U.S. patent application number 10/638803 was filed with the patent office on 2005-02-17 for monolithic tube sheet and method of manufacture.
This patent application is currently assigned to Graham, Robert G.. Invention is credited to Brenneman, Ronald G., DiSaia, Anthony S., Eslick, Herman L., Goski, Dana, Graham, Robert G..
Application Number | 20050034847 10/638803 |
Document ID | / |
Family ID | 34135737 |
Filed Date | 2005-02-17 |
United States Patent
Application |
20050034847 |
Kind Code |
A1 |
Graham, Robert G. ; et
al. |
February 17, 2005 |
Monolithic tube sheet and method of manufacture
Abstract
A monolithic refractory ceramic tube sheet for use in
all-ceramic air-to-air indirect heat exchangers, the heat exchanger
used in medium to high temperature, and high pressure applications.
A method for forming the monolithic tube sheet includes-casting a
refractory ceramic in a mold, where portions of the mold comprise
the housing of the heat exchanger. Precisely formed negatives are
used to form through channels and vacancies within the tube sheet,
which are precisely positioned within the mold allowing uniform and
flush formation of openings that receive the ceramic tubes therein.
The same mold is used to provide both tube sheets of a tube sheet
pair allowing accurate alignment of tubes within the exchanger
vessel resulting in ease of assembly and equal loading of tubes
when in use.
Inventors: |
Graham, Robert G.; (Presque
Isle, MI) ; Goski, Dana; (Columbus, OH) ;
Eslick, Herman L.; (London, OH) ; DiSaia, Anthony
S.; (Powell, OH) ; Brenneman, Ronald G.;
(Plain City, OH) |
Correspondence
Address: |
MCKELLAR STEVENS & HILL PLLC
784 SOUTH POSEYVILLE ROAD
MIDLAND
MI
48640
US
|
Assignee: |
Graham, Robert G.
Presque Isle
MI
|
Family ID: |
34135737 |
Appl. No.: |
10/638803 |
Filed: |
August 11, 2003 |
Current U.S.
Class: |
165/158 |
Current CPC
Class: |
F28F 21/04 20130101;
F28F 9/06 20130101; F28F 9/02 20130101; F28F 9/10 20130101 |
Class at
Publication: |
165/158 |
International
Class: |
F28F 009/02 |
Claims
We claim:
1. A monolithic refractory ceramic plate for supporting the
terminal ends of elongate ceramic tubes, said plate comprising an
inner face, and an outer face opposed to said inner face and
separated from the inner face by the thickness of the plate, said
plate further comprising a longitudinal axis which lies normal to
both said inner face and said outer face, each of said inner face
and said outer face comprising a peripheral edge, said plate
comprising an outer wall which corresponds to the thickness of the
plate and extends between said inner face and said outer face, said
plate comprising a central region which is surrounded by and spaced
apart from said outer wall, said central region being centered on
said longitudinal axis, said plate comprising a plurality of
through channels sized to receive the terminal ends of elongate
tubes, said plurality of through channels being located in said
central region and aligned in parallel with said longitudinal
axis.
2. The monolithic refractory plate of claim 1 wherein each of said
plurality of through channels comprise an inner end which
intersects said inner face of said plate, and each of said
plurality of through channels comprise an outer end which
intersects said outer face of said plate, wherein said inner end of
each of said plurality of through channels is provided with a
widened portion adjacent said inner face, said widened portion
comprising an arcuate vacancy which is sized and shaped to receive
an arcuate sealing member therein.
3. The monolithic refractory plate of claim 2 wherein said widened
portion is provided with a coating to provide a uniformly smooth
surface.
4. The monolithic refractory plate of claim 2 wherein said outer
end of each of said plurality of through channels is provided with
a widened portion adjacent said outer face such that the
intersection between each of said plurality of through channels and
said outer face forms a rounded convex shoulder.
5. The monolithic refractory plate of claim 4 wherein said plate is
fabricated in the shape of a cylinder, and said cylinder has a
thickness and a diameter, said plate being fabricated to have a
diameter to thickness ratio of approximately 5 to 1.
6. The monolithic refractory plate of claim 1 wherein said plate
further comprises a shell, said shell comprising a hoop formed in
the shape of a hollow cylinder, said hoop having a thickness and a
height, said hoop comprising a hoop inner face and a hoop outer
face, the hoop inner face being opposed to and separated from the
hoop outer face by the thickness of the hoop, where the thickness
of the hoop is small relative to the height of the hoop, said hoop
comprising a first hoop edge and a second hoop edge, the first hoop
edge being opposed to the second hoop edge and separated from it by
the respective hoop inner and outer faces, and said hoop inner face
confronts and abuts at least a portion of said outer wall of said
plate.
7. The monolithic refractory plate of claim 6 wherein said hoop
comprises a first flange and a second flange, wherein said first
flange lies adjacent to said first hoop edge, and wherein said
second flange lies adjacent to said second hoop edge.
8. The monolithic refractory plate of claim 7 wherein insulation
means is provided between portions of said outer wall of said plate
and said hoop inner face, and wherein insulation means is provided
between portions of said second flange of said hoop and inner face
of said plate.
9. A unitary ceramic tube sheet for supporting the terminal ends of
plural elongate ceramic tubes within a heat exchanger operating
using temperatures in the range of 1200 to 2800 degrees F. and
pressures of at least 15 psig, the tube sheet comprising a single,
unitary plate, the plate comprising a central region and a
peripheral region, said central region surrounded by and concentric
with said peripheral region, the central region comprising a
plurality of through holes sized and shaped to receive the terminal
ends of said plural elongate ceramic tubes therein, the peripheral
region comprising securement means for securing said tube sheet
within a heat exchanger.
10. The unitary ceramic tube sheet of claim 9 wherein the
peripheral region-further comprises insulation means for
maintaining a minimum required temperature in said peripheral
region during use.
11. The unitary ceramic tube sheet of claim 9 wherein the plate
comprises an inner face and an outer face, said inner face being
opposed to said outer face and separated from it by the thickness
of said plate, the plate comprising a longitudinal axis which lies
perpendicular to both said inner face and said outer face, wherein
said plurality of through holes extend through the thickness of
said plate such that they lie in parallel with the longitudinal
axis, each of said plurality of through holes comprising a circular
cross section of a first diameter, each of said plurality of
through holes having an enlarged region adjacent to said inner face
such that the intersection of each of said plurality of through
holes with said inner face comprises a circular cross section of a
second diameter, wherein the second diameter is greater than the
first diameter.
12. The unitary ceramic tubes sheet of claim 11 wherein each of
said plurality of through holes having an enlarged region adjacent
to said outer face such that the intersection of each or said
plurality of through holes with said outer face comprises a
tapering cross section, said tapering cross section having a
minimum diameter at a location spaced from said outer face, and a
maximum diameter at said intersection with said outer face.
13. The unitary ceramic tube sheet of claim 12 wherein said plate
is fabricated in the shape of a cylinder, and said cylinder has a
thickness and a plate diameter, said plate being fabricated to have
a plate diameter to thickness ratio of approximately 5 to 1.
