the embodiments described herein is
conveniently extruded from a ceramic material and this is
understood to embrace ceramic materials such as for example those
based on aluminosilicate clays, alumina, zirconia, cordierite,
titania, alone or in admixture with one another or other
ceramic-forming components.
[0022] Alternatively, the element can be formed by a pressing or
molding process in which case relatively small intermediate flat
surfaces may be included on the exterior surfaces at the junction
between the concave and convex surfaces to facilitate easy handling
of the product during forming. The intermediate flat surfaces are
short relative to the concave and convex surfaces and are intended
merely to facilitate handling in a production process in which the
elements are molded rather than extruded.
[0023] In one embodiment of the invention, the width and height
dimensions W, H of the element are unequal with the ratio of width
W to height H being from 1.25:1 to 3:1 and, in one embodiment, from
about 1.3:1 to 2.0:1. Thus, in visual terms, the cross-section
perpendicular to the length of the preferred elements of the
invention resembles the classic "dog-bone" or "bow tie" shape. In
one embodiment, the W:H ratio is about 1.5:1.
[0024] The length dimension L (FIG. 2) is preferably less than the
width W, with the width to length ratio W:L being, in one
embodiment, from 1.5:1 to 20:1 and in another embodiment, from
1.5:1 to 4:1. In one embodiment, H:L is about 8:1.
[0025] There are at least three passages 5 through the element and
the number can be from 4 to 275 and, in one embodiment, from 7 to
20. In the embodiment of FIG. 1, the passages through the element
are generally uniformly spaced, i.e., the distance between any two
adjacent passages is generally no more than 50% more than or less
than the mean distance between two adjacent passages. The passages
5 can have any desired cross-section, such as round, oval, oblate,
kidney bean shaped, regular or irregular polygon, or the like.
Combinations of two or more passage shapes within an element are
also contemplated. In the embodiment of FIG. 1, the passages 5 all
have round cross-sections.
[0026] The passages tend to reduce the pressure drop across a bed
comprising the elements. Accordingly, in one embodiment, the
passages are of sufficient number and cross sectional area to
reduce the pressure drop by at least 50%, as compared with an
equivalent packing bed comprising element without passages.
[0027] Clearly, the larger the number of passages 5, the smaller
the cross-sectional area of a single passage 5 generally must be.
In one embodiment, the maximum cross-sectional dimension D of each
of the passages 5 does not exceed two thirds of dimension H of the
element. In one specific embodiment, D does not exceed one half the
dimension H of the element and, in another embodiment, is not
greater than one third of this dimension. In one embodiment,
illustrated in FIGS. 1 and 3, the passages are identical in
dimensions and are round. In one embodiment, a ratio of D:H is at
least 1:10, and can be at least 1.5:10.
[0028] In the cross-section of the packing element, the area
represented by the total cross section of the passages can be at
least about 20% of the total cross-sectional area of the element
and can be up to about 75% of the total cross-sectional area. In
one specific embodiment, the cross sectional area of the passages
is at least 30% of the total cross-sectional area, in another
specific embodiment, at least 40%, and in another specific
embodiment, the cross sectional area of the passages is up to 67%
of the total cross-sectional area of the element.
[0029] The concave surfaces 2, 3 provide reduced width regions of
the element, which are narrowest at the midpoint of the concave
surfaces. The width and height of the element at the narrowest
point, which in the illustrated embodiment, coincides with the
width and height axes w, h, respectively, is termed the center
width N and center height M, respectively. In one embodiment, the
ratio of M:H is about 0.4 to 0.85. In a specific embodiment M:H is
from 0.5 to 0.8. In one embodiment, the ratio of N:W is about 0.6
to about 0.98. In a specific embodiment N:W is from 0.7 to
0.95.
[0030] In one embodiment, the radius of curvature of the concave
surfaces 3 is the same or substantially the same (i.e., within
.+-.10%) as that of the convex surfaces 4. In one embodiment, the
radius of curvature of the concave surfaces 2, is less than or
equal to W. In one embodiment, the radius of curvature of the
concave surfaces 3, is less than or equal to H.
[0031] With continued reference to FIG. 1, the element has a
uniform cross-section along its length, as illustrated in FIG. 2.
The concave surfaces 2, 3 can be regarded as channels in the
outside surface of the element running the length of the element. A
plurality of passages 5 run through the element parallel to the
length dimension. The passages are preferably uniform in
cross-section along the length and in the illustrated element of
FIGS. 1 and 2, have the same diameter, which represents about one
third of the height dimension H.
