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

A catalyst combustor (11) includes an inner catalyst combustion portion (20) connected to a substitute fuel supply line (LS21, 12, 16) and a substitute oxidizer supply line (LS22, 13), an outer catalyst combustion portion (40) connected to an effluent fuel supply line (LS23, 14) and an effluent oxidizer supply line (LS24, 15), and a fluid communication portion (60) connecting the inner catalyst combustion portion (20) and the outer catalyst combustion portion (40) to each other, and has a fixed relationship provided among a fluid resistance (R2) of the inner catalyst combustion portion (20), a fluid resistance (R4) of the outer catalyst combustion portion (40), and a fluid resistance (R6) of the fluid communication portion (60), whereby substantially a warming catalyst combustion is caused to occur simply in the inner catalyst combustion portion (20), and a regular catalyst combustion is caused to occur in the inner catalyst combustion portion (20) and the outer catalyst combustion portion (40).

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.

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. 1shows in block diagram an entirety of a fuel cell system1according to a first embodiment of the invention. The fuel cell system1is constituted with a fuel cell2, a fuel reforming system3, and a control system1awhich 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 system1, 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 system3to the fuel cell2, via a reformed fuel supply line LS1. This supply line LS1has a shutoff valve SV1, which is close in the startup operation of the fuel cell system1and open in the regular operation of the system1. As a gaseous fluid containing oxygen as an oxidizer, fresh air is supplied from an unshown air source to the fuel cell2, via an oxidizer supply line LS2. This supply line L2has a flow or pressure control valve CV1.

In the regular operation of the fuel cell system1, the fuel cell2generates 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 anode1a(fuel electrode), and oxygen in the fresh air is consumed at a cathode1b(oxidizer electrode). The fuel cell2has two effluent lines: an effluent fuel line LE1connected to a gas collecting region of the anode1a,where it receives a gaseous fluid containing hydrogen, as an effluent fuel; and an effluent oxidizer line LE2connected to a gas collecting region of the cathode1b,where it receives a gaseous fluid containing oxygen, as an effluent oxidizer.

The fuel reforming system3includes a vaporizer4, a fuel reformer5, and a catalyst combustion system10.

The vaporizer4has an incorporated heat exchanger (not shown) provided with a fuel injector4aand a water injector4b.The heat exchanger has heating paths which are connected at their inlet ends to a heat medium supply line LS3and at their outlet ends to an effluent fluid line LE3. The fuel injector4areceives a liquid fuel, such as methanol, from an unshown fuel source via a fuel supply line LS4, and injects atomized fuel as a fuel to be vaporized and reformed. The water injector4breceives pure water from an unshown water source via a water supply line LS5, 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 LS6.

The vaporized fuel supply line LS6is connected to the fuel reformer5. Further, an air supply line LS7having a flow or pressure control valve CV2is connected between the before-mentioned air source and the fuel reformer5. The vaporized fuel from the supply line LS6is mixed with air from the supply line LS7and cracked in the fuel reformer5, 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 LS8. This supply line LS8is bifurcate to be connected on one way to the before-mentioned reformed fuel supply line LS1, and on the other way to a reformed fuel bypass line LB that has a shutoff valve SV2, which is open in the startup operation of the fuel cell system1and close in the regular operation of the system1, in an effectively warmed phase in the startup operation, the reformer5produces 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 system10has a catalyst combustor11, a substitute fuel supply line LS21, a substitute oxidizer supply line LS22, an effluent fuel supply line LS23, and an effluent oxidizer supply line LS24.

The substitute fuel supply line LS21is connected to a liquid fuel supply line LS25, which supplies “a liquid substitute fuel” from the before-mentioned fuel source, and has a shutoff valve SV3, which is open in the startup operation of the fuel cell system1and close in the regular operation of the system1. The substitute oxidizer supply line LS22is 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 CV3. Note that the control valves CV1to CV3are controllable to their close positions.

The effluent fuel supply line LS23is simply connected to the effluent fuel line LE1and, 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 system1, as well as in a sufficiently warmed phase substantially corresponding to an interval of the regular operation of the system1. 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 LS24is simply connected to the effluent oxidizer line LE2, so that an effluent oxidizer is supplied therethrough while air is supplied from the supply line LS2. It is noted that the effluent fuel supply line LS23and the effluent oxidizer supply line LS24, as well as the effluent fuel line LE1and the effluent oxidizer line LE2, have no valves to be actuated for changeover between the startup operation and the regular operation of the fuel cell system1.

