Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including heat exchanger for reaction chamber or reactants...
Reexamination Certificate
2000-10-05
2002-09-03
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including heat exchanger for reaction chamber or reactants...
C422S198000, C422S198000, C422S220000, C422S198000, C048S061000, C048S076000
Reexamination Certificate
active
06444179
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to autothermal reformers and methods of operating such reformers.
BACKGROUND OF THE INVENTION
The search for alternative power sources has focused attention on the use of electrochemical fuel cells to generate electrical power. Unlike conventional fossil fuel power sources, fuel cells are capable of generating electrical power from a fuel stream and an oxidant stream without producing substantial amounts of undesirable by-products, such as sulfur oxides, nitrogen oxides and carbon monoxide. However, the commercial viability of fuel cell systems will benefit from the ability to efficiently and cleanly convert conventional hydrocarbon fuel sources, such as, for example, gasoline, diesel, natural gas, ethane, butane, light distillates, dimethyl ether, methanol, ethanol, propane, naphtha, kerosene, and combinations thereof, to a hydrogen-rich gas stream with increased reliability and decreased cost. The conversion of such fuel sources to a hydrogen-rich gas stream is also important for other industrial processes, as well. Several technologies are available for converting such fuels to hydrogen-rich gas streams.
Steam reformers convert hydrocarbon fuels to hydrogen-rich reformate gas streams. Fuel and steam are reacted in reactors filled with catalyst (typically nickel-, copper- or noble metal-based), and primarily hydrogen, carbon dioxide (CO
2
), and carbon monoxide (CO) are produced. For example, the following principal reactions occur in the steam reforming of methane (and natural gas):
CH
4
+
H
2
O
⇌
CO
+
3
H
2
CO
+
H
2
O
⇌
CO
2
+
H
2
CH
4
+
2
H
2
O
⇌
CO
2
+
4
H
2
&AutoLeftMatch;
(
I
)
The overall reaction (I) is highly endothermic, and is normally carried out at elevated catalyst temperatures in the range of about 650° C. to about 875° C. Such elevated temperatures are typically generated by the heat of combustion from a burner incorporated in the steam reformer.
Steam reforming is generally unsuitable for heavier fuels and is normally limited to paraffinic naphtha and lighter fuels. In addition, nickel-based steam reforming catalysts are easily poisoned by sulfur in the fuel. As a result, if the fuel to be reformed contains sulfur, the reformer is usually preceded upstream by hydrotreating apparatus such as a hydrodesulfurizer (HDS) and an H
2
S removal device, such as a metal oxide absorbent bed, in order to remove or reduce to extremely low levels any sulfur present in the fuel. This tends to increase the cost and complexity of the overall fuel processing system. Thus, steam reformers are generally unsuitable for heavier and/or sulfur-laden fuels, such as gasoline or diesel, for example.
Autothermal reforming is an approach that combines catalytic partial oxidation and steam reforming. Partial oxidation employs substoichiometric combustion to achieve the temperatures to reform the fuel. Fuel, oxidant (oxygen or air, for example), and steam are reacted to form primarily hydrogen, CO
2
and CO. An advantage of autothermal reforming technology is that the exothermic combustion reactions are used to drive the endothermic reforming reaction (I).
Autothermal reformers typically employ noble metal catalyst beds operating at temperatures of from about 870° C. to about 1300° C. In comparison to steam reformers, an advantage of autothermal reformers is that at these high operating temperatures, sulfur in the fuel, which is present primarily as H
2
S, does not significantly poison the catalyst and permits downstream sulfur removal. This may result in a simpler fuel processing system, as an HDS is not required. A further advantage of autothermal reformers is that start-up times also tend to be shorter due to the heat supplied to the catalyst bed by catalytic combustion of the fuel. Yet another advantage of autothermal reformers is that they are capable of reforming heavier fuels than steam reformers. Thus, autothermal reformers may be more desirable for use in fuel processing systems employing heavier and/or sulfur-laden fuels, such as gasoline or diesel fuel, for example.
However, conventional autothermal reformers have at least two major disadvantages, particularly with respect to fuel cell-related applications. First, conventional autothermal reformers and associated heat recovery equipment tend to be quite large, which impacts material costs and overall manufactured cost. This is especially disadvantageous in vehicular applications, where space is also at a premium. Second, it can be difficult to adequately vaporize fuels such as diesel, for example, and distribute the fuel uniformly within the catalyst bed employing conventional autothermal reformers. These disadvantages tend to be compounded in vehicular applications employing diesel, for example, as the fuel.
It is desirable to have a rugged, compact autothermal reformer capable of efficiently reforming difficult fuels, such as diesel.
SUMMARY OF THE INVENTION
An autothermal reformer for converting a fuel into a reformate stream comprising hydrogen is presented. The present reformer comprises:
(a) a closed vessel, the vessel having a top end and a bottom end, the vessel comprising at least one insulation layer adjacent the interior surface of the vessel;
(b) a first reactant manifold disposed within the vessel for receiving and distributing a first reactant stream, the first reactant manifold having a plurality of mixer tubes extending therefrom, each of the mixer tubes having an inlet end and an outlet end, the injection tubes disposed in a separator member; and
(c) a second reactant manifold disposed within the vessel for receiving and distributing a second reactant stream, the second reactant manifold comprising a plurality of injection tubes, each of the injection tubes having an inlet end and an outlet end, the injection tubes extending through the first reactant manifold and fluidly isolated therefrom;
wherein the outlet end of each of the plurality of injection tubes extends into the inlet end of one of the mixer tubes, forming a gap between the outer wall of the injection tube and the inner wall of the mixer tube.
Preferably, the gap between the mixer tubes and corresponding mixer tubes is an annular gap.
In one embodiment of the present reformer, the first reactant stream comprises substantially vaporized fuel and the second reactant stream comprises oxidant.
In a preferred embodiment, the first reactant stream comprises oxidant and the second reactant stream comprises substantially vaporized fuel.
The injection tubes and mixer tubes are arranged so as to uniformly mix and distribute the reactant stream within the present reformer. For example, the injection tubes and mixer tubes may be arranged in a hexagonal array.
The mixer tubes may comprise openings in the separator member and cooperating openings in one end of the first reactant manifold. Preferably, the first reactant manifold and mixer tubes form a shell-and-tube assembly. The length of the mixer tubes may be at least ten times the inner diameter of the mixer tubes.
The separator member that the mixer tubes are disposed comprises insulating material, preferably a ceramic composition.
The present reformer further comprises a reforming section disposed within the vessel, the reforming section comprising a combustion and gasification catalyst bed spaced apart from and in fluid communication with the reactant mixer layer, and a steam reforming catalyst bed in contact with the combustion and gasification catalyst bed. The cooperating surfaces of the reactant mixer layer and the combustion and gasification catalyst bed form a plenum therebetween. The combustion and gasification catalyst bed preferably comprises at least one monolith comprising noble metal catalyst components disposed on a porous support, where the support is preferably a ceramic honeycomb. Similarly, the steam reforming catalyst bed preferably comprises at least one monolith comprising noble metal catalyst components disposed on a porous support, where the support is preferably a c
Ballard Power Systems Inc.
McAndrews Held & Malloy Ltd.
Tran Hien
LandOfFree
Autothermal reformer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Autothermal reformer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Autothermal reformer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2870455