Note: Descriptions are shown in the official language in which they were submitted.
10~3~4
This invention relates to methods and apparatus
for combusting carbonaceous fuels, and more particularly
to methods and apparatus or combusting carbonaceous fuels
to produce a hot gaseous effluent for use as a source of
heat (e.g., in a furnace) or power (e.g., as a motive fluid
in a turbine system).
In Canadian Patent No. 1,003,651, issued January 18,
1977, in the name of William ~. Pfefferle and assigned to
the same assignee as that of the present invention, there
is disclosed a process designated catalytically-supported,
thermal combustion. According to this method, carbonaceous
fuels can be combusted very efficiently and at thermal
reaction rates in the presence of a solid oxida-tion catalyst
at temperatures below nitrogen-oxide-forming temperatures.
As described in Canadian Patent No. 1,003,651, this com-
bustion method involves essentially adiabatic combustion
of a mixture of fuel and air, or of fuel, air, and inert
!
gases, in the presence of a catalyst operating at a tem-
perature substantially above the instantaneous auto-
ignition temperature of the mixture, but below a temperaturethat would result in any substantial formation of oxides
of nitrogen. Essentially adiabatic combustion means that
the operating temperature of the catalyst does not differ
by more than about 300F, more typically no more than about
150F, from the adiabatic flame temperature of the mixture
due to heat losses from the catalyst. The instantaneous
auto-ignition temperature of the mixture is defined herein
and in Canadian Patent No. 1,003,651 to mean the temperature
at which the ignition lag of the mixture entering the
catalyst is negligible relative to the residence time in
the combustion zone of the mixture undergoing combustion.
Typically, the operating temperature of the catalyst is in
;' -1- ~
cbr/~`,
~0~ 3~
the range from about 1,700 to about 3,200 F, preferably
from about 2,000 to about 3,000F. As pointed out in
Canadian Patent No. 1,003,651, the combustion occurs under
these conditions at a rate substantially higher than the
conventional catalytic combustion rate. combustion of the
gases exiting from the catalyst zone may be substantially
complete, or combustion may continue downstream of the zone
containing the catalyst.
According to one aspect of the present invention,
there is provided a method of combusting carbonaceous fuel
including the steps of providing a first mixture of carbon-
aceous fuel and air and passing the first mixture to a
catalyst for combustion of at least a portion of the first
; mixture under essentially adiabatic conditions in the presence
of the catalyst, operating a temperature substantially above
the instantaneous auto-ignition temperature of the first
mixture but below a temperature which would result in an~
substantial formation of nitrogen oxides, to produce a
first gaseous effluent. The method further includes a
step for providing a carbonaceous fuel-containing component
differing from the first mixture, the fuel in the fuel-
containing component having an adiabatic flam temperature
o~ at least about 3,300 F when burned witll a stoichiometric
amount of air. The first effluent and the fuel-containing
component are mixed to form a second mixture having a
temperature upon mixing at least sufficient to sustain
homogeneous combustion of the second mixture and having an
adiabatic flame temperature substan~ially above the temperature
of the first effluent but below the 3,700F, thereby
homogeneously combusting the mixture to produce a second
gaseous effluent.
According to another aspect of the present
~2--
~y cbr~JO
~ 333~
invention there is provided an apparatus for combusting
carbonaceous fuel to provide a hot gaseous effluent including
means for forming a first mixture of a first carbonaceou~
fuel and air and a combustion chamber arranged to receive ~ '
the first mixture, and including extending thereacross, a
catalyst body having gas flow passageways therethrough for
combustion of the first mixture in the presence of the
catalyst under essentially adiabatic conditions to produce
a first gaseous effluent. Means is provided for supplying
a second fuel-containing component inc:luding a second
carbonaceous fuel different from the first carbonaceous
; fuel. Means is provided for mixing and thereby homogeneously
combusting a second mixture formed of the first gaseous
effluent and the second fuel containing component to produce
a second gaseous effluent.
