A desulfurizer includes a filled chamber having a raw fuel passage through which a raw fuel flows, the filled chamber being filled with a desulfurizing agent, a supply chamber disposed upstream of the filled chamber, for uniformly supplying the raw fuel to the raw fuel passage, and a discharge chamber disposed downstream of the filled chamber, for uniformly discharging the raw fuel from the raw fuel passage. The raw fuel passage has first and second reversers for reversing the direction in which the raw fuel flows. The raw fuel passage has a cross-sectional area which is smaller in a downstream portion thereof than in an upstream portion thereof.

RELATED APPLICATIONS

This application is a 35 U.S.C. 371 national stage filing of International Application No. PCT/JP2009/0064476, filed Aug. 12, 2009, which claims priority to Japanese Patent Application No. 2008-229678 filed on Sep. 8, 2008 in Japan. The contents of the aforementioned applications are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a desulfurizer for removing sulfur component from a raw fuel.

BACKGROUND ART

Typically, a solid oxide fuel cell (SOFC) employs a solid electrolyte comprising ion-conductive solid oxide such as stabilized zirconia, for example. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly. The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, normally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.

As the fuel gas supplied to the fuel cell, normally, a hydrogen gas generated from hydrocarbon raw material by a reformer is used. In general, in the reformer, a reformed raw material gas is obtained from hydrocarbon raw material of a fossil fuel or the like, such as methane or LNG, and the reformed raw material gas undergoes steam reforming, partial oxidation reforming, or autothermal reforming to produce a reformed gas (fuel gas). For this reason, before the raw material is reformed, sulfur component needs to be removed from the raw material by a desulfurizer.

For example, as shown inFIG. 16of the accompanying drawings, a desulfurizer for use with a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2008-117652 comprises a hollow cylindrical vessel1ahaving a gas flow passage SP through which a fuel gas flows, partition plates2adisposed as wall members and partition members in the gas flow passage SP, and a desulfurizing agent3awhich fills the gas flow passage SP.

Since the gas flow passage SP is segmented into a plurality of passageways by the partition plates2a, the fuel gas which flows in the gas flow passage SP is also divided into a plurality of fuel gas streams and hence, uneven flow distribution of the fuel gas is prevented in the gas flow passage SP.

Although not a desulfurizer, Japanese Laid-Open Patent Publication No. 2006-273635 discloses a reformer, which is similar in construction to the desulfurizer. As shown inFIG. 17of the accompanying drawings, the disclosed reformer has a lower plate1band an upper plate2b. The lower plate1bsupports thereon a plurality of upwardly extending partition plates3b, and the upper plate2bsupports thereon a plurality of downwardly extending partitions4b, thereby defining a fluid passage7bthat is serpentine up and down and extends from a fuel inlet5bto a fuel outlet6b.

However, the desulfurizer disclosed in Japanese Laid-Open Patent Publication No. 2008-117652 fails to meet minimum flow velocity requirements and is unable to prevent uneven flow distribution of the fuel gas, in a wide operating range from a partial load operation mode to a rated operation mode. In addition, the disclosed desulfurizer cannot absorb pulsation flows of raw fuel and hence cannot supply a desulfurized raw fuel stably. Further, if the gas flow passage SP is increased in length for a better desulfurizing capability, then the desulfurizer itself is increased in size (length) and cannot be made compact.

If the reformer disclosed in Japanese Laid-Open Patent Publication No. 2006-273635 is used as a desulfurizer, then it also finds it difficult to meet minimum flow velocity requirements and tends to fail to prevent uneven flow distribution of the fuel gas, in a wide operating range. In addition, the disclosed reformer cannot absorb pulsation flows of raw fuel and hence cannot supply a desulfurized raw fuel stably.

SUMMARY OF INVENTION

It is an object of the present invention to provide a desulfurizer which is simple in structure and small in size, is capable of maintaining a desired desulfurizing efficiency and desulfurizing capability in a wide operating range, is highly durable, and is capable of supplying a desulfurized raw fuel stably.

The present invention is concerned with a desulfurizer for removing sulfur component from a raw fuel. The desulfurizer includes a filled chamber having a raw fuel passage through which the raw fuel flows, and the filled chamber being filled with a desulfurizing agent, a supply chamber disposed upstream of the filled chamber, for uniformly supplying the raw fuel to the raw fuel passage, and a discharge chamber disposed downstream of the filled chamber, for uniformly discharging the raw fuel from the raw fuel passage. The raw fuel passage has at least one reverser for reversing the direction in which the raw fuel flows. The raw fuel passage has a cross-sectional area which is smaller in a downstream portion thereof than in an upstream portion thereof.

