CA2455037A1 - Partial oxidation reformer - Google Patents
Partial oxidation reformer Download PDFInfo
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- CA2455037A1 CA2455037A1 CA002455037A CA2455037A CA2455037A1 CA 2455037 A1 CA2455037 A1 CA 2455037A1 CA 002455037 A CA002455037 A CA 002455037A CA 2455037 A CA2455037 A CA 2455037A CA 2455037 A1 CA2455037 A1 CA 2455037A1
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- CA
- Canada
- Prior art keywords
- reforming section
- inlet
- outlet
- fuel
- partial oxidation
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- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
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Abstract
An inline partial oxidation fuel reformer includes an inlet end, a catalytic reforming section and an outlet end. The reformer may include a start up burner associated with the inlet end, an inlet flow diffuser connecting the inlet end to the reforming section, a porous thermal barrier between the inlet flow diffuser and the reforming section, and an outlet reducer connecting the reforming section to the outlet end.
Description
CANADIAN PATENT APPLICATION
File No. 45283.105/CA
PARTIAL OXIDATION REFORMER
FIELD OF THE INVENTION
The present invention relates to a partial oxidation reformer apparatus for improving direct solid oxide fuel cell reforming processes.
BACKGROUND OF THE INVENTION
Solid oxide fuel cells comprise an electrolyte sandwiched between a cathode and an anode. Oxygen reacts with electrons at the cathode to form oxygen ions, which are conducted through the ion-conducting ceramic electrolyte to the anode. At the anode, oxygen ions may combine with hydrogen and carbon monoxide to form water and carbon dioxide thereby liberating electrons. However, the direct use of hydrogen or carbon monoxide as a fuel in fuel cells depends on the availability of pure hydrogen or syngas. Currently, the production, storage and distribution of hydrogen in commercially significant quantities does not exist. Therefore, many current fuel cell designs include reformers for reforming readily available fuels to hydrogen and/or carbon monoxide.
Partial oxidation is an exothermic process whereby fuel is reacted with air with a stoichiometric excess of fuel. Under suitable conditions of pressure and temperature, partial oxidation of a fuel such as methane will result in the following shift reaction to produce syngas:
CH4+20z NCO+2Hz (1) Efficient shift - conversion requires high enough temperatures, pressures, and residence time (less soot, more complete reaction). A preferred partial oxidation reactor, therefore, should preferably mix incoming gases aggressively; have flame speeds (SL) that match the burner geometry very closely; operate over significant ranges of flows; have sufficient residence times for all of the constituents to fully react; and minimize heat loss (approaching an adiabatic process). A suitable fuel source free of nitrogenous or sulphurous impurities is also important.
In summary, the reactor must operate within relatively small flammability limits in order for optimum conversion efficiency to be realized.
S
Therefore, there is a need in the art for methods or apparatuses which mitigate the difficulties of the prior art and permit effective in-line reforming of a feed gas to produce hydrogen or syngas to feed a fuel cell.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described by way of an exemplary embodiment with reference to the accompanying simplified, diagrammatic, not-to-scale drawings. In the drawings:
Figure 1 is a cross-sectional view of one embodiment of the present invention.
Figure 2 is a schematic representation of flame liftoff during startup.
Figure 3 shows fluid velocity and static pressure contours in the inlet diffuser of one embodiment.
Figure 4 is a cross-sectional view of a preferred embodiment of the inlet diffuser.
Figure 5 is a cross-sectional view of a preferred embodiment of the outlet reducer.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides for an in-line reforming apparatus to process fuel gas.
The reformer of the present invention is intended to be a partial oxidation reforming reactor for converting fuel species such as natural gas or propane to hydrogen or syngas, which is a mixture of predominantly hydrogen and carbon monoxide. When describing the present invention, all terms not defined herein have their common art-recognized meanings.
File No. 45283.105/CA
PARTIAL OXIDATION REFORMER
FIELD OF THE INVENTION
The present invention relates to a partial oxidation reformer apparatus for improving direct solid oxide fuel cell reforming processes.
