Patent Publication Number: US-6981865-B2

Title: Catalyst combustion system, fuel reforming system, and fuel cell system

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a catalyst combustion system, a fuel reforming system using the catalyst combustion system, and a fuel cell system using the fuel reforming system. 
     There has been disclosed in Japanese Patent Publication No. 2533616 a catalyst combustor for supplying a heat medium for use at a fuel reformer to reform a fuel to be used in a fuel cell. 
     The catalyst combustor is adapted under assistance of a catalyst to perform a catalyst combustion of “a reformed fuel containing hydrogen that is effluent, as it is unused, at a cathode (a fuel electrode) of the fuel cell” (hereafter sometimes called “effluent fuel”) with “a gaseous fluid containing oxygen that is effluent, as it is unused, at an anode (an oxidizer electrode) of the fuel cell” (hereafter sometimes called “effluent oxidizer”), to provide a hot gas containing products of the catalyst combination, as the above-noted heat medium. 
     In such a regular run of a fuel cell system including the catalyst combustor, the fuel reformer, and the fuel cell, both effluent fuel and effluent oxidizer are available from the fuel cell for use at the catalyst combustor, and a heat medium is available therefrom. 
     SUMMARY OF THE INVENTION 
     In startup of the fuel cell system, however, the fuel cell has neither effluent fuel nor effluent oxidizer, and the catalyst combustor needs combination of a substitute fuel and a substitute oxidizer to be supplied in controlled quantities and timing for a catalyst combustion therein, to thereby provide an adequate heat medium for use at the fuel reformer. 
     The conventional catalyst combustor is thus provided with a set of necessary valves for individually opening and closing four fluid supply lines (effluent fuel supply line, effluent oxidizer supply line, substitute fuel supply line, and substitute oxidizer supply line), and a set of necessary actuators to be controlled for individual operations of the valves. The actuators have their weights and costs, and occupy spaces, in addition to the complexity of control system. 
     The present invention is made with such points in view. It therefore is an object of the present invention to provide: a catalyst combustion system in which a catalyst combustor can be supplied with necessary quantities of fuel and oxidizer for a catalyst combustion to provide an adequate heat medium in a stamp as well as in a regular run, without provision of conventional sets of valves and actuators, that is, with reduced numbers of valves and actuators; a fuel reforming system using the catalyst combustion system; and a fuel cell system using the fuel reforming system. 
     To achieve the object, according to an aspect of the invention, there is provided a catalyst combustion system comprising a closable first fuel supply line which supplies a fluid containing a first fuel, a closable first oxidizer supply line which supplies a fluid containing a first oxidizer for the first fuel to be combustible therewith under assistance of a catalyst, a second fuel supply line which supplies a fluid containing a second fuel different from the first fuel, a second oxidizer supply line which supplies a fluid containing a second oxidizer for the second fuel to be combustible therewith under assistance of the catalyst, and a catalyst combustor configured to alternately perform a first catalyst combustion between the first fuel and the first oxidizer and a second catalyst combustion between the second fuel and the second oxidizer, and to supply as a thermal medium a fluid containing one of a combustion product of the first catalyst combustion and a combustion product of the second catalyst combustion. The catalyst combustor comprises a first catalyst combustion portion connected to the first fuel supply line and the first oxidizer supply line, a second catalyst combustion portion connected to the second fuel supply line and the second oxidizer supply line, and a fluid communication portion connecting the first catalyst combustion portion and the second catalyst combustion portion to each other, and has a fixed relationship provided among a fluid resistance of the first catalyst combustion portion, a fluid resistance of the second catalyst combustion portion, and a fluid resistance of the fluid communication portion, whereby substantially the first catalyst combustion is caused to occur simply in the first catalyst combustion, and the second catalyst combustion is caused to occur in the first catalyst combustion portion and the second catalyst combustion portion. 
     According to another aspect of the invention, there is provided a fuel reforming system including a fuel reformer configured to reform a fuel using the heat medium of a catalyst combustion system according to the previous aspect. 
     According to another aspect of the invention, there is provided a fuel reforming system including a fuel reformer configured to reform a fuel using the heat medium of a catalyst combustion system according to the previous aspect. 
     According to still another aspect of the invention, there is provided a fuel cell system including a fuel cell having a fuel electrode configured to consume the reformed fuel of a fuel reforming system according to the previous aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
       The above and further objects and novel features of the present invention will more fully appear from the following detailed description when the same is read in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram of a fuel cell system including a fuel reforming system having a catalyst combustion system according to an embodiment of the invention; 
         FIG. 2  is a longitudinal section of a catalyst combustor of the catalyst combustion system of  FIG. 1 ; 
         FIG. 3  is a cross section along line III—III of the catalyst combustor of  FIG. 2 ; 
         FIG. 4  is a cross section along line IV—IV of the catalyst combustor of  FIG. 2 ; 
         FIG. 5  is a longitudinal section of a catalyst combustor of a catalyst combustion system according to another embodiment of the invention; 
         FIG. 6  is a cross section along line VI—VI of the catalyst combustor of  FIG. 5 ; 
         FIG. 7  is a cross section along line VII—VII of the catalyst combustor of  FIG. 5 ; 
         FIG. 8  shows a detailed section along line VIII—VIII of the catalyst combustor of  FIG. 2 , as it is common to the catalyst combustor of  FIG. 5 ; 
         FIG. 9  shows in section an essential part of a catalyst combustion portion as a modification of each embodiment; and 
         FIG. 10  shows in section an essential part of a catalyst combustion portion as another modification of each embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     There will be detailed below the preferred embodiments of the present invention with reference to the accompanying drawings. Like members are designated by like reference characters. 
       FIG. 1  shows in block diagram an entirety of a fuel cell system  1  according to a first embodiment of the invention. The fuel cell system  1  is constituted with a fuel cell  2 , a fuel reforming system  3 , and a control system  1   a  which controls various actions of operative components, such as actions of associated valves and drives, as necessary for startup (or warming) and regular operations of the fuel cell system  1 , via unshown signal and power supply connections. It is noted that the startup operation should be as short as practicable. 
     As a gaseous fluid containing hydrogen as a fuel, a reformed fuel is supplied from the fuel reforming system  3  to the fuel cell  2 , via a reformed fuel supply line LS 1 . This supply line LS 1  has a shutoff valve SV 1 , which is close in the startup operation of the fuel cell system  1  and open in the regular operation of the system  1 . As a gaseous fluid containing oxygen as an oxidizer, fresh air is supplied from an unshown air source to the fuel cell  2 , via an oxidizer supply line LS 2 . This supply line L 2  has a flow or pressure control valve CV 1 . 
