BACKGROUND
[0001] The disclosure relates to coal-fired industrial
equipment. More particularly, the disclosure relates to the
cleaning of from coal-fired industrial equipment such as
pulverized coal-fired utility boilers.
[0002] One feature of many pieces of such equipment is the use
of a rotary heat exchanger to pre-heat inlet air by
transferring heat from the exhaust flow. Exemplary rotary heat
exchangers are found in US Patents 4487252 and 5950707. In an
exemplary axial rotary heat exchanger, the exhaust and inlet
flows pass along respective angular sectors of the heat
exchanger. The flows pass through a rotating core of the heat
exchanger. The core has plates or other features that absorb
heat when in the exhaust flowpath and then lose that heat
while passing through the inlet air flow. Steam or air purges
may be used to clean the core plates.
[0003] Within equipment such as boilers, sootblowers have been
used to clean surfaces such as boiler tubes. Steam lance
sootblowers have mainly been used. Detonative or pulsed
combustion sootblowers have recently been proposed. An example
of such a sootblower is in US Patent 7011047.
SUMMARY
[0004] The burning of fuel (e.g., coal) in industrial
equipment generates an exhaust flow containing airborne
particulate. The flow is passed through a rotary heat
exchanger to preheat inlet air. The heat exchanger element is
subject to fouling and is cleaned by a pulsed combustion
device. The device is operated by introducing a fuel and
oxidizer charge to at least one conduit and initiating
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combustion of the charge. The combustion generates a shock
wave to which the element is exposed, dislodging and/or
otherwise removing the deposits.
[0005] The details of one or more embodiments are set forth in
the accompanying drawings and the description below. Other
features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a partially schematic view of a coal-fired
boiler system.
[0007] FIG. 2 is a view of a boiler unit of the system of FIG.
1.
[0008] FIG. 3 is a longitudinally cut-away view of a heat
exchanger of the system of FIG. 1 with a first detonative core
cleaning system.
[0009] FIG. 4 is a partially schematic streamwise view of the
heat exchanger of FIG. 3.
[0010] FIG. 5 is a longitudinally cut-away view of a heat
exchanger of the system of FIG. 1 with a second detonative
core cleaning system.
[0011] FIG. 6 is a partially schematic streamwise view of the
heat exchanger of FIG. 5.
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[0012] FIG. 7 is a longitudinally cut-away view of a heat
exchanger of the system of FIG. 1 with a third detonative core
cleaning system.
[0013] FIG. 8 is a partially schematic streamwise view of the
heat exchanger of FIG. 7.
[0014] FIG. 9 is a longitudinally cut-away view of a heat
exchanger of the system of FIG. 1 with a fourth detonative
core cleaning system.
[0015] FIG. 10 is a partially schematic streamwise view of the
heat exchanger of FIG. 9.
[0016] Like reference numbers and designations in the various
drawings indicate like elements.
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DETAILED DESCRIPTION
[0017] FIG. 1 shows a schematic view of a pulverized
coal-fired electric power plant 20. The exemplary plant may be
an electrical power plant having a steam generator 22
providing steam to a steam turbine electrical generator unit
24. Along a combustion flowpath, the steam generator 22 has an
upstream radiant (furnace) zone 26 followed by a downstream
convective (backpass) zone 28. The steam generator 22 receives
input flows of coal 30, air 32, and water 34.
[0018] The coal 30 passes through a pulverizer system 40. The
air flow 32 passes through an air heater 50 (discussed below)
at a downstream end of the backpass 28. The backpass heat
exchangers may comprise vertical/streamwise or
horizontal/transverse tube arrays. The air enters the furnace
42 as a preheated flow 52 partially including entrained
pulverized coal 44. The furnace serves as a combustor
combusting the coal and air mixture. A combustion flow 54
passes downstream along the combustion/exhaust flowpath.
[0019] The water flow 34 enters the convective zone 28 where
it is preheated in an economizer 56 before entering the
vertical walls (water walls-typically vertically extending
tube arrays) 58 of the furnace 42. Heat exchange from the
combustion products 54 boils the water to produce steam.
Downstream along both the gas/combustion products flowpath and
water/steam flowpath, the steam is superheated to high
temperature and, in turn, delivered to a high pressure turbine
60. Exemplary superheating occurs in a two-stage process,
first in a primary superheater 62 across the convective zone
upstream of the economizer 56 and then in a pendant secondary
superheater 64 on the radiant zone. In the radiant zone 26,
flow is primarily upward and, in the convective zone,
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primarily downward. The two zones are separated by a bull nose
66 adjacent the pendant heat exchanger (s) .
