WO2008075754A1

WO2008075754A1 - Air filter device of fuel cell

Info

Publication number: WO2008075754A1
Application number: PCT/JP2007/074593
Authority: WO
Inventors: Nobuhiko Nakagaki; Yasunari Arai; Hiroshi Arisawa; Makoto Ueno; Toyokazu Baika; Junji Nagasawa
Original assignee: Toyota Boshoku Kabushiki Kaisha; Toyota Jidosha Kabushiki Kaisha
Priority date: 2006-12-20
Filing date: 2007-12-14
Publication date: 2008-06-26
Also published as: JP2008159281A

Abstract

A filter unit 36 that removes impurity gas from intake air is provided in an intake passage of a fuel cell. The filter unit 36 has an upstream filter 37 and a downstream filter 38. The gas removal capacity of the upstream filter 37 is greater than the gas removal capacity of the downstream filter 38. The gas removal efficiency of the downstream filter 38 is higher than the gas removal efficiency of the upstream filter 37.

Description

DESCRIPTION

AIR FILTER DEVICE OF FUEL CELL

TECHNICAL FIELD

The present invention relates to a filter device of a fuel cell that is provided in an intake passage of the fuel cell and has a filter unit that removes impurity gas from intake air.

BACKGROUND ART

Such types of filter device are disclosed in, for example, Japanese Laid-Open Patent Publication Nos. 2003-

132928, 2002-58729, 2005-121294, and 2005-327684. Japanese Laid-Open Patent Publication No. 2003-132928 describes a fuel cell system in which air passes through an electrostatic filter, a blower, and a photocatalyst filter and is thus supplied to a fuel cell. The electrostatic filter adsorbs and removes dust and particles from the air. The photocatalyst filter decomposes impurity gases such as nitrogen oxides, sulfur oxides, and carbon monoxide and thus removes the gases from the air. This prevents air containing impurity matter from being fed to the fuel cell. This suppresses changes of properties of electrolyte and decrease of oxygen adsorption performance of an electrode catalyst. The power generating performance of the fuel cell is thus prevented from being lowered.

Japanese Laid-Open Patent Publication No. 2002-58729 discloses a deodorant filter having a nonwoven fabric layer impregnated with deodorant and an activated carbon layer including honeycomb structures. Granular activated carbon is embedded in respective small cells defined by the honeycomb structures. The nonwoven fabric layer is arranged upstream and the activated carbon layer is located downstream in the flow direction of the air. The nonwoven fabric layer and the activated carbon layer remove odor from the air.

Japanese Laid-Open Patent Publication No. 2005-121294 discloses a toxic substance removal device including a dust collecting filter and a gas removal filter. The dust collecting filter is formed by folding a nonwoven fabric in a pleated manner. The gas removal filter has granular activated carbon embedded in respective cells defined by a grid. The dust collecting filter removes dust from the air, and the gas removal filter removes toxic gas such as aldehydes from the air.

Japanese Laid-Open Patent Publication No. 2005-327684 discloses an air cleaning filter of a fuel cell having a low- density dust collecting filter, a high-density dust collecting filter, an ammonia filter that removes ammonia gas, and a hydrogen sulfide filter that removes hydrogen sulfide. The ammonia filter and the hydrogen sulfide filter are each formed by a honeycomb structure defined by a sheet material of activated carbon fibers and polyester fibers. The air cleaning filter thus removes dust and impurity gas from the air as the air passes sequentially through the different filters .

However, in the fuel cell system disclosed in Japanese Laid-Open Patent Publication No. 2003-132928, since the photocatalyst filter decomposes and removes the impurity gas from the air, the filter device must be arranged to be exposed to the sunlight or, if that is impossible, a light source must be provided for the filter device. Also, since the photocatalyst filter typically reacts with impurity gas at a low speed, the impurity gas cannot be removed from the air with improved efficiency if the amount of the air is great. To solve this problem, the photocatalyst may be arranged over an increased distance along the flow direction of the air so as to enhance the removal efficiency of the impurity gas. In this case, the device becomes large-sized and airflow resistance increases disadvantageously.

