U.S. patent application number 14/795036 was filed with the patent office on 2017-01-12 for tube arrangement in a once-through horizontal evaporator.
The applicant listed for this patent is ALSTOM Technology Ltd. Invention is credited to Jeffrey Fredrick Magee, Suresh Kotachary Shenoy.
Application Number | 20170010053 14/795036 |
Document ID | / |
Family ID | 56413631 |
Filed Date | 2017-01-12 |
United States Patent
Application |
20170010053 |
Kind Code |
A1 |
Shenoy; Suresh Kotachary ;
et al. |
January 12, 2017 |
TUBE ARRANGEMENT IN A ONCE-THROUGH HORIZONTAL EVAPORATOR
Abstract
Disclosed herein is a once-through evaporator comprising an
inlet manifold; one or more inlet headers in fluid communication
with the inlet manifold; one or more tube stacks, where each tube
stack comprises one or more inclined evaporator tubes; the one or
more tube stacks being in fluid communication with the one or more
inlet headers; where the inclined tubes are inclined at an angle of
less than 90 degrees or greater than 90 degrees to a vertical;
where each tube stack comprises a plurality of tubes arranged in a
plurality of columns and a plurality of rows; where a plurality of
tubes in a first column are offset from a plurality of tubes in a
second column by a distance d2 and where a plurality of tubes in a
first row are offset from a plurality of tubes in a second row by a
distance d1; where d1 varies from 0.1d2 to 1000d2; one or more
outlet headers in fluid communication with one or more tube stacks;
and an outlet manifold in fluid communication with the one or more
outlet headers.
Inventors: |
Shenoy; Suresh Kotachary;
(Johns Creek, GA) ; Magee; Jeffrey Fredrick;
(Longmeadow, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALSTOM Technology Ltd |
Baden |
|
CH |
|
|
Family ID: |
56413631 |
Appl. No.: |
14/795036 |
Filed: |
July 9, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28F 9/02 20130101; F28D
7/0066 20130101; F22B 17/12 20130101; F22B 17/00 20130101; Y02E
20/14 20130101 |
International
Class: |
F28F 9/02 20060101
F28F009/02; F28D 7/00 20060101 F28D007/00 |
Claims
1. A once-through evaporator comprising: an inlet manifold; one or
more inlet headers in fluid communication with the inlet manifold;
one or more tube stacks, where each tube stack comprises one or
more inclined evaporator tubes; the one or more tube stacks being
in fluid communication with the one or more inlet headers; where
the inclined tubes are inclined at an angle of less than 90 degrees
or greater than 90 degrees to a vertical; where each tube stack
comprises a plurality of tubes arranged in a plurality of columns
and a plurality of rows; where a plurality of tubes in a first
column are offset from a plurality of tubes in a second column by a
distance d2 and where a plurality of tubes in a first row are
offset from a plurality of tubes in a second row by a distance d1;
where d1 varies from 0.1d2 to 1000d2 one or more outlet headers in
fluid communication with one or more tube stacks; and an outlet
manifold in fluid communication with the one or more outlet
headers.
2. The once-through evaporator of claim 1, where the distances d1
and d2 are average distances.
3. The once through evaporator of claim 1, where the distance
between successive columns can be varied.
4. The once through evaporator of claim 1, where the distance
between successive rows can be varied.
5. The once through evaporator of claim 1, where the distance
between the one or more tube stacks can be varied.
6. The once-through evaporator of claim 1, where the tube stack
comprises a tube that is substantially horizontal in a direction
that is perpendicular to a direction of flow of hot gases and
inclined in a direction that is parallel to the direction of flow
of the hot gases.
7. The once-through evaporator of claim 1, where the tubes in the
tube stack are in a staggered arrangement; where the tubes in one
row are off set from the tubes in a preceding or succeeding
row.
8. The once-through evaporator of claim 1, where the tubes in the
tube stack are in a staggered arrangement, where the tubes in one
row lie directly above the tubes in a succeeding row and directly
below the tubes in a preceding row.
9. The once-through evaporator of claim 1, further comprising an
unoccupied space that is produced by a difference in a geometry of
an inclined evaporator tube stack and a horizontal evaporator tube
stack.
10. The once-through evaporator of claim 9, wherein the unoccupied
space is filled with a partial tube stack.
11. The once-through evaporator of claim 9, where the unoccupied
space contains control equipment for regulating flow of the working
fluid through the tubes.
12. The once-through evaporator of claim 1, further comprising a
baffle disposed between tube stacks.
13. The once-through evaporator of claim 1, where a tube stack
straddles a baffle.
14. The once-through evaporator of claim 1, where the tube stack
comprises a tube that is substantially horizontal in a direction
that is parallel to a direction of flow of hot gases and inclined
in a direction that is perpendicular to the direction of flow of
the hot gases.