More specifically, the first mixture of carbonaceous
fuel and air is provided and passed to a catalyst for at
least partial combustion in the presence of the catalyst
under essentially adiabatic conditions, as described above,
to produce a first gaseous effluent. Any of the fuels
mentioned in Canadian Patent No. 1,003,651 may be used to
form the first mixture and any of the fuel-air proportions
mentioned in that application may comprise the first mixture.
Similarly, although atmospheric air will usually be the source
of oxygen for combustion of the fuel in the first mixture
(as well as for combustion of the additional fuel combusted
in accordance with the principles of this invention), it
will be undexstood that the term "air" is used herein to
mean any gas or combination of gases including oxygen available
: 30 for combustion. It will sometimes be necessary herein to
refer specifically to inert or recycled gases which in
various applications of the present invention can be mixed
, ~ -3-
` cbr/ ~
,; :. . ,.. , . ,, " ,
~0~33~
with the fuel and air being combusted; this does not mean ;
that the gases referred to as air herein cannot also include
inert gases.
The first effluent produced as described above is
mixed with the second carbonaceous fuel-containing component
provided for that purpose, which may be with or without
non-fuel components (i.e., air), to form a second mixture.
Thls fuel-containing component is different from the first
mixture and advantageously may utilize a fuel different
from the fuel used in the first mixture. ~he fuel in the
second fuel-containing component is a high energy fuel ha~ing
an
-3a-
i ~ cbr~
~ 0~3334
. adiab~tic flame temperature of at.least about 3,300F if
;~ burned with a stoichiometric amount of air. The term
"stoichiometric amount of air" as used herein means the
amount of air of atmospheric Gomposition which is theoretical-
ly just sufficient for complete combustion of a~l the carbon ~
; ` in a given amount of fuel to carbon dioxide and for complete I
combustion of any hydrocarbons in the Euel to carbon dioxide
~ and water. The foregoing statement that the fuel in the
. second fuel-containing component has an adiabatic Elame te~- ¦
I perature of at least about 3,300F if burned with a stoichio-¦
i. metric amount of air does not mean that the fuel in the
,., , ' ~
second fuel-containing component is in act neces5arily
` burned with a stoichiometric amount of air in the method and ¦
,l apparatus of this invention.
The second mixture referred to above includes oxygen
. available for at least partial combustion of the fuel in
" t
the second fuel-containing component. This oxygen may be
uncombined oxygen in the first effluent, or it may be air
: in the second fuel-containing component, or both. In
addition, the second mixture has a temperature upon mixing
at leas-t sufficient to sus~ain homogeneous combustion oE
the second mixture and has an adiabatic flame temperature
- substantially above the tempera-ture of the first effluent buti
~! below abou-t 3,700F. Typically, the adiabatic flame tem- .
,
, perature of the second mixture is in the range from about .
1 1,700 to about 3,700F, preferably from about 2,500 to
about 3,300F. As used herein, the term "homogeneous
. combustion" means thermal combustion,which should be carried
.
,
, '' ~, .
,)
. : . \ 'l
~0~33~4
out with sufficiently uniform admixture of the components of I
the second mixture to avoid localized regions of substantially
higher temperatures than the average temperature of the
combustion zone. - t
The second mixture is homogeneousLy combusted to pro- t
duce a second gaseous effluent which can be used as a source
of heat or po~7er. This combustion preferably occurs at a
temperature low enough, and for a residence time of the '
mixture in the combustion zone short enough, to avoid
substantial formation of nitrogen oxides. The combustion
of the second mixture may be substantially adiabatic (for
example, if the second effluent is to be used as a motive
fluid for a turbine), or heat may be withdrawn from the
combustion zone (for example, if the system is a furnace).