     In the regular operation of the fuel cell system  1 , the fuel cell  2  generates electric power to be output via a power supply line PS. For the electric power generation, hydrogen in the reformed fuel is consumed at an anode  1   a  (fuel electrode), and oxygen in the fresh air is consumed at a cathode  1   b  (oxidizer electrode). The fuel cell  2  has two effluent lines: an effluent fuel line LE 1  connected to a gas collecting region of the anode  1   a,  where it receives a gaseous fluid containing hydrogen, as an effluent fuel; and an effluent oxidizer line LE 2  connected to a gas collecting region of the cathode  1   b,  where it receives a gaseous fluid containing oxygen, as an effluent oxidizer. 
     The fuel reforming system  3  includes a vaporizer  4 , a fuel reformer  5 , and a catalyst combustion system  10 . 
     The vaporizer  4  has an incorporated heat exchanger (not shown) provided with a fuel injector  4   a  and a water injector  4   b.  The heat exchanger has heating paths which are connected at their inlet ends to a heat medium supply line LS 3  and at their outlet ends to an effluent fluid line LE 3 . The fuel injector  4   a  receives a liquid fuel, such as methanol, from an unshown fuel source via a fuel supply line LS 4 , and injects atomized fuel as a fuel to be vaporized and reformed. The water injector  4   b  receives pure water from an unshown water source via a water supply line LS 5 , and injects atomized water. The atomized fuel and atomized water are injected into a heated region of the heat exchanger, where they are mixed and vaporized by heat from streams of a heat medium in the heating paths. Then, a vaporized fuel as a mixture of heated fuel vapor and steam is conducted from the heated region of the heat exchanger, into a vaporized fuel supply line LS 6 . 
     The vaporized fuel supply line LS 6  is connected to the fuel reformer  5 . Further, an air supply line LS 7  having a flow or pressure control valve CV 2  is connected between the before-mentioned air source and the fuel reformer  5 . The vaporized fuel from the supply line LS 6  is mixed with air from the supply line LS 7  and cracked in the fuel reformer  5 , to produce “a gaseous fluid containing a sufficient amount of hydrogen, as a hydrogen-rich adequate reformed fuel” (called “reformed fuel” as used herein) to be conducted along a reformed fuel supply line LS 8 . This supply line LS 8  is bifurcate to be connected on one way to the before-mentioned reformed fuel supply line LS 1 , and on the other way to a reformed fuel bypass line LB that has a shutoff valve SV 2 , which is open in the startup operation of the fuel cell system  1  and close in the regular operation of the system  1 , in an effectively warmed phase in the startup operation, the reformer  5  produces an inadequate reformed fuel having a gradually increasing but insufficient amount of hydrogen, which is conducted through the bypass line LB, as an effluent fuel in a sense. 
     The catalyst combustion system  10  has a catalyst combustor  11 , a substitute fuel supply line LS 21 , a substitute oxidizer supply line LS 22 , an effluent fuel supply line LS 23 , and an effluent oxidizer supply line LS 24 . 
     The substitute fuel supply line LS 21  is connected to a liquid fuel supply line LS 25 , which supplies “a liquid substitute fuel” from the before-mentioned fuel source, and has a shutoff valve SV 3 , which is open in the startup operation of the fuel cell system  1  and close in the regular operation of the system  1 . The substitute oxidizer supply line LS 22  is connected to the before-mentioned air source, and supplies air to be a gaseous fluid containing oxygen, as a “substitute oxidizer”, and has a flow or pressure control valve CV 3 . Note that the control valves CV 1  to CV 3  are controllable to their close positions. 
     The effluent fuel supply line LS 23  is simply connected to the effluent fuel line LE 1  and, on the way, to the reformed fuel bypass line LB, so that an effluent fuel is supplied therethrough in the effectively warmed phase in the startup operation of the fuel cell system  1 , as well as in a sufficiently warmed phase substantially corresponding to an interval of the regular operation of the system  1 . The effectively warmed phase and the sufficiently warmed phase will sometimes be collectively called “a warmed phase”, which follows a warming phase. The effluent oxidizer supply line LS 24  is simply connected to the effluent oxidizer line LE 2 , so that an effluent oxidizer is supplied therethrough while air is supplied from the supply line LS 2 . It is noted that the effluent fuel supply line LS 23  and the effluent oxidizer supply line LS 24 , as well as the effluent fuel line LE 1  and the effluent oxidizer line LE 2 , have no valves to be actuated for changeover between the startup operation and the regular operation of the fuel cell system  1 . 
     The catalyst combustor  11  is provided with a substitute fluid connecting piping unit  11   a  and an effluent fluid connection piping unit  11   b.  In the piping units  11   a  and  11   b,  as shown in  FIG. 2 , the four supply lines LS 21 , LS 22 , LS 23 , and LS 24  have their fluid outlet pipes: an outlet pipe  12  provided at a downstream end of the supply line LS 21  for supplying a substitute fuel in the startup operation of the fuel cell system  1 ; an outlet pipe  13  provided at a downstream end of the supply line LS 22  for supplying a gaseous substitute oxidizer in the startup operation; an outlet pipe  14  provided at a downstream end of the supply line LS 23  for supplying a gaseous effluent fuel in the above-noted warmed phase; and an outlet pipe  15  provided at a downstream end of the supply line LS 24  for supplying a gaseous effluent oxidizer in the regular operation of the system  1 . It is noted that both connection piping units  11   a  and  11   b  have no valves to be actuated for changeover between the startup operation and the regular operation of the fuel cell system  1 . 
     On the other hand, the catalyst combustor  11  has three fluid inlet tubes welded thereto: an inlet tube  17  simply connected to the outlet pipe  13 ; an inlet tube  18  simply connected to the outlet pipe  14  for introduction of the effluent fuel; and an inlet tube  19  simply connected to the outlet pipe  15  for introduction of the effluent oxidizer. 
