Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
2001-05-08
2003-11-25
Bell, Bruce F. (Department: 1746)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S010000, C429S010000
Reexamination Certificate
active
06653005
ABSTRACT:
BACKGROUND AND PRIOR ART
Recent developments in fuel cell (FC) technology have resulted in compact, light-weight devices having the ability to continuously produce electrical power via electrochemical reactions involving an oxidant (usually, air) and a fuel (most preferably, hydrogen). These devices can potentially replace conventional batteries and are particularly useful for portable electronic systems, space and military (e.g. “soldier power”) applications, transportation and other systems. However, a compact FC would require a similarly compact and light-weight source of hydrogen. Unfortunately, conventional means of storing hydrogen, including compressed gaseous or liquid hydrogen, as well as, hydrogen cryogenically adsorbed on activated carbons do not lend themselves to use in portable devices. Similarly, the advanced methods of hydrogen storage, such as metal hydrides, catalytically enhanced metal hydrides, carbon nanotubes, also result in relatively low hydrogen storage capacities (below 6 w. %).
To overcome hydrogen storage problems, there have been attempts to produce hydrogen “on demand”, i.e. generate hydrogen as needed. In this respect, hydrogen generating systems based on the reactions of different metal hydrides with water are most developed. For example, U.S. Pat. No. 3,459,510 to Litz et al. describe a hydrogen generator which produces hydrogen via the reaction of metal hydride (preferably, sodium borohydride, NaBH
4
) with water. The reaction was enhanced by the presence of a metal catalyst (preferably, Raney nickel). Recently, Amendola et al. described a catalytic system for generating hydrogen from aqueous borohydride solutions using a ruthenium catalyst (S. Amendola, M. Binder, M. Kelly, P. Petillo, S. Sharp-Goldman, Advances in Hydrogen Energy, Ed. C. Padro and F. Lau, Kluwer Academic/Plenum Publ., NY, 2000). U.S. Pat. Nos. 4,155,712 to Taschek and No. 5,593,640 to Long et al. deal with portable hydrogen generators based on the hydrolysis and thermal decomposition of metal hydrides (e.g. CaH
2
, LiAlH
4
). The common disadvantages of these systems based on hydrolysis of metal hydrides is the necessity to carry water and, most importantly, the requisite use of expensive metal hydrides which are irreversibly hydrolyzed into metal hydroxides during hydrogen production. Thus, these systems would require handling of metal hydroxide slurries, which would be very difficult, energy intensive and costly to convert back to original hydride form.
To overcome above problems, a variety of hydrocarbons and other hydrogen containing substances (e.g. alcohols) have been widely used as a source of hydrogen. Since hydrocarbon fuels can be obtained from different sources (petroleum or natural gas), they are abundant, cheap and readily available. There has been a significant progress in the area of development of hydrocarbon reformers (or processors) for producing hydrogen or hydrogen-rich gas for fuel cell applications. For example, U.S. Pat. No. 5,932,181 to Kim et al. describes a hydrogen generator which is able to produce high purity hydrogen from natural gas and water. The generator comprises a desulfurization reactor, a steam reformer, a CO conversion (or water gas shift, WGS) reactor and pressure swing adsorption (PSA) unit. Thus, the process includes the following stages:
a) steam reforming: CH
4
+H
2
O 6 CO+3H
2
(1)
b) CO conversion: CO+H
2
O 6 CO
2
+H
2
(2)
c) H
2
purification (CO
2
removal) via PSA
The system also requires a large number of heat exchangers, compressors, valves, etc. The steam reforming (SR) process requires a source of water which adds to the weight of the system. This would result in a bulky system potentially difficult to miniaturize. A similar hydrogen generating apparatus is described in U.S. Pat. No. 5,110,559 to Kondo et al. The apparatus consists of a hydrocarbon and air supply systems, a steam generator, a steam reformer, a CO shift converter and gas separation system (PSA). U.S. Pat. No. 5,470,360 to Sederquist discloses an advanced steam reformer with improved distribution of heat within the apparatus. The reformer is applicable to a fuel cell power plant. All these apparatuses are complex and bulky and suffer from the same disadvantages as the previous one. An improved method for producing hydrogen from sulfurous hydrocarbon fuels in the fuel cell electricity generation process is described in U.S. Pat. No. 5,284,717 to Yamase et al. The method is characterized by cracking and desulfurizing petroleum fuels (e.g. kerosene) followed by steam reforming of the desulfurized product. The process is multi-stage, complex and would require an additional source of water. Another multi-stage process for production of hydrogen and energy is described by Engler et al. in U.S. Pat. No. 5,888,470. The process is based on partial oxidation of hydrocarbon fuel and includes a reformer, CO-converter and two gas separation units (a membrane and PSA). Partial oxidation (PO) of natural gas (catalytic and non-catalytic) can be described by the following equation:
CH
4
+½O
2
→CO+2H
2
(3)
This reaction is followed by CO conversion (or WGS) and gas separation (PSA).
