U.S. patent application number 13/713476 was filed with the patent office on 2014-06-19 for heat exchanger and distillation column arrangement.
The applicant listed for this patent is Richard John Jibb, Karl K. Kibler, Sang Muk Kwark, Kathryn Oseen-Senda. Invention is credited to Richard John Jibb, Karl K. Kibler, Sang Muk Kwark, Kathryn Oseen-Senda.
Application Number | 20140165650 13/713476 |
Document ID | / |
Family ID | 50929356 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140165650 |
Kind Code |
A1 |
Jibb; Richard John ; et
al. |
June 19, 2014 |
HEAT EXCHANGER AND DISTILLATION COLUMN ARRANGEMENT
Abstract
A shell and tube heat exchanger and distillation column
arrangement for an air separation plant utilizing such heat
exchanger in which tubes for passage of a liquid that is used in
condensing a vapor are located within a cylindrical shell. The
tubes are arranged in an inner array of tubes and an outer array of
tubes surrounding the inner array of tubes and having more tubes
than the inner array. The inner array of tubes present a larger
average area, between tubes, for flow of the vapor in an outward,
radial direction than tubes of the outer array to lessen pressure
drop while allowing for more tubes to be located within the shell
to increase the surface area available for heat exchange between
the liquid and the vapor.
Inventors: |
Jibb; Richard John;
(Wheatfield, NY) ; Oseen-Senda; Kathryn; (Buffalo,
NY) ; Kwark; Sang Muk; (Williamsville, NY) ;
Kibler; Karl K.; (Amherst, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Jibb; Richard John
Oseen-Senda; Kathryn
Kwark; Sang Muk
Kibler; Karl K. |
Wheatfield
Buffalo
Williamsville
Amherst |
NY
NY
NY
NY |
US
US
US
US |
|
|
Family ID: |
50929356 |
Appl. No.: |
13/713476 |
Filed: |
December 13, 2012 |
Current U.S.
Class: |
62/648 ;
165/157 |
Current CPC
Class: |
F25J 2250/02 20130101;
F25J 3/04412 20130101; F28F 9/0131 20130101; F28D 7/1669 20130101;
F28F 9/0265 20130101; F25J 5/005 20130101; F28D 2021/0066
20130101 |
Class at
Publication: |
62/648 ;
165/157 |
International
Class: |
F28F 9/00 20060101
F28F009/00; F25J 3/04 20060101 F25J003/04 |
Claims
1. A shell and tube heat exchanger comprising: two opposed tube
sheets; a cylindrical shell connecting the two opposed tube sheets;
a central vapor inlet, centrally positioned with respect to a
central axis of the shell, to introduce a vapor into the shell; a
central liquid outlet, centrally positioned with respect to the
central axis of the shell, for discharging condensate produced by
condensing the vapor; tubes connecting the two opposed tube sheets
for indirectly exchanging heat between a liquid flowing within the
tubes and the vapor, thereby, condensing the vapor and producing
the condensate within the cylindrical shell and, at least in part,
inducing a flow of the vapor in an outward, radial direction toward
the shell as a result of the condensation of the vapor; the tubes
arranged in an inner array of the tubes spaced apart from one
another and surrounding the central vapor inlet and the central
liquid outlet and an outer array of the tubes surrounding the inner
array of the tubes and having a greater number of tubes than the
inner array of the tubes; and the inner array of the tubes and the
outer array of the tubes spaced apart from one another to present
areas between the tubes, the areas of the inner array of the tubes
having an average of the areas greater than that of the areas of
the tubes of the outer array of the tubes situated directly
adjacent the inner array of the tubes to lower pressure drop of the
flow of the vapor in the outward, radial direction.
2. The shell and tube heat exchanger of claim 1, wherein: the
central vapor inlet is located in one of the two opposed tube
sheets; and the central liquid outlet is located in the other of
the two opposed tube sheets;
3. The shell and tube heat exchanger of claim 2, wherein at least
one support located within the shell supports the inner array of
the tubes in an intermediate location of the inner array of the
tubes between the tube sheets to inhibit vibration within the inner
array of the tubes.
4. The shell and tube heat exchanger of claim 3, wherein the at
least one support includes: a plate having openings through which
the inner array of the tubes pass and are thereby supported; and
the plate supported within the shell and tube heat exchanger at the
intermediate location and opposite to the central vapor inlet so
that the plate also acts as a baffle to also help in inducing the
outward, radial flow of the vapor.
5. The shell and tube heat exchanger of claim 3, wherein the plate
has a star-like outer periphery having indentations located
opposite to innermost tubes of the outer array of the tubes.
6. The shell and tube heat exchanger of claim 4, wherein: the plate
is supported by a set of supports connecting the plate to the one
of the two tube sheets; and a cylindrical member extends from the
bottom of the plate towards the other of the two tube sheets to
inhibit flow of the vapor around the plate in a direction taken
from the one of the two tube sheets to the other of the two tube
sheets.
7. The shell and tube heat exchanger of claim 1 or claim 6, wherein
the inner array of the tubes is arranged in a circular pattern
having an equal spacing between the tubes.
8. The shell and tube heat exchanger of claim 1 or claim 6, wherein
the inner array of the tubes is arranged in a hexagonal pattern
having an equal spacing between the tubes.
9. The shell and tube heat exchanger of claim 7, wherein the outer
array of the tubes is arranged in a repeating hexagonal
pattern.
10. The shell and tube heat exchanger of claim 8, wherein the outer
array of the tubes is arranged in a repeating hexagonal
pattern.
