Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including specific material of construction
Reexamination Certificate
1998-11-10
2001-07-10
Knode, Marian C. (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including specific material of construction
C422S211000, C422S240000, C106S600000
Reexamination Certificate
active
06258330
ABSTRACT:
TECHNICAL FIELD
This invention relates to a fuel gas steam reformer assemblage and a method for forming the same. More particularly, this invention relates to a fuel gas steam reformer assemblage wherein the reformer gas passages are washcoated with a composite carbon-resistant alumina and alkaline earth metal oxide coating.
BACKGROUND ART
Fuel cell power plants include fuel gas steam reformers which are operable to catalytically convert a fuel gas, such as natural gas or heavier hydrocarbons, into the primary constituents of hydrogen and carbon dioxide. The conversion involves passing a mixture of the fuel gas and steam through a catalytic bed which is heated to a reforming temperature which varies depending upon the fuel being reformed. Catalysts typically used are nickel catalysts which are deposited on alumina pellets. There are three types of reformers most commonly used for providing a hydrogen-rich gas stream to fuel cell power plants. In addition, hydrocarbon fuels may be converted a hydrogen-rich gas stream by use of a partial oxidation reaction apparatus. These are a tubular thermal steam reformer, an autothermal reformer, and a catalyzed wall reformer. A typical tubular thermal steam reformer will consist of a plurality of reaction tubes which are contained in a housing that is insulated for heat retention. The reaction tubes are heated by burning excess fuel gas in the housing and passing the burner gas over the reaction tubes. The reforming temperature is in the range of about 1,250° F. to about 1,600° F. The individual reaction tubes will typically include a central exhaust passage surrounded by an annular entry passage. The entry passage is filled with the catalyzed alumina pellets, and a fuel gas-steam manifold is operable to deliver the fuel gas-steam mixture to the bottom of each of the entry passages whereupon the fuel gas-steam mixture flows through the catalyst beds. The resultant heated mixture of mostly hydrogen and carbon dioxide gas then flows through the central exhaust passages in each tube so as to assist in heating the inner portions of each of the annular catalyst beds; and thence from the reformer for further processing and utilization.
A typical autothermal reformer may be a single bed or a multiple bed tubular assembly. Autothermal reformers are often used when higher operation temperatures are required for the reforming process because the fuel to be processed is more difficult to reform. In an autothermal reformer, the reaction gasses are heated by burning excess fuel within the reaction bed by adding air to the fuel and steam mixture so that the remaining fuel-steam mixture is increased to the temperature necessary for the fuel processing reaction. Typically, wall temperatures in an autothermal reformer are in the range of about 1,400° F. to about 1,800° F. Such tubular reformers are disclosed in U.S. Pat. No. 4,098,587.
A third type of prior art reformers have utilized catalyzed wall passages such as disclosed in U.S. Pat. No. 5,733,347. Such reformers are formed from a sandwich of essentially flat plates with intervening corrugated plates which form reformer gas passages and adjacent regenerator-heat exchanger passages. Each of the reformer passage plate units is disposed directly adjacent to a burner passage plate unit so that the adjacent reformer and burner passages share a common wall.
Besides the reformer devices described above, a partial oxidation reaction apparatus may also be used to produce a hydrogen-rich fuel stream. This device is typically a chamber that is fed a hydrocarbon fuel, steam and oxidant source, usually air, so that the mixture spontaneously partially oxidizes to form a hydrogen-rich mixture. Such devices, for example, are disclosed in PGT application WO 98/08771.
Each of the aforesaid prior art reformer structures may suffer from carbon buildup and deposition on the surfaces of internal components of the reformer assemblies. Carbon buildup will clog the gas passages of the reformer ultimately, and will limit the effective service life of the reformer and thus the fuel cell power plant assembly which includes the reformer. It would obviously be desirable to produce reformer assembly components, and a method for forming such components, which would result in a reformer assembly which would be resistant to carbon build-up on surfaces of the reformer.
