CA1211325A - Solid fuel heating appliance and catalytic converters therefor - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
This specification discloses solid fuel heating appliances, and more particularly, appliances which burn wood, densified or compacted wood products, coal, charcoal, peat, compacted trash or similar solid fuels and utilize a combustor or catalytic converter. The specification discloses a combuster device for oxidizing oxidizable species in the exhaust from the combustion chamber of a solid fuel heating appliance. The device comprises a structure having a plurality of axially extending cells for passing oxidizable species therethrough and at least one leakage path for the oxidizable species through said structure, or around and adjacent said structure. The structure may preferably comprise a honeycomb arrangement of cells. In one embodiment the leakage path may have a substantially larger cross-sectional area. By the use of this device there is provided a combustor or catalytic converter for a solid fuel heating appliance wherein the plugging of the cells in the catalytic converter will not result in the leakage of smoke into the living space adjacent the wood burning stove.

Description

SOLID FUEL HE~TING APPI.IANCE:
AND CATALYTIC CONVERTERS T~IE:R~FO:F~

B~
-Thi.s invention relates to solid fuel heatiAy appliance~, S and more paxticularly, to appliances which burn wood, den3ified or compacted wood products, coal, charcoal, p3at, compacted trash or similar solid fuels and utilize a combustor or catalytic converter.
U.S. Pa~ent 4,373,452 filed Julv 28, 1980 (assigned to the assigne~ o~ th~s application) discloses the use of a catalytic converter in wood buxning stove. The catalytic converter which serve~ a~ ~ combustor provides more complete burning or oxidation of th~ volatile and particulate organic substances pre~nt in ga~es ari3ing from burning wood in a wood burning ~tove and e~p~cially those solid particles and re~ nou~ and oily droplets that cause th~ d~n~e smoke which upon deposition o~ the in~ide surface of the flue pipe or chimney ar~ generally known a~
creosote~ More paxticularly, a catalytic con~ert~r which comprises noble-metal catalysts on a suitable ~u~strate reduces the ignition tempexatures of car~on monoxlde and t~
lower boiling~ more volatile hydxocarbons present ~n thc exhaust issuing from the co~bustion of wood. A the hyd~ocarbons and carbon monoxid2 burn, the temperature of the catalyst 2S and lt~ substrate is raised which increases its catalytic activity. The elevated temperatuxs py~olyzes and crack~ th~
higher molecular weight hydrocarbons occuring in the smoke as solid particles and oily droplets, converting them to volatile compounds which readily mix with oxyy~n ~resent ancl thereby leading to their rapid oxidationO Tempe~ature continue~
to rise until the system reache~ a tempcrature at wh~ch v~

there is e~uilibrium betwQen the inl0t: ga~ tempera~u:~ O 10w xate and the amount o oxidizable material. Thi~ t~mperaturQ
~ s typicalïy 6û0C to 900C for a properly s~ze~ cata].~st sy s tem . At ( continued pa~e 2 -- 1~

~2~

~here is equilibrium between the inlat ga~ ~emp~rature, 1OW
rate and the amount of oxidizable material. Thi~ t~mpcrature is typically 600C to 900C for a properly ~i~ d cataly~ system.
At these temperatures, oxidation proceeds ~ery rapidly ~o completion 5 if the cataly~ic device has ~he appropriate voll~me and internal surfa(,e area. As conver~er t:emperatures increase, the exhaust gas temperature rises above the igni~ion point of an increasing number of its cons~i~cuents ~o that the ca~alytic combustion proces~ is augmented by thermal combustion. The high tempera-10 tur~s also break the complex hydrocarbons and other combustibles( including solid particular entrained in the çombustion gases) into compounds which will burn more easily.
As disclosed in the aforesaid UOS. patent 4,373,452 the catalytic converter comprises a number of cells which extend axially through the substrate so as to permit the stove exhaust to pass therethroughO Since the cells may be relatively smal1, e .g ., 16 cells per square inch ( about 205 cells/cm.2), it is pos~ible that some or many of the cells may become plugged with exhau~t ~terials including 20 creosote and other hydrocarbon compositions. This, i~
turn, may produce a safety hazard since the smoke from the stove which is unable to pass properly through the catalytic cor~verter may enter any living space surroundirlg the stove and create an asphyxiation hazard. It will be understood 25 ~hat such a hazard can occur when a combustor or catalytic converter is utilized in any solid fllel heating appliance whlch utilizes a solid fuel such as wood, densified or com-pacted wood products ~ coal, charcoal, peat, compacted trash and/or garbage and the like which may give off, during burning, solid particles and vapor that may lead to some temporary pluggi~g of the catalytic converter, , . . -- , .

