This invention relates to an industrial scale hydrogen producing apparatus which manufactures hydrogen from a mixed gas of steam and either hydrocarbons or methanol through a steam reforming reaction. More specifically, this invention relates to an industrial scale hydrogen producing apparatus for obtaining hydrogen of sufficiently high purity for use in solid polymer fuel cells (polymer fuel cells) at low reaction temperatures.
The content of CO in hydrogen for fuel cells, in particular solid polymer fuel cells, is preferably less than 10 ppm. Hydrogen obtained from naphtha, natural gas and town gas through a steam reforming reaction has low purity and is not, as it is, suitable for fuel cells. Hydrogen obtained through steam reforming reactions is often further refined in a carbon monoxide reformer and a hydrogen refiner to boost the hydrogen purity to a desired degree.
This approach to obtaining high-purity hydrogen requires complex manufacturing processes. These processes require high temperature and high pressure equipment and significant heat energy, with resultant high production cost. Hydrogen produced through such processes cannot be economically used in fuel cells.
As disclosed in documents, such as Japanese Patent Provisional Publication (Kokai) No. 61-17401, proposals have been made to obtain high purity hydrogen using permeable membranes which is selectively permeable to hydrogen.
The above Provisional Publication, for example, disclosed a method and an apparatus for continuously separating generated hydrogen through a selective hydrogen-permeable partitioning wall, from a reaction space which is at a temperature of 500.degree.-1000.degree. C. This method and the required equipment can be applied to CH.sub.4 /H.sub.2 O reforming reactions or reactions for producing water gas. The publication explained that it is possible to separate high purity hydrogen through this method.
Published documents, including the above publication, disclose a hydrogen producing apparatus on the scale of a laboratory, with its schematic chart shown in FIG. 9. In the conventional hydrogen producing apparatus shown in FIG. 9, reference numeral 90 indicates the reaction tube, 92 the reforming catalyst layer, and 94 the hydrogen permeation tube. The mixture of steam and hydrocarbon gas is introduced from below in the direction indicated by arrow X, reformed in the reforming catalyst layer 92, and hydrogen gas is generated. This hydrogen gas permeates the hydrogen-permeable tube 94 and flows out from the section marked with arrow Y. The reformed gas from which hydrogen has been removed flows out from the section indicated by arrow Z.
These published documents disclose hardly any method or means to boost the scale of laboratory apparatuses to an industrial level. It has not yet been determined how industrial scale production can be achieved using these laboratory-level technologies.
Many technical problems must be overcome to establish an economical hydrogen producing apparatus to boost the laboratory technologies for industrial-scale application.
One conceivable method to create a larger apparatus would involve arranging many parallel reaction tubes equipped with hydrogen permeation tubes in the reforming catalyst layer, such as the one shown in FIG. 9, and linking each inlet and outlet of these tubes with headers, so as to form a multi-tube reaction apparatus. This apparatus would have a large and complex structure, with low efficiency, low controllability and low heat efficiency. Constructing such a system would also require a large quantity of materials and would be difficult, and the equipment would thus be costly and uncompetitive.
The engineering issues, such as how separation means using hydrogen-permeable membranes could be structured or how the sections for reactions could be heated, are extremely important in increasing the scale of the apparatus. However, no specific examples or solutions for these problems have been indicated.
In order to make practical use of fuel cells a reality, it is also extremely important to supply low cost, high purity hydrogen. Creating hydrogen production techniques which are capable of producing high purity hydrogen on an industrial scale at low cost has been considered as a crucial, unresolved issue.