Combustion chamber to accommodate a split-stream of recycled gases

A combustion chamber is provided that has a vertically oriented body with an inner surface defining an inner combustion area. A burner is disposed adjacent one end of the body so that the flame of the burner when lit will extend into the combustion area. A first annular insert is disposed in the combustion area and generally surrounds the flame of the burner. The annular insert defines a first secondary gas introduction zone for introducing secondary gases into the combustion area so that the secondary gases can be oxidized by the burner flame. The insert has an inner surface presenting at least one opening for allowing fluid communication between the introduction zone and the combustion area. A second annular insert is disposed in the combustion area below the first insert. The second insert defines a secondary gas extraction zone and a second secondary gas introduction zone located below the extraction zone. The gas extraction zone and second secondary gas introduction zone are separated by a divider plate. The gas extraction zone and second secondary gas introduction zone are generally separated by an annular inner wall which has openings therein to allow fluid communication between the combustion area and the extraction zone and second secondary gas introduction zone.

BACKGROUND OF THE INVENTION 
This invention relates to a combustion chamber for supplying heated gases 
to a device in which a material is dried and/or heated, and more 
specifically, to a combustion chamber that accommodates a split-stream of 
recycled gases. 
Drying systems are important features in the manufacture and processing of 
many different materials. For example, drying systems are often used in 
drying wood chips during the manufacturing of particle board. Further, 
drying systems are of particular importance during the processing of 
ethanol. More particularly, after ethanol has been removed from grain 
during the fermentation process, it is then desirable to dry the grain to 
allow storage and resale of the grain for animal feed or other uses. 
Typical drying systems include a combustion chamber into which natural gas 
and air are supplied and combusted. The heated combustion gases in the 
combustion chamber are then induced by a draft fan into a rotating 
cylindrical dryer. The material to be dried is introduced into the dryer 
and exposed to the current of heated gases. The dried material is then 
separated from the heated gas current in a cyclone separator. The 
remaining heated gases are then typically vented to the environment. An 
example of a typical drying system of the prior art is disclosed in U.S. 
Pat. No. 3,861,055, which is incorporated herein by reference. 
A major problem with these prior art systems involves the venting of the 
combustion gases to the atmosphere. More particularly, these combustion 
gases contain various pollutants. For example, the gases oftentimes 
contain volatile organic compounds (VOC's), carbon dioxide (CO.sub.2), 
particulate and nitric oxide (NO). In addition to pollutants that result 
from the combustion process in the combustion chamber, pollutants can also 
result from the drying of the material itself. For instance, in the drying 
of wood chips or other organic material, particulate is often contained in 
the combustion gases as they are vented to the atmosphere. Because 
governmental standards set the level of pollutants that can be vented to 
the atmosphere, it is often necessary to add additional pollution control 
devices to the drying systems to reduce the pollutant levels in the gas 
stream prior to venting. These devices often are add-on oxidizers which 
oxidize the VOC's and particulate present in the gas stream to reduce such 
pollutants to an acceptable level. These pollution control devices are 
typically expensive to install and operate. 
Some prior art drying systems have attempted to address the above-discussed 
problem by recycling the combustion gases. More specifically, in one type 
of drying system, all of the combustion gases exiting the dryer are 
recycled back into a combustion chamber for oxidation. Gases are also 
taken out of the drying system at the combustion chamber and vented to the 
atmosphere. Recycled gases flowing into the combustion chamber and those 
flowing out of the combustion chamber are run through a heat exchanger 
wherein the heat from the gases flowing out of the combustion chamber and 
to the atmosphere is transferred to the recycled gases flowing into the 
combustion chamber. This type of drying system suffers from various 
disadvantages. First, because the entire quantity of combustion gases is 
recycled to the combustion chamber for oxidation, this drying system 
operates within very narrow operating parameters. More specifically, the 
prior art system only operates in an optimal manner at a particular 
capacity of the drying system. If the capacity of the drying system varies 
from the particular level, the oxidation temperature of the recycled gases 
and the inlet temperatures of the gases to the dryer could vary 
substantially. Because these factors could vary over large ranges, 
differing levels of pollutants were vented to the atmosphere depending on 
the capacity at which the prior art system was run. Further, again 
depending on the capacity, the dryer inlet temperature could vary 
substantially, thus resulting in inconsistent or incomplete drying of the 
material. 
