US20050172618A1

US20050172618A1 - Catalytic combustion heating apparatus

Info

Publication number: US20050172618A1
Application number: US11/047,582
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: JP2005221201A; DE102005005311A1

Abstract

A water repellent material, such as PTFE layer, is provided by coating on the surface of a Pt catalyst. A catalytic carrier supporting the Pt catalyst is a metallic tube, such as an aluminum tube. The coolant acting as a heating medium is supplied into this metallic tube. According to this arrangement, the catalyst surface is not covered with the moisture contained in the air, the moisture contained in the fuel gas, or the moisture contained in the exhausted catalytic combustion gas. The catalyst can directly contact with a fuel mixture. The catalyst function does not deteriorate. A sufficient amount of catalytic combustion heat is generated. Accordingly, the catalytic combustion heater can quickly increase the catalyst temperature to the activation temperature within a short time. Furthermore, the temperature of the PTFE layer can be maintained at a temperature range not exceeding its heat-resisting limit.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from earlier Japanese Patent Application No. 2004-32408 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 heating apparatus which is a preferable heat source of a home or automotive heater. The catalytic combustion heating 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 heating apparatus is based on low-temperature flameless combustion which is preferable to completely eliminate the emission of NOx. The catalytic combustion heating 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 heating 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 heating apparatus. The fuel mixture of this fuel (gas) and air is supplied to the catalyst to cause catalytic combustion.
Furthermore, if the catalytic combustion heating 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.
For example, according to a conventional catalytic combustion heating 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 increases in the combustion catalyst. 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 heating 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 heating 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 heating apparatus starts its operation, the temperature of the catalytic combustion heating 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 heating 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 heating 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 the 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 accordingly heat generation by the catalytic combustion will decrease. Furthermore, the waterdrops adhering on the catalyst surface will receive generated catalytic combustion heat, and then 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 combustion heat and the consumption of generated heat by the waterdrops. There will be a long time before the heating medium can receive a rated heat amount in the catalytic combustion heating apparatus.
For example, in a vehicle driven by a hydrogen fuel cell, the catalytic combustion heating 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 heating 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 heating 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 heating apparatus which is capable of reducing the moisture adhering on the catalyst surface after the catalytic combustion heating 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 first catalytic combustion heating apparatus including a gas mixing means, an air supplying means, a fuel supplying means, a passage, a catalyst, and a heat exchanger. 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 catalyst is supported by a catalytic carrier and disposed in the passage. And, the heat exchanger receiving a heating medium is disposed at a downstream side of the catalytic carrier in a flowing direction of the fuel mixture in the passage, to perform heat exchange between the fuel mixture and the heating medium. According to the first catalytic combustion heating apparatus of the present invention, catalytic combustion of the fuel mixture is caused in the catalyst and the generated catalytic combustion heat is transferred via the heat exchanger to the heating medium. Furthermore, the catalyst possesses a water repellent function.
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, the moisture contained in the fuel gas, or the 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 hydrogen gas, a great amount of water is produced as a result of catalytic combustion. 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.
Hereinafter, adhesion of the steam onto the catalyst will be briefly explained.
A general oxidation catalyst is made of a noble metal, such as Pt (platinum) or Pd (palladium), i.e. a metal, which is non-polar in molecule. Furthermore, a general catalytic carrier is γ alumina or cordierite which possesses the polarity due to the presence of OH group. On the other hand, the water molecule possesses the polarity due to its atomic arrangement. Therefore, the catalytic carrier and the steam draw each other according to their polarities. The steam adheres on the catalyst.
When the material possesses the water repellent function, the surface of this material is non-polar and no moisture can adhere on this surface. According to the catalytic combustion heating apparatus of the present invention, the steam does not adhere on the catalyst surface and soon leaves along with the mixture stream. Furthermore, even when waterdrops condense on the catalyst surface, the adhesive force of respective waterdrops acting against the catalyst surface is small due to the water repellent function of the catalyst. Each waterdrop has a substantially spherical shape due to surface tension acting thereon. Accordingly, the waterdrops can roll easily, when they are propelled by a fluid force of the mixture stream. The waterdrops move (i.e. roll) along the catalyst surface toward the downstream side and soon leave the catalyst. Therefore, no moisture adheres on the catalyst surface. Thus, the present invention provides a catalytic combustion heating apparatus capable of quickly increasing the catalyst temperature to the activation temperature within a short time.
According to the first catalytic combustion heating apparatus of the present invention, it is preferable that a water repellent material is provided on the catalyst to give water repellent function to the catalyst.