' Additional combustion stages similar to the combustion of
the second mixture may be pro~iaed by mixing all or ~art of
the second effluent with additional air if combustion of the
second effluent is not complete, or with additional fuel-
containing components ~ith or without additional non-fuel
components (e.g., air). Inert gases, such as the exhaust
yases of the system, may be mixed with any of the fuel or
air or both supplied to the system to improve the thermal
efficiency of the system and control temperatures in the
system. Any of the gases supplied to the system may be
25 ! preheated, e.g., by hea-t exchange with the exhaust gases
of the system, by compression in a compressor (in a ~urbine
system), or by any other means! -
- !
, .
~ 3 ~3
Further features of the invention, its nature and
various advantages will be more apparent from the accompanying
- drawings and the following detailed description of the
invention.
Brief Description of the Drawings
Figure 1 is a partly schematic, partly simplified
sectional view of combustor apparatus constructed and
adapted for operation in accordance with the principles of
this invention;
Figure 2 is a partly schematic, partly simplified
sectional view showing a turbine system including combustor
apparatus constructed and adapted for operation in accord-
ance with the principles of this invention;
Figure 3 is a partly schematic, partly sectional
.. . .
view of a furnace constructed and adapted for operat.ion in
accordance with the principles of this invention; and
Figure 4 illustrates an alternative embodiment of
the furnace of Figure 3.
Detailed Description of the Invention
In the apparatus shown in Figure 1, fuel is supplied
via line 10 having valve 12 and air is supplied via line 14
having valve 16. Fuel from line 10 and air from line 14
are mixed to form a first mixture of fuel and air in line 18.
The amounts and proportions of fuel and air in the first ,
mixture are respectively controlled by valves 12 and 16 in
;, accordance with the principles disclosed in Canadian Patent
No. 1,003,651. Thus any of the ~uels discussed in that
application may be supplied via line 10 and mixed with a.ir
from line 14 in any amounts and proportions for effecting ~:~
combustion at the desired operating temperature of
.
cbr/~u
~ ., .
~Oq3334
the catalyst under the conditions existing in tne combustion
zone containing the catalyst. If desired, the air and/or
fuel can be preheated (e.g., by compression in the system 5
compressor if the system is a turbine system, by heat
e~change with the exhaust gases of the system, etc.).
~Similarly, if desired, inert or substant~ally inert gases,
' such as the exhaust gases of the system, can he mixed with
the fuel or air or both supplied via lines 10 and 12 (or
- mixed with the first rlixture in line 18 or introduced
separately into initial mixing zone 22) for thermal efficiency
;and to control temperatures in combustor 20~ For convenience
herein, any such inert gases supplied to combustor 20 will be
referred to as "recycle gases", since in many cases these
;gases will be a recycled ~ortion of the exhaus-t gases of the
,system. However, if a stream of inert or substantially inert
gases is available from another source (e.g., a waste stream
from another process), it will be understood that the term
"recycle gases" also includes such gases. 'I
The first mixture in line 18 is passed to combustor 20
having cyclindrical housing 21, a longitudinal sectional view !
.
of which is shown in Figure 1. Although a cyclindrical
;combustor is shown in Figure 1, i-t will be understood that
a wide variety oE shapes can be employed, dependin~, for
example, on the nature and configuration oE the system in
which the combustor is used. The first mixture is introduced
.: ;
~;~ into the initial portion of combustor 20, referred to herein
as initial mixing zone 22. Although in the particular
embodiment shown in Figure 1, the first mixture of fuel and
air is formed in line 18 prior to initial mixing zone 22, it
wi'l be understood that the fuel and air alternatively can
be introduced into initial mixing zone 22 se~arately and
' - .
~ -7-
0~33~
mixed in the zone to form the first mixture. Initial
mixing zone 22 includes an ingitor 24 which operates as
discussed in Canadian Patent No. 1,003,651 to ignite the
first mixture in zone 22 to heat catalyst 25 in catalyst-
containing combustion zone 26 during start-up of the
system. While ignitor 24 is ooerating, it may be necessary
to supply fuel and air to the sys~em in different amounts
and proportions to insure a flammable mixture in zone 22
as discussed in the above-mentioned application. However,
when catalyst 25 is at normal operating temperatures, ignitor
24 normally does not operate and there is preferably no
combustion in initial mixing zone 22 prior to catalytic
zone 26 at temperatures which would result in any substantial
formation o nitrogen oxides. ~ ;
The combustion zone 26 is disposed in combustor
20 downstream of the initial mixing zone 22 so that the gases
in zone 22 pass through zone 26 to catalyst exit zone 28.