Further, these attempts to recycle gases exiting the dryer back into the 
combustion chamber suffer from other disadvantages. Because the recycled 
gases are often introduced into the combustion chamber in a haphazard and 
uncontrolled fashion, the gases may interfere with the operation of and 
efficiency of the burner flame. Furthermore, the uncontrolled introduction 
of recycled gases may result in incomplete and/or inconsistent oxidation 
of pollutants found in the recycled gases. Likewise, the removal of gases 
from the combustion chamber for venting to the environment has not been 
executed in a controlled fashion in the prior art systems. More 
specifically, the temperature of the gases removed from the combustion 
chamber was not controlled. This resulted in less than optimal efficiency 
of the system and is detrimental to the heat exchangers through which the 
vented gases will flow. 
Thus, a novel combustion chamber construction is needed to overcome the 
drawbacks and shortcomings of prior combustion chambers. Further, a 
combustion chamber is needed that can oxidize pollutants within the system 
so that external pollution control devices are not needed. Still further, 
a combustion chamber is needed that will accommodate a separated recycled 
gas stream so that only a desired portion of the recycled gas stream is 
oxidized and vented to the environment. Further yet, a combustion chamber 
is needed that provides an avenue for removal of recycled gases after 
oxidation. Still further, a combustion chamber is needed that can be used 
to control the temperature of the gases removed by removing the gases from 
a desired location within the chamber. 
SUMMARY OF THE INVENTION 
One object of the present invention is to provide a combustion chamber 
construction which provides a reduction in the emission of pollutants from 
a drying process into the atmosphere. 
Another object of the present invention is to provide a combustion chamber 
construction which accommodates a split stream of recycled gases so that a 
portion of the gases can be oxidized and vented to the environment while 
another portion is returned to the drying system. 
A further object of the present invention is to provide a combustion 
chamber construction which provides a structure to remove the gases from 
the chamber in a desired location and temperature range. 
According to one aspect of the present invention a combustion chamber is 
provided having a vertically oriented body with an inner surface defining 
an inner combustion area. A burner is disposed adjacent one end of the 
body so that the flame of the burner when lit will extend into the 
combustion area. A first annular insert is disposed in the combustion area 
and generally surrounds the flame of the burner. The annular insert 
defines a first secondary gas introduction zone for introducing secondary 
gases into the combustion area so that the secondary gases can be oxidized 
by the burner flame. The insert has an inner surface presenting at least 
one opening for allowing fluid communication between the introduction zone 
and the combustion area. A second annular insert is disposed in the 
combustion area below the first insert. The second insert defines a 
secondary gas extraction zone and a second secondary gas introduction zone 
located below the extraction zone. The gas extraction zone and second 
secondary gas introduction zone are separated by a divider plate. The gas 
extraction zone and second secondary gas introduction zone are generally 
separated by an annular inner wall which has openings therein to allow 
fluid communication between the combustion area and the extraction zone 
and second secondary gas introduction zone. 
Additional objects, advantages, and novel features of the invention will be 
set forth in part in the description which follows and in part will become 
apparent to those skilled in the art upon examination of the following, or 
may be learned by practice of the invention. The objects and advantages of 
the invention may be realized and attained by means of the 
instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
A combustion chamber embodying the principles of this invention is broadly 
designated in the drawings by the reference numeral 10. Chamber 10 has an 
outer cylindrical shell 12 with a circular base 14 and a circular cover 
16, as best seen in FIG. 2. Shell 12 includes a lower cylindrical wall 
section 18, a middle wall section 20 and an upper wall section 22. 
Lower section 18 is preferably formed integrally with base 14, and extends 
upwardly from the periphery of base 14, as best seen in FIG. 8. Lower 
section 18 is connected to middle section 20 by a connecting arrangement 
24 as best seen in FIGS. 2 and 7. Arrangement 24 includes a pair of 
annular L-shaped connecting flanges 26 and 28. Flange 26 is preferably 
welded to the outer peripheral surface of lower surface 18 adjacent its 
upper end. Flange 28 is preferably welded to the outer peripheral surface 
of middle section 20 adjacent its lower end. Flanges 26 and 28 each have a 
horizontal portion 30 which preferably have a plurality of aligned, spaced 
apart apertures for receiving bolts 32 to secure flanges 26 and 28 
together. 
