Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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-``A FLUIDIZED BED HEAT EXCHAM~,ER
UTILIZIN& ANGULARLY EXTENDING HEAT EXCHANGE TUBES
BACXGROUND OF THE I~VENTION
This invention relates to a fluidized bed heat
exchanger and, more particularly, to such a heat exchanger
employing a plurality of heat exchange tubes a portion of
each of which are immersed in the fluidized bed.
The use of fluidized beds has long been recognized
as an attractive means of generating heat. In these arrange-
ments air is passed through a bed of particulate material
which includes a mixture of inert material, a fuel materialsuch as high sulfur, bituminous coal and, usually, adsorbent
material for the sulfux released as a result of the combustion
of the coal. As a result of the air passing through the bed,
the bed is fluidized which promotes the combustion of the
fuel. The basic advantages of such an arrangement are many
and include a relatively high heat transfer rate, a substan-
tially uniform bed temperature, combustion at relatively low ~;
temperatures, ease of handling the fuel materials, a reduc-
~0 tion in corrosion and boiler fouling and a reduction in
boiler size.
When a fluidized bed of the above type is utilized ;~
in a heat exchange environment, such as in a steam generator
or boiler, a plurality of heat exchange tubes are normally
provided for passing water in a heat e~change relation to -
the fluidized bed. In most of these arrangements, the tubes
are disposed in a serpentine relationship with a great
majority of the lengths of the tubes extending horizontally,
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i.e., parallel to the upper surface of the bed. However,
" this type of arrangement results in less than optimum
operational efficiency since, for example, pumps are required
to insure satisfactory circulation of the water and steam
through the horizontal portions of the tubes. Also, for a
given required hea~ output it is difficult to maintain an
optimum temperature range for the combustion and/or other
reaction without either mechanically increasing the cooling
fluid velocity or increasing the number of tubes and, of
0 course, the number of penetrations through the bed floor or
walls. Also, it has been discovered that in the case of
horizontal tubes passing a liquid~vapor mixture in the
foregoing manner, irregular cooling of the internal surface
of the tube occurs which results in hot spotting and pre-
mature failing of the tubes. Further, with the use of
horizontally disposed heat exchange tubes it is difficult to
control the bed temperature in a linear manner. ~;
SUMMARY OF THE INVENTION
It i~ therefore an object of the present invention
'0 to provide a fluidized bed heat exchanger which, for a given
heat output, uses a minimu~ of heat exchange tubes for
maintaining an optimum temperature range for the combustion
process.
It is a further object of the present invention to
provide a heat exchanger of the above type in which a smaller
number of tubes and number of penetrations through the bed ~-
floor or walls is re~uired when compared to that of~a standard
horizontal tube heat exchanger for a given heat output.
It i~ a still further object of the present inven-
tion to provide a heat exchanger of the above type in which
a uniform cooling of the internal sùrfaces of the tubes is
achieved to prevent hot spotting and premature failing of
the tubes.
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-- It is a further object of th~ present invention to
provide a heat exchanger of the above type which eliminates the
need for circulation pumps and the necessity to mechanically
increase the cooling fluid velocity to obtain a yiven heat out-
put for a selected number of tubes.
Toward the fulfillment of these and other objects the
system of the present invention comprises a heat exchanger
comprising a housing, means defining a chamber in the housing,
means for establishing at least one bed of particulate material
containing fuel in the lower portion of the chamber, and means
for passing air through the bed to fluidize the material and
promote the combustion of the fuel, the air combining with the
gaseous products of combustion of the fuel and passing through the
upper portion of the chamber. The exchanger also comprises a steam
drum, a series of tubes connected at one end to the steam drum,
with a portion of each of the tubes extending through the lower and
upper chamber portions. The tube portions extend through the
lower chamber portion and are immersed in the bed with at least a
portion thereof extending at an acute angle to the upper surface `
of the bed. The tube portions extend through the upper chamber
portion vertically, and means connect the steam drum to the other `
end of the tubes for permitting water to pass from the steam drum,
through the tube portions, and back to the steam drum, to transfer i~
heat from the fluidized bed and the air andigaseous products of
combustion to the water.