Zone 26 includes a catalyst 25, which in the particular
' embodiment shown in Figure 1 is a body disposed transverse
to the longitudinal axis of combustor 20 and held in position
by lugs or annular rings 27 on the inner surface of combustor
"i, housing 21. Catalyst 25 preferably occupies most or all of
the flow cross-section of the combustion zone and includes
a plurality of channels from initial mixing zone 22 to catalyst
exit zone 28. At least a portion of the gases passing
through the zone 26 containing the catalyst 25 thus are com-
busted in the presence of the catalyst, under the conditions
described in Canadian Patent No. 1,003,651 and summarized
above, to produce a first gaseous effluent. Any of the
catalyst compositions and structures discussed in Canadian
Patent No. 1,003,651 may be used or solid oxidation catalyst
~5. For example, catalyst 25 may be a honeycomb catalyst
,:
cbr/Jt)
~0~3~33~
having a plurality of channels parallel to the longitudinal
axis of combustor 20. The adiabatic flame temperature of !,
the fuel-air mixture entering the catalyst is in the range
from about 1,700 to about 3,200F, preferably from about
2,000 to about 3,000F, so that for the adiabatic system
illustrated in Figure 1, the operating temperature of the ~`~
catalyst closely approaches this adiabatic flame temperature,
and, when most of the fuel is burned while in the catalyst
zone 26, the irst effluent may e~it from the catalyst ~one
.
at a temperature somewhat less than the adiabatic flame
temperature of the entering mixture. The gases exiting from
catalyst zone 26 may be completely combusted, or combustion ;
may continue downstream of zone 26 into catalyst exit zone 28.
The first effluent passes from catalyst exit zone
28 to second mixing and combustion zone 30 where it is mixed
and thermally combusted with a second fuel-containing com- r
ponent as will now be described. The second fuel-containing
component is supplied to combustor 20 via line 40 and sprayed
: .
into second mixing and combustion zone 30 by nozzle 42 for
mixing with the first effluent from catalyst exit zone 28
to produce a second mixture in zone 30. The second fuel-
containing component differs in the nature, or proportion,
or both, of the fuel, as compared with the first mixture
entering the catalyst 25, and includes fuel supplied to line
40 via line 32 having valve 34 and may also include non-
fuel components (e.g.,air) supplied to line 40 via line 36
having valve 38. As discussed in Canadian Patent No. 1,003,651
the proportions of fuel and air in the first mixture (at
least partially combusted in catalyst zone 26 as cliscussed
above) may be approximately stoichiometric if desired catalyst
operating temperature is not exceeded, or the proportions
may
_g_
cbr/.lc
.. . .
0~33.
be non-stoichiometric on the fuel-rich or fuel-lean side.
If the mixture is approximately stoichiometric, substantially !
all the fuel in the first mixture is typically combusted in
catalyst zone 26 and in catalyst exit zone 28. If the first
mixture is fuel-rich, there will be uncosmbusted fuel values
in the first effluent. If the first mixture is fuel-lean,
there will be oxygen in the first effluent available fo~
combustion of additional fuel. If there is sufficient
o~ygen available in the first effluent for combustion of the !
,fuel in the second fuel-containing component, additional air ~
may not be required or desired in the second fuel-containing li
component. On the other hand, if there is insufficient oxy- i
gen in the Eirst effluent for combustion of the fuel in the s
second ~uel-containing component or if there is uncombusted
fuel in the first effluent, the second fuel-containing com-
ponent contains air for combustion of the uel in the second
, fuel-containing component and any uncombusted fuel in the
Eirst effluent. In any event, it is preferred in accordance
with the present invention that the fuel-air mixture in the
?0 second fuel-containing component, especially when the same
:;
fuel is used, be substantially richer in fuel values than
the first fuel-air mixture.