14. A method of casting a unitary, single piece refractory plate
for supporting the terminal ends of elongate ceramic tubes within a
heat exchanger operating using temperatures in the range of 1200 to
2800 degrees F. and pressures of at least 15 psig, the unitary,
single piece refractory plate being fabricated using the following
method steps: Step 1. Provide a mold where the mold includes a
steel bottom plate, top plate, cylindrical shell, plural ball seal
negatives, and plural through channel negatives, wherein said
bottom plate comprises a short cylindrical casting plate which sits
concentrically on a short cylindrical alignment plate of larger
diameter than the casting plate, said plural ball seal negatives
are used for forming vacancies to receive spherical ball seals
therein, said plural ball seal negatives being machined to exact
tolerances, coated with release agents, and mounted to an upper
surface of the casting plate, said plural through channel negatives
are used for forming generally cylindrical through channels within
the unitary, single piece refractory plate, said plural through
channel negatives being machined to exact tolerances, coated with
release agents, and then secured to an upper end of a respective
said plural ball seal negative, said cylindrical shell comprises a
hollow cylinder, said cylinder comprising an outer diameter, an
first edge, an second edge, said first edge being opposed to and
separated from said second edge by the height of the cylinder, the
cylinder comprising an inner surface and an outer surface, said
inner surface being opposed to and separated from the outer surface
by the thickness of the cylinder, the cylinder comprising a first
flange which extends from said first edge of said cylinder and a
second flange which extends from said second edge of said cylinder,
said top plate comprises a short cylinder having a top plate
diameter, a top plate upper surface, and a top plate lower surface,
wherein said top plate diameter is equal to the shell outer wall
diameter, such that in use, the alignment plate is secured to the
first flange of the cylindrical shell such that the casting plate
is concentric with and surrounded by the first flange, such that
the periphery of the alignment plate abuts a lower face of the
first flange, such that an upper face of the casting plate and an
upper face of the first flange provide a bottom surface for the
mold, and such that the cylindrical shell provides outer walls for
the mold, the plural ball seal negatives are secured to the bottom
surface of the mold using precisely located predrilled through
holes within the bottom plate, the top plate is secured to the
second flange of the cylindrical shell, the top plate comprising a
centrally aligned opening which surrounds the plural through
channel negatives such that the plural through channel negatives
extend upward through said centrally aligned opening therein, Step
2. Line portions of the mold with sheet insulation material so as
to maintain an outer shell temperature of 250 deg F. during use,
Step 3. Cast the unitary, single piece refractory plate by
placement of said mold on top of a vibrating table, preparation of
refractory material as a wet mix, and pouring said wet mix into
said mold through the top plate centrally aligned opening, said top
plate centrally aligned opening being sized to provide a space
between the top plate and each of said plural through channel
negatives, Step 4. After the refractory is cast into the mold, it
is vibrated to remove air pockets from the material and provide a
dense, uniform mass, Step 5. The entire mold with cast refractory
is leveled to ensure a finished product having surfaces that are
square relative to cylindrical shell walls, Step 6. The entire
leveled mold with cast refractory is covered with an inner layer of
wet burlap and an outer layer of plastic so as to prevent quick
dehydration, to prevent formation of a skin, and to allow slow
maturation of the casting, Step 7. Allow to air dry for at least 24
hours, Step 8. Remove top plate from said unitary, single piece
refractory plate casting, Step 9. Remove bottom plate and plural
ball seal negatives, leaving the cylindrical shell about said
unitary, single piece refractory plate casting and leaving the
plural through channel negatives in place within the said unitary,
single piece refractory plate casting, Step 10. Prepare and treat
any cosmetic surface blemishes due to air bubbles in mold during
maturation found in plural ball seal vacancies using a sourizing
cement, Step 11. Place casting on a rack in curing furnace to
remove free and chemical water, and to burn out through channel
negatives, and cure for approximately 72 hours.
15. The method of casting a unitary, single piece refractory plate
of claim 14 wherein said portions of said mold which are lined with
said sheet insulation material comprise the inner surface of the
cylindrical shell at locations spaced from said second edge of said
cylindrical shell, and a portion of said first flange which both
confronts said refractory plate and which is spaced apart from said
inner surface of said cylindrical shell.
16. The method of casting a unitary single piece refractory plate
of claim 14 wherein said top plate lower surface is provided with
an outwardly extending bead, said bead comprising a half-round
cross section, said bead spaced from the peripheral edge of said
top plate such that it forms a circular channel in the top face of
the casting for receiving gasketing material therein.
17. A method for forming a unitary, single-piece refractory tube
sheet for supporting the terminal ends of elongate ceramic tubes
within a heat exchanger operating using temperatures in the range
of 1200 to 2800 degrees F. and pressures of at least 15 psig, the
unitary, single piece refractory tube sheet being fabricated by
casting in place, as a monolithic structure, within an outer shell
wall of the heat exchanger.
18. The method for forming said unitary, single-piece refractory
tube sheet of claim 17 wherein a mold is used to form said casting
of said unitary, single piece refractory tube sheet, wherein said
mold comprises a cold-rolled steel bottom plate, a top plate, said
cylindrical outer shell wall, plural machined ball seal negatives
for forming ball seal sockets within said unitary single-piece
refractory tube sheet, and plural negatives for forming through
channels within said unitary, single-piece refractory tube sheet,
wherein the bottom plate comprises a short cylindrical casting
plate and a short cylindrical alignment plate, said casting plate
comprising a first height and first diameter, a casting plate upper
surface, and a casting plate lower surface, said alignment plate
comprising a second height and second diameter, an alignment plate
upper surface, and an alignment plate lower surface, wherein said
second diameter is greater than the first diameter and wherein said
casting plate lower surface is secured to said alignment plate
upper surface such that the casting plate and alignment plate are
concentric, each of said plural machined ball seal negatives
comprises an arcuate body portion, said body portion having a
truncated upper surface and a truncated lower surface, each
respective lower surface of said plural ball seal negatives being
mounted to said casting plate upper surface, each of said plural
negatives for forming through channels comprises an elongate body
portion having an first end and a second end, wherein each
respective second end of said plural negatives for forming through
channels is secured to a respective upper surface of one of said
ball seal negatives, said outer shell wall comprises a thin-walled
hollow steel cylinder, the cylinder comprising an upper edge, a
lower edge, and a shell wall outer diameter, wherein the lower edge
of the outer shell wall is secured to said alignment plate, said
top plate comprising short cylinder having a third height and third
diameter, a top plate upper surface, a top plate lower surface, and
a central opening, wherein said third diameter is equal to the
shell outer wall diameter, such that in use, the casting plate is
secured to the alignment plate, the alignment plate is secured to
the lower edge of the outer shell wall, thus forming said mold
wherein the casting plate provides a mold bottom surface, wherein
said outer shell wall provides cylindrical mold side walls, and
said plural machined ball seal negatives and said plural negatives
for forming through channels are positioned within the mold using
precisely located predrilled through-holes within the bottom plate,
and wherein the top plate is secured to said upper edge of said
outer shell wall such that the tube negatives extend upward through
said central opening therein, thereby forming a mold top surface,
and the top plate is secured to said upper edge of said outer shell
wall.
19. The method for forming said unitary, single-piece refractory
tube sheet of claim 18 wherein the following method steps are used:
Step 1. Cast the tube sheet by placement of wet casting material in
mold, the casting material placed within the mold by passing it
through a vacancy between the tube negatives and the top plate,
Step 2. Vibrate casting to remove air pockets and to density
casting material, Step 3. Level the mold to ensure a finished
product having surfaces that are square relative to shell walls,
Step 4. Cover the entire leveled form with a bilayer covering, said
bilayer covering comprising an inner layer of wet burlap and an
outer layer of plastic, said bilayer covering used to prevent quick
dehydration and formation of a skin, and to allow slow maturation
of the casting, Step 5. Air dry for at least 24 hours, Step 6.
Strip casting of top plate, bottom plate, and ball seal negatives,
Step 7. Place casting on a rack in curing furnace to remove free
and chemical water, and to burn out through channel negatives, cure
for approximately 72 hours.
20. The method as claimed in claim 19 wherein insulation means are
provided between portions of the outer shell wall and the casting
material.
21. The method of forming said single piece refractory tube sheet
of claim 19 wherein said plural machined ball seal negatives and
said plural negatives for forming through channels are precisely
positioned on the upper surface of the casting plate using
precisely located predrilled through holes within the bottom
plate.
22. The method for forming said single piece refractory tube sheet
of claim 21 wherein the top plate comprises a peripheral edge, and
the peripheral edge of said top plate is secured to said upper edge
of said outer shell wall thereby forming a mold top surface.
23. The method for forming said single piece refractory tube sheet
of claim 22 wherein the top plate is provided with a centrally
positioned opening, and the body portion of each of said plural
negatives for forming a through channel extends upwards through
said centrally positioned opening in said top plate.
24. The method of forming said single piece refractory tube sheet
of claim 23 wherein said top plate lower surface is provided with
an outwardly extending bead, said bead comprising a half-round
cross section, said bead spaced from the peripheral edge of said
top plate such that it forms a circular channel in the top face of
the casting for receiving gasketing material therein.
