U.S. patent application number 13/676514 was filed with the patent office on 2013-06-13 for screen basket having diagonal slots for top separator of a digester.
This patent application is currently assigned to Andritz Inc.. The applicant listed for this patent is Andritz Inc.. Invention is credited to Richard M. GROGAN, Jay SHEERER.
Application Number | 20130146547 13/676514 |
Document ID | / |
Family ID | 47294774 |
Filed Date | 2013-06-13 |
United States Patent
Application |
20130146547 |
Kind Code |
A1 |
SHEERER; Jay ; et
al. |
June 13, 2013 |
SCREEN BASKET HAVING DIAGONAL SLOTS FOR TOP SEPARATOR OF A
DIGESTER
Abstract
A screen basket in a top separator for a cellulosic material
treatment vessel, the screen basket includes: a cylindrical plate
having a vertical joint connecting opposite edges of the plate,
rows of slots extending through the plate, and each slot has a
curved or chamfered inlet corner edge adjacent an inside surface of
the plate and is oblique to a vertical axis of the basket.
Inventors: |
SHEERER; Jay; (Queensbury,
NY) ; GROGAN; Richard M.; (Queensbury, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Andritz Inc.; |
Glen Falls |
NY |
US |
|
|
Assignee: |
Andritz Inc.
Glens Falls
NY
|
Family ID: |
47294774 |
Appl. No.: |
13/676514 |
Filed: |
November 14, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61567761 |
Dec 7, 2011 |
|
|
|
Current U.S.
Class: |
210/767 ;
210/455; 210/497.01 |
Current CPC
Class: |
D21C 7/06 20130101; D21D
5/16 20130101 |
Class at
Publication: |
210/767 ;
210/497.01; 210/455 |
International
Class: |
D21D 5/16 20060101
D21D005/16 |
Claims
1. A screen basket for top separator for a cellulosic material
treatment vessel, the screen basket comprising: a cylindrical plate
having a vertical joint connecting opposite edges of the plate, and
rows of slots extending through the plate, wherein each slot has a
curved or chamfered inlet corner edge adjacent an inside surface of
the plate and each slot is oblique to a vertical axis of the
basket.
2. The screen basket of claim 1 where the curved corner inlet slot
edge is at least one of rounded, chamfered, sloped or inclined.
3. The screen basket of claim 1 wherein the curved inlet corner
edge has a radius of curvature in a range of one third to two
thirds a thickness of the plate.
4. The screen basket of claim 1 wherein the curved or chamfered
corner edge is only at a lower edge of each slot.
5. The screen basket of claim 1 wherein the slots are each offset
along an axis from the inside surface to an outside surface of the
plate by an angle of between 5 degrees to 45 degrees.
6. The screen basket of claim 1 wherein the curved or chamfered
inlet corner edge is limited to an upper corner edge or a lower
corner edge.
7. The screen basket of claim 1 wherein the slots are oblique to
the vertical axis at an angle of 1 degree to 75 degrees.
8. The screen basket of claim 1 wherein the rows of slots uniform
in height and orientation of the slots.
9. The screen basket of claim 1 wherein the slots in each row are
uniform in shape and dimensions, and the dimensions of the slots
differ from row to row.
10. A method for extracting a liquid from a top separator of a
treatment vessel, the method comprising: feeding a slurry of
cellulosic material and a liquid in the top separator screen basket
of a vessel, wherein the slurry of cellulosic material and liquid
flows into the screen basket; extracting a portion of the liquid in
the slurry of cellulosic material and liquid through a screen
basket assembly, wherein the screen basket formed of a screen
basket plate within the top separator and is formed around a
conveyor screw device, and the screen basket plate includes slots
having curved or chamfered inlet corner edges adjacent an inside
surface of the screen basket plate and facing a flow of slurry of
cellulosic material and liquid, and deflecting cellulosic material
flowing through the top separator with the curved or chamfered
inlet corner edges to avoid the material become caught in the slots
of the screen basket.
11. A top separator for use in a treatment vessel comprising: a
rolled plate formed into a cylindrical screen; rows of diagonal
slots formed in the plate and oriented horizontally; a single
welded joint extending vertically between abutting edges of the
plate. a conveyor screw within interior to the cylindrical screen,
wherein a gap between an outer edge of the screw and an interior
surface of the cylindrical screen is no greater than ten
thousandths of an inch; a housing supporting the cylindrical screen
and forming a liquid chamber between the housing and screen, and a
vertical shaft supporting the screw and extending vertically
through the cylindrical screen.