15. The once-through evaporator of claim 1, where the tubes in the
tube stack are in an inline arrangement, where the tubes in one row
lie directly above the tubes in a succeeding row and directly below
the tubes in a preceding row.
16. A method comprising: discharging a working fluid through a
once-through evaporator; where the once-through evaporator
comprises: an inlet manifold; one or more inlet headers in fluid
communication with the inlet manifold; one or more tube stacks,
where each tube stack comprises one or more inclined evaporator
tubes; the one or more tube stacks being in fluid communication
with the one or more inlet headers; where the inclined tubes are
inclined at an angle of less than 90 degrees or greater than 90
degrees to a vertical; where each tube stack comprises a plurality
of tubes arranged in a plurality of columns and a plurality of
rows; where a plurality of tubes in a first column are offset from
a plurality of tubes in a second column by a distance d2 and where
a plurality of tubes in a first row are offset from a plurality of
tubes in a second row by a distance d1; where d1 varies from 0.1d2
to 1000d2; one or more outlet headers in fluid communication with
one or more tube stacks; and an outlet manifold in fluid
communication with the one or more outlet headers; discharging a
hot gas from a furnace or boiler through the once-through
evaporator; and transferring heat from the hot gas to the working
fluid.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to a heat recovery
steam generator (HRSG), and more particularly, to a tube
arrangement for controlling flow in an HRSG having inclined tubes
for heat exchange.
BACKGROUND
[0002] A heat recovery steam generator (HRSG) is an energy recovery
heat exchanger that recovers heat from a hot gas stream. It
produces steam that can be used in a process (cogeneration) or used
to drive a steam turbine (combined cycle). Heat recovery steam
generators generally comprise four major components--the
economizer, the evaporator, the superheater and the water
preheater. In particular, natural circulation HRSG's contain
evaporator heating surface, a drum, as well as the necessary piping
to facilitate the appropriate circulation ratio in the evaporator
tubes. A once-through HRSG replaces the natural circulation
components with once-through evaporator and in doing so offers
in-roads to higher plant efficiency and furthermore assists in
prolonging the HRSG lifetime in the absence of a thick-walled
drum.
[0003] An example of a once through evaporator heat recovery steam
generator (HRSG) 100 is shown in the FIG. 1. In the FIG. 1, the
HRSG comprises vertical heating surfaces in the form of a series of
vertical parallel flow paths/tubes 104 and 108 (disposed between
the duct walls 111) configured to absorb the required heat. In the
HRSG 100, a working fluid (e.g., water) is transported to an inlet
manifold 105 from a source 106. The working fluid is fed from the
inlet manifold 105 to an inlet header 112 and then to a first heat
exchanger 104, where it is heated by hot gases from a furnace (not
shown) flowing in the horizontal direction. The hot gases heat tube
sections 104 and 108 disposed between the duct walls 111. A portion
of the heated working fluid is converted to a vapor and the mixture
of the liquid and vaporous working fluid is transported to the
outlet manifold 103 via the outlet header 113, from where it is
transported to a mixer 102, where the vapor and liquid are mixed
once again and distributed to a second heat exchanger 108. This
separation of the vapor from the liquid working fluid is
undesirable as it produces temperature gradients and efforts have
to be undertaken to prevent it. To ensure that the vapor and the
fluid from the heat exchanger 104 are well mixed, they are
transported to a mixer 102, from which the two phase mixture (vapor
and liquid) are transported to another second heat exchanger 108
where they are subjected to superheat conditions. The second heat
exchanger 108 is used to overcome thermodynamic limitations. The
vapor and liquid are then discharged to a collection vessel 109
from which they are then sent to a separator 110, prior to being
used in power generation equipment (e.g., a turbine). The use of
vertical heating surfaces thus has a number of design
limitations.
[0004] Due to design considerations, it is often the case that
thermal head limitations necessitate an additional heating loop in
order to achieve superheated steam at the outlet. Often times
additional provisions are needed to remix water/steam bubbles prior
to re-entry into the second heating loop, leading to additional
design considerations. In addition, there exists a gas-side
temperature imbalance downstream of the heating surface as a direct
result of the vertically arranged parallel tubes. These additional
design considerations utilize additional engineering design and
manufacturing, both of which are expensive. These additional
features also necessitate periodic maintenance, which reduces time
for the productive functioning of the plant and therefore result in
losses in productivity. It is therefore desirable to overcome these
drawbacks.
SUMMARY
[0005] Disclosed herein is a once-through evaporator comprising an
inlet manifold; one or more inlet headers in fluid communication
with the inlet manifold; one or more tube stacks, where each tube
stack comprises one or more inclined evaporator tubes; the one or
more tube stacks being in fluid communication with the one or more
inlet headers; where the inclined tubes are inclined at an angle of
less than 90 degrees or greater than 90 degrees to a vertical;
where each tube stack comprises a plurality of tubes arranged in a
plurality of columns and a plurality of rows; where a plurality of
tubes in a first column are offset from a plurality of tubes in a
second column by a distance d2 and where a plurality of tubes in a
first row are offset from a plurality of tubes in a second row by a
distance d1; where d1 varies from 0.1 d2 to 1000d2 to suit the
optimal degree of heat blending; one or more outlet headers in
fluid communication with one or more tube stacks; and an outlet
manifold in fluid communication with the one or more outlet
headers.
