US20050042567A1

US20050042567A1 - Catalytic reaction heater

Info

Publication number: US20050042567A1
Application number: US10/911,623
Authority: US
Inventors: Hirokuni Sasaki; Masanori Uehara
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2003-08-06
Filing date: 2004-08-05
Publication date: 2005-02-24
Also published as: DE102004038140A1; JP2005055098A

Abstract

A catalytic reacting section generates heat based on a catalytic reaction of a gas mixture of a fuel and an oxygen containing gas. A fuel supplying device supplies the fuel into the catalytic reacting section. An air supplying device supplies air into the catalytic reacting section. An exhaust gas passage is provided at a downstream side of the catalytic reacting section to discharge an exhaust gas from the catalytic reacting section. A bypass passage directly supplies part of the air from air supplying device into the exhaust gas passage, so that the air is separately supplied into the catalytic reacting section and into the bypass passage.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a catalytic reaction heater generating heat based on a catalytic reaction of a gas mixture of a fuel and an oxygen containing gas.
A conventional catalytic reaction heater generally includes a catalytic reacting section, a fuel supply section, an oxygen containing gas supplying section, and an exhaust gas passage.
The catalytic reacting section generates heat based on a catalytic reaction of a gas mixture of a fuel and an oxygen containing gas (i.e. a gas containing oxygen). The fuel supply section supplies fuel to the catalytic reacting section. The oxygen containing gas supplying section supplies oxygen containing gas to the catalytic reacting section. The exhaust gas is discharged from the catalytic reacting section via the exhaust gas passage.
The fuel is, for example, a hydrogen or methane gas. The oxygen containing gas is the air.
When the catalytic reaction heater is left for a long time in a low-temperature environment, it is necessary to heat the catalytic reacting section up to a relatively high temperature of approximately 300° C. to activate the catalyst. In this case, the low-temperature environment includes a room temperature as well as lower temperatures (e.g. −30° C.) below a freezing point.
To promptly increase the temperature of the catalytic reacting section, an electric heater is conventionally provided to forcibly heat the catalyst when the exhaust gas temperature is low (refer to the Japanese patent application Laid-open No. 5-98952). The electric heater can maintain the catalyst in an activated condition.
For example, an electric heating catalyst (hereinafter, referred to EHC) is used. An auxiliary catalyst support is a metal honeycomb. When the catalytic reaction heater is activated, the auxiliary catalyst support receives current and generates heat until the temperature of this catalyst reaches an active level.
However, saving electric power, reducing the total number of parts, and assuring immediate activation are important factors for the catalytic reaction heater. In this respect, it is desirable to adopt an EHC-less arrangement capable of immediately activating the catalyst and assuring quick response without relying on an EHC.
The inventors of this invention think it important to effectively utilize the heat generated by the catalytic reacting section as thermal energy for heating the catalyst. This is a key factor in promptly increasing the temperature of the catalyst when the catalytic reaction heater is activated under a low-temperature environment.
In this case, the excess ratio of oxygen containing gas (i.e. excess oxygen ratio) in a gas mixture supplied into the catalytic reacting section is reduced. The oxygen containing gas amount becomes relatively small in the gas mixture to be supplied into the catalytic reacting section. This is effective in suppressing heat release into the oxygen containing gas.
For example, the oxygen containing gas is air. The excess air ratio of a gas mixture represents a ratio of reaction air amount to fuel amount. Reducing the excess air ratio of a gas mixture supplied into the catalytic reacting section is equal to decreasing the air amount to be supplied into the catalytic reacting section. As a result, heat release into the air can be suppressed.
Accordingly, heat of catalytic reaction can be effectively used to increase the temperature of the catalyst or the catalyst support. The catalyst can be promptly warmed up to high temperatures within a short time. Realizing quick activation of the catalyst is preferable in suppressing an overall amount of unreacted gas being undesirably discharged out of the catalytic system.
However, simply reducing the excess air ratio of a gas mixture supplied into the catalytic reacting section will cause a counter effect that the gas mixture supplied to the catalytic reacting section becomes rich in the fuel gas concentration.
In an initial stage of the catalytic reaction, the temperature is so low that the catalyst cannot be sufficiently activated. A relatively large amount of fuel gas causes no reaction in the catalytic reacting section and exits from the catalytic reacting section into the exhaust gas passage. The fuel gas concentration is high in the exhaust gas discharged from the catalytic reacting section. The fuel gas concentration should be suppressed below an explosion limit.
There is a conventional catalyst containing platinum, palladium or other noble metal. This catalyst is incorporated into a catalytic reaction heater to cause a catalytic reaction with hydrogen or other fuel having higher reactivity. This catalytic reaction heater is expected to satisfy temperature conditions for catalytic reaction.
However, the environment of the catalyst contains a significant amount of moisture. The moisture generally deteriorates reactivity of the catalyst. Under a low-temperature/ high-humidity environment, the moisture is adsorbed by the catalyst or the catalyst support. The adsorbed moisture prevents the catalyst from contacting with a fuel gas and the air. Furthermore, the adsorbed moisture prevents these gases from diffusing in the catalyst. Accordingly, the reactivity of the catalyst is worsened especially when the EHC is used to increase the temperature of the catalyst.