The catalyst combustor11is provided with a substitute fluid connecting piping unit11aand an effluent fluid connection piping unit11b.In the piping units11aand11b,as shown inFIG. 2, the four supply lines LS21, LS22, LS23, and LS24have their fluid outlet pipes: an outlet pipe12provided at a downstream end of the supply line LS21for supplying a substitute fuel in the startup operation of the fuel cell system1; an outlet pipe13provided at a downstream end of the supply line LS22for supplying a gaseous substitute oxidizer in the startup operation; an outlet pipe14provided at a downstream end of the supply line LS23for supplying a gaseous effluent fuel in the above-noted warmed phase; and an outlet pipe15provided at a downstream end of the supply line LS24for supplying a gaseous effluent oxidizer in the regular operation of the system1. It is noted that both connection piping units11aand11bhave no valves to be actuated for changeover between the startup operation and the regular operation of the fuel cell system1.

On the other hand, the catalyst combustor11has three fluid inlet tubes welded thereto: an inlet tube17simply connected to the outlet pipe13; an inlet tube18simply connected to the outlet pipe14for introduction of the effluent fuel; and an inlet tube19simply connected to the outlet pipe15for introduction of the effluent oxidizer.

The outlet pipe12has at its downstream end a fuel injector16joined to the inlet tube17, by inserting its atomizing tip16ainto the tube17. While the supply line LS22supplies the gaseous substitute oxidizer to be simply let through the outlet pipe13into the inlet tube17, a liquid substitute fuel supplied from the supply line LS21is let through the outlet pipe12and atomized at the tip16aof the fuel injector16using 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 tube17, thereby having a gaseous mixture therebetween supplied to the inlet tube17. It should be noted that this inlet tube17is an integral part of the catalyst combustor11to which a gaseous substitute fuel is supplied by a fluid supply line (LS21with16) constituted with the supply line LS21having the outlet pipe12provided with the fuel injector16.

As shown inFIG. 2toFIG. 4andFIG. 8, the catalyst combuster11, outline in a cylindrical form, is made up by: a cylindrical inner catalyst combustion portion20which extends over an axial length L of the combustor11and has (as a space defined therein) on its upstream side a cylindrical inner gas chamber21and on its downsteream side a cylindrical inner accommodation chamber31substantially equal in diameter to an in direct communication with the inner gas chamber21: a cylindrical (or more specifically, annular) outer catalyst combustion portion40which also extends over the length L, coaxially with the inner catalyst combustion portion20, and has (as a space defined therein) on its upstream side a cylindrical (or annular) outer gas chamber41and on its downstream side a cylindrical (or annular) outer accommodation chamber51substantially equal in inside and outside diameters to and in direct communication with the outer gas chamber41; and a fluid communication portion60interposed between the inner gas chamber21and the outer gas chamber41. The inner gas chamber21is in fluid communication with inside of the inlet tube17arranged 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 chamber31, at high speeds, inspiring fluids from therearound via later-described communication holes62, having a very minor fraction of the mixture branching outside. The outer gas chamber41is in fluid communication with the inlet tubes18and19arranged 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 wall61, with enhanced tendencies to invade through the communications holes62into the inner gas chamber21, and with suppressed tendencies to flow toward the outer gas chamber51. The inner gas chamber21has a small fluid resistance R2thereacross, and the outer gas chamber41also has a small fluid resistance R4thereacross. The inner catalyst combustion portion20has a smaller heat capacity than the outer catalyst combustion portion40. It should be noted that a catalyst in concern promotes a significant catalyst combustion above a critical temperature.

As shown inFIG. 2andFIG. 3, the fluid communication portion60is constituted with a fluid-containing cylindrical separation wall61which extends for separation between the inner and outer gas chambers21and41, 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 wall61. An arbitrary hole62may 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 holes62represents a fluid resistance R6of the fluid communication portion60. The separation wall61is welded at its upstream end61ato a circular central part22aof a circular end plate22of the catalyst combustor11, and radially outwardly flanged at its downstream end61b.The inlet tube17is inserted and welded to the central part22aof the end plate22.