[0006] Disclosed herein too is a method comprising discharging a
working fluid through a once-through evaporator; where the
once-through evaporator comprises an inlet manifold; one or more
inlet headers in fluid communication with the inlet manifold; one
or more tube stacks, where each tube stack comprises one or more
inclined evaporator tubes; the one or more tube stacks being in
fluid communication with the one or more inlet headers; where the
inclined tubes are inclined at an angle of less than 90 degrees or
greater than 90 degrees to a vertical; where each tube stack
comprises a plurality of tubes arranged in a plurality of columns
and a plurality of rows; where a plurality of tubes in a first
column are offset from a plurality of tubes in a second column by a
distance d2 and where a plurality of tubes in a first row are
offset from a plurality of tubes in a second row by a distance d1;
where d1 varies from 0.1d2 to 1000d2 to suit the optimal degree of
heat blending; one or more outlet headers in fluid communication
with one or more tube stacks; and an outlet manifold in fluid
communication with the one or more outlet headers; discharging a
hot gas from a furnace or boiler through the once-through
evaporator; and transferring heat from the hot gas to the working
fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Referring now to the Figures, which are exemplary
embodiments, and wherein the like elements are numbered alike:
[0008] FIG. 1 is a schematic view of a prior art heat recovery
steam generator having vertical heat exchanger tubes;
[0009] FIG. 2 depicts a schematic view of an exemplary once-through
evaporator that uses a counterflow staggered arrangement;
[0010] FIG. 3 depicts an exemplary embodiment of a once-through
evaporator;
[0011] FIG. 4(A) depicts one exemplary arrangement of the tubes in
a tube stack of a once-through evaporator;
[0012] FIG. 4(B) depicts an isometric view of an exemplary
arrangement of the tubes in a tube stack of a once-through
evaporator;
[0013] FIG. 5 depicts an end-on schematic view of a counterflow
staggered arrangement of tubes in a tube stack in a once-through
evaporator;
[0014] FIG. 6A is an expanded end-on view of a tube stack of the
FIG. 4;
[0015] FIG. 6B is a depiction of a plane section taken within the
tube stack of the FIG. 5A and depicts a staggered tube
consideration;
[0016] FIG. 7A depicts an elevation end-on view of tubes that are
inclined in one direction while being horizontal in another
direction; the tubes are arranged in a staggered fashion;
[0017] FIG. 7B is a depiction of a plane section taken within the
tube stack of the FIG. 6A and depicts a staggered tube
configuration;
[0018] FIG. 8 depicts that the spacing between successive tube
stacks can be varied; and
[0019] FIG. 9 depicts a once-through evaporator having 10
vertically aligned zones or sections that contain tubes through
which hot gases can pass to transfer their heat to the working
fluid.
DETAILED DESCRIPTION
[0020] Disclosed herein is a heat recovery steam generator (HRSG)
that comprises a single heat exchanger or a plurality of heat
exchangers whose tubes are arranged to be "non-vertical". By
non-vertical, it is implied the tubes are inclined at an angle to a
vertical. By "inclined", it is implied that the individual tubes
are inclined at an angle less than 90 degrees or greater than 90
degrees to a vertical line drawn across a tube. In one embodiment,
the tubes can be horizontal in a first direction and inclined in a
second direction that is perpendicular to the first direction.
[0021] In particular, in a heat recovery steam generator, the
heating surfaces--also called finned tubes--are generally
horizontally disposed. In one embodiment detailed herein, the
heating surfaces may be staggered as a result of which the
prevailing heat transfer mode is also staggered. Such an
arrangement is not limited by thermal head, no remixing of the
heated fluid is generally used, nor is there a temperature gradient
as depicted with the vertically disposed once through heat
exchanger. The staggering may result from angular variations in the
tube as shown in the FIG. 2 below.
[0022] These angular variations in the tube along with the angle of
inclination are shown in the FIG. 2. The FIG. 2 shows a section of
a tube that is employed in a tube stack of the once-through
evaporator. The tube stack shows that the tube is inclined to the
vertical in one or more directions.
[0023] While the tube in the FIG. 2 is shown to be inclined in two
directions, it can be inclined in only one direction if desired. In
the FIG. 2, the tube is inclined in one direction at an angle of
.theta.1 to the vertical, while it is inclined in a second
direction at an angle of .theta.2 to the vertical. In the FIG. 2,
it may be seen that .theta.1 and .theta.2 can vary by up to 90
degrees to the vertical. If the angle of inclination .theta.1 and
.theta.2 are equal to 90 degrees, then the tube is stated to be
substantially horizontal. If on the other hand only one angle
.theta.1 is 90 degrees while the other angle .theta.2 is less than
90 degrees or greater than 90 degrees, then the tube is said to be
horizontal in one direction while being inclined in another
direction. In yet another embodiment, it is possible that both
.theta.1 and .theta.2 are less than 90 degrees or greater than 90
degrees, which implies that the tube is inclined in two directions.