SUMMARY OF THE INVENTION

In view of the above-described problems, the present invention has an object to provide a catalytic reaction heater which is capable of promptly increasing the temperature of the catalyst and reducing the emission of any unreacted gas.
In the following description of the summary, the reference numerals in parentheses are used to show the correspondence to components, portions, or the like disclosed in the following preferred embodiments of the present invention. However, it is needless to say that the essential features of the present invention should not be construed as being limited to those practical examples.
In order to accomplish the above and other related objects, the present invention provides a catalytic reaction heater including a catalytic reacting section (60), fuel supplying means (30), oxygen containing gas supplying means (40), and an exhaust gas passage (80). The catalytic reacting section (60) generates heat based on a catalytic reaction of a gas mixture of a fuel and an oxygen containing gas. The fuel supplying means (30), provided at an upstream side of the catalytic reacting section (60), supplies fuel into the catalytic reacting section (60). The oxygen containing gas supplying means (40), provided at the upstream side of the catalytic reacting section (60), supplies oxygen containing gas into the catalytic reacting section (60). The exhaust gas passage (80) is provided at a downstream side of the catalytic reacting section (60) to discharge an exhaust gas from the catalytic reacting section (60). Furthermore, the catalytic reaction heater of this invention includes a bypass passage (100) having one end connected to the upstream side of the catalytic reacting section (60) and the other end connected to the downstream side of the catalytic reacting section (60). Via the bypass passage (100), part of the oxygen containing gas supplied from the oxygen containing gas supplying means (40) is directly supplied into the exhaust gas passage (80). Accordingly, the oxygen containing gas is separately supplied into the catalytic reacting section (60) and into the bypass passage (100).
According to this invention, all of the fuel is supplied from the fuel supplying means (30) into the catalytic reacting section (60). On the other hand, the oxygen containing gas is partly supplied via one line from the oxygen containing gas supplying means to the catalytic reacting section (60). Furthermore, part of the oxygen containing gas is directly supplied via another line from the oxygen containing gas supplying means to the exhaust gas passage (80).
According to this arrangement, the catalytic reacting section (60) receives a gas mixture having a low excess ratio of oxygen containing gas. Part of the air, bypassing the catalytic reacting section (60), directly enters into the exhaust gas passage (80) and merges with the unreacted gas discharged from the catalytic reacting section (60). The air dilutes the unreacted gas. Thus, the unreacted gas having a low concentration is discharged via the exhaust gas passage (80).
The excess ratio of oxygen containing gas is identical with the excess air ratio when the oxygen containing gas is air. The excess air is generally known as an amount of air in a combustion process greater than the amount theoretically required for complete oxidation. The excess air ratio represents a ratio of the actual air-fuel mixture ratio to the theoretical air-fuel mixture ratio.
The present invention provides the arrangement capable of simultaneously realizing the above effects. In this case, it is not necessary to change an overall amount of the oxygen containing gas supplied from the oxygen containing gas supplying means (40).
The oxygen containing gas supplying means is, for example, a device equipped with a fan or a blower to introduce an oxygen containing gas, such as air, from the outside. This kind of device has insufficient response in controlling the oxygen containing gas flow amount. It is generally difficult to accurately control the oxygen containing gas flow amount to be supplied into the catalytic reaction heater.
The present invention provides the bypass passage (100) to accurately change the flow amount of the oxygen containing gas supplied into the catalytic reacting section (60). Open-and-close controlling the bypass passage (100) is effective in assuring good response in controlling the flow amount of the oxygen containing gas supplied into the catalytic reacting section (60).
Changing the flow amount of the oxygen containing gas supplied into the catalytic reacting section (60) in this manner cannot be realized by controlling the load of the oxygen containing gas supplying means.
According to the present invention, it is not necessary to change the overall amount of the oxygen containing gas supplied from the oxygen containing gas supplying means (40). The load of the oxygen containing gas supplying means (40) can be fixed to a stationary value.
In other words, the present invention can change the flow amount of an oxygen containing gas supplied into the catalytic reacting section (60) without changing the load of the oxygen containing gas supplying means (40).
In this manner, the catalytic reaction heater of the present invention supplies a gas mixture into the catalytic reacting section (60) under the condition that the excess ratio of oxygen containing gas is low. Although, the catalytic reacting section (60) generates heat, the amount of heat release into the oxygen containing gas can be suppressed to a lower level. Thus, the present invention can promptly increase the temperature of the catalyst and accordingly can reduce the emission of any unreacted gas even in the EHC-less arrangement.
Furthermore, the catalytic reaction heater of the present invention directly supplies part of the oxygen containing gas via the bypass passage (100) into the exhaust gas passage (80). The concentration of an unreacted gas in the exhaust gas can be reduced.
Accordingly, the present invention can provide a catalytic reaction heater capable of promptly increasing the temperature of the catalyst and reducing the emission of any unreacted gas.
According to a preferable embodiment of the present invention, the catalytic reaction heater further includes bypass passage controlling means (10) and temperature detecting means (90). The bypass passage controlling means (10) is provided for open-and-close controlling the bypass passage (100). The temperature detecting means (90) is provided for detecting the temperature of the exhaust gas discharged from the catalytic reacting section (60). The bypass passage controlling means (110) is controlled based on information supplied from the temperature detecting means (90).
According to this arrangement, the temperature detecting means (90) is used to judge whether the temperature of the catalytic reacting section (60) has reached an active level of the catalyst. The bypass passage controlling means (110), controlling opening/closing of the bypass passage (100), can control the excess ratio of oxygen containing gas in a gas mixture supplied into the catalytic reacting section (60).
According to this arrangement, the excess ratio of oxygen containing gas supplied into the catalytic reacting section (60) can be adequately adjusted in accordance with the temperature of the catalytic reacting section (60).
More specifically, the temperature of the catalytic reacting section (60) reaches an active level of the catalyst. After that, the bypass passage controlling means (110) controls opening/closing of the bypass passage (100) to maintain the catalyst temperature at a desirable level which is determined beforehand considering heat durability of the catalytic reacting section (60).
After the temperature of the catalytic reacting section (60) has reached the active level of the catalyst, all of the oxygen containing gas can be supplied into catalytic reacting section (60). In this case, the excess ratio of the supplied oxygen containing gas is large.
The oxygen containing gas has excellent dilution effect (i.e. heat release effect). This is effective in suppressing the combustion temperature of the catalytic reacting section (60) from excessively increasing. The performance of the catalyst or the catalyst support does not deteriorate.
On the contrary, when the catalytic reacting section (60) is in a low temperature condition, the bypass passage controlling means (110) controls the bypass passage (100) to open. The catalytic reacting section (60) can receive a gas mixture having a low excess ratio of oxygen containing gas.
It is preferable that the temperature detecting means (90) is provided at a downstream side of the catalytic reacting section (60).
Furthermore, it is preferable that the bypass passage controlling means is a valve means (110).
Furthermore, it is preferable that the bypass passage controlling means (110) is a deformable member that is deformable in response to temperature change and is provided at a position where the deformable member is heated by the exhaust gas discharged from the catalytic reacting section.
According to this arrangement, the bypass passage controlling means (110) deforms in response to temperature change of the exhaust gas discharged from the catalytic reacting section. The bypass passage (100) opens or closes in accordance with deformation of the bypass passage controlling means (110). This arrangement requires no temperature detecting means (90).
In this case, it is preferable that the deformable member is a bimetal or a shape memory member.
Furthermore, it is preferable that control means (ECU) is provided for controlling the fuel supplying means (30) to increase and decrease a supply amount of the fuel according to a temperature change of the catalytic reacting section (60).
According to this arrangement, the fuel supply amount can be adequately adjusted based on the temperature environment in a startup condition.