As shown inFIG. 2toFIG. 3, the inner catalyst combustion portion20is constituted with: the circular end plate22of which the central part22acooperates with the separation wall61to define the inner gas chamber21; a cylindrical heat insulating separator32defining the inner accommodation chamber31; and a cylindrical substrate33which is accommodated to be fitted gas-tight in the accommodation chamber31, 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 separator32is constituted with a cylindrical inner casing32awhich is brought into abutment at its upstream end32a1on the flanged downstream end61bof the separation wall61and inwardly bent at its downstream end32a2for hooking or stopping the substrate33, an inner heat insulating layer32bwhich is formed over an inside of the cylindrical casing32a,and an outer heat insulating layer32cwhich is formed over an outside of the inner casing32a.

Again as shown inFIG. 2toFIG. 4, the outer catalyst combustion portion40is constituted with: a cylindrical upstream outer casing42cooperating with the separation wall61and the annular part22bof the end plate22to define the outer gas chamber41; a cylindrical outer case52cooperating with the heat insulating separator32to define the outer accommodation chamber51; and a cylindrical (or annular) substrate53which is accommodated to be fitted gas-tight in the accommodation chamber51, 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 (>N or >>N),” (hereafter sometimes collectively referred to “54”). The substrate53has a smaller mesh than the substrate33, or in other words, the meshing of the latter33is coarser or rougher than that of the former53. The upstream outer casing42has at its upstream end an outward flanged part42afastened by bolts49to a peripheral flange22cof the end plate22, and at its downstream end an inward projected part42band an outward flanged part42c.It should be noted that the heat capacity of the inner catalyst combustion portion20substantially depends on a heat capacity of the substrate33, and that of the outer catalyst combustion portion40substantially depends on a heat capacity of the substrate53. It also is noted that the substrate33has a significantly smaller heat capacity than the substrate53.

As best shown inFIG. 8, the outer case52is constituted with: a cylindrical downstream outer casing52awhich is integrally formed at its upstream end with an outward flanged part52a1fastened by bolts59(FIG. 2) to the outward flanged part42cof the upstream outer casing42and at its downstream end with an inward projected part52a2configured to hook or stop the substrate53and to support a cross member58(FIG. 2) for stopping the heat insulating separator32and with a downstream extension52a3configured to define a cylindrical combustion product (heat medium) outlet space70to be common to the inner and outer catalyst combustion portions20and40(FIG. 2) and to be connected to the heat medium supply line LS3(FIG. 1); a refractory mortar layer52blining over an inside of the downstream outer casing52aand a corresponding region of an end face of the inward projected part42bof the upstream outer casing42; and a gas-tight filler52cof heat insulating materials filled between the refractory mortar layer52band the substrate53.

As illustrated inFIG. 8, an arbitrary catalyst combustion path part54-m (1≦m≦M) in the substrate53is constituted with: a corresponding straight combustion path55-m (1≦m≦M) (hereafter sometimes collectively referred to “55”) axially extending as a fluid path through the substrate53and communicating at its upstream end with the outer gas chamber41and at its downstream end with the combustion product outlet space70; and a corresponding set56-m (1≦m≦M) of films of a catalyst configured as a whole to define the combustion path55-m with a corresponding fluid resistance {rm: 1≦m≦M} thereacross. A parallel connection of respective fluid resistances {rm} of a total of M combustion paths55(or of M combustion path parts54) represents a fluid resistance R5across the outer accommodation chamber51(or of the substrate53).

Likewise, as schematically shown inFIG. 2andFIG. 4, an arbitrary catalyst combustion path part34-n (1≦n≦N) in the substrate33is constituted with: a corresponding straight combustion path35-n (1≦n≦N) (hereafter sometimes collectively referred to “35”) axially extending as a fluid path through the substrate33and communicating at its upstream end with the inner gas chamber21and at its downstream end with the combustion product outlet space70; and a corresponding set36-n (1≦n≦N) of films of the above-noted catalyst configured as a whole to define the combustion path35-n with a corresponding fluid resistance {rn: 1≦n≦N} thereacross. A parallel connection of respective fluid resistances {rn} of a total of N combustion paths35(or of N combustion path parts34) represents a fluid resistance R3across the inner accommodation chamber31(or of the substrate33). The N combustion paths34have a greater average sectional area than the M combustion paths54, so that an average of the fluid resistances {rn} of the former34is smaller than that of the fluid resistances {rm} of the latter54. It is noted that the combustion paths34as well as the combustion paths54may 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 sets36and a total of M sets56of films of catalyst, in order for a capacity of catalyst combustion process to be maximized in the regular operation of the fuel cell system1.