With the above arrangement of the present invention, since the raw fuel that is supplied to the desulfurizer is temporarily stored in the supply chamber, the raw fuel is supplied uniformly to the entire area of the raw fuel passage. The desulfurized raw fuel flows from the filled chamber and is temporarily stored in the discharge chamber. Therefore, the desulfurized raw fuel is discharged uniformly from the entire area of the raw fuel passage. Consequently, the entire area of the desulfurizing agent can effectively be utilized, resulting in an improved desulfurizing efficiency.

Further, the raw fuel passage has the reversers for reversing the direction in which the raw fuel flows. Therefore, the overall length of the desulfurizer is reduced, whereas the raw fuel passage is effectively elongated. Since the raw fuel and the desulfurizing agent are held in contact with each other over a long period of time, the desulfurizer has a high desulfurizing capability.

Furthermore, the cross-sectional area of the raw fuel passage is smaller in its downstream portion than in its upstream portion. Thus, in a partial load operation mode, the raw fuel flows through the region of the raw fuel passage which has a smaller cross-sectional area at a minimum flow velocity. In a rated operation mode, the raw fuel flows through the entire raw fuel passage at a minimum flow velocity. Accordingly, in a wide operating range, the raw fuel passage is effective to prevent the raw fuel from unevenly flowing, and is also effective to utilize the desulfurizing agent in its entirety over a long period of time. The desulfurizer is therefore highly durable and can be serviced for maintenance at increased time intervals.

The desulfurizer can have a function as a pressure regulation chamber (buffer tank). Therefore, the desulfurizer can absorb raw fuel pulsation flows and can supply a desulfurized raw fuel stably, thereby allowing a fuel cell combined therewith to operate stably.

DESCRIPTION OF EMBODIMENTS

As shown inFIG. 1, a fuel cell system10which incorporates a desulfurizer according to a first embodiment of the present invention is used in various applications, e.g., used as a stationary fuel cell system, a vehicle-mounted fuel cell system, or the like.

The fuel cell system10comprises a fuel cell module (SOFC module)12for generating electrical energy in power generation by electrochemical reactions of a fuel gas (hydrogen gas) and an oxygen-containing gas (air), a combustor13(e.g., torch heater) for raising the temperature of the fuel cell module12, a desulfurizer14according to the first embodiment for removing sulfur component from a raw fuel (e.g., city gas) chiefly containing hydrocarbon to produce the fuel gas (more specifically, desulfurized raw fuel), a fuel gas supply apparatus (including a fuel gas pump)16for supplying the desulfurized raw fuel to the fuel cell module12, an oxygen-containing gas supply apparatus18(including an air pump) for supplying the oxygen-containing gas to the fuel cell module12, a water supply apparatus (including a water pump)20for supplying water to the fuel cell module12, a power converter22for converting the direct current electrical energy generated in the fuel cell module12to electrical energy according to the requirements specification, and a control device24for controlling the amount of electrical energy generated in the fuel cell module12.

The fuel cell module12includes a fuel cell stack34formed by stacking a plurality of solid oxide fuel cells32in a vertical direction. The fuel cells32are formed by stacking electrolyte electrode assemblies and separators. Though not shown, each of the electrolyte electrode assemblies includes a cathode, an anode, and a solid electrolyte (solid oxide) interposed between the cathode and the anode. For example, the electrolyte is made of ion-conductive solid oxide such as stabilized zirconia (seeFIG. 2).

At an upper end of the fuel cell stack34in the stacking direction, a heat exchanger36for heating the oxygen-containing gas before the oxygen-containing gas is supplied to the fuel cell stack34, an evaporator38for evaporating water to produce a mixed fuel of a desulfurized raw fuel and water vapor, and a reformer40for reforming the mixed fuel to produce a reformed gas are provided.

At a lower end of the fuel cell stack34in the stacking direction, a load applying mechanism41for applying a tightening load to the fuel cells32of the fuel cell stack34in the stacking direction indicated by the arrow A is provided.

The reformer40is a preliminary reformer for reforming higher hydrocarbon (C2+) such as ethane (C2H6), propane (C3H8), and butane (C4H10) contained in the desulfurized city gas (fuel gas), into a fuel gas chiefly containing methane (CH4), by steam reforming. The operating temperature of the reformer40is several hundred ° C.

The operating temperature of the fuel cell32is high, at several hundred ° C. In the electrolyte electrode assembly, methane in the fuel gas is reformed to obtain hydrogen, and the hydrogen is supplied to the anode.

The heat exchanger36heats the air, which is a fluid to be heated, by a consumed reactant gas discharged from the fuel cell stack34(hereinafter also referred to as the exhaust gas or the combustion exhaust gas). The fuel gas supply apparatus16and the desulfurizer14are connected to the evaporator38through the raw fuel channel48.