12. The top separator of claim 11 where the diagonal slots include
a curved corner inlet slot edge that is at least one of rounded,
chamfered, sloped and inclined.
13. The top separator of claim 12 wherein the curved inlet corner
edge has a radius of curvature in a range of one third to two
thirds a thickness of the plate.
14. The top separator of claim 12 wherein the curved or chamfered
corner edge is only at a lower edge of each slot.
15. The top separator of claim 11 wherein the slots are each offset
along an axis from the inside surface to an outside surface of the
plate by an angle of between 5 degrees to 45 degrees.
16. The top separator of claim 11 wherein the curved or chamfered
inlet corner edge is limited to an upper corner edge or a lower
corner edge.
17. The top separator of claim 11 wherein the slots are oblique to
the vertical axis at an angle of 1 degree to 75 degrees.
18. The top separator of claim 11 wherein the rows of slots uniform
in height and orientation of the slots.
19. The screen basket of claim 11 wherein the slots in each row are
uniform in shape and dimensions, and the dimensions of the slots
differ from row to row.
Description
BACKGROUND OF THE INVENTION
[0001] The present application is generally directed to making pulp
and is more specifically directed to top separators for pulp
digester systems including digesters, impregnation vessels or other
treatment vessels used in the processing of cellulosic material
such as the production of pulp.
[0002] Wood chips and other cellulosic fibrous material are treated
in treatment vessels, such as digester vessels and impregnation
vessels. These treatment vessels can be continuous or batch and
contain a section near the top of the vessel where hot vapor (such
as steam) or other hot gaseous material is used to heat the
cellulosic material or wood chips entering the vessel, commonly
referred to as vapor phase vessels (digesters) or they can be
hydraulically filled vessels where liquid is used to heat the
cellulosic material, commonly referred to as hydraulic vessels
(digesters). In this application the term "wood chips" refers to
all cellulosic fibrous material and is not limited to true "wood"
based material. An impregnation vessel is typically used to infuse
liquids and chemicals into the fibers of wood chips. A digester
vessel chemically separates fibers in the chips and material by
removing lignin. The chips after the removal of lignin are referred
to as pulp. In this application, impregnation and digester vessels
are both treatment vessels and either, or both, could use the top
separator described.
[0003] The wood chips are treated in a digester vessel with heat,
liquid, and chemicals to convert the chips to pulp. A continuous
digester vessel is typically an upright cylinder with an upper
inlet to receive chips in a continuous flow. The chips flow slowly
through the digester vessel, 100 to 300 feet tall (30 to 100
meters) in a generally downward direction. The digester vessel may
be a hydraulic or vapor phase vessel.
[0004] The wood chips are typically transported, e.g., pumped or
via another pressure transferring means, to a treatment vessel in a
slurry through conduits, e.g., pipes, which feed the wood chips to
the top of the treatment vessel. The liquid content of the slurry
used to transport the chips tends to be substantially higher than
the necessary or desired liquid content of the treatment vessel.
Liquid is removed as the slurry enters the treatment vessel. The
removed liquid may be reintroduced to the wood chips being
transported to the treatment vessel. After removal of a portion of
the liquid, the slurry of wood chips and a reduced amount of liquid
are discharged from the top separator and move down through the
treatment vessel.
[0005] A conventional screen basket for a top separator is formed
by parallel bars separated by narrow gaps. Conventional top
separators are described in U.S. Pat. No. 6,325,889; U.S. Pat. No.
7,105,076; U.S. Pat. No. 7,309,401 and U.S. Pat. No. 7,658,818. The
bars extend vertically and form a circular array of bars, wherein
the circle is a horizontal cross-section. The bars are held
together by one or more horizontal wires, horizontal metal rings or
backing bars.
[0006] The gaps between the bars of a conventional top separator
tend to become blocked with fibers and other debris, such as rocks.