Referring toFIG. 2, in the catalyst combustor11, the inner catalyst combustion portion20has a fluid resistance R1thereacross equivalent to a serial connection of the fluid resistance R2of the inner gas chamber21and the fluid resistance R3across the inner accommodation chamber31(or of the substrate33), such that R1=R2+R3. The outer catalyst combustion portion40has a fluid resistance R6thereacross equivalent to a serial connection of the fluid resistance R4of the outer gas chamber41and the fluid resistance R5across the outer accommodation chamber51(or of the substrate53), such that Ro=R4+R5. The fluid resistance R6of the fluid communication portion60is serially connected to the fluid resistance R2or the inner gas chamber21.

Referring toFIG. 1toFIG. 4, the catalyst combustor11is configured to have fixed relationships among internal fluid resistances {R1, R0, R2, R3(rn), R4, R5(rm), R6(rt)} thereof, for example such that:R2<R3or R2<<R3,R4<R5or R4<<R5,R2∝R4<R6or R2∝R4<<R6, i.e. (R2+R6)∝(R4+R6)∝R6,rn<rmor rn<<rm,Ri<Roor Ri<<Ro, and/orRi+R6∝Roor Ri+R6=Ro,
so that, in the “startup operation” of the fuel cell system1,substantially, a warming catalyst combustion between the substitute fuel and the substitute oxidizer is caused to occur simply in the inner catalyst combustion portion20(or more specifically in the substrate33) 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 substrate53of the outer catalyst combustion portion40which is high of heat capacity, and
that, in the “regular operation” of the fuel cell system1,a regular catalyst combustion between the effluent fuel and the effluent oxidizer is caused to occur in both the inner catalyst combustion portion20(or more specifically in the substrate33) and the outer catalyst combustion portion40(or more specifically in the substrate53), in particular proportionally or evenly, as required.

In the warming phase of the startup operation in which the shutoff valve SV1is close but the shutoff valve SV3is open and the control valve CV3is in its open position whereas the control valves CV1and CV2are in their close or crack-open positions as necessary and the shutoff valve SV2is to be opened when necessary for bypassing an amount of reformed fuel, the fuel injector16injects and atomized substitute fuel into a flow of a supplied substitute oxidizer in the inlet tube17, whereby a gaseous mixture therebetween is introduced into the inner gas chamber21, where it flows downstream along the separation wall61, and enters the substrate33in the inner accommodation chamber31with a priority, where it contacts the catalyst36, whereby its warmer catalyst combustion is promoted, generating gaseous combustion products, which flow out of the substrate33and enter the outlet space70, wherefrom they are supplied as a heat medium via the supply line LS3to the heating side of the heat exchanger in the vaporizer4, and discharged therefrom via the effluent line LE3. In due course in the warming phase, the vaporizer4may start generating a vaporized fuel to be supplied via the supply line LS6to the fuel reformer5. 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 catalyst36,56.

Although, when the gaseous mixture passes the inner gas chamber21, a minor fraction thereof branches via the communication holes62of the fluid communication portion60into the outer gas chamber41and enters the substrate53in the outer accommodation chamber51, the branching fraction is maintained very small by relationships (for example Ri<Roor Ri<<Ro) among fluid resistances such as the fluid resistance R6across the separation wall61and the fluid resistance R5of the substrate53which has fine meshes54. As the substrate33which has a low heat capacity is accommodated in the heat insulating separator32which suppresses heat dissipation from the inner accommodation chamber31, the catalyst33can be warmed in a short while. The branching fraction of gaseous mixture gradually starts a preparatory warming catalyst combustion in the substrate53.