     The outlet pipe  12  has at its downstream end a fuel injector  16  joined to the inlet tube  17 , by inserting its atomizing tip  16   a  into the tube  17 . While the supply line LS 22  supplies the gaseous substitute oxidizer to be simply let through the outlet pipe  13  into the inlet tube  17 , a liquid substitute fuel supplied from the supply line LS 21  is let through the outlet pipe  12  and atomized at the tip  16   a  of the fuel injector  16  using air, so that “a gaseous fluid containing a system of droplets of substitute fuel” (hereafter called “gaseous substitute fuel” or “substitute fuel”) is injected into streams of substitute oxidizer in the inlet tube  17 , thereby having a gaseous mixture therebetween supplied to the inlet tube  17 . It should be noted that this inlet tube  17  is an integral part of the catalyst combustor  11  to which a gaseous substitute fuel is supplied by a fluid supply line (LS 21  with  16 ) constituted with the supply line LS 21  having the outlet pipe  12  provided with the fuel injector  16 . 
     As shown in  FIG. 2  to  FIG. 4  and  FIG. 8 , the catalyst combuster  11 , outline in a cylindrical form, is made up by: a cylindrical inner catalyst combustion portion  20  which extends over an axial length L of the combustor  11  and has (as a space defined therein) on its upstream side a cylindrical inner gas chamber  21  and on its downsteream side a cylindrical inner accommodation chamber  31  substantially equal in diameter to an in direct communication with the inner gas chamber  21 : a cylindrical (or more specifically, annular) outer catalyst combustion portion  40  which also extends over the length L, coaxially with the inner catalyst combustion portion  20 , and has (as a space defined therein) on its upstream side a cylindrical (or annular) outer gas chamber  41  and on its downstream side a cylindrical (or annular) outer accommodation chamber  51  substantially equal in inside and outside diameters to and in direct communication with the outer gas chamber  41 ; and a fluid communication portion  60  interposed between the inner gas chamber  21  and the outer gas chamber  41 . The inner gas chamber  21  is in fluid communication with inside of the inlet tube  17  arranged for axial introduction of the mixture of substitute fuel and substitute oxidizer. The axial introduction allows for a major fraction of the mixture to smoothly flow straight to the inner gas chamber  31 , at high speeds, inspiring fluids from therearound via later-described communication holes  62 , having a very minor fraction of the mixture branching outside. The outer gas chamber  41  is in fluid communication with the inlet tubes  18  and  19  arranged for radial introduction of the effluent fuel and the effluent oxidizer. The radial introduction allows for major fractions of the supplied fluids to smoothly spread abut a later-described separation wall  61 , with enhanced tendencies to invade through the communications holes  62  into the inner gas chamber  21 , and with suppressed tendencies to flow toward the outer gas chamber  51 . The inner gas chamber  21  has a small fluid resistance R 2  thereacross, and the outer gas chamber  41  also has a small fluid resistance R 4  thereacross. The inner catalyst combustion portion  20  has a smaller heat capacity than the outer catalyst combustion portion  40 . It should be noted that a catalyst in concern promotes a significant catalyst combustion above a critical temperature. 
     As shown in  FIG. 2  and  FIG. 3 , the fluid communication portion  60  is constituted with a fluid-containing cylindrical separation wall  61  which extends for separation between the inner and outer gas chambers  21  and  41 , and has a set of axial arrays { 62 -i: 1≦i≦I}, { 62 -j: I+1≦j≦J}, { 62 -k: J+1≦k≦K}, and { 62 -l: K+1≦l≦L} (where I, J, K, and L are given integers and i, j, k, and l are arbitrary integers in defined ranges) of fluid communications holes “ 62 - 1 ,  62 - 2 , . . . ,  62 -i, . . . ,  62 -I,  62 -(I+1), . . . ,  62 -j, . . . ,  62 -J,  62 -(J+1), . . . ,  62 -k, . . . ,  62 -K,  62 -(K+1), . . . ,  62 -l, . . . ,  62 -L” (hereafter collectively referred to “ 62 ”) provided through the separation wall  61 . An arbitrary hole  62  may be circular, elliptic, triangular, rectangular, polygonal, or any form else in section that can provide a necessary fluid resistance r (1≦f≦L). A parallel connection of respective fluid resistances {r} of a total of L fluid communication holes  62  represents a fluid resistance R 6  of the fluid communication portion  60 . The separation wall  61  is welded at its upstream end  61   a  to a circular central part  22   a  of a circular end plate  22  of the catalyst combustor  11 , and radially outwardly flanged at its downstream end  61   b.  The inlet tube  17  is inserted and welded to the central part  22   a  of the end plate  22 . 
     As shown in  FIG. 2  to  FIG. 3 , the inner catalyst combustion portion  20  is constituted with: the circular end plate  22  of which the central part  22   a  cooperates with the separation wall  61  to define the inner gas chamber  21 ; a cylindrical heat insulating separator  32  defining the inner accommodation chamber  31 ; and a cylindrical substrate  33  which is accommodated to be fitted gas-tight in the accommodation chamber  31 , and formed (to be meshed) in a honeycomb shape in a later-described fashion with a set of axially extending catalyst combustion path (or mesh) parts “ 34 - 1 , . . . ,  34 -(n−1),  34 -n, . . . , where n is an arbitrary integer in a range defined by a given integer N such that 1≦n≦N,” (hereafter sometimes collectively referred to “ 34 ”). The heat insulating separator  32  is constituted with a cylindrical inner casing  32   a  which is brought into abutment at its upstream end  32   a   1  on the flanged downstream end  61   b  of the separation wall  61  and inwardly bent at its downstream end  32   a   2  for hooking or stopping the substrate  33 , an inner heat insulating layer  32   b  which is formed over an inside of the cylindrical casing  32   a,  and an outer heat insulating layer  32   c  which is formed over an outside of the inner casing  32   a.    