As the gaps between the bars becomes blocked, the volume of the
liquid removed from the slurry is reduced and adversely affects the
overall operation of the treatment vessel. These adverse effects
can include reduced amount of liquid removed by the top separator,
reduced availability of heat energy that can be extracted from the
liquid extracted by the top separator, a greater requirement for
externally supplied liquid to transport the wood chips to the
treatment vessel, and non-optimal treatment of the wood chips in
the treatment vessel. There is a long felt need for a screen basket
for a top separator with reduced tendencies for the slots in the
screen basket becoming blocked or clogged.
BRIEF DESCRIPTION OF THE INVENTION
[0007] A novel screen basket has been developed comprising a solid
screen plate, rolled to form a basket, the plate having openings in
the plate of slanted slots having curved or chamfered inlet edges
to minimize chips begin caught on the edges and to deflect chips
into the wood mass. The curved or chamfered inlet slot edges are
adjacent the inside surface of the screen plate and face the wood
chip or pulp flow. The curved inlet slot edges may be rounded,
sloped, chamfered, or inclined. For example, inlets may have a
generous radius of curvature equal to one third to two thirds the
thickness of the plate. The curved or chamfered inlets may be only
on the lower side surface of a slot or on the upper and lower slot
side surfaces. A curved or chamfered inlet only on the lower side
surface is suitable for a continuous digester in which the wood
chip or pulp flow is generally downward and chips tend to impinge
on the inlet edge of the lower sides of slots. Curved or chamfered
inlets on both the upper and lower side surfaces of slots are
suitable for both continuous and batch digesters. In addition, the
lower side surface of the slot may be horizontal in cross-section
or be inclined upward from the inside surface of the plate to the
outer surface. Such a horizontal or upwardly inclined lower slot
surface tends to deflect chips in the slot out of the slot and into
the pulp stream.
[0008] A screen basket for a top separator for a cellulosic
material treatment vessel, the screen basket comprising: a
cylindrical plate having a vertical joint connecting opposite edges
of the plate, and rows of slots extending through the plate,
wherein each slot has a curved or chamfered inlet corner edge
adjacent an inside surface of the plate and each slot is oblique to
a vertical axis of the basket. The curved corner inlet slot edge
may be at least one of rounded, chamfered, sloped or inclined. The
curved or chamfered inlet corner edge has a radius of curvature in
a range of one third to two thirds a thickness of the plate. The
curved or chamfered corner edge is only at one of a lower edge or
upper edge of each slot.
[0009] The slots may be each offset along an axis from the inside
surface to an outside surface of the plate by an angle of between 5
degrees to 45 degrees, or 5 degrees to 30 degrees, or 5 degrees to
15 degrees or any variant therein. The slots may be oblique to the
vertical axis at an angle of 1 degree to 75 degrees, or 30 degrees
to 60 degrees, or preferably 40 degrees to 50 degrees or 45
degrees. The rows of slots may be uniform in height and orientation
of the slots or the slots in each row may be uniform in shape and
dimensions, while the dimensions of the slots differ from row to
row.
[0010] A method has been conceived for extracting a liquid from a
top separator of a treatment vessel, the method comprising: feeding
a slurry of cellulosic material and a liquid in the top separator
screen basket of a vessel, wherein the slurry of cellulosic
material and liquid flows into the screen basket; extracting a
portion of the liquid in the slurry of cellulosic material and
liquid through a screen basket assembly, wherein the screen basket
formed of a screen basket plate within the top separator and is
formed around a conveyor screw device, and the screen basket plate
includes slots having curved or chamfered inlet corner edges
adjacent an inside surface of the screen basket plate and facing a
flow of slurry of cellulosic material and liquid, and deflecting
cellulosic material flowing through the top separator with the
curved or chamfered inlet corner edges to avoid the material from
becoming caught in the slots of the screen basket.
[0011] A top separator has been conceived for use in a treatment
vessel comprising: a rolled plate formed into a cylindrical screen;
rows of diagonal slots formed in the plate and oriented
horizontally; a single welded joint extending vertically between
abutting edges of the plate; a conveyor screw within interior to
the cylindrical screen, wherein a gap between an outer edge of the
screw and an interior surface of the cylindrical screen is thirty
thousandths of an inch; a housing supporting the cylindrical screen
and forming a liquid chamber between the housing and screen, and a
vertical shaft supporting the screw and extending vertically
through the cylindrical screen.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a front view of a conventional continuous digester
shown schematically and partially cut away.