BACKGROUND OF THE INVENTION
Solid oxide fuel cells comprise an electrolyte sandwiched between a cathode and an anode. Oxygen reacts with electrons at the cathode to form oxygen ions, which are conducted through the ion-conducting ceramic electrolyte to the anode. At the anode, oxygen ions may combine with hydrogen and carbon monoxide to form water and carbon dioxide thereby liberating electrons. However, the direct use of hydrogen or carbon monoxide as a fuel in fuel cells depends on the availability of pure hydrogen or syngas. Currently, the production, storage and distribution of hydrogen in commercially significant quantities does not exist. Therefore, many current fuel cell designs include reformers for reforming readily available fuels to hydrogen and/or carbon monoxide.
Partial oxidation is an exothermic process whereby fuel is reacted with air with a stoichiometric excess of fuel. Under suitable conditions of pressure and temperature, partial oxidation of a fuel such as methane will result in the following shift reaction to produce syngas:
CH4+20z NCO+2Hz (1) Efficient shift - conversion requires high enough temperatures, pressures, and residence time (less soot, more complete reaction). A preferred partial oxidation reactor, therefore, should preferably mix incoming gases aggressively; have flame speeds (SL) that match the burner geometry very closely; operate over significant ranges of flows; have sufficient residence times for all of the constituents to fully react; and minimize heat loss (approaching an adiabatic process). A suitable fuel source free of nitrogenous or sulphurous impurities is also important.
In summary, the reactor must operate within relatively small flammability limits in order for optimum conversion efficiency to be realized.
S
Therefore, there is a need in the art for methods or apparatuses which mitigate the difficulties of the prior art and permit effective in-line reforming of a feed gas to produce hydrogen or syngas to feed a fuel cell.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described by way of an exemplary embodiment with reference to the accompanying simplified, diagrammatic, not-to-scale drawings. In the drawings:
Figure 1 is a cross-sectional view of one embodiment of the present invention.
Figure 2 is a schematic representation of flame liftoff during startup.
Figure 3 shows fluid velocity and static pressure contours in the inlet diffuser of one embodiment.
Figure 4 is a cross-sectional view of a preferred embodiment of the inlet diffuser.
Figure 5 is a cross-sectional view of a preferred embodiment of the outlet reducer.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides for an in-line reforming apparatus to process fuel gas.
The reformer of the present invention is intended to be a partial oxidation reforming reactor for converting fuel species such as natural gas or propane to hydrogen or syngas, which is a mixture of predominantly hydrogen and carbon monoxide. When describing the present invention, all terms not defined herein have their common art-recognized meanings.
-2-An idealized equation for the partial oxidation reforming of a hydrocarbon can be written as:
CnHmOp + x(OZ + 3.76N2 ) + (2n - 2x - p)H20 = nCOz + (2n - 2x - p + m l 2)Hz +
CnHmOp + x(OZ + 3.76N2 ) + (2n - 2x - p)H20 = nCOz + (2n - 2x - p + m l 2)Hz +
3.76N2 (2) where x is oxygen to fuel molar ratio. This ratio is a very important parameter because it determines the amount of water required to convert the carbon, the hydrogen yield in moles, the concentration of hydrogen in mol% in the product and the heat of reaction.
When x = 0, this equation defines endothermic steam reformation. When x = 12.5, this equation defines combustion, which is of course highly exothermic but has very low hydrogen yields. A partial oxidation reactor should be operated in a manner than the overall reaction is exothermic, but at a low value of x where higher yields of hydrogen are favoured. At lower temperatures and absent conditions favouring the water-gas shift reaction, carbon is predominantly converted to carbon monoxide as well as to carbon dioxide.