     Again as shown in  FIG. 2  to  FIG. 4 , the outer catalyst combustion portion  40  is constituted with: a cylindrical upstream outer casing  42  cooperating with the separation wall  61  and the annular part  22   b  of the end plate  22  to define the outer gas chamber  41 ; a cylindrical outer case  52  cooperating with the heat insulating separator  32  to define the outer accommodation chamber  51 ; and a cylindrical (or annular) substrate  53  which is accommodated to be fitted gas-tight in the accommodation chamber  51 , and formed (to be meshed) in a honeycomb shape in a later-described fashion with a set of axially extending catalyst combustion path (or mesh) parts “ 54 - 1 , . . . ,  54 -(m−1),  54 -m, . . . , where m is an arbitrary integer in a range defined by a given integer M such that 1≦m≦M (&gt;N or &gt;&gt;N),” (hereafter sometimes collectively referred to “ 54 ”). The substrate  53  has a smaller mesh than the substrate  33 , or in other words, the meshing of the latter  33  is coarser or rougher than that of the former  53 . The upstream outer casing  42  has at its upstream end an outward flanged part  42   a  fastened by bolts  49  to a peripheral flange  22   c  of the end plate  22 , and at its downstream end an inward projected part  42   b  and an outward flanged part  42   c.  It should be noted that the heat capacity of the inner catalyst combustion portion  20  substantially depends on a heat capacity of the substrate  33 , and that of the outer catalyst combustion portion  40  substantially depends on a heat capacity of the substrate  53 . It also is noted that the substrate  33  has a significantly smaller heat capacity than the substrate  53 . 
     As best shown in  FIG. 8 , the outer case  52  is constituted with: a cylindrical downstream outer casing  52   a  which is integrally formed at its upstream end with an outward flanged part  52   a   1  fastened by bolts  59  ( FIG. 2 ) to the outward flanged part  42   c  of the upstream outer casing  42  and at its downstream end with an inward projected part  52   a   2  configured to hook or stop the substrate  53  and to support a cross member  58  ( FIG. 2 ) for stopping the heat insulating separator  32  and with a downstream extension  52   a   3  configured to define a cylindrical combustion product (heat medium) outlet space  70  to be common to the inner and outer catalyst combustion portions  20  and  40  ( FIG. 2 ) and to be connected to the heat medium supply line LS 3  ( FIG. 1 ); a refractory mortar layer  52   b  lining over an inside of the downstream outer casing  52   a  and a corresponding region of an end face of the inward projected part  42   b  of the upstream outer casing  42 ; and a gas-tight filler  52   c  of heat insulating materials filled between the refractory mortar layer  52   b  and the substrate  53 . 
     As illustrated in  FIG. 8 , an arbitrary catalyst combustion path part  54 -m (1≦m≦M) in the substrate  53  is constituted with: a corresponding straight combustion path  55 -m (1≦m≦M) (hereafter sometimes collectively referred to “ 55 ”) axially extending as a fluid path through the substrate  53  and communicating at its upstream end with the outer gas chamber  41  and at its downstream end with the combustion product outlet space  70 ; and a corresponding set  56 -m (1≦m≦M) of films of a catalyst configured as a whole to define the combustion path  55 -m with a corresponding fluid resistance {r m : 1≦m≦M} thereacross. A parallel connection of respective fluid resistances {r m } of a total of M combustion paths  55  (or of M combustion path parts  54 ) represents a fluid resistance R 5  across the outer accommodation chamber  51  (or of the substrate  53 ). 
     Likewise, as schematically shown in  FIG. 2  and  FIG. 4 , an arbitrary catalyst combustion path part  34 -n (1≦n≦N) in the substrate  33  is constituted with: a corresponding straight combustion path  35 -n (1≦n≦N) (hereafter sometimes collectively referred to “ 35 ”) axially extending as a fluid path through the substrate  33  and communicating at its upstream end with the inner gas chamber  21  and at its downstream end with the combustion product outlet space  70 ; and a corresponding set  36 -n (1≦n≦N) of films of the above-noted catalyst configured as a whole to define the combustion path  35 -n with a corresponding fluid resistance {r n : 1≦n≦N} thereacross. A parallel connection of respective fluid resistances {r n } of a total of N combustion paths  35  (or of N combustion path parts  34 ) represents a fluid resistance R 3  across the inner accommodation chamber  31  (or of the substrate  33 ). The N combustion paths  34  have a greater average sectional area than the M combustion paths  54 , so that an average of the fluid resistances {r n } of the former  34  is smaller than that of the fluid resistances {r m } of the latter  54 . It is noted that the combustion paths  34  as well as the combustion paths  54  may be identical or different in configuration and/or size, as necessary for facilitation of manufacture or for a particular fluid condition. It is desirable to increase a proportion of effectively used catalyst in a sum of a total of N sets  36  and a total of M sets  56  of films of catalyst, in order for a capacity of catalyst combustion process to be maximized in the regular operation of the fuel cell system  1 . 
     Referring to  FIG. 2 , in the catalyst combustor  11 , the inner catalyst combustion portion  20  has a fluid resistance R 1  thereacross equivalent to a serial connection of the fluid resistance R 2  of the inner gas chamber  21  and the fluid resistance R 3  across the inner accommodation chamber  31  (or of the substrate  33 ), such that R 1 =R 2 +R 3 . The outer catalyst combustion portion  40  has a fluid resistance R 6  thereacross equivalent to a serial connection of the fluid resistance R 4  of the outer gas chamber  41  and the fluid resistance R 5  across the outer accommodation chamber  51  (or of the substrate  53 ), such that Ro=R 4 +R 5 . The fluid resistance R 6  of the fluid communication portion  60  is serially connected to the fluid resistance R 2  or the inner gas chamber  21 . 
     Referring to  FIG. 1  to  FIG. 4 , the catalyst combustor  11  is configured to have fixed relationships among internal fluid resistances {R 1 , R 0 , R 2 , R 3 (r n ), R 4 , R 5 (r m ), R 6 (r t )} thereof, for example such that:
         R 2 &lt;R 3  or R 2 &lt;&lt;R 3 ,   R 4 &lt;R 5  or R 4 &lt;&lt;R 5 ,   R 2 ∝R 4 &lt;R 6  or R 2 ∝R 4 &lt;&lt;R 6 , i.e. (R 2 +R 6 )∝(R 4 +R 6 )∝R 6 ,   r n &lt;r m  or r n &lt;&lt;r m ,   R i &lt;R o  or R i &lt;&lt;R o , and/or   R i +R 6 ∝R o  or R i +R 6 =R o ,
 
so that, in the “startup operation” of the fuel cell system  1 ,
   substantially, a warming catalyst combustion between the substitute fuel and the substitute oxidizer is caused to occur simply in the inner catalyst combustion portion  20  (or more specifically in the substrate  33 ) which is low of heat capacity, i.e. without an influential or significant catalyst combustion caused between a fuel and an oxidizer conducted in the substrate  53  of the outer catalyst combustion portion  40  which is high of heat capacity, and
 
that, in the “regular operation” of the fuel cell system  1 ,
   a regular catalyst combustion between the effluent fuel and the effluent oxidizer is caused to occur in both the inner catalyst combustion portion  20  (or more specifically in the substrate  33 ) and the outer catalyst combustion portion  40  (or more specifically in the substrate  53 ), in particular proportionally or evenly, as required.       