11. A distillation column arrangement for an air separation plant
comprising: a higher pressure distillation column configured to
separate nitrogen from the air and thereby to produce a
nitrogen-rich vapor column overhead and a crude liquid oxygen
column bottoms; a lower pressure distillation column configured to
further refine the crude liquid oxygen and thereby to produce an
oxygen-rich liquid and a lower pressure nitrogen-rich vapor column
overhead; a condenser reboiler for condensing at least part the
nitrogen-rich vapor column overhead produced in the higher pressure
column and for partially vaporizing an oxygen-rich liquid produced
in the lower pressure column; means for introducing the oxygen-rich
liquid within tubes of the condenser reboiler; and the condenser
reboiler comprising; two opposed tube sheets; a cylindrical shell
connecting the two opposed tube sheets and located within a bottom
region of the lower pressure column; a central vapor inlet
centrally positioned with respect to a central axis of the shell
and connected to an inlet conduit communicating between the central
vapor inlet and the higher pressure column to receive a
nitrogen-rich vapor stream composed of the nitrogen-rich vapor
column overhead and thereby introduce the nitrogen-rich vapor
stream into the shell; a central liquid outlet centrally positioned
with respect to the central axis of the shell and connected to a
piping network having a first conduit connected to the higher
pressure column for introducing a reflux stream composed of the
part of the nitrogen-rich liquid into the higher pressure column
and a second conduit connected to the lower pressure column for
introducing another reflux stream composed of another part of the
nitrogen-rich liquid into the lower pressure column; the tubes of
the condenser reboiler connecting the two opposed tube sheets for
indirectly exchanging heat between the oxygen-rich liquid flowing
within the tubes and the nitrogen-rich vapor, thereby condensing
the nitrogen-rich vapor and producing the nitrogen-rich liquid
within the cylindrical shell, at least partially vaporizing the
oxygen-rich liquid within the tubes and, at least in part, inducing
a flow of the nitrogen-rich vapor in an outward, radial direction
toward the shell as a result of the condensation of the
nitrogen-rich vapor; the tubes arranged in an inner array of the
tubes spaced apart from one another and surrounding the central
vapor inlet and the central liquid outlet and an outer array of the
tubes surrounding the inner array of the tubes and having a greater
number of tubes than the inner array of the tubes; and the inner
array of the tubes and the outer array of the tubes spaced apart
from one another to present areas between the tubes, the areas of
the inner array of the tubes having an average of the areas greater
than that of the areas of the tubes of the outer array of the tubes
situated directly adjacent the inner array of the tubes to lower
pressure drop of the flow of the nitrogen-rich vapor in the
outward, radial direction.
12. The distillation column arrangement of claim 11, wherein: the
central vapor inlet is located in one of the two opposed tube
sheets; and the central liquid outlet is located in the other of
the two opposed tube sheets;
13. The distillation column arrangement of claim 12, wherein: the
oxygen-rich liquid is composed of the oxygen-rich liquid column
bottoms produced in the lower pressure column; and the oxygen-rich
liquid circulation means comprises: the inner array of the tubes
and the outer array of the tubes open at opposite ends thereof; the
condenser reboiler submerged within the oxygen-rich liquid column
bottoms; and the oxygen-rich liquid flowing within the inner array
of the tubes and the outer array of the tubes through a
thermosiphon effect.
14. The distillation column arrangement of claim 12, wherein at
least one support located within the shell supports the inner array
of the tubes in an intermediate location of the inner array of the
tubes between the tube sheets to inhibit vibration within the inner
array of the tubes.
15. The distillation column arrangement of claim 14, wherein the at
least one support includes: a plate having openings through which
the inner array of the tubes pass and are thereby supported; and
the plate supported within the shell and tube heat exchanger at the
intermediate location and opposite to the central vapor inlet so
that the plate also acts as a baffle to also help in inducing the
outward, radial flow of the vapor.
16. The distillation column arrangement of claim 13, wherein the
plate has a star-like outer periphery having indentations located
opposite to innermost tubes of the outer array of the tubes.
17. The distillation column arrangement of claim 16, wherein: the
plate is supported by a set of supports connecting the plate to the
one of the two tube sheets; and a cylindrical member extends from
the bottom of the plate towards the other of the two tube sheets to
inhibit flow of the vapor around the plate in a direction taken
from the one of the two tube sheets to the other of the two tube
sheets.
18. The distillation column arrangement of claim 11 or claim 17,
wherein the inner array of the tubes is arranged in a circular
pattern having an equal spacing between the tubes.
19. The distillation column arrangement of claim 11 or claim 17,
wherein the inner array of the tubes is arranged in a hexagonal
pattern having an equal spacing between the tubes.
20. The distillation column arrangement of claim 18, wherein the
outer array of the tubes is arranged in a repeating hexagonal
pattern.
21. The distillation column arrangement of claim 19, wherein the
outer array of the tubes is arranged in a repeating hexagonal
pattern.
Description
FIELD OF THE INVENTION
[0001] The present invention provides a shell and tube heat
exchanger having tubes located within a shell and a distillation
column arrangement useful for air separation in which the heat
exchanger operably associates higher and lower pressure columns in
a heat transfer relationship to vaporize an oxygen-rich liquid
produced in the lower pressure column through indirect heat
exchange with a nitrogen-rich vapor produced in the higher pressure
column to condense the nitrogen-rich vapor. More particularly, the
present invention relates to such a heat exchanger in which the
tubes are arranged in inner and outer arrays and the inner arrays
present a greater average open area between the tubes thereof than
that of the outer array of tubes to lower pressure drop.
BACKGROUND OF THE INVENTION
[0002] Shell and tube heat exchangers are used in a variety of
industrial processes to indirectly exchange heat between a liquid
and a vapor. Such heat exchangers have an arrangement of tubes
located within a shell. The liquid is introduced into the tubes
where the liquid at least partially vaporizes through indirect heat
exchange with a vapor that is introduced into the shell. As a
result of the heat exchange, the vapor condenses and the condensate
is discharged from the shell. Typically, the tubes are supported by
tube sheets located at opposite ends of the shell that is of
cylindrical configuration. One of the tube sheets has an inlet for
the vapor and the other of the tubesheets has an outlet for
discharging the resulting condensate.