The oxygen-containing gas supply apparatus18is connected to the air supply pipe42, and the air branch channel46is connected to a switching valve44provided at a position in midstream of the air supply pipe42. The air branch channel46is connected to the combustor13. For example, the combustor13has a torch heater, and the air and electric current are supplied to the combustor13. The water supply apparatus20is connected to the evaporator38through a water channel50. The fuel cell module12and the combustor13are surrounded by heat insulating material52.

The fuel gas supply apparatus16, the oxygen-containing gas supply apparatus18, and the water supply apparatus20are controlled by the control device24. A detector54for detecting the fuel gas is electrically connected to the control device24. For example, a commercial power source56(or other components such as a load or a secondary battery) is connected to the power converter22.

As shown inFIGS. 3 and 4, the desulfurizer14includes a hollow cylindrical tubular body (tubular casing)60which extends vertically. The tubular body60has a supply port62aon its lower end for being supplied with a raw fuel and a discharge port62bon its upper end for discharging a desulfurized raw fuel. The supply port62ais connected to the outlet side (downstream side) of the fuel gas supply apparatus16, and the discharge port62bis connected to the inlet side of the fuel cell module12.

The tubular body60contains therein a filled chamber66having a raw fuel passage64for passing the raw fuel therethrough and which is filled with a desulfurizing agent65for removing sulfur component from the raw fuel to produce a desulfurized raw fuel, a supply chamber68defined between an upstream end of the filled chamber66and the supply port62a, for uniformly supplying the raw fuel to the filled chamber66, and a discharge chamber70defined between a downstream end of the filled chamber66and the discharge port62b, for uniformly discharging the desulfurized raw fuel from the filled chamber66. The raw fuel passage64has a first reverser64aand a second reverser64bfor reversing the direction in which the raw fuel flows, as described in detail later.

The desulfurizer14includes a first mesh member72awhich divides the supply chamber68and the filled chamber66from each other, and a second mesh member72bwhich divides the filled chamber66and the discharge chamber70from each other. Though the desulfurizer14includes both the first and second mesh members72a,72binFIG. 4, the desulfurizer14may have either one of the first and second mesh members72a,72b,rather than both.

As shown inFIGS. 4 and 5, the tubular body60houses therein three partition plates74a,74b,74cextending from the center of the tubular body60radially outwardly to the inner circumferential surface of the tubular body60. These partition plates74a,74b,74cdivide the space in the tubular body60, i.e., the raw fuel passage64, into a first passage region76a, a second passage region76b, and a third passage region76c.

The first passage region76a, the second passage region76b, and the third passage region76chave respective cross-sectional areas S1, S2, S3which have the relationship: S1>S2>S3.

The first passage region76ahas a lower end, i.e., an upstream end, held in fluid communication with the supply chamber68, and an upper end, i.e., a downstream end, held in fluid communication with an upper end, i.e., an upstream end, of the second passage region76bthrough a recess78awhich is defined in an upper end portion of the partition plate74a. The second passage region76bhas a lower end, i.e., a downstream end, held in fluid communication with a lower end, i.e., an upstream end, of the third passage region76cthrough a recess78bwhich is defined in a lower end portion of the partition plate74b. The third passage region76chas an upper end, i.e., a downstream end, held in fluid communication with the discharge chamber70.

As shown inFIG. 4, the raw fuel passage64in the tubular body60includes the first passage region76athat is held in fluid communication with the supply chamber68, the first reverser64athat is defined by the recess78aat the upper end of the first passage region76a, the second passage region76bwhose cross-sectional area is different from that of the first passage region76aso that the cross-sectional area of the raw fuel passage64changes across the first reverser64a, the second reverser64bthat is defined by the recess78bat the lower end of the second passage region76b, and the third passage region76cwhose cross-sectional area is different from that of the second passage region76bso that the cross-sectional area of the raw fuel passage64changes across the second reverser64b. The first reverser64aand the second reverser64bare arrayed on a circle that is concentric with the center of the tubular body60(seeFIG. 5).

The raw fuel passage64is designed such that the velocity at which the raw fuel flows through the first passage region76ahaving the maximum cross-sectional area at a maximum flow rate (i.e., in a rated operation mode) is the same as the velocity at which the raw fuel flows through the third passage region76chaving the minimum cross-sectional area at a minimum flow rate (i.e., in a partial load operation mode).

The desulfurizer14may include a pressure-detecting means80for detecting the inner pressure thereof. In this case, as shown inFIG. 2, the control device24serves as a control means for controlling the pump rotation speed of the fuel gas supply apparatus16such that the detected inner pressure of the desulfurizer14is kept within a certain range.

Operation of the fuel cell system10, in relation to the desulfurizer14according to the first embodiment, will be described below.

As shown inFIG. 2, when the fuel gas supply apparatus16is operated, it supplies a raw fuel, e.g., a city gas (containing CH4, C2H6, C3H8, and C4H10) or the like to the raw fuel channel48. The raw fuel flows through the desulfurizer14, and then, a desulfurized raw fuel is obtained.