The water repellent material is, for example, PTFE (poly.tetra.fluoro.ethylene) which is an organic polymer material. This material is non-polar and non-conductive. Accordingly, when a non-polar and non-conductive PTFE layer is formed, for example, by coating on the catalyst, the catalyst surface becomes non-polar. No moisture can adhere on the catalyst surface.
According to this arrangement, the water repellent function equipped catalyst can be easily formed at a low cost.
According to the first catalytic combustion heating apparatus of the present invention, it is preferable that the catalytic carrier is made of a water repellent material to give water repellent function to the catalyst.
In this case, when the catalytic carrier is made of a water repellent material, i.e. a non-polar material, such as a alumina or titania (TiO₂, titanium dioxide), the non-polar catalyst can be supported by the non-polar catalytic carrier. Thus, the catalyst surface is non-polar and possesses the water repellency.
This arrangement prevents the moisture from adhering and staying on the catalyst surface. Thus, it becomes possible to provide a catalytic combustion heating apparatus capable of quickly increasing the catalyst temperature to the activation temperature within a short time.
According to the first catalytic combustion heating apparatus of the present invention, it is preferable that a water repellent material is provided on the catalyst. For example, the water repellent material is a PTFE layer which is an organic polymer material. This arrangement can ensure the water repellency of the catalyst surface and prevent the moisture from adhering and staying on the catalyst surface. Thus, it becomes possible to provide a catalytic combustion heating apparatus capable of quickly increasing the catalyst temperature to the activation temperature within a short time.
According to the first catalytic combustion heating apparatus of the present invention, it is preferable that the catalytic carrier includes a plurality of metallic tubes disposed parallel to each other and normal to the flowing direction of the fuel mixture. The metallic tubes have both ends opened to an annular passage. And, the heating medium is supplied into the annular passage and the metallic tubes.
A general catalytic carrier is made of the ceramics, such as cordierite, and configured into a honeycomb structure. The catalyst, such as Pt, is supported on the surface of this catalytic carrier. The ceramics have small thermal conductivities and small thermal capacities. Therefore, the catalyst temperature quickly increases to the activation temperature within a short time after the catalytic combustion heating apparatus starts its operation.
On the other hand, the organic polymer material (i.e. water repellent material), such as PTFE, has a heat-resisting limit of approximately 200° C. If the temperature of the organic polymer material exceeds this heat-resisting limit, the water repellent material starts decomposing and the water repellent function will soon disappear. Therefore, to maintain the water repellent function of the catalyst, it is definitely necessary to maintain the catalyst temperature to an appropriate temperature range not exceeding the heat-resisting limit of the water repellent material.
As a method for maintaining the catalyst temperature to an appropriate temperature range not exceeding the heat-resisting limit of the water repellent material, it may be possible to increase the air supply amount to decrease the hydrogen gas concentration in the fuel mixture. According to this method, part of the catalytic combustion heat is consumed to increase the air temperature so as to prevent the catalyst temperature from exceeding the heat-resisting limit of the water repellent material. However, the air supplying device will be required to have a large power. The size of the catalytic combustion heating apparatus will increase.
Therefore, according to the above-described preferred arrangement of the catalytic combustion heating apparatus of the present invention, the catalytic combustion heat transmitted to the catalyst is partly transferred via the metallic tube (i.e. catalytic carrier) to the heating medium. Thus, this arrangement can prevent excessive increase of the catalyst temperature without increasing the size of the catalytic combustion heating apparatus. More specifically, the catalyst temperature does not exceed the heat-resisting limit of the water repellent material.
In this case, the heat transfer rate (i.e. the degree of heat transfer from the catalyst surface to the heating medium via the metallic tube) varies depending on the thermal conductivity and the thickness of the metallic tube, the inner diameter of the metallic tube (i.e. a heating medium amount in the metallic tube), and the shifting speed of the heating medium in the metallic tube. For example, if the inner diameter of the metallic tube is sufficiently large, the heating medium will be able to easily pass the metallic tube. The heat transfer rate from the catalyst surface to the heating medium will increase. The catalyst temperature remains in a temperature range not exceeding the heat-resisting limit of the water repellent material. However, it will take a long time to increase the catalyst temperature. Hence, the inner diameter of the metallic tube must be set to an optimum value to quickly increase the catalyst temperature without exceeding the heat-resisting limit of the water repellent material.
For example, it is now assumed that the metallic tube is an aluminum tune having a smaller specific heat. And, the inner diameter of the metallic tube is set to a smaller value so that no substantial flow of the heating medium occurs in the metallic tube even when a pressure is applied by the heating medium supplied into the annular passage. In this case, the heating medium in the metallic tube will show the following behavior. The pressure acting from the heating medium supplied into the annular passage is in a level sufficient to circulate the heating medium in the heat exchanger to transfer the heat via the heat exchanger to the heating medium. Furthermore, to suppress the substantial flow of the heating medium in the metallic tube under such a heating medium pressure, the setting of the inner diameter of the metallic tube should satisfy the requirement that a contact force between the inner wall surface of the metallic tube and the heating medium becomes equal to or larger than the force acting to the heating medium in the metallic tube by the heating medium pressure.