` The fuel supplled via line 32 may be the same as the
fuel supplied via line 10 but in a different mixture with
air, or it may`be a dif~erent fuel. In any event, the fuel
in the second fuel-containing component is a high energy
fuel having an adiabatic flame temperature of at least about
3,300F if burned with a stoichiometric amount of air. One
of the advantages of this invention is that fuel which may be
inconvenient or unsuitable for combustion in -the presence
-10-
~, ' 107333~ . . i'
'
of the catalyst in zone 26 can be supplie~ via line 32 and
. combusted downstream of the catalyst. Thus, for example".
'i fuels substantially contaminated with sulfur which might
.
: poison the catalyst in zone 26 can be supplied via line 32
and combusted without dan~er to the catalystO Other examples
'are fuels yielding combustion products with substantial ash
content, and fueis having high boiling points and difficult
" to vaporize and admix intimately with air prior to contacting¦
:~ ',Ithe catalyst 25 upon reaching the inlet to zone 26. .,
~. As in the case of the components supplied via lines 10
and 14, either or both of the components supplied via lines
~32 and 36 can be preheated lf desired by any of the means
mentioned above. Similarly, recycle gases can be mixed
', ~wi,th either or both of the components supplied via lines 32
'~ 15 ~;and 36 for thermal eEficiency and to control temperatures
in combustor 20, particularly in mixing and combustion
zone 30.
, !;
~, , As mentioned above, thè'second fuel-containing component
'is mixed with the first efluent to form a second mixture in
zone 30. This second mixture has a temperature at least
j i
sufficient to sustain homogeneous combustion of the second
mixture and has an adiabatic flame temperature substantiall~
above the temperature o the first effluent but below about
3,700F. Typically, the temperature of the second mixture
'',upon mixing is at least about 1,700F, preferably at least
',about 2,000F, and the adiabatic flame temperature of the 3
`second mixture is in the range from about 1,700 to about
3,700F, preferably from about 2,500 to about 3,300F. ',
. ' 'i
., i
.. . . . .
~ 3~3~
,
; In second mixing and combustion zone 30 the second mixture
jis thermally combusted to produce a second gaseous effluent. ¦
Nozzle 42 may be positioned at a point where combustion
of the gases exiting from the zone 26 containing the catalyst;
is still continuing, so that combustion ~s con-t'inuous from ¦
zone 28 to zone 30, or nozzle 42 may be positioned at a
point where combustion of the firs-t effluent has stopped so
,' ,that there is a discontinuity in combustion from zone 28 to
'zone 30. The second gaseous effluent is used as a source
; 10 ,'of heat or power. For exa~ple, heat may be withdrawn from
, the gases in zone 30 by heat exchange, e.g., to generate
j ,stea~.
lternatively, the combustion taking place in combustor
1 ~20 may be substantially adiabatic throughout and the second
'"' 15 effluent,may be conducted from the combustor via line 50 for
", ,transfer of heat therefrom at another location or for use as
' a motive 1uid for a turbine. The exhausted second effluent
subsequently exits from the system. Additional heat' may be
recovered from the exhaust gases to preheat the fuel or air
~1 20 or both supplied to the system as mentioned above. A portion
of the exhaust cJaSes may be mixed with the fuel or air or
,both supplied to the system as the above-mentioned recycle
,gases. , , ,
Although only'one nozzle ~2 is shown in the simplified
-~ 25 schematic of Figure 1, it will be understood that any number
and arrangement of such nozzles can be provided to insure
effectively complete mixing of the second fuel-containing Ç.
component with the first effluent, as is desirable to insure
homogeneous combustion of the resulting second mixture with
.
.
