U.S. patent application number 12/133917 was filed with the patent office on 2009-12-10 for vertical combined feed/effluent heat exchanger with variable baffle angle.
This patent application is currently assigned to LUMMUS NOVOLENT GMBH/LUMMUS TECHNOLOGY INC.. Invention is credited to Krishnan S. Chunangad, Mark S. Karrs, Bashir I. Master.
Application Number | 20090301699 12/133917 |
Document ID | / |
Family ID | 41398773 |
Filed Date | 2009-12-10 |
United States Patent
Application |
20090301699 |
Kind Code |
A1 |
Karrs; Mark S. ; et
al. |
December 10, 2009 |
VERTICAL COMBINED FEED/EFFLUENT HEAT EXCHANGER WITH VARIABLE BAFFLE
ANGLE
Abstract
A shell and tube heat exchanger, such as a vertical combined
feed/effluent heat exchanger (VCFE), including: a shell having a
fluid inlet and a fluid outlet; a plurality of baffles mounted in
the shell to guide the fluid into a helical flow pattern through
the shell; wherein a helix angle .alpha. of a baffle proximate the
inlet is different than a helix angle .beta. of a baffle proximate
the outlet.
Inventors: |
Karrs; Mark S.; (Lincoln
Park, NJ) ; Chunangad; Krishnan S.; (Landing, NJ)
; Master; Bashir I.; (Wayne, NJ) |
Correspondence
Address: |
OSHA LIANG L.L.P.
TWO HOUSTON CENTER, 909 FANNIN, SUITE 3500
HOUSTON
TX
77010
US
|
Assignee: |
LUMMUS NOVOLENT GMBH/LUMMUS
TECHNOLOGY INC.
Bloomfield
NJ
|
Family ID: |
41398773 |
Appl. No.: |
12/133917 |
Filed: |
June 5, 2008 |
Current U.S.
Class: |
165/159 |
Current CPC
Class: |
F28F 9/22 20130101; F28F
2009/228 20130101; F28D 7/1607 20130101; F28D 2021/0064
20130101 |
Class at
Publication: |
165/159 |
International
Class: |
F28F 9/22 20060101
F28F009/22 |
Claims
1. A heat exchanger comprising: a shell having a fluid inlet and a
fluid outlet; a plurality of baffles mounted in the shell to guide
the fluid into a helical flow pattern through the shell; wherein a
helix angle .alpha. of a baffle proximate the inlet is different
than a helix angle .beta. of a baffle proximate the outlet.
2. The heat exchanger of claim 1, wherein helix angle .beta. is
less than helix angle .alpha..
3. The heat exchanger of claim 1, wherein helix angle .alpha. is
less than helix angle .beta..
4. The heat exchanger of claim 1, wherein the helix angle of the
plurality of baffles decreases from the fluid inlet to the fluid
outlet.
5. The heat exchanger of claim 1, wherein the helix angle of the
plurality of baffles increases from the fluid inlet to the fluid
outlet.
6. The heat exchanger of claim 1, wherein a baffle intermediate the
baffle proximate the inlet and the baffle proximate the outlet has
a helix angle .gamma. intermediate helix angles .alpha. and
.beta..
7. The heat exchanger of claim 1, wherein helix angle .alpha. is
less than helix angle .beta., and wherein helix angle .alpha. is
within the range from about 5.degree. to about 35.degree. and
wherein helix angle .beta. is within the range from about
15.degree. to about 45.degree..
8. The heat exchanger of claim 7, wherein helix angle .alpha. is
within the range from about 5.degree. to about 25.degree..
9. A shell and tube heat exchanger comprising: an tubeside inlet
manifold having a first fluid inlet therein; an tubeside outlet
manifold having a first fluid outlet therein; a plurality of tubes
extending between the manifolds and in fluid communication
therewith; a shell extending between the manifolds and encompassing
said tubes, the shell having a second fluid inlet and a second
fluid outlet therein; a plurality of baffles mounted in the shell
to guide the second fluid into a helical flow pattern through the
shell; wherein a helix angle .alpha. of a baffle proximate the
second fluid inlet is different than a helix angle .beta. of a
baffle proximate the second fluid outlet.
10. The heat exchanger of claim 9, wherein helix angle .beta. is
less than helix angle .alpha..
11. The heat exchanger of claim 9, wherein helix angle .alpha. is
less than helix angle .beta..
12. The heat exchanger of claim 9, wherein the helix angle of the
plurality of baffles decreases from the fluid inlet to the fluid
outlet.