25. The method of forming said single piece refractory tube sheet
of claim 19 wherein said casting material comprises a calcium
aluminate cement bonded with mullite, bauxite, and calcined
aluminas.
26. The method of forming said single piece refractory tube sheet
of claim 19 wherein said plural machined ball seal negatives are
formed of ultra high molecular weight polyethylene.
27. The method of forming said single piece refractory tube sheet
of claim 19 wherein said plural negatives for forming through
channels are formed of polyvinyl chloride.
28. A unitary refractory ceramic tube sheet in combination with a
ceramic air-to-air indirect heat exchanger, the heat exchanger for
use in operation conditions which include temperatures in the range
of 1200 to 2800 degrees F. and pressures of at least 15 psig,
wherein the heat exchanger comprises an array of elongate ceramic
tubes in a parallel configuration housed within an elongate vessel,
the vessel comprising a vessel first end and a vessel second end,
each elongate ceramic tube within said array of elongate ceramic
tubes comprising a first terminal end, a second terminal end, and a
body portion which extends between said first terminal end and said
second terminal end, said tube sheet comprises a single-piece,
monolithic refractory ceramic plates, said plate comprising an
inner face, and an outer face opposed to said inner face and
separated from th e inner face by the thickness of the plate, said
plate further comprising a longitudinal axis which lies normal to
both said inner face and said outer face, said longitudinal axis
lying parallel to each elongate ceramic tube, each of said inner
face and said outer face comprising a peripheral edge, each of said
inner face and said outer face comprising a central region which is
surrounded by and spaced apart from said peripheral edge, said
central region being centered on said longitudinal axis, said plate
comprising a plurality of through channels sized to receive the
terminal ends of said ceramic elongate tubes, said plurality of
through channels being located in said central region and aligned
in parallel with said longitudinal axis, each of said plurality of
through channels comprise an inner end which intersects said inner
face of said plate, and each of said plurality of through channels
comprise an outer end which intersects said outer face of said
plate, said tube sheet supporting the respective first terminal
ends of said elongate ceramic tubes by receiving said first
terminal ends within said respective inner ends of said through
channels.
29. The unitary refractory ceramic tube sheet in combination with a
ceramic air-to-air indirect heat exchanger of claim 28 wherein said
plate is fabricated in the shape of a cylinder, and said cylinder
has a thickness and a diameter, said plate being fabricated to have
a diameter to thickness ratio of approximately 5 to 1.
30. The unitary refractory ceramic-tube sheet in combination with a
ceramic air-to-air indirect heat exchanger of claim 28 wherein said
plate comprises an outer wall which corresponds to the thickness of
the plate and extends between said inner face and said outer face,
said plate further comprises a shell, said shell comprising a hoop
formed in the shape of a hollow cylinder, said hoop having a
thickness and a height, said hoop comprising a hoop inner face and
a hoop outer face, the hoop inner face being opposed to and
separated from the hoop outer face by the thickness of the hoop,
where the thickness of the hoop is small relative to the height of
the hoop, said hoop comprising a first hoop edge and a second hoop
edge, the first hoop edge being opposed to the second hoop edge and
separated from it by the respective hoop inner and outer faces, and
said hoop inner face confronts and abuts at least a portion of said
outer wall of -0.20 said plate, said hoop comprises a first flange
and a second flange, wherein said first flange lies adjacent to
said first hoop edge, and wherein said second flange lies adjacent
to said second hoop edge.
31. The unitary refractory ceramic tube sheet in combination with a
ceramic air-to-air indirect heat exchanger of claim 30 wherein
insulation means is provided between portions of said outer wall of
said plate and said hoop inner face, and is provided between
portions of said second flange of said hoop and inner face of said
plate.
32. The unitary refractory ceramic tube sheet in combination with a
ceramic air-to-air indirect heat exchanger of claim 30 wherein each
of said inner ends of said plurality of through channels comprises
an enlarged region which is sized and shaped so as to receive a
sealing member therein, and each of said outer ends of said
plurality of through channels comprises a tapering cross section,
said tapering cross section having a minimum diameter at a location
spaced from said outer face, and a maximum diameter at said
intersection with said outer face.
33. A unitary ceramic tube sheet for supporting the terminal ends
of plural elongate ceramic tubes within a heat exchanger operating
using temperatures in the range of 1200 to 2800 degrees F. and
pressures of up to 15 psig, the tube sheet comprising a single,
unitary plate, the plate comprising a central region and a
peripheral region, said central region surrounded by and concentric
with said peripheral region, the plate comprises an inner face and
an outer face, said inner face being opposed to said outer face and
separated from it by the thickness of said plate, the plate
comprising a longitudinal axis which lies perpendicular to both
said inner face and said outer face the central region comprising a
plurality of through holes sized and shaped to receive the terminal
ends of said plural elongate ceramic tubes therein, wherein said
plurality of through holes extend through the thickness of said
plate such that they lie in parallel with the longitudinal axis,
each of said plurality of through holes comprising a circular cross
section of a first diameter, each of said plurality of through
holes comprising an enlarged region adjacent to said outer face
such that the intersection of each of said plurality of through
holes with said outer face comprises a generally circular cross
section of a second diameter, wherein the second diameter is
greater than the first diameter, said enlarged region comprising
tube sheet threads formed on the surface thereof, the tube sheet
further comprising an elongate hollow plug positioned within each
of said plurality of through holes, said plug comprising a first
end and a second end, said second end separated from said first end
by a mid portion, said plug comprising an exterior and an interior,
wherein said exterior of said first end is provided with plug
threads formed on the surface thereof, said plug threads sized and
shaped to matingly engage said tube sheet threads so as to allow
securement and positional adjustment of said plug within each of
said plurality of through holes, said second end of said plug
comprising an articulating socket, said articulating socket
received within each of said plurality of through holes such that
it lies adjacent to said inner face of said plate, said
articulating socket receiving and supporting the terminal end of an
elongate ceramic tube therein such that the terminal end of an
elongate ceramic tube is capable of rotational motions, said
articulating socket comprising a spherical mating surface which
lies between the mid portion and the second end, the second end
terminating in a longitudinally aligned extension of the interior
surface such that it extends beyond the exterior surface to form an
insertion ring, said insertion ring comprising an insertion ring
exterior surface which is sized to be received within the interior
of said elongate ceramic tube when in use.
34. A combination unitary tube sheet and plural adjustable tube
securement means, wherein said plural adjustable tube securement
means are for use in securing and adjusting the terminal ends of
plural elongate ceramic tubes supported by said unitary tube sheet
within a heat exchanger vessel, wherein said unitary tube sheet
comprises a monolithic refractory ceramic plate, the plate
comprising an inner face and an outer face, said inner face being
opposed to said outer face and separated from it by the thickness
of said plate, a longitudinal axis which lies perpendicular to both
said inner face and said outer face, a plurality of through holes
sized and shaped to receive the terminal ends of said plural
elongate ceramic tubes therein, said plurality of through holes
extending through the thickness of said plate such that they lie in
parallel with the longitudinal axis, and wherein one of said plural
adjustable tube securement means resides within each of said
plurality of through holes.
35. The combination unitary tube sheet and plural adjustable tube
securement means of claim 34 wherein said plural adjustable tube
securement means comprises a plug, said plug comprising an elongate
hollow tube provided with exterior threads at a first end and a
second end which is opposed to the first end, said first end of
said plug is received within a vacancy formed at the intersection
of each of said plurality of through holes and the outer face of
said tube sheet, said vacancy comprising a generally cylindrical
void in said outer face, said void comprising a threaded region,
said threaded region being sized and shaped to matingly received
the exterior threads of said first end of said plug
therewithin.
36. The combination unitary tube sheet and plural adjustable
securement means of claim 35 wherein said first end of said plug is
provided a gasket between said plug and said tube sheet for
preventing fluid leakage between the plug and said respective
through hole.
37. The combination unitary tube sheet and plural adjustable
securement means of claim 36 wherein said second end of said plug
terminates in an articulating socket, said articulating socket
receiving and supporting the terminal end of an elongate ceramic
tube therein such that rotational motions of the terminal end of an
elongate ceramic tube are allowable.