In the deodorant filter disclosed in Japanese Laid-Open Patent Publication No. 2002-58729, the activated carbon layer, which is formed by the granular activated carbon, is arranged downstream in the air flow. If the filter is used as a gas removable device, the downstream activated carbon layer cannot sufficiently remove impurity gas. To solve this problem, the upstream nonwoven fabric layer may be replaced by an activated carbon fiber layer to remove the impurity gas from the air also at the upstream side of the air flow. However, since the activated carbon fiber layer cannot remove a great of impurity gas, the activated carbon fiber layer becomes saturated soon and the life of the filter is shortened.

In the filter device disclosed in Japanese Laid-Open Patent Publication No. 2005-121294, the filter has a single layer structure formed of granular activated carbon. Thus, as in the case of Japanese Laid-Open Patent Publication No. 2002-58729, the filter solely cannot sufficiently remove impurity gas. To solve this problem, the dimension of the layer formed of the granular activated carbon may be increased in the direction of the air flow to enhance gas removal efficiency. However, such size increase disadvantageously raises airflow resistance and increases pressure loss.

In the filter device described in Japanese Laid-Open Patent Publication No. 2005-327684, the two gas removal filters each have a honeycomb structure formed of activated carbon fibers or the like. However, such configuration exhibits low gas removal capacity and shortens the life of the filters. Further, the airflow resistance is raised and pressure loss is increased.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide a small-sized filter device of a fuel cell that maintains long-term and highly efficient removal of impurity gas from air fed to the fuel cell and suppresses increase of pressure loss.

To achieve the foregoing objective and in accordance with a first aspect of the present invention, a filter device of a fuel cell that is provided in an intake passage of the fuel cell is provided. The filter device includes a filter unit that removes impurity gas from intake air. The filter unit has an upstream filter and a downstream filter. The upstream filter is located in an upstream section of the intake passage, and the downstream filter is located in a downstream section in the intake passage. A gas removal capacity of the upstream filter is greater than the gas removal capacity of the downstream filter, and a gas removal efficiency of the downstream filter is higher than the gas removal efficiency of the downstream filter.

In the above described filter device, the size of the upstream filter is preferably set in such a manner that a space velocity of the upstream filter falls in the range of 50,000 to 300,000 when a flow rate of intake air is 4 mVmin.

In the above described filter device, the upstream filter is preferably formed of a granular adsorption material, In the above described filter device, the upstream filter preferably has a frame, which is divided into a plurality of cells, and each of the cells preferably receives the granular adsorption material.

In the above described filter device, the downstream filter is preferably formed of a fibrous adsorption material.

According to the present invention, the upstream filter exhibiting high gas removal capacity removes most of impurity gas from the air fed to the fuel cell. The rest of the impurity gas is then removed by the downstream filter exhibiting high gas removal efficiency. Thus, by the time the air passes through the upstream filter, the concentration of the impurity gas in the air is greatly lowered. This prevents the gas removal efficiency of the downstream filter from decreasing in a short time. In this manner, the upstream and downstream filters of the filter unit cooperate with each other to maintain long-term and highly efficient removal of the impurity gas from the air fed to the fuel cell with low pressure loss and thus prevent the pressure loss from increasing. This makes it unnecessary to increase the lengths of the passages in the filters, and the filter device becomes small-sized.

Further, it is particularly preferred that the size of the upstream filter be set in such a manner that space velocity of the upstream filter falls in the range of 50,000 to 300,000 when the intake air flow rate is 4 mVmin. This improves the gas removal capacity and the gas removal efficiency of the filter unit. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a diagram showing a fuel cell system having a filter device according to the present invention; Fig. 2 is a cross-sectional view showing a filter device according to a first embodiment of the invention;

Fig. 3(A) is a side view showing an upstream filter of a filter unit of the filter device shown in Fig. 2;

Fig. 3 (B) is a cross-sectional view showing the upstream filter;

Fig. 4 is a side view showing a portion of a downstream filter of the filter unit;

Fig. 5 is a graph representing the relationship between gas removal amount and gas removal efficiency of filter units of examples and comparative examples;

Fig. 6 is a graph representing the relationship between intake air flow rate and airflow resistance of the filter units of the examples and the comparative examples;

Fig. 7 is a cross-sectional view showing a filter device according to a second embodiment of the invention;

Fig. 8 is a cross-sectional view showing a filter device according to a third embodiment of the invention;

Fig. 9 is a cross-sectional view showing a filter device according to a fourth embodiment of the invention; Fig. 10 is a cross-sectional view showing an upstream filter of a filter device according to a fifth embodiment of the invention;