13. The heat exchanger of claim 9, wherein the helix angle of the
plurality of baffles increases from the fluid inlet to the fluid
outlet.
14. The heat exchanger of claim 9, wherein a baffle intermediate
the baffle proximate the inlet and the baffle proximate the outlet
has a helix angle .gamma. intermediate helix angles .alpha. and
.beta..
15. The heat exchanger of claim 9, wherein helix angle .alpha. is
less than helix angle .beta., and wherein helix angle .alpha. is
within the range from about 5.degree. to about 35.degree. and
wherein helix angle .beta. is within the range from about
15.degree. to about 45.degree..
16. The heat exchanger of claim 15, wherein helix angle .alpha. is
within the range from about 5.degree. to about 25.degree..
17. A process for exchanging heat with a mixed phase fluid, the
process comprising: feeding a mixed phase fluid comprising a vapor
and at least one of an entrained liquid and an entrained solid to a
heat exchanger, the heat exchanger comprising: a shell having a
fluid inlet, and a fluid outlet; a plurality of baffles mounted in
the shell to guide the fluid into a helical flow pattern through
the shell; converting the mixed phase fluid to essentially all
vapor; and indirectly exchanging heat between the mixed phase fluid
and a heat exchange medium; wherein a helix angle .alpha. of a
baffle proximate the inlet maintains a velocity of the mixed phase
fluid greater than a terminal velocity of the entrained liquid or
solid; and wherein a helix angle .beta. of a baffle proximate the
outlet is greater than helix angle .alpha. of the baffle proximate
the inlet.
18. The process of claim 10, wherein the converting comprises
evaporating the entrained liquid.
19. The process of claim 10, wherein the converting comprises
combusting the entrained solid.
20. The heat exchanger of claim 17, wherein helix angle .alpha. is
within the range from about 5.degree. to about 35.degree. and
wherein helix angle .beta. is within the range from about
15.degree. to about 45.degree..
Description
FIELD OF THE DISCLOSURE
[0001] Embodiments disclosed herein relate generally to a heat
exchanger. More specifically, embodiments disclosed herein relate
to a heat exchanger, such as a shell and tube heat exchanger,
configured to efficiently process two-phase flow.
BACKGROUND
[0002] Numerous configurations for heat exchangers are known and
used for a variety of applications. One of the widely used
configurations, a shell and tube heat exchanger, as illustrated in
FIG. 1, includes a cylindrical shell 10 housing a bundle of
parallel pipes 12, which extend between two end plates 14 so that a
first fluid 16 can pass through the pipes 12. Meanwhile, a second
fluid 18 flows in and through the space between the two end plates
so as to come into contact with the pipes. To provide an improved
heat exchange between the two fluids, the flow path of the second
fluid 18 is defined by intermediate baffles 20 forming respective
passages, which are arranged so that the second fluid flow changes
its direction in passing from one passage to the next. The baffles
20, configured as either partial circular segments as shown
(partial segmental baffles), or as annular rings and discs, are
installed perpendicular to a longitudinal axis 22 of the shell 10
to provide a zigzag flow 24 of the second fluid 18.
[0003] In this arrangement, the second fluid has to sharply change
the direction of its flow several times along the length of the
shell. This causes a reduction in the dynamic pressure of the
second fluid and non-uniform flow velocity thereof, which, in
combination, adversely affect the performance of the heat
exchanger. For example, a perpendicular position of the baffles
relative to the longitudinal axis of the shell results in a
relatively inefficient heat transfer rate/pressure drop ratio.
Additionally, such baffle arrangements produce flow bypass through
baffle-to-shell and pipe-to-baffle clearances, resulting in flow
maldistribution, eddies, back-flow, and higher rates of fouling,
among other undesired consequences.
[0004] Pressure drop, flow distribution, and heat transfer
efficiencies are important variables, especially in the many
industrial chemical processes where a vapor phase reaction is
desired between liquid phase feed and product streams. Example
processes may include naphtha reforming, naphtha hydrotreating,
diesel and kerosene hydrotreating, light hydrocarbon isomerization
and metathesis, and many other industrially important processes.
Such processes will typically include feed/effluent heat exchange
equipment, where the heat required to vaporize the reactor feed
stream is recovered by condensation or partial condensation of the
reactor effluent. Such heat transfer equipment has historically
been arranged as conventional horizontal shell and tube heat
exchangers.