[0003] Shell and tube heat exchangers are used in a variety of
locations within an air separation plant. In an air separation
plant, air is compressed and then purified of higher boiling
impurities such as water vapor and carbon dioxide in a
pre-purification unit. The pre-purification unit employs beds of
adsorbent that are operated in an out-of-phase cycle to adsorb the
water vapor and carbon dioxide and thus, produce a compressed and
purified air stream. The pre-purification unit can also be designed
to remove carbon monoxide and hydrocarbons that may be present in
the air. The resulting compressed and purified air is then cooled
to a temperature that is at or near the dew point of the air and
then introduced into a distillation column arrangement having
higher and lower pressure columns that are arranged in a heat
transfer relationship by a shell and tube heat exchanger such as
described above. In this regard, the higher pressure column will
typically operate at between 5 and 6 bara and the lower pressure
column will operate at between 1.1 and 1.5 bara.
[0004] The air is separated within the higher pressure column into
a nitrogen-rich vapor column overhead and a crude liquid oxygen
column bottoms also known as kettle liquid. A stream of the kettle
liquid is further refined in the lower pressure column into a
nitrogen-rich vapor column overhead and an oxygen-rich liquid. In
an air separation plant the shell and tube heat exchanger is
employed as a condenser-reboiler to condense a stream of the
nitrogen-rich vapor through indirect heat exchange with the
oxygen-rich liquid, thereby to partially vaporize the oxygen-rich
liquid and provide boilup to the lower pressure column. Such a
condenser reboiler can be situated within a sump of the lower
pressure column. The liquid nitrogen is used both as reflux to the
higher and lower pressure columns and also, optionally, as a liquid
product. It is to be noted that shell and tube heat exchangers are
used in other places within the air separation plant, for instance,
as an argon condenser to condense argon within an argon column
attached to the lower pressure column to produce an argon
product.
[0005] U.S. Pat. No. 4,436,146 illustrates a shell and tube heat
exchanger employed as a condenser reboiler in a double column
arrangement of an air separation plant. The condenser reboiler
functions to condense nitrogen-rich vapor overhead of the higher
pressure distillation column through indirect heat exchange with an
oxygen-rich liquid produced in the lower pressure column. The
resulting nitrogen-rich vapor will condense at the higher pressure
of the higher pressure column and thereby supply the heat of
vaporization for the oxygen-rich liquid. In the shell and tube heat
exchanger shown in this patent, the tubes are open at opposite ends
that the heat exchanger sits in a pool of the oxygen-rich liquid
that collects as a column bottoms within the low pressure column.
The vaporization of the oxygen-rich liquid within the tubes
entrains the liquid which rises in the tubes. The resulting
oxygen-rich vapor provides boilup within the lower pressure column
and unvaporized or residual oxygen-rich liquid is returned to the
pool of the oxygen-rich liquid collected in the bottom of the lower
pressure column. Such a heat exchanger is known as a thermosiphon
reboiler. The nitrogen-rich vapor condenses on the exterior of the
tubes and is discharged to a piping network from which the
resulting nitrogen-rich liquid is introduced into both the higher
and lower pressure columns as reflux and can be taken as a liquid
product.
[0006] U.S. Pat. No. 4,436,146 incorporates features that are
employed in condenser reboilers and also, shell and tube heat
exchangers generally. For instance, a baffle plate is provided
opposite to the vapor inlet to help urge the flow of the incoming
nitrogen vapor in an outward, radial direction of the shell.
Beneath this plate is an elongated cylindrical member that will
collect non-condensable substances in the air such as neon and
helium. Additionally, the area provided at the exterior of the
tubes for heat transfer can be enhanced by provision of length-wise
extending fins, also known as fluting. Further, the shell can be
provided with a bellows-like expansion joint that will help reduce
tensile or compressive loading between the tube sheets and the
tubes and the tubesheets and the shell arising from the existence
of a temperature gradient between the tubes and shell which would
tend to cause an unequal expansion or contraction therebetween.
[0007] U.S. Pat. No. 5,699,671 discloses a shell and tube heat
exchanger that can be used as a condenser reboiler within a double
column arrangement of an air separation plant such as has been
described above. The type of heat exchanger shown in this patent is
known as a downflow heat exchanger because the condensing liquid
flows in a downward direction of the tubes. In this patent a
reservoir is provided for collecting the oxygen-rich liquid. The
tubes penetrate the tube sheet and extend into the reservoir to
receive the oxygen-rich liquid. A central conduit extends
downwardly, into the reservoir and is in registry with the inlet
for the nitrogen-rich vapor situated within the tubesheet to feed
the nitrogen-rich vapor into the shell. The oxygen-rich liquid
flows downwardly through the tubes and partially vaporizes. The
liquid that is not vaporized is collected as a liquid column
bottoms within the lower pressure column and the resulting vapor
provides boilup within the lower pressure column. It is to be noted
that the internal surface of each of the tubes can be provided with
a thin metallic film coating having a high porosity and a large
interstitial surface area to increase the surface area for
boiling.
[0008] In any application of a shell and tube heat exchanger, it is
important that the heat transfer area per unit volume available for
indirectly exchanging heat between the vapor and the liquid be as
large as possible so that the heat exchanger is as compact as
possible. In air separation, this heat transfer area will also have
a major effect on the costs of operation of the plant as well as
the profitability of the sale of the separated components of the
plant, for instance, liquid oxygen produced in the lower pressure
column. The reason for this relates to the operation of the higher
and lower pressure columns. At the lower operational pressure of
the lower pressure column, the oxygen-rich liquid is sufficiently
cold enough to condense the higher pressure, nitrogen-rich vapor
produced in the higher pressure column or in other words create a
sufficient temperature difference across the tubes to condense the
higher pressure, nitrogen-rich vapor. As this temperature
difference is decreased, the saturation temperature of the higher
pressure, nitrogen-rich vapor will be lower. As result, the degree
to which the air needs be compressed will also be lower. Since a
major expense in operating an air separation plant is its
electrical power costs incurred in motors used to drive compressors
that compress the air, it is desirable that the plant be operated
at pressure that is as low as possible.