More specifically, when the catalytic reaction heater starts operating in a low-temperature environment, the oxygen containing gas supplying means (40) can gradually increase the fuel supply amount under a condition that the supply amount of oxygen containing gas is fixed to a constant value.
When the catalyst has low activity in a low-temperature startup condition, the fuel supply amount is relatively small and accordingly the gas mixture has a higher excess ratio of oxygen containing gas. When the catalyst temperature reaches a sufficiently higher level, the fuel supply amount is relatively large and accordingly the gas mixture has an adequate excess ratio of oxygen containing gas.
The oxygen containing gas has excellent dilution effect. The unreacted gas having a lower concentration is discharged from the exhaust gas passage.
As described above, in the low-temperature/high-humidity environment, the moisture tends to adsorb on the catalyst or on the catalyst support. The adsorbed moisture prevents the catalyst from contacting with a fuel gas and the air. Furthermore, the adsorbed moisture prevents these gases from diffusing in the catalyst.
The catalytic reacting section is arranged by a catalyst support disposed on a base material and a catalyst disposed on this catalyst support. The catalyst support has numerous pores securing a sufficient surface for supporting the catalytic source. The base material is made of a ceramic honeycomb.
When the catalyst is left in a low-temperature/ high-humidity condition, the moisture is adsorbed on the surface of the catalyst support or adsorbed into the pores of the catalyst support. Thus, the catalyst is partly covered by the moisture. The catalyst may be soaked in the water. The adsorbed moisture prevents the catalyst from contacting with a fuel gas and the oxygen containing gas. Furthermore, the adsorbed moisture prevents these gases from diffusing in the catalyst. As a result, the reactivity of the catalyst is worsened.
This phenomenon is generally referred to as capillary condensation. The capillary condensation phenomenon is often recognized in conventional catalytic reaction heaters before they start operating.
To solve the above problem, the inventors of this invention have conducted research and development. According to experimental result, the capillary condensation is greatly dependent on the pore size of the catalyst support. The capillary condensation occurs when the pore size is small.
Furthermore, according to various evaluation results, it is desirable that the catalyst support used in the catalytic reacting section (60) has the pore diameter exceeding a predetermined range. The capillary condensation phenomenon does not occur even in a high-humidity environment.
In this respect, it is preferable that the catalytic reacting section (60) uses a catalyst support (62) having an average pore diameter equal to or greater than 10 nm.
Using the catalyst support (62) having the average pore diameter equal to or greater than 10 nm is effective in reducing the moisture amount adsorbing on the catalyst or on the catalyst support in a low-temperature/high-humidity environment. The catalyst can maintain adequate reactivity.
Namely, the present invention can suppress the capillary condensation phenomenon as much as possible in a high-humidity environment by combining the above-described various arrangements. Thus, the present invention can provide a catalytic reaction heater which is capable of promptly increasing the temperature of the catalyst and reducing the emission of any unreacted gas.
In general, the pore diameter size of the catalyst support regulates a surface area of the catalyst support. When the catalyst support (62) has an average pore diameter equal to or greater than 10 nm, each pore has a large diameter. When the catalyst support has a limited volume, the surface area of the catalyst support becomes small.
In this case, the catalyst support may have poor characteristics (in the number of pores as well as in the surface area). This will greatly restrict the catalyst amount held by the catalyst support. Even if an excessive amount of catalyst is held on this catalyst support, the fuel will not sufficiently react with the oxygen containing gas. The fuel and the oxygen containing gas will not sufficiently diffuse. A greater part of the catalyst will not contribute to the reaction. Thus, holding an excessive amount of catalyst on the catalyst support is not practical. Accordingly, the amount of available catalyst is small and the reaction amount is limited to a small value.
In view of the foregoing, it is preferable that the catalytic reacting section (60) has a catalyst support (62) having pore diameters ranging from 1 nm to at least 10 nm.
Using the catalyst support (62) having the pore diameters widely ranging from 1 nm to at least 10 nm is effective in realizing the catalytic reacting section (60) which has good property against capillary condensation and assures a sufficient amount of catalytic reaction.
Furthermore, it is preferable that the catalytic reacting section (60) has at least two kinds of catalyst supports (62) different in their average pore diameters.
According to this arrangement, it is possible to combine a catalyst support having a smaller average pore diameter to hold a sufficient amount of catalyst and another catalyst support having a greater average pore diameter to assure good property against capillary condensation. Thus, the catalytic reacting section (60) can possess good property against capillary condensation and also can assure a sufficient amount of catalytic reaction for excellent reactivity.
Furthermore, it is preferable that the catalytic reacting section (60) is divided into a plurality of sub sections, including a first sub catalytic reacting section (60 a) positioned at an upstream side and a second sub catalytic reacting section (60 b) positioned at a downstream side. The average pore diameter of a catalyst support used in the first sub catalytic reacting section (60 a) is greater than the average pore diameter of a catalyst support used in the second sub catalytic reacting section (60 b).
According to this arrangement, the first sub catalytic reacting section (60 a) is positioned at the upstream side and the second sub catalytic reacting section (60 b) is positioned at the downstream side. The catalyst support used in the catalytic reacting section (60 a) has a greater average pore diameter to assure the good property against capillary condensation.
The heat of catalytic reaction generated from the upstream side catalytic reacting section (60 a) can be utilized as heat energy for heating the downstream side catalytic reacting section (60 b). Accordingly, the downstream side catalytic reacting section (60 b) can dry and remove the residual moisture. Thus, the downstream side catalytic reacting section (60 b) can use the catalyst support having a smaller average pore diameter to hold a sufficient amount of catalyst, while suppressing the capillary condensation.
As a result, the catalytic reacting section (60) can possess good property against capillary condensation and also can assure a sufficient amount of catalytic reaction.
Furthermore, it is preferable that the catalytic reacting section (60) uses a catalyst support (62) made of a ceramic.
Furthermore, it is preferable that the ceramic is an alumina.
Especially, the catalyst support (62) made of an alumina can show good property against capillary condensation when the catalyst support (62) has an average pore diameter equal to or greater than 10 nm.
Furthermore, it is preferable that the catalytic reacting section (60) uses a catalyst containing noble metal.
Furthermore, it is preferable that the fuel is hydrogen.
Furthermore, it is preferable that the oxygen containing gas is air.
Furthermore, it is preferable that the catalytic reaction heater further includes a heat exchanging section (70) provided between the catalytic reacting section (60) and the exhaust gas passage (80) for receiving heat generated from the catalytic reacting section (60) and heating a heating medium based on heat exchange between the received heat and the heating medium.
Furthermore, it is preferable that a water repellent treatment is applied to a surface of a catalyst support (62) used in the catalytic reacting section (60).
This arrangement effectively prevents the moisture from adsorbing on the surface of the catalyst support (62) as well as on pore surfaces. Thus, the catalyst support (62) used in the catalytic reacting section (60) has good property against capillary condensation.
Moreover, the present invention provides a catalytic reaction heater including a catalytic reacting section (60), fuel supplying means (30), oxygen containing gas supplying means (40), an exhaust gas passage (80), and a bypass passage (100). The catalytic reacting section (60) generates heat based on a catalytic reaction of a gas mixture of a fuel and an oxygen containing gas. The fuel supplying means (30), provided at an upstream side of the catalytic reacting section (60), supplies the fuel into the catalytic reacting section (60). The oxygen containing gas supplying means (40), provided at the upstream side of the catalytic reacting section (60), supplies the oxygen containing gas into the catalytic reacting section (60). And, the exhaust gas passage (80), provided at a downstream side of the catalytic reacting section (60), discharges an exhaust gas from the catalytic reacting section (60). The bypass passage (100) supplies part of the oxygen containing gas from the oxygen containing gas supplying means (40) into the exhaust gas passage (80) in a startup condition of the catalytic reacting heater, so that the gas mixture introduced into the catalytic reacting section (60) has a low excess rate of oxygen containing gas in the startup condition of the catalytic reacting heater.