[0005] Increasing unit design capacities (economy of scale)
requires large volumetric throughput with a resultant impact on the
number of shells required to transfer the heat at the limited
temperature differentials. However, due to the flow hydraulics
issues, i.e., two phase inlet flow, varying composition and
molecular weight of the vapor and liquid phases, and variable
volumetric flow and pressure drop resulting from phase change, the
arrangement of conventional exchanger shells in several parallel
and series arrangements is problematic. Symmetrical piping is an
unreliable means to effect partitioning of two phase flow. As the
vapor molecular weight can be much lower than the associated
liquid, especially in hydrotreating services where the vapor is
largely composed of hydrogen, the maldistribution of vapor with the
liquid entering an exchanger can have a marked impact on the
associated boiling curve and, consequently, the mean temperature
difference (MTD) of the boiling operation.
[0006] The concept of vertical combined feed/effluent heat
exchanger (VCFE) was developed to overcome these drawbacks by
integrating large surfaces into a single vertical shell. Such units
have been deployed commercially in different configurations,
including: tubeside boiling/shellside condensing in single
segmental baffle design; tubeside condensing/shellside boiling in
single segmental baffle design; tubeside boiling/shellside
condensing in helical baffle design; tubeside condensing/shellside
boiling in helical baffle design. Helically baffled exchangers are
described, for example, in U.S. Pat. Nos. 5,832,991, 6,513,583, and
6,827,138.
[0007] On a theoretical basis, shellside boiling is favored to
reduce the required surface, as the shellside boiling coefficient
is enhanced by the relatively larger volume of the shellside due to
mass transport effects. However, fouling considerations must also
be addressed, as the tubeside will normally be easier to clean.
[0008] A drawback of the shellside boiling arrangement is
considered at partial load or turndown operation, where the
shellside velocities may not be sufficient to prevent phase
separation and backflow of the liquid fraction back down to the
inlet. Such buildup of heavy liquid fraction at high residence time
can result in fouling.
[0009] The main drawback of any tubeside boiling arrangement is
that the vapor and liquid fractions must be evenly distributed in
each of a multiplicity of tube inlets, in order to maintain the
expected boiling characteristics in each tube, and an inexpensive
and low pressure drop method to achieve this distribution has not
been found.
[0010] Accordingly, there exists a need for heat exchanger and
baffle designs for effectively processing two-phase inlet flow in
vertical units.
SUMMARY OF THE DISCLOSURE
[0011] In one aspect, embodiments disclosed herein relate to a heat
exchanger including: a shell having a fluid inlet and a fluid
outlet; a plurality of baffles mounted in the shell to guide the
fluid into a helical flow pattern through the shell; wherein a
helix angle .alpha. of a baffle proximate the inlet is different
than a helix angle .beta. of a baffle proximate the outlet.
[0012] In another aspect, embodiments disclosed herein relate to a
shell and tube heat exchanger including: a tubeside inlet manifold
having a first fluid inlet therein; a tubeside outlet manifold
having a first fluid outlet therein; a plurality of tubes extending
between the manifolds and in fluid communication therewith; a shell
extending between the manifolds and encompassing said tubes, the
shell having a second fluid inlet and a second fluid outlet
therein; a plurality of baffles mounted in the shell to guide the
second fluid into a helical flow pattern through the shell; wherein
a helix angle .alpha. of a baffle proximate the second fluid inlet
is different than a helix angle .beta. of a baffle proximate the
second fluid outlet.
[0013] In another aspect, embodiments disclosed herein relate to a
process for exchanging heat with a mixed phase fluid, the process
including: feeding a mixed phase fluid comprising a vapor and at
least one of an entrained liquid and an entrained solid to a heat
exchanger, the heat exchanger including: a shell having a fluid
inlet, and a fluid outlet; a plurality of baffles mounted in the
shell to guide the fluid into a helical flow pattern through the
shell; converting the mixed phase fluid to essentially all vapor;
and indirectly exchanging heat between the mixed phase fluid and a
heat exchange medium; wherein a helix angle .alpha. of a baffle
proximate the inlet maintains a velocity of the mixed phase fluid
greater than a terminal velocity of the entrained liquid or solid;
and wherein a helix angle .beta. of a baffle proximate the outlet
is greater than helix angle .alpha. of the baffle proximate the
inlet.
[0014] Other aspects and advantages will be apparent from the
following description and the appended claims.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a diagrammatic view of flow distribution in a
conventional shell and tube heat exchanger.
[0016] FIG. 2 is a schematic drawing of a vertical combined
feed/effluent heat exchanger with variable heat baffle angle
according to embodiments disclosed herein.