38. The combination unitary tube sheet and plural adjustable
securement means of claim 37 wherein said articulating socket
comprises a spherical mating surface which lies between the first
end and the second end such that it is adjacent to said second end,
the second end terminating in an insertion ring, said insertion
ring comprising a longitudinal extension of the interior surface of
the plug, said insertion ring comprising an insertion ring exterior
surface which is sized to be received within the interior of said
elongate ceramic tube when in use.
Description
BACKGROUND OF THE INVENTION
[0001] Heat exchangers are devices built for efficient heat
transfer from one fluid to another. Conventional heat exchangers
accomplish this heat transfer using a wide variety of interfaces
and fluids. This invention is concerned with indirect heat transfer
between two fluids of different temperatures across a dividing
wall. More specifically, this invention is concerned with an
indirect air-to-air heat exchanger, for use in high temperature,
high pressure applications, which uses an array of parallel tubes
extending lengthwise within an elongate hollow vessel. The array of
tubes is supported at each end of the vessel using a tube sheet.
Tube sheets are used to receive the terminal ends of the tubes such
that the tubes extend in a direction normal to the tube sheet face.
The terminal ends of the tubes are seated within through channels
in the tube sheet that allows fluid to pass between the interior of
the tube and the opposing side of the tube sheet. A housing that
forms the heat exchanger vessel encloses the tubes and tube sheets.
In the ideal heat exchanger, there is no fluid leakage at the
interface of the tube sheet and vessel walls, and there is no fluid
leakage at the interface of the tube sheet and tube. The vessel
housing includes a dome at each end of the vessel that channels
fluid to or from the tube sheet. The heat exchanger vessel is also
provided with transversely aligned inlet and outlet ports that
allow a second fluid to flow within the body of the vessel about
the exterior of the tubes.
[0002] In such heat exchangers, a first fluid is passed from within
a dome at a first end of the heat exchanger, through the tube
sheet, through the interior of each tube within the tube array,
through a second tube sheet, exiting through a second dome at the
second end of the heat exchanger. A second fluid enters the body of
the heat exchanger vessel through an inlet port such that it passes
transversely through the tube array, passing about the exterior of
the tubes, and exiting the vessel via the outlet port. The heat
exchangers may be used as described as a single unit, or may be
attached in series, dome to dome, with additional vessels to form a
heat exchange system.
[0003] It is well understood that heat transfer is equally
efficient regardless of whether the heating fluid is designated to
be the first fluid and the heated fluid to be-second fluid, as it
is to allow the opposite to be the case. For purposes of discussion
of this invention, we will consider the first fluid to be the fluid
to be heated, and the second fluid to be the heating fluid.
[0004] This invention is also concerned with heat exchangers
operated at high pressures. For purposes of discussion, the first
fluid is provided at high pressure, that is to say, that the fluids
within the domes and tubes are at high pressure. As a result, the
outer (dome) side of the tube sheet is at a high pressure, and
relatively low temperature, while the inner (vessel) side of the
tube sheet is at a relatively low pressure and high
temperature.
[0005] An example of such a heat exchange system is found in a
turbine power generation system wherein the first fluid is
compressed and then heated within the heat exchanger, the heated
compressed fluid then being used to propel an expander to generate
power. In this system, the second, heating fluid is the exhaust gas
of a manufacturing process.
[0006] Conventional heat exchangers, operating in the temperature
range of 800 to 1200 degrees F., and under pressures in the range
of 0.25 to 2 psig, are constructed using metal tubes and tubes
sheets. Typically, the metal tubes are secured to metal tube sheets
by welding, or other well-known means. Such heat exchangers fail
when operated at higher temperatures, and have a short life span
when used with corrosive fluids as found in exhaust gases from
industrial operations.
[0007] Heat exchangers that must operate in more severe conditions,
as found in this invention, are fabricated with ceramic components.
Such heat exchangers function well in moderate (1200 degrees F.) to
high-(2800 degrees F.) temperatures, at high pressures (15 psig and
greater), and are resistant to corrosive fluids. Ceramic tubes and
tube sheets are well suited to use in severe operating conditions.
However, the material properties of ceramics generate other design
considerations. For example, loads need to be distributed evenly
across the tube array to prevent any one tube from being
overloaded. Thermal expansion of both the tubes and the tube sheets
needs to be considered in the design so as to avoid additional
stresses at the interface between these components. Finally, fluid
leakage between the first and second fluids, such as found at the
interface between tube and tube sheet, as well as between the tube
sheet and vessel walls must be addressed.
[0008] The prior art ceramic tube sheets, such as the tube sheet
disclosed in U.S. Pat. No. 5,979,543 to Graham, have been formed of
plural individual ceramic tiles, each ceramic tile receiving and
supporting multiple ceramic tube-ends. The individual ceramic tiles
are then assembled and cemented together to form a generally planar
tube sheet. Disadvantages to this type of tube sheet are fluid
leakage at the cemented joint between tiles, and difficulty
obtaining exact and precise alignment of tiles both within a tube
sheet and between tube sheet pairs. Precise alignment between tube
sheet pairs is required since it prevents problems with tube
assembly, and insures that the tubes are equally loaded during
operation.
SUMMARY OF THE INVENTION
[0009] The invention is a unitary (one-piece) ceramic tube sheet
for use in heat exchangers, and the method of manufacturing the
same. More specifically, the invention is a monolithic refractory
ceramic tube sheet for use in all-ceramic air-to-air indirect heat
exchangers, the heat exchanger used in medium to high temperature,
and high pressure applications such as extraction of thermal energy
from industrial waste gases for use in a wide variety of
applications such as heating clean ambient air.
[0010] By forming the ceramic tube sheet as a unitary block or
monolith, the fluid leakage between joined ceramic tiles, as in the
prior art is eliminated. Fabrication and assembly of the tube sheet
is vastly simplified since multiple small tiles do not have to be
assembled and cemented together. Additionally, since the same form
may be used to create both tube sheets used within a single heat
exchanger, the alignment of ceramic tubes between tube sheet pairs
is easily accomplished. This precise alignment of the tubes between
the tube sheet pairs is critical since it prevents problems with
tube assembly, and insures that the tubes are equally loaded during
operation.
[0011] The monolithic refractory ceramic tube sheet is described in
combination with an adjustable, articulating, sealing plug. The
plug is provided in a length such that it extends across the
thickness of the tube sheet, and the exterior is provided with
threads adjacent the outer (dome side) face of the tube sheet.
These threads engage mating threads formed in the tube sheet
through channels, allowing the position of the plug to be
longitudinally adjusted within the through channel. This ability to
adjust the longitudinal position of the plug allows compensation
for variations in tube length, and ensures that each tube can be
equally loaded at assembly. Additionally, the plug can be
completely removed from the outer face of the inventive tube sheet,
allowing replacement of a ceramic tube from the dome-side of tube
sheet, or outside the heat exchanger itself Adjacent to the inner
(tube side) face of the tube sheet, the plug is provided with an
articulated, sealing joint which receives and supports the terminal
ends of a ceramic tube. This joint allows rotational motions of the
terminal end of the tube, and prevents fluid leakage within the
through channel.
[0012] A method for forming the monolithic tube sheet is provided.
Casting a refractory ceramic in a mold, where portions of the mold
comprise the housing of the heat exchanger, forms the monolithic
tube sheet. Thus, the tube sheet is cast in place within the
housing. This is advantageous since the tube sheet takes on the
form of the shell, minimizing fluid leakage between the casting and
the shelf wall. Additionally, this step further reduces steps in
the assembly of the heat exchanger. Precisely formed negatives are
used to form through channels and vacancies within the tube sheet,
which are carefully and precisely placed within the mold. This
precision allows uniform and flush formation of openings that
receive the ceramic tubes therein, which is critical so that when
assembled and in use each ceramic tube can be equally loaded.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 an exploded perspective view of a partial assembly of
a heat exchanger, illustrating the use of a pair of monolithic tube
sheets to support the terminal ends of ceramic tubes.
[0014] FIG. 2 is a side section view of a monolithic tube sheet
illustrating the longitudinal orientation of the through channels
as well as the relationship of the cast plate to the outer
shell.
