US20050172619A1

US20050172619A1 - Catalytic combustion apparatus

Info

Publication number: US20050172619A1
Application number: US11/047,613
Authority: US
Inventors: Hirokuni Sasaki
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2004-02-09
Filing date: 2005-02-02
Publication date: 2005-08-11
Also published as: DE102005005307A1; JP2005221202A

Abstract

A water separating filter, disposed between a gas mixing chamber and a catalytic combustion chamber in a passage, includes numerous fine passages for trapping waterdrops or steam contained in a fuel mixture produced from the gas mixing chamber and letting the trapped waterdrops or steam dwell in the water separating filter. The fuel mixture contains no water components when it flows into the catalytic combustion chamber. No moisture adheres on the catalyst surface. The fuel mixture surely contacts with the catalyst. The catalytic combustion is stably maintained. The catalytic combustion heat is not consumed by the waterdrops for the latent heat required in the process of evaporation. A catalytic combustion heater can quickly increase the catalyst temperature to the active temperature within a short time.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from earlier Japanese Patent Application No. 2004-32409 filed on Feb. 9, 2004 so that the description of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a catalytic combustion apparatus which is a preferable heat source of a home or automotive heater. The catalytic combustion apparatus is equipped with a catalyst to cause combustion of the fuel mixture of air and fuel. The generated catalytic combustion heat is used to increase the temperature of a heating medium.
The catalytic combustion apparatus is based on low-temperature flameless combustion which is preferable to completely eliminate the emission of NOx. The catalytic combustion apparatus is advantageous in high flame safety, high absorption rates with respect to low-temperature heated materials, and high efficiency of far infrared radiation. Accordingly, the catalytic combustion apparatus can realize a great amount of energy saving.
In general, a combustible gas, such as hydrogen gas or LPG (liquefied petroleum gas) is preferably used as fuel gas for the catalytic combustion apparatus. The fuel mixture of this fuel (gas) and air is supplied to the catalyst to cause catalytic combustion.
Furthermore, if the catalytic combustion apparatus using the hydrogen gas is installed in a vehicle driven by a hydrogen fuel cell, the fuel (i.e. hydrogen gas) can be commonly used. The exhaust gas (i.e. so-called off-gas) discharged from the hydrogen fuel cell contains unreacted hydrogen gas having been not used for electric power generation. In general, the off-gas is processed to remove the water components before it is again supplied into the hydrogen fuel cell. The off-gas can be used as part of the fuel supplied into the catalytic combustion apparatus, for the purpose of saving the energy required for the off-gas processing.
For example, according to a conventional catalytic combustion apparatus, the fuel supplying device supplies the fuel mixture of hydrogen gas and air into a flow path. An electrically heated catalyst, a combustion catalyst, and a heat exchanger including a heating medium circulating therein are provided in this order from the upstream side of this flow path.
When the electrically heated catalyst is activated, the fuel mixture of hydrogen gas and air starts burning. The combustion gas of the electrically heated catalyst flows into the combustion catalyst. The temperature of the combustion catalyst increases. The fuel mixture of hydrogen gas and air can also burn in the high-temperature combustion catalyst (refer to the Japanese Patent Application Laid-open No. 2002-122311 corresponding to the United States Patent Application Publication No. U.S. 2003/0031971 A1).
The above-described conventional catalytic combustion apparatus uses a Pt (platinum) catalyst which has excellent reaction activity. The Pt catalyst can cause catalytic combustion even when the mixture temperature is low. Therefore, the Pt catalyst is preferably used for the catalytic combustion apparatus.
Regarding the catalyst, there is a characteristic temperature (i.e. activation temperature) at which the function of catalyst, i.e. oxidation function, can be sufficiently obtained. In other words, when the catalyst temperature is lower than the activation temperature, the catalyst has insufficient activity.
Immediately after the catalytic combustion apparatus starts its operation, the temperature of the catalytic combustion apparatus is still low.
When the catalyst temperature is lower than the activation temperature, the oxidation function is not obtained sufficiently. The generated catalytic combustion heat can be used to increase the catalyst temperature. The catalyst temperature reaches the activation temperature, and a stable catalytic combustion is realized. Namely, the heat amount generated from the catalytic combustion apparatus, i.e. the heat amount to be transferred to the heating medium, increases to a rated heat amount.
When the temperature of the catalytic combustion apparatus is low, the steam such as moisture contained in the air and moisture generated by the catalytic combustion may condense on a low-temperature catalyst surface and adhere on this catalyst surface. Especially, when the fuel is hydrogen gas, a great amount of water is produced as a product of catalytic combustion. Thus, the produced moisture or waterdrops will adhere on the catalyst surface. Furthermore, in a case that this apparatus is installed in a vehicle driven by a hydrogen fuel cell to process the exhaust gas (containing hydrogen) of this fuel cell, the exhaust gas (i.e. the fuel gas) contains water produced from the fuel cell. Thus, waterdrops may adhere on the catalyst surface.
When waterdrops adhere on the catalyst surface, the catalyst cannot directly contact with the fuel mixture of fuel and air. Thus, the catalytic combustion is not stably maintained, and the heat generation by the catalytic combustion will decrease. Furthermore, the waterdrops adhering on the catalyst surface will absorb the generated catalytic combustion heat to evaporate and flow together with the mixture stream toward the downstream side of the passage. In other words, the waterdrops consume the generated catalytic combustion heat. Accordingly, it will take a long time until the catalyst temperature reaches the activation temperature, because of the reduction of catalytic heat generation and the consumption of generated heat by the waterdrops. Thus, there will be a long time before the heating medium can receive a rated heat amount in the catalytic combustion apparatus.
For example, in a vehicle driven by a hydrogen fuel cell, the catalytic combustion apparatus can be used not only for the heating of a vehicle compartment and processing of the exhaust gas but also for the warming up of the fuel cell. In this case, if the temperature of the heating medium increases slowly in the catalytic combustion apparatus, a long time will be required to warm up the fuel cell. There will be a long time before the fuel cell can generate a regular output in the startup condition of the vehicle driven by this fuel cell.
To solve the problems, according to the above-described conventional catalytic combustion apparatus, the electrically heated catalyst is provided at the upstream side of the combustion catalyst. In response to electric power supply, the electrically heated catalyst causes the fuel mixture of hydrogen gas and air to burn. Accordingly, the temperature of the fuel mixture quickly increases before the fuel mixture flows into the combustion catalyst. And, the combustion catalyst is free from adhesion of the moisture.
However, this conventional apparatus absolutely requires addition of the electrically heated catalyst. The electrically heated catalyst increases the electric power consumption and decreases the energy efficiency.
On the other hand, causing the combustion of a fuel mixture of hydrogen gas and air at the upstream side of the catalyst will be possible with spark ignition of the fuel mixture. The high-temperature fuel mixture supplied to the catalyst can increase the temperature of the catalyst. In this case, the combustion of hydrogen can be sustained with flame propagation and accordingly the electric power consumption can be suppressed.
However, there is a difficulty in causing the combustion of the fuel mixture with the spark ignition, because the mixing ratio of the hydrogen and the air for obtaining the ignitable fuel mixture is limited to a very narrow range. Furthermore, the combustion of the fuel mixture caused with the spark ignition will rapidly increase the temperature. Accordingly, the problems caused by high temperatures must be solved.