In this case, steam bubbles appear when the temperature of the heating medium in the metallic tube reaches a boiling point. The steam bubbles grow bigger with the heat transmitted from the catalyst to the heating medium. Then, the steam bubbles shift in the metallic tube toward one end or both ends of the metallic tube. Subsequently, the steam bubbles contact with low-temperature heating medium in the annular passage. Thus, the temperature of the steam bubbles decreases and accordingly the steam bubbles will soon contract and disappear. The cooled heating medium is again heated by the heat transferred from the catalyst surface via the metallic tube. Thus, the temperature of the heating medium in the metallic tube again reaches a boiling point. During the catalytic combustion, the heating medium in the metallic tube repeats the above-described sequential behavior; i.e. boiling of heating medium→growth of bubbles→contraction and collapse of bubbles→boiling of heating medium. As a result, the catalyst temperature is stably maintained at a temperature range near the boiling point of the heating medium. Furthermore, the heating medium amount in the metallic tube is small. Accordingly, the heating medium starts boiling within a short time after the catalytic combustion heating apparatus starts its operation. In other words, the catalyst temperature quickly increases within a short time after the catalytic combustion heating apparatus starts its operation.
Accordingly, the above-described preferred arrangement of the catalytic combustion heating apparatus of the present invention can surely prevent excessive increase of the catalyst temperature. More specifically, the catalyst temperature does not exceed the heat-resisting limit of the water repellent material. The water repellent function of the water repellent material can be stably maintained. It becomes possible to provide a catalytic combustion heating apparatus capable of quickly increasing the catalyst temperature to the activation temperature within a short time after the catalytic combustion heating apparatus starts its operation.
According to the first catalytic combustion heating apparatus of the present invention, it is preferable that an auxiliary catalytic carrier supporting an auxiliary catalyst is disposed between the catalytic carrier and the heat exchanger in the flowing direction of the fuel mixture in the passage.
In this case, the water repellent function equipped catalyst section is positioned at the upstream side of the second catalyst. The catalytic combustion heat generated by the water repellent function equipped catalyst section is used to increase the temperature of the fuel mixture. Therefore, the fuel mixture flowing into the second catalyst has a higher temperature than the fuel mixture in the water repellent function equipped catalyst section. Therefore, all of the moisture contained in the air, the moisture contained in the fuel gas, and the moisture contained in the exhausted catalytic combustion gas immediately evaporates and accordingly no waterdrops adhere on the surface of the second catalyst. The second catalyst is not required to possess the water repellent function.
Namely, the water repellent function equipped catalyst has the capability of increasing the temperature of the fuel mixture flowing into the second catalyst to a predetermined higher level to eliminate the waterdrops adhering on the surface of the second catalyst.
This arrangement can minimize the amount of the water repellent function equipped catalyst required for catalytic combustion heating apparatus. Therefore, the cost increase of the catalytic combustion heating apparatus can be minimized.
Furthermore, to accomplish the above and other related objects, the present invention provides a second catalytic combustion heating apparatus including a gas mixing means, an air supplying means, a fuel supplying means, a passage, and a heat exchanger. 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. And, the heat exchanger receiving a heating medium is disposed in the passage to perform heat exchange between the fuel mixture and the heating medium. According to the second catalytic combustion heating apparatus of the present invention, catalytic combustion of the fuel mixture is caused by a catalyst and the generated catalytic combustion heat is transferred via the heat exchanger to the heating medium. The heat exchanger includes a plurality of tubes each having an inner passage in which the heating medium flows and fins each being disposed in a space between neighboring tubes for receiving heat transferred from the tubes. The catalyst is supported on at least one surface of the tubes and the fins. And, the catalyst possesses a water repellent function.
In this case, the heat exchanger has a capability of functioning as a catalytic carrier. The water repellent function equipped catalyst is supported by the heat exchanger. Namely, the catalytic carrier and the heat exchanger can be integrated into a single unit.
This arrangement can minimize the size of the catalytic combustion heating apparatus (especially the longitudinal size of the mixture passage), and can eliminate the adhesion and detention of the moisture on the catalyst surface. Thus, it becomes possible to provide a catalytic combustion heating apparatus capable of quickly increasing the catalyst temperature to the activation temperature within a short time.
Furthermore, the catalytic combustion occurring in the heat exchanger can improve the efficiency in transferring the generated catalytic combustion heat to the heating medium. As a result, the thermal efficiency of the catalytic combustion heating apparatus can be improved.
According to the second catalytic combustion heating apparatus of the present invention, it is preferable that a water repellent material is provided on the catalyst to give water repellent function to the catalyst. This makes it possible to easily form the water repellent function equipped catalyst at a low cost.
According to the first or second catalytic combustion heating apparatus of the present invention, it is preferable that the fuel is hydrogen gas.
Therefore, even when the catalytic combustion heating apparatus of the present invention is used as a fuel cell stack preheating apparatus of a fuel cell system using the hydrogen fuel, the catalyst temperature can be quickly increased quickly to the activation temperature within a short time after the catalytic combustion heating apparatus starts its operation.