Connecting arrangement 24 also serves to locate and support an abutment 
ring 34. Ring 34 helps to maintain the alignment of and preserve the shape 
of an adjacent liner section as will be further described below. Ring 34 
is preferably formed of a flat annular piece of metal. Ring 34 is 
supported at its vertical location by positioning an outer portion of the 
ring between horizontal portions 30 of flanges 26 and 28, so that bolts 32 
secure sections 18 and 20 together and secure ring 34 at its vertical 
location. 
Middle section 20 is connected to upper section 22 by a connecting 
arrangement 36, as best shown in FIG. 6. Connecting arrangement 36 is 
similar to connecting arrangement 24. More specifically, arrangement 36 
has annular L-shaped connecting flanges 38 and 40 which are identical to 
flanges 26 and 28 described above. Flange 38 is welded to the peripheral 
surface of middle section 20 adjacent its upper end and flange 40 is 
welded to upper section 22 adjacent its lower end. Flanges 38 and 40 each 
have a horizontal portion 42 which each have a plurality of aligned, 
spaced apart apertures for receiving bolts 32 to secure flanges 38 and 40 
together. Connecting arrangement 36 is used to secure an annular support 
shelf 44 at a vertical location within shell 12. Shelf 44 is used to 
support a middle lining section, as will be more fully described below. 
Shelf 44 is preferably formed of a flat annular piece of metal. As with 
abutment ring 34, shelf 44 is secured at its vertical location by 
positioning an outer portion of shelf 44 between horizontal portions 42 of 
flanges 38 and 40. Further, shelf 44 is held in place by aligning 
apertures formed in the shelf with the apertures in flanges 38 and 40, and 
securing bolts 32 in the aligned apertures. 
Cover 16 is secured to upper section 22 by a connecting arrangement 46, as 
best shown in FIGS. 3 and 5. Connecting arrangement 46 includes an annular 
L-shaped connecting flange 48, which is identical to flanges 26, 28, 38, 
and 40. Flange 48 is welded to the peripheral surface of upper section 22 
adjacent its upper end. Cover 16 has an annular connecting portion 50 that 
is connected to the horizontal portion of flange 48 by aligning a 
plurality of spaced apart apertures formed in both structures and 
disposing bolts 32 through the aligned apertures. As with connecting 
arrangement 36, connecting arrangement 46 serves to secure an annular 
support shelf 52 at its vertical location. Shelf 52 is used to support an 
upper liner section, as will be more fully described below. As with shelf 
44, shelf 52 is preferably made of a flat annular piece of metal. An outer 
portion of shelf 52 is positioned between the horizontal portion of flange 
48 and connecting portion 50. Shelf 52 has a plurality of apertures which 
align with the apertures in both flange 48 and connecting portion 50, so 
that bolts 32 can be used to secure support shelf 52 at its vertical 
position. 
Preferably, circular base 14, lower section 18, middle section 20, upper 
section 22, connecting flanges 26, 28 38, 40, and 48, cover 16, abutment 
ring 34, and support shelves 44 and 52 are all made of carbon steel. 
A lower hollow cylindrical liner 54, a middle hollow cylindrical liner 56, 
and an upper hollow cylindrical liner 58 are concentrically received 
inside of cylindrical shell 12 and form a combustion area 60 in their 
interiors, as best shown in FIG. 2. A burner 62 is attached to the upper 
surface of cover 16, and is connected to an air blower and a burner fuel 
inlet duct (not shown). Burner 62 extends through a hole 64 in cover 16 so 
that a burner outlet 66 is at least partially disposed in combustion area 
60 as shown in FIG. 3. 
Lower liner 54 is generally cup-shaped and completely sealed along its 
lower end. Lower liner 54 has a circular floor 68 which rests upon 
supports 70 of circular base 14 as shown in FIGS. 2 and 8. The cylindrical 
sidewall of liner 54 extends upwardly from floor 68 to a position adjacent 
abutment ring 34 as best shown in FIG. 7. More specifically, the outer 
peripheral surface of liner 54 adjacent an upper end 72 thereof is spaced 
inwardly from an inner edge 74 of abutment ring 34 so that an annular 
space 76 is formed between lower liner 54 and inner edge 74. Abutment ring 
34 maintains alignment of and reduces outward bowing of liner section 54 
when the liner is subjected to elevated temperatures associated with 
combustion area 60. 