More specifically, as shown inFIGS. 3 and 4, the raw fuel is introduced into the supply chamber68through the supply port62aon the lower end of the desulfurizer14. The raw fuel is then supplied uniformly into the first passage region76ahaving the maximum cross-sectional area. The raw fuel flows vertically upwardly through the first passage region76awhile being desulfurized by the desulfurizing agent65.

When the raw fuel reaches the upper end of the first passage region76a, the raw fuel is reversed in direction by the first reverser64a, and introduced into the second passage region76bhaving the medium cross-sectional area. The raw fuel flows vertically downwardly through the second passage region76bwhile being desulfurized by the desulfurizing agent65. Then, when the raw fuel reaches the lower end of the second passage region76b, the raw fuel is reversed in direction by the second reverser64b, and introduced into the third passage region76chaving the minimum cross-sectional area. The raw fuel flows vertically upwardly through the third passage region76cwhile being desulfurized by the desulfurizing agent65. Thereafter, the raw fuel is discharged uniformly into the discharge chamber70which is held in fluid communication with the third passage region76c. Thus, the desulfurized raw fuel is discharged from the discharge port62binto the raw fuel channel48.

On the other hand, as shown inFIG. 2, when the water supply apparatus20is operated, it supplies water to the water channel50. When the oxygen-containing gas supply apparatus18is operated, it supplies an oxygen-containing gas, e.g., air, to the air supply pipe42.

Thus, the evaporator38mixes the desulfurized raw fuel flowing through the raw fuel channel48with water vapor to produce a mixed fuel. The reformer40reforms the mixed fuel by steam-reforming, and removes (reforms) hydrocarbon of C2+to produce a reformed gas chiefly containing methane. The reformed gas flows through an outlet of the reformer40, and is supplied to the fuel cell stack34. Thus, the methane in the reformed gas is reformed, and hydrogen gas is then obtained. The fuel gas which primarily contains the hydrogen gas is supplied to the anodes, not shown, of the fuel cells32.

The air supplied from the air supply pipe42to the heat exchanger36moves along the heat exchanger36, and is heated to a predetermined temperature by heat exchange with the exhaust gas (to be described later). The air heated by the heat exchanger36is supplied to the fuel cell stack34, and the air is supplied to the cathodes (not shown).

Thus, in each of the electrolyte electrode assemblies, by electrochemical reactions of the fuel gas and the air, power generation is performed. The hot exhaust gas (several hundred ° C.) discharged to the outer circumferential region of each of the electrolyte electrode assemblies flows through the heat exchanger36, and heat exchange with the air is carried out. The air is heated to a predetermined temperature, and the temperature of the exhaust gas is decreased.

When the exhaust gas moves along the evaporator38, the water passing through the water channel50is evaporated. After the exhaust gas passes through the evaporator38, the exhaust gas is discharged to the outside.

According to the first embodiment, since the raw fuel that is supplied to the desulfurizer14is temporarily stored in the supply chamber68, the raw fuel is supplied uniformly to the entire area of the first passage region76a. The desulfurized raw fuel flows from the filled chamber66and is temporarily stored in the discharge chamber70. Therefore, the desulfurized raw fuel is discharged uniformly from the entire area of the third passage region76c. Consequently, the entire area of the desulfurizing agent65can effectively be utilized, whereby desulfurizing efficiency is easily improved.

Further, the raw fuel passage64has the first reverser64aand the second reverser64bfor reversing the direction in which the raw fuel flows. Therefore, the overall length of the desulfurizer14is reduced, whereas the raw fuel passage64is effectively elongated. Since the raw fuel and the desulfurizing agent65are held in contact with each other over a long period of time, the desulfurizer14has a high desulfurizing capability.

Furthermore, the cross-sectional area of the raw fuel passage64is smaller in its downstream portion than in its upstream portion. Specifically, the raw fuel passage64includes the first passage region76ahaving the maximum cross-sectional area S1, the second passage region76bhaving the medium cross-sectional area S2, and the third passage region76chaving the minimum cross-sectional area S3, the first through third passage regions76a,76b,76cbeing successively arranged in the order named from upstream toward downstream with respect to the direction in which the raw fuel flows.

In a partial load operation mode, the raw fuel flows through the third passage region76chaving the minimum cross-sectional area (if necessary, also through the second passage region76b) at a minimum flow velocity. In a rated operation mode, the raw fuel flows through the entire raw fuel passage64(including the first through third passage regions76a,76b,76c) at a minimum flow velocity.