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 cross-sectional view showing the catalytic combustion heater in accordance with the first embodiment of the present invention, taken along a line III-III of FIG. 2;
FIG. 4 is an enlarged view showing a portion indicated by VI in FIG. 2;
FIGS. 5A to 5C are cross-sectional views showing the condition of coolant in an aluminum tube of a first catalyst section of the catalytic combustion heater in accordance with the first embodiment of the present invention, wherein FIG. 5A shows the coolant condition at the coolant temperature equal to or less than 99° C., FIG. 5B shows the coolant condition at the coolant temperature in a range from 100° C. to 119° C., and FIG. 5C shows the coolant condition at the coolant temperature of about 120° C.;
FIG. 6 is a partly cross-sectional view showing a catalytic combustion heater in accordance with a second embodiment of the present invention; and
FIG. 7 is a partly cross-sectional view showing a catalytic combustion heater in accordance with a 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 heating apparatus in accordance with a preferred embodiment of the present invention will be explained with reference to a catalytic combustion heater 1 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. FIG. 3 is a cross-sectional view showing the catalytic combustion heater 1 in accordance with the first embodiment of the present invention, taken along a line III-III of FIG. 2. FIG. 4 is an enlarged view showing a portion indicated by VI in FIG. 2. FIGS. 5A to 5C are cross-sectional views showing the condition of coolant in an aluminum tube 51 of a first catalyst section 5 of the catalytic combustion heater 1 in accordance with the first embodiment of the present invention, wherein FIG. 5A shows the coolant condition at the coolant temperature equal to or less than 99° C., FIG. 5B shows the coolant condition at the coolant temperature in a range from 100° C. to 119° C., and FIG. 5C shows the coolant condition at the coolant temperature of about 120° C.
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 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 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 first catalyst section 5, a second catalyst section 6, 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.
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 first catalyst section 5 is disposed at the downstream side of the gas mixer 4 (i.e. the right side of the gas mixer 4 in FIG. 2).
The second catalyst section 6 is disposed at the downstream side of the first catalyst section 5. Both the first catalyst section 5 and the second catalyst section 6 cause catalytic combustion of the fuel mixture. The first catalyst section 5 forms a heat generating section of the catalytic combustion heater 1 in accordance with the first embodiment of the present invention. The first catalyst section 5 consists of a plurality of aluminum (i.e. metallic) tubes 51 and a water gallery 52. Each aluminum (i.e. metallic) tube 51 is a catalytic carrier. The water gallery 52 is an annular passage forming an outer peripheral portion of the passage 8 so as to surround the aluminum tubes 51. The aluminum tubes 51 are parallel to each other and disposed normal to the flowing direction of the fuel mixture. More specifically, the aluminum tubes 51 extend in the direction perpendicular to the sheet of FIG. 2. As shown in FIG. 3, each aluminum tube 51 is opened at both ends to the water gallery 52. In other words, each aluminum tube 51 is gastightly connected at its both ends to the water gallery 52. Furthermore, as shown in FIG. 4, each aluminum tube 51 carries a Pt (platinum) catalyst 53 on the outer cylindrical surface thereof. Furthermore, as shown in FIG. 4, a PTFE (poly.tetra.fluoro.ethylene) layer is coated on the outer surface of the Pt catalyst 53. The PTFE layer is a water repellent material and is also an organic polymer material. Furthermore, the water gallery 52 is molded out of an aluminum plate. Furthermore, the water gallery 52 has a coolant inlet pipe 55 and a coolant return pipe 56. The later-described coolant is introduced into the water gallery 52 from the coolant inlet pipe 55 and discharged out of the water gallery 52 from the coolant return pipe 56. As shown in FIG. 1, the coolant inlet pipe 55 and the coolant return pipe 56 are connected to the outlet side and to the inlet side of the pump 102 of the heating system 100, respectively. The coolant supplied from the pump 102 is partly supplied to the water gallery 52 of the first catalyst section 5 via the coolant inlet pipe 55. The coolant passes through the water gallery 52 and respective aluminum tubes 51 and then returns via the coolant return pipe 56 to the pump 102. Furthermore, the inside spaces of respective aluminum tubes 51 and the water gallery 52 are filled with the coolant (i.e. the heating medium). According to the first embodiment of the present invention, the coolant used in the catalytic combustion heater 1 is the solution of ethylene glycol.
The first embodiment of the present invention defines an inner diameter “d” of the aluminum tube 51 of the catalytic combustion heater 1 in the following manner.
In the condition that the inside space of the aluminum tube 51 is filled with the coolant, no substantial flow of the coolant should occur in the aluminum tube 51 in response to the pressure applied when the coolant is introduced into the water gallery 52 from the pump 102. In other words, the pressure acting from the coolant of the water gallery 52 to the coolant of the aluminum tube 51, more specifically the pressure difference between both ends of the aluminum tube 51, is set to be equal to or slightly smaller than the adhesive force acting between the inner wall surface of the aluminum tube 51 and the coolant. Accordingly, for a while after the catalytic combustion heater 1 starts its operation, no substantial flow of the coolant occurs in the aluminum tube 51 even when the coolant circulates in the water gallery 52. According to the catalytic combustion heater 1 of the first embodiment of the present invention, the diameter size “d” is approximately 1 mm.