Lower liner 54 has an outlet port 78 formed on a portion of its sidewall, 
as shown in FIGS. 2 and 11. Outlet port 78 allows fluid communication 
between a dryer inlet duct 80 and combustion area 60, so that gases within 
the combustion area can be conveyed from area 60 through duct 80 and into 
the dryer, as more fully described below. Duct 80 extends through an 
opening in the sidewall of lower wall section 18 to achieve its connection 
with outlet port 78. 
Liner section 54 can further have a removable bottom protector plate 82 
shown in FIGS. 2 and 8. Plate 82 sits on braces 83 extending upwardly from 
floor 68. The lower portion of combustion area 60 is subject to intense 
radiation from the burner flame, and thus, is the area most likely to 
suffer thermal damage. Plate 82 generally covers floor 68 and is removable 
to allow easy replacement of the portion of the liner section most likely 
to suffer thermal damage. 
Disposed within lower liner 54 and located above outlet port 78 is an 
insert 84. Insert 84 has an outer cylindrical wall 86 to which an annular 
top plate 88, an annular divider plate 90 and an annular bottom plate 92 
are attached. Preferably, plates 88, 90 and 92 are attached to cylindrical 
wall 86 by welding. Further, insert 84 can be held within lower liner 54 
with suitable attaching means, such as by welding. Connected between top 
plate 88 and divider plate 90 is an inner wall 94. Inner wall 94 is 
preferably in the shape of a truncated cone, but could be shaped 
differently, such as a cylindrical wall. Outer wall 86, top plate 88, 
divider plate 90 and inner wall 94 define a vent gas zone 96. Vent gas 
zone 96 is in fluid communication with combustion area 60, and more 
specifically, the area of combustion area 60 defined by inner wall 94 
through adjustable ports 98. Ports 98 extend through openings 100 in inner 
wall 94. Ports 98 are shown in FIGS. 2 and 9 as being rectangular in 
shape, but other shapes could be used. Extending through lower wall 
section 18, lower liner 54 and outer cylindrical wall 86 is a vent gas 
duct 102. Vent gas duct 102 terminates at a vent gas outlet port 104 in 
outer cylindrical wall 86. 
Connected between divider plate 90 and bottom plate 92 is an inner wall 
106, which is preferably in the shape of a truncated cone oriented 
opposite to that of the truncated cone formed by inner wall 94. 
Alternatively, other shapes may be formed by inner wall 106, such as a 
straight cylindrical wall. Outer wall 86, inner wall 106, divider plate 90 
and bottom plate 92 define a recycled gas introduction zone 108. Recycled 
gas introduction zone 108 is in fluid communication with combustion area 
60 through adjustable ports 110, and more specifically with the portion of 
combustion area 60 defined by inner wall 106. Adjustable ports 110 extend 
through openings 112 in a similar fashion to adjustable ports 98. 
Extending through lower wall section 18, lower liner 54, and outer 
cylindrical wall 86 is a recycle gas duct 114 which terminates at recycle 
gas inlet port 116 in outer wall 86. Insert 84 allows a portion of the 
gases in combustion area 60 to be removed from combustion chamber 10 and 
also allows recycled gases to be introduced into combustion chamber 10, as 
is more fully described below. 
Middle liner section 56 is supported or hung from support shelf 44, as best 
shown in FIG. 6. More specifically, the upper end of liner section 56 has 
an outwardly extending annular ridge 118 disposed adjacent its upper end. 
The lower surface of ridge 118 rests upon the upper surface of shelf 44 to 
support liner section 56 in a hanging fashion. Further, the outer 
peripheral surface of liner section 56 adjacent ridge 118 is spaced from 
an inner edge 120 of support shelf 44 so that an annular gap 122 is formed 
between shelf 44 and the outer peripheral surface of the liner. Because of 
the provision of this gap and because the ridge 118 is simply resting on 
shelf 44, and not rigidly secured thereto, middle liner 56 can freely 
expand outwardly when subjected to the expanded temperatures within the 
combustion area. More specifically, middle liner 56 will tend to expand 
laterally when the combustion chamber reaches elevated temperatures for 
extended periods of time. As this happens, annular ridge 118 simply slides 
outwardly along shelf 44. The liner can expand outwardly until the outer 
peripheral surface of middle liner 56 engages inner edge 120 of shelf 44. 