[0015] FIG. 3 is a side section detail view of a portion of the
monolithic tube sheet of FIG. 2, illustrating the O-ring groove
formed in the outer face of the tube sheet and the configuration of
insulation at outer shell wall.
[0016] FIG. 4 is a side section detail view of a portion of the
monolithic tube sheet of FIG. 2, illustrating the tube through
channel configuration.
[0017] FIG. 5 is a side section detail view of a portion of the
monolithic tube sheet of FIG. 2, illustrating the widening of the
tube through channel at its intersection with the outer face of the
tube sheet.
[0018] FIG. 6 is a side section detail view of a portion of the
monolithic tube sheet of FIG. 2, illustrating the vacancy formed at
the intersection of the tube through channel and the inner face of
the tube sheet for receiving a ball seal therein.
[0019] FIG. 7 is a side section view of the assembled tube sheet
mold.
[0020] FIG. 8 is a side section detail view of a portion of the
assembled tube sheet mold of FIG. 7, illustrating the securement of
the negatives to the bottom plate of the mold using a precisely
positioned through bolt.
[0021] FIG. 9 is a side section view of the tube sheet mold,
illustrating placement of insulation material along a portion of
the outer shell wall and along a portion of the inner flange.
[0022] FIG. 10 is a side section view of the assembled tube sheet
mold with casting material within the mold and the top plate in
place.
[0023] FIG. 11 is a top perspective view of the assembled tube
sheet mold illustrating the central opening in the top plate that
allows the negatives to extend beyond the top plate, and also
provides a means by which casting material is added to the
mold.
[0024] FIG. 12 is a side sectional detail view of a tube assembled
within a through channel, illustrating a second embodiment of the
inventive tube sheet which employs an adjustable, articulating plug
within the through channel.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Monolithic Tube Sheet
[0026] Referring to FIGS. 1 and 2, the inventive tube sheet 10 will
now be described in detail. Tube sheet 10 is a monolithic
refractory ceramic plate for use in all-ceramic air-to-air indirect
heat exchangers. These ceramic heat exchangers are used in medium
to high temperature, and high pressure applications where metal
components are unsuitable. One such application is the extraction
of thermal energy from industrial waste gases for use in heating
clean ambient air it is, however, within the scope of this
invention to employ the inventive concept in other severe
environment applications, which include, but are not limited to,
those found in the power and aerospace industries.
[0027] The indirect heat exchanger of this invention allows
efficient heat transfer from one fluid to another across a tube
wall. A first fluid is passed through an array of parallel,
elongate tubes such that it flows within the tube interior spaces.
The tube array is enclosed within a vessel. A second fluid is
passed through the vessel and about the exterior of the tubes such
that it flows in a direction perpendicular to the tube array. It is
important to note that the heat exchanger will function equally
well regardless of whether the heating fluid flows within the tubes
or about their exterior. For purposes of describing the instant
invention, the first fluid, which travels through the hollow
interior of the tubes, is clean ambient compressed air that is to
be heated. The second fluid is a hot, contaminated industrial waste
exhaust gas, and is used as the heating medium. The second fluid
passes in a cross flow across and about the tubes, heating the
first fluid.
[0028] Within the illustrative heat exchanger 1, a pair of opposed
tube sheets 10 are used at either end of the heat exchanger vessel
to support the terminal ends 3, 4 of multiple elongate tubes 2
which lie in a parallel configuration in alignment with
longitudinal axis 5 of heat exchanger 1. Tubes 2 are supported
between tube sheets 10 such that they are under longitudinal
compression. This compression loading is used to improve the
function of a seal at the junction of tube 2 and tube sheet 10.
[0029] For purposes of description of this invention, the number of
tubes employed is 52, the tube outer diameter is approximately 2.5
inches, the tube inner diameter is approximately 2 inches, and the
tube length is approximately 10 feet. The array of tubes is
surrounded by vessel walls 6, which include inflow 7 and outflow 8
ports, aligned perpendicularly to longitudinal axis 5, which
provide for cross-flow of the second fluid across and around the
tube array. However, it is understood that the number of tubes
employed, tube diameter, and tube length are determined by the neat
transfer requirements of the specific application, and varies from
heat exchanger to heat exchanger. Any dimensions provided herein
are to illustrate scale and proportion, and may be altered to meet
the design requirements of a specific application.
[0030] Tube sheet 10 is a monolithic, or single-piece, refractory
ceramic plate 15 enclosed within a shell 30. Plate 15 is provided
with an inner face 20 that faces the interior space of the heat
exchanger vessel, and an outer face 22, which is opposed to inner
face 20 and separated from it by the thickness of plate 15. Inner
face 20 and outer face 22 are mutually bounded by peripheral edge
24. Inner face 20 and outer face 22 are parallel planes that lie
perpendicular to the longitudinal axis 5 of heat exchanger 1.
[0031] Within the illustrative heat exchanger 1 described herein,
plate 15 has a circular cross section. It is within the scope of
this invention, however, to form tube sheet 10 with other cross
sectional shapes which include, but are not limited to, polygons,
as required by the design requirements of the specific application.
Within heat exchanger 1, tube sheet 10 is subjected to high
longitudinal pressures on outer face (dome side) 22, as well as
opposing longitudinal pressures on inner face 20 due to the
compression loading of tubes 2. The combined weight of the plural
ceramic rods is supported by inner face 20.
[0032] In the illustrative embodiment, plate 15 is approximately 60
inches in diameter and approximately 121/2 inches thick. Thus tube
sheet 10 is provided with a diameter to thickness ratio of
approximately 5 to 1. This thick plate design compensates for the
opposing longitudinal loads on plate 15 due to compressed fluid
pressures on outer face 22 and compression pressures on tubes 2 on
inner face 20, as well as the transverse load on inner face 20 due
to the weight of the ceramic tubes, taking into consideration
material properties and safety factors. It is understood that plate
diameter and thickness are determined by design requirements of the
specific application and will vary from heat exchanger to heat
exchanger. Any dimensions provided herein are to illustrate scale
and proportion, and may be altered to meet the design requirements
of a specific application. However, it should also be understood
that in all designs for this application, the ratio of diameter to
thickness of plate 15 is relatively large, resulting in plate 15
having a substantive thickness.
[0033] Through channels 28 extend through the thickness of plate 15
such that they intersect inner face 20 and outer face 22, providing
fluid communication between the opposing sides of the tube sheet
10. Through channels 28 have a circular cross section and are of
generally uniform diameter across the thickness of plate 15, except
at the regions adjacent to the respective inner 20 and outer 22
faces. This diameter is approximately that of the inner diameter of
tube 2, which in the illustrative embodiment is approximately 2
inches. The number of through channels 28 corresponds exactly to
the number of tubes 2. Each terminal end 3, 4 of each respective
tube 2 is received within an arcuate seal vacancy 80 formed in
through channel 28 at the inner face 20 of tube sheet 10.
[0034] To prevent fluid leakage between terminal ends 3, 4 of tube
2 and tube sheet 10, a seal is used at each respective terminal end
3, 4. Referring to FIG. 6, seal vacancy 80 is formed at the
intersection of through channel 28 and inner face 20, and is sized
and shaped to receive a seal therein. In the preferred embodiment,
seal vacancy 80 is generally spherical in shape so as to receive
the preferred seal therein. The preferred seal is a innovative
three oint ball seal which is described in detail in U.S. Pat. No.
6,206,603, that issued on March 27, 2001. Seal vacancy wall 82 is
coated with a smooth, fine grain, high temperature cement 84 to
provide a uniform and imperfection-free surface that will optimize
the performance of the seal.
[0035] Outer face 22 is enclosed within dome 9. When tube sheet 10
is located at the fluid inlet side of heat exchanger 1, outer face
22 serves to direct the first fluid into through channels 28 and
thus tubes 2. When tube sheet 10 is located at the fluid outlet
side of heat exchanger 1, outer face 22 serves to direct the
outflow of the first fluid from through channels 28. The heat
exchanger unit may be used as a single entity, or may be attached
in series (dome 9 to dome 9) with other heat exchanger units. As
illustrated in FIG. 3, O-ring channel 29 is a depression formed on
outer face 22 adjacent to but spaced apart from peripheral edge 24.