SUMMARY OF THE INVENTION

In view of the above-described problems, the present invention has an object to provide a catalytic combustion apparatus which is capable of reducing the moisture adhering on the catalyst surface after the catalytic combustion apparatus starts its operation and also capable of quickly increasing the catalyst temperature to an activation temperature within a short time.
In order to accomplish the above and other related objects, the present invention provides a catalytic combustion apparatus including a gas mixing means, an air supplying means, a fuel supplying means, a passage, a catalytic combustion section, and a liquid collecting means. The gas mixing means is capable of forming a fuel mixture of air and fuel. The air supplying means is capable of supplying the air to the gas mixing means. The fuel supplying means is capable of supplying the fuel to the gas mixing means. The passage, connected to the gas mixing means, receives the fuel mixture formed by and supplied from the gas mixing means. The catalytic combustion section, disposed at a downstream side of the gas mixing means, includes a catalyst supported by a catalytic carrier. And, the liquid collecting means, having numerous fine passages for collecting liquid, is interposed between the gas mixing means and the catalytic combustion section in a flowing direction of the fuel mixture in the passage.
When the catalyst temperature is still low after the catalytic combustion heating apparatus starts its operation, the steam such as moisture contained in the air, moisture contained in the fuel gas, or moisture contained in the exhausted catalytic combustion gas may condense on the low-temperature catalyst surface and adhere on this catalyst surface. Especially, when the fuel is off-gas discharged from the hydrogen fuel cell, the off-gas will include a great amount of water produced as a result of reaction in the fuel cell. Thus, the produced moisture or waterdrops will adhere on the catalyst surface.
When the catalyst surface is covered with the moisture, the catalyst cannot contact with the fuel mixture. This leads to deterioration of the catalyst function. In other words, the heat generation amount by the catalytic combustion will decrease. Furthermore, the generated catalytic combustion heat will be consumed to evaporate the waterdrops adhering on the catalyst. The temperature of the catalyst will increase slowly. Thus, it will take a long time to increase the catalyst temperature to the activation temperature.
According to the arrangement of the catalytic combustion apparatus of the present invention, the fuel mixture produced from the gas mixing means passes through the liquid collecting means before it flows into the catalytic combustion section. As the liquid collecting means includes numerous fine passages, the water components (such as waterdrops or steam) contained in the fuel mixture collide with wall surfaces of these fine passages and adhere thereon. Therefore, the liquid collecting means of the present invention can remove the water components (such as waterdrops or steam) from the fuel mixture.
Thus, the waterdrops or steam can be sufficiently removed from the fuel mixture before the fuel mixture flows into the catalytic combustion section. Therefore, the catalytic combustion apparatus of the present invention can prevent the moisture from adhering on the catalyst surface during the operation of the catalytic combustion section, and also can quickly increase the catalyst temperature to the active temperature within a short time.
When the water particles are large, the liquid collecting means can surely trap the water (e.g. waterdrops). When the water particles are small, the liquid collecting means may not be able to trap all of the water components (e.g. the steam). However, such smaller water particles hardly adhere on the catalyst surface and accordingly will not condense on the catalyst surface or will not deteriorate the catalyst function.
After the catalytic combustion apparatus starts its operation, the amount or volume of the water components dwelling in the liquid collecting means increases with elapsed time. At the same time, the temperature increases in the catalytic combustion section. The liquid collecting means receives the radiation heat from the catalytic combustion section and accordingly the temperature of the liquid collecting means increases. Therefore, the water components dwelling in the liquid collecting means will evaporate and flow together with the fuel mixture into the catalytic combustion section. However, the catalytic combustion section is in a sufficiently higher temperature range higher than the active temperature of the catalyst. The steam flowing together with fuel mixture does not adhere on the catalyst surface and immediately flows out of the catalytic combustion section.
According to the catalytic combustion apparatus of the present invention, it is preferable that the liquid collecting means includes a heater.