Fig. 11 is a partial side view showing an upstream filter of a filter unit according to a sixth embodiment of the invention;

Fig. 12 is a cross-sectional view showing an upstream filter of a filter unit according to a seventh embodiment of the invention;

Fig. 13 is a partial cross-sectional view showing a filter unit according to an eighth embodiment of the invention;

Fig. 14 is a cross-sectional view showing a filter unit according to a ninth embodiment of the invention; and

Fig. 15 is a cross-sectional view showing a filter device according to a tenth embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment)

A first embodiment of the present invention will now be described with reference to Figs. 1 to 6.

A fuel cell system according to the invention is configured as follows.

As illustrated in Fig. 1, a fuel cell system 21 has a fuel cell 22 formed by a solid-state high-molecular electrolyte type fuel cell and a controller 24 that controls operation of the fuel cell 22. Hydrogen gas is supplied from a high-pressure cylinder 23 to the fuel cell 22. The fuel cell 22 also receives air containing oxygen through a filter device 26 and a blower 27. The filter device 26 removes impurity gas such as sulfur dioxide (SO₂) from the air. The hydrogen supplied by the high-pressure cylinder 23 and the filtered air electrochemically react with each other in the fuel cell 22. In this manner, electric energy is obtained. An inverter 28 converts the DC power produced by the fuel cell 22 into AC power.

The configuration of the filter device 26 will hereafter be explained.

As shown in Fig. 2, the filter device 26 has a casing 31 formed by a first casing forming body 32 and a second casing forming body 33. One side surface of the first casing forming body 32 is open. The second casing forming body 33 closes the opening of the first casing forming body 32 in such a manner that the opening is selectively opened and closed. An inlet 34 is formed in the first casing forming body 32 and an outlet 35 is formed in the second casing forming body 33. A filter unit 36 is arranged between the inlet 34 and the outlet 35 in the casing 31. The air fed to the fuel cell 22 passes through the filter unit 36 so that impurity gas is removed from the air.

The filter unit 36 has an upstream filter 37 and a downstream filter 38. The upstream filter 37 is arranged upstream in the flow of the air. The downstream filter 38 is located adjacent to and downstream of the upstream filter 37. The gas removal capacity of the upstream filter 37 is greater than the gas removal capacity of the downstream filter 38. The gas removal efficiency of the downstream filter 38 is higher than the gas removal efficiency of the upstream filter 37.

With reference to Figs. 3(A) and 3(B), the upstream filter 37 has a frame 39 formed of paper, synthetic resin, or metal. A plurality of cells 39a are defined in the frame 39. Granular adsorption material 40 such as activated carbon, zeolite, or silica gel, is provided in each of the cells 39a. Front and rear openings of each cell 39a is covered by a cover 39b. The cover 39b is formed of air-permeable woven fabric and holds the granular adsorption material 40 so that ^• the granular adsorption material 40 does not fall from the cells 39a. The volume (surface area S x height H) of the upstream filter 37 is set in such a manner that the space velocity SV of the upstream filter 37 becomes 50,000 to 300,000 when the intake air flow rate of the fuel cell 22 is 4 m³/min. The space velocity is defined as the volume per hour of the fluid passing through the filter divided by the volume of the filter.

Further, the amount of granular adsorption material 40 provided in each cell 39a of the frame 39 of the upstream filter 37 is set in such a manner that the volume of the cell 39a falls in the range of 1.1 to 2 times the volume of the granular adsorption material 40. This suppresses movement of the granular adsorption material 40 in each cell 39a when the upstream filter 37 is vibrated. The cell 39a is thus prevented from being damaged by the granular adsorption material 40. The height of the cell 39a is set in such a range the space velocity SV falls in the range of 50,000 to 300,000. For example, the granular adsorption material 40, which is formed of granular activated carbon, has large adsorption surfaces. This increases the gas removal capacity and the gas removal effect is maintained for a long time. Further, the walls defining each cell 39a extend in the flow direction of the air and thus promotes smooth flow of air. This decreases airflow resistance and lowers pressure loss.