BRIEF DESCRIPTION OF THE DRAWINGS
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The above description, as well as further objects,
features, and advantages of the present invention, will be
more fully appreciated by reference to the following description
30 of a presently-preferred but nonetheless illustrative ~-
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-- embodiment in accordance with the pxesent invention, when
taken in connection with the accompanying drawings wherein:
Fig. 1 is a schematic cross-sectional view of the
heat exchanger of the present invention;
Fig. 2 is a schematic horizontal cross-sectional
view o the heat exchanger of the present invention taken
along the line 2-2 of Fig. l; and
Figs. 3-6 are partial views of a portion of the
componentry of Fig. l showing alternate arrangements of the
immersed portions of the tubes.
DESCRIPTION OF THE PREFERRED EMBODI`MENTS
Referring specifically to Fig. l of the`drawings
the reference numeral lO refers in general to the fluidized
bed heat exchanger of the present invention which, for the
purposes of example, is shown in the form of a steam generator.
The generator includes an outer vessel having a top wall or
roof 12, an upper front wall 14a, a lower front wall 14b, a
rear wall 16, and two sidewalls, one of which is shown by
the reference numerai 18.
A pair of spaced partition walls 20 and 22 extend
parallel to the rear wall 16 and between the sidewalls 18 `;
and define chambers 24 and 26. A horizontally extending air
distribution plate 28 extends between the partition wall 22
and the rear wall 16, between the two sidewalls 18 near the ;
lower portion o~ each chamber 24 and 26, and in a spaced ~
relation to the floor of the vessel to define air distribu- `; -
tion chambers 30 and 32 respectively. Two beds of particu-
late material, shown in general by the reference numerals 34
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-- and 36, are disposed in the chambers 24 and 26, respectively
and are supported by the plate 28. Each bed of particulate
material includes a mixture of crushed coal and an inert
material such as commercial grade hematite iron ore. Also,
a fine limestone or dolomite can be included for use as an
adsorbent for the sulfur released during the combustion of
the fuel r in a conventional manner.
As better shown in Fig. 2, two spreader coal
feeders 38 and 40 are mounted to one sidewall 18 for intro-
ducing the fuel and limestone mixture into the beds 34 and
36, respectively, while a limestone feed pipe 42 is mounted
in the wall 16 for introducing the limestone into the bed 34
and a limestone feed pipe 44 is mounted through the latter
sidewall 18 for introducing limestone into the bed 36. A
drain 46 is provided for each of the beds 3~ and 36 and ~;
extends through the plate 28 for permitting the spent par-
ticulate material to discharge from the bèd as will described -
in detail later.
As also shown with reference to Fig. 2, each of
the walls 16, 18, 20, and 22 are formed by a plurality of
tubes having two longitudinally extending fins connected to
diametrically opposite portions thereof with the fins of
adjacent tubes being welded together to farm a gas-tight
structure. Further, an outer layer of insulating material
~8 extends around and encloses the tubular rear wall 16 and
the sidewalls 18 and also forms the roaf 12 and the upper ;~
and lower front walls 14a and 14b of the vessel.
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Referring again to Fig. 1, two air distribution
ducts 50 and 52 are disposed immediately below the air
distribution chambers 30 and 32, respectively, for distri-
buting air to the latter chambers and into the beds 34 and
36, respectively. The air flows through the ducts 50 and 52
under the control of dampers 54 and 55, respectively, located
in the ducts and then upwardly through the chambers 30 and
32 and the plate 28 to fluidize the beds 34 and 36 and
promote the combustion of the particulate fuel matexial.
The air, after passing through the beds 34 and 36 and taking
part in the combustion reactions combines with the gaseous
products of combustion and exits outwardly from the chambers
24 and 26, respectively, in a manner to be described in
detail later.
A water/steam circulation system is provided
between the partition wall 22 and the upper front wall 14a ;
and includes an upper steam drum 56 and a lower water, or
mud, drum 58. A boiler bank 60 is also provided and consists
of a multiplicity of spaced tubes connecting the steam drum
~0 56 and the water drum 58 to place them in fluid communica-
tion. The steam drum 56 is supported by external support
structure (not shown) and the water drum 58 is supported
by the steam drum through the boiler bank 60.
Two pairs of downcomers 62 and 64 extend down-
wardly from the steam drum, with one downcomer of each pair
being shown in Fig. 1. The downcomer 62 is connected to a
series of horizontal feed pipes 65 and 66 located at the
lower portion of the vessel with one feed pipe of each series
being shown in Fig. 1. The feed pipes 65 are connected in
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fluid communication with a horizontal header 68 and a
horizontal header 70 which, in turn, are connected in fluid
communication with the lower ends of the tubes forming the
partition wall 22 and one of the sidewalls 18, respectively.