It is to be noted that by "substantially horizontal" it is implies
that the tubes are oriented to be approximately horizontal (i.e.,
arranged to be parallel to the horizon within .+-.2 degrees). For
tubes that are inclined, the angle of inclination .theta.1 and/or
.theta.2 generally vary from about 55 degrees to about 88 degrees
with the vertical. In an exemplary embodiment, it is desirable for
the tube to be inclined to the vertical in at least one
direction.
[0024] The section (or plurality of sections) containing the
horizontal tubes is also termed a "once-through evaporator",
because when operating in subcritical conditions, the working fluid
(e.g., water, ammonia, or the like) is converted into vapor
gradually during a single passage through the section from an inlet
header to an outlet header. Likewise, for supercritical operation,
the supercritical working fluid is heated to a higher temperature
during a single passage through the section from the inlet header
to the outlet header.
[0025] The once-through evaporator (hereinafter "evaporator")
comprises parallel tubes that are disposed non-vertically in at
least one direction that is perpendicular to the direction of flow
of heated gases emanating from a furnace or boiler.
[0026] The FIGS. 3, 4(A), 4(B) and 10 depicts an exemplary
embodiment of a once-through evaporator. The FIG. 3 depicts a
plurality of vertical tube stacks in a once-through evaporator 200.
In one embodiment, the tube stacks are aligned vertically so that
each stack is either directly above, directly under, or both
directly above and/or directly under another tube stack. The FIG.
4(A) depicts one exemplary arrangement of the tubes in a tube stack
of a once-through evaporator; while the FIG. 4(B) depicts an
isometric view of an exemplary arrangement of the tubes in a tube
stack of a once-through evaporator;
[0027] The evaporator 200 comprises an inlet manifold 202, which
receives a working fluid from an economizer (not shown) and
transports the working fluid to a plurality of inlet headers
204(n), each of which are in fluid communication with vertical tube
stacks 210(n) comprising one or more tubes that are substantially
horizontal. The fluid is transmitted from the inlet headers 204(n)
to the plurality of tube stacks 210(n). For purposes of simplicity,
in this specification, the plurality of inlet headers 204(n),
204(n+1) . . . and 204(n+n'), depicted in the figures are
collectively referred to as 204(n). Similarly the plurality of tube
stacks 210(n), 210(n+1), 210(n+2) . . . and 210(n+n') are
collectively referred to as 210(n) and the plurality of outlet
headers 206(n), 206(n+1), 206(n+2) and 206(n+n') are collectively
referred to as 206(n).
[0028] As can be seen in the FIG. 3, multiple tube stacks 210(n)
are therefore respectively vertically aligned between a plurality
of inlet headers 204(n) and outlet headers 206(n). Each tube of the
tube stack 210(n) is supported in position by a plate 250 (see FIG.
4(B)). The working fluid upon traversing the tube stack 210(n) is
discharged to the outlet manifold 208 from which it is discharged
to the superheater. The inlet manifold 202 and the outlet manifold
208 can be horizontally disposed or vertically disposed depending
upon space requirements for the once-through evaporator. From the
FIGS. 3 and 4(A), it may be seen that when the vertically aligned
stacks are disposed upon one another, a passage 239 is formed
between the respective stacks. A baffle system 240 may be placed in
these passages to prevent the by-pass of hot gases. This will be
discussed later.
[0029] The hot gases from a source (e.g., a furnace, boiler or
turbine) (not shown) travel perpendicular or transverse to the
direction of the flow of the working fluid in the tubes 210. With
reference to the FIG. 3, the hot gases travel away from the reader
into the plane of the paper, or towards the reader from the plane
of the paper. In one embodiment, the hot gases travel counterflow
to the direction of travel of the working fluid in the tube stack.
Heat is transferred from the hot gases to the working fluid to
increase the temperature of the working fluid and to possibly
convert some or all of the working fluid from a liquid to a vapor.
Details of each of the components of the once-through evaporator
are provided below.
[0030] As seen in the FIGS. 3 and/or 4(A), the inlet header
comprises one or more inlet headers 204(n), 204(n+1) . . . and
(204(n) (hereinafter represented generically by the term "204(n)"),
each of which are in operative communication with an inlet manifold
202. In one embodiment, each of the one or more inlet headers
204(n) are in fluid communication with an inlet manifold 202. The
inlet headers 204(n) are in fluid communication with a plurality of
horizontal tube stacks 210(n), 210(n+1), 210(n'+2) . . . and 210(n)
respectively ((hereinafter termed "tube stack" represented
generically by the term "210(n)"). Each tube stack 210(n) is in
fluid communication with an outlet header 206(n). The outlet header
thus comprises a plurality of outlet headers 206(n), 206(n+1),
206(n+2) . . . and 206(n), each of which is in fluid communication
with a tube stack 210(n), 210(n+1), 210(n+2) . . . and 210(n) and
an inlet header 204(n), 204(n+1), (204(n+2) . . . and 204(n)
respectively.