[0020] Steam from the high pressure turbine 60 continues along
the water/steam flowpath and returns to the boiler to be
reheated. Exemplary reheating is in a two-stage process, with
a primary reheating (e.g., in a heat exchanger 70 across the
convective zone between the primary superheater 62 and
economizer 56) and a secondary reheating (e.g., in a pendant
reheater 72 spanning the radiant and convective zones).
Thereafter, the re-heated steam is delivered to an
intermediate pressure turbine 80.
[0021] Steam exiting the intermediate pressure turbine 80 is
directed to a low pressure turbine 82. Steam (and optionally
water) exiting low pressure turbine 82 may proceed to a
condenser 84 for correction and processing (e.g., to return as
the stream 34). Energy extracted by the turbines drives an
electrical generator 90 to produce electrical power.
[0022] After heating the water in the backpass region, the
flow 54 heats the incoming air in the air heater 50 and then
may proceed to a pollution control system 100. The exemplary
system 100 includes an upstream chemical scrubber 102 and a
downstream particulate removal device 104 (e.g., a bag house
or electrostatic precipitator). Thereafter, the combustion
products may pass through a stack 110 for discharge to
atmosphere.
[0023] FIG. 2 shows the air heater 50 as a rotary air heater
having a housing or body 120. The housing 120 has a first
portion 122 along the exhaust flowpath 124 and a second
portion 126 along the inlet air flowpath 128. A heat transfer
core 130 is mounted within the housing to rotate about an axis
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132. FIG. 3 shows the exemplary core 130 as including a hub
140 supported by an axle to be driven by an electric motor for
rotation about the axis 132. A plurality of heat transfer
surfaces 142 (e.g., plates) extend radially outward from the
hub to a periphery 144. The core has a first axial surface 150
and a second axial surface 152. In the exemplary
implementation, the first axial surface 150 is upstream along
the exhaust flowpath and the second axial surface 152 is
downstream. Depending upon implementation, the surface will
not be a single face but, rather, will be formed by discrete
portions (e.g., edge portions of plates). The rotation of the
core brings heat transfer portions of the core 130
sequentially through the exhaust gas flowpath and the inlet
air flowpath. The exemplary heat exchanger is positioned so
that the heat exchange is counterflow (i.e., the exhaust flow
and air inlet flow are in opposite directions).
[0024] As so-far described, the system is illustrative of just
one of a variety of plant configurations to which the present
invention may be applied. According to the present invention,
one or more detonative cleaning systems may be located along
the air/combustion products flowpath and positioned to clean
the element.
[0025] FIGS. 3 and 4 show an exemplary cleaning system 220.
The exemplary system 220 includes a plurality of pulsed
combustion devices 222 and 223. In the exemplary
implementation, two devices are shown, the first device 222
being upstream of the core along the exhaust flowpath and the
second device 223 being downstream of the core along the
exhaust flowpath. Each device 222, 223 has a conduit 224
having an outlet 226 at one end in interior 228 of the housing
120 and facing an associated core axial end 150, 152.
Exemplary combustion conduits have lengths of 0.5-4m and
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cross-sectional areas of 20-730cm2. The conduit 224 may include
one or more inlets for receiving fuel and oxidizer. FIG. 2
shows exemplary fuel and oxidizer lines 240 and 242 coupled to
common fuel and oxidizer sources 244 and 246 (e.g., tank
systems). Exemplary fuel consists in majority part, by mass,
of fuel selected from the group consisting of hydrogen,
hydrocarbon fuels, and their mixtures. Exemplary oxidizer
consists essentially of oxygen (e.g., from liquid oxygen
tanks). Alternative oxidizer is compressed air. Ignitors
(e.g., spark plugs 248) may be positioned to ignite admitted
fuel/oxidizer charges.
[0026] The exemplary system further includes a control module
250 which may be connected to a central control system 252.
Additional structural and operational details may be similar
to those of pulsed combustion cleaning apparatus such as shown
in US Pregrant Patent Publications 2005-0112516 and US 2005-
0199743, the disclosures of which are incorporated by
reference herein as if set forth at length.
[0027] The control system 252 may operate the devices 222 and
223 to repeatedly combust charges of the fuel and oxidizer.
Exemplary combustion includes detonation producing associated
shock waves 270. The Shockwaves may pass along the core
plates, cleaning the plate surfaces.