In one embodiment, as shown in Figure 1, an in-line partial oxidation apparatus comprises an inlet end (10), a start-up burner (12), an inlet flow diffuser (14), a porous thermal barrier (16), a reforming section (18) which includes a catalyst bed (20) which may also be referred to as the reaction zone, and an outlet reducer (22) leading to the outlet end (24). Feed gases and reactants flow from the inlet end to the outlet end.
The design of the reforming apparatus may be optimized to meet the following desirable characteristics. Design characteristics and the effect on process variables may be modelled using a Computational Fluid Dynamics (CFD) software package (FLUENT). The unit should preferably be able to startup from room temperature to operating temperature without external heating and without slipping oxygen once the reactor's lowest temperature is above 200°C. Heat loss should be minimized. The aspect ratio of the reaction zone must be well suited to the catalyst to ensure appropriate velocities and residence times. The flow in the reaction zone must be as uniformly distributed as possible. It is also desirable to minimize pressure drop.
One design feature of the present invention is aimed at optimizing the temperature profile of the gas flow. It is preferred that the temperature of the reactants should increase from room temperature to the reaction temperature in as short a time as possible to avoid cracking of the feed gas which results in soot formation. This is a particular problem with the higher carbon fuel species such as propane. In one embodiment, the reaction zone (20) and the outlet reducer(22) is blanketed with thermal insulation (30) to help minimize heat loss from the reaction zone and the reactant gas flow. However, the inlet end of the apparatus is not insulated up to the thermal barrier (18) to maximize heat loss during startup. As well, the thermal barrier is comprised of a heat insulating material to retard heat conductance from the reaction zone to the incoming gas stream in the inlet gas diffuser. Preferably, the thermal barrier is comprised of a ceramic foam material which provides the necessary porosity to minimize pressure drop while providing a thermal barner between the reaction zone and the inlet gas diffuser. As well, the thermal barrier serves to physically retain the catalyst in the reaction zone.
In one embodiment, a burner (12) is used to accommodate start-up. The unit is started near stoichiometric combustion to begin the warm up with the help of an igniter. As the unit's temperatures rise, the mixture can be made more fuel rich (increasing the fuel concentration).
The flame remains anchored at the burner until the mixture is too fuel rich to sustain uncatalyzed combustion, at which point the flame "lifts-ofP' and the oxidation reaction moves to the beginning of the catalyst zone as shown schematically in Figure 2. Once the flame has lifted off, the burner no longer functions as a burner and instead serves to mix air and fuel in the incoming gas stream.
Once the unit has reached operating temperatures and flows, the characteristics of the inlet become very important. One key constraint on the unit is low pressure drop (< 0.5 PS)D at full flow - 29.25 SLPM Propane, 243.65 SLPM Air). The trade off is that it is very difficult to achieve good mixing without introducing mixers that cause a high pressure drop. Also, in one embodiment, the flow enters the system in a 3/4" tube. In order to minimize the pressure drop across the catalyst bed, a diameter of 4.5" is required.
When x = 0, this equation defines endothermic steam reformation. When x = 12.5, this equation defines combustion, which is of course highly exothermic but has very low hydrogen yields. A partial oxidation reactor should be operated in a manner than the overall reaction is exothermic, but at a low value of x where higher yields of hydrogen are favoured. At lower temperatures and absent conditions favouring the water-gas shift reaction, carbon is predominantly converted to carbon monoxide as well as to carbon dioxide.
In one embodiment, as shown in Figure 1, an in-line partial oxidation apparatus comprises an inlet end (10), a start-up burner (12), an inlet flow diffuser (14), a porous thermal barrier (16), a reforming section (18) which includes a catalyst bed (20) which may also be referred to as the reaction zone, and an outlet reducer (22) leading to the outlet end (24). Feed gases and reactants flow from the inlet end to the outlet end.
The design of the reforming apparatus may be optimized to meet the following desirable characteristics. Design characteristics and the effect on process variables may be modelled using a Computational Fluid Dynamics (CFD) software package (FLUENT). The unit should preferably be able to startup from room temperature to operating temperature without external heating and without slipping oxygen once the reactor's lowest temperature is above 200°C. Heat loss should be minimized. The aspect ratio of the reaction zone must be well suited to the catalyst to ensure appropriate velocities and residence times. The flow in the reaction zone must be as uniformly distributed as possible. It is also desirable to minimize pressure drop.