In this case, it is preferable to activate the heater of the liquid collecting means as soon as the catalytic combustion apparatus starts its operation. The heater increases the temperature of the liquid collecting means. The temperature of the steam increases when the steam passes through the liquid collecting means. The water particles in the steam become smaller. Thus, the above-described preferred embodiment of the present invention can surely prevent the steam from adhering on the catalyst surface when the fuel mixture containing the steam flows into the catalytic combustion section.
Furthermore, the generated heat of the heater can promote temperature increase in the liquid collecting means and also promote re-evaporation of the water components dwelling in the liquid collecting means. Accordingly, a relatively small amount of water dwells in the liquid collecting means. The liquid collecting means can be downsized.
According to the catalytic combustion apparatus of the present invention, it is preferable that the heater is an electric heating element.
In this case, the heater is easy to control its heat generation amount. Thus, the energy consumption of the heater can be minimized by adequately adjusting the heat generation amount of the heater.
According to the catalytic combustion apparatus of the present invention, it is preferable that the liquid collecting means is made of an electric conductive substance and generates heat in response to supplied electric power.
In this case, the liquid collecting means can generate heat. In other words, no heater is required. Accordingly, the total number of required parts decreases. The catalytic combustion apparatus can be downsized. The temperature of the steam increases when the steam passes through the liquid collecting means. And, the water particles of the steam become smaller. Thus, the steam does not adhere on the catalyst surface when the fuel mixture containing the steam flows into the catalytic combustion section,
Furthermore, the liquid collecting means having the heat generation capability can quickly increase the temperature of the liquid collecting means. This is effective in saving the electric power consumption in the liquid collecting means.
According to the catalytic combustion apparatus of the present invention, it is preferable that the collecting means is a porous gas-permeable solid material.
The porous gas-permeable solid material is, for example, made of monolith ceramics, such as a sintered metal, and includes fine passages formed in a complicated manner. Thus, the porous gas-permeable solid material can surely trap the waterdrops or steam contained in the fuel mixture.
Furthermore, using the monolith ceramics is preferable because the porous gas-permeable solid material can be easily configured into an adequate shape installable in a passage of the catalytic combustion apparatus.
According to the catalytic combustion apparatus of the present invention, it is preferable that the fuel is hydrogen gas.
For example, in a case that the catalytic combustion apparatus of the present invention is used as fuel cell stack preheating apparatus in a hydrogen fuel cell system, the catalyst temperature quickly increases to the active temperature within a short time after the catalytic combustion apparatus starts its operation.
It is further preferable that the catalytic combustion apparatus of the present invention further includes a heat exchanger disposed at a downstream side of the catalytic combustion section in the passage, and the heat exchanger includes a heating medium for causing heat exchange between the heating medium and combustion gas supplied from the catalytic combustion section.
In this case, the generated heat of the catalytic combustion section is transferred to the heating medium of the heat exchanger. The heating medium moves to a predetermined place where the heat of the heating medium is released. More specifically, even in a case that the catalytic combustion apparatus is located far from the place where the generated heat is utilized, the heating medium can easily and efficiently convey the generated heat of the catalytic combustion section to the place where the generated heat is utilized

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description which is to be read in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic view showing an overall arrangement of a heating system including a catalytic combustion heater in accordance with a first embodiment of the present invention;
FIG. 2 is a partly cross-sectional view showing the catalytic combustion heater in accordance with the first embodiment of the present invention;
FIG. 3 is a partly cross-sectional view showing a catalytic combustion heater in accordance with a second embodiment of the present invention;
FIG. 4 is a partly cross-sectional view showing a catalytic combustion heater in accordance with a third embodiment of the present invention;
FIG. 5A is a view showing the detailed structure of a water separating filter in accordance with the first embodiment of the present invention;
FIG. 5B is a view showing the detailed structure of a water separating filter in accordance with the second embodiment of the present invention; and
FIG. 5C is a view showing the detailed structure of a water separating filter in accordance with the third embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be explained hereinafter with reference to attached drawings.