Thus, inner edge 120 maintains the alignment of middle liner 56 and 
reduces outward bowing of the liner section so that the generally circular 
shape thereof is maintained. 
A lower end 124 of middle liner 56 is concentrically positioned within 
upper end 72 of lower liner 54, as shown in FIG. 7. Lower liner 54 and 
middle liner 56 are not, however, attached or secured to one another in 
any way. Thus, when elevated temperatures exist in combustion area 60, 
middle liner 56 is free to expand downwardly. Further, lower liner 54 is 
free to expand upwardly. Additionally, because of annular space 76 between 
lower liner 54 and inner edge 74 of abutment ring 34, lower liner 54 can 
expand outwardly until it engages edge 74, although this outward expansion 
is somewhat limited by insert 84. Further, the outer peripheral surface of 
middle section 56 and the inner surface of lower liner 54 are slightly 
spaced from one another so that when elevated temperatures exist in the 
combustion area the surfaces will engage to form a seal that reduces heat 
leakage from the combustion area. 
Upper liner 58 is solely supported by or hung from support shelf 52, as 
best seen in FIGS. 3 and 5. More specifically, upper liner 58 has an 
annular ridge 126 extending outwardly from its upper end. The lower 
surface of ridge 126 rests on the upper surface of shelf 52 to support the 
liner in a hanging fashion. An annular space 128 is also provided between 
the outer peripheral surface of upper liner 58 adjacent ridge 126 and an 
inner edge 130 of shelf 52. Because of the provision of annular space 128 
and because ridge 126 is not fixedly secured to shelf 52, but resting 
thereupon, upper liner 58 is able to expand outwardly when subjected to 
elevated temperatures within the combustion area. More specifically, as 
the temperature increases, ridge 126 can slide outwardly along shelf 52 
until the outer peripheral surface of upper liner 58 engages edge 130. 
Thus, edge 130 serves to maintain the alignment of liner 58 and reduces 
outward bowing of the liner so that the generally circular shape thereof 
is maintained. 
The lower end 132 of upper liner 58 is concentrically positioned within the 
upper end of middle liner 56, as shown in FIG. 6. Middle liner 56 and 
upper liner 58 are not attached or secured to one another in any way. 
Thus, upper liner 58 is free to expand downwardly when subjected to 
elevated temperatures. Additionally, the outer peripheral surface of upper 
liner 58 and the inner surface of middle liner 56 are slightly spaced from 
one another so that when elevated temperatures exist in the combustion 
area, the surfaces will engage to form a seal that reduces heat leakage 
from the combustion area. 
Upper liner 58 further has a circular lid portion 134 extending inwardly 
from its upper edge to cover the upper end of the liner as best shown in 
FIGS. 3 and 5. Lid 134 has a hole 136 for receiving the lower end of 
burner 62 so that the burner outlet 66 can be disposed in combustion area 
60. 
Upper liner 58 has an annular insert 138 disposed in its interior to form 
an annular recycle gas introduction zone 140 as best shown in FIGS. 2, 3, 
and 4. More specifically, insert 138 has an inner cylindrical wall 142 
spaced from and concentrically received in upper liner 58. Wall 142 is 
attached on its upper end to lid portion 134 and extends downwardly 
therefrom. Insert 138 also has an annular lower plate 144 which is 
attached at its outer edge to upper liner 58 and at its inner edge to wall 
142. Thus, zone 140 is bounded by upper liner 58, cylindrical wall 142, 
annular plate 144, and lid portion 134. Zone 140 completely encircles the 
burner flame (shown in phantom lines in FIG. 2) extending downwardly into 
combustion area 60 from burner 62. Zone 140 is in fluid communication with 
a recycled gas duct 146 via an inlet port 148. Duct 146 extends through an 
opening in upper wall section 22 of outer shell 12 to connect with port 
148 as best shown in FIG. 4. Duct 146 is used to supply recycled gases to 
the combustion chamber after the gases have been separated from dried 
material, as will be more fully explained below. Wall 142 of insert 138 
has a plurality of spaced apart, generally rectangular openings 150 which 
allow fluid communication between zone 140 and combustion area 60, as 
shown in FIGS. 2, 3, and 4. Openings 150 are defined by ports 151 
extending into zone 140 from wall 142. Each port 151 has a directional 
plate 152 that extends into zone 140 from wall 142 and is generally 
tangential to wall 142, as best seen in FIG. 4. Each port also has a 
generally triangular upper plate 154 extending from the upper edge of 
directional plate 152 to wall 142 and a generally triangular lower plate 
156 extending from the lower edge of plate 152 to wall 142. Thus, each 
opening 150 is defined by plates 152, 154, and 156 so that the opening is 
generally tangential to wall 142. Openings 150 formed by ports 151 allow 
recycled gases in zone 140 to be introduced into combustion area 60 in 
such a manner that the gases are directed generally tangentially to wall 
142 and form a rotating film along wall 142 that extends and flows 
downwardly as depicted by the arrows in FIG. 4. This rotational film 
surrounds the burner flame. 