[0013] FIG. 2 is a front view, of a conventional top separator,
shown in cross-section of the digester shown schematically in FIG.
1.
[0014] FIG. 3 is a front view of a novel screen basket for the top
separator, showing the screen basket in cross-section.
[0015] FIGS. 4, 5 and 6 show the interior surface of a portion of
the novel screen basket, the portion of the basket in
cross-section, and the outer surface of the portion of the screen
basket, respectively.
[0016] FIG. 7 shows a cross-section of a slot in the novel screen
basket.
[0017] FIG. 8 shows a cross-section of an alternative slot for the
novel screen basket.
DETAILED DESCRIPTION OF THE INVENTION
[0018] FIG. 1 is a side view of a continuous vertical digester
vessel 10 for processing wood chips into pulp. Though a vertical
continuous digester is shown, the screen basket and screen slots
described herein are applicable to other types of digesters,
impregnation or other treatment vessels. The digester shown in FIG.
1 is typically referred to as a vapor phase digester. It is
understood by one skilled in the art that a top separator (as
described in this invention) is and can be used in both vapor phase
any hydraulic phase treatment vessels, treatment vessels such as
impregnation vessels or digesters or even in systems where the
separator is located outside of the treatment vessel such as
described in U.S. Pat. No. 5,413,677. The digester vessel 10 may
comprise a cylindrical wall 12 that typically forms a column of,
for example, 100 feet (30 meters) tall. The top and bottom of the
digester vessel are capped. A top separator 14 may be mounted to
the top cap 16 of the vessel. A discharge outlet 18 may be mounted
to the bottom cap 20.
[0019] The wood chips 21 enter the digester vessel as a slurry
through the top separator 14. The slurry is formed of wood chips
and liquid such as cooking chemicals and water (many times referred
to as liquor). The slurry flows to the top separator through a
conduit 22, which may be coupled to pumps, high pressure feeders, a
chip supply bin or pretreatment vessel. The slurry flowing into the
inlet of the top separator 14 has a liquor to chip ratio that is
high relative to the desired ratio of liquor to chips for the
process preformed in the digester vessel. The top separator
extracts liquor from the slurry entering the treatment vessel. The
extracted liquor flows through an outlet conduit 24 and may be
added to inlet conduit 22 feeding the slurry to the top
separator.
[0020] Wood chips 21 are continually added to a continuous
treatment vessel while the chips already in the treatment vessel
are processed and pulp 26 is discharged from the bottom of the
vessel. Heat energy and pressure may be added to the vessel such as
by injecting steam 28 into the top of the vessel. As the chips and
liquid cooking chemicals move down through the treatment vessel,
heat, pressure and chemical reactions within the vessel dissolve or
break-down the lignin binding fibers together in the chips. The
removal of the lignin releases the fibers from being bound within
the chips and converts the chips to pulp.
[0021] The chips may form a pile (dotted line 23 represents the top
of the pile) in the vessel that is at least partially immersed in
the liquid of cooking chemicals, generally referred to as cooking
liquor (see dotted line 25 representing liquid surface). In a vapor
phase vessel 10, a vapor filled region may be in the upper portion
of the vessel that is above the chip pile and surface of the
cooking liquor. In a hydraulic vessel, the liquor may fill the
vessel such that there is no vapor filled area in the vessel.
[0022] Screen assemblies 18 may be at one or more elevations in the
digester vessel 10. The screen assemblies are conventionally formed
of screen plates 30 in an annular array and mounted to the wall of
the vessel. Each screen plate is typically a rectangular metal
plate having a slight arch to conform to the curvature of the
cylindrical vessel. Slots in the screen plates may be vertical or
slanted. Cooking liquor is extracted from the wood chips in the
vessel through the slots of the screen plates. The fibrous pulp 26
and remaining spent cooking liquor is discharged as pulp from the
outlet 18 at the bottom 20 of the digester vessel.