-12-
~ 3339~ I
,reasonable uniformity of temperature, in zone 30. Similarly~ !
although additional fuel-containing component is introduced
. at only one location along the longitudinal axis of combus- j
-tor 20 in Figure 1, it will be understood that any number ~'
of successive mixing and combustion zone,s similar to æone 30 '
; can be provided along the length of the downstream portion
~of combustor 20 with additional fuel-containing component
' supplied to each of these zones..
, A turbine system constructe`d and operated in accordance ¦
: . :
'i 10 ',with the princlples of this invention is shown in Figure 2.
, ''Combustor 20 in this system is sir.lilar to combustor 20.in
. ~Figure 1, except that two successive mixing and co~bustion
,'zones 30a and 30b, each similar to the mixing and combustion ~.
'20ne 30 in Figure 1, are provided in the combustor shown in
:~ 15 . Figure 2. In the turbine system of Figure 2, air is brought
. .
' .into the system via line 6 and compressed in compressor 8-.
: ;
'"Power to drive compressor 8 is supplied from turbine 52 via
shaft 54. Compressed air exits from compressor 8 via line 14.'
Typically, the air in line 14 is at elevated temperature as
~ well as pressure. For example, depending on the compression
ratio of compressor 8, the air in line 14 may be at a tempera-
ture as high as about 1,100F.
At least a portion of the air in line 14 passes through ',
valve 16 and is mixed with a portion of the fuel supplied
to the system via line 10 to form a first mixture of fuel
':and air in line 18 similar to the first mixture in line 18 ' ~.
; in Figure 1. The amount of fuel from line 10 going to line 18,
.is controlled by valve 12 as in Figure 1. The Eirst mixture
. . . . , ~,
-13-
,
. . : . .:. .
:1 0~333~ ,
in line 18 is supplied to initial mixing zone 2~ of combus- ~
; tor 20. From initial mixing zone 22 the first mixture passesj
to the catalyst-containing zone 26 and is at least partially !
combusted therein, as in zone 26, in Figure 1, to produce a
first ~aseous efEluent which passes to catalyst exit zone 28.
In second mixing and combustion zone 30a, the first effluent
is mixed with a second fuel-containing component supplied via'
line 40a and nozzle 42a to form a second mixture having sim- .
ilar characteristics to those of the second mixture in Fig- ¦
- 10 ure 1 and which is homogeneously combusted in zone 30a, under
;~ ; conditions similar to tne combustion of the second mixture
in Figure 1, to produce a second gaseous effluent. Fuel is
supplied to line 40~ from line 10 in an amount determined t
by valve 34a. This fuel is similar to the fuel in the second
', fuel-containing component in Figure 1 in that it is a high
~energy fuel having an adiabatic~flame temperature of at least~
~' :about 3,300F if burned with a stoichiometric amount of air.
In the embodiment shown in Figure 2 the same fuel is suppliedi
throughout the system although it will be understood that
different fuels can be supplied to different combustion zones
if desired as cliscussed above in connection with Figure 1.
The second fuel-containing component in line 40a may also in-~
clude air supplied from line 14 via valve 38a and mixed with
the fuel in line 40a.
The second gaseous effluent is passed to third mixing
and combustion zone 30b, where it is mixed with a third
fuel-containing component supplied to the co~bustor via line
40b and nozzle 42b to produce a third mixture. Fuel is
supplied to line 40b from line 10 in an amount determined by
; 30 valve 34b. Again, although this is the same Euel supplied
to the other combustion zones of the system, in the particular
embodiment shown in Figure 2, a different fuel may be supplied
.
. . , , :
, ,,; ", : .
~ 333~
`, I
if desired. In any event, this fuel is a high energy uel
. having an adiabatic flame temperature of at least about 3,300F
if burned with a stoichiometric amount o air. The third
fuel-containing component in line 40b may also include air
supplied from line 14 via valve 33b and ,mixed with the fuel
in line 40b. The third mlxture formecl in zone 30b also has
; properties similar to those of the second mixture in Figure 1
- Thus the temperature of the third mixture is at least su~
. ficient to sustain homogeneous combustion of the third mixture
~: 10 ~,and has an adiabatic flame temperature at least above the
~I temperature of the first effluent but below about 3,7Q0F.
