U.S. patent application number 12/416498 was filed with the patent office on 2010-10-07 for economical use of air preheat.
This patent application is currently assigned to ALSTOM TECHNOLOGY LTD. Invention is credited to Glenn D. Mattison.
Application Number | 20100251975 12/416498 |
Document ID | / |
Family ID | 42173486 |
Filed Date | 2010-10-07 |
United States Patent
Application |
20100251975 |
Kind Code |
A1 |
Mattison; Glenn D. |
October 7, 2010 |
ECONOMICAL USE OF AIR PREHEAT
Abstract
An economical heat recovery system [100] is described for use in
a boiler [26] includes an air preheater [150] that receives hot
flue gasses [FG1] and inlet air and creates heated air [A2] and
incremental air [A2']. The incremental air [A2'] is provided to a
regenerative heat capture and transfer (RHCT) system [300]
positioned to receive the incremental air [A2'] from the air
preheater [150]. The RHCT includes a heat exchanger [310] that
preheats feed water [WF1] for the boiler [26]. Since a heat
exchanger [310] receives clean air as opposed to those of the prior
are, it may be made more efficient with more heat exchange units in
closer proximity, since there is little chance of blockage. Also,
there is less maintenance with the present invention.
Inventors: |
Mattison; Glenn D.;
(Wellsville, NY) |
Correspondence
Address: |
ALSTOM Power Inc.
200 Great Pond Drive, P.O. Box 500
WINDSOR
CT
06095
US
|
Assignee: |
ALSTOM TECHNOLOGY LTD
Baden
CH
|
Family ID: |
42173486 |
Appl. No.: |
12/416498 |
Filed: |
April 1, 2009 |
Current U.S.
Class: |
122/1C ;
165/104.31 |
Current CPC
Class: |
F23J 15/06 20130101;
F28D 2021/0019 20130101; Y02E 20/348 20130101; F28D 19/047
20130101; F23L 15/04 20130101; F28D 19/042 20130101; F22D 1/36
20130101; F23L 2900/15043 20130101; F23J 2219/80 20130101; Y02E
20/34 20130101 |
Class at
Publication: |
122/1.C ;
165/104.31 |
International
Class: |
F22D 1/00 20060101
F22D001/00; F28D 15/00 20060101 F28D015/00 |
Claims
1. An economical flue gas heat recovery system for use with a
boiler [26] comprising: a regenerative heat capture and transfer
(RHCT) system [300] configured to receive a heated air stream [A2']
from an air preheater [50], to receive a water feed [WF1] from a
water supply [65], to transfer heat from the heated air stream
[A2'] to the water feed [WF1] to create a heated water supply feed,
and to output a heated water supply feed [WF2] to a boiler
[26].
2. The system of claim 1 wherein the RHCT system [300] comprises a
heat exchanger 310 configured to receive the water feed WF1 and the
heated air stream A2'.
3. The system of claim 2 wherein the heat exchanger [310] is
further configured to transfer heat from the incremental air stream
[A2'] to the water supply feed WF1.
4. The system of claim 2 further comprising an air preheater 150
configured to provide the incremental air stream [A2'] to the RHCT
system 300.
5. The system of claim 4 wherein the air preheater 150 is
configured to receive flue gases [FG1] from said boiler [26] and to
transfer heat from the flue gases [FG1] to an air stream input
[A1].
6. The system of claim 3 wherein the heated air stream [A2'] is
substantially free of post combustion particulate matter.
7. The system of claim 4 wherein the RHCT system [300] is
configured to receive a portion of an input air stream [A2] from
the air preheater [150] as incremental air [A2'] and to transfer
heat from the incremental air [A2'] to feed water [WF1] for said
boiler [26].
8. The system of claim 7 further comprising a pump [340] for
pumping feed water [WF1] through the heat exchanger [310].
9. An economical heat recovery system [100] for use with a boiler
[26] that boils water feed from a water supply [125] supplied to
it, comprising: an air preheater [150] for receiving heated flue
gasses [FG1] produced by boiler [26], for receiving input air [A1]
and for creating incremental air [A2']; a regenerative heat capture
and transfer (RHCT) system [300] adapted to receive the incremental
air [A2'], said water feed [WF1], then transfer heat from the
incremental air [A2'] to the water feed [WF1], create preheated
water feed [WF2] and supplied preheated water feed [WF2] to boiler
[26].