One design feature of the present invention is aimed at optimizing the temperature profile of the gas flow. It is preferred that the temperature of the reactants should increase from room temperature to the reaction temperature in as short a time as possible to avoid cracking of the feed gas which results in soot formation. This is a particular problem with the higher carbon fuel species such as propane. In one embodiment, the reaction zone (20) and the outlet reducer(22) is blanketed with thermal insulation (30) to help minimize heat loss from the reaction zone and the reactant gas flow. However, the inlet end of the apparatus is not insulated up to the thermal barrier (18) to maximize heat loss during startup. As well, the thermal barrier is comprised of a heat insulating material to retard heat conductance from the reaction zone to the incoming gas stream in the inlet gas diffuser. Preferably, the thermal barrier is comprised of a ceramic foam material which provides the necessary porosity to minimize pressure drop while providing a thermal barner between the reaction zone and the inlet gas diffuser. As well, the thermal barrier serves to physically retain the catalyst in the reaction zone.
In one embodiment, a burner (12) is used to accommodate start-up. The unit is started near stoichiometric combustion to begin the warm up with the help of an igniter. As the unit's temperatures rise, the mixture can be made more fuel rich (increasing the fuel concentration).
The flame remains anchored at the burner until the mixture is too fuel rich to sustain uncatalyzed combustion, at which point the flame "lifts-ofP' and the oxidation reaction moves to the beginning of the catalyst zone as shown schematically in Figure 2. Once the flame has lifted off, the burner no longer functions as a burner and instead serves to mix air and fuel in the incoming gas stream.
Once the unit has reached operating temperatures and flows, the characteristics of the inlet become very important. One key constraint on the unit is low pressure drop (< 0.5 PS)D at full flow - 29.25 SLPM Propane, 243.65 SLPM Air). The trade off is that it is very difficult to achieve good mixing without introducing mixers that cause a high pressure drop. Also, in one embodiment, the flow enters the system in a 3/4" tube. In order to minimize the pressure drop across the catalyst bed, a diameter of 4.5" is required.
-4-A preferred diffuser, shown in Figures 3 and 4, was designed and modeled with a Computational Fluid Dynamics (CFD) software package (FLUENT) to quantify how well the diffuser design distributed the flow (Figure 3). The preferred diffuser expands approximately three times in diameter in a length approximately S times the inlet diameter.
It is particularly preferred that the expansion section make up about 75% of the overall length and be slightly concave, with a radius of curvature of approximately 1.8 times the overall length of the diffuser.
Therefore, in one embodiment, the inlet end is approximately 1.5" and the expanded end is approximately 4.5" in diameter. The overall length of the diffuser is about 7.3" with an expansion section of about 5.6". The radius of curvature of the expansion section is 12".
The catalyst used may be any suitable partial oxidation catalyst which is well-known in the art. For reforming propane, a particularly preferred catalyst is a pellet catalyst made by Sud-Chemie called G43a. It is a nickel/platinum oxidation catalyst on an alumina substrate. The catalyst is very selective to forming combustion products (C02 and H20). The catalyzed oxidation (combustion) is very prompt and has been demonstrated to occur in the first 10% of the catalyst bed. As a result, the temperature of the process increases sharply upon entering the reaction zone, minimizing coking. Due to there being excess fuel, the combustion products will further react with the remaining propane to form CO and Hz through the partial oxidation reaction, catalyzed by the nickel. The overall reactions are exothermic.
The size of the tubing of the outlet of the reformer must be as small as possible to allow inexpensive manifolding to be used, without introducing appreciable pressure drop. Preferably, the outlet diameter is at least 1" in diameter. A preferred embodiment of the reducer tube may have the dimensions shown in Figure 5.