As in the case of the second mixture both in.Figure 1 and
i
Figure 2, the temperature of the third mixtur~ is typically
;l at least about 1,700F, preferably at least about 2,000F,
lS ; and the adiabatic flame temperature of.the third mixture is
; in the range from about 1,700 to.about 3,700F, preferably
from about 2,500 to about 3,300F~ The third mixture is
homogeneously combusted in zone 30b to produce a third
gaseous effluent which exits from combustor 20 via line 50.
. To avoid substantially or minimize sharply any formation
; of oxides of nitrogen in either of the thermal combustionzones 30a and 30b, especially when the adiabatic flame tem-
perature is in the approximate range of 3,300F to 3,700F,
. ,
,:the residence time of the mixture undergoing combustion ,
25 ,should be limited, ~ith or without air-quenching on leavin~
;.one or both of the thermal combustion zones, since nitrogen
oxide formation is a function of both time and temperature
for a given combustion mixture.
,
. -15-
~33~
The third gaseous effluent in line 50 is supplied as
; a motive fluid to drive turbine 52. A portion of the power
produced by turbine 52 is used to drive compressor 8 via
i shaft 54 as mentioned above. The remaining power is available
on shaft 54 for the purpose for which the system is being
operated (e.g., to drive an electrical power gene~ator).
The gases exiting from turbine 52 via line 56 are exhausted
~rom the system, generally into the atmosphere.
A furnace system constructed and adapted for operation
in accordance with the principles of this invention is shown !
in Figure 3. In the system oE Figure 3 a vertically dis- i
posed furnace housing 160 has a pluarlity of laterally
extending enclosures 162 spaced around its periphery near
the bottom of the housing. Although in the particular
embodiment shown in Figure 3 housing 160 is basically
cylindrical and enclosures 162 therefore extend radially
from housing 160, any of a wide variety of configurations
can be employed, as will be apparent to those skilled in the '
art. Each of enclosures 162 is similar to the initial portioj
of combustor 20 in Figures 1 and 2. Each enclosure 162
therefore includesan initial mixing zone 122 similar to
initial mixing zone 22 in Figures 1 and 2 and a zone 126,
containing a catalyst, similar to catalyst zone 26 in Figures
1 and 2. A portion of a first mixture of fuel and air
similar to the first mixture of Figure 1 and formed as
described below is supplied to each of enclosures 162 and at
least partly combusted in the associated catalyst zone lZ6
as in catalyst zone 26 in Figure 1 to produce a first
gaseous effluent, which en-ters the lower portion 130 of the
30 interior of housing 160 (referred to herein as second mixing !
and combustion zone 13O)A In zone 130 tlle first effluent
-16-
~ 33.~4
'
'from all.of enclosures 162 is m.ixed ~ith a second fuel- ¦
containing component formed as described below and supplied
' , to zone 130 by diffuser 142 to prod~ce a second mixture
similar to the second mixture fornied in zone 30 in Figure 1. ,
~ 5 This second mixture is homogeneously combusted in zone 130
`,, as in zone 30 in Figure 1 to pro~uce a second gaseous
. e~fluent. Heat is ~ithdrawn from this second gaseous
effluent as it rises in housing 160 to heat steam in a system~
. of boiler tubes (not shown) connected between lines 174'and
;, . 10 ,176. When the second effluent is too cool for further
~ efficient transfer of heat to the liquid water condensate
.~being vaporized to steam in the.boiler tube sys~em, the
second effluent exits from the upper portion of housing 160
. via line 150. Line 150 may conduct the second effluent to ¦.