10. The economical heat recovery system [100] of claim 9, wherein
the RHCT system comprises: an heat exchanger [310] adapted to
receive the incremental air [A2'] from the air preheater [150],
receive the water feed [WF1] and transfer heat from the incremental
air [A2'] to water feed [WF1] to create preheated water feed [WF2],
and a pump coupled to said water supply [125] and to the heat
exchanger [310] for pumping the feed water [WF1] from water supply
[125] through the heat exchanger [310] and the preheated water feed
[WF2] to the boiler [26].
11. The economical heat recovery system [100] of claim 9, wherein
at least some incremental air [A2'] from air preheater [150] is
provided to the RHCT [300].
12. The economical heat recovery system [100] of claim 9, wherein
leakage gasses [360] from the air preheater [150] are provided to
the RHCT [300].
13. The economical heat recovery system [100] of claim 10, wherein:
the heat exchanger [310] is designed with tolerances that do not
include additional internal space for particulate buildup.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to U.S. patent application
"Reagent Drying Via Excess Air Preheat" by Kevin O'Boyle and
incorporates this patent application by reference as if set forth
in its entirety herein. The O'Boyle patent application is being
filed on the same day as the present patent application and both
applications have the same owner.
FIELD OF THE INVENTION
[0002] The present invention is directed to a system for
efficiently capturing wasted heat from a flue gas output of a
boiler. More particularly, the present invention is directed to a
system for capturing wasted heat from a flue gas output of a boiler
to preheat the feed water to the boiler.
BACKGROUND
[0003] Many power generation systems are powered by steam generated
via coal or oil fired boilers. These power generation systems will
often incorporate exhaust processing and heat recovery (EPHRS)
systems to reduce flue gas emissions and/or recover heat energy
expelled via the flue gas stream from the boiler.
[0004] A typical power generation system is generally depicted in
the diagram shown as FIG. 1. FIG. 1 shows a power generation system
10 that includes a steam generation system 25 and an exhaust
processing and heat recovery system (EPHRS) 15 and an exhaust stack
90. The steam generation system 25 includes a boiler 26.
[0005] The EPRS 15 includes an air preheater 50, a particulate
removal system 70 and a flue gas scrubber system, shown here as a
wet scrubber system 80. The particulate removal system 70 may be,
for example, an electrostatic precipitator (ESP), a fabric filter
system (Bag House) or the like. A forced draft (FD) fan 60 is
provided to introduce air into the cold side of the air preheater
50.
[0006] The air preheater 50 is a device designed to heat air before
it is introduced to another process such as, for example,
combustion in the combustion chamber of a boiler 26. The air
preheater heats the air stream input A2 to the boiler 26
capturing/recovering heat expelled from the boiler 26 via the flue
gas stream from the boiler. By recovering heat from the flue gas
(FG1) emitted from the combustion chamber of the boiler 26 the
thermal efficiency of the boiler 26 can be increased and the amount
of heat lost through the flue gas FG4 out of stack 90 is
reduced.
[0007] In general, it is desirable to reduce the temperature of the
flue gas FG2 leaving the air preheater 50 and before it is
introduced to processing devices such as, for example, an
electrostatic precipitator (ESP) used as particulate removal system
70. By increasing the airflow Al passing into the air preheater 50,
it is possible to extract more heat from the flue gas stream FG1
and thereby further reduce the temperature of the flue gas stream
FG2 that reaches the ESP 70.
[0008] However, this process also results in an increased volume of
available heated air. It is often not feasible in a typical power
generation system to direct the entire flow of heated air into the
combustion chamber of the boiler 26 without negatively affecting
the efficiency of the boiler 26.
[0009] One alternative for increasing the efficiency of the boiler
26 has been to introduce an "economizer" section 55 between the
boiler 26 and the air preheater 50. This economizer section 55 is a
type of heat exchanger used to capture heat from an air stream and
transfer the heat into a fluid stream, such as, for example, water.