[0031] The terms `n" is an integer value, while "n'" can be an
integer value or a fractional value. n' can thus be a fractional
value such as 1/2, 1/3, and the like. Thus for example, there can
therefore be one or more fractional inlet headers, tube stacks or
outlet headers. In other words, there can be one or more inlet
headers and outlet headers whose size is a fraction of the other
inlet headers and/or outlet headers. Similarly there can be tube
stacks that contain a fractional value of the number of tubes that
are contained in the other stack. It is to be noted that the valves
and control systems having the reference numeral n' do not actually
exist in fractional form, but may be downsized if desired to
accommodate the smaller volumes that are handled by the fractional
evaporator sections. In one embodiment, there can be at least one
or more fractional tube stacks in the once-through evaporator. In
another embodiment, there can be at least two or more fractional
tube stacks in the once-through evaporator.
[0032] In one embodiment, the once-through evaporator can comprise
2 or more inlet headers in fluid communication with 2 or more tube
stacks which are in fluid communication with 2 or more outlet
headers. In one embodiment, the once-through evaporator can
comprise 3 or more inlet headers in fluid communication with 3 or
more tube stacks which are in fluid communication with 3 or more
outlet headers. In another embodiment, the once-through evaporator
can comprise 5 or more inlet headers in fluid communication with 5
or more tube stacks which are in fluid communication with 5 or more
outlet headers. In yet another embodiment, the once-through
evaporator can comprise 10 or more inlet headers in fluid
communication with 10 or more tube stacks which are in fluid
communication with 10 or more outlet headers. There is no
limitation to the number of tube stacks, inlet headers and outlet
headers that are in fluid communication with each other and with
the inlet manifold and the outlet manifold. Each tube stack is
sometimes termed a bundle or a zone.
[0033] The FIG. 9 depicts another exemplary assembled once-through
evaporator. The FIG. 9 shows a once-through evaporator of the FIG.
3 having 10 vertically aligned tube stacks 210(n) that contain
tubes through which hot gases can pass to transfer their heat to
the working fluid. The tube stacks are mounted in a frame 300 that
comprises two parallel vertical support bars 302 and two horizontal
support bars 304. The support bars 302 and 304 are fixedly attached
or detachably attached to each other by welds, bolts, rivets, screw
threads and nuts, or the like.
[0034] Disposed on an upper surface of the once-through evaporator
are rods 306 that contact the plates 250. Each rod 306 supports the
plate and the plates hang (i.e., they are suspended) from the rod
306. The plates 250 (as detailed above) are locked in position
using clevis plates. The plates 250 also support and hold in
position the respective tube stacks 210(n). In this FIG. 9, only
the uppermost tube and the lowermost tube of each tube tack 210(n)
is shown as part of the tube stack. The other tubes in each tube
stack are omitted for the convenience of the reader and for
clarity's sake.
[0035] Since each rod 306 holds or supports a plate 250, the number
of rods 306 are therefore equal to the number of the plates 250. In
one embodiment, the entire once-through evaporator is supported and
held-up by the rods 306 that contact the horizontal rods 304. In
one embodiment, the rods 306 can be tie-rods that contact each of
the parallel horizontal rods 304 and support the entire weight of
the tube stacks. The weight of the once-through evaporator is
therefore supported by the rods 306.
[0036] Each section is mounted onto the respective plates and the
respective plates are then held together by tie rods 300 at the
periphery of the entire tube stack. A number of vertical plates
support these horizontal heat exchangers. These plates are designed
as the structural support for the module and provide support to the
tubes to limit deflection. The horizontal heat exchangers are shop
assembled into modules and shipped to site. The plates of the
horizontal heat exchangers are connected to each other in the
field.
[0037] The FIG. 5 depicts one possible arrangement of the tubes in
a tube stack. The FIG. 5 is an end-on view that depicts two tube
stacks that are vertically aligned. The tube stacks 210(n) and
210(n+1) are vertically disposed on one another and are separated
from each other and from their neighboring tube stacks by baffles
240. The baffles 240 prevent non-uniform flow distribution and
facilitate staggered and counterflow heat transfer. In one
embodiment, the baffles 240 do not prevent the hot gases from
entering the once-through device. They facilitate distribution of
the hot gases through the tube stacks. As can be seen in the FIG.
5, each tube stack is in fluid communication with a header 204(n)
and 204(n+1) respectively. The tubes are supported by metal plates
250 that have holes through which the tubes travel back and forth.