,successive heat exchanges 172 and 178 for preheating
;'respectively condensate returned to the system via line 170
and air brought into the system via line 180. The preheated
condensate is supplied to the boiler tube systèm'associa~ed
~li-th housing 160 via line 174 and the fully heated steam
exits from that boiler tube system via line 176. The
. preheated air is distributed to the system via line 114.
The second effluent is finally exhausted from the system via i
line 182.
' I~he first mixture of fuel and air mentioned above is
25 .formed in line 118 by mixing fuel supplied via line 110 having
valve 112 with air from line 114 supplied via valve 116. As
mentioned above, this first mixture has the characteristics .
specified above.for the first mixture in Figure 1. Fuel for
the second'fuel-containing component is supplied to diffuser
142 via line 132 having valve 134 and line 140. This fuel
may be the same as that supplied via line 110 or it may be a
difEerent fuel. In any event, the fuel in the second fuel-
; containing component is a high energy fuel having an adiabatic
1ame temperature of at least about ,3,300F if burned with a ¦
~, stoichiometric amount of air. The second fuel-containing
component may also include air supplied from line 114 via
valve 138.
~' 5 Figure 4 shows a modification of the furnace of E~igure 3 '
, in which a portion of the final combustion effluent of the
furnace can be mixed as recycle gases with either the first
:1 .
-` ~ mi~ture of fuel and air or the second fuel-containing compo-
'~ nent, or-both, to control temperatures in the furnace and
~ 10 ; improve the thermal efficiency of the furnace. The recycle
.. . .
~` gases help ~o control temperatures in the system by diluting
i'' the fuel-air mixtures with which they are, mixed. Such use of~
these gases also may improve the thermal efficiency of the
system by c'onserving heat values within the system which would
15 ' otherwise be lost to the atmosphere. The furnace of Figure 4¦
is identical to the,furnace of Figure 3 with' the additio,n of
line 184 for drawing off and recycling a portion of the final'
combustion effluent between heat exchangers 172 and 178. The~,
recycle gases in line 184 are typically substantially inert
since it is usually preferable to operate a furnace with no
more air in excess of the stoichiometric amount for the total'
amount of fuel supplied to the furnace than is actually
necessary to insure complete combustion of all that fuel, , t
'although thes~ recycle gases may contain some-oxygen available
`for combustion. mhe recycle gases in line 184 are also-
typically at a temperature above ambient temperature. A
portion of the recycle gases in line 184 ~ay be supplled to
line 118 via valve 186 and mixed with the first mixture of
' fuel and air in, line 118. Alternatively or in addition, a
further por-tion of the recycle ~ases in line 184 may be
supplied to line 140 via valve 188 and mixed with the second '
fuel-containing component in line 140.
-18-
~Oq3:~3
: Although in the particular e~bodiment shown in Figure 4
the recycle gases are withdrawn between heat exchanges 172
and 178, it will be understood that these gases can be with- ¦
drawn at any point (e.g., ahead of heat exchanger 172 or
~, 5 after heat exchanger 178)u Similarly, although the recycle
' yases are mixed with the first mixture ~nd with the second ',
fuel-containing component after the fuel and air have been
mixed, it will be understood that these three components can ¦
be mixed in any order. Alternatively, any one or more of
these components can be supplied ~o the furnace separately
and mixed in the furnace te..g., in initial mixing'zones 122
in the case of the gases comprising the first mixture or in ~-
'second mixing and combustion zone 130 in the case of the .gases comprising the second fuel-containing component). J
' It is to be understood that the embodi.ments shown and
,described herein are illustrative of the principles of this
invention only and that various modifications may be imple- j'
mented by those skilled in the art without departing from the,
scope and spirit of the invention. For example, although
heat exchange to steam is employed in the furnace systems
shown in Figures 3 and 4, heat exchange to any other medium
(e.y., air) may alternatively be emp:loyed, or the furnace may
'comprise a pipe still with khe heat being transferred directl~
to a fluid being pro_essed in the still.
-19-
, , ~