[0009] The heat transfer area will have a direct effect on the
temperature difference; namely, the higher the heat transfer area
provided by the tubes, the lower the temperature difference.
Therefore, in a shell and tube heat exchanger, particularly, for
use in an air separation plant, it is desirable to have as many
tubes as possible within the shell to maximize the heat transfer
area through which heat transfer can occur. However, the problem
with simply increasing the number of tubes in the same volume is
that pressure drop within the heat exchanger will also increase. As
can be appreciated, as the number of tubes is increased, the space
between the tubes decreases resulting in the higher pressure drop
for the vapor as its proceeds in the outward, radial direction.
However, as the pressure drop increases, the advantage of providing
more tubes to increase the heat transfer area diminishes given that
the vapor to be condensed nevertheless has to be compressed to a
sufficient pressure to compensate for the increased pressure
drop.
[0010] As will be discussed, the present invention provides a shell
and tube heat exchanger and a distillation column arrangement for
an air separation plant in which, among other advantages, the tubes
are in an arrangement that will decrease pressure drop and allow
for more tubes to be used to increase heat transfer area.
SUMMARY OF THE INVENTION
[0011] The present invention provides a shell and tube heat
exchanger that comprises two opposed tube sheets, a cylindrical
shell connecting the two opposed tube sheets, a central vapor inlet
and a central liquid outlet. The central vapor inlet is centrally
positioned with respect to a central axis of the shell to introduce
a vapor into the shell. The central liquid outlet is centrally
positioned with respect to the central axis of the shell for
discharging condensate produced by condensing the vapor. In a
specific embodiment of the present invention, the central vapor
inlet can be located in one of the two opposed tube sheets and the
central liquid outlet can be located in the other of the two
opposed tube sheets.
[0012] Tubes connect the two opposed tube sheets for indirectly
exchanging heat between a liquid flowing within the tubes and the
vapor, thereby, condensing the vapor and producing the condensate
within the cylindrical shell. The condensation of the vapor, at
least in part, induces a flow of the vapor in an outward, radial
direction toward the shell. The tubes are arranged in an inner
array of the tubes spaced apart from one another and surrounding
the central vapor inlet and the central liquid outlet and an outer
array of the tubes surrounding the inner array of the tubes and
having a greater number of tubes than the inner array of the tubes.
The inner array of the tubes and the outer array of the tubes are
spaced apart from one another to present areas between the tubes.
The areas of the inner array of the tubes have an average of the
areas greater than that of the areas of the tubes of the outer
array of the tubes situated directly adjacent the inner array of
the tubes to lower pressure drop of the flow of the vapor in the
outward, radial direction.
[0013] Since there will be an average open area between tubes
greater than that of the tubes of the outer array situated directly
adjacent the inner array of tubes, the velocity of the gas will be
reduced to a level that is less than that which would otherwise
have been obtained had the inner and outer array presented the same
average area between tubes. This reduction in velocity will reduce
pressure drop of the vapor as it flows in the outward, radial
direction towards the shell. Since there will be some condensation
of the vapor due to the heat transfer provided at the inner array
of tubes, the flow and therefore, the velocity of the vapor will be
reduced after passage of the vapor through the inner array of tubes
to also reduce pressure drop within the flow of the vapor.
Consequently, it is possible to stack more tubes within the heat
exchanger than would have been possible if all of the tubes were
set at an equal spacing.
[0014] The present invention also provides a distillation column
arrangement for an air separation plant that comprises, a higher
pressure distillation column, a lower pressure distillation column
and a condenser reboiler. The higher pressure distillation column
is configured to separate nitrogen from the air and thereby to
produce a nitrogen-rich vapor column overhead and a crude liquid
oxygen column bottoms. The lower pressure distillation column is
configured to further refine the crude liquid oxygen and thereby to
produce an oxygen-rich liquid and a lower pressure nitrogen-rich
vapor column overhead. The condenser reboiler partially vaporizes
an oxygen-rich liquid produced in the lower pressure column and
condenses at least part of the nitrogen-rich vapor column overhead
produced in the higher pressure column. A means is provided for
introducing the oxygen-rich liquid within tubes of the condenser
reboiler. The condenser reboiler has the features of the shell and
tube heat exchanger discussed above. In this regard, the condenser
reboiler is provided with the two opposed tube sheets, a
cylindrical shell, a central vapor inlet, a central liquid outlet.
The central vapor inlet is centrally positioned with respect to a
central axis of the shell and connected to an inlet conduit
communicating between the central vapor inlet and the higher
pressure column to receive a nitrogen-rich vapor stream composed of
the nitrogen-rich vapor column overhead and thereby introduce the
nitrogen-rich vapor stream into the shell. The central liquid
outlet is centrally positioned with respect to the central axis of
the shell and connected to a piping network having a first conduit
connected to the higher pressure column for introducing a reflux
stream composed of the part of the nitrogen-rich liquid into the
higher pressure column and a second conduit connected to the lower
pressure column for introducing another reflux stream composed of
another part of the nitrogen-rich liquid into the lower pressure
column. In a specific embodiment, the central vapor inlet can be
located in one of the two opposed tube sheets and the central
liquid outlet can be located in the other of the two opposed tube
sheets.