     In the warming phase of the startup operation in which the shutoff valve SV 1  is close but the shutoff valve SV 3  is open and the control valve CV 3  is in its open position whereas the control valves CV 1  and CV 2  are in their close or crack-open positions as necessary and the shutoff valve SV 2  is to be opened when necessary for bypassing an amount of reformed fuel, the fuel injector  16  injects and atomized substitute fuel into a flow of a supplied substitute oxidizer in the inlet tube  17 , whereby a gaseous mixture therebetween is introduced into the inner gas chamber  21 , where it flows downstream along the separation wall  61 , and enters the substrate  33  in the inner accommodation chamber  31  with a priority, where it contacts the catalyst  36 , whereby its warmer catalyst combustion is promoted, generating gaseous combustion products, which flow out of the substrate  33  and enter the outlet space  70 , wherefrom they are supplied as a heat medium via the supply line LS 3  to the heating side of the heat exchanger in the vaporizer  4 , and discharged therefrom via the effluent line LE 3 . In due course in the warming phase, the vaporizer  4  may start generating a vaporized fuel to be supplied via the supply line LS 6  to the fuel reformer  5 . It is noted that the substitute fuel as well as the effluent fuel is combustible with the substitute oxidizer, and with the effluent oxidizer as well, under assistance of (i.e., by contact on) the catalyst  36 ,  56 . 
     Although, when the gaseous mixture passes the inner gas chamber  21 , a minor fraction thereof branches via the communication holes  62  of the fluid communication portion  60  into the outer gas chamber  41  and enters the substrate  53  in the outer accommodation chamber  51 , the branching fraction is maintained very small by relationships (for example R i &lt;R o  or R i &lt;&lt;R o ) among fluid resistances such as the fluid resistance R 6  across the separation wall  61  and the fluid resistance R 5  of the substrate  53  which has fine meshes  54 . As the substrate  33  which has a low heat capacity is accommodated in the heat insulating separator  32  which suppresses heat dissipation from the inner accommodation chamber  31 , the catalyst  33  can be warmed in a short while. The branching fraction of gaseous mixture gradually starts a preparatory warming catalyst combustion in the substrate  53 . 
     In the effectively warmed phase of the startup operation in which the shutoff valve SV 1  is kept close and the shutoff valve SV 3  is still open while the shutoff valve SV 2  is opened and the control valves CV 2  and CV 3  are in their controlled open positions whereas the control valve CV 1  may be controlled to be yet close or to a crack-open position as necessary, a significant amount of vaporized fuel is supplied to the fuel reformer  5 , where it is reformed, and a significant amount of gaseous reformed fuel is conducted, via the supply line LS 8  and the bypass line LB, into the effluent fuel supply line LS 23 , wherefrom it is supplied into the outer gas chamber  41 , where it is divided into: those streams which join a minor fraction of a gaseous mixture between (a maintained amount of) substitute fuel and (an increased amount of) substitute oxidizer (as the mixture is supplied in the inner gas chamber  21  and the minor fraction is branched to the outer gas chamber  41 ), thus entering together with the minor fraction into the substrate  53 , where they contact the catalyst  56 , whereby their warming catalyst combustion is promoted, generating a gradually increasing amount of gaseous combustion products; and those streams which branch through the communication holes  62  of the fluid communication portion  60  into the inner gas chamber  21 , joining the gaseous mixture therein to enter the substrate  33 , where they contact the catalyst  36 , whereby their enhanced warming catalyst combustion is promoted, generating an increased amount of gaseous combustion products. The respective amounts of gaseous combustion products are collected from the substrates  53  and  33  in the outlet space  70 , wherefrom they are supplied as an increased amount of heat medium to the vaporizer  4 . If the control valve CV 1  is controlled to the crack-open position, the control valve CV 3  may be set to an initial open position or controlled to a slightly wider open position. 
     In the regular operation, the shutoff valve SV 3  is closed to stop the supply of substitute fuel and the control valve CV 3  is set to its close position to control the supply of substitute oxidizer to a zero flow, whereas the control valve CV 2  is set to its regular open position to supply necessary air via the supply line LS 7  to the fuel reformer  5 , the shutoff valve SV 2  is closed to close the bypass line LB, the shutoff valve SV 1  is opened to supply a sufficient reformed fuel via the supply line LS 1  to the fuel cell  2 , and the control valve CV 1  is set to its regular open position to supply sufficient air to the fuel cell  2 , so that an effluent fuel is supplied from the effluent line LE 1 , via the supply line LS 23  and the outlet pipe  14 , to the inlet tube  18  and hence to the outer gas chamber  41  of the catalyst combustor  11 , and an effluent oxidizer is supplied from the effluent line LE 2 , via the supply line LS 24  and the outlet pipe  15 , to the inlet tube  19  and hence to the outer gas chamber  41  of the catalyst combustor  11 , where it is mixed with the effluent fuel, forming a gaseous mixture flowing downstream along the separation wall  61 . The mixture is substantially uniformly distributed about the fluid communication portion  60  and substantially evenly divided into: those streams which flow inside the outer gas chamber  41 , thus entering the substrate  53 , where they contact the catalyst  56 , whereby their regular catalyst combustion is promoted, generating a necessary amount of gaseous combustion products; and those streams which branch through the communication holes  62  of the fluid communication portion  60  into the inner gas chamber  21 , where they flow downstream to enter the substrate  33 , where they contact the catalyst  36 , whereby their regular catalyst combustion is promoted, generating a necessary amount of gaseous combustion products. The respective amounts of gaseous combustion products are collected from the substrates  53  and  33  in the outlet space  70 , wherefrom they are supplied as a required amount of heat medium to the vaporizer  4 . The even division of the mixture is effected for the catalyst  36 ,  56  to have a maximized processing capacity, by provision of balanced relationships (for example R i +R 6=R   o  or R i +R 6 =R o ) among fluid resistances including the fluid resistances {r 1 } of the communication holes  62 , the fluid resistances {r n } of the combustion paths  35 , and the fluid resistances {r m } of the combustion paths  55 . 