hdjl~stable and closeable bypas~es have recently been utilized or proposed between ~ combustion chamber ~nd an exhaust flue or chamber of a wood burning stove as disclosed in co-pending U.S~ application Serial No. 136,687, of Albertsen filed April 2, 1980, (in Canada Serial No. 374,510; in EPO
~erial No. 81-301,389.3 published 7 October, 1981), and U.S.
patents 4,345,528 and 4,330,503 o Allaire et al filed July 28, 1~80, all of which are assigned to the asslgnee of this invention.
The main purpose of these bypasses is to minimize ~ack pressure within the stove having a combustor or catalytic converter when the door of the stove is open which can result in the intro-duction of smoke into the living space around the stove. Such a bypass is spaced a substantial distance from the catalytic converter.
Summary of the Invent_on It is an object of this invention to provide a combus-tor or catalytic converter for a solid fuel hea~ing appliance wherein the danger of asphyxiation is minimized.
It is a further obj~ct of this invention to provide ~o à combustor or catalytic converter for a solid fuel heating appliance wherein the plugging of the cells in the catalytic converter will not result in the leakage of smoke into the living space adjacent the wood burniny stove~
It is a further specific object of this invention ~5 to provide a combustor or catalytic converter in a solid fuel heating appliance wherein the hazard of asphyxlation is minimized without adversely affecting the efficiency of the s to~ .
It is a still further object of this invention to provide a combustor or catalytic eonverter for a solid fuel heating appliance wherein the hazard of asphyxiation is minimized while at the same time op~imizing o~sidation 5f carborl monoxide ~ hydrocarbons and other combustibles ( including . i. solid particles entrained in the combustion gases~

Thus, the present inrention provides in a b~o~d embodi-ment, a solid fuel. heating appliance comprisiny:
a combustion chamber;
a flue for removing exhaust from said chamber;
a combustor having a plurality of cells extending there-through for oxidizing oxidlzable species in said exhaust;

at least one leakage path around said cells located immediately adjacent said combustori a container surrounding the periphery of said combustor, said leakage path extending between said container and said combustor; and said combustor being rnounted non-rotatably with respect to said container.

In another broad embodiment, the present invention pro-vides a combustor for oxidizing oxidizable species in the exhaust of a solid fuel heating appliance comprising:
a honeycomb structure having a plurality of axially extending cells for passing oxidi~ahle species therethrough, a container for said structure at the periphery thereof;
a leakage path between said container and the periphery of said structure;
said leakage path ha~ing a substantially larger 5 cro5s-sectional area than any of said cells; and said combustor being mounted non-rotatably with res~ect to said container.

- 3a -~'2~

In accordance with these and other objec~s of the invention, a preferred embodiment of the invention comprise~
a solid fuel heating appliance in ~he o~1 of a wood burning stove of the type including a combustion chamber, a ~lue ~or j removing exhaust from the combus~ion chamber and a combustor or catalytic conver~cer means having a plurality of cells extendin~ therethrough for oxidizing oxidizable species in the exhaust. Other solid fuel hea~ing appliances ~hich ~ay embody the invention include boilers, inci.nerators and the likeO
In accordance with this invention, at least one leakage path, as a pa~sive bypass, is provided around the cells and is located immediately adjacent the combustor or catalytic convert~r. In several embodiments of the invention, the lea~age path is located at the periphery of the catalytic ; converter. In one of the several embodiments, the leakage path may be provided a spaced distance from the catalytic c~nverter but nevertheless in ~he vicinity immedia~ely adjacent the catalytic converter. In another of these several embodiments of the invention, a leakage path may be provided between a contain~r cr the c~calytic converter a~.d the periphery of th~ catalytic converter. In still another ~f these several embodiments, ~he catalytic converter i5 movably mounted wi~hin an opening and provided s~Jith the leakage path adjacent to the periphery, which may also permit a variation in the size of tne leakage path. In yet another embodiment of the inventlon, ~he leakage path may be prolirided by ont~ or more axially extending a~l enlarged openings wi~hin ~che interior of ~he catalytic converter itself~
In order to provide sufficient leakage, t:he overall transverse cross-sectional area of ~he leakage path mus~ be ~ 4 _ substantially greater than the transverse cross-sectional area of any of the individual cells. Preferablyr the trans~
verse cross-sectional area oE the leakaye path i5 subs~anti~lly greater than the average cell transverse c-oss-sectional area of substantially all of the cells. For example, it is de~irable to have a transverse cross~sectional area of the leakage path which is at least two and preferably four times as great as the average cell transverse cross-sectional area~ In any event, the leakage pa~h should provide for at leas! 105 and pre.~erably 10~ to ~0~ of the overall flow of exhau3~ through the converter itself and the leakage path.