First Embodiment

Hereinafter, a catalytic combustion apparatus in accordance with a preferred embodiment of the present invention will be explained with reference to a catalytic combustion heater which is installed in a fuel cell vehicle using the hydrogen fuel and is preferably used for the air-conditioning (heating) system of a vehicle compartment.
FIG. 1 is a schematic view showing an overall arrangement of a heating system 100 including a catalytic combustion heater 1 in accordance with a first embodiment of the present invention. FIG. 2 is a partly cross-sectional view showing the catalytic combustion heater 1 in accordance with the first embodiment of the present invention.
The heating system 100 includes, as shown in FIG. 1, the catalytic combustion heater 1, a heater core 101, and a pump 102. The catalytic combustion heater 1 heats the water (i.e. a heating medium). The heater core 101 receives the water heated by the catalytic combustion heater 1, and exchanges the heat of the heating medium with the air. The warm air supplied from the heater core 101 is used for air-conditioning (i.e. heating) of a vehicle compartment. The pump 102 is disposed between the catalytic combustion heater 1 and the heater core 101 to forcibly circulate the water (i.e. the heating medium) between them.
The catalytic combustion heater 1 and the fuel cell (i.e. driving power source) of this vehicle use the common fuel (i.e. hydrogen). The catalytic combustion heater 1 causes the catalytic combustion of hydrogen to increase the temperature of water (i.e. heating medium).
Hereinafter, the arrangement of the catalytic combustion heater 1 in accordance with the first embodiment of the present invention will be explained in more detail.
As shown in FIG. 2, the catalytic combustion heater 1 includes a passage 81 formed in a casing 8. The fuel mixture of hydrogen gas (i.e. fuel) and air is supplied into the passage 81. A blower 2, a hydrogen introducing section 32, a gas mixer 4, a water separating filter 5, a catalytic combustion chamber 6 serving as a catalytic combustion section, and a heat exchanger 7 are disposed in this order from the upstream side of the passage 81. The blower 2 is an air supplying means of the present invention. A hydrogen supplying apparatus 3, assembled with the catalytic combustion heater 1, is a fuel supplying means of the present invention. The hydrogen gas supplied from the hydrogen supplying apparatus 3 is introduced via the hydrogen introducing section 32 into the passage 81. The gas mixer 4 is a gas mixing means of the present invention which mixes the air and the hydrogen gas to form a fuel mixture of hydrogen gas and air.
The casing 8 is made of a heat-resisting metal, such as a stainless steel plate. As shown in FIG. 2, the casing 8 forms therein the passage 81 into which the fuel mixture of hydrogen gas (i.e. fuel) and air is supplied.
The blower 2 (i.e. the air supplying means) is disposed at an upstream end of the passage 81 (i.e. the left end of the passage 81 in FIG. 2). The blower 2, driven by a motor, introduces the air via a filter (not shown) from the outside and supplies the introduced air into the passage 81. The hydrogen introducing section 32 is disposed at the downstream side of the blower 2 (i.e. the right side of the blower 2 in FIG. 2). The hydrogen introducing section 32 supplies hydrogen gas (i.e. fuel) to the gas mixer 4. The detailed arrangement of the gas mixer 4 will be explained later.
The fuel supplying means for supplying the fuel into the gas mixer 4 consists of the hydrogen supplying apparatus 3, the hydrogen introducing section 32, and a hydrogen passage 31. The hydrogen supplying apparatus 3 adjusts the pressure of the hydrogen gas supplied from the outside to a predetermined value. Furthermore, the hydrogen supplying apparatus 3 controls the flow rate of the hydrogen gas supplied into the gas mixer 4 to a desired value. The hydrogen introducing section 32, disposed at an upstream side of the gas mixer 4, uniformly introduces the hydrogen gas into the gas mixer 4. The hydrogen gas is supplied from the hydrogen gas supplying apparatus 3 via the hydrogen passage 31 into the hydrogen introducing section 32.
The hydrogen gas supplied into the hydrogen gas supplying apparatus 3 is supplied from a hydrogen tank (not shown) of a fuel cell system installed in a vehicle. Furthermore, the hydrogen gas is also supplied from the passage of off-gas (i.e. exhaust gas) discharged from the fuel cell (not shown), according to the catalytic combustion heater 1 of the first embodiment of the present invention. For example, it is desirably that the off-gas is mainly supplied into the hydrogen gas supplying apparatus 3. In this case, the hydrogen gas of the hydrogen tank (not shown) is additionally supplied to the hydrogen gas supplying apparatus 3 only when the available off-gas cannot satisfy a hydrogen gas flow rate required for the catalytic combustion heater 1.
More specifically, the hydrogen supplying apparatus 3 (i.e. the fuel supplying means) supplies the hydrogen gas via the hydrogen passage 31 to the hydrogen introducing section 32 of the passage 81. The hydrogen introducing section 32 uniformly introduces the hydrogen gas into the passage 81 in an outer peripheral direction of the passage 81. The gas mixer 4 (i.e. the gas mixing means) is disposed at a downstream side of the hydrogen introducing section 32 (i.e. the right side of the hydrogen introducing section 32 in FIG. 2).
The gas mixer 4 is, for example, arranged by a so-called static mixer. The static mixer includes helical stationary vanes (not shown) disposed in a pipe passage (not shown). When the air and the hydrogen gas pass the gas mixer 4 in the direction from the upstream side to the downstream side (i.e. from the left to the right in FIG. 2), the helical stationary vanes stir and mix these gases to form the fuel mixture of hydrogen gas and air. The hydrogen concentration of this mixture becomes substantially uniform in a cross-sectional area of the passage 81 which is normal to the flowing direction of this mixture. The water separating filter 5, serving as gas mixing means of the present invention, is disposed at the downstream side of the gas mixer 4 (i.e. the right side of the gas mixer 4 in FIG. 2).