Lower plate 144 of insert 138 also has a plurality of spaced apart 
generally rectangular openings 158. Openings 158 on plate 144 are formed 
by ports 160 extending upwardly from plate 144 into zone 140. Each port 
160 includes a generally rectangular plate 162 extending upwardly from 
lower plate 144 and a pair of triangular side plates 164. In addition to 
recycled gases entering combustion area 60 through openings 150, recycled 
gases also enter combustion area 60 through openings 158. More 
specifically, because openings 158 are spaced around annular plate 144, 
gases will exit through the openings and into combustion area 60 to form a 
rotational film along the inner surfaces of liner sections 54, 56, and 58. 
Ports 160 direct the gases downwardly. The rotational film of recycled 
gases exiting openings 150 joins with the film formed by the recycled 
gases exiting openings 158 so that a continuous rotational film of 
recycled gases generally from the top of the combustion chamber 
downwardly. 
Liner sections 54, 56, and 58; ridges 118 and 126; insert 138; and ports 
148 and 160 are all preferably made of stainless steel. However, these 
structures could also be made of other suitable heat resistant materials. 
Although sections 54, 56, and 58 are described above and depicted in the 
figures as having a cylindrical shape, they can also be made in any other 
suitable shape, for example a conical or elliptical shape. Further, 
although annular inserts 138 and 84 are depicted in the figures as having 
a cylindrical shape, it also can be made in any other suitable shape, for 
example, a conical or elliptical shape. It being understood that the shape 
of inserts 138 and 84 correspond to the shape of sections 54, 56, and 58. 
Each shell section 18, 20 and 22 has an annular insulation layer 166 
extending inwardly from its inner surface as best shown in FIGS. 3, 5, 6, 
7, and 8. Each layer 166 is spaced from the outer surface of its 
respective liner 54, 56 or 58 by an annular gap 168. Gaps 168 allow liner 
sections 54, 56, and 58 room to expand outwardly when subjected to the 
heat of the burner flame. Cover 16 also has an insulation layer 170 
disposed between the inner surface of the cover and the upper surface of 
lid portion 134, as best seen in FIGS. 3 and 5. Layer 170 generally 
surrounds burner 62. A lower insulation layer 172 is disposed below floor 
68 and above base 14, as shown in FIG. 8. Insulation layers 166, 170, and 
172 are preferably made of a ceramic wool type insulation. 
In operation, burner 62 is supplied with fuel and combustion gases and 
burner 62 is lit to produce a flame within combustion area 60 as shown in 
FIG. 2. Gases from combustion area 60 are conveyed via dryer inlet duct 80 
to a rotary dryer 174 as shown in FIG. 1. Within dryer 174 the stream of 
heated gases coming from the combustion chamber is exposed to the material 
to be dried. Thereafter, the dried material and the combustion gases are 
separated from one another by, for instance, a cyclone separator (not 
shown). At least a portion of the separated combustion gases are then 
conveyed back to the combustion chamber. More specifically, the separated 
gases are carried through a duct until they encounter a damper 176. Damper 
176 divides the stream of heated gases into a first stream 178 and a 
second stream 180, as best seen in FIGS. 1 and 12. First stream 178 is 
conveyed to combustion chamber 10 through recycle gas duct 146 and inlet 
port 148. These gases will swirl within insert 138 and will eventually 
exit zone 140 and enter combustion area 60 through openings 150 and 158. 