[0023] The wood chips enter bottom or top of the top separator 14
depending on whether the separator is inverted. An inverted top
separator, such as shown in FIGS. 1 and 2, may be used in a vapor
phase digester vessel. As the slurry of chip enter the top
separator, a screw conveyor 32 moves the chips through the
separator. The screw conveyor may be driven turned by a gear and
motor arrangement 34 coupled by a vertical shaft 35 (FIG. 2) for
the screw conveyor. A screen basket 36 forms a cylindrical wall
around the outer edges of the screw conveyor. The screen basket has
slots to allow liquor from the slurry to flow into an annular
chamber 38 and flow into the liquor outlet conduit 24. As the wood
chips move through the separator, the chips are discharged (see
arrows 40) from the top separator and flow down to the chip pile 23
in the vessel 10.
[0024] FIG. 2 is a schematic diagram of the top separator 14,
showing the screen basket 36 in cross-section. The screen basket 36
includes a cylindrical shell. A support structure for the basket
may include a cylindrical housing 42 that mounts to the top cap 16
of the digester vessel and supports the screen basket. The housing
42 may also define the chamber 38 for liquor extracted through the
screen basket.
[0025] The screen basket has cylindrical inner wall that is
adjacent the outer edges 44 of the screw conveyor. The gap 46
between the edges 44 of the screw conveyor and the wall of the
screen basket narrow, such as less than thirty thousandths of an
inch. Due to the narrow gap 46 and the rotation of the screw, the
edges of the screw move across the surface of the inner wall of the
screen basket. The screen basket may have structural rigidity and
be built to tight tolerances to ensure that gap 46 remains constant
as the edges 44 of the conveyor swipe across the interior surface
of the screen basket.
[0026] FIG. 3 is a side view of an exemplary screen basket 36 which
is a metal plate formed into a cylindrical shell. The screen basket
may have a diameter of 36 to 96 inches and a vertical length of 48
to 120 inches. These dimensions are exemplary.
[0027] Slots 48 extend through the plate of the screen basket and
are sized to allow liquor to pass and block fibers and the wood
chips. The slots are slanted with respect to vertical and
horizontal orientations. The slots are arranged in rows 50 that may
be horizontal rows extending completely around the cylinder of the
screen basket.
[0028] The screen basket 36 may be formed of a metal plate rolled
to form a cylinder, wherein the edges of the plate are welded along
a vertical joint 51. Rather than a metal material, the screen
basket may be formed of another material suitable for use in a
treatment vessel which typically houses an environment having
acidic and alkaline chemicals. Due to the narrow diameter of the
screen basket and the proximity of the screw conveyor, the
thickness of the plate forming the screen basket will tend to be
thicker than the thickness of screen plates 30 used elsewhere in
the treatment vessel such as extraction screens within a digester
vessel as shown in FIG. 1. The relatively greater thickness and
single vertical weld of the screen basket assists in minimizing
damage to the interior surface of the screen basket due to
continuous mechanical action of the conveyor screw device.
[0029] The screen basket differs in several respects from a
conventional screen plate 30 mounted to the sidewall of a digester
vessel in that the screen basket of this invention (used for
example in the top separator of a treatment vessel) requires
substantial structural rigidity in view of the narrow gap 46 and
the proximity of the edges of the screw conveyor. Further, the
screen basket may be formed of a single metal plate rolled into a
cylinder, whereas a screen plate 30 is assembled with other plates
to form the screen assembly. Each plate 30 need have a relatively
small arc which conforms to the wall of the vessel. Because of the
close tolerances of the gap between the conveyor screw device and
the screen basket surface, the screen basket may be formed as a
precision piece having narrow machining tolerances.
[0030] The slots 48 may be arranged in rows 50 on the screen
basket. Each slot may have, for example, a length of three (3) to
fourteen (14) inches (8 mm to 36 mm). The vertical height of each
row 50 may be 2 to 10 inches (5 mm to 25 mm). The number of slots
in each row is dependent on the circumference of the screen basket.
The number of slots in each row and the dimensions, e.g., vertical
height, each row may be uniform in the screen basket or vary from
row to row. Within any row 50, the slots sizes (slot width, relief
angle and diagonal angle relative to the horizontal) may remain
constant from slot to slot. The slot size (slot width, relief angle
and diagonal angle relative to the horizontal) may vary from row to
row. The number of rows may depend on the desired open area in the
screen basket to allow for the desired flow of liquor extracted
from the chip slurry in the top separator.