O-ring channel 29 is provided with a half-round cross sectional
profile. Positioning of O-ring channel 29 on outer face 22 is
determined by thermal considerations. In the illustrative
embodiment, O-ring channel 29 is spaced -approximately 31/2 inches
from peripheral edge 24, resulting in a circular channel of
approximately 53 inches diameter on outer face 22. However, it is
understood that channel spacing relative to peripheral edge 24 may
be adjusted to accommodate the design considerations of a specific
heat exchanger.
[0036] When assembled to dome 9, an O-ring is received within
O-ring channel 29 as a gasket to prevent fluid and pressure leakage
between tube sheet 10 and dome 9. Specifically, the O-ring
maintains pressure within the heat exchanger vessel by preventing
fluid from bypassing tube sheet 10 and passing through the porous,
permeable insulation 60, 62 (discussed below) used between tube
sheet 10 and shell 30. The O-ring forces fluid to pass through tube
sheet through channels 28 and subsequent tubes 2. In the preferred
embodiment, the O-ring is formed of round, seamless copper tubing
of 1/2 inch outer diameter. In use, the O-ring is compressed
between tube sheet 10 and dome 9, forming an effective seal.
Additional sealing may be obtained by coating outer face 22 with a
caulk-like high temperature (1500 degrees F.) sealing compound
prior to assembly.
[0037] Through channel 28 is provided with a widened portion 90 at
its intersection with outer face 22. As shown in FIG. 5, this
region of through channel 28 adjacent to the intersection with
outer face 22 is provided with a gradually increasing diameter and
the intersection between the through channel 28 and the outer face
forms a rounded convex shoulder. This widening and rounding of the
opening prevents a pressure drop from occurring at the outer face
as the first fluid passes to or from tube 2 into dome 9.
[0038] Tube sheet 10 is enclosed by a thin-walled hollow
cylindrical shell or hoop 30. Shell 30 provides a means to attach
tube sheet 10 to the heat exchanger vessel 6, and bears
longitudinal load due the high pressures within the heat exchanger
vessel. Shell 30 is provided with a shell outer face 34, which
corresponds to the exterior surface of the heat exchanger 1 in the
region surrounding tube sheet 10. Shell interior face 32 is opposed
to shell exterior face 34 and separated from it by the thickness of
the shell wall. Shell interior face 32 confronts peripheral edge 24
of tube sheet plate 15. Shell 30 is provided with a shell outer
edge 36 and shell inner edge 38. Shell outer edge 36 is opposed to
shell inner edge 38, and separated from it by the longitudinal
length of the shell.
[0039] Outer flange 40 extends outwardly from shell exterior face
34 such that it overlies shell exterior face 34 adjacent to shell
outer edge 36, and is aligned flush with shell outer edge 36. Outer
flange 40 is provided with 56 flange through holes 49 that extend
through its height, equally spaced adjacent to and along the flange
exterior face 44. Flange through holes 49 are aligned with
corresponding flange through holes on a similar flange provided on
dome 9, and receive fasteners therein to secure the outer portion
of tube sheet 10 to dome 9.
[0040] Inner flange 50 abuts shell inner edge 38 such that it forms
a T-shaped cross section where shell 30 is represented by the
vertical portion of the T, and inner flange 50 is represented by
the cross portion of the T. The cross portion has an interior leg
53 which extends radially inward toward longitudinal axis 5, which
is also referred to as the mantle. Exterior leg 51 extends radially
outward away from longitudinal axis 5, relative to shell 30.
Interior leg 53 of inner flange 50 takes the entire thrust of the
high longitudinal pressures on outer face (dome side) 22 of tube
sheet 10 within the heat exchanger vessel, and is therefore a
relatively substantial member. In the illustrative embodiment,
inner flange 50 is approximately 4 inches thick, and interior leg
53 extends inwardly from shell 30 approximately 6 inches.
[0041] Inner flange 50 is provided with a flange interior face 52
and flange exterior face 54 that is opposed to flange interior face
52. Inner flange 50 is also provided with a flange first face 56
and a flange second face 58 which is opposed to flange first face
56. Along interior leg 53, flange first face 56 confronts inner
face 20 of plate 15 adjacent to peripheral edge 24.
[0042] Exterior leg 51 is used to secure the inner portion of tube
sheet 10 to a flange on vessel walls 6. Exterior leg 51 is provided
with 56 flange through holes 59 which extend through its height,
equally spaced adjacent to and along the flange exterior face 54.
Flange through holes 59 are aligned with corresponding flange
through holes on the vessel wall flange, and receive fasteners
therein to secure the inner portion of tube sheet 110 to a flange
on vessel walls 6.
[0043] In the preferred embodiment, shell 30 is fabricated from
steel. It is, however, within the scope of the invention to form
shell 30 from other materials that are able to meet design
requirements. In the preferred embodiment, outer flange 40 and
inner flange 50, also fabricated from steel, are welded to shell
30.
[0044] Portions of the interior of shell 30 are lined with thin
sheet thermal insulation. Shell interior face insulation 60
overlies shell interior face 32 from shell inner edge 38 to a
location spaced apart from shell outer edge 36. This leaves a
region adjacent to shell outer edge 36 that is not lined with
insulation material. In this region, peripheral edge 24 of plate 15
confronts and abuts shell interior face 32 (see FIG. 3) so as to
prevent relative motion of plate 15 within shell 30, and to prevent
flu id flow between the ceramic material of plate 15 and the shell
due to the porosity of the insulation material.
[0045] Flange insulation 62 is positioned on the flange first face
56 at locations that are spaced from shell interior face 32. The
unlined portion of flange first face 56 adjacent to shell interior
face 32 allows plate 15 to bear the operating pressure load without
crushing (thus reducing the effectiveness) of flange insulation
62.
[0046] In the preferred embodiment, the material is a microporous
thermal insulation formed of bonded silica powders with reinforcing
glass filaments such as the material commercially available under
the name MICROTHERM. The sheet thermal insulation acts to reduce
heat loss through the shell wall, maintain a desired interior
temperature, and prevent thermal fatigue of the shell material by
maintaining an outer shell temperature of 250 deg F. during
use.
[0047] An alternative embodiment of the inventive tube sheet will
now be described. Second embodiment tube sheet 310 (FIG. 12) is
identical to tube sheet 10 in that it is a monolithic ceramic
refractory plate housed within shell 30 as described above.
However, each of the plural through channels 328 of second
embodiment tube sheet 310 are modified to accommodate a
longitudinally adjustable sealing plug 330, one of which resides
within each through channel 328 so as to receive and support the
terminal ends 3, 4 of ceramic tubes 2.
[0048] Plural through channels 328 are located in the central
region of tube sheet 310, and extend from inner face 320 to outer
face 322 as described above for tube sheet 10. However, the shape
of through channels 328 has been modified to accommodate plug 330.
The intersection of each through channel 328 and outer face 322 is
enlarged to form vacancy 325 having a generally circular cross
section of a diameter which is greater than that of the through
channel 328. Vacancy 325 is provided with a tapered portion 362
adjacent to outer face 322 that allows easy insertion of tube 2 and
plug 330 into through channel 328. Threads 323 are provided on the
remaining surfaces of vacancy 325 for engagement with mating
threads 332 on the exterior surface 336 of plug 330. With the
exception of vacancy 325, each through channel 328 has a circular
cross section and is of generally uniform diameter across the
thickness of tube sheet 310, exiting at inner face 320.
[0049] Plug 330, a generally elongate hollow tube, is provided with
a first end 333, a mid portion 335, and a second end 334, where
second end 334 is separated from first end 333 by mid portion 335,
and is provided with an exterior surface 336 and an interior
surface 337. Plug 330 resides within and along the entire length of
each through channel 328 such that first end 333 lies generally
flush with outer face 322, and second end 334 lies generally flush
with inner face 320. Threads 332 are provided on the exterior
surface 336 of first end 333. Threads 332 are sized and shaped to
matingly engage threads 323 located on the surfaces of vacancy 325
so as to allow securement and longitudinal positional adjustment of
plug 330 within each through channel 328.