[0032] In one embodiment, the element is symmetrical about h and w
axes. Each of four quadrants of the packing element includes at
least one generally circular corner passage 5a which is generally
centrally positioned in the area surrounded by the convex surface
4, such that the convex surface defines an arc having a midpoint
within the corner passage 5a, which midpoint, in one embodiment, is
coincident with a midpoint of the passage 5a.
[0033] In addition to the four corner passages 5a, each quadrant
defines at least one additional intermediate passage 5b or portion
thereof, located intermediate the corner passage 5a and the center
C of the element, represented by the intersection of h and w axes.
A central round passage 5c is located with its midpoint at the
center C of the element. Additional passages 5d intersect the w
axis.
[0034] In the embodiment of FIG. 3, a ceramic packing element 6 has
small flat exterior surfaces 7 which connect the concave and convex
sections. The shape is however otherwise the same.
[0035] In FIG. 4, four optional ways of forming the ends of the
elements are shown. In FIGS. 4a to 4d the drawing shows, (for left
and right ends respectively in each case), concave and straight-cut
ends; two dentate-cut ends; two concave ends; and dentate and
concave ends.
[0036] In the embodiment of FIGS. 5 and 6, an element 8 having a
peripheral shape similar to that of FIG. 1 is shown, although a
peripheral shape with flat exterior surfaces 7, similar to that of
FIG. 3 is also contemplated.
[0037] As with the element of FIG. 1, the element is symmetrical
about h and w axes. A central round passage 5c is located at the
center C of the element. Four corner passages 5a are positioned as
described for FIG. 1. Instead of the two intermediate passages 5b,
intermediate the corner passages 5a and the central passage 5c is a
kidney bean-shaped passage 5e, which extends across the w axis and
thus portions of the passage 5e are located in adjacent quadrants.
A second kidney bean-shaped passage 5e, which is a mirror image of
the first in shape and location, is defined by the other two
quadrants. The kidney bean-shaped passage 5e includes inner and
outer arcuate surfaces 10, 11, respectively. The inner surface 10
is shorter in length than the outer surface 11 and is parallel or
generally parallel thereto. In the illustrated embodiment, the
arcuate surfaces 10, 11 each define an arc of a respective
imaginary circle having a midpoint which is at or adjacent to the
center C of the element, although the midpoint of the imaginary
circles can be closer to or further from the passage 5e than the
center C of the element. The arcuate surfaces 10, 11 are connected
at ends thereof by convex surfaces 12, 13, although it is also
contemplated that surfaces 12, 13 may be straight or slightly
concave. The arcuate surfaces 10, 11 and convex surfaces 12, 13
extending therefrom together subtend an angle .A-inverted. which is
less than 120.degree., more preferably, about 90.degree.. The
kidney bean-shaped passage 5e can have a largest dimension D which
is up to about 2/3 of the height H of the element. In one
embodiment, D is less than or equal to M.
[0038] The kidney bean-shaped passage 5e provides for a
structurally strong element while optimizing the flow through the
element. Theoretical calculations show that the pressure drop of a
gas flow across a packing bed formed with elements of the type
illustrated in FIG. 5 is significantly less than experienced with
spherical elements, and in one embodiment, is less than about 50%
of the pressure drop with spherical beads.
[0039] The ratio of the total area of the passages to the area of
the element can be the same as that described for FIGS. 1 and 2. In
one specific embodiment, the passages 5, in total, occupy 35-50% of
the cross sectional area of the element 8. The ratio of W:L and H:L
can be the same as that for the embodiment of FIG. 1. In one
embodiment, H:L is from about 5:1 to 15:1 and in another
embodiment, about 8:1.
[0040] The element 8 has a uniform cross section in the length
dimension, as shown in FIG. 2, i.e., it has a first planar surface
14 which is parallel to an opposed second planar surface 15,
although it is also contemplated that a structure as shown in FIGS.
4a-4d may be employed.
[0041] In addition to use the use as a bed limiter or as a regular
packing element providing mass and/or heat transfer surfaces, it is
possible to provided that the element has a porous construction
making it suitable for use also as carrier for a catalyst deposited
within the pores of the element as well as within the through
passages of the element. It is possible therefore to provide for a
catalyst bed comprising conventional porous catalyst-on-carrier
components and limit that bed with elements according to the
invention that not only provide the bed-limiting function but also
serve to react with any remaining reactants that were not converted
during passage through the portion of the bed containing the
catalyst-bearing components.
[0042] It is foreseeable that elements with the design features
described above and having bed-limiting functions could be provided
by elements made from plastic materials rather than ceramics.
* * * * *