Contrastingly, as illustrated in Fig. 4, the downstream filter 38 is formed by a fibrous adsorption material 41 formed by tangling fine powder adsorption material 43 such as activated carbon with fibers 42 and fixing the powder adsorption material 43 and the fibers 42 with adhesive. The density of the fibrous adsorption material 41 is set in the range of 100 g/m² to 300 g/m² and the fiber diameter of the fibrous adsorption material 41 is set in the range of 10 μm to 50 μm. The fibrous adsorption material 41 decreases the pressure loss compared to the granular type, thus ensuring high gas removal efficiency with low pressure loss. As a result, the fibrous adsorption material 41 functions as a dust removing filtering element. The volume of the upstream filter 37 is set in such a manner that the space velocity SV of the upstream filter 37 becomes 50,000 to 300,000 when the flow rate of the air is 4 m³/min. In other words, as the space velocity SV becomes greater, the time in which the air is retained in the upstream filter 37 becomes shorter. This lowers the gas removal efficiency. In contrast, as the space velocity SV becomes lower, the time in which the air is retained in the upstream filter 37 becomes longer. The gas removal efficiency is thus improved. Nonetheless, if the space velocity SV is lowered with the intake air flow rate maintained at a level not less than a predetermined value, the volume of the filter becomes great and the pressure loss increases. However, as long as the space velocity SV is set in the above-described range, gas removal efficiency required for a fuel cell is maintained continuously for a long time. Thus, increase of the pressure loss is suppressed while the flow rate of the air is maintained at a certain level or higher.

The filter device of the present embodiment is particularly suitable for a fuel cell that requires an intake air flow rate of 3 m³/min to 5 mVmin. Since the adsorption material 43 of the downstream filter 38 is fine, the speed of the reaction that results in removal of the gas is extremely high. Thus, the space velocity SV of the downstream filter 38 does not have to be taken into consideration.

In the present embodiment, the filter unit 36 of the filter device 26 is configured by the upstream filter 37 and the downstream filter 38, as shown in Fig. 2. The gas removal capacity of the upstream filter 37 is greater than the gas removal capacity of the downstream filter 38. The gas removal efficiency of the downstream filter 38 is greater than the gas removal efficiency of the upstream filter 37. Thus, as the air fed to the fuel cell 22 flows into the casing 31 through the inlet 34 and passes through the upstream filter . 37, most of the impurity gas (for example, 75% of the gas) is removed from the air by the upstream filter 37. Also, since the upstream filter 37 is formed of the material exhibiting improved gas removal capacity, the gas removal efficiency of the upstream filter 37 is maintained at this level, which is 75%, for a long time. Afterwards, the air passes through the downstream filter 38, which removes the rest of the impurity gas from the air.

The concentration of the impurity gas in the air that has passed through the upstream filter 37 is as small as approximately a quarter (25%) of the concentration of the gas in the air that has yet to pass through the upstream filter 37. Thus, the life of the downstream filter 38 of the case in which the upstream filter 37 is provided becomes approximately four times as long as the life of the downstream filter 38 of a case in which the upstream filter

37 is not provided. Further, since the material forming the downstream filter 38 exhibits high gas removal efficiency, the impurity gas is removed from the air with improved efficiency, which is, for example, greater than or equal to 98%. In this manner, the air is cleansed by removing the impurity gas and supplied from the casing 31 to the fuel cell 22 through the outlet 35.

Accordingly, in the filter device 26 of the present embodiment, the upstream filter 37 and the downstream filter

38 cooperate with each other to remove the impurity gas from the air fed to the fuel cell 22 continuously for a long period of time and with high efficiency. This suppresses increase of pressure loss.

The first embodiment has the following advantages. (1) The upstream filter 37 is formed of the material exhibiting great gas removal capacity. Thus, the upstream filter 37 maintains the gas removal efficiency of approximately 75% for a long time. The downstream filter 38 is formed of the material exhibiting high gas removal efficiency. This allows the downstream filter 38 to remove the impurity gas from the air with the high efficiency that is greater than or equal to 98%. As has been described, by the time the air reaches the downstream filter 38, the amount of the impurity gas in the air is decreased by a great amount Thus, the downstream filter 38 maintains high removal efficiency for a long time. This prolongs the life of the filter unit 36 and decreases the pressure loss.

(2) Since the upstream filter 37 and the downstream filter 38 effectively adsorb the impurity gas, a long removal path becomes unnecessary unlike a case in which the impurity gas is removed by photocatalyst . This suppresses increase of airflow resistance and downsizes the device.