[0028] Particular physical and operational parameters will
depend on the characteristics of the heat exchanger. For
coal-powered plants, this may partially be influenced by the
nature of the particular coal being burned, and the nature of
the particular heart exchanger core. The exemplary devices 222
and 223 may be fired simultaneously (e.g., repetitively and
without interruption while the furnace is in operation or
sequentially).
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[0029] An exemplary control and firing protocol involves a
series of discharges timed to provide full circumferential
coverage. For example, the coverage of a single firing may be
deemed effective for a relatively small sector (e.g., ~10°,
more broadly 5-20°). The firing may be synchronized to the
rotation of the core so as to provide complete coverage. If
the firing cycle is short enough, consecutive sectors may be
progressively sequentially cleaned with the next uncleaned
sector being cleaned immediately after the prior sector. If
the cycle/refresh rate is not sufficient for this, an
uncleaned sector may be allowed to pass unaddressed through
the cleaning zone. For example, one full revolution plus the
sector increment (e.g., the ~10°) could pass between each of
the firings (an exemplary thirty-six total firings, each
separated from the prior firing by 370°, if the increment is
10°) .
[0030] Other timing variations involve redundant coverage of
firings, repeat firings along a given sector, and the like.
Other variations involve different delays between firings. For
example, if the cycle/refresh rate is sufficient the second
firing could be made before a full revolution has passed from
the first firing, but sill leaving an intervening uncleaned
portion. With the 10° example, the second firing could be
more than 10° but less than 370° after the first, etc. For
example the second firing could be 180° after the first. The
third could be 190° after the second. The fourth could be 180°
after the third, with subsequent alternating 190° and 180°
intervals. There could be a rotation sensor 280 for detecting
rotation of the core and coupled to the control system to
permit the synchronization.
[0031] An exemplary operation is a continuous operation with
individual discharges/firings at a fixed frequency (or nearly
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fixed due to the synchronization with rotation noted above).
An exemplary nominal frequency is 0.5-2.0 firings per minute.
Alternatively, each full cleaning of the core may be initiated
responsive to sensed parameters passing a predetermined first
threshold and/or the passage of a predetermined interval. An
exemplary interval may be up to daily. An exemplary sensed
condition may involve a pressure difference across the core on
one or both of the hot side and cool side (e.g., as detected
by upstream pressure sensor 284 and downstream pressure sensor
286). The cleaning may continue until the sensed condition has
passes (below for a pressure drop) a predetermined second
threshold.
[0032] FIGS. 5 and 6 show an alternate system configuration
having respective upstream and downstream devices 320 and 322.
the devices have conduits 324 which may be similar to conduits
224 except for the outlet 326. Relative to the outlet 226, the
outlet 326 is closer to the wall surface of the body 120. The
outlet 326, however is directed obliquely relative to the
adjacent core surface/end 150, 152 to compensate so that the
wave 340 has adequate coverage.
[0033] FIGS. 7 and 8 show an alternate system configuration
having respective upstream and downstream devices 420 and 422.
the devices have conduits 424 which may be similar to conduits
224 except for having multiple outlets 426, 428, 430, and 432
in a linear array along the side of the conduit. The array
extends to a closed end 434. The conduit 424 may thus have a
greater penetration into the flowpath. The outlets, however
may produce overlapping shock waves 450 which yield a more
radially uniform and circumferentially concentrated net
effect.
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[0034] FIGS. 9 and 10 show an alternate system configuration
having respective upstream and downstream devices 520 and 522.
the devices have conduits 524 which may be similar to conduits
424 except for one-to-all of: a progressive (e.g., step-wise)
decrease in conduit cross-sectional area along the array of
outlets 526, 528, 530, and 532; a progressive decrease in
outlet size ; and a progressive decrease in outlet spacing.
The array extends to a closed end 534. The outlets, may
produce overlapping shock waves 450, 452, 454, and 456 which
yield a more radially progressive distribution that
compensates for the relatively slower speed of inboard
portions of the core passing through the influence of the
shock waves. The circumferential span of the effective
Shockwave footprint on the core may thus radially increase.
[0035] One or more embodiments have been described.
Nevertheless, it will be understood that various modifications
may be made. For example, when implemented in a reengineering
or upgrade of an existing system configuration or system,
details of the existing configuration may influence details of
any particular implementation. Although illustrated with
respect to a coal-burning plant, the invention applies to
other heat transfer facilities that produce particulate. Some
prime examples would be trash incinerators and biomass/wood
burners. Although shown fixed, the conduits may be retractable
(e.g., as are retractable sootblowers) Accnrdinnly, other
embodiments are within the scope of the following claims.