FIG. 5A is a view showing an inlet side of the water separating filter 5 shown in FIG. 2. The water separating filter 5 of FIG. 2 is arranged by a so-called monolith ceramic carrier having a honeycomb structure as shown in FIG. 5A. According to this arrangement, the water separating filter 5 (i.e. the monolith ceramic carrier) has numerous passages 5 a divided by partition walls 5 b so as to constitute a honeycomb structure. For example, the monolith ceramic carrier can be manufactured through an extrusion step of molding a mixture of a cordierite material and an organic binder and a sintering step of burning the molded member. The number of fine passages 5 a arranging the water separating filter 5 (i.e. the monolith ceramic carrier) is in the range from 900 to 1200 per inch. As the cordierite material contains the organic binder being added in the mixing process, the organic binder burns down and leaves numerous cavities in the process of sintering the mixture of a cordierite material and an organic binder. Thus, numerous cavities are opened to the surfaces of respective passages 5 a of the monolith ceramic carrier. These cavities form complicated inside paths communicating with each other in the sintered cordierite body, and accordingly provide numerous fine passages in the water separating filter 5. These fine passages are winding and extending from the upstream side to the downstream side of the water separating filter 5. Accordingly, when the fuel mixture of air and hydrogen gas is produced from the gas mixing chamber 4, the fuel mixture repetitively collides with the wall surfaces of these fine passages in the process of passing through the water separating filter 5 from the left side to the right side in FIG. 2. Accordingly, small particles of waterdrops or steam contained the fuel mixture collide with the wall surfaces of these fine passages in the water separating filter 5 and adhere on the wall surfaces. Thus, the water separating filter 5 can surely trap and collect the small particles of waterdrops or steam contained the fuel mixture.
In this manner, the water components are removed from the fuel mixture before the fuel mixture flows into the catalytic combustion chamber 6. Thus, the catalytic combustion heater 1 is free from the problems of the conventional catalytic combustion apparatus. More specifically, in a condition immediately after the catalytic combustion apparatus starts its operation, the water components contained in the fuel mixture do not adhere on the low-temperature catalyst surface. The fuel mixture can surely contact with the catalyst and accordingly the catalytic combustion is stably maintained. Furthermore, the catalytic combustion heat is not consumed by the waterdrops for the latent heat required in the process of evaporation. The catalyst temperature can quickly increase to the active temperature within a short time.
The water separating filter 5 can possess excellent water collecting property if the fuel mixture frequently collides with the wall surfaces of the fine passages in the process of passing through the water separating filter 5. The collisions between the fuel mixture and the water separating filter 5 generally increase when the cordierite has small particle (or grain) diameters and when the water separating filter 5 has a small percentage of voids (i.e. a ratio of the volume of all voids to the volume of the water separating filter 5). However, using the cordierite having small particle (or grain) diameters and the water separating filter 5 having a small percentage of voids will encounter with the reduction in the fuel mixture flow rate due to undesirable increase of the air flow resistance in the water separating filter 5. To solve this problem, it will be necessary to increase the output or powers (or pressures) of the blower 3 and the hydrogen supplying apparatus. The size of the catalytic combustion heater 1 will increase. Hence, to realize the water separating filter 5 capable of attaining higher water collecting efficiency while suppressing the pressure loss, it is necessary to optimize the particle (or grain) diameters of the cordierite and the void volume (i.e. percentage of voids) of the water separating filter 5.
The catalytic combustion chamber 6 causes the catalytic combustion of the fuel mixture containing air and hydrogen gas, and produces high-temperature combustion gas. More specifically, the catalytic combustion chamber 6 forms a heating section of the catalytic combustion heater 1 in accordance with the first embodiment of the present invention. The catalytic combustion chamber 6 includes a honeycomb catalytic carrier which is made of the monolith ceramics, such as alumina or cordierite, and carries a catalyst, such as Pt (platinum).
The heat exchanger 7 is disposed at the downstream side of the catalytic combustion chamber 6 (i.e. the right side of the catalytic combustion chamber 6 in FIG. 2). The coolant is, for example, water or a solution of ethylene glycol. The heat exchanger 7 receives the high-temperature fuel mixture produced by the catalytic combustion and causes heat exchange between the high-temperature fuel mixture and the coolant (i.e. the heating medium). The heat exchanger 7 includes a plurality of tubes 71 and fins 72 disposed in the passage 81. Each tube 71 extends in the direction normal to the flowing direction of the fuel mixture. Each fin, disposed in a space between neighboring tubes 71, receives the heat transferred from the tubes 71. The tubes 71 and the fins 72 are exposed to the high-temperature fuel mixture. The coolant flows in respective tubes 71. It is thus desirable that the tubes 71 and the fins 72 are made of heat resisting and corrosion resisting materials. According to the catalytic combustion heater 1 of the first embodiment of the present invention, the tubes 71 and the fins 72 are made of a stainless steel plate. Furthermore, as shown in FIG. 1, the heat exchanger 7 is connected to the heater core 101 via a heater delivery pipe 73 to supply high-temperature coolant of the heat exchanger 7 to the heater core 101 of the heating system 100. Furthermore, the heat exchanger 7 is connected to the heater core 101 via a heater return pipe 74. The pump 102 provided in the heater return pipe 74 receives the coolant returning from the heater core 101 and supplies pressurized coolant to the heat exchanger 7. The coolant returns from the heater return pipe 74 and flows into each tube 71 from one end thereof. While the coolant flows in respective tubes 71, the coolant receives the heat from the high-temperature fuel mixture flowing outside respective tubes 71. The temperature of the coolant increases as a result of heat exchange with the fuel mixture. The heated coolant exits out of each tube 71 from the other end thereof. Then, the heated coolant is supplied via the heater delivery pipe 73 to the heater core 101.
Next, the characteristic features of the catalytic combustion heater 1 in accordance with the first embodiment of the present invention, i.e. the functions and effects brought by the arrangement of the water separating filter 5 will be explained with reference to the operation of the catalytic combustion heater 1.
(1) Immediate After Starting the Operation of Catalytic Combustion Heater 1
When the catalytic combustion heater 1 starts its operation, the blower 2 supplies the air to the gas mixing chamber 4 and the hydrogen supplying apparatus 3 supplies the hydrogen gas (i.e. off-gas) to the gas mixing chamber 4. The fuel mixture produced from the gas mixing chamber 4 flows into the water separating filter 5.
