Patent Grant
7153334
The present invention relates to hydrocarbon reformation and, more particularly, to the reformation of a hydrocarbon stream in the production of hydrogenous fuels.
Carbonaceous material is removed from a catalyst within an autothermal reformer and catalyst heating mechanisms are improved by introducing an isolated oxidant stream into the autothermal reformer prior to introduction of hydrocarbon fuel into the reformer. A hydrocarbon stream is introduced into the autothermal reformer following removal of the carbonaceous material. A concurrent supply of the hydrocarbon stream and the oxidant stream to the autothermal reformer is maintained such that an exothermic reaction driven by the oxidant stream provides heat to an endothermic reaction driven by water vapor added to the hydrocarbon stream.
In accordance with one embodiment of the present invention, a method of operating a fuel reforming system comprising an autothermal reformer is provided. According to the method, carbonaceous material is removed from a catalyst within the autothermal reformer and the temperature of the catalyst is increased by introducing an isolated oxidant stream into the autothermal reformer. The oxidant stream is substantially free of hydrocarbon fuel and water vapor and is introduced into the autothermal reformer when a temperature of the catalyst is low enough to ensure that heat generated from an exothermic reaction of the oxidant stream and the carbonaceous material is insufficient to raise the temperature of the catalyst above the maximum operating temperature TMAX of the catalyst. A hydrocarbon stream is introduced into the autothermal reformer following removal of a substantial portion of the carbonaceous material from the catalyst by the isolated oxidant stream. A concurrent supply of the hydrocarbon stream and the oxidant stream to the autothermal reformer is maintained such that an exothermic reaction driven by the oxidant stream provides heat to an endothermic reaction driven by the water vapor in the hydrocarbon stream. A hydrogenous gas product stream is generated from the exothermic and endothermic reactions.
In accordance with another embodiment of the present invention, a fuel reforming system comprising an autothermal reformer and a system controller is provided. The system controller is programmed to (i) affect removal of carbonaceous material from a catalyst within the autothermal reformer and increasing the temperature of the catalyst by causing an isolated oxidant stream to be introduced into the autothermal reformer, wherein the oxidant stream is introduced into the autothermal reformer when a temperature of the catalyst is low enough to ensure that heat generated from an exothermic reaction of the oxidant stream and the carbonaceous material is insufficient to raise the temperature of the catalyst above the maximum operating temperature TMAX of the catalyst; (ii) cause a hydrocarbon stream to be introduced into the autothermal reformer following removal of the carbonaceous material; and (iii) cause a concurrent supply of the hydrocarbon stream and the oxidant stream to the autothermal reformer to be maintained such that an exothermic reaction driven by the oxidant stream provides heat to an endothermic reaction driven by the water vapor in the hydrocarbon stream.
Additional embodiments of the present invention may be gleaned from the present specification.
The following detailed description of specific embodiments of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:
Referring now to
The specific reformer configuration and catalyst criteria utilized in affecting steam reforming and partial oxidation reforming in the autothermal reactor 20 of the present invention are beyond the scope of the present invention. For example, by way of illustration and not limitation, the reformer may be configured to generate a hydrogenous gas product stream comprising H2 and at least one of CO and CO2 from a hydrocarbon stream.
For the purposes of describing and defining the present invention, it suffices to note that the respective reactions can be run in separate catalytic reactors in good thermal contact, in a single catalytic reactor, or in any other suitable manner. It is also noted that reference to a “catalyst” herein contemplates the use of a single element catalyst, a catalytic compound, a combination of independent catalytic compounds or elements, a plurality of independent catalyst elements or compounds, or any other suitable catalytic material.
The present inventors have recognized that autothermal reformer catalysts may be characterized by a number of different temperatures or temperature states. For example, the “light-off” temperature of a catalyst is the temperature at which the catalyst contributes to the reforming process, for example, by converting HC to desirable reactant products like CO2, CO and H2. The catalytic carbon bum off temperature of a catalyst is the temperature above which an carbon/oxygen exothermic reaction will be initiated by an oxidant passing over a carbon-contaminated catalyst. Referring to
According to the present invention, carbonaceous material contaminating a reformer catalyst is removed from the catalyst within the autothermal reformer 20 by introducing an isolated oxidant stream 22 into the autothermal reformer 20. The resulting exothermic reaction of the oxidant and the carbonaceous material results in removal of the carbonaceous material and increases the temperature of the catalyst, reducing some of the challenges associated with reformer start-up.