Further, economizers are typically designed with finned tubes that
improve the transfer of heat. In boilers, economizers are heat
exchange devices that heat fluids, usually water, up to but not
normally beyond the boiling point of that fluid. Economizers are so
named because they can make use of the enthalpy in fluid streams
that are hot, but not hot enough to be used in a boiler, thereby
recovering more useful enthalpy and improving the boiler's
efficiency. The economizer is a device that is coupled to boiler 26
which saves energy by using the exhaust flue gases FG from the
boiler 26 to preheat/heat the feed water WF from a water supply
65.
[0010] FIG. 1 it shows that economizer 150 is configured to receive
the flue gas stream FG from the boiler 26, and to pass the flue gas
stream FG1 on to the air preheater 50. In this example, the
economizer 55 acts to transfer heat from the flue gas stream FG to
feed water WF that is provided to the boiler 25. This allows
"pre-heated" water to be introduced into the boiler 25, thereby
reducing the need for additional heat energy to heat the boiler
water to a desired temperature.
[0011] The flue gas stream FG/FG1 will generally contain a
substantial level of particulate matter. This particulate matter is
typically removed from the flue gas stream after the flue gas
stream FG2 has passed through the particulate removal system 70.
However, until the flue gas stream is subjected to particulate
removal operations, the presence of particulate matter in the flue
gas stream is typically high. Since the economizer 55 receives the
flue gas stream prior to it being subjected to dust removal
operations, it is possible for particulate matter to get caught in
between the heat exchange elements of the economizer 55 if the
spacing between the heat exchange elements is not sufficient. To
avoid having particulate get caught between the heat exchange
elements, it is important that the spacing between heat transfer
elements of the economizer be large enough to allow most, if not
all, particulate matter to freely pass through the economizer 55.
This large spacing leads to inefficiency.
[0012] If the spacing between heat transfer elements was smaller,
particulate matter that are too large to pass between the heat
exchange elements of the economizer will become caught and begin to
accumulate within the economizer 55. This accumulation of particles
will typically increase and eventually impede flow of the flue gas
stream through the economizer 55 if steps are not taken to
remove/clear the accumulations. The impeded flow of the flue gas
stream reduces the effectiveness of the economizer 55. Further, it
will be necessary to take steps to clear the accumulations from the
economizer 55 in order to keep in operating properly. This leads to
increased maintenance time and costs.
[0013] Currently, there is a need for an efficient heat exchanger
in a boiler system which makes use of wasted heat and requires less
maintenance than prior art systems.
SUMMARY OF THE INVENTION
[0014] The present invention may be embodied as an economical heat
recovery system [100] for use with a boiler [26] that boils water
feed from a water supply [125] supplied to it.
[0015] It includes an air preheater [150] for receiving heated flue
gasses [FG1] produced by boiler [26], for receiving input air [A1]
and for creating incremental air stream [A2'].
[0016] It also includes a regenerative heat capture and transfer
(RHCT) system [300] adapted to receive the incremental air stream
[A2'], said water feed [WF1], then transfer heat from the
incremental air stream [A2'] to the water feed [WF1], create
preheated water feed [WF2] and supplied preheated water feed [WF2]
to boiler [26].
[0017] The RHCT uses a heat exchanger [310] to receive the
incremental air stream [A2'] from the air preheater, receive the
water feed [WF1] and transfer heat from the incremental air [A2']
to water feed [WF1] to create preheated water feed [WF2]. A pump
330 coupled to said water supply [125] and to the heat exchanger
[310] pumps the feed water [WF1] from water supply [125] through
the heat exchanger [310] and the preheated water feed [Wf2] to the
boiler [26].
[0018] The placement of the RHCT after the air preheater [150]
allows the RHCT to be designed in a much more efficient manner and
require less maintenance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The present invention may be better understood and its
numerous objects and advantages will become apparent to those
skilled in the art by reference to the accompanying drawings in
which:
[0020] FIG. 1 is a block diagram depicting a portion of a power
generation system 10 according to the prior art.
[0021] FIG. 2 is a simplified block diagram depicting an embodiment
of a power generation system 100 according to the present invention
that incorporates a regenerative heat capture and transfer system
(RHCT) 300.
[0022] FIG. 3 is a simplified block diagram depicting another
embodiment of a power generation system 100 that incorporates a
RHCT system 300 according to the present invention.