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 catalytic reaction heater in accordance with a first embodiment of the present invention;
FIG. 2 is a view schematically showing the condition of moisture adsorbed on a catalyst or on a catalyst support used in a catalytic reacting section;
FIGS. 3A and 3B are views schematically showing the mechanism of causing capillary condensation, wherein FIG. 3A shows no capillary condensation and FIG. 3B shows capillary condensation:
FIG. 4 is a graph showing the relationship between relative humidity and pore diameter of capillary condensation according to the Kelvin's theory;
FIG. 5 is a schematic view showing an overall arrangement of a catalytic reaction heater in accordance with a second embodiment of the present invention; and
FIG. 6 is a schematic view showing an overall arrangement of a catalytic reaction heater in accordance with a third embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will be explained with reference to attached drawings. The same reference numerals are attached to the same or equivalent components or portions throughout the drawings.

First Embodiment

FIG. 1 is a schematic view showing an overall arrangement of a catalytic reaction heater S1 in accordance with a first embodiment of the present invention.
The catalytic reaction heater S1 according to this embodiment, installed in an automotive vehicle, generates heat based on a catalytic reaction of a gas mixture (i.e. hydrogen-air gas mixture) of a fuel (e.g. hydrogen) and an oxygen containing gas (e.g. air).
As shown in FIG. 1, a casing 10 of the catalytic reaction heater S1 has a gas mixing section 20 provided at an upstream portion of the gas passage for mixing the fuel (e.g. hydrogen) and the oxygen containing gas (e.g. air).
A fuel supplying device 30, serving as fuel supplying means, supplies hydrogen (i.e. fuel) into the gas mixing section 20. An air supplying device 40, serving as oxygen containing gas supplying means, supplies air into the gas mixing section 20. This embodiment uses hydrogen because of its excellent reactivity. Alternatively, methane or comparable gas can be also used as the fuel of catalytic reaction heater S1. Besides the air, any other oxygen containing gas can be used.
A flow regulating plate 50, provided in the gas mixing section 20, regulates the air stream introduced from the air supplying device 40 to the gas mixing section 20. The flow regulating plate 50 is, for example, a plate having numerous through-holes.
The air supplying device 40, introducing the air from the outside into the casing 10, is a fan or a blower which is driven by an electric motor.
The fuel supplying device 30, supplying hydrogen into the gas mixing section 20, is an electrically driven injector that variably controls a fuel supply amount by changing the pressure of fuel (hydrogen) and the injection time.
In the casing 10, a catalytic reacting section 60 is provided at a downstream side of the gas mixing section 20. The catalytic reacting section 60 generates heat based on a catalytic reaction of a gas mixture of the fuel (hydrogen) supplied from the fuel supplying device 30 and the air (oxygen containing gas) supplied via the flow regulating plate 50 from the air supplying device 40.
The catalytic reacting section 60 is arranged by a catalyst support disposed on a base material (substrate) and a catalytic source supported by this catalyst support. The catalyst support has numerous pores securing a sufficient surface for supporting the catalytic source.
The base material, used in the catalytic reacting section 60, is made of a ceramic honeycomb. According to this embodiment, the base material is a monolith of cordierite (2MgO.2Al₂O₃.5SiO₂) which is a mixed body of alumina (Al₂O₃), magnesia (MgO), and silica (SiO₂).
The catalyst support used in the catalytic reacting section 60 is a ceramic or an activated carbon. According to this embodiment, the catalyst support is an alumina having numerous pores.
Furthermore, the catalytic source used in the catalytic reacting section 60 is noble metallic catalyst or metallic oxide. According to this embodiment, the catalytic source is a catalyst containing platinum (Pt), palladium (Pd), or other noble metals.
According to this embodiment, a heat exchanging section 70 is provided in the gas passage of the casing 10 at a downstream side of the catalytic reacting section 60. The heat exchanging section 70 receives heat generated from the catalytic reacting section 60. The heat exchanging section 70 accommodates a heating medium. The heating medium is heated based on heat exchange between the received heat and the heating medium.
Although not limited to a specific type, the heat exchanging section 70 of this embodiment is a fin-tube type heat exchanger consisting of numerous fins assembled with laminated tubes. The reaction gas of the catalytic reacting section 60 passes the clearances of laminated tubes. Meanwhile, cooling water (i.e. heating medium) flows in the tube.
Thus, the heat exchanging section 70 allows heat exchange between the heat generated from the catalytic reacting section 60 and the cooling water. According to this embodiment, a cooling water passage 72 is connected to the heat exchanging section 70. Furthermore, a circulation pump (not shown) is provided in the cooling water passage 72 to circulate the cooling water.
The gas passage in the casing 10 is configured into an exhaust gas passage 80 at the downstream side of the heat exchanging section 70. The exhaust gas discharged from the catalytic reacting section 60 flows in the exhaust gas passage 80 and goes out of the catalytic reaction heater S1. More specifically, the catalytic reacting section 60 produces a heated gas based on the catalytic reaction. The produced heated gas first passes the heat exchanging section 70 in which the temperature of the gas decreases through heat exchange. The cooled gas then enters into the exhaust gas passage 80.
Furthermore, a temperature detecting device 90 is provided the gas passage of the casing 10. The temperature detecting device 90 detects the temperature of an exhaust gas resulting from the catalytic reaction caused in the catalytic reacting section 60. Thus, the temperature detecting device 90 can detect the temperature of the catalytic reacting section 60 when the catalytic reacting section 60 is operating. The temperature detecting device 90 is provided at a downstream side of the catalytic reacting section 60. The temperature detecting device 90 is in a space intervening between the catalytic reacting section 60 and the heat exchanging section 70.
The temperature detecting device 90 is, for example, a thermistor type sensor, a thermocouple type sensor, an optical sensor, or any other temperature sensor. The temperature detecting device 90 can be installed at any other place as far as it can detect the temperature of an exhaust gas resulting from the catalytic reaction caused in the catalytic reacting section 60. It is therefore possible to provide the temperature detecting device 90 in the catalytic reacting section 60.
Furthermore, according to this embodiment, a control section (e.g. ECU installed in an automotive vehicle) 200 is associated with the catalytic reaction heater S1. The control section 200 controls the operation of fuel supplying device 30 to variably adjust the fuel supply amount. The control section 200 controls the operation of air supplying device 40 to variably adjust the air supply amount. The control section 200 controls the operation of the circulation pump equipped in the heat exchanging section 70. Furthermore, the control section 200 receives a detection signal from the temperature detecting device 90.
As described above, the catalytic reaction heater S1 of this embodiment includes the catalytic reacting section 60, the fuel supplying device 30, the air supplying device (i.e. oxygen containing gas supplying means) 40, and the exhaust gas passage 80. The catalytic reacting section 60 generates heat based on a catalytic reaction of a gas mixture of the fuel and the oxygen containing gas. The fuel supplying means 30, provided at the upstream side of the catalytic reacting section 60, supplies the fuel (e.g. hydrogen) into the catalytic reacting section 60. The air supplying device (i.e. oxygen containing gas supplying means) 40, provided at the upstream side of the catalytic reacting section 60, supplies the oxygen containing gas (e.g. air) into the catalytic reacting section 60. The exhaust gas passage 80, provided at the downstream side of the catalytic reacting section 60, discharges an exhaust gas from the catalytic reacting section 60.
Furthermore, the catalytic reaction heater S1 of this embodiment includes the bypass passage 100 having one end connected to the upstream side of the catalytic reacting section 60 and the other end connected to the downstream side of the catalytic reacting section 60. The bypass passage 100 directly supplies part of the air (i.e. oxygen containing gas) supplied from the air supplying device (i.e. oxygen containing gas supplying means) 40 into the exhaust gas passage 80. Thus, the air (i.e. oxygen containing gas) is separately supplied into the catalytic reacting section 60 and into the bypass passage 100.
More specifically, according to this embodiment, the bypass passage 100 is an independent pipe separated from the gas passage in the casing 10. An inlet of the bypass passage 100 opens to a portion of the casing 10 positioned downstream of the air supplying device 40 and upstream of the flow regulating plate 50. An outlet of the bypass passage 100 opens to the exhaust gas passage 80.
The catalytic reaction heater S1 of this embodiment operates in the following manner. The catalytic reaction heater S1 basically generates heat based on a catalytic reaction (i.e. oxidation reaction) of a supplied fuel (i.e. hydrogen) and transfers the generated heat via the heat exchanging section 70 to the cooling water to heat the cooling water.
First of all, when the catalytic reaction heater S1 starts its operation, the control section 200 sends control signals to the fuel supplying device 30, the air supplying device 40, the heat exchanging section 70, and the circulation pump, respectively. Furthermore, the control section 200 receives a detection signal from the temperature detecting device 90.
The fuel supplying device 30 supplies hydrogen (i.e. fuel) to the gas mixing section 20. The air supplying device 40 supplies air (i.e. oxygen containing gas) to the gas mixing section 20. The hydrogen and air are mixed together into a gas mixture in the gas mixing section 20. Then, the gas mixture is sent from the gas mixing section 20 to the catalytic reacting section 60. The catalytic reacting section 60 produces a high-temperature gas based on a catalytic reaction.