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CLAIMS
WE CLAIM:
1. An apparatus comprising:
a combustor;
an inlet air flowpath extending to the combustor;
an exhaust flowpath extending from the combustor;
a rotary heat exchanger along the inlet air flowpath and
exhaust flowpath; and
a pulsed-combustion device positioned to direct a shock
wave toward a core of the heat exchanger and comprising:
a source of fuel and oxidizer;
at least one combustion conduit coupled to the
source to receive charges of said fuel and oxidizer; and
at least one ignitor coupled to the combustion
conduit to ignite the charges.
2. The apparatus of claim 1 wherein:
the combustor is a coal-burning furnace.
3. The apparatus of claim 1 wherein:
the pulsed combustion device comprises first and second
said conduits, the first conduit having an outlet upstream of
the core along the exhaust flowpath and the second conduit
having an outlet downstream of the core along the exhaust
flowpath.
4. The apparatus of claim 3 wherein:
the first and second conduits each have a plurality of
outlets at different radial positions relative to an axis of
rotation of the core.
5. The apparatus of claim 4 wherein:
the first and second conduits have a decreasing
cross-sectional area within the exhaust flowpath; and
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the plurality of outlets are along respective portions of
different cross-sectional area.
6. The apparatus of claim 1 wherein:
said combustion conduits have outlets aimed transverse to
a downstream direction of the flowpath.
7. The apparatus of claim 1 wherein:
at least four of said combustion conduits are positioned
at essentially a common streamwise location along the exhaust
flowpath.
8. The apparatus of claim 1 further comprising:
a smokestack forming an outlet of the exhaust flowpath to
atmosphere.
9. The apparatus of claim 1 wherein the source comprises:
a first source of said fuel, said fuel consisting in
majority part, by mass, of fuel selected from the group
consisting of hydrogen, hydrocarbon fuels, and their mixtures;
and
a second source of said oxidizer, said oxidizer
consisting essentially of oxygen.
10. The apparatus of claim 1 wherein:
said combustion conduits have lengths of 0.5-4m and
cross-sectional areas of 20-730cm2.
11. The apparatus of claim 1 further comprising:
a controller configured to fire the device a plurality of
times to provide circumferential coverage of the core.
12. The apparatus of claim 11 wherein:
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the controller configured to synchronize firing of the
device relative to rotation of the core.
13. An apparatus comprising:
a combustor;
an exhaust flowpath extending from the combustor;
an inlet air flowpath extending to the combustor;
a rotary heat exchanger along the inlet air flowpath and
exhaust flowpath; and
pulsed-combustion means for cleaning a core of the rotary
heat exchanger.
14. The apparatus of claim 13 wherein the combustor is a
fossil fuel-burning furnace;
15. The apparatus of claim 13 being a boiler system
16. A method for operating a plant comprising:
burning a plant fuel and generating a flow containing
particles;
passing the flow through a heat exchanger to heat an
inlet air flow; and
cleaning a core of the heat exchanger by a pulsed
detonation process including:
introducing a fuel and oxidizer charge to at least
one conduit;
initiating combustion of the charge; and
exposing the core to shock waves generated by
combustion.
17. The method of claim 16 wherein:
the passing of the flow comprises an axial flow through
the core while the core rotates about a core axis.
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18. The method of claim 16 wherein:
the plant fuel is selected from the group consisting of
coal, fuel oil, hydrocarbon gas biomass, trash, and
combinations thereof.
19. The method of claim 16 wherein:
the cleaning comprises exposing said core to said shock
waves from a plurality of said conduits.
20. The method of claim 16 wherein:
the cleaning comprises exposing the core to shock waves
from opposed outlets of one or more pairs of said conduits.
21. The method of claim 16 wherein:
the charge comprises hydrogen as a by weight majority of
the fuel.
22. The method of claim 16 wherein:
the at least one conduit is operated with an air purge
before each charge introduction.
23. The method of claim 16 wherein:
the cleaning is initiated responsive to a sensed
condition of the core.
24. The method of claim 16 wherein:
the conduit is fired a plurality of times in
synchronization with rotation of the core so as to provide a
full circumferential cleaning of the core.
Dated this 14th day of December, 2007
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The burning of fuel (e.g., coal) in industrial equipment generates an exhaust flow containing airborne particulate. The flow is passed through a rotary heat exchanger to preheat inlet air. The heat exchanger element is subject to fouling
and is cleaned by a pulsed combustion device. The device is operated by introducing a fuel and oxidizer charge to at least one conduit and initiating combustion of the charge. The
combustion generates a shock wave to which the element is exposed, dislodging and/or otherwise removing the deposits.