[0023] FIG. 4 is an enlarged block diagram depicting an embodiment
of the RHCT system 300 of FIGS. 2 and 3.
[0024] FIG. 5 is a simplified block diagram depicting another
embodiment of a power generation system 100 that incorporates a
RHCT system 300 according to the present invention.
[0025] FIG. 6 is an enlarged block schematic diagram depicting the
capture of heated leakage air from a rotary air preheater.
DESCRIPTION OF THE INVENTION
[0026] FIG. 2 is a simplified block diagram depicting an embodiment
of a power generation system 100 according to the present invention
that incorporates a regenerative heat capture and transfer system
(RHCT) 300. In this embodiment a power generation system 100 is
provided that includes a steam generation system 25, an exhaust
processing and heat recovery system (EPHRS) 15, a regenerative heat
capture and transfer system (RHCT) 300, a water supply 125 and an
exhaust stack 90.
[0027] Steam generation system 25 includes a boiler 26. The EPRS 15
includes a regenerative air preheater 50, a particulate removal
system 70 and a wet scrubber system 80. A forced draft (FD) fan 60
is provided to introduce an air stream Al into the cold side input
of the air preheater 50. In turn, air preheater 50 heats the air
stream Al and outputs it as a heated air stream A2 that is fed to
an air intake of the combustion chamber (not shown) of boiler 26
for combustion.
[0028] Exhaust gases FG1 expelled from the combustion chamber (not
shown) of boiler 26 are received by a hot side input of the air
preheater 50. These exhaust gases FG1 are cooled via the air
preheater 50 and output as a cooler temperature exhaust gas stream
FG2. Previously, gasses leaving air preheater 150 had to remain hot
enough to prevent condensation of compounds in the flue gas. This
reduced corrosion of the equipment downstream from the preheater
50.
[0029] Now, with the advent of corrosion reducing equipment and
processes, corrosion is less of a problem. Therefore, there may be
a greater amount of heat recovered that is fed back into the
system. This results in higher boiler efficiency.
[0030] Exhaust gas stream FG2 is then processed to remove
particulate matter via particulate removal system 70. The
particulate removal system 70 may be, for example, an electrostatic
precipitator (ESP), a fabric filter system (Bag House) or the
like.
[0031] The processed exhaust stream FG3 may be further processed
via, for example, a wet scrubber 80 to remove, for example,
sulfuric oxide (SO.sub.2). This processed stream FG4 is then output
for introduction to the exhaust stack 90.
[0032] Regenerative heat capture and transfer system (RHCT) 300 is
configured to receive an air stream A2' and extract thermal energy
therefrom. Air stream A2' is a portion of air stream A2 expelled
from the air preheater 50. In turn, the thermal energy extracted
from air stream A2' is transferred to a water feed supply WF1 which
is then output as heated water feed WF2 and introduced to boiler
26. RHCT 300 is configured and positioned so as to transfer thermal
energy from the input air stream A2' to water feed WF1 without
receiving contaminates. Air streams A2/A2' are clean air stream
that do not mix with the flue gas streams that have significant
amount of particulate matter. Further, since no flue gas is used by
the RHCT 300 to heat the water feed supply WF1, the RCHT 300 is not
subjected to particulate matter that is often found in the flue gas
stream FG.
[0033] Air preheater 150 can now be designed to be a high
efficiency air preheater transferring a greater amount of heat.
Also, air preheater 150 may be designed to output a greater volume
of heated air than can be efficiently put to use by the steam
generation system 25, creating excess heated air.
[0034] FIG. 3 is a simplified block diagram depicting another
embodiment of a power generation system 100 that incorporates a
RHCT system 300 according to the present invention. In this
embodiment, air preheater 150 has one flue gas duct and two heated
input air ducts. The output of one heated air duct releases heated
air stream A2. This is provided to boiler 26. The second heated air
duct provides incremental air stream A2' that is passed to RHCT
300.
[0035] The remaining parts of FIG. 3 perform the same function as
the parts of other figures having the same reference number.