To ensure that the heat generated from the exothermic reaction of oxygen in the oxidant stream 22 and the carbonaceous material in the reformer 20 does not raise the temperature of the catalyst above its operating temperature, or above a temperature at which thermal damage to the catalyst would occur, the oxidant stream 22 is introduced into the autothermal reformer 20 when the temperature of the reformer catalyst is low enough to ensure that heat generated from an exothermic reaction of the oxidant stream and the carbonaceous material is insufficient to raise the temperature of the catalyst above the maximum operating temperature TMAX of the catalyst. The oxidant stream 22 may be introduced when the temperature of the reformer catalyst is above or below its catalytic light-off temperature. The temperature of the catalyst should be at least high enough to generate the carbon bum-off exotherm, i.e., at least as high as the catalytic carbon burn off temperature of the catalyst. In this manner, the isolated oxidant stream may be utilized to raise the temperature of the catalyst safely while removing carbonaceous material. Of course, it is contemplated that the oxidant stream 22 may be introduced when the temperature of the reformer catalyst is below the catalytic carbon bum off temperature of the catalyst, provided heat from the oxidant stream or some other source is able to raise the temperature of the catalyst above the catalytic carbon bum off temperature.
The present inventors have recognized that care must be taken to ensure that the heat QEX generated by the exothermic reaction of the oxygen and the carbonaceous material 20 will not raise the temperature of the catalyst above TMAX. If the exothermic reaction is initiated during operation, at shut-down, immediately following shut-down, or at any other time when the catalyst is near the operating temperature of the reformer 20 TOP, the heat QEX generated by the exothermic reaction will be more likely to raise the temperature of the catalyst above TMAX than it would be if the exothermic reaction were initiated prior to introduction of hydrocarbon fuel into the reformer, near a relatively cool temperature state TCOLD of the reformer 20.
For example, the temperature of the catalyst may be maintained below TMAX by introducing the isolated oxidant stream 22 into the autothermal reformer 20 as part of a start-up sequence of the fuel reforming system 10 because the temperature of the catalyst is typically near TCOLD at start-up. Although preferred temperatures for introduction of the isolated oxidant stream will vary greatly depending upon the nature of the reformer catalyst and the fuel to be reformed, in some embodiments of the present invention the isolated oxidant stream 20 may be introduced into the autothermal reformer at any time when the temperature of the catalyst is between about 200° C. and about 600° C. or, more commonly, between about 300° C. and about 500° C. The isolated oxidant stream 22 may comprise a substantially pure oxygen stream, a combination of oxygen and an inert gas, or a gaseous mixture, such as air, that includes oxygen. The isolated oxidant stream 22 may be provided such that it is substantially free of hydrocarbon fuel and water vapor. It is contemplated, however, that there may be system reasons to include water vapor in the oxidant stream, particularly where it can be considered inert, i.e., where the catalyst has not reached its catalytic light of temperature.
A hydrocarbon stream 24, typically comprising a hydrocarbon fuel to be reformed and water vapor, is introduced into the autothermal reformer 20 following removal of a substantial portion, a majority, or substantially all of the carbonaceous material from the catalyst by the isolated oxidant stream. In this manner, the operational efficiency and effectiveness of the autothermal reformer 20 may be optimized. It is noted that the desired extent of removal of the carbonaceous material will depend upon the operational preferences of those practicing the present invention. To further optimize the efficiency and the effectiveness of the hydrocarbon reforming process, the hydrocarbon fuel is typically not introduced into the reformer until after the catalyst reaches or exceeds its catalytic light-off temperature. Of course, instances are contemplated where such a condition need not be followed.
As is illustrated in
Typically, a concurrent supply of the hydrocarbon stream and the oxidant stream to the autothermal reformer are maintained such that the exothermic reaction driven by the oxidant stream provides heat to the endothermic reaction driven by the water vapor in the hydrocarbon stream. The resulting exothermic and endothermic reactions lead to generation of a hydrogenous gas product stream 25 at the output of the reformer 20.
A programmable system controller 26 and an input flow controller 28 may be provided for controlling the manner in which the oxidant and hydrocarbon streams 22, 24 are supplied to the reformer 20. It is contemplated that suitable equipment like power supplies, user interfaces, temperature sensors, flow meters, particulate matter sensors, etc., may be provided to complement the operations of the programmable controller 26.
As is illustrated in
Referring now to
It is noted that terms like “preferably,” “commonly,” and “typically” are not utilized herein to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the present invention.
For the purposes of describing and defining the present invention, it is noted that the terms “substantially” and “about” are utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The terms “substantially” and “about” are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.
Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present invention are identified herein as preferred or particularly advantageous, it is contemplated that the present invention is not necessarily limited to these preferred aspects of the invention.
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