     The present embodiment has, among others, the following advantages:
         (1) a short warming in a startup operation due to a catalyst combustion of substitute fuel in a restricted catalyst region (within  33 ) with a restricted heat capacity;   (2) a still shortened warming in the startup operation due to the provision of heat insulating layers  32   b,    32   c  keeping combustion heat in a substrate  33  from escaping outside;   (3) a yet shortened warming in the startup operation due to a major fraction of a gaseous mixture flowing into the substrates  33  which is low of heat capacity;   (4) an actuator-less control allowed simply by combination of communication holes  62  and substrates  33 ,  53  different of mesh size;   (5) an actuator-less control in the startup operation allowed for a major fraction of a mixture of substitute fuel and substitute oxidizer to be conducted to the substrate  33  irrespective of the provision of communication holes  62 , by relationships (for example r n &lt;r m  or r n &lt;&lt;r m ) of fluid resistances (such as r n  and r m ); and   (6) an actuator-less control in a regular operation allowed for a process capacity of catalyst  36 ,  56  to be maximized, by a uniform distribution and even division of a mixture of effluent fuel and effluent oxidizer that is implemented by relationships (for example R i +R b =R o +R 6 =R o ) of fluid resistances (such as r f , r n , r m ).       

     In the embodiment described, the inner and outer catalyst combustion portions  20  and  40  are configured as coaxial cylinders in outline. However, they may be configured in any forms else that have like relationships among internal fluid resistances to the above embodiment, as illustrated below. 
       FIG. 5  to  FIG. 7  show a catalyst combustion system  110  in a fuel system  1  according to a second embodiment of the invention. 
     As shown in  FIG. 5 , the catalyst combustion system  110  has a catalyst combustor  111 , a substitute fuel supply line LS 21 , a substitute oxidizer supply line LS 22 , an effluent fuel supply line LS 23 , and an effluent oxidizer supply line LS 24 . The supply lines LS 21 , LS 22 , LS 23 , and LS 24  have their fluid outlet pipes  12 ,  13 ,  14 , and  15 . The catalyst combustor  111  has three fluid inlet tubes  17 ,  18 , and  19  welded thereto. The outlet pipe  12  has at its downstream end a fuel injector  16  joined to the inlet tube  17 , by inserting its atomizing tip  16   a  into the tube  17 . 
     As shown in  FIG. 5  to  FIG. 7 , the catalyst combustor  111 , cylindrical in outline, is made up by: a lower catalyst combustion portion  120  which is outlined in the form of a “cut cylinder with a minor are closed by a chord in section” (hereafter referred to “minor are shape”) and extends over an axial length L of the combustor  111  and which has (as a space defined therein) on its upstream side a lower gas chamber  121  of a minor are shape and on its downstream side a lower accommodation chamber  131  of a minor are shape substantially equal in size to and in direct communication with the lower gas chamber  121 ; an upper catalyst combustion portion  130  which is outlined in the form of a “cut cylinder with a major arc closed by a chord in section” (hereafter referred to “major arc shape”) and extends over the length L, with its chordal bottom put on a chordal top of the lower catalyst combustion portion  120 , and which has (as a space defined therein) on its upstream side an upper gas chamber  141  of a major arc shape and on its downstream side an upper accommodation chamber  151  of a major arc shape substantially equal in size to and in direct communication with the upper gas chamber  141 ; and a fluid communication portion  160  interposed between the lower gas chamber  121  and the upper gas chamber  141 . The lower gas chamber  121  is in fluid communication with inside of the inlet tube  17  arranged for axial introduction of a mixture of a substitute fuel and a substitute oxidizer. This axial introduction allows for a major fraction of the mixture to smoothly flow straight to the lower gas chamber  131 , at high speeds, inspiring fluids from thereabove via later-described communication holes  162 , having a very minor fraction of the mixture branching through the communication holes  162 . The upper gas chamber  141  also is in fluid communication with the inlet tubes  18  and  19  arranged for axial introduction of an effluent fuel and an effluent oxidizer to be mixed there ( 141 ). This axial introduction allows for major fractions of introduced fluids to smoothly spread over a later-described separation wall  161 , with tendencies to invade through the communications holes  162  into the lower gas chamber  121  and with tendencies to flow toward the upper gas chamber  151 . The lower gas chamber  121  has a small fluid resistance R 12  thereacross, and the upper gas chamber  141  also has a smaller fluid resistance R 14  thereacross. The lower catalyst combustion portion  120  has a smaller heat capacity than the upper catalyst combustion portion  140 . 
     As shown in  FIG. 5  and  FIG. 6 , the fluid communication portion  160  is constituted with a fluid-guiding flat rectangular separation wall  161  which extends for separation between the lower and upper gas chambers  121  and  141 , and has a set of axial arrays { 162 -i: 1≦i≦1}, { 162 -j: I+1≦j≦J}, { 162 -k: J+1≦k≦K}, and { 162 -l; K+1≦l≦L} of fluid communication holes “ 162 -i (1≦i≦I),  162 -j (1+I≦j≦J),  162 -k (J+1≦k≦K), and  162 -l (K+1≦l≦L)” (hereafter collectively referred to “ 162 ”) provided through the separation wall  161 . An arbitrary hole  162  may be circular, elliptic, triangular, rectangular, polygonal, or any form else in section that can provide a necessary fluid resistance r s  (1≦l≦L). A parallel connection of respective fluid resistances {r 1 } of a total of L fluid communication holes  162  represents a fluid resistance R 16  of the fluid communication portion  160 . The separation wall  161  is welded at its upstream end  161   a  to a lower minor-arc part  122   a  of a circular end plate  122  of the catalyst combustor  111 , and vertically flanged at its downstream end  161   b.  The inlet tube  17  is inserted and welded to the minor-arc part  122   a  of the end plate  122 . The inlet tubes  18  and  19  are inserted and welded to an upper major-arc part  122   b  of the end plate  122 . 
     As shown in  FIG. 5  to  FIG. 7 , the lower catalyst combustion portion  120  is constituted with: the lower minor-arc part  122   a  of the circular end plate  122 ; a lower minor-arc part  242  of a later-described cylindrical upstream casing  142  that cooperates with the separation wall  161  and the minor-arc part  122   a  of the end plate  122  to define the lower gas chamber  121 ; a later-described flat heat insulating separator  132  between the lower and upper accommodation chambers  131  and  151 ; a lower minor-arc part  252  of a later-described cylindrical downstream case  152  that cooperates with the heat insulating separator  132  to define the lower accommodation chamber  131 ; and a minor-arc-shape lower substrate  133  which is accommodated to be fitted gas-tight in the lower accommodation chamber  131 , and formed (to be meshed) in a honeycomb shape (in like fashion to  FIG. 8 ) with a set of axially extending catalyst combustion path (or mesh) parts “ 134 -n (1≦n≦N)” (hereafter sometimes collectively referred to “ 134 ”). 