In the effectively warmed phase of the startup operation in which the shutoff valve SV1is kept close and the shutoff valve SV3is still open while the shutoff valve SV2is opened and the control valves CV2and CV3are in their controlled open positions whereas the control valve CV1may 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 reformer5, where it is reformed, and a significant amount of gaseous reformed fuel is conducted, via the supply line LS8and the bypass line LB, into the effluent fuel supply line LS23, wherefrom it is supplied into the outer gas chamber41, 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 chamber21and the minor fraction is branched to the outer gas chamber41), thus entering together with the minor fraction into the substrate53, where they contact the catalyst56, whereby their warming catalyst combustion is promoted, generating a gradually increasing amount of gaseous combustion products; and those streams which branch through the communication holes62of the fluid communication portion60into the inner gas chamber21, joining the gaseous mixture therein to enter the substrate33, where they contact the catalyst36, 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 substrates53and33in the outlet space70, wherefrom they are supplied as an increased amount of heat medium to the vaporizer4. If the control valve CV1is controlled to the crack-open position, the control valve CV3may be set to an initial open position or controlled to a slightly wider open position.

In the regular operation, the shutoff valve SV3is closed to stop the supply of substitute fuel and the control valve CV3is set to its close position to control the supply of substitute oxidizer to a zero flow, whereas the control valve CV2is set to its regular open position to supply necessary air via the supply line LS7to the fuel reformer5, the shutoff valve SV2is closed to close the bypass line LB, the shutoff valve SV1is opened to supply a sufficient reformed fuel via the supply line LS1to the fuel cell2, and the control valve CV1is set to its regular open position to supply sufficient air to the fuel cell2, so that an effluent fuel is supplied from the effluent line LE1, via the supply line LS23and the outlet pipe14, to the inlet tube18and hence to the outer gas chamber41of the catalyst combustor11, and an effluent oxidizer is supplied from the effluent line LE2, via the supply line LS24and the outlet pipe15, to the inlet tube19and hence to the outer gas chamber41of the catalyst combustor11, where it is mixed with the effluent fuel, forming a gaseous mixture flowing downstream along the separation wall61. The mixture is substantially uniformly distributed about the fluid communication portion60and substantially evenly divided into: those streams which flow inside the outer gas chamber41, thus entering the substrate53, where they contact the catalyst56, whereby their regular catalyst combustion is promoted, generating a necessary amount of gaseous combustion products; and those streams which branch through the communication holes62of the fluid communication portion60into the inner gas chamber21, where they flow downstream to enter the substrate33, where they contact the catalyst36, 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 substrates53and33in the outlet space70, wherefrom they are supplied as a required amount of heat medium to the vaporizer4. The even division of the mixture is effected for the catalyst36,56to have a maximized processing capacity, by provision of balanced relationships (for example Ri+R6=Roor Ri+R6=Ro) among fluid resistances including the fluid resistances {r1} of the communication holes62, the fluid resistances {rn} of the combustion paths35, and the fluid resistances {rm} of the combustion paths55.

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 (within33) with a restricted heat capacity;(2) a still shortened warming in the startup operation due to the provision of heat insulating layers32b,32ckeeping combustion heat in a substrate33from escaping outside;(3) a yet shortened warming in the startup operation due to a major fraction of a gaseous mixture flowing into the substrates33which is low of heat capacity;(4) an actuator-less control allowed simply by combination of communication holes62and substrates33,53different 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 substrate33irrespective of the provision of communication holes62, by relationships (for example rn<rmor rn<<rm) of fluid resistances (such as rnand rm); and(6) an actuator-less control in a regular operation allowed for a process capacity of catalyst36,56to 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 Ri+Rb=Ro+R6=Ro) of fluid resistances (such as rf, rn, rm).

In the embodiment described, the inner and outer catalyst combustion portions20and40are 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. 5toFIG. 7show a catalyst combustion system110in a fuel system1according to a second embodiment of the invention.

As shown inFIG. 5, the catalyst combustion system110has a catalyst combustor111, a substitute fuel supply line LS21, a substitute oxidizer supply line LS22, an effluent fuel supply line LS23, and an effluent oxidizer supply line LS24. The supply lines LS21, LS22, LS23, and LS24have their fluid outlet pipes12,13,14, and15. The catalyst combustor111has three fluid inlet tubes17,18, and19welded thereto. The outlet pipe12has at its downstream end a fuel injector16joined to the inlet tube17, by inserting its atomizing tip16ainto the tube17.