(3) In the upstream filter 37, the granular adsorption material 40 is received in each of the cells 39a of the frame 39. This prevents the granular adsorption material 40 from moving downward, despite of an upright posture of the upstream filter 37. Thus, the granular adsorption material 40 is deployed in a uniformly distributed state and thus allowed to efficiently remove impurity gas from the air. Further, since the granular adsorption material 40 is retained in the cells 39a, movement of the granular adsorption material 40 is suppressed. This prevents damages to the cells 39a by the granular adsorption material 40.

(Second Embodiment)

A second embodiment of the present invention will hereafter be explained with reference to Fig- 7. In the following description, respective embodiments including the second embodiment will be explained mainly on the differences between these embodiments and the first embodiment with regard to configurations, operations, and advantages of the embodiments .

As shown in Fig. 7, a filter device 26 has two casings 31A, 31B, each of which is formed by a first casing forming body 32 and a second casing forming body 33. The second casing forming body 33 of the first casing 31A and the first casing forming body 32 of the second casing 31B are connected together through a connection cylinder 46. An inlet 34 is defined in the first casing forming body 32 of the first casing 31A and an outlet 35 is defined in the second casing forming body 33 of the second casing 31B. An upstream filter 37 and a downstream filter 38, which form a filter unit 36, are separately received in the first casing 31A and the second casing 31B, respectively.

The second embodiment thus has the following advantage.

(4) Since the filter device 26 has two separate casings, each of the casing becomes small-sized. The filter device 26 is thus advantageously arranged in separate narrow spaces.

(Third Embodiment)

A third embodiment of the present invention will now be described with reference to Fig. 8.

As shown in Fig. 8, a casing 31 has a casing body 31a and a lid 31b. An opening is defined in the upper surface of the casing body 31a. The lid 31b closes the opening of the casing body 31a in such a manner that the opening is selectively opened and closed. An inlet 34 and an outlet 35 are defined in the casing body 31a. A filter unit 36 is formed by an upstream filter 37 and a downstream filter 38. The filters 37, 38 are arranged in the casing 31 as spaced from each other at a certain interval along the flow direction of the air.

The third embodiment has the following advantage.

(5) By removing the lid 31b from the casing body 31a, the upper surface of the casing body 31a becomes open to a great extent. This facilitates replacement of the filters 37, 38.

(Fourth Embodiment)

A fourth embodiment of the present invention will hereafter be described with reference to Fig. 9.

As shown in Fig. 9, as in the case of the third embodiment, a casing 31 includes a casing body 31a with an opening defined in its upper surface and a lid 31b closing the opening of the casing body 31a in such a manner that the opening is selectively opened and closed. A filter unit 36 is configured by an upstream filter 37, an intermediate filter 47, and a downstream filter 38. The filters 37, 47, 38 are received in the casing 31 and spaced at certain intervals along the flow direction of the air. The gas removal capacity of the intermediate filter 47 is greater than the gas removal capacity of the downstream filter 38 and smaller than the gas removal capacity of the upstream filter 37. The gas removal efficiency of the intermediate filter 47 is greater than the gas removal capacity of the upstream filter 37 and smaller than the gas removal capacity of the downstream filter 38. The fourth embodiment has the following advantage.

(6) Since the filter unit 36 is the multiple-stage filter formed by the filters 37, 47, 38, the gas removal capacity and the gas removal efficiency of the filter unit 36 are further enhanced compared to the first embodiment.

(Fifth Embodiment)

A fifth embodiment of the present invention will be explained in the following with reference to Fig. 10.

As illustrated in Fig. 10, an upstream filter 37 of a filter unit 36 is configured differently from the corresponding configurations of the other embodiments.

Specifically, a frame 39 is divided into a greater number of cells 39a and each of the cells 39a is sized smaller. Each adjacent pair of the cells 39a are separated from each other by an air-permeable partition wall 44. Further, the upstream opening of one of the adjacent pair of the cells 39a is sealed by a corresponding seal member 48 and the downstream opening of the other of the cells 39a is sealed by a corresponding seal member 48.

The fifth embodiment has the following advantage.

(7) The upstream filter 37 filters off dust from the air by means of the partition walls 44 and retains the dust in the cells 39a of the frame 39. Thus, the upstream filter 37 functions as a dust removal filter in addition to a gas removal filter.