If the flow velocity of the raw fuel becomes lower than the minimum flow velocity (e.g., 1 m/s) in the desulfurizer14, then the raw fuel tends to flow unevenly, causing a certain region of the desulfurizing agent65to be deteriorated rapidly, and hence making it less durable. If the raw fuel passage64comprises only passage regions having a small cross-sectional area in order to prevent the raw fuel from flowing unevenly, then the raw fuel passage64needs to be elongated in order to achieve a desired desulfurizing capability, and hence is liable to cause a high pressure loss in the rated operation mode.

According to the first embodiment, the raw fuel passage64includes the first passage region76a, the second passage region76b, and the third passage region76cwhich have different cross-sectional areas. In a wide operating range, the raw fuel passage64thus constructed is effective to prevent uneven flow distribution of the raw fuel and to prevent a pressure loss from occurring, and is also effective to utilize the desulfurizing agent65in its entirety over a long period of time. The desulfurizer14is therefore highly durable and can be serviced for maintenance at increased time intervals.

The first passage region76a, the second passage region76b, and the third passage region76care arranged such that their cross-sectional areas are successively smaller from upstream toward downstream in the order named with respect to the direction in which the raw fuel flows. Accordingly, the raw fuel passage64has a function as a pressure regulation chamber (buffer tank). Even if the fuel gas supply apparatus16causes raw fuel pulsation flows, the raw fuel passage64, i.e., the desulfurizer14, absorbs such raw fuel pulsation flows. The fuel cell module12is thus prevented from producing unstable electric output levels.

In the desulfurizer14, the cross-sectional area of the first passage region76ais reduced to the cross-sectional area of the second passage region76bby passing through the first reverser64a, and the cross-sectional area of the second passage region76bis reduced to the cross-sectional area of the third passage region76cby passing through the second reverser64b. The desulfurizer14has the hollow cylindrical tubular body60, and the first reverser64aand the second reverser64bare arrayed on a circle that is concentric with the center of the tubular body60.

Therefore, the raw fuel passage64is effectively elongated while the overall length of the desulfurizer14is reduced. As the raw fuel and the desulfurizing agent65are held in contact with each other over a long period of time, the desulfurizer14has a high desulfurizing capability. Moreover, the desulfurizer14is simplified in structure and reduced in size.

The desulfurizer14has the discharge port62bheld in fluid communication with the discharge chamber70, and the downstream second reverser64bis positioned below the discharge port62b. Accordingly, the raw fuel flows through the raw fuel passage64upwardly toward the discharge port62b, and hence is kept in contact with the desulfurizing agent65over a long period of time. The desulfurizer14has a high desulfurizing capability and is reduced in size.

When the desulfurizing agent65is deteriorated and fragmented into small pieces after it has been used over a long period of time, since the raw fuel flows upwardly as an upward flow, the fragmented pieces of the desulfurizing agent65are prevented from accumulating in a lower portion of the desulfurizer14. Accordingly, the raw fuel is enabled to effectively flow through the desulfurizing agent65, so that the overall area of the desulfurizing agent65can effectively be utilized and the desulfurizing agent65can be used over a long period of time. In addition, the fragmented pieces of the desulfurizing agent65are prevented from flowing downstream of the desulfurizer14. Consequently, any pressure losses and auxiliary losses caused by devices connected downstream of the desulfurizer14, e.g., the reformer40, the fuel cell module12, pipes, etc., are reduced, and those devices are increased in efficiency and service life.

According to the first embodiment, the raw fuel passage64has an even number of (two) reversers, i.e., the first reverser64aand the second reverser64b. Therefore, the supply chamber68and the discharge chamber70are allowed to be positioned on the respective opposite ends of the desulfurizer14. Therefore, the pipe for supplying the raw fuel and the pipe for discharging the desulfurized raw fuel are not placed closely together, but are easily positioned and connected to the desulfurizer14.

Further, the supply port62awhich is held in fluid communication with the supply chamber68is positioned below the discharge port62bwhich is held in fluid communication with the discharge chamber70. Since the raw fuel flows through the raw fuel passage64from the lower supply port62ato the upper discharge port62b, the raw fuel and the desulfurizing agent65are kept in contact with each other over a long period of time. Therefore, the desulfurizer14has a high desulfurizing capability and is reduced in size.

When the desulfurizing agent65is deteriorated and fragmented into small pieces after it has been used over a long period of time, since the raw fuel flows upwardly as an upward flow, the fragmented pieces of the desulfurizing agent65are prevented from accumulating in a lower portion of the desulfurizer14. Accordingly, the raw fuel is enabled to effectively flow through the desulfurizing agent65, so that the overall area of the desulfurizing agent65can effectively be utilized and the desulfurizing agent65can be used over a long period of time. In addition, the fragmented pieces of the desulfurizing agent65are prevented from flowing downstream of the desulfurizer14. Consequently, any pressure losses and auxiliary losses caused by devices connected downstream of the desulfurizer14, e.g., the reformer40, the fuel cell module12, pipes, etc., are reduced, and those devices are increased in efficiency and service life.

