Device for treating vaporized fuel gas

Abstract: A device for treating vaporized fuel gas comprises a canister (1) which is capable of quickly heating activated carbon therein through the resistance thereof up to a required temperature to bring about desorption of the vaporized fuel gas. The canister comprises a container (2) having a vaporized fuel gas inlet port (6) and an exit port (9). An aggregate (13) of activated carbon (12) is placed in the container to adsorb the vaporized fuel gas, and at least one pair of electrodes (14,15) are provided for heating the activated carbon through the resistance thereof, to bring about desorption of the vaporized fuel gas. A highly electrically conductive activated carbon is used having an electric resistance of not more than 500 Ω/2.5 3 cm 3 .

Description: This invention relates to a device for mounting on an automobile for treating vaporized fuel gas and, more particularly, to an improvement in such a device which comprises a container having a vaporized fuel gas inlet port and an exit port, an aggregate of activated carbon in the container for adsorbing the vaporized fuel gas, and at least one pair of electrodes for heating the activated carbon through the resistance of the activated carbon, to bring about desorption of the vaporized fuel gas. We have previously proposed a device of this type in Japanese Patent Laid-Open No. 6-280694. In this proposal the activated carbon is heated through the resistance thereof to bring about desorption of the vaporized fuel gas by raising the temperature of the vaporized fuel gas adsorbed by the activated carbon, whereby to enhance the kinetic energy and to promote the desorption of the vaporized fuel gas from the activated carbon. Such a device is caused to deteriorate by any accumulation of residual gas that remains adsorbed by the activated carbon, i.e. is not desorbed. Thus, in order to enhance the durability of the device, the desorption should be effected efficiently and to a sufficient degree. In a widely known device using normal activated carbon, however, an electric current flows in only small amounts between the two electrodes due to high electric resistance and, as a result there is a problem in heating the activated carbon up to a required temperature. US-A-3608273 discloses a filtering apparatus which uses a charge of particulate activated carbon and other materials having resistivities of about 20 to 50 ohms per centimeter. EP-A-0745416 and US-A-5658372 disclose further filtering devices which principally use a monolithic filter comprising activated carbon. According to the present invention there is provided a device for treating vaporized fuel gas, comprising a container having a vaporized fuel gas inlet port and an exit port, a charge of activated carbon in the container for adsorbing vaporized fuel gas, the activated carbon being highly electrically conductive, and at least one pair of electrodes for heating the activated carbon through the resistance thereof to bring about desorption of the vaporized fuel gas, characterised in that the charge of activated carbon is in the form of pellets, the pellets having an electric resistance of not more than 500 Ω/2.5 3 cm 3 , and in that the activated carbon in the pellets has an average porous diameter not smaller than 7Å (70 nm) and not larger than 37Å (370 nm). Thus, in a preferred form the invention provides a device in the form of a canister which is capable of quickly heating the activated carbon by means of the resistance of the activated carbon, up to a required temperature, by increasing the amount of current that flows between the said electrodes. We have considered the molecular sieve property of the activated carbon, with regard to the relationship between the average porous diameter and the adsorption (adhesion and holding) of butane-type components. That is, once the butane-type components are adhered to the activated carbon having the above-mentioned average porous diameter, the activated carbon has the ability to hold the butane-type components until the desorption operation is effected. Therefore, the above-mentioned activated carbon is capable of adsorbing the vaporized fuel gas to a sufficient degree. Moreover, as the activated carbon is highly electrically conductive it permits the vaporized fuel gas to be favorably desorbed upon the heating of the activated carbon due to the resistance thereof. An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Fig. 1 is a front view of a device according to the invention; Fig. 2 is a sectional view along the line 2-2 of Fig. 1; Fig. 3 is a sectional view along the line 3-3 of Fig. 2; Fig. 4 is a diagram schematically illustrating a testing facility for adsorbing and desorbing of n-butane; Fig. 5 is a perspective view of a cell for testing the residual effect of the electric resistance; Fig. 6 is a graph showing the relationship between the adsorption times and the adsorbed amounts of n-butane, and the relationship between the desorption times and the residual amounts of n-butane; Fig. 7 is a graph showing the relationship between the electric resistance of the activated carbon and the residual amount of n-butane; Fig. 8 is a graph showing the relationship between the average porous diameters of the activated carbon and the maximum adsorbed amount of n-butane; and Fig. 9 is a graph showing the relationship between the average porous diameter of the activated carbon and the residual amount of n-butane. Figs. 1 to 3 illustrate a device 1 in the form of a canister, for treating vaporized fuel gas. The device 1 comprises a container 2 made of a polyamide 66, the container including a cylindrical main body 3 with an end wall 7 and a closure plate 4 for closing the open end of the cylinder. The closure plate 4 has a hollow cylindrical portion 5 which protrudes outwardly from the central portion thereof and defines a vaporized fuel gas inlet port 6. The hollow cylindrical portion 5 is connected to a fuel tank (not shown). The main body 3 has another hollow cylindrical portion 8 that protrudes outwardly from a central portion of the end wall 7 and forms a vaporized fuel gas exit port 9. The hollow cylindrical portion 8 is connected to an air intake system of an engine (not shown). Inside the container 2 are filter layers 10 and 11 made of a glass wool, in contact with the closure plate 4 and the end wall 7 respectively. The space between the two filter layers 10 and 11 is filled with an aggregate 13 of pelletized activated carbon 12 for adsorbing the vaporized fuel gas. At least one pair of aluminum plate electrodes 14 and 15 are mounted opposed to each other, on the inner surfaces of a peripheral wall 16 of the main body 3, and are buried in the aggregate 13. Lead wires 17 and 18 of the electrodes 14 and 15 extend outwards, penetrating through the peripheral wall 16, and are connected to a DC power source (not shown). The electrodes 14 and 15 are used for heating the activated carbon 12 through the resistance thereof. The main body 3 is further provided with a thermocouple 19 penetrating through the peripheral wall 16, the thermocouple 19 operating so that the temperature of the activated carbon 12 will not exceed a predetermined temperature. As the activated carbon 12, there is used a highly electrically conductive activated carbon having an electric resistance of not more than 500 Ω/2.5 3 cm 3 . The highly electrically conductive activated carbon 12 can be quickly heated through the resistance thereof up to a required temperature with the voltage of a 12 V battery mounted on a car. This makes it possible to effect the desorption of the vaporized fuel gas efficiently and to a sufficient degree. Furthermore, owing to its quick response, the desorption can be effected depending upon the operation conditions of the engine. Accordingly, the vaporized fuel can be reliably supplied to the engine. The highly electrically conductive activated carbon in the aggregate 13 has an average porous diameter not smaller than 7 Å and not larger than 37 Å. A highly electrically conductive activated carbon having such an average porous diameter adsorbs the vaporised fuel gas containing butane-type components to a sufficient degree. Concretely described below is an example of using an n-butane (n-C 4 H 10 ) as a vaporised fuel gas. Fig. 4 illustrates a testing facility 20. In this testing facility 20, a nitrogen gas source 22 is connected to the inlet port 6 of the canister 1 through a first tubular passage 21. A first cock 23 and a first flow meter 24 are provided in the first tubular passage 21 extending from the side of the canister 1. Furthermore, an n-butane source 26 is connected, via a second tubular passage 25, to the first tubular passage 21 between the canister 1 and the first cock 23. A second cock 27 and a second flow meter 28 are provided in the second tubular passage 25 extending from the side of the canister 1. The two lead wires 17 and 18 and the thermocouple 19 are connected to a DC power source 29 (regulated DC power supply, maximum application voltage of 100 V, maximum current of 20 A, manufactured by Kikusui Denshi Co.). The amount of current flowing between the two electrodes 14 and 15 is controlled depending upon the temperature data of the thermocouple 19, and the activated carbon 12 is maintained at a constant temperature. The elements of the device 1 have sizes as follows: Container 2: the main body 3 has an inner diameter of 46 mm, a length of 80 mm and a thickness of 2 mm. Electrodes 14 and 15: 30 mm high, 60 mm long, 1 mm thick, and separated by 35 mm from each other. Activated carbon 12: pellets, contained in an amount of 100 cm 3 , having a diameter of about 2 mm and a thickness of about 2 to 6 mm. The electric resistance of the activated carbon 12 is measured by using an electric resistance measuring cell 30 (VOAC 7512, manufactured by Iwasaki Tsushinki Co.) shown in Fig. 5. The cell 30 comprises an electrically insulating channel member 31 made of an FRP, and a pair of aluminum plate electrodes 33 and 34 which close U-shaped openings 32 at the ends of the channel. Space 35 between the electrodes 33 and 34 is filled with the activated carbon 12. Then the electric resistance between the two electrodes 33 and 34 is measured and the measured value is regarded to be the electric resistance of the activated carbon 12. Here, the space 35 has a volume measuring 2.5 cm high, 2.5 cm wide and 2.5 cm deep, i.e., has a volume of 2.5 3 cm 3 (15.625 cm 3 ). Therefore, the electric resistance of the activated carbon 12 is expressed as ohms per 2.5 3 cm 3 . The adsorption and desorption of n-butane were tested according to the procedure described below. (a) First, the weight of a canister 1 that has not been used is measured. (b) Referring to Fig. 4, the first tubular passage 21 is connected to the canister 1. In this case, the canister 1 is not connected to the DC power source device 29. (c) The first cock 23 is opened, and nitrogen gas having a purity of 99.999% is supplied from the nitrogen gas source 22 into the canister 1 at a flow rate of one liter per minute for 5 minutes through the inlet port 6 and thence to the exit port 9, so as to replace the gas in the canister 1 with nitrogen gas. (d) While the nitrogen gas is being supplied under the above mentioned conditions, the second cock 27 is opened, and n-butane having a purity of 99% is supplied from the n-butane source 26 at a flow rate of one liter per minute. Thus a mixture of nitrogen gas and n-butane is supplied into the canister 1 through the inlet port 6 and thence to the exit port 9, and the amount of n-butane adsorbed by the activated carbon 12 is measured with the passage of time. To measure the amount of adsorption, the first tubular passage 21 is disconnected from the canister 1 after the passage of a predetermined period of time, and the weight of the canister 1 is measured. From the measured weight is subtracted the weight of the canister 1 before being tested, and the difference is regarded as being the adsorbed amount of n-butane. When the mixed gas has been allowed to flow for about 10 minutes, the adsorption of n-butane by the activated carbon 12 reaches the saturated state. Therefore, the supply of the mixed gas is discontinued and then the adsorbed amount of n-butane is determined, i.e. the maximum amount of adsorption is found. (e) The first tubular passage 21 and the DC power source device 29 are now connected to the canister 1. (f) It may be regarded that a battery mounted on a car with a voltage of 12 V is applied across the two electrodes 14 and 15 from the DC power source device 29 in order to heat the activated carbon 12 through the resistance thereof. The amount of current is adjusted depending upon the temperature data from the thermocouple 19, whereby the temperature of the activated carbon 12 is controlled so as not to exceed 120°C. The first cock 23 is now opened, and nitrogen gas having a purity of 99.999% is supplied from the nitrogen gas source 22 into the canister 1 at a flow rate of two liters a minute for 20 minutes through the inlet port 6 and thence to the exit port 9, to effect the desorption of n-butane while measuring the residual amount of n-butane with the passage of time. This residual amount is measured by measuring the weight of the canister 1 in the same manner as described above. After the nitrogen gas has been allowed to flow for 20 minutes, the weight of the canister 1 before being tested is subtracted from the weight of the canister 1 after the testing, in order to find the final residual amount of n-butane. Table 1 shows characteristics of the activated carbons used in the tests 1 to 6. Test No. Activated carbon Material Electric Resistance (Ω/2.5 3 cm 3 ) Average porous diameter (Å) 1 Coconut shell 296 17 2 Coal 108 27 3 Phenolic resin 21 37 4 Coconut shell 497 7 5 Coconut shell 350 4 6 Wood 627 45 Table 2 shows maximum temperatures of the activated carbon being tested, maximum amounts of adsorption of n-butane, effective amounts of adsorption, and final residual amounts in tests Nos. 1 to 6. Here, the effective amount of adsorption stands for a value obtained by subtracting the final residual amount from the maximum amount of adsorption, i.e. stands for the amount of desorption of n-butane. Test No. Max. temp. of activated Carbon (°C) being tested n-Butane Max. amount of adsorption (g) Effective amount of adsorption (g) Residual amount (g) 1 83 9.4 9.3 0.1 2 95 9.1 9.0 0.1 3 120 8.7 8.5 0.2 4 70 7.7 7.5 0.2 5 77 5.1 4.9 0.2 6 60 6.3 5.4 0.9 Fig. 6 illustrates the relationship between the adsorption times and the maximum adsorbed amount of n-butane and the relationship between the desorption times and the residual amount, related to tests Nos. 1 to 6. In Fig. 6, numerals (1) to (6) correspond to tests Nos. 1 to 6, respectively. This relationship is analogous in the subsequent drawings, also. It will be understood from Fig. 6 that the adsorption of. n-butane reaches the saturated state in 10 minutes after the start of the testing and, thereafter, the desorption of n-butane takes place. , The average gas desorption rates during two minutes from the start of desorption were as set forth below in, for example, tests Nos. 3, 4 and 6. Test No. 3 3.75 g/min. Test No. 4 2.50 g/min. Test No. 6 1.15 g/min. Fig. 7 is a graph showing the relationship between the electric resistance of the activated carbon and the residual amounts of n-butane in tests Nos. 1 to 6, based upon Tables 1 and 2. As will be clear from Table 2 and Fig. 7, the highly electrically conductive activated carbon having an electric resistance of not more than 500 Ω/2.5 3 cm 3 can be heated through the resistance thereof to a temperature of not lower than 70°C with a voltage which is as low as 12 V, as is done in tests Nos. 1 to 5, and thus the n-butane is desorbed efficiently and to a sufficient degree. Fig. 8 is a graph showing the relationship between the average porous diameters of the activated carbon and the maximum adsorbed amount of n-butane in tests Nos. 1 to 6, based upon Tables 1 and 2. As will be clear from Fig. 8, when highly electrically conductive activated carbon has an average porous diameter not smaller than 7 Å and not larger than 37 Å, as used as in tests Nos. 1 to 4, the maximum adsorbed amount of n-butane can be increased. In this case, a corresponding effect can be obtained even when the aggregate of activated carbon only partly consists of highly conducting activated carbon having the above-mentioned average porous diameter. Fig. 9 is a graph showing the relationship between the average porous diameter of the activated carbon and the residual amount of n-butane in tests Nos. 1 to 6, based upon Tables 1 and 2. As will be clear from Fig. 9, when highly electrically conductive activated carbon having an average porous diameter not smaller than 7 Å and not larger than 37 Å is used, as in tests Nos. 1 to 4, the residual amount of n-butane also tends to decrease. It will thus be understood that the present invention is able to provide a device which is capable of desorbing vaporized fuel gas efficiently and to a sufficient degree by quickly heating the activated carbon through the resistance of the activated carbon up to a required temperature to bring about desorption of the vaporized fuel gas. Further, the device is capable of adsorbing the vaporized fuel gas to a sufficient degree in addition to obtaining the above-mentioned effect.

Claims: A device for treating vaporized fuel gas, comprising a container (2) having a vaporized fuel gas inlet port (6) and an exit port (9), a charge (13) of activated carbon (12) in the container for adsorbing vaporized fuel gas, the activated carbon being highly electrically conductive, and at least one pair of electrodes (14,15) for heating the activated carbon through the resistance thereof to bring about desorption of the vaporized fuel gas, characterised in that the charge (13) of activated carbon (12) is in the form of pellets, the pellets having an electric resistance of not more than 500 Ω/2.5 3 cm 3 , and in that the activated carbon in the pellets has an average porous diameter not smaller than 7 Å (70 nm) and not larger than 37 Å (370 nm). A device as claimed in claim 1, characterised in that said pellets have a diameter of about 2 mm. A device as claimed in claim 1 or 2, characterised in that said pellets have a thickness of 2 to 6 mm.

Inventors: INOUE MASAHIRO, TAKIZAWA JUN, INOUE, MASAHIRO, TAKIZAWA, JUN
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1998
Main classification: F02M25
IPC codes: F02M25