As shown inFIG. 5toFIG. 7, the catalyst combustor111, cylindrical in outline, is made up by: a lower catalyst combustion portion120which 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 combustor111and which has (as a space defined therein) on its upstream side a lower gas chamber121of a minor are shape and on its downstream side a lower accommodation chamber131of a minor are shape substantially equal in size to and in direct communication with the lower gas chamber121; an upper catalyst combustion portion130which 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 portion120, and which has (as a space defined therein) on its upstream side an upper gas chamber141of a major arc shape and on its downstream side an upper accommodation chamber151of a major arc shape substantially equal in size to and in direct communication with the upper gas chamber141; and a fluid communication portion160interposed between the lower gas chamber121and the upper gas chamber141. The lower gas chamber121is in fluid communication with inside of the inlet tube17arranged 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 chamber131, at high speeds, inspiring fluids from thereabove via later-described communication holes162, having a very minor fraction of the mixture branching through the communication holes162. The upper gas chamber141also is in fluid communication with the inlet tubes18and19arranged 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 wall161, with tendencies to invade through the communications holes162into the lower gas chamber121and with tendencies to flow toward the upper gas chamber151. The lower gas chamber121has a small fluid resistance R12thereacross, and the upper gas chamber141also has a smaller fluid resistance R14thereacross. The lower catalyst combustion portion120has a smaller heat capacity than the upper catalyst combustion portion140.

As shown inFIG. 5andFIG. 6, the fluid communication portion160is constituted with a fluid-guiding flat rectangular separation wall161which extends for separation between the lower and upper gas chambers121and141, 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), and162-l (K+1≦l≦L)” (hereafter collectively referred to “162”) provided through the separation wall161. An arbitrary hole162may be circular, elliptic, triangular, rectangular, polygonal, or any form else in section that can provide a necessary fluid resistance rs(1≦l≦L). A parallel connection of respective fluid resistances {r1} of a total of L fluid communication holes162represents a fluid resistance R16of the fluid communication portion160. The separation wall161is welded at its upstream end161ato a lower minor-arc part122aof a circular end plate122of the catalyst combustor111, and vertically flanged at its downstream end161b.The inlet tube17is inserted and welded to the minor-arc part122aof the end plate122. The inlet tubes18and19are inserted and welded to an upper major-arc part122bof the end plate122.

As shown inFIG. 5toFIG. 7, the lower catalyst combustion portion120is constituted with: the lower minor-arc part122aof the circular end plate122; a lower minor-arc part242of a later-described cylindrical upstream casing142that cooperates with the separation wall161and the minor-arc part122aof the end plate122to define the lower gas chamber121; a later-described flat heat insulating separator132between the lower and upper accommodation chambers131and151; a lower minor-arc part252of a later-described cylindrical downstream case152that cooperates with the heat insulating separator132to define the lower accommodation chamber131; and a minor-arc-shape lower substrate133which is accommodated to be fitted gas-tight in the lower accommodation chamber131, and formed (to be meshed) in a honeycomb shape (in like fashion toFIG. 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 casing142has at its upstream end an outward flanged part142afastened by bolts149to a peripheral flange122cof the end plate122, and at its downstream end an inward projected part142band an outward flanged part142c.

The rectangular separation wall161is contacted and welded at its left and right sides161con and to the cylindrical upstream casing142.

The heat insulating separator132is constituted with a flat rectangular plate132awhich is brought into abutment at its upstream end132a1on the flanged downstream end161bof the separation wall161and bent downward at its downstream end132a2for hooking or stopping the substrate133, a lower heat insulating layer132bwhich is formed over a downside of the rectangular plate132a,and an upper heat insulating layer132cwhich is formed over an upside of the plate132a.