The second catalyst section 6 is disposed next to and at the downstream side of the first catalyst section 5 as shown in FIG. 2. The second catalyst section 6 includes a honeycomb carrier which is made of the ceramics, such as alumina or cordierite, and carries a catalyst, such as Pt (platinum). The second catalyst section 6 has the arrangement of a general monolith catalyst.
The heat exchanger 7 is disposed at the downstream side of the second catalyst section 6 (i.e. the right side of the second catalyst section 6 in FIG. 2). The heat exchanger 7 receives the high-temperature fuel mixture produced by catalytic combustion and causes heat exchange between the high-temperature fuel mixture and the coolant (i.e. the heating medium). According to the catalytic combustion heater 1 of the first embodiment of the present invention, 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 a heat resisting and corrosion resisting material. According to the catalytic combustion heater 1 of the first embodiment of the present invention, the tubes 71 and the fins 72 ares 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 first catalyst section 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
Immediately after the catalytic combustion heater 1 starts its operation, temperatures of the first catalyst section 5 and the coolant are low (i.e. at the ambient temperature level). Accordingly, the moisture contained in the air, the moisture contained in the fuel gas, or the moisture contained in the exhausted catalytic combustion gas will turn into the steam or waterdrops. The steam or waterdrops will adhere on the surface of the Pt catalyst 53 of the first catalyst section 5. More specifically, the steam or waterdrops will adhere on the PTFE layer 54 (i.e. water repellent material). However, due to the water repellency of the PTFE layer 54, the steam or waterdrops will immediately slide and flow along the surface of the PTFE layer 54 together with the fuel mixture and the exhaust gas of the catalytic combustion. Then, the steam or waterdrops will soon evaporate by the heat of the exhaust gas of the catalytic combustion. Therefore, according to the catalytic combustion heater 1 of the first embodiment of the present invention, none of the moisture contained in the air, the moisture contained in the fuel gas, and the moisture contained in the exhausted catalytic combustion gas can adhere on the catalyst.
This arrangement prevents the catalyst surface from being covered with the moisture contained in the air, the moisture contained in the fuel gas, or the moisture contained in the exhausted catalytic combustion gas. With this arrangement, the fuel mixture can surely contact with the catalyst. The catalyst function can be maintained appropriately. In other words, a sufficient amount of heat is generated by the catalytic combustion. Accordingly, the generated catalytic combustion heat can be efficiently used to increase the catalyst temperature. It becomes possible to provide the catalytic combustion heater 1 capable of quickly increasing the catalyst temperature to the activation temperature within a short time.
Furthermore, the generated catalytic combustion heat is transferred via the aluminum tube 51 to the coolant in the aluminum tube. Thus, the temperature of the coolant increases. As explained previously, no substantially flow of the coolant occurs in the aluminum tube 51. And the inner diameter “d” of the aluminum tube 51 is small (i.e. approximately 1 mm). In other words, the circulation amount of the coolant in the aluminum tube 51 is very small. Accordingly, a small amount of heat is transferred from the Pt catalyst 53 to the coolant via the aluminum tube 51. Most of the generated catalytic combustion heat is used to increase the catalyst temperature.
Furthermore, immediately after the catalytic combustion heater 1 starts its operation, the coolant in the aluminum tube 51 contains no bubbles as shown in FIG. 5A. The coolant temperature is equal to or less than 99° C. In this case, the temperature of Pt catalyst 53, i.e. the temperature of PTFE layer 54, is equal to or less than.
The catalytic combustion of the first catalyst section 5 can sufficiently increase the temperature of the fuel mixture flowing into the second catalyst section 6. Therefore, the temperature of the second catalyst section 6 quickly increases to the activation temperature within a short time. Accordingly, the catalyst surface of the second catalyst section 6 is not covered with the moisture contained in the air, the moisture contained in the fuel gas, or the moisture contained in the exhausted catalytic combustion gas, although the second catalyst section 6 has no coating of PTFE layer 54.
(2) Further Time Elapse Since Operation Start of Catalytic Combustion Heater 1 (Part I)
When a significant of time has passed since start of operation in the catalytic combustion heater 1, the coolant temperature in the aluminum tube 51 continuously increases with elapsed time. When the coolant temperature exceeds 100° C., the coolant starts boiling. Numerous small bubbles B appear in the coolant of the aluminum tube 51 as shown in FIG. 5B. In this case, the temperature of Pt catalyst 53, i.e. the temperature of PTFE layer 54, is approximately 120° C.
(3) Further Time Elapse Since Operation Start of Catalytic Combustion Heater 1 (Part II)
Furthermore, when the operation time of the catalytic combustion heater 1 has passed, the growth of bubbles B in the coolant of the aluminum tube 51 is promoted and neighboring bubbles B start merging into a larger bubble. When the coolant temperature reaches 120° C., the bubbles B in the coolant grow as large as the inner diameter of the aluminum tube 51 as shown in FIG. 5C. Due to buoyancy, the large bubbles B start moving in the aluminum tube 51 toward the water gallery 52. In this case, the temperature of Pt catalyst 53, i.e. the temperature of PTFE layer 54, is approximately 140° C.