The recycled gases exiting these openings form a circulating film around 
the burner flame which coats or wipes the inner surface of wall 142 as 
well as the inner surface of upper liner 58 and middle liner 56. Both 
swirling films of gases will mix with the combustion gases when insert 84 
is encountered. More specifically, the recycled gases will encounter top 
plate 88 which forces the gases toward the center of combustion chamber 60 
wherein the heated recycled gases are mixed with the newly combusted 
gases. A portion of the heated recycled gases are removed from combustion 
chamber 60 through adjustable ports 98. This portion of the heated 
recycled gas stream is thus conveyed to vent gas zone 96 and outward 
through vent gas duct 102 as best seen in FIGS. 9 and 13. The vent gases 
are then passed through a pair of heat exchangers 182 and 184. The vent 
gases passing through heat exchangers 182 and 184 are conveyed through a 
vent duct 186 and are then vented to the atmosphere through stack 188. 
Second stream 180 of the recycled gases is conveyed through a second 
chamber of heat exchangers 182 and 184, as best seen in FIG. 12. After 
passing through the heat exchangers, the recycled gas is conveyed into 
recycled gas introduction zone 108 through recycled gas duct 114 as best 
seen in FIGS. 1 and 10. Exchangers 182 and 184 are thus used to exchange 
heat between the recycled gas stream and the heated recycled gas material 
exiting combustion chamber 60 at outlet port 104. The vent gases exiting 
through stack 188 may also be passed through a second heat exchanger prior 
to their removal. Passing through the second chamber of this heat 
exchanger (not shown) would be first stream 178. 
The swirling film of recycled gases introduced by insert 138 along with the 
hanging structure of liners 56 and 58 allows the use of a less expensive 
and more easily manufactured material, such as stainless steel, as the 
construction material for the combustion chamber. More specifically, the 
swirling film of recycled gases adjacent the inner surface of the liner 
sections absorbs a great deal of the radiant energy being emitted by the 
burner flame. The recycled gases typically have a high water vapor content 
and a high carbon dioxide content and, thus, are very opaque. Therefore, a 
substantial amount of radiation emitted by the burner flame will be 
absorbed by the swirling film and will not pass through to the inner 
surface of the liners. Further, the wiping of the inner surface of the 
liners with the recycled gases enhances heat transfer between the liner 
sections and the gas film. Hence, at least a portion of the thermal energy 
found in the liners may be dissipated to the recycled gas stream. Further, 
the film of recycled gases, through absorption of thermal energy, reduces 
the pollutants found in the recycled gases through oxidation. Therefore, 
the provision of the swirling film of recycled gases serves a dual 
function in that it absorbs thermal energy that would normally pass 
through the liners, and further by absorbing this energy, pollutants found 
within the recycled gases are oxidized. 
The unique structure of combustion chamber 10, and specifically insert 84, 
allows a portion of the heated recycled gases to be removed from 
combustion area 60. Heat exchangers 182 and 184 capture some of the heat 
in these gases prior to being vented to the atmosphere. Heat exchangers 
182 and 184 also allow second stream 180 to be heated prior to being 
introduced into combustion area 60 through insert 84. 
Adjustable ports 98 and 110 allow adjustment or manipulation of which 
portion of the recycled heated gas is removed from combustion area 60 and 
allow introduction of second stream 180 into a desired location within 
combustion area 60. More specifically, ports 98 and 110 can be adjusted so 
that the terminal edge of each port is further within combustion area 60. 
Sliding ports 98 and 110 inwardly will remove a different mixture and 
temperature of gases from combustion area 60. Conversely, ports 98 and 110 
can be adjusted so that the terminal edge of each port is further removed 
from combustion area 60. Thus, the temperature of the gases exiting and 
entering the heat exchanger can be controlled to a degree. 
From the foregoing, it will be seen that this invention is one well adapted 
to obtain all of the ends and objects hereinabove set forth, together with 
other advantages which are inherent to the structure. It will be 
understood that certain features and subcombinations are of utility and 
may be employed without reference to other features and subcombinations. 
This is contemplated by and is within the scope of the claims. 
Since many possible embodiments may be made of the invention without 
departing from the scope thereof, it is to be understood that all matter 
herein set forth or shown in the accompanying drawings is to be 
interpreted as illustrative and not in a limiting sense.