The tubes are serpentine i.e., they travel back and forth between
the inlet header 204(n) and the outlet header 206(n) in a
serpentine manner. The working fluid is discharged from the inlet
header 204(n) to the tube stack, where it receives heat from the
hot gas flow that is perpendicular to the direction of the tubes in
the tube stack.
[0038] The FIG. 6A is an expanded end-on view of the tube stack
210(n+1) of the FIG. 5. In the FIG. 6A, it can be seen that two
tubes 262 and 264 emanate from the inlet header 204(n+1). The two
tubes 262 and 264 emanate from the header 204(n+1) at each line
position 260. The tubes in the FIG. 6A are inclined from the inlet
header 204(n) to the outlet header 206(n), which is away from the
reader into the plane of the paper.
[0039] The tubes are in a zig-zag or staggered arrangement (as can
be seen in the upper left hand of the FIG. 6A), with the tube 262
traversing back and forth (in and out of the plane of the paper) in
a serpentine manner between two sets of plates 250, while the tube
264 traverses back and forth (in and out of the plane of the paper)
in a serpentine manner between the two sets of plates 250 in a set
of holes that are in a lower row of holes from the holes through
which the tube 262 travels. It is to be noted, that while this
specification details two sets of plates 250, the FIG. 6A shows
only one plate 250. In actuality, each tube stack may be supported
by two or more sets of plates as seen previously in the FIG. 4(B).
In short, the tube 262 travels through holes in the odd numbered
columns (1, 3, 5, 7, . . . ) in odd numbered rows, while the tube
264 travels through even numbered columns (2, 4, 6, 8, . . . ) in
even numbered rows. This produces a zig-zag looking arrangement.
This zig-zag arrangement is produced because the holes in even
numbered hole columns of the metal plate are off-set from the holes
in the odd numbered hole columns. As a result in the zig-zag
arrangement; the tubes in one row are off set or staggered
vertically from the tubes in a preceding or succeeding row. With a
staggered arrangement the heating circuit can lie in two flow paths
so as to avoid low points in the boiler and the subsequent
inability to drain pressure parts.
[0040] Specifically, shown in FIGS. 6B and 7B below are parallel
water/steam circuits 1, 2, 3, 4, and so on. In the arrangements
shown in the FIGS. 6B and 7B are inherent static head differential
effects that need to be considered when designing the equipment.
These static head differentials can lead to suboptimal flow and
temperature distribution across the once-through section and hence
a less than optimal design configuration. However, due to the
relatively cooler exhaust gas temperature downstream of, for
instance finned tubes 4c and 3d, there exists a cooling effect on
finned tube 3c (See FIG. 7B). This dynamic is termed "heat
blending". When this dynamic plays out across the entire heat
exchanger it partially negates the static head effects and
therefore the exact extent of heat blending is not necessarily
optimal.
[0041] The FIG. 6B is a depiction of a plane section taken within
the tube stack. The plane is perpendicular to the direction of
travel of fluid in the tubes and the FIG. 6B shows the
cross-sectional areas of the 7 serpentine tubes at the plane. As
can be seen, the tubes (as viewed by their cross-sectional areas)
are in a vertically staggered configuration. Because of the
serpentine shape, the heating surface depicts the parallel tube
paths in a staggered configuration that supports counterflow fluid
flow and consequently counterflow heat transfer. By counterflow
heat transfer it is meant that the flow in a section of a tube in
one direction runs counter to the flow in another section of the
same tube that is adjacent to it. The numbering shown in the FIG.
6B denotes a single water/steam circuit. For example in tube 1, the
section 1a contains fluid flowing away from the reader, while the
section of tube 1b next to it contains fluid that flows towards the
reader. The different tube colors in the FIG. 6B indicates an
opposed flow direction of the working fluid. The arrows show the
direction of fluid flow in a single pipe.
[0042] The FIG. 7A depicts an isometric end-on view of tubes that
are inclined in one direction while being horizontal in another
direction. In the case of the tubes of the FIG. 7A, the tubes
(i.e., 1a, 1b) are horizontal in a direction that is generally
perpendicular to the hot gas flow, while being inclined at an angle
of .theta.1 in a direction parallel to the hot gas flow. In one
embodiment, the tube stack comprises tubes that are substantially
horizontal in a direction that is parallel to a direction of flow
of the hot gases and inclined in a direction that is perpendicular
to the direction of flow of the hot gases as shown in the FIG.
8.
[0043] The angle .theta.1 can vary from 55 degrees to 88 degrees,
specifically from 60 degrees to 87 degrees, and more specifically
80 degrees to 86 degrees. The inclination of the tubes in one or
more directions provides unoccupied space 270 between the duct wall
280 and the rectangular geometrical shape that the tube stack would
have occupied if the tubes were not inclined at all. This
unoccupied space 270 may be used to house control equipment. This
unoccupied space may lie at the bottom of the stack, the top of the
stack or at the top and the bottom of the stack. Alternatively,
this unoccupied space can be used to facilitate counterflow of the
hot gases in the tube stack.