The raw fuel passage64includes the first passage region76a, the second passage region76b, and the third passage region76c, such that the cross-sectional area of the raw fuel passage64is reduced stepwise from upstream toward downstream across the first reverser64aand the second reverser64b.Though the present invention is simple in structure, the following is achieved. That is, in a partial load operation mode, the raw fuel flows through the third passage region76chaving the minimum cross-sectional area (if necessary, also through the second passage region76b) at a minimum flow velocity, and in a rated operation mode, the raw fuel flows through the entire raw fuel passage64(including the first through third passage regions76a,76b,76c) at a minimum flow velocity.

Accordingly, in a wide operating range, the raw fuel passage64thus constructed is effective to prevent uneven flow distribution of the raw fuel, and to utilize the desulfurizing agent65in its entirety over a long period of time. The desulfurizer14is therefore highly durable and can be serviced for maintenance at increased time intervals.

In addition, the desulfurizer14has a function as a pressure regulation chamber. Therefore, the desulfurizer14can stably supply the desulfurized raw fuel, thus enabling the fuel cells32to operate stably.

Furthermore, the raw fuel passage64is designed such that the velocity at which the raw fuel flows through the first passage region76aat a maximum flow rate is the same as the velocity at which the raw fuel flows through the third passage region76cat a minimum flow rate. Therefore, in a partial load operation mode, the raw fuel flows through the third passage region76cat a minimum flow velocity, and in a rated operation mode, the raw fuel flows through the entire raw fuel passage64at a minimum flow velocity.

Accordingly, in a wide operating range, the raw fuel passage64is effective to prevent uneven flow distribution of the raw fuel, and to utilize the desulfurizing agent65in its entirety over a long period of time. The desulfurizer14is therefore highly durable and can be serviced for maintenance at increased time intervals.

The desulfurizer14includes the first mesh member72awhich divides the supply chamber68and the filled chamber66from each other, and the second mesh member72bwhich divides the filled chamber66and the discharge chamber70from each other. The first mesh member72ais capable of removing dust particles and foreign matter from the raw fuel and also of preventing the fragmented desulfurizing agent65from flowing upstream toward the supply port62a. The second mesh member72bis capable of preventing the fragmented desulfurizing agent65from flowing downstream toward the discharge port62b.

Further, the fuel cell module12comprises a solid oxide fuel cell (SOFC) module used for a high-temperature fuel cell system. Thus, the fuel cell system10which incorporates the fuel cells32having a wide operating range is capable of suitably preventing uneven flow distribution and pulsation flows, and can be reduced in size. In addition, temperature changes are suppressed, and hence, such a fuel cell system is optimum for use as a high-temperature fuel cell system.

Incidentally, instead of the solid oxide fuel cell module, the present invention is also suitably applicable to other types of fuel cell modules. For example, molten carbonate fuel cells (MCFC), phosphoric acid fuel cells (PAFC), hydrogen membrane fuel cells (HMFC), solid polymer electrolyte fuel cells (PEFC), etc can be adopted suitably.

FIG. 6is a perspective view of a desulfurizer90according to a second embodiment of the present invention.FIG. 7is a sectional plan view of the desulfurizer90.FIG. 8is a schematic diagram showing an expanded representation of a raw fuel passage in the desulfurizer90.

Those parts of the desulfurizer90which are identical to those of the desulfurizer14according to the first embodiment are denoted by identical reference characters, and will not be described in detail below. Similarly, those parts of desulfurizers according to third through fifth embodiments to be described below which are identical to those of the desulfurizer14according to the first embodiment are denoted by identical reference characters, and will not be described in detail below.

As shown inFIG. 7, the desulfurizer90comprises a hollow cylindrical tubular body60which houses therein a plurality of partition plates92athrough92gextending from the center of the tubular body60radially outwardly to the inner circumferential surface of the tubular body60. These partition plates92athrough92gdivide the space in the tubular body60into a first passage region94a, two second passage regions94b1,94b2, and four third passage regions94c1,94c2,94c3,94c4.

The partition plates92a,92gare angularly spaced from each other by an angle α1of 120°. The partition plates92a,92bare angularly spaced from each other by an angle α2of 60°. The partition plates92b,92care angularly spaced from each other by an angle α2of 60°. The partition plates92c,92dare angularly spaced from each other by an angle α3of 30°. The partition plates92d,92eare angularly spaced from each other by an angle α3of 30°. The partition plates92e,92fare angularly spaced from each other by an angle α3of 30°. The partition plates92f,92gare angularly spaced from each other by an angle α3of 30°.