(4) Further Time Elapse Since Operation Start of Catalytic Combustion Heater 1 (Part III)
As soon as the large bubbles B go out of the aluminum tube 51 and enter into the water gallery 52, the coolant of the water gallery 52 flows into the aluminum tube 51 so as to fill the space having been occupied by the outgoing bubbles B.
The low-temperature coolant flows into the water gallery 52 after the heat of the coolant is released from the heater core 101 of the heating system 100 as shown in FIG. 1.
According to the catalytic combustion heater 1 of the first embodiment of the present invention, the coolant temperature in the water gallery 52 is approximately 80° C. Therefore, if the bubbles B in the aluminum tube 51 are replaced by the coolant of the water gallery 52, the coolant temperature in the aluminum tube 51 will decrease to approximately 80° C. Thus, the temperature of Pt catalyst 53, i.e. the temperature of PTFE layer 54, will decrease to approximately 100° C.
Furthermore, after the operation time of the catalytic combustion heater 1 has passed, the coolant temperature in the aluminum tube 51 again increases and the coolant in the aluminum tube 51 repeats the cycle of above-described phases (2)→(3)→(4)→(2).
In short, during the operation of the catalytic combustion heater 1, the coolant temperature in the aluminum tube 51 is maintained in the range of 80° C. to 120° C. On the other hand, the temperature of Pt catalyst 53, i.e. the temperature of PTFE layer 54, is maintained in the range of 100° C. to approximately 140° C. In other words, the temperature of PTFE layer 54 is maintained at the level somewhat higher than the boiling point of the coolant.
Accordingly, the temperature of PTFE layer 54 can be surely controlled to a temperature range not exceeding the heat-resisting limit of the PTFE layer 54 (i.e. 200° C.).
According to the above-described catalytic combustion heater 1 of the first embodiment of the present invention, the PTFE layer 54 (i.e. water repellent material) is provided by coating on the Pt catalyst 53. Furthermore, the catalytic carrier supporting the Pt catalyst 53 is the aluminum tube 51 (i.e. the metallic tube) in which the coolant (i.e. the heating medium) is supplied.
This arrangement prevents the catalyst surface from being covered with the moisture contained in the air, the moisture contained in the fuel gas, or the moisture contained in the exhausted catalytic combustion gas. With this arrangement, the fuel mixture can surely contact with the catalyst. The catalyst function can be maintained appropriately. In other words, a sufficient amount of heat is generated by the catalytic combustion. Accordingly, the generated catalytic combustion heat can be efficiently used to increase the catalyst temperature. It becomes possible to provide the catalytic combustion heater 1 capable of quickly increasing the catalyst temperature to the activation temperature within a short time.
Furthermore, the setting of the inner diameter of the aluminum tube 51 satisfies the requirement that no substantial flow of the coolant occurs in the aluminum tube 51 in response to the pressure applied when the coolant is introduced into the water gallery 52 from the pump 102, in the condition that the inside space of the aluminum tube 51 is filled with the coolant. In other words, the pressure acting from the coolant of the water gallery 52 to the coolant of the aluminum tube 51, more specifically the pressure difference between both ends of the aluminum tube 51, is set to be equal to or slightly smaller than the adhesive force acting between the inner wall surface of the aluminum tube 51 and the coolant.
With this setting, it becomes possible to intermittently allow the coolant to flow into the aluminum tube 51 only when the coolant temperature in the aluminum tube 51 exceeds the boiling point of the coolant. Thus, the temperature of PTFE layer 54 can be maintained in the temperature somewhat higher than the boiling point of the coolant, more specifically in the range from 100° C. to approximately 140° C. Accordingly, the temperature of PTFE layer 54 can be surely controlled to a temperature range not exceeding the heat-resisting limit of the PTFE layer 54 (i.e. 200° C.).
Furthermore, according to the above-described catalytic combustion heater 1 of the first embodiment of the present invention, the second catalyst section 6 is disposed between the first catalyst section 5 and the heat exchanger 7 in the flowing direction of the fuel mixture in the passage 81.
In this case, the fuel mixture flowing into the second catalyst section 6 has a higher temperature than the fuel mixture of the first catalyst section 5 positioned at the upstream side of the second catalyst section 6. More specifically, the mixture temperature increases with the catalytic heat generation in the first catalyst section 5 before the fuel mixture enters into the second catalyst section 6. Therefore, all of the moisture contained in the air, the moisture contained in the fuel gas, and the moisture contained in the exhausted catalytic combustion gas immediately evaporates and accordingly no waterdrops adhere on the surface of the second catalyst. The second catalyst is not required to possess the water repellent function.
This arrangement can minimize the amount of water repellent material, more specifically the amount of PTFE layer 54, used in the catalytic combustion heater 1. Therefore, the cost increase of the catalytic combustion heater 1 can be minimized.
Although the above-described catalytic combustion heater 1 according to the first embodiment of the present invention includes the second catalyst section 6, it is possible to omit the second catalyst section 6.