According to this embodiment, a chemical reaction of the hydrogen (fuel) and the air (oxygen containing gas) occurs according to the following chemical formula 1.
H₂+O₂/2→H₂O (1)
As shown in this formula 1, the theoretical chemical reaction occurs with hydrogen of 1 mol and oxygen of ½ mol. The air contains oxygen by approximately 20%. The rest of the air is nitrogen. Considering the composition of the air, the excess air ratio should be determined. It is needless to say that the excess air ratio is different when the fuel is methane (CH₄).
According to this embodiment, to cause the catalytic reaction shown by the above-described chemical formula 1, the control section 200 adjusts the ratio of hydrogen and air in such a manner that, in an ordinary driving conditions, the catalytic reacting section 60 produces a high-temperature gas whose temperature (i.e. combustion temperature) is approximately 600° C. In this case, the excess air ratio (i.e. excess ratio of oxygen containing gas) is approximately 5.
As well known in the field of conventional catalytic reaction heaters, when the excess air ratio is large, the combustion temperature is low. When the excess air ratio is small, the combustion temperature is high.
The high-temperature gas produced from the catalytic reacting section 60 flows into the heat exchanging section 70. The heat exchanging section 70 cools the high-temperature gas through heat exchange with the cooling water. Namely, the heat exchanging section 70 receives the heat generated from the catalytic reacting section 60 and causes the heat exchange between the received heat and the cooling water serving as a heating medium.
The gas, having been cooled by the heat exchanging section 70, flows into the exhaust gas passage 80 and then exits out of the catalytic reaction heater S1. The cooling water, having been heated in the heat exchanging section 70, flows into appropriate portions in an automotive vehicle to warm up these portions. The catalytic reaction heat produced by the catalytic reaction heater S1 can be utilized in this manner.
According to this embodiment, in a startup operation of the catalytic reaction heater S1, the fuel supplying device 30 supplies hydrogen (fuel) to the catalytic reacting section 60. At the same time, the air supplying device 40 supplies the air (i.e. oxygen containing gas) into the catalytic reacting section 60. In this case, the air (i.e. oxygen containing gas) is separately supplied to the catalytic reacting section 60 and to the exhaust gas passage 100. Namely, this embodiment provides one line connected to the catalytic reacting section 60 for directly guiding the air into the catalytic reacting section 60. Furthermore, this embodiment provides the other line bypassing the catalytic reacting section 60 for directly guiding the air into the exhaust gas passage 100.
According to the arrangement of this embodiment, the catalytic reacting section 60 causes a catalytic reaction of a gas mixture having a low excess air ratio. More specifically, when an overall excess air ratio of the gas mixture is 5, the gas mixture supplied into the catalytic reacting section 60 has a lower excess air ratio of approximately 3.
On the other hand, in the exhaust gas passage 80, the air supplied from bypass passage 100 can merge into the unreacted gas discharged from the catalytic reacting section 60. More specifically, in the above case that the overall excess air ratio of the gas mixture is 5, the air amount corresponding to 2 (=5−3) in terms of the excess air ratio bypasses the catalytic reacting section 60 and directly enters into the exhaust gas passage 80.
Accordingly, in the exhaust gas passage 80, the bypass air can dilute the unreacted gas (e.g. unreacted hydrogen). The catalytic reaction heater S1 discharges the exhaust gas containing the unreacted gas having been adequately diluted into a lower concentration. In this case, the air supplying device (i.e. oxygen containing gas supplying means) 40 can fix the overall amount of supplied air (i.e. oxygen containing gas).
The air supplying device 40 is, for example, a fan or a blower which introduces the air from the outside. This kind of device has insufficient response in controlling the air flow amount. It is generally difficult to accurately control the air (i.e. oxygen containing gas) flow amount to be supplied into the catalytic reaction heater.
According to this embodiment, the bypass passage 100 is provided to accurately change the air flow amount supplied into the catalytic reacting section 60. Changing the air flow amount supplied into the catalytic reacting section 60 in this manner cannot be realized by controlling the load of the air supplying device 40.
In this respect, according to this embodiment, it is not necessary to change an overall amount of the air supplied from the air supplying device 40. The load of the air supplying device 40 can be fixed to a constant value. Thus, this embodiment can change the air flow amount supplied into the catalytic reacting section 60 without changing the load of the air supplying device 40.
According to this embodiment, the gas mixture supplied into the catalytic reacting section 60 has a lower excess air ratio. Although, the catalytic reacting section 60 generates heat, the amount of heat release into the air can be suppressed to a lower level. Thus, this embodiment can promptly increase the temperature of the catalyst and accordingly can reduce the emission of any unreacted gas even in the EHC-less arrangement.
Furthermore, according to this embodiment, part of the air is directly supplied via the bypass passage 100 into the exhaust gas passage 80. The concentration of an unreacted gas in the exhaust gas can be reduced.
Accordingly, this embodiment provides a catalytic reaction heater capable of promptly increasing the temperature of the catalyst and reducing the emission of any unreacted gas.
Furthermore, according to this embodiment, the fuel supplying device 30 can change the fuel (i.e. hydrogen) pressure and the injection time to adjust the fuel supply amount. It is preferable to change the fuel supply amount of fuel supplying device 30 in accordance with temperature change of the catalytic reacting section 60. This is effective to appropriately adjust the fuel supply amount in accordance with temperature environment in a startup condition.
More specifically, the temperature detecting device 90 detects the temperature of an exhaust gas discharged from the catalytic reacting section 60. The fuel supply amount can be increased or decreased by controlling the fuel supplying device 30 based on information supplied from the temperature detecting means 90.
Furthermore, the following control method will be used. When the temperature detecting device 90 detects the catalyst temperature having reached a sufficiently high temperature (e.g. 300° C.), the control section 200 controls the fuel supplying device 30 to reduce the fuel supply amount.
In this case, the gas mixture supplied into the catalytic reacting section 60 has a high excess air ratio (e.g. excess air ratio =7). This is effective in preventing the combustion temperature in the catalytic reacting section 60 from excessively increasing. It is possible to set the temperature considering heat durability of the catalyst.
As well known in the catalytic reaction heaters, when the excess air ratio is large, the combustion temperature is low. When the excess air ratio is small, the combustion temperature is high. Preventing the combustion temperature from excessively increasing in the catalytic reacting section 60 is effective in preventing the catalyst and the catalyst support from deteriorating due to excessive heat.
Furthermore, the following control method can be used when the fuel supplying device 30 increases or decreases the fuel supply amount based on temperature information of the catalytic reacting section 60.
When the catalytic reaction heater starts its operation under a low-temperature environment, the control section 200 controls the air supplying device (i.e. oxygen containing gas supplying means) 40 to fix the air (i.e. oxygen containing gas) supply amount to a constant value. Meanwhile, the control section 200 controls the fuel supplying device 30 to gradually increase the fuel (i.e. hydrogen) supply amount.
When the catalytic reaction heater is operating in a low-temperature condition (e.g. a lower temperature below the freezing point), the catalyst has insufficient activity. The fuel supply amount is relatively small. The gas mixture has a high excess ratio of oxygen containing gas (e.g. excess air ratio =7). When the catalyst reaches a sufficiently high temperature (e.g. 300° C.), the catalyst has sufficient activity. The fuel supply amount is relatively large. The gas mixture has an adequate excess ratio of oxygen containing gas (e.g. excess air ratio =5).
When the fuel supply amount is controlled in this manner, temperature increasing characteristics of the catalyst cannot be increased so high. However, immediately after the catalytic reaction heater starts its operation, the fuel supply amount is small and the fuel can easily bum. The air has excellent dilution effect. The discharged unreacted gas has a lower concentration.
As apparent from the foregoing description, this embodiment provides a catalytic reaction heater including a catalytic reacting section, fuel supplying means, oxygen containing gas supplying means, an exhaust gas passage, and a bypass passage. The catalytic reacting section generates heat based on a catalytic reaction of a gas mixture of a fuel and an oxygen containing gas. The fuel supplying means, provided at an upstream side of the catalytic reacting section, supplies the fuel into the catalytic reacting section. The oxygen containing gas supplying means, provided at the upstream side of the catalytic reacting section, supplies the oxygen containing gas into the catalytic reacting section. The exhaust gas passage, provided at a downstream side of the catalytic reacting section, discharges an exhaust gas from the catalytic reacting section. The bypass passage supplies part of the oxygen containing gas from the oxygen containing gas supplying means into the exhaust gas passage in a startup condition of the catalytic reacting heater, so that the gas mixture introduced into the catalytic reacting section has a low excess rate of oxygen containing gas in the startup condition of the catalytic reacting heater. In other words, this embodiment utilizes the bypass arrangement to supply a gas mixture of fuel rich state into the catalytic reacting section in the startup condition of the catalytic reacting heater.