A compact hydrogen generator is disclosed in U.S. Pat. No. 4,737,161 to Szydlowski. The apparatus catalytically reforms a hydrocarbon fuel to a hydrogen rich gas for fueling a fuel cell stack. The device features a cylindrical housing with an axial burner and a helical catalyst tube outside of the burner and inside of the housing. U.S. Pat. No. 5,780,179 to Okamoto describes a steam reformer-fuel cell system, where hydrogen is humidified by the recycled water. U.S. Pat. No. 5,938,800 to Verrill, et al. and U.S. Pat. No. No. 5,897,970 to Isomura et al. describe multi-fuel compact reformers for fuel cell applications. Both patents feature a steam reformer coupled with a hydrogen separating membrane (e.g. Pd-based membrane). The use of selective hydrogen membrane allows to avoid bulky PSA system for the separation of gases and can potentially result in smaller units. However, the apparatuses are complex and require to carry a significant amount of water (e.g. in the first patent, 2-4 moles of steam per mole of carbon in the fuel) (although, some amount of water from the exhaust of FC could be recycled to the reactor). U.S. Pat. No. 5,997,594 to Edlund et al. discloses a steam reformer with internal hydrogen purification as a source of high purity hydrogen for a polymer electrolyte fuel cell (PEFC). The apparatus includes a steam reformer with internal bulk hydrogen purification and polishing, an integrated combustion method utilizing waste gas to heat the reformer, an efficient integration of heat transfer, resulting in a compact design of the unit. Hydrogen is purified using a thin Pd alloy membrane. A steam-hydrocarbon reformer with a catalytic membrane is disclosed in U.S. Pat. No. 5,229,102 to Minet et al. The use of ceramic membrane permeable to hydrogen and carrying catalytically active metallic substance allowed to significantly reduce the maximum temperature of the process and simplify the design. A steam/methane weight ratio of 3/1 to 5/1 was required to operate the reactor.
A number of patents (e.g. U.S. Pat. Nos. 5,366,819; 5,763,114; 5,858,314; 5,641,585; 5,601,937) deal with a hydrogen generator integrated with a solid oxide fuel cell (SOFC). For example, U.S. Pat. No. 5,366,819 to Hartvigsen et al. discloses a reformer integrated with SOFC. A thermally integrated steam reformer is located inside the stack furnace housing stacks of SOFC. De-sulfurized natural gas as a feedstock was reformed with a steam over Ni- or Ru-based catalysts. Similarly, U.S. Pat. No. 5,641,585 to Lessing et al. describes a miniature ceramic SOFC with a built-in hydrocarbon reformer using Ni-catalyst. Light hydrocarbons (e.g. propane and butane) are preferred feedstocks for this apparatus. There are several disadvantages common to all these integrated hydrogen generator-SOFC systems. First of all, very high operating temperatures at whi
Bell Bruce F.
Law Offices of Brian S. Steinberger , P.A.
Seattuto Donald V.
Steinberger Brian S.
University of Central Florida
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