[0036] FIG. 4 is an enlarged block diagram depicting an embodiment
of the RHCT system 300 of FIGS. 2 and 3. In this embodiment, the
RHCT 300 includes heat exchanger 310 and pump 330. Heat exchanger
310 is preferably configured to receive a portion A2' of the heated
air stream A2 from the air preheater 150.
[0037] Since the RCHT 300 is not subjected to the particulate
matter typically found in the flue gas stream FG, it is possible
for the heat exchange elements (not shown) used in the economizer
to be placed in much closer proximity to each other and thereby
provide for more surface area available to contact the air stream
A2/A2'. In this way, the efficiency of the heat exchanger 310 can
be significantly enhanced since the greater the surface area of the
heat exchange elements that is provide, the more heat that can be
captured for a given volume. Further, since the heat exchange
elements are not subjected to much particulate matter, the threat
of blockage due to accumulations of particulate matter in the
economizer is greatly reduced, if not completely avoided.
[0038] In this particular case the finned tubes will not be exposed
to coal ash (only preheated air); therefore, the fin density
spacing can be reduced significantly from that of a typical
economizer tube designed for exposure to flyash. Thus, the size of
the economizer should be more efficient and smaller.
[0039] By coupling RHCT 300 to air preheater 150 instead of the
boiler flue gas output, heat is more efficiently removed from the
exhaust gases FG1, transferred to an air stream (A2'), introduced
into the water feed [WF1/WF2] to supply boiler 26 than was
previously possible in prior art systems.
[0040] FIG. 5 is a block diagram depicting another embodiment of a
power generation system 100 that incorporates a RHCT system 300
according to the present invention.
[0041] Here incremental air stream [A2'] and/or leakage gasses 360
from exhaust conduits 361, 363 are provided to RHCT. Fan 367
facilitates the flow of leakage gasses 360.
[0042] FIG. 6 is an enlarged block schematic diagram depicting the
capture of heated leakage gasses 360 from a rotary air preheater
150.
[0043] Hot flue gasses FG1 are passed into a hot side of an air
preheater 150. A wheel 151 rotates on an axle 152. A motor causes
rotation of wheel 151.
[0044] Wheel 151 has a plurality of air conduits passing through
the wheel. Each of these has heating elements that heat us as flue
gas FG1 passes through the conduits. These heating elements rotate
to the cool side of the wheel where inlet air A1 is received. The
inlet air comes in contact with the hot heating elements and is
heated into preheated air A2 that exits the air preheater 150.
Heating element cool as the input air A1 passes over them.
[0045] Wheel 151 continues to rotate and the heating elements come
in contact with hot flue gasses FG1 again, absorbing heat. This
process then continues.
[0046] There are outer seals 157, 158 that stop most of the leakage
of hot flue gasses past the outer edge of wheel 151.
[0047] There are also inner seals that stop most of the flue gas
leakage toward the inner hub section of wheel 151. However, some
flue gas leaks past the seals and into inner plenums between the
wheel and housing 154.
[0048] In this embodiment, a leakage outlet 325 is provided. This
outlet may be implemented as an opening in the housing 154, which
allows access to the plenum 159. An exhaust conduit 361 is provided
for exhausting gas/air that may accumulate in the internal plenum
159. A fan device 367 may be provided to allow leakage gasses 360
to be exhausted from the internal plenum 159 more easily.
[0049] A further leakage outlet may also be provided so that
leakage gases accumulating within the internal plenum 365 may be
readily exhausted through another exhaust conduit 361.
[0050] Fan 367 also draws the leakage gasses 360 from exhaust
conduit 363. The leakage gasses 360 and/or incremental air stream
[A2'] are provided to the RHCT 300 to further heat the feed water
[WF1]. Use of this wasted heat increases the efficiency of the
boiler.
[0051] A separate fan may be employed for each exhaust conduit if
so desired.
[0052] It should be emphasized that the above-described embodiments
of the present invention, particularly, any "preferred"
embodiments, are merely possible examples of implementations,
merely set forth for a clear understanding of the principles of the
invention. Many variations and modifications may be made to the
above-described embodiment(s) of the invention without departing
substantially from the spirit and principles of the invention. All
such modifications and variations are intended to be included
herein within the scope of this disclosure and the present
invention and protected by the following claims.
* * * * *