[0031] To help support the screen basket, rows of horizontal rings
52, ribs or other stiffeners may be attach to the basket at the
horizontal solid ring region between the rows of slots in the
basket. Flanges 54, 56 at the top and bottom of the screen basket
provided supports for mounting the screen basket to the housing 42
and the top cap of the digester or treatment vessel. The flanges
may be metal rings that hold the top and bottom of the screen plate
in a cylindrical shape.
[0032] FIGS. 4 to 7 show screen basket in detail. FIG. 4 shows an
outer surface 60 of a portion of the screen basket. FIG. 5 is a
cross-sectional view of the screen basket taken along lines 5-5
shown in FIG. 3. FIG. 6 shows an interior surface 62 of the screen
basket. FIG. 7 is a cross-sectional view of the screen basket taken
along lines 7-7 in FIG. 4.
[0033] The slots 48 in the rows 50 of slots in the screen basket
are configured to minimize the clogging of cellulosic material in
the screens. Each slot may have a width (throat) of 3 to 9 mm and a
length of 25 to 100 mm. The slots may be wide at the outer surface
60 of the screen basket and narrow to the interior surface 62. The
slots may taper from the inside to outer surfaces of the basket at
relief angle 63 of 5.degree. to 45.degree., or 5.degree. to
30.degree., or 5.degree. to 15.degree. or any variant therein.
Further, the slots may be offset such that the opening 64 of each
slot is axially offset from the exit 66. The offset may be
generally aligned with the swiping motion of the edges of the
conveyor screw. This offset is selected to enhance the effect of
pumping the liquor through the slots due to the swiping motion of
the conveyor screw. The offset may orient the axis of the slot at
an angle, e.g., 10 to 25 degrees, or 15 degrees. The offset is
opposite to the swiping direction of the edges of the screw
conveyor. The offset reduces the tendency of fibers entering the
slots by pointing the axis of the slot away from the direction of
chip flow through the top separator. Similarly, the slots 48 may be
oriented at an angle 68 of 45 degrees or in a range of 40 to 50
degrees or zero (vertical) to 75 degrees. The angle of the slots
may be arranged to slant the slots in the opposite direction as the
rotation of the screw conveyor.
[0034] FIG. 8 shows in cross-section another exemplary slot 70 in a
screen basket for a top separator, wherein the slot has a curved or
chamfered edge 72 at the inlet opening 74. The slot extends through
the plate 76 of the screen basket. The thickness (T) of the plate
may be 9 to 10 mm, 8 to 11 mm or 7 to 12 mm. The throat (x), which
is the narrowest portion of the slot, may have a width of 3 mm to 8
mm, such as 6 mm.
[0035] The slot may expand from the inlet opening 74 to the outlet
opening 90 at a relief angle (.beta.) of 15 to 45 degrees, such as
30 degrees. The axis (see flow arrow 80) of the slot may be offset
in a direction opposite to the movement (see arrow 82) of the edges
of the screw conveyor. The offset may be at an angle such as 30
degrees formed by the angle (.omega.) of one of the sides slot and
one-half the relief angle for the slot.
[0036] The upper and lower edges of the slots may be curved, e.g.,
uniform radius of curvature, or chamfered. Avoiding sharp angles in
the slots reduces the tendency of fibers being cut or caught at the
edges of the slots. The edges of the slots at the opening 74 may be
rounded, chamfered, sloped or inclined. For example, the openings
74 may have a generous radius of curvature equal to one third to
two thirds the thickness of the plate.
[0037] The curved or chamfered edge 72 may be only on the side of a
slot facing the direction of movement 82 of the edges of the screw
conveyor. For a top separator having an upper inlet, the slots may
have a curved or chamfered edge at the lower edge of the slot
opening. For an inverted top separator, the curved or chamfered
edge may be at the upper edge of the slot openings. The curved or
chamfered edge 72 may be is less susceptible to catching fibers
(cellulosic material) in the slurry flowing through the top
separator. The curved or chamfered inlet on the slot tends to
deflect cellulosic material into the flow and away from the slot.
The curvature of the slot inlet may be defined by a radius of the
curvature. The radius may be, for example, one-third to two-third
of the thickness of the plate.
[0038] While the invention has been described in connection with
what is presently considered to be the most practical and preferred
embodiment, it is to be understood that the invention is not to be
limited to the disclosed embodiment, but on the contrary, is
intended to cover various modifications and equivalent arrangements
included within the spirit and scope of the appended claims.
* * * * *