The partition plates92a,92gjointly define therebetween a first passage region94ahaving a maximum cross-sectional area. The partition plates92a,92band the partition plates92b,92cjointly define therebetween respective second passage regions94b1,94b2each having a medium cross-sectional area. The partition plates92c,92d, the partition plates92d,92e, the partition plates92e,92f, and the partition plates92f,92gjointly define therebetween respective third passage regions94c1,94c2,94c3,94c4each having a minimum cross-sectional area.

The partition plate92ahas a first reverser98adefined in an upper end portion thereof by a recess. The partition plate92bhas a second reverser98bdefined in a lower end portion thereof by a recess. The partition plate92chas a third reverser98cdefined in an upper end portion thereof by a recess. The partition plate92dhas a fourth reverser98ddefined in a lower end portion thereof by a recess. The partition plate92ehas a fifth reverser98edefined in an upper end portion thereof by a recess. The partition plate92fhas a sixth reverser98fdefined in a lower end portion thereof by a recess.

As schematically shown inFIG. 8, the desulfurizer90has a raw fuel passage98. The raw fuel passage98includes the first passage region94a, a second passage region94bwhich refers to a combination of the second passage regions94b1,94b2, and a third passage region94cwhich refers to a combination of the third passage regions94c1,94c2,94c3,94c4. The first passage region94a, the second passage region94b, and the third passage region94chave the same volume as each other.

According to the second embodiment, firstly, a raw fuel that is introduced into the supply chamber68from the supply port62aon the lower end of the desulfurizer90is supplied to the first passage region94ahaving the maximum cross-sectional area, and flows upwardly through the first passage region94a. Then, the raw fuel is reversed in direction by the first reverser98a, and introduced into the second passage region94b1having the medium cross-sectional area.

The raw fuel flows downwardly through the second passage region94b1, and then is reversed in direction by the second reverser98b. Thereafter, the raw fuel is introduced into the second passage region94b2, and flows upwardly through the second passage region94b2. The raw fuel which has reached the upper end of the second passage region94b2is reversed in direction by the third reverser98c. Thereafter, the raw fuel is introduced into the third passage region94c1having the minimum cross-sectional area, and flows downwardly through the third passage region94c1.

The raw fuel is reversed in direction by the fourth reverser98d, and is introduced into the third passage region94c2and flows upwardly through the third passage region94c2. Thereafter, the raw fuel is reversed in direction by the fifth reverser98e, and is introduced into the third passage region94c3and flows downwardly through the third passage region94c3. The raw fuel is reversed in direction by the sixth reverser98f, is introduced into the third passage region94c4and flows upwardly through the third passage region94c4. Thereafter, the raw fuel is discharged from the discharge chamber70into the discharge port62b.

Thus, the desulfurizer90according to the second embodiment offers the same advantages as the desulfurizer14according to the first embodiment. In addition, the first passage region94a, the second passage region94b, and the third passage region94chave the same volume as each other, while the first passage region94a, the second passage region94b, and the third passage region94chave different cross-sectional areas.

In a partial load operation mode, the raw fuel is desulfurized mainly in the region of the raw fuel passage98that has a smaller cross-sectional area, e.g., in the third passage region94c. In a rated operation mode, the raw fuel is desulfurized in the entire regions of the raw fuel passage98, i.e., the first passage region94a, the second passage region94b, and the third passage region94c. Accordingly, the desulfurizer90is capable of stably desulfurizing the raw fuel in a wide operating range, and is highly durable.

FIG. 9is a perspective view of a desulfurizer100according to a third embodiment of the present invention, andFIG. 10is a sectional side elevational view of the desulfurizer100.

As shown inFIGS. 9 and 10, the desulfurizer100includes a box-shaped casing102having a supply chamber68defined in a lower portion near one end thereof and held in fluid communication with a supply port62aon the lower end of the casing102, and a discharge chamber70defined in an upper portion near the other end thereof and held in fluid communication with a discharge port62bon the upper end of the casing102. The casing102defines therein a filled chamber66including a raw fuel passage104which has a first reverser104aand a second reverser104bfor reversing the direction in which the raw fuel flows.

The casing102includes partition plates106a,106bdisposed therein. The first reverser104ais formed by cutting off an upper end portion of the partition plate106a, and the second reverser104bis formed by cutting off a lower end portion of the partition plate106b. The raw fuel passage104includes a first passage region108aformed on the upstream side thereof and having a maximum cross-sectional area, a second passage region108bformed on the downstream side of the first passage region108aand having a medium cross-sectional area, and a third passage region108cformed on the downstream side of the second passage region108band having a medium cross-sectional area.

The first passage region108a, the second passage region108b, and the third passage region108chave respective cross-sectional areas such that the cross-sectional area of the raw fuel passage104is reduced stepwise from upstream toward downstream across the first reverser104aand the second reverser104b. The desulfurizer100according to the third embodiment offers the same advantages as the desulfurizer14,90according to the first and second embodiments. In addition, the desulfurizer100according to the third embodiment is simpler in structure and hence more economical.