DETAILED DESCRIPTION
[0017] In one aspect, embodiments herein relate generally to a heat
exchanger. More specifically, embodiments disclosed herein relate
to a heat exchanger, such as a shell and tube heat exchanger,
configured to efficiently process two-phase flow. Even more
specifically, embodiments disclosed herein relate to a heat
exchanger having baffles configured to direct a shell side fluid
flow in a helical flow pattern, where a helix angle of a baffle
proximate the inlet is different than a helix angle of a baffle
proximate the outlet.
[0018] Heat exchangers having baffles with a varied helix angle
according to embodiments disclosed herein have been found to be
useful for shellside fluids undergoing a phase change, such as
evaporation, condensation, combustion, and the like. For example,
for a two-phase inlet flow, such as a vaporizing liquid-vapor
mixture, helix angles proximate to the inlet may be provided to
maintain sufficient fluid velocity to avoid phase separation of the
vapor and the liquid. The helix angle of baffles proximate the
shellside fluid inlet may be close to a position perpendicular to
the tubes, thus causing the incoming dense fluid to swirl at a high
velocity. As the liquid vaporizes due to heat transfer within the
exchanger, the helix angle of the baffles may be further from
perpendicular, such as for baffles closer to the shellside outlet,
providing for heat exchange at lower velocities for the less dense
vapor and a relatively low pressure drop through the heat
exchanger.
[0019] As the phase separation (vapor-liquid, vapor-solid, etc.) is
a function of the relative densities, particle and/or droplet size,
and the vapor phase velocity, heat exchangers having baffles with a
varied helix angle according to embodiments disclosed herein are
not subject to shellside phase separation at the same throughput as
would occur for a heat exchanger having a constant baffle angle.
Accordingly, heat exchangers having baffles with a varied helix
angle according to embodiments disclosed herein may be used at
significantly reduced throughput levels, thus avoiding the
drawbacks typical associated with vertical heat exchangers
operating at partial load or turndown operation.
[0020] The helix angle used for the baffles proximate the shellside
inlet and outlet may depend on the type of operation. For example,
for a fluid mixture including a vapor and a vaporizing liquid or
combusting solid, the helix angle of baffles proximate the inlet
may be greater than the helix angle of baffles proximate the
outlet. In this manner, the velocity of the two-phase mixture may
be maintained greater than a transport velocity of the entrained
solid or liquid, thus avoiding phase separation. As the fluid
vaporizes or the solid combusts, a lower helix angle may be used.
In other embodiments, the helix angle may gradually decrease along
the longitudinal length of the shell. As another example, for an
inlet feed including a vapor to be condensed within the heat
exchanger, the helix angle of baffles proximate the shellside inlet
may be less than the helix angle of baffles proximate the shellside
outlet, thus increasing the velocity of the mixture during the
condensing operation.
[0021] Referring now to FIG. 2, a schematic drawing of a vertical
combined feed/effluent heat exchanger having baffles with varied
helix angles according to embodiments disclosed herein is
illustrated. Heat exchanger 30 may include a tubeside inlet
manifold 32 having a fluid inlet 34 therein. Tubeside inlet
manifold 32 may also have a vent 36 disposed therein. Heat
exchanger 30 may also include a tubeside outlet manifold 38 having
a fluid outlet 40 therein. A plurality of tubes 42 may extend
between the tubeside inlet manifold 32 and outlet manifold 38,
allowing for transport of a fluid from the inlet manifold 32 to
outlet manifold 38 through tubes 42. FIG. 2 illustrates the use of
four tubes, however it is to be understood that any number of tubes
may be used.
[0022] Shell 44 extends between inlet and outlet manifolds 32, 38,
encompassing tubes 42, and includes a shellside fluid inlet 46 and
a shellside fluid outlet 48. Located within shell 44 is a plurality
of baffles 50. Baffles 50 may include, for example, helical baffles
as described in U.S. Pat. Nos. 5,832,991, 6,513,583, and 6,827,138,
the entire contents of each which are incorporated herein by
reference. Baffles 50 may include tube orifices (not shown) to
allow tubes 42 to pass through baffles 50, and to allow baffles 50
to retain tubes 42 in an aligned and desired location. Baffles 50
may act to guide the shellside fluid into a helical flow pattern
through the shell.