Brief Descrlption of the Drawings FI~. 1 is a sectional vie~ of a solid f~el heating ~ppliance comprising a wood burning stove repre~en~ing a .5 preferred embodiment of the invention includi~g a oombustor in the form o a catalytic converter mounted in accordance with this invention;
FIG. 2 is an enlarged fragmentary view of the cata-lytic converter and mounting shown in FIG. l;
~0 FIG. 3 is a bot~om view of a catalytic con~erter and mounting taken along line 3-3 of FIG. 2;
FIG. 4 is a sectional view of a catalytic converter and mounting in yet another embodimen or the inven~ion;
FIG. 5 is a bottom view of the catalyt:ic conver~er ~5 and mounting taken along line 5-5 of ~IG. 4;
~ IG. 6 is a sectional view of a catalytic converter and mounting comprisir.g yet another ~mbodiment of the invention;
FI(;. 7 is a bot~om view of the catalytic converter and its moun~ing ~aken along line 7-7 o FIG. 6;

t FIG. 8 i~ a sectional view of a catalytic converter and mounting in still ano~her embodiment of the invention; and FIG. 9 i~ a bottom view of the cataly~ic conv~rter and mounting taken along line 9-9 of FIG. 8.

S Detailed Description of a Preferred Embodiment _ Referring to E~IGo 1~ a solid :uel heating appliance comprising a wood burnlng stove ~.0 is sho~7n including a primzry wood combustion chamber 12 in ~he lower portion of ~he stove and the exhaust or secondary combustion chamber 14 .0 in the upper portion of the stove. A combus~or in the form of a catal~tic converter 16 is located bet~een the pri~ar~
combustion chamber 12 and the exhaust or secondary combustion chamber 14 to promo~e more complete burning or oxldation of the carbon monoxide, ~ydrocarbons and other combustibles .5 ( including solid particLes en~rained in combustion gases) ex i t i Ag from the primary combustion chamber 12.
The stove 10 includes a grate 18 within the ~rimary combustion chamber for supporting ~he wood to be burned ~hereinO Air to the primary combustion chamber 12 is supplied 'O through a primary combustion air inlet 20. A secondary combustion air inlet 22 is coupled to a maniold 24 which provides air or oxygen to thQ inlet face of th~ catalytlc converter 16 so as to optimize the oxidation or burning wi~h the catalytic converter. The manifold 24 is positioned and '5 designed in the appliance so as to provide adequate ~remixing of the secondary air from the manifold 24 ~ith the combus~ion gases and fumes before they enter the converter 16d Additional combu~ion or oxidation and/or heat exchange ~o living space occurs wlthin ~he chamber 14 before ~he exhaus~ ga~es leave through a flue 26.
An adjustable or cioseable bypass to the flue 26 is preferably provided by a damper 28 which is attached ~t a pivot or hinge position 30 a~ a wall 31 uf the ~tove 10 (similar to copending Canadian application Seri~l ~lo. 37~,510, althouyh it Tnay optionally be like the damper in U.S. Patent 4,330,503).