FIG. 11is a perspective view of a desulfurizer120according to a fourth embodiment of the present invention, andFIG. 12is a sectional side elevational view of the desulfurizer120.

As shown inFIGS. 11 and 12, the desulfurizer120includes a casing122, which is essentially trapezoidal as seen from front. The casing122has a supply chamber68defined in a lower portion near one end thereof and held in fluid communication with a supply port62aon the lower end of the casing122, and a discharge chamber70defined in an upper portion near the other end thereof and held in fluid communication with a discharge port62bon the upper end of the casing122. The casing122defines therein a raw fuel passage124which has a first reverser124aand a second reverser124bfor reversing the direction in which the raw fuel flows.

The casing122includes two partition plates126a,126bdisposed therein which are inclined in respective directions. The first reverser124ais formed by cutting off an upper end portion of the partition plate126a, and the second reverser124bis formed by cutting off a lower end portion of the partition plate126b.

The raw fuel passage124includes a first passage region128ahaving a maximum cross-sectional area, a second passage region128bhaving a medium cross-sectional area, and a third passage region128chaving a minimum cross-sectional area. The first passage region128a, the second passage region128b, and the third passage region128care defined by the partition plates126a,126b.

The first passage region128ahas a maximum width H1at its upstream inlet end and a minimum width H2at its downstream outlet end. The second passage region128bhas a maximum width H2at its upstream inlet end and a minimum width H3at its downstream outlet end. The third passage region128chas a maximum width H3at its upstream inlet end and a minimum width H4at its downstream outlet end.

Thus, in the raw fuel passage124, the first passage region128a, the second passage region128b, and the third passage region128chave respective cross-sectional areas progressively continuously reduced from upstream toward downstream. The desulfurizer120according to the fourth embodiment offers the same advantages as the desulfurizer according to the first, second, and third embodiments. In addition, since the cross-sectional area of the raw fuel passage124is progressively continuously reduced from the supply chamber68toward the discharge chamber70, the desulfurizer120according to the fourth embodiment is capable of preventing a pressure loss from increasing as much as possible.

FIG. 13is a fragmentary front elevational view, partly in cross section, of a desulfurizer140according to a fifth embodiment of the present invention.FIG. 14is a perspective view of the desulfurizer140, andFIG. 15is a sectional plan view of the desulfurizer140.

As shown inFIGS. 13 through 15, the desulfurizer140includes a hollow cylindrical tubular body142. The tubular body142has a supply chamber68defined in an upper portion thereof and held in fluid communication with a supply port62aon the upper end of the tubular body142, and a discharge chamber70defined in an upper portion thereof and held in fluid communication with a discharge port62bon the upper end of the tubular body142. The tubular body142defines therein a filled chamber66including a raw fuel passage144which provides fluid communication between the supply port62aand the discharge port62b. The raw fuel passage144has a first reverser144a, a second reverser144b, and a third reverser144cfor reversing the direction in which the raw fuel flows.

The tubular body142houses a plurality of partition plates146athrough146dextending from the center of the tubular body142radially outwardly to the inner circumferential surface of the tubular body142. The first reverser144ais formed by cutting off a lower end portion of the partition plate146a. The second reverser144bis formed by cutting off an upper end portion of the partition plate146b. The third reverser144cis formed by cutting off a lower end portion of the partition plate146c.

The partition plates146a,146dare angularly spaced from each other by a maximum angle, defining therebetween a first passage region148ahaving a maximum cross-sectional area. The partition plates146a,146bdefine therebetween a second passage region148bhaving a medium cross-sectional area. The partition plates146b,146cand the partition plates146c,146ddefine therebetween respective third passage regions148c1,148c2each having a minimum cross-sectional area.

According to the fifth embodiment, the desulfurizer140has an odd number of reversers, i.e., the first reverser144a, the second reverser144b, and the third reverser144c. Therefore, the supply chamber68and the discharge chamber70are disposed in one of the axially opposite ends of the desulfurizer140, e.g., in the upper end of the tubular body142. Therefore, the pipe for supplying the raw fuel and the pipe for discharging the desulfurized raw fuel are placed closely together, allowing the desulfurizer140to be positioned flexibly.

The desulfurizer140according to the fifth embodiment is illustrated as having the hollow cylindrical tubular body142as with the desulfurizers according to the first and second embodiments. However, the desulfurizer140according to the fifth embodiment may have a casing similar in shape to either one of the casings of the desulfurizers according to the third and fourth embodiments.

While the invention has been particularly shown and described with reference to preferred embodiments, it will be understood that variations and modifications can be effected thereto by those skilled in the art without departing from the scope of the invention as defined by the appended claims.