When the fuel mixture passes through the water separating filter 5, the waterdrops or steam contained in the air supplied from the blower 2 or the waterdrops or steam contained in the off-gas (i.e. the hydrogen gas supplied from the hydrogen supplying apparatus 3) collides the wall surfaces of the fine passages in the water separating filter 5 and adheres on these surfaces.
In the condition that the catalytic combustion heater 1 just starts its operation, the water separating filter 5 is still in a low temperature level near the ambient temperature. Accordingly, the waterdrops or steam, if trapped by the water separating filter 5, will dwell there in the form of liquid.
Furthermore, the waterdrops or steam contained in the fuel mixture may collide with the waterdrops trapped on the wall surfaces of the fine passages in the water separating filter 5. In this case, the waterdrops or steam will adhere on the trapped waterdrops.
In this manner, the water separating filter 5 can remove the waterdrops or steam contained in the fuel mixture. The fuel mixture containing no waterdrops or steam flows into the catalytic combustion chamber 6.
The catalytic combustion chamber 6 immediately causes the catalytic combustion of the fuel mixture. The generated catalytic combustion heat increases the temperature of the catalyst supported by the catalytic combustion chamber 6. As the fuel mixture contains no water components, no moisture adheres on the catalyst surface. The fuel mixture can surely contact with the catalyst. The catalytic combustion is stably maintained. The catalytic combustion heat is not consumed by the waterdrops for the latent heat required in the process of evaporation. Thus, according to the catalytic combustion heater 1 of the first embodiment of the present invention, the catalyst temperature can quickly increase to the active temperature within a short time.
Furthermore, according to the catalytic combustion heater 1 of the first embodiment of the present invention, the water separating filter 5 is made of cordierite. The surface of cordierite possesses the polarity. On the other hand, the water molecules possess the polarity due to their atomic arrangements. Therefore, the wall surfaces of the fine passages in the water separating filter 5 and the waterdrops or steam draw each other according to their polarities. The waterdrops or steam adheres on the catalyst. More specifically, the catalytic combustion heater 1 of the first embodiment of the present invention positively utilizes the intermolecular attractions brought by the cordierite to realize the water separating filter 5 having excellent properties for collecting waterdrops or steam. Accordingly, it becomes possible to attain higher efficiency in collecting the waterdrops or steam contained in the fuel mixture.
The porous gas-permeable solid material possessing the polarity is not limited to the cordierite. For example, γ alumina is a preferable material for forming the water separating filter 5. Even when the water separating filter 5 is made of γ alumina, it is possible to utilize the above-described intermolecular attractions for collecting the waterdrops or steam.
(2) In a Case that a Predetermined Time Has Elapsed After the Catalytic Combustion Heater 1 Starts its Operation.
After the catalytic combustion heater 1 starts its operation, the water separating filter 5 receives radiation heat from the catalytic combustion chamber 6 and accordingly the temperature increases in the water separating filter 5.
Accordingly, the water components dwelling in the water separating filter 5 absorb the heat of the water separating filter 5 and soon evaporate from the water separating filter 5. The steam of evaporated water components flows together with the stream of the fuel mixture. Thus, the steam of evaporated water components departs the water separating filter 5 and flows into the catalytic combustion chamber 6.
Furthermore, the waterdrops or steam contained in the fuel mixture 10 newly flows into the water separating filter 5 from the gas mixing chamber 4. The waterdrops or steam once adheres on the water separating filter 5 and soon evaporates from there. Alternatively, the waterdrops or steam evaporates in the process of passing through the water separating filter 5. Then, the steam of evaporated water components flows together with the stream of the fuel mixture. Thus, the steam of evaporated water components departs the water separating filter 5 and flows into the catalytic combustion chamber 6. The catalytic combustion chamber 6 is kept at higher temperatures. Accordingly, the steam flows into the catalytic combustion chamber 6 together with the fuel mixture, and then goes out of the catalytic combustion chamber 6 without adhering on the catalyst surface.
According to the catalytic combustion heater 1 of the above-described first embodiment of the present invention, the water separating filter 5 (i.e. the liquid collecting means) is interposed between the gas mixing chamber 4 and the catalytic combustion chamber 6 in the flowing direction of the fuel mixture in the passage 8. The water separating filter 5 includes numerous fine passages.
The air contains a significant amount of water component. Thus, the fuel mixture produced from the gas mixing chamber 4 contains water components. According to the catalytic combustion heater 1 of the first embodiment of the present invention, the hydrogen gas is the off-gas discharged from the fuel cell. The off-gas contains a great amount of steam as a reaction product discharged from the fuel cell.
According to the catalytic combustion heater 1 of the first embodiment of the present invention, the water separating filter 5 surely traps the waterdrops or steam contained in the fuel mixture produced from the gas mixing chamber 4. The trapped water dwells in the water separating filter 5.
Thus, the water components can be removed from the fuel mixture before the fuel mixture flows into the catalytic combustion chamber 6. As the fuel mixture contains no water components, no moisture adheres on the catalyst surface. The fuel mixture can surely contact with the catalyst. The catalytic combustion is stably maintained. The catalytic combustion heat is not consumed by the waterdrops for the latent heat required in the process of evaporation. Thus, it becomes possible to realize the catalytic combustion heater 1 capable of quickly increasing the catalyst temperature to the active temperature within a short time.
According to the above-described catalytic combustion heater 1 of the first embodiment of the present invention, the water separating filter 5 is made of cordierite. However, the water separating filter 5 can be made of any other porous gas-permeable solid material capable of trapping waterdrops or steam. For example, the water separating filter 5 can be made of γ alumina or comparable material other than the ceramics, such as a sintered metal.