Capillary Condensation Inhibiting Arrangement

According to this embodiment, the catalytic reacting section 60 is arranged by the catalyst support disposed on the base material and the catalytic source supported by this catalyst support. The catalyst support, made of a ceramic honeycomb or the like, has numerous pores securing a sufficient surface for supporting the catalytic source.
To suppress the capillary condensation phenomenon, the catalytic reacting section 60 of this embodiment can employ one of the following variable capillary condensation inhibiting arrangements.
The “capillary condensation phenomenon” appears when the catalyst is left in a low-temperature/high-humidity condition. The moisture existing in such an environment tends to adsorb on the surface of the catalyst support or into the pores of the catalyst support. Thus, the catalyst is partly covered by the moisture. The catalyst may be soaked in the water. The adsorbed moisture prevents the catalyst from contacting with hydrogen (i.e. fuel) and the air (i.e. oxygen containing gas). Furthermore, the adsorbed moisture prevents these gases from diffusing in the catalyst. As a result, the reactivity of the catalyst is worsened.
First of all, the inventors of this invention propose a first arrangement characterized in that the catalyst support used in the catalytic reacting section 60 has an average pore diameter equal to or greater than 10 nm.
Through research and development, the inventors of this invention have reached the first arrangement as a prospective capillary condensation inhibiting arrangement. According to the inventors, the capillary condensation is greatly dependent on the pore size of each catalyst support. The capillary condensation occurs when the pore size is small.
FIG. 2 is a view schematically showing the condition of moisture adsorbed on the catalyst or on the catalyst support used in the catalytic reacting section 60.
The catalyst support 62 made of γ-alumina is disposed on the base material 61 made of cordierite. The catalyst 66, such as platinum, palladium or the like, is held on the surface of catalyst support 62 or in the pore 64.
In FIG. 2, the moisture W adsorbed in a right pore 64 is gaseous. The catalyst 66 is not soaked in the moisture W. The catalyst 66 can contact with the fuel gas ‘G’ and the air ‘A’ and according causes a catalytic reaction.
However, in FIG. 2, the moisture condenses into water in a left pore 64 and accordingly the left pore 64 is partly filled with liquefied moisture W′. In other words, the capillary condensation is recognized in the left pore 64. The catalyst 66 soaked in the condensed moisture W′ cannot contact with the fuel gas ‘G’ or the air ‘A’ and accordingly causes no catalytic reaction.
FIGS. 3A and 3B are views schematically showing the mechanism of causing capillary condensation. As described above, the capillary condensation greatly depends on the pore size of catalyst support 62. The capillary condensation occurs when the pore size is small.
A pore 64 of catalyst support 62 shown in FIG. 3A has a large diameter. The adsorbed moisture W is gaseous and does not condense into water. On the other hand, a pore 64 of catalyst support 62 shown in FIG. 3B has a small diameter. The adsorbed moisture W easily condenses into water due to surface tension.
The following formula 1 is Kelvin's theory that determines the conditions (generation and timing) of capillary condensation.
ln(p/p ₀)=2Vm·γ·cosθ/(r·R·T) (2)
where p/p₀represents a relative humidity, Vm represents a molecular volume of water, γ represents a surface tension of water, θ represents a contact angle between water and the catalyst support, ‘r’ represents a radius of pore 64, R represents a gas constant, and T represents an absolute temperature.
FIG. 4 shows the relationship between relative humidity (units: RH %) and pore diameter of catalyst support 62 causing the capillary condensation (units: nm) according to the Kelvin's theory, based on the catalyst support 62 made of γ-alumina.
In FIG. 4, an abscissa represents the relative humidity and an ordinate represents the pore diameter causing the capillary condensation (although written as “pore diameter of capillary condensation” in the drawing). The hatched region below a curve shown in FIG. 4 represents a region where the capillary condensation is recognized.
As understood from FIG. 4, the capillary condensation easily occurs when the catalyst support 62 is left in a high-humidity environment.
Furthermore, the capillary condensation easily occurs when the pore size of catalyst support 62 is large.
For example, when the relative humidity is 60 RH %, it is understood from FIG. 4 that the capillary condensation occurs when the pore diameter is equal to or less than approximately 4 nm. And, no capillary condensation occurs when the pore diameter exceeds approximately 4 nm.
Furthermore, it is understood from FIG. 4 that, when the relative humidity is approximately 80%, no capillary condensation will occur if the pore diameter is equal to or greater than 10 nm.
From the above result, it is preferable to use a first arrangement as the capillary condensation inhibiting arrangement. The first arrangement of this embodiment includes the catalyst support 62 used in the catalytic reacting section 60. The catalyst support 62 of the first arrangement has an average pore diameter equal to or greater than 10 nm. For example, α-alumina can be preferably used as the catalyst support 62 having an average pore diameter equal to or greater than 10 nm.
Using catalyst support 62 having the average pore diameter equal to or greater than 10 nm is effective in reducing the moisture amount adsorbing on the catalyst 66 or on the catalyst support 62 in a low-temperature/high-humidity environment. Thus, the catalyst 66 can maintain adequate reactivity in the catalytic reacting section 60.
Namely, by employing the first arrangement, this embodiment can suppress the capillary condensation phenomenon as much as possible in a high-humidity environment. The catalyst support 62 can possess good property against capillary condensation. Thus, this embodiment can provide a catalytic reaction heater which is capable of promptly increasing the temperature of the catalyst and reducing the emission of any unreacted gas.
In general, the pore diameter size of the catalyst support regulates a surface area of the catalyst support. When the catalyst support 62 has an average pore diameter equal to or greater than 10 nm according to the first arrangement, each pore has a large diameter. When the catalyst support has a limited volume, the surface area of the catalyst support becomes small.
In this case, the catalyst support has poor characteristics (in the number of pores as well as in the surface area). This will greatly restrict the catalyst amount held by the catalyst support. Even if an excessive amount of catalyst is held on this catalyst support, the fuel will not sufficiently react with the oxygen containing gas. The fuel and the oxygen containing gas will not sufficiently diffuse. An increased part of the catalyst will not contribute to the reaction. Thus, holding an excessive amount of catalyst on the catalyst support is not practical. Accordingly, the amount of available catalyst is small and the reaction amount is limited to a small value.
Considering the above, the inventors of this invention propose the following capillary condensation inhibiting arrangement as a second arrangement.
The second arrangement is characterized in that the catalyst support 62 used in the catalytic reacting section 60 has pore diameters ranging from 1 nm to at least 10 nm.
Using the catalyst support 62 having the pore diameters widely ranging from 1 nm to at least 10 nm is effective in realizing the catalytic reacting section 60 which has good property against capillary condensation and assures a sufficient amount of catalytic reaction.
Furthermore, according to the second arrangement, a surface of catalyst support 62 having a smaller pore diameter (e.g. less than 10 nm) can support a greater amount of catalyst. Another surface of catalyst support 62 having a greater pore diameter (e.g. greater than 10 nm) can assure satisfactory property against capillary condensation. The heat of catalytic reaction generated in a region where the pore diameter is large can be effectively used as thermal energy for drying the moisture in a region where the pore diameter is small.
Accordingly, by employing the second arrangement, this embodiment can realize the catalytic reacting section 60 which is capable of supporting a greater amount of catalyst for excellent reactivity as well as assuring good property against capillary condensation.
Furthermore, the inventors of this invention propose the following capillary condensation inhibiting arrangement as a third arrangement, to obtain effects similar to those of the second arrangement.
The third arrangement is characterized in that the catalyst support 62 used in the catalytic reacting section 60 has at least two kinds of catalyst supports 62 different in their average pore diameters.
According to this arrangement, it is possible to combine a first catalyst support having a smaller average pore diameter to hold a sufficient amount of catalyst and a second catalyst support having a greater average pore diameter to assure good property against capillary condensation.
Accordingly, by employing the third arrangement, this embodiment can realize the catalytic reacting section 60 which is capable of supporting a greater amount of catalyst for excellent reactivity as well as assuring good property against capillary condensation.
For example, activated carbon or γ-alumina is a preferable material for the first catalyst support having a smaller average pore diameter according to the third arrangement. And, α-alumina is a preferable material for the second catalyst support having a greater average pore diameter according to the third arrangement.