[0050] In the preferred embodiment, plug 330 is formed of silicon
carbide. However, it is well within the scope of this invention to
form plug 330 from alternative materials, which include, but are
not limited to, silicon nitride (Si.sub.3N.sub.4), a ceramic body
containing a percentage of a thermally conductive material such as
30% alumina oxide (Al.sub.2O.sub.3) and 70% silicon carbide (SiC),
or metallic ceramics such as metal particle reinforced ceramic
tube.
[0051] To minimize fluid leakage between plug 330 and through
channel 328, plug gasket 360 is provided about the exterior surface
336 of plug 330 at the intersection of mating threads 323, 332 and
tapered portion 362. Plug gasket 360 is received within a gasket
channel 361 formed in through channel 328 such a first side borders
threads 323, 332, and the opposed side abuts tapered portion
362.
[0052] Plug gasket 360 is annular, and preferably a compressible
ceramic. It functions to absorb the expansion of these components
at high temperatures, maintaining tight conformation between plug
330 and through channel 328. It also provides high temperature
resistance and sealing against differential pressures through a
range of variable tube lengths. However, it is within the scope of
this invention to use other sealing means designed for use in this
extreme environment which include, but are not limited to,
compressible ceramic fiber mat, ceramic paper, or high temperature
(1500 degrees F.) ceramic sealant, a caulk-like substance which
maintains a seal high temperature.
[0053] Second end 334 of plug 330 is provided with an articulating
sealing joint 340 and terminates in an insertion ring 350 that
receives the terminal end 3,4 of ceramic tube 2. Articulating
scaling joint 340 is spaced apart from insertion ring 350 such that
it lies between insertion ring 350 and mid portion 335.
Articulating sealing joint 340 consists of a spherical interface
345 formed through second end 334, resulting in two abutting
components 342, 343 which are capable of relative rotational
motions due to the spherical shape of their mutually confronting
surfaces. Spherical interface 345 provides a large area of contact
between the two articulating components 342, 343, resulting in an
efficient fluid sealing mechanism between the components 342, 343,
as well as between articulating sealing joint 340 and tube sheet
310.
[0054] A portion of exterior surface 336 is removed at the terminus
of second-end 334 so as to form an annular shaped, longitudinally
aligned extension of interior surface 337, referred to as insertion
ring 350. Insertion ring 350 has an outer diameter which is less
than that of exterior surface 336 of plug 330, such that ledge 352
is formed at the discontinuity. The outer diameter of insertion
ring 350 is slightly less than the interior diameter of tube 2 so
that in use, insertion ring 350 is received within the hollow
interior of terminal end 3, 4 of tube 2, supporting terminal end 3,
4. Terminal end 3, 4 surrounds insertion ring 350, and abuts ledge
352.
[0055] Through channel 238 is provided with a slight tapered
widening at the intersection of through channel 328 and inner face
320 of tube sheet 310. This widening prevents interference between
terminal end 3, 4 of tube 2 and tube sheet 310 during any
deflection of tube 2 during use.
[0056] Longitudinal adjustment of plug 330 is achieved by securing
plug 330 to tube sheet 310 by engaging threads 332 of plug 330 with
threads 323 on the surfaces of vacancy 325 by screwing plug 330
into through channel 328. This ability to adjust the longitudinal
position of plug 330 within through channel allows compensation for
variations in tube length, ensures that each tube is equally loaded
at assembly, and maximizes the sealing characteristics of
articulating joint 340. Additionally, plug 330 can be completely
removed from outer face 322 of tube sheet 310, allowing replacement
of tube 2 from the dome-side of tube sheet 310, or outside the heat
exchanger itself.
[0057] Method of Manufacture
[0058] The method of manufacturing the inventive monolithic
refractory ceramic tube sheet 10, intended for use in a heat
exchanger operating using temperatures in the range of 1200 to 2800
degrees F. and pressures of 15 psig or greater, will now be
described in detail.
[0059] The unitary, single piece refractory plate is fabricated by
casting tube sheet 10 in place, as a monolithic structure, within
outer shell wall 30 of heat exchanger 1. Plate 15 of tube sheet 10
is formed of a castable refractory ceramic material. The material
selected to form plate 15 is required to have thermal expansion
characteristics compatible with those of the ceramic tubes, have
crushing strength characteristics which meet the pressure
requirements of the ends of the heat exchanger vessel, and to be
relatively resistant to thermal shock.
[0060] Suitable refractory materials for this application include,
but are not limited to, those bonded with calcium aluminate
cements, those bonded with hydratable alumina, or those bonded with
phosphates. Aggregates can range in composition containing various
quantities of bauxite, tabular alumina, fused aluminas, fused
silica, silicon carbides, natural and synthetic mullite, flint,
spinels and magnesias. In the preferred embodiment, the castable
refractory ceramic is formed of calcium aluminate bonded with
mullite, bauxite, and calcined aluminas.
[0061] Method step 1. Provide a mold 100 to receive the cast
refractory material (FIG. 7). The components of mold 100 include a
bottom plate 110, a top plate 150, cylindrical shell 30, and
negatives 160, 180 for forming vacancies within mold 100.
[0062] Shell 30, described above, provides the cylindrical outer
wall of mold 100. As previously discussed, the cylindrical shape of
shell 30 is used for illustrative purposes. It is well within the
scope of this invention to provide shell 30 with other cross
sectional shapes, which include, but are not limited to, polygons.
Bottom plate 110 and top plate 150 are described below as
cylindrical in shape, but those skilled in the art will recognize
that the shape of these components can be modified to accommodate
variation in the shape of shell 30.
[0063] Bottom plate 110 comprises a short cylindrical cold rolled
steel casting plate 120 that sits concentrically on a short
cylindrical alignment plate 130.
[0064] Casting plate 120 has a casting plate upper surface 122, and
a casting plate lower surface 124; a height of approximately 41/2
inches and a diameter of approximately 48 inches. Casting plate
upper surface 122 is machined to ensure a precisely flat, true
surface.
[0065] Alignment plate 130 has an alignment plate upper surface
132, and alignment plate lower surface 134, a height of
approximately 1 inch and a diameter of approximately 67 inches.
Alignment plate 130 is provided with 56 peripheral through holes
118 that extend through its height equally spaced adjacent to and
along the peripheral edge of alignment plate 130. Peripheral
through holes 118 are predrilled with the exact pattern of the
holes of inner flange 50, and thus are used as a reference or guide
to align bottom plate 110 with shell 30, and to ensure that bottom
plate 110 is centered on longitudinal axis 5 of tube sheet 10. When
assembled, bolts 199 extend through both peripheral through holes
118 and flange through holes 59 so as to secure bottom plate 110 to
shell 30.
[0066] Casting plate lower surface 124 is secured to alignment
plate upper surface 132' such that the casting plate and alignment
plate are concentric. Inner flange 50 of shell 30 is secured to the
alignment plate upper surface 132 such that the peripheral edge of
casting plate 120 confronts and abuts flange interior face 52 of
inner flange 50. The outer diameter of casting plate 120 is sized
so as to be received within inner flange 150 with a tight fit so
that casting material is not able to seep between these confronting
members.
[0067] Bottom plate 110 also provided with 52 predrilled
negative-locating through-holes 116 through the combined thickness
of the casting plate 120 and alignment plate 130, arranged within a
generally geometric, preferably rectangular area. This geometric
area is centered on the centerline of bottom plate 110 and spaced
apart from its peripheral edge, where the centerline is co-linear
with longitudinal axis 5. Through holes 116 are precisely
positioned and used to secure negatives 160, 180 in the desired
location on casting plate upper surface 122.
[0068] Precise positioning of negative-locating through-holes 116
is critical since an exact match is required for alignment of tubes
2 with an opposing tube sheet mounted at an opposite end of the
heat exchanger vessel. To this end, mold components bottom plate
110, top plate 150, and negatives 160, 180 are used twice, to
fabricate both tube sheets for use in a single heat exchanger.