Second Embodiment

FIG. 3 is a partly cross-sectional view showing a catalytic combustion heater 1 in accordance with a second embodiment of the present invention.
A catalytic combustion heater 1 in accordance with the second embodiment of the present invention is different from the catalytic combustion heater 1 in accordance with the first embodiment of the present invention in that the water separating filter 5 has a modified arrangement.
FIG. 5B shows the detailed structure of the water separating filter 5 shown in FIG. 3. The water separating filter 5 includes an electric heater 51 embedded therein so as to extend inside the filter body and cross some of passages Sa.
More specifically, the water separating filter 5 includes the electric heater 51 which is, for example, made of a nichrome wire or a nickel wire. The electric heater 51 can be embedded in the cordierite in the process of molding the water separating filter 5. Furthermore, as shown in FIG. 3, the electric heater 51 is electrically connected via lead wires 52 and 53 to an external device (not shown) provided outside the catalytic combustion heater 1.
According to the arrangement of the second embodiment, it is preferable to supply electric power to the electric heater 51 as soon as the catalytic combustion heater 1 starts its operation. The temperature of the electric heater 51 increases early. The temperature of the water separating filter 5 increases quickly compared with the catalytic combustion heater 1 disclosed in the first embodiment of the present invention.
The catalytic combustion heater 1 in accordance with the second embodiment of the present invention can reduce the dwelling time of the waterdrops or steam in an event that the waterdrops or steam is trapped in the water separating filter 5 after the catalytic combustion heater 1 starts its operation.
The water separating filter 5 not only traps the waterdrops or steam contained in the fuel mixture but also stores the trapped water components. More specifically, the radiation heat from the catalytic combustion chamber 6 increases the temperature of the water separating filter 5. The waterdrops or steam flows into the water separating filter 5 and once adheres on the high-temperature water separating filter 5. Then, the waterdrops or steam promptly evaporates with the heat transferred from the water separating filter 5. The waterdrops or steam may evaporate when it flows in the water separating filter 5. The length of the water separating filter 5 in the mixture flowing direction should be sufficiently long to surely store all of the trapped water components without any leakage to the outside.
According to the catalytic combustion heater 1 in accordance with the second embodiment of the present invention, the water separating filter 5 is equipped with the electric heater 51. The electric heater 51 can reduce the time required for the waterdrops or steam having newly flowed into the water separating filter 5 to evaporate before it goes out of the water separating filter 5. In other words, the catalytic combustion heater 1 in accordance with the second embodiment of the present invention can reduce the water amount stored in the water separating filter 5. The length of the water separating filter 5 in the fuel mixture flowing direction can be reduced. Accordingly, the catalytic combustion heater 1 can be downsized.
According to the catalytic combustion heater 1 of the second embodiment of the present invention, the electric heater 51 is embedded in the water separating filter 5. In other words, the electric heater 51 and the water separating filter 5 are integrated into one unit. However, it is possible to separately form the electric heater 51 and the water separating filter 5 as two independent components and dispose the electric heater 51 at the upstream side of the water separating filter 5 in the passage 81.