(Sixth Embodiment)

A sixth embodiment of the present invention will now be explained with reference to Fig. 11.

As shown in Fig. 11, an upstream filter 37 of a filter unit 36 is formed by tangling granular adsorption material 40 such as activated carbon with resin fibers 49 and fixing the granular adsorption material 40 and the resin fibers 49 together. In this case, it is preferred that the ratio of the mass of the resin fibers 49 to the mass of the granular adsorption material 40 is set to 1:9 to 4:6. It is also preferred that the thickness of each of the resin fibers 49 is set to 4 to 12 decitex.

The upstream filter 37 of the sixth embodiment has the following advantage.

(8) Since the granular adsorption material 40 is fixed by the resin fibers 49, the granular adsorption material 40 is prevented from moving or being concentrated at a certain position in the cells 39a. This prevents the cells 39a from being damaged due to vibration of the granular adsorption material 40.

(Seventh Embodiment)

A seventh embodiment of the invention will now be described with reference to Fig. 12.

Referring to Fig. 12, an upstream filter 37 of a filter unit 36 includes a plurality of air-permeable buffer members 50, which are stacked together while being spaced at certain intervals. A space between each adjacent pair of the air- permeable buffer members 50 receives granular adsorption material 40. Each of such spaces is sealed by a frame 39. Each of the air-permeable buffer members 50 is formed by, for example, a sponge or a nonwoven fabric. The granular adsorption material 40 is formed of, for example, activated carbon. The frame 39 is formed of, for example, paper. The airflow resistance of each air-permeable buffer member 50 is set to a level smaller than or equal to a tenth of the airflow resistance of the upstream filter 37 as a whole. The density of the air-permeable buffer member 50 is set in the range of 50 to 200 g/m².

The seventh embodiment has the following advantage.

(9) The air-permeable buffer members 50 absorb impact applied to the granular adsorption material 40. This prevents the frame 39 and the air-permeable buffer members 50 from being damaged by vibration of the granular adsorption material 40. Further, the air-permeable buffer members 50 allow the upstream filter 37 to function also as a dust removal filter.

(Eighth Embodiment)

An eighth embodiment of the present invention will be explained in the following, with reference to Fig. 13.

As illustrated in Fig. 13, a filter unit 36 includes a dust removal filtering element 51, a downstream filter 38, and an upstream filter 37 that are provided as an integral body. The upstream filter 37 is held between the dust removal filtering element 51 and the downstream filter 38. The dust removal filtering element 51 is formed by a nonwoven fabric that is folded in a pleated manner. The downstream filter 38 is formed by a fibrous activated carbon that is folded in a pleated manner. The upstream filter 37 is formed of granular adsorption material 40 such as activated carbon.

The eighth embodiment has the following advantage. (10) The dust removal filtering element 51 is arranged upstream from the upstream filter 37, which is formed of the granular adsorption material 40. The dust removal filtering element 51 thus traps and removes dust from the air.

(Ninth Embodiment)

A ninth embodiment of the present invention will hereafter be described with reference to Fig. 14.

As shown in Fig. 14, a filter unit 36 includes a frame 39, an upstream filter 37, and a downstream filter 38, which are provided as an integral body. The upstream filter 37 and the downstream filter 38 are received in the frame 39. The frame 39 is formed of, for example, paper. The upstream filter 37 is formed of granular adsorption material 40 such as activated carbon. The downstream filter 38 is formed by fibrous activated carbon that is folded in a pleated manner. A space between each adjacent pair of the pleats of the downstream filter 38 at the upstream side is filled with the granular adsorption material 40. The granular adsorption material 40 may be a type that functions as the upstream filter 37 or the downstream filter 38.

The ninth embodiment has the following advantage.

(11) The granular adsorption material 40 is received also in the space between each adjacent pair of the pleats of the downstream filter 38. Thus, the space in the filter unit 36 is effectively used to improve the gas removal capacity or the gas removal efficiency.

(Tenth Embodiment) A tenth embodiment of the present invention will hereafter be explained with reference to Fig. 15.

As shown in Fig. 15, a filter device 26 has two casings 31A, 31B, which are connected together by a connection cylinder 46, as in the second embodiment. An inlet 34 is defined in a side surface of the first casing 31A and an outlet 35 is defined in a side surface of the second casing 31B. The first casing 31A retains liquid 52 that forms an upstream filter 37 and is capable of dissolving impurity gas. The second casing 31B accommodates a downstream filter 38. The liquid 52 is water or oil. The downstream filter 38 is formed of, for example, fibrous activated carbon. Although not illustrated, the casing 31A has an outlet port and an inlet port. The liquid 52 is discharged from the casing 31A through the outlet port and replaced by unused liquid 52 through the inlet port. The liquid 52 contains adsorption improving agent .

The tenth embodiment has the following advantage.

(12) Since the upstream filter 37 is formed of the liquid 52, the upstream filter 37 removes dust from the air.

[Examples]

In the examples, granular activated carbon with the sizes of 4 to 8 meshes and the bulk density of 0.3 kg/1 to 0.7 kg/1 was used for the upstream filter 37 of the filter unit 36. As the downstream filter 38, fibrous activated carbon with potassium carbonate added to the surface of the activated carbon was used. The entire surface of the fibrous activated carbon was covered with a nonwoven fabric of PET (polyethylene terephthalate) . The filter used as the upstream filter 37 had a filter opening area set in such a manner that the face velocity of the upstream filter 37 becomes 1 m/sec when the intake air flow rate was 4 mVmin. As shown in Table 1, in the filter unit of Examples 1, 2, and 3, the space velocity SV of the upstream filter 37 was set to 120,000, 50,000, and 300, 000, respectively. Contrastingly, in the filter unit 36 of Comparative Examples 1 and 2, the space velocity SV of the upstream filter 37 was set to 550,000 and 25, 000, respectively. Figs. 5 and 6 show the relationship between the amount of removed impurity gas and the removal efficiency of the impurity gas and the relationship between the intake air flow rate and the airflow resistance, respectively.

[Table 1]

As is clear from Fig. 5, the life of the filter unit from when the filter unit was first used to when the gas removal efficiency dropped to 98% or less was sufficiently extended in Examples 1 to 3 and Comparative Example 2, but not in Comparative Example 1. Also, as is shown in Fig. 6, the airflow resistance required for the fuel cell was ensured in Examples 1 to 3 and Comparative Example 1 but not in Comparative Example 2. Specifically, the airflow resistance when the intake air flow rate was 4 m³/min, which was 600 Pa, W 2

was used as a reference value. If the airflow resistance was not more than the reference value, it was determined that the airflow resistance was at a satisfactory level. Fig. 6 shows that desirable gas removal life and desirable airflow resistance were obtained with Examples 1 to 3.

(Modified Embodiments)

The illustrated embodiments may be modified in the following forms.

In the first embodiment, the frame 39 of the upstream filter 37 may be formed by a sheet of paper containing adsorption material such as activated carbon. This further enhances gas removal capacity.

In the fourth embodiment, the filter unit 36 may be formed by a multilayer filter including four or more layers.

In each of the illustrated embodiments, the adsorption material of the upstream filter 37 or the downstream filter 38 may be modified to a porous body, fibers, or a solid that absorbs gas. Further, adsorption improving agent may be added to these substances.

Claims

1. A filter device of a fuel cell, the filter device being provided in an intake passage of the fuel cell, the filter device including a filter unit that removes impurity gas from intake air, the filter device being characterized in that the filter unit has an upstream filter and a downstream filter, the upstream filter being located in an upstream section of the intake passage, and the downstream filter being located in a downstream section in the intake passage, wherein a gas removal capacity of the upstream filter is greater than the gas removal capacity of the downstream filter, and a gas removal efficiency of the downstream filter is higher than the gas removal efficiency of the downstream filter.

2. The filter device according to claim 1, being characterized in that the size of the upstream filter is set in such a manner that a space velocity of the upstream filter falls in the range of 50,000 to 300,000 when a flow rate of intake air is 4 m³/min.

3. The filter device according to claims 1 or 2, being characterized in that the upstream filter is formed of a granular adsorption material.

4. The filter device according to claim 3, being characterized in that the upstream filter has a frame, the frame being divided into a plurality of cells, each of the cells receiving the granular adsorption material.

5. The filter device according to any one of claims 1 to 4, being characterized in that the downstream filter is formed of a fibrous adsorption material.