In a similar manner, the feed pipes 66 are connected to a
horizontal header 72 which is connected in flow communica-
tion with the lower ends of the tubes forming the partition
wall 20. The downcomers 64 are connected to a series of feed
pipes 74 and 76, one of each of which are shown in Fig. 1,
with the feed pipes 74 being connected in fluid communication
with a header 77 which, in turn, is connected to the lower
ends of the tubes forming the rear wall 16. Although not
clear from the drawings it is understood that the fieed pipes
76 are connected to a header (not shown) which is in fluid
communication with the lower ends of the tubes forming the
other sidewall 18.
An upper header 78, located adjacent the roof 12
is connected to the upper ends of the tubes forming the
sidewall 18 shown in Fig. l for receiving the fluid from the;~
20 latter~ A plurality of rlser tubes 79 are connected between ;
the header 78 and the steam drum 56 for passing the 1uid
back to the steam drum. It is understood that another
header similar to header 78 is provided in connection with
the tubes forming the other sidewall 18 and~ is connected,
via additional tubes, to the steam drum 56.
Referring again to Fig. l, the upper portions of
the tubes forming the walls 16, 20, and 22 are bent into a ;~
horizontal configuration as shown and are connected to the
steam drum 56 to complete the flow circuit. In this respect
it is noted that the finned portions of the tubes forming
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- the walls 20 and 22 texminate at points shown by the reference
numerals 20a and 22a, respectively but that the tubes forming
these walls continue upwardly and are bent over as shown for
connection to the steam drum 56. As a result, the air and
gaseous products of combustion from the beds 34 and 36 can
pass through the spaces thus defined between the upper
portions of the tubes forming the walls 20 and 22, as they
exit from the chambers 24 and 26, respectively, as will be
described in detail later.
An additional circuit for the passage of the water
and steam is provided by two series of bed tubes ~0 and 82
which are connected at their lower ends to the headers 77
and 72, respectively, and which pass upwardly in a substan-
tially vertical manner through the air distribution chambers
30 and 32, and into the lower portions of the beds 34 and
36, respectively. The bed tubes 80 and 82 are then bent at
an angle to the upper surface of the beds 34 and 36, respec-
tively, and e~tend diagonally across the beds whereby they
are bent again to extend vertically upwardly through the
remaining portions of the chambers 24 and 26, respectively,
before they are bent a~ain into a substantially horizontal
configuration for connection to the steam drum 56.
A gas outlet 90 is provided in the upper front
wall 14a for the discharge of the air and gaseous products
of cQmbustion from the chambers 24 and 26. In passing from ;
the latter chambers the air and gaseous products of combustion
pass over the boiler bank 60 to add heat to the water/steam
in the tubes forming the boiler bank as will be described
in detail later. A steam outlet 92 is provided in the steam
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drum 56 for providing for the discharge of the steam to
another unit, such as a steam turbine, or the like.
In operation, the particulate fuel material in the
beds 34 and 36 is ignited by ignitors, or the like (not
shown) disposed in the beds and preferably in an ignition
zone at the ends of the beds, in a conventional manner. Air
is passed through the air ducts 50 and 52 under control of
the dampers 54 and into the air distribution chambers 30 and
32, respectivelv, for passage upwardly through the plate 28
and into the beds 34 and 36, respectively. This fluidizes
the particulate bed material and promotes the combustion of
the fuel material, after which the excess air combines with
the gaseous products of the combust~on of the fuel material .
and flows upwardly into the upper portions of the chambers
24 and 26 before exiting from the chambers and passing . : :
across the boiler bank 60 before discharging through the
vessel via the outlet 90.
Water is circulated from the steam drum 56 through
the boiler bank 60 and into the water drum 58 and, from the
downcomers 62 and 64 to the bed tu~es 80 and 82 and the
tubes forming the walls 16, 18, 20, and 22, as described ~-:
previously. The hot air and gases passing over the boiler
bank 60 add heat to the water passing through the tubes of : -
the latter, to convert a portion of it to steam with the ..
water/steam mixture.rising in the tubes by natural convec-
tion and passing back into the steam drum 56. It is under-
stood that the steam drum 56 may be provided with separators
to separate the steam from the watex in a conventional
manner before the steam exits from the steam outlet 92. The
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~ heat generated by the fluidized beds 34 and 36 also adds
heat to the water flowing through the tube banks 80 and 82
disposed in the chambers 24 and 26 and particularly those
portions thereof immersed in the fluidized beds 34 and 36.