Second Embodiment

FIG. 6 is a partly cross-sectional view showing the catalytic combustion heater 1 in accordance with a second embodiment of the present invention.
The catalytic combustion heater 1 according to the second embodiment of the present invention is different from the catalytic combustion heater 1 according to the first embodiment of the present invention in that the first catalyst section has a modified arrangement and the second catalyst section 6 is omitted.
More specifically, according to the catalytic combustion heater 1 of the second embodiment of the present invention, the catalyst section includes only one catalyst section 9 as shown in FIG. 6. The catalyst section 9 includes a catalytic carrier 91 having a honeycomb structure. The catalytic carrier 91 is made of a water repellent material such as a alumina. The catalytic carrier 91 supports a catalyst such as Pt (platinum).
When the material possesses a water repellent function, its surface is generally non-polar. Accordingly, water molecules having negative polarities cannot adhere on the surface of this material.
As the material of the catalytic carrier, such as cordierite or γ alumina, possesses a polarity, the steam having the polarity can easily adhere on the surface of the catalytic carrier. As a result, the steam can also adhere on the surface of the catalyst.
According to the catalytic combustion heater 1 of the second embodiment of the present invention, the catalytic carrier 91 of the catalyst section 9 is made of a alumina. As a alumina includes substantially no OH group, the catalytic carrier 91 is non-polar. The catalyst arranged by Pt (platinum) is also non-polar. Accordingly, the steam cannot adhere on the surface of the catalyst because of non-polarity of Pt platinum).
Like the catalytic combustion heater 1 in accordance with the first embodiment of the present inventions the arrangement of the second embodiment prevents the catalyst surface from being covered with the moisture contained in the air, the moisture contained in the fuel gas, or the moisture contained in the exhausted catalytic combustion gas. With this arrangement, the fuel mixture can surely contact with the catalyst. The catalyst function can be maintained appropriately. In other words, a sufficient amount of heat is generated by the catalytic combustion. Accordingly, the generated catalytic combustion heat can be efficiently used to increase the catalyst temperature. Thus, the second embodiment provides the catalytic combustion heater 1 capable of quickly increasing the catalyst temperature to the activation temperature within a short time.
Furthermore, in the catalytic combustion heater 1 according to the second embodiment of the present invention, it is possible to form a PTFE layer (i.e. the water repellent material) by coating on the surface of Pt in the catalyst section 9. In this case, it becomes possible to surely prevent the steam and the waterdrops from adhering on the catalyst surface.
Furthermore, in the catalytic combustion heater 1 according to the second embodiment of the present invention, the material of the catalytic carrier 91 is a alumina. However, the material of the catalytic carrier 91 is not limited to a alumina and accordingly any other water repellent material, such as titania (TiO2, titanium dioxide), can be used.
Furthermore, in the catalytic combustion heater 1 according to the second embodiment of the present invention, it is possible to dispose the second catalyst section 6 between the catalyst section 9 and the heat exchanger 7 in the flowing direction of the fuel mixture in the passage 81, like the catalytic combustion heater 1 according to the first embodiment of the present invention.