The downstream case152is constituted with: a cylindrical downstream casing152awhich is integrally formed at its upstream end with an outward flanged part152a1fastened by bolts159to the flanged part142cof the upstream casing142and at its downstream end with an inward projected part152a2configured to hook or stop the before-mentioned lower substrate33and a later-described upper substrate53and with a downstream extension152a3configured to define a cylindrical combustion product (heat medium) outlet space170to be common to the lower and upper catalyst combustion portions120and140and to be connected to a heat medium supply line (LS3inFIG. 1); a refractory mortar layer (similar to52binFIG. 8) lining over an inside of the downstream casing152aand a corresponding region of an end face of the inward projected part142bof the upstream casing142; and a gas-tight filler (similar to52cinFIG. 8) of heat insulating materials filled between the refractory mortar layer and the upper and lower substrates133and153.

The rectangular plate132aof the heat insulating separator132is contacted and welded at its left and right sides132a3on and to the cylindrical casing152aof the downstream case152.

Again as shown inFIG. 5toFIG. 7, the upper catalyst combustion portion140is constituted with: an upper major-arc part342of the cylindrical upstream casing142that cooperates with the separation wall161and the major-arc part122bof the end plate122to define the upper gas chamber141; an upper major-arc part352of the cylindrical downstream case152that cooperates with the heat insulating separator132to define the upper accommodation chamber151; and a major arc shape upper substrate153which is accommodated to be fitted gas-tight in the accommodation chamber151, and formed (to be meshed) in a honeycomb shape (in like fashion toFIG. 8) with a set of axially extending catalyst combustion path (or mesh) parts “154-m (1≦m≦M (>N or >>N))” (hereafter sometimes collectively referred to “154”). The upper substrate153has a smaller mesh than the lower substrate133, or in other words, the meshing of the latter133is coarser or rougher than that of the former153.

The heat capacity of the lower catalyst combustion portion120substantially depends on a heat capacity of the lower substrate133, and that of the upper catalyst combustion portion140substantially depends on a heat capacity of the upper substrate153. The lower substrate133has a significantly smaller heat capacity than the upper substrate153.

As schematically shown inFIG. 2andFIG. 4(or like the case ofFIG. 8), an arbitrary catalyst combustion path part134-n (1≦n≦N) in the lower substrate133is constituted with: a corresponding straight combustion path135-n (1≦n≦N) (hereafter sometimes collectively referred to “135”) axially extending as a fluid path through the substrate133and communicating at its upstream end with the lower gas chamber121and at its downstream end with the combustion product outlet space170; and a corresponding set136-n (1≦n≦N) of films of a catalyst configured as a whole to define the combustion path135-n with a corresponding fluid resistance {rn: 1≦n≦N} thereacross. A parallel connection of respective fluid resistances {rn} of a total of N combustion paths135(or of N combustion path parts134) represents a fluid resistance R13across the lower accommodation chamber131(or of the lower substrate133).

Likewise, an arbitrary catalyst combustion path part154-m (1≦m≦M) in the upper substrate153is constituted with: a corresponding straight combustion path155-m (1≦m≦M) (hereafter sometimes collectively referred to “155”) axially extending as a fluid path through the substrate153and communicating at its upstream end with the upper gas chamber141and at its downstream end with the combustion product outlet space170; and a corresponding set156-m (1≦m≦M) of films of the above-noted catalyst configured as a whole to define the combustion path155-m with a corresponding fluid resistance {rm: b≦m≦M} thereacross. A parallel connection of respective fluid resistances {rm} of a total of M combustion paths155(or of M combustion path parts154) represents a fluid resistance R15across the upper accommodation chamber151(or of the upper substrate153).

The N combustion paths134have a greater average sectional area than the M combustion paths154, so that an average of the fluid resistances {rn} of the former134is smaller than that of the fluid resistances {rm} of the latter154. The combustion paths134as well as the combustion paths154may 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 sets136and a total of M sets156of films of catalyst, in order for a capacity of catalyst combustion process to be maximized in a regular operation of the fuel cell system1.

Referring toFIG. 5, in the catalyst combustor111, the lower catalyst combustion portion120has a fluid resistance RLand thereacross equivalent to a serial connection of the fluid resistance R12of the lower gas chamber121and the fluid resistance R13across the lower accommodation chamber131(or of the lower substrate133), such that RL=R12+R13. The upper catalyst combustion portion140has a fluid resistance RUthereacross equivalent to a serial connection of the fluid resistance R14of the upper gas chamber141and the fluid resistance R15across the upper accommodation chamber151(or of the upper substrate153), such that RU=R14+R15. The fluid resistance R16of the fluid communication portion160is serially connected to the fluid resistance R12of the lower gas chamber121.