I.n accordance with this invention, the catalytic converter 16 is mounted between the primary combustion chamber 12 and the chamber 14 so as to provide the leakage path around the axially extended cells of the catalytic converter 16 as be~t shown in FIGs. 2 and 3. More specifically, the catalytic converter 16 comprises an open-ended honeycomb structure with a plurality of axially extendi~g cells 32 lS supported on rods 34 which extends transversely across a c~lindrical structure 36 extendirlg downwardly from a wall 38 ~eparatin~ the primary combustion chamber 12 from the chamber 14~ Since the catalytic conver~.er 16 ~s o~ lesser diameter than the opening through the tubular or cylindrical structure 36, exhaust from the primary ~mbustion chamber is permitted to flow around the periphery of the catalytLc converter 16 as depicted by arrows 40. Thi~ flow of exhaust gases as depicted by arrows 40 assures that~ even if the axially exte~ding cells 32 of the catalytic converter 16 should become plugged preventing the flow of exhaust gases through the axially extending cells 32 as depicted by arrows ~2, exhaust gases will still be permitted to pass from the primary combus ion chamber 1~ to the chamber 14 and hence to the flue 26 without backing up and entering the livin~ space surrounding the stove 10.

As also shown in FIGs 0 1 and 2 ~ the mounting of the catalytic conver~er 16 includes a cylindrical insulating member 44 having a centra.l opening ~5 subs~antially corresponding in diameter with t:he openirlg of the cylindrical struoture 36.
The insulating material 44 in conjunction with the eylindrical member 36 provides a container for the catalytic converter which permits the e~tablishment of a leakage path 40 between the catalytlc converter and the container. 8y utilizing the insulatlon material 44, the exhaust gases which pass through ) the leakage path 44 are maintained in close proximi~.y to the catalytic converter 16 and heat genera~ed a~ the catalytic converter 16 is re.ai..e~ ~o ~s to create an elevat2d ~empera-ture at the outlet of the catalytic converter 16 to assure at le~st some ox.idation or combustion Oc the carbon monoxide, j hydrocarbons and other combustibles (including sol.id particles entrained in the combustion gases) flowing through the leakage path even thou~h that exhaust does not ~ass through the small cells of the catalytic converter 16 itself.
In order to abricate the StruGture shown in FIGs.
1 through 3, a refractory insulating material 44 such as F~BERFR~X~ refractory fi~er produc~s, may be secured to the wall 3~ by means of a refractory of cement, such as QF 180 cement made and sold by the Carborurldum Company. The rods 34 pass through openings in the metallic cylindri~al structure 36. . A~thollgh the rods 34 need not be fas~ened in place within those opening~, it may be desirable to provide fasteners at the ends of the rods 34, e.g~, nuts recelved by threaded porti3ns of the rods 34.
Another embodiment OL the ca~aly~ic conver~e~
O moun~ed in a wood burning stove with a leakage path for -- 8 ~

