Chemistry of inorganic compounds – Hydrogen or compound thereof – Elemental hydrogen
Reexamination Certificate
2002-03-05
2004-11-23
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Hydrogen or compound thereof
Elemental hydrogen
C252S391000
Reexamination Certificate
active
06821501
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process and apparatus for the production of pure hydrogen by steam reforming, and to the use of the hydrogen in a zero emission hybrid power system incorporating a fuel cell. The process integrates the steam reforming and shift reaction to produce pure hydrogen with minimal production of CO and virtually no CO in the hydrogen stream, provides for CO
2
capture for sequestration, employs a steam reforming membrane reactor, and is powered by flameless distributed combustion that provides great improvements in heat exchange efficiency.
BACKGROUND OF THE INVENTION
The production of electrical power in the most efficient manner with minimization of waste is the focus of much research. It would be desirable to improve efficiency in the production of electricity, separate and use by-product CO
2
in other processes, and produce minimal NO
x
. The wide availability of natural gas with the highest H:C ratio (4:1) of any fossil fuel makes it a prime candidate for electricity production with minimum CO
2
emissions.
In the production of electricity by conventional means only about 35% of the hydrocarbon fuel is converted to electricity and approximately 5% of that is lost over power lines. Even with modern turbines the efficiency is about 45%. In the case of the additional production of electricity by a “bottom cycle” where high temperature exhaust is used to boil water and produce more electricity, the combined efficiency is only about 60% in the lab. In addition, though about 3-5% m CO
2
is produced as exhaust from turbines, it is very difficult and expensive to capture due to the low concentration in the exhaust streams.
Electricity can be produced in fuel cells using pure hydrogen. Hydrogen production is commercially proven, but expensive. One method of producing hydrogen is steam methane reforming where hydrocarbons and water are reacted to form CO and H
2
, followed by a separate water-gas-shift reaction where CO is reacted with H
2
O to form CO
2
and H
2
. The commercial application of these reactions in many refineries commonly involves a series of reactors including a steam reforming reactor, and several post reactors to address the production of CO in the reformer. The post reactors include a high temperature shift reactor, a low temperature shift reactor, and a CO
2
absorber separator. Water and CO
2
separation is necessary to achieve pure hydrogen. The reforming reactor is run at high pressure to avoid hydrogen recompression downstream. The pressure lowers the equilibrium conversion since reforming produces a positive net mole change. The steam reforming reaction is very endothermic, about 206 kJ/mole; and the shift reaction is exothermic, providing about 41 kJ/mole. The conventional steam reforming reactors are operated above 900° C. to push the equilibrium toward complete formation of CO and H
2
. The high temperature causes severe corrosion and stress problems on the equipment. Steam reforming reactors are generally large to accomplish economies of scale. In addition, the typical operation of the shift reactor at a lower temperature than the reforming reactor makes it impractical to combine these two chemical reactions in one reactor. Furthermore, designs currently known do not lend themselves to being scaled down to a smaller size or to making it possible to efficiently control the temperature at various points.
Even if a reactor was capable of producing only CO
2
and H
2
and the conventional post reactors could be eliminated, the issue of CO
2
separation would remain.
In experimental work the use of membranes to harvest hydrogen from a reforming process is known. For example, U.S. Pat. No. 4,810,485 discloses a hydrogen forming process which comprises conducting in a hydrogen production zone a chemical reaction forming mixed gases including molecular hydrogen, contacting one side of a hydrogen ion porous and molecular gas nonporous metallic foil with said mixed gases in said hydrogen production zone, dissociating said molecular hydrogen to ionic hydrogen on said one side of said metallic foil, passing said ionic hydrogen through said metallic foil to its other side, and withdrawing hydrogen from said other side of said metallic foil, thereby removing hydrogen from said hydrogen production zone. This process takes place at a temperature of from about 1000° F. to 1400° F.
U.S. Pat. No. 5,525,322 discloses a process for the simultaneous recovery of hydrogen and hydrogen isotopes from water and from hydrocarbons which comprises mixing carbon monoxide and water with the feed mixture forming a gas mixture such that the reversible reactions CO+H
2
O ⇄CO
2
+H
2
and CH
4
+H
2
O⇄CO+3H
2
can occur, flowing the gas mixture over a heated nickel catalyst such that the equilibrium of the reactions permits subsequent generation of H isotopes, contacting the resulting gas mixture with a heated palladium membrane, and removing the H isotopes which have permeated the Pd membrane. The reactor is heated by enclosing it in a split-hinge tube furnace.
U.S. Pat. No. 5,741,474 discloses a process for producing high-purity hydrogen which includes heating a reforming chamber provided with a hydrogen-separating membrane, feeding into the reforming chamber hydrocarbon, steam, and oxygen or air to give rise to steam reforming and partial oxidation therein to produce a reaction gas, and passing the reaction gas through the hydrogen-separating membrane to recover high-purity hydrogen. The heat possessed by the portion of the reaction gas not permeable into the hydrogen-separating membrane and the heat generated by the partial oxidation are utilized for the heating and reforming of the hydrocarbon, water and oxygen or air.
U.S. Pat. No. 5,861,137 discloses a compact, mobile steam reformer that includes a tubular hydrogen permeable and hydrogen selective membrane. A reforming bed surrounds at least part of the membrane. An inlet to the reforming bed receives a mixture of alcohol or hydrocarbon vapor and steam and an outlet from the reforming bed releases reforming byproduct gases. A heating element heats the reforming bed to an operating temperature and a second bed including a methanation catalyst is placed at the permeate side of the membrane. A reformer outlet withdraws hydrogen gas from the second bed. In one aspect, the heating element is a third bed including an oxidation catalyst surrounding at least a portion of the first bed. The reforming byproduct gases released from the reforming bed mix with an air source and catalytically ignite to generate heat and thermally support the process of reforming within the reforming bed.
U.S. Pat. No. 5,229,102 discloses a steam reforming process that does not require a shift reactor. It requires a gas turbine to produce hot exhaust gases. That reference discloses a process employing the steps of:
a) providing a generally tubular, porous, ceramic membrane, and providing a heated reaction zone in a container into which the membrane is received,
b) wherein the membrane carries a catalytically active metallic substance,
c) passing a hydrocarbon and steam containing first fluid stream into the reaction zone and into contact with one side of the membrane to produce CO
2
and H
2
,
d) and passing a stream containing second fluid stream adjacent the opposite side of the membrane in such manner as to promote hydrogen diffusion through the membrane from said one side to said opposite side thereof,
e) and removing hydrogen from the opposite side of the membrane.
This process takes place at lower temperatures than are typical of conventional reforming, i.e. 300-750° C., however it requires a gas turbine or gas engine to produce hot exhaust gas and the generated heat is transferred into the reaction zone to maintain the temperature.
U.S. Pat. No. 5,938,800 discloses a compact hydrogen generation system that comprises a fuel means for supplying a pressurized, vaporized fuel and steam mixture, a steam reformer having a catalyst bed in communication with the fuel means, and hydrogen fi
Matzakos Andreas Nikolaos
Mikus Thomas
Ward John Michael
Wellington Scott Lee
Medina Maribel
Shell Oil Company
Silverman Stanley S.
Tsang Y. Grace
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