     The upstream casing  142  has at its upstream end an outward flanged part  142   a  fastened by bolts  149  to a peripheral flange  122   c  of the end plate  122 , and at its downstream end an inward projected part  142   b  and an outward flanged part  142   c.    
     The rectangular separation wall  161  is contacted and welded at its left and right sides  161   c  on and to the cylindrical upstream casing  142 . 
     The heat insulating separator  132  is constituted with a flat rectangular plate  132   a  which is brought into abutment at its upstream end  132   a   1  on the flanged downstream end  161   b  of the separation wall  161  and bent downward at its downstream end  132   a   2  for hooking or stopping the substrate  133 , a lower heat insulating layer  132   b  which is formed over a downside of the rectangular plate  132   a,  and an upper heat insulating layer  132   c  which is formed over an upside of the plate  132   a.    
     The downstream case  152  is constituted with: a cylindrical downstream casing  152   a  which is integrally formed at its upstream end with an outward flanged part  152   a   1  fastened by bolts  159  to the flanged part  142   c  of the upstream casing  142  and at its downstream end with an inward projected part  152   a   2  configured to hook or stop the before-mentioned lower substrate  33  and a later-described upper substrate  53  and with a downstream extension  152   a   3  configured to define a cylindrical combustion product (heat medium) outlet space  170  to be common to the lower and upper catalyst combustion portions  120  and  140  and to be connected to a heat medium supply line (LS 3  in  FIG. 1 ); a refractory mortar layer (similar to  52   b  in  FIG. 8 ) lining over an inside of the downstream casing  152   a  and a corresponding region of an end face of the inward projected part  142   b  of the upstream casing  142 ; and a gas-tight filler (similar to  52   c  in  FIG. 8 ) of heat insulating materials filled between the refractory mortar layer and the upper and lower substrates  133  and  153 . 
     The rectangular plate  132   a  of the heat insulating separator  132  is contacted and welded at its left and right sides  132   a   3  on and to the cylindrical casing  152   a  of the downstream case  152 . 
     Again as shown in  FIG. 5  to  FIG. 7 , the upper catalyst combustion portion  140  is constituted with: an upper major-arc part  342  of the cylindrical upstream casing  142  that cooperates with the separation wall  161  and the major-arc part  122   b  of the end plate  122  to define the upper gas chamber  141 ; an upper major-arc part  352  of the cylindrical downstream case  152  that cooperates with the heat insulating separator  132  to define the upper accommodation chamber  151 ; and a major arc shape upper substrate  153  which is accommodated to be fitted gas-tight in the accommodation chamber  151 , and formed (to be meshed) in a honeycomb shape (in like fashion to  FIG. 8 ) with a set of axially extending catalyst combustion path (or mesh) parts “ 154 -m (1≦m≦M (&gt;N or &gt;&gt;N))” (hereafter sometimes collectively referred to “ 154 ”). The upper substrate  153  has a smaller mesh than the lower substrate  133 , or in other words, the meshing of the latter  133  is coarser or rougher than that of the former  153 . 
     The heat capacity of the lower catalyst combustion portion  120  substantially depends on a heat capacity of the lower substrate  133 , and that of the upper catalyst combustion portion  140  substantially depends on a heat capacity of the upper substrate  153 . The lower substrate  133  has a significantly smaller heat capacity than the upper substrate  153 . 
     As schematically shown in  FIG. 2  and  FIG. 4  (or like the case of  FIG. 8 ), an arbitrary catalyst combustion path part  134 -n (1≦n≦N) in the lower substrate  133  is constituted with: a corresponding straight combustion path  135 -n (1≦n≦N) (hereafter sometimes collectively referred to “ 135 ”) axially extending as a fluid path through the substrate  133  and communicating at its upstream end with the lower gas chamber  121  and at its downstream end with the combustion product outlet space  170 ; and a corresponding set  136 -n (1≦n≦N) of films of a catalyst configured as a whole to define the combustion path  135 -n with a corresponding fluid resistance {r n : 1≦n≦N} thereacross. A parallel connection of respective fluid resistances {r n } of a total of N combustion paths  135  (or of N combustion path parts  134 ) represents a fluid resistance R 13  across the lower accommodation chamber  131  (or of the lower substrate  133 ). 
     Likewise, an arbitrary catalyst combustion path part  154 -m (1≦m≦M) in the upper substrate  153  is constituted with: a corresponding straight combustion path  155 -m (1≦m≦M) (hereafter sometimes collectively referred to “ 155 ”) axially extending as a fluid path through the substrate  153  and communicating at its upstream end with the upper gas chamber  141  and at its downstream end with the combustion product outlet space  170 ; and a corresponding set  156 -m (1≦m≦M) of films of the above-noted catalyst configured as a whole to define the combustion path  155 -m with a corresponding fluid resistance {r m : b≦m≦M} thereacross. A parallel connection of respective fluid resistances {r m } of a total of M combustion paths  155  (or of M combustion path parts  154 ) represents a fluid resistance R 15  across the upper accommodation chamber  151  (or of the upper substrate  153 ). 
     The N combustion paths  134  have a greater average sectional area than the M combustion paths  154 , so that an average of the fluid resistances {r n } of the former  134  is smaller than that of the fluid resistances {r m } of the latter  154 . The combustion paths  134  as well as the combustion paths  154  may be identical or different in configuration and/or size, as necessary for facilitation of manufacture or for a particular fluid condition. It is desirable to increase a proportion of effectively used catalyst in a sum of a total of N sets  136  and a total of M sets  156  of films of catalyst, in order for a capacity of catalyst combustion process to be maximized in a regular operation of the fuel cell system  1 . 