Third Embodiment

FIG. 7 is a partly cross-sectional view showing the catalytic combustion heater 1 in accordance with a third embodiment of the present invention.
The catalytic combustion heater 1 according to third embodiment of the present invention is different from the catalytic combustion heater 1 according to the first embodiment of the present invention in that both the first catalyst section 5 and the second catalyst section 6 are omitted. Instead, the tubes 71 and the fins 72 of the heat exchanger 7 have surfaces supporting the catalyst, i.e. Pt (platinum). Furthermore, a water repellent material such as a PTFE layer is coated on the surface of Pt (platinum).
Like the catalytic combustion heater 1 in accordance with the first embodiment of the present invention, the arrangement of the third embodiment prevents the catalyst surface from being covered with the moisture contained in the air, the moisture contained in the fuel gas, or the moisture contained in the exhausted catalytic combustion gas. Thus, the third embodiment provides the catalytic combustion heater 1 capable of quickly increasing the catalyst temperature to the activation temperature within a short time.
Furthermore, the entire length of the passage 81 in the catalytic combustion heater 1 can be shortened. In other words, the length of the catalytic combustion heater 1 in the flowing direction of the fuel mixture can be shortened. The catalytic combustion heater 1 can be downsized.
Furthermore, using the heat exchanger 7 capable of functioning as the catalytic carrier is effective in reducing the total number of required parts and also reducing the cost of the catalytic combustion heater 1.
According to the above-described third embodiment of the present invention, the fins 4 used in the catalytic combustion heater 1 are identical in arrangement with those of the catalytic combustion heater 1 disclosed in the first or second embodiment of the present invention. It is therefore possible to employ a simple bimetal structure for the fins 4 supporting the oxidation catalyst 41. The temperature of the oxidation catalyst 41 can be quickly increased to the activation temperature within a short time after the catalytic combustion heater 1 starts its operation. Furthermore, the temperature of the oxidation catalyst 41 can be maintained in the activation temperature range.
Although the catalytic combustion heater 1 according to any one of the first to third embodiments of the present invention uses the hydrogen gas, the fuel is not limited to the hydrogen gas and accordingly the catalytic combustion heater 1 can use other gas.
Furthermore, in the case that the water repellent material is supported on the surface of the catalyst, completely covering the entire surface of the catalyst with the water repellent material is not preferable because the catalytic function deteriorates. In this respect, it is preferable that the water repellent material occupies approximately 30% to 60% of the entire weight of the catalyst.
Moreover, the moisture removed from the low-temperature catalyst surface by the present invention is not limited to the moisture contained in the air, the moisture contained in the fuel gas, or the moisture contained in the exhausted catalytic combustion gas. For example, the present invention is preferably applicable to prevent the catalyst surface from being covered with the moisture contained in the off-gas discharged from the fuel cell.

Claims

1. A catalytic combustion heating 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;

a catalyst supported by a catalytic carrier and disposed in said passage; and

a heat exchanger receiving a heating medium and disposed at a downstream side of said catalytic carrier in a flowing direction of said fuel mixture in said passage, to perform heat exchange between said fuel mixture and said heating medium,

wherein

catalytic combustion of said fuel mixture is caused in said catalyst and the generated catalytic combustion heat is transferred via said heat exchanger to said heating medium, and

said catalyst possesses a water repellent function.

2. The catalytic combustion heating apparatus in accordance with claim 1, wherein a water repellent material is provided on said catalyst to give said water repellent function to said catalyst.

3. The catalytic combustion heating apparatus in accordance with claim 1, wherein said catalytic carrier is made of a water repellent material to give said water repellent function to said catalyst.

4. The catalytic combustion heating apparatus in accordance with claim 3, wherein a water repellent material is provided on said catalyst.

5. The catalytic combustion heating apparatus in accordance with claim 1, wherein said catalytic carrier includes a plurality of metallic tubes disposed parallel to each other and normal to the flowing direction of said fuel mixture, said metallic tubes have both ends opened to an annular passage, and said heating medium is supplied into said annular passage and said metallic tubes.

6. The catalytic combustion heating apparatus in accordance with claim 1, wherein an auxiliary catalytic carrier supporting an auxiliary catalyst is disposed between said catalytic carrier and said heat exchanger in the flowing direction of said fuel mixture in said passage.

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

8. A catalytic combustion heating 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 heat exchanger receiving a heating medium and disposed in said passage to perform heat exchange between said fuel mixture and said heating medium,

wherein

catalytic combustion of said fuel mixture is caused by a catalyst and the generated catalytic combustion heat is transferred via said heat exchanger to said heating medium,

said heat exchanger includes a plurality of tubes each having an inner passage in which said heating medium flows and fins each being disposed in a space between neighboring tubes for receiving heat transferred from said tubes,

said catalyst is supported on at least one surface of said tubes and said fins, and

said catalyst possesses a water repellent function.

9. The catalytic combustion heating apparatus in accordance with claim 8, wherein a water repellent material is provided on said catalyst to give said water repellent function to said catalyst.

10. The catalytic combustion heating apparatus in accordance with claim 8, wherein said fuel is hydrogen gas.