Second Embodiment

FIG. 5 is a schematic view showing an overall arrangement of a catalytic reaction heater S2 in accordance with a second embodiment of the present invention.
The catalytic reaction heater S2 according to this embodiment, like the catalytic reaction heater S1 of the first embodiment, includes a catalytic reacting section 60, a fuel supplying device 30, an air supplying device (i.e. oxygen containing gas supplying means) 40, an exhaust gas passage 80, and a bypass passage 100. The air is partly supplied from the air supplying device 40 to the catalytic reacting section 60 and partly supplied via the bypass passage 100 to the exhaust gas passage 80.
According to the second embodiment, a bypass passage controlling device 110 is additionally provided to open-and-close control the bypass passage 100. FIG. 5 shows a shutoff valve serving as the bypass passage controlling device 110 of this embodiment.
The shutoff valve 110 is driven by an electric motor. The control section 200 controls the operation of this shutoff valve 110. According to the arrangement shown in FIG. 5, the shutoff valve 110 is located near the outlet of bypass passage 100. However, the shutoff valve 110 can be installed at any other portion in the bypass passage 100.
Furthermore, like the above-described first embodiment, the catalytic reaction heater S2 according to this embodiment includes a temperature detecting device 90 detecting the temperature of an exhaust gas discharged from the catalytic reacting section 60.
The control section 200 performs open-and-close control of the bypass passage 100 by controlling the shutoff valve (i.e. bypass passage controlling device) 110 based on information obtained from the temperature detecting device 90.
According to this arrangement, the temperature detecting device 90 detects the temperature of the catalytic reacting section 60. The control section 200 makes a judgment as to whether the catalyst has an active temperature based on the temperature information obtained by temperature detecting device 90. Furthermore, the control section 200 causes the shutoff valve 110 to open-and-close control the bypass passage 100 and accordingly adjusts the excess air ratio of a gas mixture supplied into the catalytic reacting section 60. Thus, the second embodiment enable the control section 200 to set an appropriate excess air ratio for a gas mixture supplied into the catalytic reacting section 60 in accordance with the temperature of the catalytic reacting section 60.
More specifically, the temperature of the catalytic reacting section 60 reaches an active level of the catalyst. After that, the control section 200 causes the shutoff valve 110 to open/close control the bypass passage 100 to maintain the catalyst temperature at a desirable level which is determined beforehand considering heat durability of the catalytic reacting section 60.
According to this arrangement, after the temperature of catalytic reacting section 60 has reached the active level of the catalyst, all of the air is supplied into the catalytic reacting section 60. In this case, the excess air ratio is high. The air has excellent dilution effect (i.e. heat release effect). This is effective in suppressing the combustion temperature of the catalytic reacting section 60 from excessively increasing. The performance of the catalyst or the catalyst support does not deteriorate.
On the contrary, when the catalytic reacting section 60 is in a low temperature condition, the shutoff valve 110 opens the bypass passage 100. The catalytic reacting section 60 can receive a gas mixture having a low excess air ratio.
Accordingly, this embodiment can provide a catalytic reaction heater which is capable of promptly increasing the temperature of the catalyst and reducing the emission of any unreacted gas.
According to this embodiment, the control section 200 can control the fuel supplying device 30 to increase or decrease the fuel supply amount in accordance with temperature change of the catalytic reacting section 60. It becomes possible to set an appropriate fuel supply amount in accordance with startup temperature environment.
In this case, the control section 200 can use the following control method. When the catalytic reaction heater S2 starts its operation under a low-temperature environment (below a freezing point), the control section 200 controls the air supplying device (i.e. oxygen containing gas supplying means) 40 to fix the air (i.e. oxygen containing gas) supply amount to a constant value. And, the control section 200 closes the shutoff valve (i.e. bypass passage controlling device) 110.
All of the air is supplied from the air supplying device 40 to the catalytic reacting section 60. In this case, the control section 200 controls the fuel supplying device 30 to gradually increase the fuel (i.e. hydrogen) supply amount.
When the catalytic reaction heater S2 is operating in a low-temperature startup condition, the catalyst has insufficient activity. The fuel supply amount is relatively small. The gas mixture has a high excess air ratio (e.g. excess air ratio =7). When the catalyst reaches a sufficiently high temperature, the catalyst has sufficient activity. The fuel supply amount is relatively large. The gas mixture has an adequate excess air ratio (e.g. excess air ratio =5).
When the fuel supply amount is controlled in this manner, temperature increasing characteristics of the catalyst cannot be increased so high. However, immediately after the catalytic reaction heater S2 starts its operation, the fuel supply amount is small and the fuel can easily burn. The air has excellent dilution effect. The discharged unreacted gas (i.e. unreacted hydrogen) has a lower concentration.
After finishing the above low-temperature startup control, the control section 200 controls the shutoff valve 110 to open the bypass passage 100. The above-described effect of using the bypass passage 100 is obtained.

Modified Bypass Passage Controlling Device

The bypass passage controlling means 110 of this embodiment can be arranged by a deformable member that is deformable in response to temperature change.
For example, bimetals can be used as the member deformable in response to temperature change. As well known in the art, a bimetal consists of two bonded metal plates mutually different in the coefficient of linear expansion. The bimetal causes bending or warpage in response to temperature change.
Besides bimetals, shape memory members, such as shape memory alloys and shape memory resins, can be used as the member deformable in response to temperature change.
These shape memory members are well known in the art. For example, shape memory alloys are (CuNi)₃Al, AuCd, In—Tl, CuAuZn, CuZn, TiNi, NiAl, AgCd, and Fe₃Pt which are based on reversible martensitic transformation.
The shape memory resins are plastic materials which temporarily leave a permanent deformation when immediately cooled after they are deformed at a temperature exceeding a glass transition point. However, when the shape memory resins are heated again up to the glass transition point, the permanent deformation disappears.
Such a temperature-sensitive deformable member, when it is used as the bypass passage controlling device 110, should be provided at a position where this deformable member is heated by the exhaust gas discharged from the catalytic reacting section 60.
For example, as shown in FIG. 5, it is preferable to provide the temperature-sensitive deformable member (serving as the bypass passage controlling device 110) adjacent to the output of the bypass passage 100. Namely, the shutoff valve 110 shown in FIG. 5 can be replaced by the temperature-sensitive deformable member.
Providing the bypass passage controlling device 110 closely to the outlet of bypass passage 100 is advantageous in that the heat of catalytic reaction is effectively transmitted to the bypass passage controlling device 110 via a pipe of bypass passage 100 or through the convection of exhaust gas.
When the bypass passage controlling device 110 is arranged by a temperature-sensitive deformable member, the bypass passage controlling device 110 deforms in accordance with temperature change of the exhaust gas. The bypass passage 100 is opened or closed in accordance with the deformation of the deformable member.
For example, a diaphragm-type actuator (valve) is practically used as the bypass passage controlling device 110 deformable in response to temperature change. In this case, in the initial startup condition, the catalytic reacting section 60 receives a gas mixture having a low excess air ratio and accordingly discharges high-temperature exhaust gas. When the diaphragm-type valve is subjected to the high-temperature exhaust gas, the valve closes the bypass passage 100.
Accordingly, the above-described effects of shutoff valve 110 can be obtained even when the bypass passage controlling device 110 is arranged by the temperature-sensitive deformable member. In this case, the temperature detecting device 90 and the bypass passage controlling device 110 require no motor or a comparable driving device.
Furthermore, in this embodiment, the catalytic reacting section 60 can employ any one of the above-described various capillary condensation inhibiting arrangements to suppress capillary condensation phenomenon.