Negative-locating through holes 116 are arranged in a geometric
layout that determines the arrangement of the tube array within
vessel 6. As shown in FIGS. 1 and 4, tube through channels 28 are
arranged about the centerline 5 of heat exchanger 1 in a
rectangular grouping, with the centers of through channels 28 on
alternating rows staggered so as to maximize the uniformity of heat
transfer across the array.
[0069] Referring now to FIG. 8, plural arcuate ball seal negatives
160 are used to create vacancies in the inner face 22 of tube sheet
10. In the preferred embodiment, each ball seal negative 160 is
provided with a generally spherical body portion 162, a truncated
upper surface 164, and a truncated lower surface 166. Upper surface
164 is provided with an upwardly extending tab, up-set 168. Up-set
168 is received within a lower end of through channel negative 180'
as a means to align and anchor through channel negative 180 on the
upper surface 164 of ball seal negative 160.
[0070] It is understood that the shape of the ball seal negative
160 is not limited to the generally spherical shape described
above. The shape of the negative is determined by the shape of the
seal employed at the junction between the terminal end of tube 2
and tube sheet 10. In this invention, a generally spherical ball
seal is the preferred sealing device, but other sealing mechanisms
may be substituted. Thus, providing negatives having alternative
exterior shapes, which correspond to alternative sealing
mechanisms, are well within the scope of this invention.
[0071] Each, ball seal negative 160 is located on upper surface of
casting plate in alignment with a negative-locating through-hole
116 and secured by a core bolt 190 that through the bottom plate
110. Ball seal negatives 160 must be exactly flush with upper
surface of casting plate 120 to prevent seepage of castable
material between casting plate 120 and the lower surface 166 of
ball seal negative 160.
[0072] In the illustrative embodiment, 52 ball seal negatives are
formed of nylon and machined to exact tolerances. In the preferred
embodiment, the material used to form ball seal negatives 160 is
ultra high molecular weight polyethylene. This material is selected
because of its ability to maintain the desired shape under the
weight of the refractory material when being cast, while being
flexible enough such that the refractory material will not crack
during the curing stage. It is well within the scope of this
invention, however, to fabricate ball seal negatives 160 from
machined materials or materials cast from urethane, plastic, or
rubber.
[0073] Plural through channel negatives 180 are used to create
fluid through channels within the unitary, single piece refractory
plate 15. Through channel negatives 180 are fabricated of an
elongate section of plastic pipe. The pipe is provided with an
enlarged upper end 182 which is sized and shaped to provide the
shaped widening 90 at the outer face 22 of tube sheet 10, and a mid
portion 186 and lower end 184 of uniform outer diameter sized to
meet the requirements if the inner diameter of the tube sheet
through channels 28. Hollow lower end 184 slides over up set 168 so
as to secure and align through channel negative 180 to the upper
end 168 of ball seal negatives 160.
[0074] Core bolt 190 is long enough to extend completely through
bottom plate 110, ball seal negative 160, and through channel
negative 180. Core bolt 190 is secured to the alignment plate lower
surface 134 using a first nut 191 and washer 192, to the upper
surface 164 of ball seal negative 160 using a second nut 193 and
washer 194, and to the upper end 182 of through channel negative
180 using a third nut 195 and washer 196.
[0075] The number of through channel negatives 180 corresponds
exactly to the number of through channels required within tube
sheet 10. In the illustrative embodiment, 52 through channel
negatives are provided. In the preferred embodiment, the polyvinyl
chlorate (PVC) is used to form through channel negatives 180. As in
the case of ball seal negatives 160, the material is selected
because of its ability to maintain the desired shape under the
weight of the refractory material when being cast, while being
flexible enough such that the refractory material will not crack
during the curing stage. It is well within the scope of this
invention to fabricate through channel negatives 180 from machined
materials or materials cast from urethane, plastic, or rubber.
[0076] Top plate 150 comprises a cylinder having a top plate upper
surface 152 and a top plate lower surface 154. Top plate 150 is a
short cylinder, having an approximate height of 1" and approximate
diameter of 67 inches in the illustrative embodiment. The purpose
of top plate 150 is to create a flush refractory casting surface
that corresponds to tube sheet outer face 22. Central opening 158,
a large opening in the central portion of top plate 150, surrounds
upper ends 182 of through channel negatives 180, and provides an
opening in mold 100 through which refractory ceramic material is
cast. Central opening 158 may be provided in a generally circular
shape (FIG. 11), or may be provided in any convenient alternative
shape including, but not limited to, polygonal.
[0077] Lower surface 154 of top plate 150 is provided with an
outwardly extending half-round bead 156. Bead 156 extends about the
periphery of top plate 150 such that it is spaced apart from both
its peripheral edge and central opening 158. In use, bead 156
extends into the cast material and forms O-ring channel 29 in tube
sheet outer face 22.
[0078] Top plate 150 is provided with 56 peripheral through holes
155 which extend through its height, equally spaced adjacent to and
along the peripheral edge of top plate 150. Peripheral through
holes 155 are predrilled with the exact pattern of the holes of
outer flange 40, and are used to secure top plate 150 to shell 30
during the casting procedure. When assembled, bolts 197 extend
through both peripheral through holes 155 and outer flange through
holes 49 so as to top bottom plate 150 to shell outer edge 36.
[0079] Method step 2. Coat negatives 160, 180 with release
agents.
[0080] Method step 3. Line portions of the mold with sheet
insulation material so as to reduce heat loss through the shell
wall, maintain a desired interior temperature, and prevent thermal
fatigue of the shell material by maintaining an outer shell
temperature of 250 deg F. during use. Insulation (shell insulation
60) is placed overlying shell interior face 32 from shell inner
edge 38 to a location spaced apart from shell outer edge 36.
Insulation (flange insulation 62) is also positioned on flange
first face 56 of inner flange 50 at locations that-are spaced from
shell interior face 32.
[0081] Method step 4. Prepare refractory ceramic material as a wet
mix.
[0082] Method step 5. Cast the monolithic refractory ceramic plate
15 by placement of mold 100 on top of a vibrating table, and
pouring the wet mix into mold 100 through top plate central opening
158, between top plate 150 and plural through channel negatives
180.
[0083] Method step 6. After the refractory is cast into the mold,
vibrate the mold (electrically or pneumatically) to remove air
pockets from the material and provide a dense, uniform mass. The
preferred refractory ceramic material requires 2800-3000 vibrations
per minute for approximately 20 minutes.
[0084] Method step 7. The entire mold 100 with cast refractory
material is leveled to ensure a finished product having inner 20
and outer 22 faces which are normal to the cylindrical walls of
shell 30.
[0085] Method step 8. The entire leveled form with cast refractory
material is covered with a bi-layer covering which consists of an
inner layer of wet burlap and an outer layer of plastic. This
bi-layer covering prevents quick dehydration- and formation of a
"skin", and allows slow maturation of the casting. A curing
compound may also be used to provide a uniform cure and prevent
pocketing of water.
[0086] Method step 9. Allow to air dry for 24-48 hours, depending
on the thickness of plate 15.
[0087] Method step 10. Remove top plate 150 from monolithic plate
15. Additional drying time may be required.
[0088] Method step 11. Remove bottom plate 110 and plural ball seal
negatives 160, leaving shell 30 in place about plate 15 and leaving
the plural through channel negatives 180 in place within plate
15.
[0089] Method step 12. Coat seal vacancy wall 82 with a smooth,
fine grain, high temperature air-setting cement 84 to provide a
uniform and imperfection-free surface which will optimize the
performance of the seal.
[0090] Method step 13. Place casting on a rack in a curing furnace
and cure at temperatures to remove free and chemical water, and to
burn out through channel negatives. Curing is completed in a 72
hour ramp cycle.
[0091] The method steps described above provide the inventive
unitary, single piece refractory tube sheet 10, which is cast in
place, as a monolithic structures within the cylindrical walls of
shell 30 for use in heat exchanger 1.
[0092] While we have shown and described the preferred embodiment
of our invention, it will be understood that the invention may be
embodied otherwise than as herein specifically illustrated and
described, and that certain changes in the form and arrangements of
parts and the specific manner of practicing the invention may be
made within the underlying idea or principles of the invention
within the scope of the appended claims.
* * * * *