[0015] The tubes of the condenser reboiler connect the two opposed
tube sheets for indirectly exchanging heat between the oxygen-rich
liquid flowing within the tubes and the nitrogen-rich vapor,
thereby condensing the nitrogen-rich vapor and producing the
nitrogen-rich liquid within the cylindrical shell, at least
partially vaporizing the oxygen-rich liquid within the tubes and,
at least in part, inducing a flow of the nitrogen-rich vapor in an
outward, radial direction toward the shell as a result of the
condensation of the nitrogen-rich vapor. The tubes in the inner and
outer array of the tubes are arranged in the same manner as the
shell and tube heat exchanger discussed above to lower pressure
drop of the flow of the nitrogen-rich vapor in the outward, radial
direction.
[0016] The oxygen-rich liquid can be composed of the oxygen-rich
liquid column bottoms produced in the lower pressure column. The
oxygen-rich liquid circulation means can comprise the inner array
of the tubes and the outer array of the tubes open at opposite ends
thereof and with the condenser reboiler submerged within the
oxygen-rich liquid column bottoms. The oxygen-rich liquid flows
within the inner array of the tubes and the outer array of the
tubes through a thermosiphon effect.
[0017] In either the shell and tube heat exchanger or the condenser
reboiler, at least one support can be located within the shell to
support the inner array of the tubes in an intermediate location of
the inner array of the tubes between the tube sheets to inhibit
vibration within the inner array of the tubes. The at least one
support can include a plate having openings through which the inner
array of the tubes pass and are thereby supported. The plate is
supported within the shell and tube heat exchanger at the
intermediate location and opposite to the central vapor inlet so
that the plate also acts as a baffle to also help in inducing the
outward, radial flow of the vapor. The plate can be provided with a
star-like outer periphery having indentations located opposite to
innermost tubes of the outer array of the tubes. This, as will be
discussed, will help in the assembly of the heat exchanger.
Further, the plate can be supported by a set of supports connecting
the plate to the one of the two tube sheets. A cylindrical member
extends from the bottom of the plate towards the other of the two
tube sheets to inhibit flow of the vapor around the plate in a
direction taken from the one of the two tube sheets to the other of
the two tube sheets.
[0018] Again, in either the shell and tube heat exchanger or the
condenser reboiler, the inner array of the tubes can be arranged in
a circular pattern having an equal spacing between the tubes.
Alternatively, the inner array of the tubes can be arranged in a
hexagonal pattern having an equal spacing between the tubes.
Further, in either the circular or hexagonal pattern of tubes, the
outer array of the tubes is arranged in a repeating hexagonal
pattern.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] While the specification concludes with claims distinctly
pointing out the subject matter that Applicants regard as their
invention, it is believed that the invention will be better
understood when taken in connection with the drawings in which:
[0020] FIG. 1 is a fragmentary elevational, sectional view of a
distillation column arrangement in accordance with the present
invention for an air separation plant;
[0021] FIG. 2 is an elevational sectional view of a condenser
reboiler, also in accordance with the present invention, used in
the distillation column arrangement of FIG. 1 with tubes removed to
illustrate internal features of the condenser reboiler;
[0022] FIG. 3 is a plan sectional view of a tube arrangement of the
condenser reboiler shown in FIG. 1;
[0023] FIG. 4 is a plan view of an alternative embodiment of an
arrangement of tubes in the condenser reboiler shown in FIG. 1;
[0024] FIG. 5 is plan view of yet a further, alternative embodiment
of the arrangement of tubes in the condenser reboiler shown in FIG.
1; and
[0025] FIG. 6 is a top plan view of a baffle plate used within the
condenser reboiler shown in FIG. 1.
DETAILED DESCRIPTION
[0026] With reference to FIG. 1, a distillation column arrangement
1 for an air separation plant in accordance with the present
invention is shown. Distillation column arrangement 1 has higher
and lower pressure distillation columns 2 and 3 and two condenser
reboilers 4A and 4B of the same design linking the higher and lower
pressure distillation columns 2 and 3 in a heat transfer
relationship. The distillation column arrangement 1 is specifically
designed to conduct a distillation process in connection with a
cycle known as the Linde double column cycle that has been
discussed in some detail above.
[0027] It is understood, however, that the distillation column
arrangement 1 is but one application of the present invention which
has more general applicability to any heat exchanger of shell and
tube design and in any application thereof. As such, although for
exemplary purposes the present invention is discussed below with
respect to condenser reboilers, the invention and such discussion
would have application to any shell and tube heat exchanger used in
condensing a vapor through indirect heat exchange with a fluid.
[0028] Distillation column arrangement 1, as well known in the art,
is used in the separation of nitrogen from oxygen to produce
nitrogen and oxygen enriched products. Although not illustrated, as
also well known, in an air separation plant, incoming air is
compressed, purified and cooled to a temperature suitable for its
rectification. The purified and cooled air is then introduced into
the higher pressure distillation column 2 where an ascending vapor
phase is contacted with the descending liquid phase by known mass
transfer contacting elements, generally indicated by reference
number 10, which can be structured packing, random packing or sieve
trays or a combination of packing and trays. The ascending vapor
phase of the air becomes evermore rich in nitrogen as it ascends
and a descending liquid phase becomes evermore rich in oxygen. As a
result, a bottoms liquid known as crude liquid oxygen or kettle
liquid collects in the bottom of the higher pressure column 2 and a
nitrogen-rich vapor collects in a top portion 12 thereof.
[0029] A stream of the kettle liquid that collects within the
higher pressure column 2 is introduced into the lower pressure
column 3 for further refinement. Again, ascending vapor and liquid
phases are contacted within mass transfer contacting elements such
as generally indicated by reference number 14. The liquid phase
becomes evermore rich in oxygen as it descends within the lower
pressure column 3 to form an oxygen-rich liquid column bottoms 16.
As is also known in the art, as the liquid descends, the
concentration of the argon within the liquid phase will increase.