exhaust gases is shown in FIGs. 4 and 5. In this embodiment,a cylindrical structure 136 is provided having an interior opening which substantially correspond~ with the dimen~ion of the catalytic converter 16 so that there is no leakage path between the catalytic converter and the container 136 for the catalytic con~erter. The leakaye path around the catalytic converter 16 i5 provided by a vent structure 138 located immediately adjacent the cataly~ic converter 16.
The vent structure 138 incLudes an elbow 140 which directs the leaked exhaust gas back to the high temperature area above the ca~aly~io converter 16 so as to assure, to the degree possible, combustion and oxidation of the carbon mono~ide, various hydrocarbons and othar combustibles (including solid particles entrained in the combustion gases~ which ar~
leaked around the catalytic converter 16, In order to mount the catalytic converter 16 within the cylindrical struGture 136, the structure 136 includes small flange segments 142 which are of insufficient length or depth to substantially block th~ cells 32 while at the same time having sufficient len~th and depth to a~sure that the catalytic converter 16 i~ retained within the cylindrical structure 1360 In the emb~diment of the invention shown in FIGs. 6 and 7, ~he leakage around the cells of the catalytic con-verter 16 occurs as a result of enlarged openir.gs ex~ending through the interior of (and thereby being adjacent to) the con~erter itself. For thls purpose, the catalytic converter 16 include~ a plurality oE openings ~00 having substantially larger tran5verse cross~sectional areas than the cell transverse cross-sectional area of ~he average or even the largest of the cells 32 through the catalytic converter 16. If so desired, the conlJerter 16 may include only one openirlg 200 where such a slngle opening will provide a~equate l~akage, The converter 16 is mounted within a cylirldrical s~ructure ~36 as shown in FIGs. 6 and 7 using a refractory eement such as Super 3000 cemen~ made and sold by Combustion Engineering, Inc.
FIGs. 8 and 9 disclose yet another embodiment of the invention wherein the catalytic converter 16 is mounted .0 within a metallic ring 300 which is pivotally supported on a cylindrical structure 336 by means of pins 338 which ext~nd through openings in the cylindrical structure 3360 In the embodim nts of ~IGs. 8 and 9, the leakage flow 340 is provided by the annular opening between the rir.g 300 and the structure L5 336 and may be adjusted by change in the angle of rotation of the ring 300 about pins 338. As the catalytic structure 16 and the supporting metallic ring 300 is pivoted out of the horizontal plane, the size of the leakage path 340 increases.
In the embodiment of FIGs. 8 and 9, it will be appreciated that the ceramic s~ructure 16 may be mounted within the ring 300 by suitable means including a refractory cemen~
such as Combustion Engineering Super 3G00 cement. It will al~o be appreciated that it may be desirable to displace the manifold 24 (Fig. 1) for the secondary combustion air so as to pe~mit ~ub~tantial ar.d free rot~tiorl of the catalytic con~erter 16 within the ring 300.
It will be appreciated that it is important that the leakag~ path arou~d the cells 32 of the converter 16 be in ~he vicini~y of ~he converter sueh ~hat the elevated temperatures in the vicinity of the converter can as~ist as s much a5 po~sible in oxidizing or burning the carbon monoxide, hydrocarbons and other combu~tible~ Sincluding solid par-ticl~
within the exhaust gases which flow through the 1Qa3~age path . It is also important that the volume of f low t".rough the leakage path be con~istent with the object~ve that most of the exhau-qt gase~ flow through the catalytic conv~rter while at the same ~ime providing sufficien~ 10w through the leakage path to avoid the backing up of smoke if the cell3 o the catalytic converter should become ~locked In this regard, it is desirable that the tra~sver3e cro~-sectional area of the lea.~age pa~h(s) be such t~at at least 10~ and preferably 10~ to 40% of the overall flo~ of ex~aust ga~es goes through the lea~age path(s~ Lnstead of the axiall~
exterlding cells. Where the leakage pa~hs are provided ~y enlarged openings of s~uare transverse cros3-section i~ t~e catalytic converter 16 ha~ing square trans~er~e cross-sectional cells 32 as shown ~n FIGs. 6 and 7, th~ amount of leakage for any given cell distri~ution can be calculated from the fcllowin~ e~_ation for the total flow t~r~u~h the I combustor:

Q 56 8~L ~ 1 1 2 2 n n where Q = total ~olume 10w through the com~ustor;
~P = pressure drop acro~s co~bus~ox;
; ~ - gas vi3co~ity;
L a combustox langth;

Nl numb2r of holes of insid2 dimen~io~ Xl;
N2- - number OL nole~ af in~id~ dtm~nsion Xz, Nn = number of holes o in~ide d~men~ion ~n;

It will be appreciated that A = combustor frontal area - Nl ( Tl ~ X~
N2 ( T2 ~ ~2) Nn (Tn -~ xn)2 where Tl, Tz, Tn are wall 'chicknesses, From the fore~oing equation for C~, the perc~ntage of flow through the leakage path of a given size opening may be expressed as: Nn X4 - - -- x 100~
(N, X4 ~ ~2 X4 ... + Nn X4) Assuming, for example, a catalytic converter of 14.38 cm.
( 5. 66 inches) in diameter with 4 square transverse cross-~ectioned cell5 per square crn. ~16 square trans~erse cross-sectioned cells per square inch), the per~ent of fiow through the leakage path u~ing various ~ized holes of square transverse cross-section in various numbers may be calculated:

Large Hole Number of ~ Flow Through _ Size Xn Lar~e Holes L~rge ~ol~ _

2.5~ cm. ( 1,0 inch) 1 60%
1.91 cm. (0v75 inch) 1 29-~
1,52 em. (0060 inch) 2 2S~
1.27 cm. (0.50 inch) 3 20%
As noted in the oregoing, it is preerred that the percen~
tage of leakage flow be 10~ to 40% and the hole sizes of 1,91 cm., 1.52 cm. and 1.27 cm. with the n~mber of hQles indicated falling within thi~ ranye. A hole si2e of ~.54 cm. (1.0 inche~) in this particular catalytic converter str~cture produces a percentage of flow which is somewhat higher than the preferred range. On the other hand, the s~aller si~e holes and the n~lmbers indicated provide sufficient flow without any substan-~i~l ri~k of hole plugging. In gerleral~ de~irabl~ to provide leakage paths haviny tran$verse cro~3-sectional areas which are at least two and pr~ferably four time~ a3 large as the average cell transverse cro~s-sectional area c~f ~he cell~
It will be appreciated by ~killed persons in this field of terhnology that the converter structure may optionally be formed with cells o transverse cross-sectlon other ~han square~ Thus~ ~he configura~ion of ~ransverse cross-~ection for con~erter cell~ may be circular, oval, any polygon, etc~
Such persons can reasonably formulate a suitable formula for percentage 'flow ~hrough large holes with respect to any seleotion o any otheE transverse cell cross~section~l configuara~ion, based on analogy and guidance of the preceding lS formula for ~quare cells.
In the catalytic converters 16, it is, of cour~e, ex-treme.l~ important to assure proper combustion for oxidation of the carbon monoxide, hydroc~rbons and other combustables (in~
cludiny ~solid particles entra1ned in ~he combustion gases~
exitir.g the primary comb~stion chamber 1~. ~etail~ concerning the catalytic converter 15 are set forth in the aforesaid U.S. ~atent 4,373,452 In all of the various embodiMents of the invention, it will be appreciated that the leakage path(~) around the axially ext~nding cells of the catal~tic converter i8 ( are) located in the immediate vicinity of the catal~tic converter~
Thi~ i~, of course 7 i.mportant, as set orth in the foregoing in order to subject the leaked exhaust gases to high tempera-tures ther~by as~uri~g, to the degree possibl~e, combustion or oxidation of carbon mons~xide, hydrocarbons and other combustibles ( including solid particles) within the leakage exhaust gases themselves. As shown in FIG. 1, a leakage path within the vicinity of the catalytic converter 16 is to be distinguished from any leakage resul~ing from a bypas~ of exhaust gases provided at a position more remote from the catalytic converter. The function served by the bypass opened and closed by the damper 28 is entirely different from the Eunction served by the leakage path in the immediate vicinity of the catalytic converter 16. See the aforesaid Albertsen U.S. a~plication Serial ~lo. 136,687, (Canadian Serial No. 374,510).
Al though a wood burning stove has been shown and described in detail, it will be appreciated that the invention may be embodied in other solid fuel heating appliances which can utiliæe various solid fuels including densified or compacted wood products, coal, charcoal, peat and compacted trash and~or garbage and the like which may give off during burnin~, solid particles and vapors that may lead to some temporary plugging of the catalytic converter. Such appliances may take the form of stoves as well as boilers, incinerators and the like, especially those well-suited for residential use~
Although particular embodiments of the invention have been shown and described, it wilL be ur.derstood that various modifications may be m~de which will fall within the true spirit and scope of the invention as set forth in the appe nded c l a ims .

Claims (8)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A solid fuel heating appliance comprising:
a combustion chamber:
a flue for removing exhaust from said chamber;
a combustor having a plurality of cells extending therethrough for oxidizing oxidizable species in said exhaust;
at least one leakage path around said cells located immediately adjacent said combustor;
a container surrounding the periphery of said com-bustor, said leakage path extending between said container and said combustor; and said combustor being mounted non-rotatably with respect to said container.

2. The appliance of claim 1 wherein said container comprises a tubular member and a support member extending transverse to the tubular member for supporting said combustor.

3. The appliance of claim 1 wherein the leakage path extends substantially along the combustor substantially around the entire periphery of the combustor.

4. The appliance of claim 1 wherein said container comprises a leakage path spaced from said combustor including means directing the exhaust gases to the catalytic converter.

5. A combustor for oxidizing oxidizable species in the exhaust of a solid fuel heating appliance comprising:
a honeycomb structure having a plurality of axially extending cells for passing oxidizable species therethrough;
a container for said structure at the periphery thereof;
a leakage path between said container and the periphery of said structure;
said leakage path having a substantially larger cross-sectional area than any of said cells; and said combustor being mounted non-rotatably with respect to said container.

6. The combustor of claim 5 wherein the leakage path extends substantially around the entire periphery of the structure.

7. The combustor of claim 5 wherein the overall flow through the leakage path is at least 10% of the overall flow of the exhaust through the structure.

8. The combustor of claim 5 wherein the overall flow through the leakage path is 10% to 40% of the overall flow through the converter including the cells in the leakage path.