[0044] In one embodiment, this unoccupied space 270 can contain a
fractional stack, i.e., a stack that is a fractional size of the
regular stack 210(n) as seen in the FIGS. 4(A) and 4(B). In another
embodiment, baffles can also be disposed in the unoccupied space to
deflect the hot gases into the tube stack with an inline flow.
[0045] In the FIG. 7A, it may be seen that tubes are also staggered
with respect to the exhaust gas flow. This is depicted in FIG. 7B,
which depicts a plane section taken within the tube stack. The
plane is generally perpendicular to the direction of travel of the
working fluid in the tubes. As in the case of the tubes of the FIG.
6B, the fluid flow in the FIG. 7B is also in a counterflow
direction. The numbering shown in the FIG. 7B denotes a single
water/steam circuit. The arrows show the direction of fluid flow in
a single tube. Since the tubes in the tube stack are inclined, the
working fluid travels upwards from right to left. While the FIGS.
5, 6B, 7A, 7B show the hot gas flow from left to right, it can also
flow in the opposite direction from right to left. If the hot gas
flow is from right to left, the direction of flow in a single tube
would be the opposite of that shown in the FIG. 6B.
[0046] The staggered counterflow horizontally arranged heating
surface (FIG. 7B) with horizontally/inclined arranged water/steam
(working fluid) circuits permits a balance between increased
minimum flow and increased pressure drop from a choking device.
Furthermore, the heating surface is minimized due to the staggered
and counterflow heat transfer mode leading to minimal draft loss
and parasitic power. However, for a given balance, this may lead to
high parasitic power loss due to the flow choking requirements
and/or the separator water discharge considerations, or both. This
is because the pressure drop across the flow choking device can be
significant as can the water discharged from the separator.
[0047] In one embodiment, the tubes in a tube stack are arranged in
a plurality of columns and rows as may be seen in the FIG. 6B. The
tubes of the staggered counterflow arrangement of the FIG. 6B may
be arranged in a plurality of columns (Col. 1, Col. 2, Col. 3, . .
. and so on). For example, the Column 1 contains tubes 1b, 3b, 5b,
7b, and so on, while the Row 1 contains tubes 1a, 1b, 1c (not
shown), 1d (not shown) and so on. A first column of tubes is
separated from a neighboring second column of tubes by a distance
d2. The first column of tubes is separated from a third column of
tubes by a distance d2+d5. In one embodiment, the distance d2 is an
average distance. In another embodiment, as the distance d2 is
increased, the distance d5 is reduced and vice versa. In other
words, the distance between a first tube in Column 1 and an
adjacent second tube in Column 2 may vary from one pair of rows to
the next depending upon design considerations. The purpose of
varying d1 and d2 (and consequently d4 and d5) is to optimize the
extent of heat blending so as to address the coincident static head
differential effects present in the design in question.
[0048] In a similar manner, a first row of tubes is separated from
a neighboring second row of tubes by a distance d1. The first row
of tubes is separated from a third row of tubes disposed on the
opposite side of tubes from the second row of tubes by a distance
of d1+d4. In other words as d1 increases, d4 decreases and vice
versa. The location of the tube 2b (relative to tube 1b and 3b)
determines the temperature of the exhaust gas stream that contacts
it. In short the ratio of d1 to d4 determines the average
temperature of the exhaust gas stream that contacts the tube
2b.
[0049] In one embodiment, the distance d1 is an average distance
between the tubes in one row and the tubes in a neighboring row. In
another embodiment, the distance between a first tube in Row 1 and
an adjacent second tube in Row 2 may vary from one pair of columns
to the next depending upon design considerations.
[0050] With regard to the arrangements shown in the FIG. 6B, it may
be seen that the tubes 1b-1a and 2b-2a can operate in parallel.
However, tube 2b sees exhaust flow and temperature from both tubes
1b and from 3b. In other words, (with reference to the FIG. 6B) the
tubes in column 2 (Col. 2) may see a large portion of a lower
temperature exhaust gas stream (than the temperature of the exhaust
gas stream impinging on the tube 1b and 3b) depending upon its
location relative to the upstream tubes (1b and 3b) in column 1
(Col. 1). The relative position of the downstream tube 2b to the
upstream tubes 1b and 3b determines the temperature of the blended
heat stream (from tubes 1b and 3b) that it (tube 2b) encounters. In
short the column of tubes located downstream of another column of
tubes may see reduced temperatures. The location of the tubes in
the column 2 may therefore be varied in relationship to their
positions with respect to the tubes in column 1 in order to adjust
the amount of heat absorbed by the tubes in the column 2. The same
situation can occur in the FIG. 7B in the case of the tubes in
column 2 relative to the tubes in the column 1.