Although not illustrated, an argon and oxygen containing vapor
stream could be removed from the lower pressure column 3 and then
further refined in an argon column to produce an argon-rich
product. Further, although not illustrated, a stream of the
oxygen-rich liquid column bottoms 16 could be taken as a product
directly or vaporized within the main heat exchanger to help cool
the air or pumped and then vaporized within a heat exchanger
against a boosted pressure stream of air to produce a product at
pressure. The resulting liquid air could also be introduced into
the lower pressure column 3 and/or the higher pressure column 2. As
with the higher pressure column 2, the vapor phase within the lower
pressure distillation column 3 will become evermore rich in
nitrogen as it ascends.
[0030] The descending liquid phase in each of the higher and lower
pressure distillation columns 2 and 3 is initiated by refluxing the
columns with a nitrogen-rich liquid produced by condensing the
nitrogen-rich vapor collected in the top portion 12 of higher
pressure column 2 through indirect heat exchange with the
oxygen-rich liquid column bottoms 16 of the lower pressure column
3. All of such vapor need not, however, be condensed in that some
of it could be removed as a high pressure product. This indirect
heat exchange is carried out within condenser reboilers 4A and 4B.
Although two of such heat exchangers are shown, as would be known
to those skilled in the art, there could be only one or more than
two of such heat exchangers in a specific application of the
present invention. A stream of the nitrogen-rich vapor "A" is
introduced into an inlet conduit 18 that branches out to condenser
reboiler 4A and 4B through inlet branches 20 and 22. As will be
discussed, the nitrogen-rich vapor indirectly exchanges heat with
the oxygen-rich liquid column bottoms 16 ascending in tubes thereof
to partially vaporize the liquid and to fully condense the vapor.
The liquid ascends within the tubes by the thermosiphon effect,
discussed above. The vaporization of the oxygen-rich liquid column
bottoms 16 initiates formation of the ascending vapor phase within
lower pressure distillation column 3 as shown by arrowheads "B".
Although not illustrated, liquid that is not vaporized is returned
to the bottom of the lower pressure distillation column 3.
[0031] The resulting condensate that consists of nitrogen-rich
liquid is discharged from the condenser reboilers 4A and 4B by a
piping network 24 that includes branches 26 and 28 connected to the
condenser reboilers 4A and 4B to collect the nitrogen-rich liquid
shown by arrowhead "C". A first conduit 30 is connected to the
higher pressure column 2 for introducing a reflux stream "D"
composed of the part of the nitrogen-rich liquid into the higher
pressure column and a second conduit 32 is connected to the lower
pressure column 3 for introducing another reflux stream "E"
composed of another part of the nitrogen-rich liquid into the lower
pressure column. Preferably, a liquid distributor 34 is provided
within the top portion 12 of the higher pressure column 2 to
collect the reflux and distribute it to the underlying mass
transfer contacting elements 10. Although not illustrated, a
similar arrangement would be used in connection with the
introduction of liquid reflux stream "E" into the top of the lower
pressure column 3.
[0032] With reference to FIG. 2, condenser reboiler 4A is
illustrated. The same design would be used in condenser reboiler
4B. Condenser reboiler 4A is a shell and tube heat exchanger that
is provided with two opposed tube sheets 36 and 38. A cylindrical
shell 40 connects the tube sheets 36 and 38. A bellows-like
expansion joint 42 can be provided for purposes mentioned above,
namely, differential expansion. Tube sheet 36 is provided with a
central vapor inlet 44 to allow the nitrogen-rich vapor "A" to
enter the shell 40. An inlet pipe 46 can be connected to the tube
sheet 36 in registry with the central vapor inlet 44 for connection
of the central vapor inlet 44. Inlet pipe 46 is in turn connected
to branch 20 of the inlet conduit 18. The same provision can be
made with respect to condenser reboiler 4B that also has an inlet
pipe 46 connected to branch 22 of the inlet conduit 18. A central
liquid outlet 48 is provided in the tube sheet 38 for discharging
the condensate produced by condensing the nitrogen-rich vapor and
thereby forming the nitrogen-rich liquid "C". Outlet pipe 50 can be
connected to the tube sheet 38 in both condenser reboilers 4A and
4B for connection to branches 26 and 28 of the piping network 24.
It is to be noted that as well known in the art, other possible
configurations for inlets and outlets are possible. However, in the
illustrated embodiment, the central vapor inlet 44 and the central
liquid outlet 48 are centrally positioned with respect to the
central axis 2-2 of the shell 40 which is cylindrical.
[0033] The tubesheets 36 and 38 are connected by tubes 52 which are
all of the same design and diameter. It is to be noted that all of
the tubes 52 could be provided with an outer fluted surface and the
interior of the tubes could be provided with an enhanced boiling
surface such as been discussed above. The incoming nitrogen-rich
vapor "A" will be condensed through indirect heat exchange with the
oxygen-rich liquid column bottoms flowing upwardly through the
tubes 52 due to the thermosiphon effect. Since the nitrogen-rich
vapor "A" centrally enters the shell 40, through the central vapor
inlet 44 and then flows in an outward, radial direction where the
nitrogen-rich vapor "A" is successively condensed, a pressure
gradient will be created in the flow of the nitrogen-rich vapor due
to such condensation. The result of this gradient is that the flow
of nitrogen-rich vapor "A" will be displaced from an axial flow,
with respect to shell 40, to a flow in an outward, radial direction
as shown by arrowheads "A'" and "A''". As will be discussed, a
baffle plate 66 can also be provided that will also have an effect
of urging the incoming flow in the outward radial direction
"A''".