The portion of the water that is not converted to steam will
recirculate in the foregoing manner and additional feedwater
is supplied to the drum 56 through an lnlet (not shown) to `~
replenish the water that is converted to steam.
Figs. 3-6 depict alternate embodiments of the
particular arrangement of the bed tubes and their relation
to the fluidized beds. These alternate embodiments will be
described in connection with the fluidi~ed bed 34 and its
associated bed tubes, and other components that are identi-
cal to the components in the previous embodiment are referred
to by the same reference numerals.
In the embodiment of Fig. 3, a series of bed tubes
94 is provided which extend from a header 95 disposed exter-
nally of the vessel and adjacent the rear wall 16. The
tubes 94 extend through the wall 16 and diagonally through
20 the bed 34 before bendtng upwardly into a vertical direction ~`
as shown. Otherwise this embodiment is identical to that of
the previous embodiment. ~
In the embodiment of Fig. 4 two series of bed -
tubes 96 and 98 are provided and extend in a substantially
"Y" configuration with the lower ends of both series of
tubes being connected to a common lower header 100. The bed
tubes 96 include outwardly slanted portions 96b extending
through the bed 34 and vertical portions 96c which extend
through the remaining portion of the chamber 24 before
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bending across to the steam drum 56. ~he tubes 98 are
arranged in a similar manner and therefore are not described
in any further detail.
According to the embodiment of Fig. 5, a first and
second series of bed tubes 102 and 104, respectively, are
provided in the fluidized bed 34 and are configured to form
an inverted Y as shown. Each bed tube 102 includes a
vertical portion 102a connected to a header 106 disposed
below the plate 28, a portion 102b extending through the
fluidized bed and slanted inwardly towards the center of the
bed, and an upper portion 102c extending vertically through
the remaining portion of the chamber 24 and bending across
for connection to the steam drum 56. The tubes 104 may be
configured in a similar manner with the exception that the
lo~er portions of these tubes are connected to a header 108.
In the embodiment of Fig. 6 a first series of bed
tubes 110 have slanted portions llOa extending from a header
112 disposed externally of the vessel and adjacent the wall 16
and through the latter wall and the bed 34. The tubes 110
have yertical portions llOb which extend from the upper
portion of the bed 34 and through the upper chamber 24
before'they are bent for connection to the steam drum 56.
Another series of bed tubes 114 are connected to a-header
116 disposed adjacent the wall 20 and are configured in a
manner similar to the tubes 110.
It is understood that in each of the embodiments l
of Figs. 3-6, another bed, similar to bed 36 of the first .
embodiment, can be provided adjacent the bed 34 and can
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contain bed tubes that are identical to the beds tubes
described above in connection with bed 34.
The advantages of the foregoing arrangement are
numerous. For example, the disposition of the slanted
portions of the bed tubes 80 and 82 in the fluidized beds 34
and 36 increases the efficiency of the steam generator to the
extent that a relatively hi~h heat output can be attained
without mechanically increasing the cooling fluid velocity. ~ ,
Also only a relatively small number of tubes is required to
attain a given heat output thus reducing the tube surface
outside the bed and the number of penetrations through the
bed floor. Also, due to the upflow of the fluid inside the
slanted portions of the bed tubes, the fluid becomes lighter
with increases in temperature and the resulting distribution
of steam and water in the tubes promotes a uniform moistening
of the inner wall af tubes thus preventing hot spotting and
premature tube failure. Further, the bed temperature can be
controlled in a linear fashion by simply modifying the bed
height to change the amount of cooling surfaces. Still ~ -
further, circulation pumps to pass the fluid through the bed
tubes are not required due to the natural circulation result~ ~
ing from the slanted tube arrangement. ~` -
It is also understood that the present invention
has been described in connection with a steam generator only `~
~or the purposes of example and can be used in other appli- ~
cations consistent with the foregoing. ~ ;;
Other latitudes of modification, change and sub-
stitution are intended in the foregoing disclosure and in
some instances some features of the invention will be employed
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~- without a corresponding use of other features. Accordingly,
it is appropriate that the appended claims be construed
broadly and in a manner consistent with the spirit and scope
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of the invention herein.
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