Chemistry of inorganic compounds – Hydrogen or compound thereof – Elemental hydrogen
Reexamination Certificate
2000-10-10
2003-02-18
Langel, Wayne A. (Department: 1754)
Chemistry of inorganic compounds
Hydrogen or compound thereof
Elemental hydrogen
C055S457000, C055S459100, C422S147000, C422S187000, C422S198000, C422S227000, C423S579000
Reexamination Certificate
active
06521205
ABSTRACT:
FIELD OF THE INVENTION
The invention is in the field of methods and apparatus for the production of hydrogen by thermal decomposition of water.
BACKGROUND TO THE INVENTION
Hydrogen has long been viewed as an ideal combustible energy source. The product of hydrogen combustion in air is essentially water, although under some conditions traces of oxides of nitrogen may also be produced. Hydrogen combustion produces no carbon dioxide, a major ‘greenhouse’ gas which figures prominently in concerns about the deteriorating state of the environment, particularly in urban areas. Recent developments in fuel cell technology, and the high overall energy efficiency of fuel cells, have helped to produce conditions favorable to the more widespread adoption and use of hydrogen fuel.
Production of hydrogen is now mainly carried out by reforming hydrocarbons, such as methane, and to a lesser extent, by electrolysis of water. These processes typically involve the use of energy sources that create pollution. For example, hydrocarbon consumption at thermal power stations is part of the hydrogen production chain in some electrolytic processes. As a result, there is a long-felt need for efficient methods to transform water, either directly or indirectly, into hydrogen.
There are a number of thermal processes for producing hydrogen from water that may make use of solar energy. One such process is the direct decomposition of water in solar furnaces at very high temperatures, typically in the range of 2200-2500° C. Many of these processes are not very efficient, yielding only 10-15% of the available hydrogen. A number of references disclose methods of obtaining hydrogen from a solar-powered thermal water dissociation reaction by selectively extracting either the hydrogen or oxygen through a porous material such as metallic nickel. (see U.S. Pat. Nos. 5,397,559; 4,233,127; 4,053,576; 5,306,411; as well as “Possibilities of Separating Water Thermaolysis Products in Solar Furnaces”, Shakhbazov et al. 1977, Gelioteknika, Vol. 13, No. 6, pp. 71-72, UDC 621.472). A potentially important limitation to the commercial implementation of such diffusion methods is that the rate of gas separation depends significantly on the area of diffusion surface available. Very large diffusion or membrane surface areas may be required for large scale production of hydrogen. It may therefore be necessary to heat large diffusion areas to very high temperatures to allow the separation of the desired molecule to occur prior to cooling of the gasses, in order to prevent recombination of hydrogen and oxygen. The heating of such large areas may pose significant commercialization problems due to radiant energy loses and attendant inefficiencies.
U.S. Pat. Nos. 4,030,890 and 4,071,608 to Diggs propose separating hydrogen from oxygen by centrifugal forces. Diggs discloses a chamber for separating hydrogen and oxygen which has an oxygen outlet and a hydrogen outlet. The oxygen outlet is circumferentially located in the peripheral walls of the chamber close to the bottom of the chamber, at the end of the chamber where water vapor is introduced. The hydrogen outlet in the Diggs device is axially located at the top end of the chamber, at the opposite end of the chamber from the end where water vapor is introduced. This arrangement of hydrogen and oxygen outlets in the Diggs device is predicated upon a particular spacial distribution of oxygen and hydrogen gases in the vortex of the reaction chamber. However, the behavior of heated gases in a vortex tube is complex. In a process sometimes termed the Ranque effect, a gas stream may be separated in a vortex tube into two outlet streams, one of which is hotter and one which is colder than the temperature of the gas feed (see U.S. Pat. No. 1,952,281). In such a process, it is taught in the art that pressure and compositional gradients form in the tube both axially and radially with the result that the vortex core contains a cooled gas that flows in a direction opposite to the direction of flow of the heated gas at the periphery of the vortex. This effect may be used to separate vapors from a gas stream, as disclosed in U.S. Pat. Nos. 4,343,772 and 5,843,801. In contrast, U.S. Pat. No. 3,922,871 discloses alternative flow parameters that are suggested to produce the opposite stratification of gas temperatures within a vortex, with the hotter gas localized in the vortex core. Although this reference does not teach specific gas separations, it is illustrative of the variability that may be encounter in vortex gas flow.
There is a need for alternative methods and devices for production of hydrogen by thermal dissociation of water, particularly methods and devices that may be adapted for use with solar energy.
SUMMARY OF THE INVENTION
In one aspect, the invention provides a process for producing hydrogen from water including heating water to a water dissociating temperature to form a dissociated water reaction mixture comprising hydrogen gas and oxygen gas. A vortex is formed of the reaction mixture to subject the reaction mixture to a centrifugal force about a longitudinal axis of an interior space of a vortex tube reactor, so that there is radial stratification of the hydrogen gas and the oxygen gas in the interior space of the vortex tube reactor. Hydrogen gas is preferentially extracted from the reaction mixture at spaced apart points along the longitudinal axis of the interior space of the vortex tube reactor. Alternatively, the process may include preferentially extracting oxygen gas from peripheral portions of the vortex at longitudinally spaced apart points along the circumference of the vortex tube reactor. The water may be heated to a dissociating temperature with concentrated solar radiation focused on the vortex tube reactor, and the water dissociating temperature may be between about 1800° C. and about 3000° C. The reaction mixture may be contacted with a catalyst that catalyzes the dissociation of the water into hydrogen and oxygen. A vacuum may be applied to preferentially extract the hydrogen or oxygen gases.
In another aspect, the invention provides a vortex tube reactor comprising an elongate wall having first and second ends, the wall and ends together defining an interior space having a longitudinal axis and adapted to house a vortex. An inlet port is provided in the first end for tangentially introducing a gas into the interior space to initiate circumferential movement of the gas in the interior space about the longitudinal axis to form the vortex. A hydrogen draw tube may be provided concentrically located in the interior space along the longitudinal axis, the hydrogen draw tube being porous to hydrogen gas at longitudinally spaced apart points. Alternatively, an oxygen draw tube may be provided concentrically located in the interior space adjacent to the cylindrical wall, the oxygen draw tube being porous to oxygen gas at longitudinally spaced apart points. The reactor may be comprised of a refractory material adapted to withstand a water dissociating temperature.
Although solar energy may be used in accordance with the invention to disassociate water into hydrogen and oxygen, other sources of heat may be used. The radiant energy capture unit may also have application in solar distillation processes, and solar heated boiler systems used to generate steam for heating and for turbine use, especially in solar turbine electric systems.
By removing one of the dissociation products from within the vortex reactor, the equilibria of the dissociation reaction may be driven further to completion. The stratification in the vortex tube of the oxygen and hydrogen may also shift the equilibrium of the dissociation reaction towards completion. Preferably, operating temperatures in the final reactor are maintained at levels close to the primary reactor, to facilitate rapid equilibration. With inadequate residence time or fall off in temperature of the final reactor, residual material from the transition zone remaining in the final reactor can be separated at a heavy ends exit port and sent f
Langel Wayne A.
SHEC Labs—Solar Hydrogen Energy Corporation
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