Third Embodiment

FIG. 4 is a partly cross-sectional view showing a catalytic combustion heater 1 in accordance with a third embodiment of the present invention.
A catalytic combustion heater 1 in accordance with the third embodiment of the present invention is different from the catalytic combustion heater 1 in accordance with the first embodiment of the present invention in that the water separating filter 5 has a modified arrangement.
FIG. 5C shows the detailed structure of the water separating filter 5 shown in FIG. 4. The water separating filter 5 includes collector plates 56 disposed at its upper and lower ends. The water separating filter 5 includes lead wires 54 and 55 extending from these upper and lower collector plates 56 to the outside.
More specifically, the water separating filter 5 is an electric conductive substance and is a porous gas-permeable solid material. Furthermore, as shown in FIG. 4, the water separating filter 5 is electrically connected via the lead wires 54 and 55 to an external device (not shown) provided outside the catalytic combustion heater 1. The water separating filter 5, when it receives electric power, generates Joule heat due to its electric resistance. The generated heat increases the temperature of the water separating filter 5.
The electric conductive and porous gas-permeable solid material for the water separating filter 5 according to the third embodiment of the present invention is, for example, a sintered metal or electrically conductive ceramics.
According to the arrangement of the third embodiment, it is preferable to supply electric power to the water separating filter 5 as soon as the catalytic combustion heater 1 starts its operation. The temperature of the water separating filter 5 increases quickly compared with the catalytic combustion heater 1 disclosed in the first embodiment of the present invention.
Accordingly, the catalytic combustion heater 1 according to the third embodiment of the present invention brings substantially the same effects as those of the catalytic combustion heater 1 according to the second embodiment of the present invention. More specifically, the water separating filter 5 capable of generating Joule heat can reduce the time required for waterdrops or steam having newly flowed into the water separating filter 5 to evaporate before it goes out of the water separating filter 5. In other words, the catalytic combustion heater 1 in accordance with the third embodiment of the present invention can reduce the length of the water separating filter 5 in the fuel mixture flowing direction. Accordingly, the catalytic combustion heater 1 can be downsized.
The catalytic combustion heater 1 disclosed in the first, second, or third embodiment of the present invention includes the heat exchanger 7 incorporated in the heating system 100 to increase the temperature of the coolant (i.e. heating medium). However, application of the catalytic combustion heater 1 according to the present invention is not limited to the temperature increase of the heating medium in the heating system 100. For example, it is possible to remove the heat exchanger 7 from the catalytic combustion heater 1 when the combustion gas discharged from the catalytic combustion chamber 6 is directly used for the warm-air heating.
The combustion gas discharged from the catalytic combustion chamber 6 contains no harmful substances such as NOx because the combustion gas (i.e. the product of the catalytic combustion based on the hydrogen fuel) is the mixture of air and steam (H₂O). This is why the combustion gas discharged from the catalytic combustion heater 1 can be directly used for the warm-air heating of a vehicle compartment or any other room.
Furthermore, according to the above-described first to third embodiments of the present invention, the catalytic combustion heater 1 uses a hydrogen fuel. However, the fuel is not limited to the hydrogen gas. Accordingly, it is possible to use other type of gaseous fuel.
The catalytic combustion apparatus according to the present invention can be preferably used to remove the water components contained in the air in a low combustion temperature or remove the water components produced from the catalytic combustion of the hydrogen fuel gas. Furthermore, the catalytic combustion apparatus according to the present invention can be used to remove the water components contained in the off-gas discharged from the fuel cell. The off-gas contains unreacted hydrogen gas with a great amount of water components. Accordingly, if the off-gas is reused as fuel gas, the water components will adhere on the surface of the catalyst. Even in such a case, the catalytic combustion apparatus of the present invention can suppress the moisture adhesion on the catalyst surface.

Claims

1. A catalytic combustion apparatus comprising:

gas mixing means for forming a fuel mixture of air and fuel;

air supplying means for supplying said air to said gas mixing means;

fuel supplying means for supplying said fuel to said gas mixing means;

a passage connected to said gas mixing means and receiving said fuel mixture formed by and supplied from said gas mixing means; and

a catalytic combustion section disposed at a downstream side of said gas mixing means, including a catalyst supported by a catalytic carrier,

wherein

liquid collecting means having numerous fine passages for collecting liquid and interposed between said gas mixing means and said catalytic combustion section in a flowing direction of said fuel mixture in said passage.

2. The catalytic combustion apparatus in accordance with claim 1, wherein said liquid collecting means includes a heater.

3. The catalytic combustion apparatus in accordance with claim 2, wherein said heater is an electric heating element.

4. The catalytic combustion apparatus in accordance with claim 1, wherein said liquid collecting means is made of an electric conductive substance and generates heat in response to supplied electric power.

5. The catalytic combustion apparatus in accordance with claim 1, wherein said liquid collecting means is a porous gas-permeable solid material.

6. The catalytic combustion apparatus in accordance with claim 1, wherein said fuel is hydrogen gas.

7. The catalytic combustion apparatus in accordance with claim 1, further including a heat exchanger disposed at a downstream side of said catalytic combustion section in said passage and including a heating medium for causing heat exchange between said heating medium and combustion gas supplied from said catalytic combustion section.