     Referring to  FIG. 5 , in the catalyst combustor  111 , the lower catalyst combustion portion  120  has a fluid resistance R L  and thereacross equivalent to a serial connection of the fluid resistance R 12  of the lower gas chamber  121  and the fluid resistance R 13  across the lower accommodation chamber  131  (or of the lower substrate  133 ), such that R L =R 12 +R 13 . The upper catalyst combustion portion  140  has a fluid resistance R U  thereacross equivalent to a serial connection of the fluid resistance R 14  of the upper gas chamber  141  and the fluid resistance R 15  across the upper accommodation chamber  151  (or of the upper substrate  153 ), such that R U =R 14 +R 15 . The fluid resistance R 16  of the fluid communication portion  160  is serially connected to the fluid resistance R 12  of the lower gas chamber  121 . 
     Referring to  FIG. 5  to  FIG. 7  (and  FIG. 1 ), the catalyst combustor  111  is configured to have fixed relationships among internal fluid resistances {R L , R U , R 12 , R 13 (r n ), R 14 , R 15 (r m ), R 16 (r i )} thereof, for example such that:
         R 12 &lt;R 13  or R 12 &lt;&lt;R 13 ,   R 14 &lt;R 15  or R 14 &lt;&lt;R 15 ,   R 12 =R 14 &lt;R 16  or R 12 =R 14 &lt;&lt;R 16 , i.e. (R 12 +R 16 )=(R 14 +R 16 )=R 16 ,   r n &lt;r m  or r n &lt;&lt;r m ,   R L &lt;R U  or R L &lt;&lt;R U , and/or   R L +R 16 =R U  or R L +R 16 =R U ,
 
so that, in a “startup operation” of the fuel cell system  1 ,
   substantially, a warming catalyst combustion between a substitute fuel and a substitute oxidizer is caused to occur simply in the lower catalyst combustion portion  120  (or more specifically in the lower substrate  133 ), i.e. without an influential or significant catalyst combination caused between a fuel and an oxidizer conducted in the substrate  153  of the upper catalyst combustion portion  140 , and that, in a “regular operation” of the fuel cell system  1 ,   a regular catalyst combustion between an effluent fuel and an effluent oxidizer is caused to occur in both the lower catalyst combustion portion  120  (or more specifically in the lower substrate  133 ) and the upper catalyst combustion portion  140  (or more specifically in the upper substrate  153 ), in particular proportionally or evenly, as required.       

     This second embodiment has like advantages to the previous first embodiment, and an additional advantage such that an axial introduction of effluent fuel and effluent oxidizer to a major arc shape upper catalyst gas chamber  141  permits a faster and efficient regular catalyst combustion. 
     The lower catalyst combustion portion ( 120 ) may comprise a lower gas chamber  21  and a lower substrate  133 . Likewise, the upper catalyst combustion portion ( 140 ) may comprise an upper gas chamber  41  and an upper substrate  153 . Then, the catalyst combustor  111  may have a combination ( 142 + 152 ) of a cylindrical upstream casing  142  and a cylindrical downstream case  152  with a flat heat insulating separator  132 , as a cylindrical enclosure ( 142 + 152 ) circumscribed about the upper and lower catalyst combustion portions ( 120  and  140 ). 
     In the first and second embodiments, an arbitrary or particular combustion path  35 ,  55 ,  135 , or  155  may be configured in any form else, as necessary, for facilitation of manufacture or for a particular fluid condition, in particular for a velocity of a gaseous mixture of substitute or effluent fuel and oxidizer to be faster at an upstream end, where fuel concentration is relatively high, than at a downstream end, where fuel concentration is relatively low, in order for the catalyst combustion to be possibly uniform in both startup and regular operations over lengths of combustion paths in the inner or lower and outer or upper substrates  33  or  133  and  53  or  153 , and further for the catalyst warming to be possibly even in the startup operation over lengths of combustion paths in the inner or lower substrate  33  or  133 . 
     To this point,  FIG. 9  and  FIG. 10  show path parts  304  and  404 , respectively, as modification of an arbitrary pair or particular (for example, central or peripheral) pair of neighboring combustion path parts  34 ,  54 ,  134 , or  154 . 
     In the modifications of  FIG. 9 , each path part  304  is constituted with: a corresponding elongate conical combustion path  305  axially extending as a fluid path through a substrate  303 , having a greater sectional area at an upstream end  305   a  thereof than at a downstream end  305   b  thereof; and a corresponding set  306  of films of a catalyst configured as a whole to define the combustion path  305  with a corresponding fluid resistance r n  or r m  thereacross. 
     In the modification of  FIG. 10 , each path part  404  is constituted with: a corresponding tubular combustion path  405  axially extending as a fluid path through a base portion  403   a  of a substrate  403 , having a greater sectional area at an upstream end  405   a  thereof than at a downstream end  405   b  thereof, as it is achieved by provision of a raised part  403   b  of the substrate  403  extending along the combustion path  405 , from the upstream end  405   a  to an axially intermediate point, with a gradually reduced width; and a combination  406  of a corresponding set  406   a  of films of a catalyst formed on a wall of the base portion  403   a  of the substrate  403  and a conformal set  406   b  of films of the catalyst formed on the raised part  403   b  of the substrate  403 , as they ( 406   a,    406   b ) are configured as a whole to define the combustion path  405  with a corresponding fluid resistance r n  or r m  thereacross. 
     In the foregoing embodiments, it should be noted that the control valve CV 1  of the air supply line LS 2  may be controlled to a reduced open or crack-open in the effectively warmed phase in the startup operation of the fuel cell system  1 . In this case, an effluent oxidizer is supplied through the supply line LS 24  during the effectively warmed phase and the sufficiently warmed phase, i.e., over the warmed phase. However, the fluid resistance relationship described causes the effluent oxidizer in the effectively warmed phase to flow like that in the regular operation, without extra control. 
     It will be seen that the shutoff valves SV 1  to SV 3  as well as control valves CV 1  to CV 3  may be controlled for a regular operation of the fuel cell system  1  to cover an entirety of the warmed phase. 
     It is noted that in each embodiment described the fuel source of the catalyst combustor  11  may be different from that of the fuel reformer  5 , and the air source of the catalyst combustor  11  may be different from that of the fuel reformer  5  and/or the fuel cell  2 . The substitute fuel may be any fuel else, if it is gaseous, when supplied in the combustor  11 , and combustible by contact on the catalyst, with sufficient combustion products to provide an adequate amount of effective heat medium. The substitute oxidizer may be any oxidizer else, if it is gaseous, when supplied in the combustor  11 , and active enough in oxidization to promote the catalyst combustion. 
     The contents of Japanese Patent Application no. 2000-41194 are incorporated herein by reference. 
     While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.