Referring toFIG. 5toFIG. 7(andFIG. 1), the catalyst combustor111is configured to have fixed relationships among internal fluid resistances {RL, RU, R12, R13(rn), R14, R15(rm), R16(ri)} thereof, for example such that:R12<R13or R12<<R13,R14<R15or R14<<R15,R12=R14<R16or R12=R14<<R16, i.e. (R12+R16)=(R14+R16)=R16,rn<rmor rn<<rm,RL<RUor RL<<RU, and/orRL+R16=RUor RL+R16=RU,
so that, in a “startup operation” of the fuel cell system1,substantially, a warming catalyst combustion between a substitute fuel and a substitute oxidizer is caused to occur simply in the lower catalyst combustion portion120(or more specifically in the lower substrate133), i.e. without an influential or significant catalyst combination caused between a fuel and an oxidizer conducted in the substrate153of the upper catalyst combustion portion140, and that, in a “regular operation” of the fuel cell system1,a regular catalyst combustion between an effluent fuel and an effluent oxidizer is caused to occur in both the lower catalyst combustion portion120(or more specifically in the lower substrate133) and the upper catalyst combustion portion140(or more specifically in the upper substrate153), 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 chamber141permits a faster and efficient regular catalyst combustion.

The lower catalyst combustion portion (120) may comprise a lower gas chamber21and a lower substrate133. Likewise, the upper catalyst combustion portion (140) may comprise an upper gas chamber41and an upper substrate153. Then, the catalyst combustor111may have a combination (142+152) of a cylindrical upstream casing142and a cylindrical downstream case152with a flat heat insulating separator132, as a cylindrical enclosure (142+152) circumscribed about the upper and lower catalyst combustion portions (120and140).

In the first and second embodiments, an arbitrary or particular combustion path35,55,135, or155may 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 substrates33or133and53or153, and further for the catalyst warming to be possibly even in the startup operation over lengths of combustion paths in the inner or lower substrate33or133.

To this point,FIG. 9andFIG. 10show path parts304and404, respectively, as modification of an arbitrary pair or particular (for example, central or peripheral) pair of neighboring combustion path parts34,54,134, or154.

In the modifications ofFIG. 9, each path part304is constituted with: a corresponding elongate conical combustion path305axially extending as a fluid path through a substrate303, having a greater sectional area at an upstream end305athereof than at a downstream end305bthereof; and a corresponding set306of films of a catalyst configured as a whole to define the combustion path305with a corresponding fluid resistance rnor rmthereacross.

In the modification ofFIG. 10, each path part404is constituted with: a corresponding tubular combustion path405axially extending as a fluid path through a base portion403aof a substrate403, having a greater sectional area at an upstream end405athereof than at a downstream end405bthereof, as it is achieved by provision of a raised part403bof the substrate403extending along the combustion path405, from the upstream end405ato an axially intermediate point, with a gradually reduced width; and a combination406of a corresponding set406aof films of a catalyst formed on a wall of the base portion403aof the substrate403and a conformal set406bof films of the catalyst formed on the raised part403bof the substrate403, as they (406a,406b) are configured as a whole to define the combustion path405with a corresponding fluid resistance rnor rmthereacross.

In the foregoing embodiments, it should be noted that the control valve CV1of the air supply line LS2may be controlled to a reduced open or crack-open in the effectively warmed phase in the startup operation of the fuel cell system1. In this case, an effluent oxidizer is supplied through the supply line LS24during 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 SV1to SV3as well as control valves CV1to CV3may be controlled for a regular operation of the fuel cell system1to cover an entirety of the warmed phase.

It is noted that in each embodiment described the fuel source of the catalyst combustor11may be different from that of the fuel reformer5, and the air source of the catalyst combustor11may be different from that of the fuel reformer5and/or the fuel cell2. The substitute fuel may be any fuel else, if it is gaseous, when supplied in the combustor11, 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 combustor11, and active enough in oxidization to promote the catalyst combustion.

The contents of Japanese Patent Application no. 2000-41194 are incorporated herein by reference.