[0023] Baffles 50 are arranged within heat exchanger 30 such that
baffles 50 proximate the shellside inlet 46 have a different helix
angle than baffles 50 proximate shellside outlet 48. The helix
angle of the baffles may be determined, for example, by "unwinding"
the helix, forming a two-dimensional representation of the helical
pattern. As illustrated in FIG. 2 for baffle 50a, the helix angle
would then be determined as the arctangent of the shell
circumference C divided by the pitch p (longitudinal distance
traversed by a baffle arc extending 360.degree.). The pitch is
equal to:
p=C*tan(.beta.);
where .beta. is the helix angle. Therefore, helix angle .beta. is
equal to arctan (p/C).
[0024] As illustrated, heat exchanger 30 is equipped with helical
baffles 50 oriented vertically. Baffles 50 proximate shellside
inlet 46 may have a helix angle .alpha.. Baffles 50 proximate
shellside outlet 48 may have a helix angle .beta. with respect to
longitudinal axis A-A of shell 44. Thus, for example, for a
vaporizing two-phase shellside feed stream entering via shellside
inlet 46, the baffles 50 proximate the inlet 46 are arranged at a
low helix angle .alpha.; i.e., closer to perpendicular with respect
to axis A-A than baffles 50 proximate shellside outlet 48, having a
helix angle .beta. where heat exchange is expected to be gas/gas at
a higher shellside volumetric flow, such as due to evaporation,
combustion, and/or heating of the shellside fluid. A low helix
angle .alpha. may thus cause the two-phase inlet flow to swirl in a
helical path at a velocity sufficient to avoid phase separation.
Because the shellside fluid is gas/gas proximate outlet 48, a helix
angle .beta. greater than helix angle .alpha. may be used, thus
resulting in a lower pressure drop than where angle .alpha. is used
along the entire length of shell 44.
[0025] In some embodiments, baffles intermediate shellside fluid
inlet 46 and outlet 48 may have a helix angle .gamma. intermediate
that of helix angles .alpha., .beta.. For example, the helix angles
of baffles 50 may gradually increase or decrease from inlet 46 to
outlet 48, depending on the type of service (e.g., condensing,
evaporating, etc.). In other embodiments, the helix angles for
baffles 50 may undergo one or more step changes.
[0026] As mentioned above, heat exchangers having baffles with a
varied helix angle according to embodiments disclosed herein may be
useful where two-phase fluid flow is expected. Lower helix angles
where two-phase flow is expected may provide for a higher vapor
phase velocity, avoiding shellside phase separation. The helix
angles of baffles proximate the inlet and outlet may be a function
of the relative densities of the two phases, particle or droplet
size of the solids and/or liquids (related to the transport
velocity of the particles or droplets), typical feed rates, partial
load or turndown feed rates, temperature rise of the shellside
fluid and other variables as known to those skilled in the art.
[0027] The vertical combined feed/effluent heat exchangers
described herein may use baffles having an approximate helix angle
within the range from about 5.degree. to 45.degree., inclusive. Any
combination of baffle angles .alpha., .beta. and .gamma. (if
present) which creates an appropriate helix angle may be used in
accordance with embodiments disclosed herein.
[0028] For example, in some embodiments, helix angle .alpha. may be
within the range from about 5.degree. to about 45.degree.; within
the range from about 5.degree. to about 35.degree. in other
embodiments; and from about 5.degree. to about 25.degree. in yet
other embodiments.
[0029] In other embodiments, baffle angle .beta. may be within the
range from 15.degree. to about 45.degree.; within the range from
about 25.degree. to about 45.degree. in other embodiments; and from
about 35.degree. to about 45.degree. in yet other embodiments.
[0030] Heat exchangers according to embodiments disclosed herein
may advantageously be used with shellside fluids having two or more
phases. Advantageously, heat exchangers according to embodiments
disclosed herein may provide for a shellside fluid flow velocity to
minimize or avoid phase-separation of fluids passing through the
shell, such as by having baffles with a small helix angle where
two-phase flow is expected. Additionally, use of larger helix
angles where single phase flow is expected may advantageously
provide for a lower pressure drop than where a constant helix angle
is used throughout the shell. Thus, compared to traditional heat
exchangers having baffles with a constant helix angle, heat
exchangers according to embodiments disclosed herein may maintain
two-phase fluid flow even at significantly reduced throughput
levels, thus advantageously allowing for a broader throughput
range.
[0031] While the disclosure includes a limited number of
embodiments, those skilled in the art, having benefit of this
disclosure, will appreciate that other embodiments may be devised
which do not depart from the scope of the present disclosure.
Accordingly, the scope should be limited only by the attached
claims.
* * * * *