DISCLOSURE OF THE INVENTION
This invention relates to a composite coating, and a method for forming the same, for use in fuel cell steam reformer assemblies which will result in decreased or no carbon deposition on reformer components that are covered by the composite coating. The composite coating includes an underlying alumina component and an outermost carbon formation-inhibiting metal oxide component. The reformer assembly will have it's interior steel walls coated with the alumina component, and the alumina component will have an amorphous or polycrystalline metal oxide layer formed over the underlying alumina component. Certain passages in the reformer assembly can also be provided with a metal oxide particulate bed that promotes the conversion of carbon in the steam-fuel mixture to carbon monoxide, which is subsequently converted to carbon dioxide.
The metal oxide which is used for the carbon deposition-inhibiting coating is preferably an alkaline earth metal oxide such as CaO or MgO; mixtures of alkaline earth metal oxides such as (CaO)
X
(MgO)
Y
, where “X” and “Y” are numbers between 0 and about 1; an alkaline earth metal oxide substituted with an alkali metal oxide such as Ca
(1−X)
Na
X
O, wherein “X” is a number between 0 and about 0.2; a rare earth oxide such as La
2
O
3
or CeO
2
; a rare earth oxide substituted with other rare earths, such as Ce
(1−X)
Gd
X
O
2
, wherein “X” is a number between 0 and about 0.2; a rare earth substituted with alkaline earths such as (CaO)
X
.La
2
O
3
; and/or metals from the Periodic Table Group VIII transition metals, such as (NiO)
X
.La
2
O
3
, wherein “X” is a number between 0 and about 1.0.
Typical compositions are as follows:
TABLE 1
Tested
Compound
Examples
Values
Range of Values
alkaline earth
(CaO)
X
· (MgO)
Y
pure
X and Y are
metal oxides
between 0.0 and
about 1.0
alkaline earth
Na
X
Ca
(1−X)
O
0.08
X is between
metal oxides
0.0 and about 0.2
substituted
with alkali
metal oxides
rare earth oxides
CeO
2
or La
2
O
3
pure
rare earth
Gd
X
Ce
(1−X)
O
2
X is between
oxides substituted
0.0 and about 0.2
with rare earths
rare earth
(CaO)
X
· La
2
O
3
0.2
X is between
oxides substituted
0.0 and about 1.0
with alkaline
earths
rare earth
(NiO)
X
· La
2
O
3
0.15
X is between
oxides substituted
0.0 and about 1.0
with group
VIII
transition metals
The metal oxide coating will be formed as an amorphous or polycrystalline coating which is derived from a solution of a nitrate, acetate or citrate salt of the metal which is dissolved in water, and in which a hydroxide of the metal is suspended to form the slurry. The hydroxide may be added as a metal hydroxide or formed by addition of less than a stoichiometric amount of a base such as NaOH or NH
4
OH to the solution which may result in a slurry or a sol-gel mixture with a percentage of soluble salts in the solution. A small amount of a surfactant is added to the slurry to aid in the dispersion of the hydroxide and increase the wetting of the reformer surfaces in question by the slurry.
In order to form a calcium oxide coating, Ca(OH)
2
solid is mixed with a concentrated solution of Ca(NO
3
)
2
.5H
2
O to form the slurry. To form a lanthanum-nickel oxide coating, a solution of nickel acetate and lanthanum nitrate is made with the desired cation ration. The slurry is made by adding ammonium hydroxide which co-precipitates a portion of the nickel and lanthanum as a hydroxide. Often, the precipitate initially occurs as a sol-gel which, upon standing, ripens into a slurry. The reformer surfaces in question may be coated by the suspension in either the sol-gel state or the slurry state. Subsequent heat treatment of the coating will convert the coating to a
Lesieur Roger R.
Setzer Herbert J.
Doroshenk Alexa A.
International Fuel Cells LLC
Jones William W.
Knode Marian C.
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