[0051] The relative position of the tubes in column 2 can be
adjusted relative to the position of tubes in column 1 to suit a
given application. With reference once again to the FIG. 6B, it may
be seen that the distance between two adjacent tubes in the
1.sup.st column is d1 while the distance between adjacent tubes in
the first column and the second column is d2. A triangle contacting
the tube in the first column and the second column is represented
by XYZ. The angle .alpha. between lines XZ and YZ may vary
depending upon the lengths of d1 and d2. In an embodiment, the
angle .alpha. between lines XZ and YZ may vary from 2 degrees to 88
degrees and the d1 can vary from 0.1d2 to 1000d2, preferably 0.5d2
to 500d2 and more preferably d2 to 100d2. This analysis applies to
the tube configuration shown in the FIG. 7B as well.
[0052] In another embodiment depicted in the FIG. 8, with reference
to the FIGS. 4A, 4B, 5, and 7A, the distance d3 between two
adjacent sections 210(n) and 210(n+1) (the region occupied by the
baffles 214) can be adjusted to increase or to decrease the amount
of the incident exhaust gas stream from one section 210(n)
impinging on another section 210(n+1). In an embodiment, the
distance d3 can vary from d1 to 1000d1.
[0053] Maximum Continuous Load" denotes the rated full load
conditions of the power plant.
[0054] "Once-through evaporator section" of the boiler used to
convert water to steam at various percentages of maximum continuous
load (MCR).
[0055] "Approximately Horizontal Tube" is a tube horizontally
orientated in nature. An "Inclined Tube" is a tube in neither a
horizontal position or in a vertical position, but dispose at an
angle therebetween relative to the inlet header and the outlet
header as shown.
[0056] It will be understood that, although the terms "first,"
"second," "third" etc. may be used herein to describe various
elements, components, regions, layers and/or sections, these
elements, components, regions, layers and/or sections should not be
limited by these terms. These terms are only used to distinguish
one element, component, region, layer or section from another
element, component, region, layer or section. Thus, "a first
element," "component," "region," "layer" or "section" discussed
below could be termed a second element, component, region, layer or
section without departing from the teachings herein.
[0057] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting. As
used herein, singular forms like "a," or "an" and "the" are
intended to include the plural forms as well, unless the context
clearly indicates otherwise. It will be further understood that the
terms "comprises" and/or "comprising," or "includes" and/or
"including" when used in this specification, specify the presence
of stated features, regions, integers, steps, operations, elements,
and/or components, but do not preclude the presence or addition of
one or more other features, regions, integers, steps, operations,
elements, components, and/or groups thereof.
[0058] Furthermore, relative terms, such as "lower" or "bottom" and
"upper" or "top," may be used herein to describe one element's
relationship to another elements as illustrated in the Figures. It
will be understood that relative terms are intended to encompass
different orientations of the device in addition to the orientation
depicted in the Figures. For example, if the device in one of the
figures is turned over, elements described as being on the "lower"
side of other elements would then be oriented on "upper" sides of
the other elements. The exemplary term "lower," can therefore,
encompasses both an orientation of "lower" and "upper," depending
on the particular orientation of the figure. Similarly, if the
device in one of the figures is turned over, elements described as
"below" or "beneath" other elements would then be oriented "above"
the other elements. The exemplary terms "below" or "beneath" can,
therefore, encompass both an orientation of above and below.
[0059] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
disclosure belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and the present
disclosure, and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
[0060] Exemplary embodiments are described herein with reference to
cross section illustrations that are schematic illustrations of
idealized embodiments. As such, variations from the shapes of the
illustrations as a result, for example, of manufacturing techniques
and/or tolerances, are to be expected. Thus, embodiments described
herein should not be construed as limited to the particular shapes
of regions as illustrated herein but are to include deviations in
shapes that result, for example, from manufacturing. For example, a
region illustrated or described as flat may, typically, have rough
and/or nonlinear features. Moreover, sharp angles that are
illustrated may be rounded. Thus, the regions illustrated in the
figures are schematic in nature and their shapes are not intended
to illustrate the precise shape of a region and are not intended to
limit the scope of the present claims.
[0061] The term and/or is used herein to mean both "and" as well as
"or". For example, "A and/or B" is construed to mean A, B or A and
B.
[0062] The transition term "comprising" is inclusive of the
transition terms "consisting essentially of" and "consisting of"
and can be interchanged for "comprising".
[0063] While this disclosure describes exemplary embodiments, it
will be understood by those skilled in the art that various changes
can be made and equivalents can be substituted for elements thereof
without departing from the scope of the disclosed embodiments. In
addition, many modifications can be made to adapt a particular
situation or material to the teachings of this disclosure without
departing from the essential scope thereof. Therefore, it is
intended that this disclosure not be limited to the particular
embodiment disclosed as the best mode contemplated for carrying out
this disclosure.
* * * * *