[0034] As has been discussed above, it is desirable to maximize the
surface area provided by the tubes 52 for the indirect heat
exchange. However, as the number of tubes 52 increases, the
pressure drop within the condenser reboiler 4A with respect to the
nitrogen-rich vapor will also increase. The reason for this is that
as the number of tubes 52 increases, there will be less area
between the tubes for the nitrogen-rich vapor to flow and
therefore, the velocity of the nitrogen-rich vapor between tubes
52, on average, will increase to in turn increase the pressure
drop. This would be true in any shell and tube heat exchanger and
in any application thereof. However, in case of an air separation
plant, the end effect would be increased compression requirements
for the incoming air to the plant to overcome the increased
pressure drop that would negate the advantage of having the
increased surface area for the indirect heat exchange.
[0035] With reference to FIG. 3, the present invention allows for a
low pressure drop operation while at the same time an increased
surface area for the indirect heat exchange by providing an inner
array of tubes 54 that can be arranged in a circle as shown by the
dashed line 56 and an outer array of tubes 58 surrounding the inner
array of tubes 54 with a closer spacing than the inner array of
tubes 54 and with a greater number of tubes 54 than in the inner
array. Specifically, the area between tubes 54 available for the
flow of the nitrogen-rich vapor "A" in the outward, radial
direction "A''" is given by a product of the space "S.sub.1"
between tubes 54 and the height of the tubes "H" divided by two. It
is understood that since baffle plate 66 is situated at half of the
height "H", then the relevant height is "H" divided by two.
However, if a baffle plate were situated at a different level, the
relevant dimension would change. Also, if a balffle plate were not
present, then of course the relevant area dimension would be equal
to "H", shown in FIG. 2. The area between tubes 58 of the outer
array is given by a product of the space "S.sub.2" between the
tubes 58 and the height "H/2". As is apparent, the space "S.sub.1"
is greater than "S.sub.2" and therefore, the area available for
flow of the nitrogen-rich vapor "A" between the tubes 52 of the
inner array is greater than that between the tubes 58. As a result,
the velocity of the nitrogen-rich vapor "A" as it flows through the
inner array of tubes 54 is less than it would otherwise have been
the case had all of the tubes 52 been arranged with the spacing of
the outer array of tubes 58. This results in a reduced pressure
drop for the flow of the nitrogen-rich vapor at least between the
inner array of tubes 52. At the same time, the nitrogen-rich vapor
is also being condensed through indirect heat exchange with the
oxygen-rich liquid 16 that provides a pressure gradient which in
turn causes nitrogen-rich vapor flow between the tubes 58 of the
outer array that are located directly adjacent the inner array of
tubes 54. As the nitrogen-rich vapor flows in the outward, radial
direction, pressure drop will be less due to the decrease in the
nitrogen mass flow. Consequently, the outer array of tubes 58 can
be packed more closely to provide an enhanced surface area for the
heat exchange between the nitrogen-rich vapor and the oxygen-rich
liquid column bottoms 16 to reduce the average temperature
difference and therefore, the required pressure of the
nitrogen-rich vapor and consequently, the degree to which the
incoming air to the air separation plant has to be compressed.
[0036] With reference to FIG. 4, an inner array of tubes 54' is
provided that is arranged in a hexagonal array shown by the shown
by the dashed line 60. Additionally, the outer array of tubes 58'
is arranged in a repeating hexagonal array shown by the dashed line
62. Although less apparent in FIG. 3, the outer array of tubes 58
shown therein are situated in such an array. The space "S.sub.1"
between the inner array of tubes 54' is greater than the space
"S.sub.2'" of the outer array of tubes 58' to lower pressure drop
in the same manner as has been discussed with the tube arrangements
shown in FIG. 3.
[0037] Although regular spacing for the inner array of tubes 54 and
54' is illustrated in FIGS. 3 and 4, all that is required is that
the average area between the tubes of the inner array be less than
that of the outer array of tubes that are located directly adjacent
the inner array. This is illustrated in FIG. 5 in which the inner
array of tube 54'' are arranged in a hexagonal pattern 64 as shown
by the dashed line. The inner array of tubes 54'' is formed by
removing two tubes at opposite ends of the hexagonal pattern 60
shown in FIG. 4. As a result two pairs of tubes 54'' are separated
by a space "S.sub.3" and the remainder of all tubes are separated
by a space "S.sub.2'" that is less than the space "S.sub.3". If the
average of the spaces and therefore the areas presented between
tubes 54'' and the adjacent row of tubes 58'' is compared, then
such average area of the inner row of tubes 54'' will be less than
the average area of the outer row of tubes 58''. As used herein and
in the claims, such "average of the areas" means an arithmetic
average in which the sum of all of the areas between tubes is
divided by the number of areas. This lower average area of the
inner array of tubes 54'' than the next adjacent row of tubes 58''
of the outer array will result in a decrease in pressure drop. In
fact, referring to FIG. 3, if one such tube 54 of the inner array
were removed, there would be a positive effect in reducing pressure
drop because such removal would result in a decrease in velocity of
the nitrogen-rich vapor. However, it is preferred that the spacing
between tubes be regular, at least for the inner array of tubes so
that the nitrogen rich vapor is distributed evenly in the outward,
radial direction. Having said this, the same is not true for the
outer array of tubes, for instance tubes 58 of FIG. 3. As the tubes
lie further out from the geometric circular center of the shell,
the superficial velocity of the nitrogen-rich vapor will decrease
and therefore outer tubes can be spaced closer than inner tubes to
result in a further increase the surface area available for the
indirect heat transfer.
[0038] Therefore, in accordance with the present invention, the
average area for the inner array of tubes, for instance 54, will
always be less than that of the outer array of tubes, for instance
58, that are located directly adjacent the inner array. The average
area of the inner array is not always less than that of succeeding
tubes of the outer array that are not located directly adjacent the
inner array. For clarity of this concept, tubes 54 of the inner
array shown by the dashed line 56 and two tubes of the outer array
has been labeled as tubes 58a for purposes of showing the tubes 58
that are located adjacent the inner array of tubes which must
present a greater average area than the inner array of tubes.