Third Embodiment

FIG. 6 is a schematic view showing an overall arrangement of a catalytic reaction heater S3 in accordance with a third embodiment of the present invention.
The catalytic reaction heater S3 according to this embodiment, like the catalytic reaction heater S1 of the first embodiment, includes a catalytic reacting section 60, a fuel supplying device 30, an air supplying device (i.e. oxygen containing gas supplying means) 40, an exhaust gas passage 80, and a bypass passage 100. The air is partly supplied from the air supplying device 40 to the catalytic reacting section 60 and partly supplied via the bypass passage 100 to the exhaust gas passage 80.
According to this embodiment, the catalytic reacting section 60 is divided into a plurality of sub sections, including a first sub catalytic reacting section 60 a positioned at an upstream side and a second sub catalytic reacting section 60 b positioned at a downstream side. The average pore diameter of a catalyst support used in the first sub catalytic reacting section 60 a is greater than the average pore diameter of a catalyst support used in the second sub catalytic reacting section 60 b.
According to the arrangement shown in FIG. 6, the catalytic reacting section 60 includes the upstream side catalytic reacting section 60 a and the downstream side catalytic reacting section 60 b which are serially disposed. According to this embodiment, the catalytic reacting section 60 can be divided into three or more serially disposed sub sections so that the average pore diameter is large at the upstream side and small at the downstream side.
For example, activated carbon or γ-alumina is a preferable material for the catalyst support used in the downstream side catalytic reacting section 60 b having a smaller average pore diameter. And, α-alumina is a preferable material for the upstream side catalytic reacting section 60 a having a greater average pore diameter.
According to this arrangement, the first sub catalytic reacting section 60 a is positioned at the upstream side and the second sub catalytic reacting section 60 b is positioned at the downstream side. The catalyst support used in the upstream catalytic reacting section 60 a has a greater average pore diameter to assure the good property against capillary condensation.
The heat of catalytic reaction generated from the upstream side catalytic reacting section 60 a can be utilized as heat energy for heating the downstream side catalytic reacting section 60 b. Accordingly, the downstream side catalytic reacting section 60 b can dry and remove the residual moisture.
Thus, the downstream side catalytic reacting section 60 b can use the catalyst support having a smaller average pore diameter to hold a sufficient amount of catalyst, while suppressing the capillary condensation.
As described above, the catalytic reaction heater S3 according to this embodiment has excellent effects. The catalytic reacting section 60, as a whole, can possess good property against capillary condensation and satisfactory reactivity.
According to this embodiment, the control section 200 can control the fuel supplying device 30 to increase or decrease the fuel supply amount in accordance with temperature change of the catalytic reacting section 60. It becomes possible to set an appropriate fuel supply amount in accordance with startup temperature environment.
Furthermore, in this embodiment, the catalytic reacting section 60 can employ any one of the above-described various capillary condensation inhibiting arrangements to suppress capillary condensation phenomenon.
Moreover, according to this embodiment, it is possible to provide a bypass passage controlling device constituted by an appropriate shutoff valve or a temperature-sensitive deformable member as described above.

Other Embodiments

In each of the above-described embodiments, it is preferable to apply a water repellent treatment to the surface of a catalyst support used in the catalytic reacting section 60.
For example, as a practical water repellent treatment, it is possible to coat a water repellent resin, such as Teflon (trademark) or fluorine resin, on a surface of an alumina catalyst support. The catalyst, such as Pt and Pd, is held on the coated surface of this catalyst support.
Applying the water repellent treatment on the catalyst support in this manner effectively prevents the moisture from adsorbing on the surface of the catalyst support as well as on pore surfaces. Thus, the catalyst support used in the catalytic reacting section has good property against capillary condensation.
Although the heat exchanging section 70 is provided between the catalytic reacting section 60 and the exhaust gas passage 80, it is possible to omit the heat exchanging section 70 in each of the above-described embodiments. Alternatively, it is possible to provide a plurality of heat exchanging sections.
Furthermore, each of the above-described embodiments brings the effect of promptly increasing the temperature of the catalyst and reducing the emission of any unreacted gas without employing an EHC (i.e. electric heating catalyst). However, it is desirable to employ an EHC arrangement.
Furthermore, the present invention provides the catalytic reaction heater characterized by the bypass arrangement including the bypass passage controlling device for separately supplying the oxygen containing gas into the catalytic reacting section and into the exhaust passage via the bypass passage. Furthermore, the present invention regulates the pore diameter in the catalytic reacting section. Other portions and components can be modified adequately.
Moreover, application of the catalytic reaction heater according to the present invention is not limited to automotive vehicles.

Claims

1. A catalytic reaction heater comprising:

a catalytic reacting section for generating heat based on a catalytic reaction of a gas mixture of a fuel and an oxygen containing gas;

fuel supplying means provided at an upstream side of said catalytic reacting section for supplying said fuel into said catalytic reacting section;

oxygen containing gas supplying means provided at the upstream side of said catalytic reacting section for supplying said oxygen containing gas into said catalytic reacting section;

an exhaust gas passage provided at a downstream side of said catalytic reacting section to discharge an exhaust gas from said catalytic reacting section; and

a bypass passage, having one end connected to the upstream side of said catalytic reacting section and the other end connected to the downstream side of said catalytic reacting section, for directly supplying part of said oxygen containing gas from said oxygen containing gas supplying means into said exhaust gas passage, so that said oxygen containing gas is separately supplied into said catalytic reacting section and into said bypass passage.

2. The catalytic reaction heater in accordance with claim 1, further comprising

bypass passage controlling means for open-and-close controlling said bypass passage,

temperature detecting means for detecting the temperature of the exhaust gas discharged from said catalytic reacting section, and

means for controlling said bypass passage controlling means based on information supplied from said temperature detecting means.

3. The catalytic reaction heater in accordance with claim 2, wherein said temperature detecting means is provided at a downstream side of said catalytic reacting section.

4. The catalytic reaction heater in accordance with claim 2, wherein said bypass passage controlling means is a valve means.

5. The catalytic reaction heater in accordance with claim 2, wherein said bypass passage controlling means is a deformable member that is deformable in response to temperature change and is provided at a position where said deformable member is heated by the exhaust gas discharged from said catalytic reacting section.

6. The catalytic reaction heater in accordance with claim 5, wherein said deformable member is a bimetal.

7. The catalytic reaction heater in accordance with claim 5, wherein said deformable member is a shape memory member.

8. The catalytic reaction heater in accordance with claim 1, wherein control means is provided for controlling said fuel supplying means to increase and decrease a supply amount of said fuel according to a temperature change of said catalytic reacting section.

9. The catalytic reaction heater in accordance with claim 1, wherein said catalytic reacting section uses a catalyst support having an average pore diameter equal to or greater than 10 nm.

10. The catalytic reaction heater in accordance with claim 1, wherein said catalytic reacting section has a catalyst support having pore diameters ranging from 1 nm to at least 10 nm.

11. The catalytic reaction heater in accordance with claim 1, wherein said catalytic reacting section has at least two kinds of catalyst supports different in their average pore diameters.

12. The catalytic reaction heater in accordance with claim 1, wherein

said catalytic reacting section is divided into a plurality of sub sections, including a first sub catalytic reacting section positioned at an upstream side and a second sub catalytic reacting section positioned at a downstream side, and

an average pore diameter of a catalyst support used in said first sub catalytic reacting section is greater than an average pore diameter of a catalyst support used in said second sub catalytic reacting section.

13. The catalytic reaction heater in accordance with claim 1, wherein said catalytic reacting section uses a catalyst support made of a ceramic.

14. The catalytic reaction heater in accordance with claim 13,

wherein said ceramic is an alumina.

15. The catalytic reaction heater in accordance with claim 1, wherein said catalytic reacting section uses a catalyst containing noble metal.

16. The catalytic reaction heater in accordance with claim 1, wherein said fuel is hydrogen.

17. The catalytic reaction heater in accordance with claim 1, wherein said oxygen containing gas is air.

18. The catalytic reaction heater in accordance with claim 1, further comprising a heat exchanging section provided between said catalytic reacting section and said exhaust gas passage for receiving heat generated from said catalytic reacting section and heating a heating medium based on heat exchange between the received heat and said heating medium.

19. The catalytic reaction heater in accordance with claim 1, wherein a water repellent treatment is applied to a surface of a catalyst support used in said catalytic reacting section.

20. A catalytic reaction heater comprising:

a bypass passage for supplying part of said oxygen containing gas from said oxygen containing gas supplying means into said exhaust gas passage in a startup condition of said catalytic reacting heater, so that the gas mixture introduced into said catalytic reacting section has a low excess rate of oxygen containing gas in the startup condition of said catalytic reacting heater.