As will be apparent to those skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the scope of the invention claimed herein. The various features and elements of the described invention may
It is particularly preferred that the expansion section make up about 75% of the overall length and be slightly concave, with a radius of curvature of approximately 1.8 times the overall length of the diffuser.
Therefore, in one embodiment, the inlet end is approximately 1.5" and the expanded end is approximately 4.5" in diameter. The overall length of the diffuser is about 7.3" with an expansion section of about 5.6". The radius of curvature of the expansion section is 12".
The catalyst used may be any suitable partial oxidation catalyst which is well-known in the art. For reforming propane, a particularly preferred catalyst is a pellet catalyst made by Sud-Chemie called G43a. It is a nickel/platinum oxidation catalyst on an alumina substrate. The catalyst is very selective to forming combustion products (C02 and H20). The catalyzed oxidation (combustion) is very prompt and has been demonstrated to occur in the first 10% of the catalyst bed. As a result, the temperature of the process increases sharply upon entering the reaction zone, minimizing coking. Due to there being excess fuel, the combustion products will further react with the remaining propane to form CO and Hz through the partial oxidation reaction, catalyzed by the nickel. The overall reactions are exothermic.
The size of the tubing of the outlet of the reformer must be as small as possible to allow inexpensive manifolding to be used, without introducing appreciable pressure drop. Preferably, the outlet diameter is at least 1" in diameter. A preferred embodiment of the reducer tube may have the dimensions shown in Figure 5.
As will be apparent to those skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the scope of the invention claimed herein. The various features and elements of the described invention may
-5-be combined in a manner different from the combinations described or claimed herein, without departing from the scope of the invention.
-6-
Claims (5)
1. An in-line partial oxidation fuel reformer comprising an inlet end, a reforming section including a catalyst, and an outlet end, the reforming comprising:
(a) a start-up burner associated with the inlet end;
(b) an inlet flow diffuser connecting the inlet end to the reforming section;
(c) a porous thermal barrier between the inlet flow diffuser and the reforming section;
and (d) an outlet reducer connecting the reforming section to the outlet end;
whereby a gas stream comprising a fuel gas and air or oxygen and their reactants flow through the inlet end, the inlet flow diffuser, the thermal barrier, the reforming section, and finally the outlet reducer to the outlet end.
(a) a start-up burner associated with the inlet end;
(b) an inlet flow diffuser connecting the inlet end to the reforming section;
(c) a porous thermal barrier between the inlet flow diffuser and the reforming section;
and (d) an outlet reducer connecting the reforming section to the outlet end;
whereby a gas stream comprising a fuel gas and air or oxygen and their reactants flow through the inlet end, the inlet flow diffuser, the thermal barrier, the reforming section, and finally the outlet reducer to the outlet end.
2. The fuel reformer of claim 1 wherein the porous thermal barrier comprises a ceramic foam.
3. The fuel reformer of claim 2 wherein the ceramic foam comprises alumina or zirconia.
4. The fuel reformer of claim 1, 2 or 3 further comprising heat insulation blanketing the reforming section and the outlet reducer, but not the inlet flow diffuser.
5. The fuel reformer of claim 1 wherein the fuel gas comprises propane.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US31993603P | 2003-02-11 | 2003-02-11 | |
| US60/319,936 | 2003-02-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2455037A1 true CA2455037A1 (en) | 2004-04-23 |
Family
ID=32680701
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002455037A Abandoned CA2455037A1 (en) | 2003-02-11 | 2004-01-13 | Partial oxidation reformer |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2455037A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9987612B1 (en) | 2017-04-13 | 2018-06-05 | Caterpillar Inc. | Reactor assembly |
-
2004
- 2004-01-13 CA CA002455037A patent/CA2455037A1/en not_active Abandoned
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9987612B1 (en) | 2017-04-13 | 2018-06-05 | Caterpillar Inc. | Reactor assembly |
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| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |