Chemistry of inorganic compounds – Hydrogen or compound thereof – Elemental hydrogen
Reexamination Certificate
2001-03-19
2003-12-09
Silver, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Hydrogen or compound thereof
Elemental hydrogen
C252S373000, C422S198000, C422S211000
Reexamination Certificate
active
06660244
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application Nos. 2000-79388 filed on Mar. 22, 2000 and 2000-383485 filed on Dec. 18, 2000 including the specification, drawings and abstract are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a hydrogen generating system and a method which reforms liquid raw materials to generate hydrogen rich gas, and to a vaporizer utilized in the system.
2. Description of the Related Art
Hydrogen to be supplied to systems, such as fuel cells, in which hydrogen is consumed is generated by reforming liquid raw materials, for example. As the liquid raw materials, liquefied natural gas, gasoline, other hydrocarbons, alcohols, ethers and aldehydes and the like are used in general. In a hydrogen generating system, these raw materials and water are vaporized by a vaporizer and made to undergo a reforming reaction in the presence of a catalyst such as platinum to thereby generate hydrogen rich reformed gas. In order to run the reaction stably, the reforming reaction is maintained in a predetermined temperature and pressure condition by feedback control or the like. This reformed gas is treated to decrease the concentration of components, such as carbon monoxide, and then supplied to a hydrogen consumption system, for example, a fuel cell.
In the hydrogen generating system, the quantity of hydrogen to be generated must follow the quantity of hydrogen to be consumed in a hydrogen consumption system. It is known that the rate-determining step as to the quantity of hydrogen to be generated is vaporization in a vaporizer. Therefore, an improvement in the speed of response of vaporization is required to improve the speed of response of the generation of hydrogen.
The following technologies are proposed with the intention of improving the speed of response of vaporization. For instance, a structure in which the vapor generated during a low load operation is accumulated in an accumulator and the quantity of vapor to be generated is compensated for by the accumulated vapor during a high load operation is disclosed in Japanese Patent Laid-Open Publication No. HEI 8-121705. Also, a structure in which vapor is always generated in a quantity much greater than the quantities required at each point in time is disclosed in Japanese Patent Laid-Open Publication No. HEI 2000-119001.
However, the above systems give rise to the following problems concerning an improvement in the speed of response of the quantity of hydrogen to be generated. In the structure described in Japanese Patent Laid-Open Publication No. HEI 8-121705, the accumulator constitutes an obstacle to the miniaturization of equipment. In recent years, a method in which a hydrogen generating system and a fuel cell are mounted on a mobile body such as a vehicle has been investigated. In such a case, because very severe restrictions are imposed on the mount space, there is a strong demand for miniaturization. Also, in the structure described in Japanese Patent Laid-Open Publication No. HEI 8-121705, a reduction in the temperature of the accumulated vapor must be suppressed to allow the reforming reaction to proceed efficiently, thus making the system more complex. Also, the structure described in Japanese Patent Laid-Open Publication No. HEI 2000-119001 has the problem of low energy efficiency because of the generation of excess vapor.
The systems disclosed in above publications also give rise to the following problems caused by pressure control in the reforming section, particularly at start-up. First, there a pressure control valve tends to be excessively restricted to maintain target pressure when there is an insufficient amount of reformed gas. Therefore, when generation of reformed gas is started, there is a possibility that delay of pressure control may cause the pressure in the reforming section to exceed the target value. Second, a rather high pressure is maintained at a relatively low temperature condition causing vaporized raw materials to be condensed and there is a possibility of the generated liquid adhering to the catalyst thereby decreasing the activity of the catalyst.
SUMMARY OF THE INVENTION
It is an object of the invention, first, to improve the speed of response of the quantity of hydrogen to be generated by improving the speed of response of the vaporization of raw materials and the like in a hydrogen generating system. Together with this improvement in response characteristics, the object of the invention is also to attain miniaturization of the equipment, to improve energy efficiency and to maintain the temperature of the vapor. It is an object of the invention, second, to provide a technology for avoiding the problems of vapor, which are caused by pressure control at start-up in the hydrogen generating system.
In the invention, at least part of the foregoing problems has been solved by the improvement in pressure control in a hydrogen generating system. In other words, conventionally, pressure in a hydrogen generating system is controlled such that it is kept in such a constant condition suitable for reformation and the like. The invention, however, adopts a structure in which pressure in the system is changed according to the operational conditions of the system at each point in time or the operational conditions required as shown below.
A hydrogen generating system which is a first embodiment of the invention comprises a vaporizing section, a reforming section and a pressure regulator, and further comprises a controller for controlling the pressure regulator on the basis of a quantitative requirement for hydrogen to be generated.
The vaporizing section is a unit for vaporizing liquid raw materials and is constructed of, for example, a vaporizer. The reforming section is a unit which reforms the vapor supplied from the vaporizing section. The reforming section includes a variety of units used to conduct a chemical reaction for generating hydrogen rich gas from raw materials. These units include a reforming unit which generates hydrogen and carbon monoxide (CO) by the vapor-reforming or partial oxidation of raw materials, a shift reaction unit which generates hydrogen and carbon dioxide by a shift reaction from carbon monoxide and water and a CO oxidation unit which selectively oxidizes carbon monoxide. The reforming section is provided with at least one of these units.
As described above, the speed of response of the generation of hydrogen in the hydrogen generating system is determined by the rate of vaporization. As commonly known, the rate of vaporization is affected by the pressure in the vaporizing section. According to the invention, not only the rate of vaporization but also the speed of response of the generation of hydrogen can be improved by controlling the pressure in the vaporizing section according to the quantitative requirement for hydrogen to be generated. Also, no large-scale equipment such as an accumulator is required and an improvement in the speed of a response can be achieved. It is also unnecessary to accumulate vaporized gas and therefore there is no problem due to the lowered vapor temperature. Moreover, because it is also unnecessary to generate excess vapor, energy efficiency can also be improved.
In the first embodiment, a pressure regulator may be provided in the vaporizing section. It is preferable to adopt a structure in which the vaporizing section is provided with a vapor generating section and a vapor heating section where the pressure in the vapor generating section is regulated by the pressure regulator. The vapor generating section is supplied with liquid raw materials while the pressure therein is regulated with a pressure regulator, forming a vapor-liquid mixed section of the raw materials. The vapor heating section is connected to a vapor phase portion of the vapor generating section and heats the raw materials of the vapor phase portion. This structure makes it possible to obtain a vapor having a desired temperature relatively easily.
Regulation o
Hattori Kyo
Kajiwara Shigeto
Negishi Yoshimasa
Takada Kazumasa
Tanaka Hiromi
Medina Maribel
Silver Stanley S.
Toyota Jidosha & Kabushiki Kaisha
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