[0039] Rather than the hexagonal pattern shown for the outer array
of tubes 58 of FIG. 3, other arrangements could be used. For
instance, circular arrangements could be used and with the number
of tubes increasing in each successive circular row of tubes as
viewed in the outward radial direction of flow. The hexagonal array
is, however, preferred for the outer array of tubes. Although such
circular arrays are possible, the hexagonal array gives a tighter
spacing than a circular array and a higher efficiency.
[0040] In the practice of the present invention, although as
mentioned above, positive results can be obtained by simply
removing a tube from the inner array, more predicable results can
be obtained. In this regard, in a practical application of the
present invention, the velocity would first be computed in the
spacings "S.sub.1" provided in the inner array of tubes 54. This
would be done by dividing the mass flow by the product of the
minimum flow area between adjacent tubes and the fluid bulk
density. From this velocity, the frequency of shedding of vortices
from the back of the tubes is computed as described in Heat
Exchanger Design Handbook, "Flow induced vibration," Ch.
4.6.1-4.6.6, Hemisphere Publishing Corporation (1987) and compared
with the natural frequency of the tubes to make certain that the
computed frequency is not at the natural frequency and in fact is
preferably below 80 percent or above 120 percent of such frequency.
This frequency is computed by the following formula.
f n = .beta. 2 .pi. A ( EI M ) 0.5 ##EQU00001##
(2) [0041] .beta.: Dimensionless geometry number [0042] M.sub.o:
Unit mass (kg/m) [0043] A: Unit area (m.sup.2) [0044] E: Young's
Modulus (N/m.sup.2) [0045] I: Momentum (m.sup.4)
[0046] Next the velocity for the adjacent row of tubes in the outer
array, namely tubes 58 situated directly adjacent tubes 54, is
calculated. This is done by dividing the mass flow by the product
of the minimum flow area and the bulk fluid density. The pressure
drop can then be calculated from the first row of tubes 54 to
succeeding rows using well known pressure drop correlations for
flow across a tube bank such as disclosed in the Heat Exchanger
Design Handbook, "Banks of Plain and Finned Tubes,", Chapters
2.2.4-7 to 11. A spacing is then chosen for the inner array of
tubes 54 that will lower pressure drop from the center to the
periphery.
[0047] With reference again to FIG. 2, the incoming nitrogen-rich
vapor "A" is also deflected in the outward, radial direction by
means of a baffle plate 66. Baffle plate 66 is connected to the
tubesheet 36 by means of a set of supports 68. Extending from the
underside of baffle plate 66 is a cylindrical member 70 that helps
prevent a flow of the nitrogen rich vapor "A" directly to the
central liquid outlet 48 and that acts to trap components of the
air, for instance, neon and helium, that would not be condensed
within the condenser reboiler 4A. A tube 72 can be provided to
discharge such incondensable substances from the lower pressure
column 3 through a tube 73, shown in FIG. 1, that connect to the
tube(s) 72 and penetrates the shell of the lower pressure column 3.
Baffle plate 66 is set at half of the length of the tubes 54 and
58. This spacing, however, may need to be varied to ensure that
vapor velocity exists at the outermost tube 58 located adjacent the
shell 40 to prevent the build up of condensable substances in the
vapor.
[0048] With reference to FIG. 6, baffle plate 66 is provided with a
series of openings 73 through which the inner array of tubes 54
pass. While these openings 73 are in a circular pattern, this may
be varied in case of other tube arrangements. For instance, in case
of the tube arrangement shown in FIG. 4, the openings 73 would have
a hexagonal pattern to match that of the inner array of tubes 54'.
The baffle plate 66 thereby also serves as a central support for
the inner array of tubes 54 which can vibrate due to the shedding
of vortices at a rate matching the natural frequency of the tube,
or due to turbulent buffeting resulting from high velocity in the
gap between tubes. In this regard, depending upon the length of the
tubes 52 used within a shell tube heat exchanger, such as the
illustrated condenser reboiler 4A, more than one such central
support for the tubes could be provided. Additionally, the outer
periphery of the baffle plate 66 is of star-like configuration that
is provided by indentations 74 that abut the row of the outer array
of tubes 58 situated directly adjacent the inner array of tubes 54.
Preferably, condenser reboiler is assembled in a horizontal
orientation and such indentations 74 provide support for the
adjacent row of tubes 58 to help in the assembly process.
[0049] It is understood that baffle plate 66, while required in the
condenser reboiler specifically illustrated in the Figures, is not
required in all cases. For example, if a shell and tube heat
exchanger were fabricated in accordance with the present invention
that has a lesser height "H" than that illustrated, then a baffle
plate and intermediate support of the inner array of tubes 54 might
not be required.
[0050] As mentioned previously, the above discussion would have
applicability to the design of any shell and tube heat exchanger.
It would also have application to any shell and tube heat exchanger
used in connection with a double distillation column for an air
separation plant. In this regard, although the condenser-reboiler
was illustrated as a thermosiphon type of heat exchanger, a
condenser reboiler in accordance with the present invention could
also be constructed as a down flow type. In such case, a liquid
reservoir would receive oxygen-enriched liquid from the overlying
mass transfer contacting element which could be structured packing
as shown by reference number 14. The collected liquid would then be
distributed to the tubes which would flow in a downward direction
where it would be partially vaporized through the indirect heat
exchange with the nitrogen-rich vapor. The liquid phase would
collect as the oxygen-rich liquid column bottoms and the vapor
phase would provide boilup in the low pressure column 3.
[0051] While the present invention has been described with
reference to preferred embodiments, as will be understood by those
skilled in the art, numerous additions and omission can be made
without departing from the spirit and scope of the present
invention as set forth in the appended claims.
* * * * *