Reformer and Method of Startup

Abstract

A linear reformer for liberating hydrogen from a hydrogen containing feedstock, operable on both gaseous and liquid fuels, has a linear burner distributor with at least two fuel distribution apertures for distribution of fuel, a supply of air, where the fuel and air mix in a linear mixing cavity to form a catalytically combustible mixture, a catalytic burner element, an electric heater in heat transferring relation to at least one of the burner distributor and the catalytic burner element, a catalyst bed, a boiler for boiling and heating the feedstock, and an exhaust heat exchanger effective for pre-heating the supply of air to the burner. The burner distributor, catalyst bed, feedstock boiler, and exhaust heat exchanger are all linear elements with a common parallel axis, such that heat exchange gases from the burner travel transversely to the common parallel axis, and where the burner distributor receives heat from the electric heater such that incoming fuel may be at least partially vaporized, and the electric heater heats the catalytic burner element to sufficient temperature such that the vaporized fuel and air mixture initiates catalytic combustion.

Description

FIELD OF THE INVENTION

This invention relates to the start-up and operation of reformers used for generating hydrogen for a variety of uses. A linear burner distributor for supplying reformer heat is disclosed, where burner fuel is supplied through multiple openings in the distributor. A linear electric heater in heat coupling relation to the distributor is described where the heater vaporizes the burner fuel upon reformer startup. The heater may also pre-heat a catalytic burner element to the necessary temperature for light-off. A method for initiating burner operation is also described. The invention is particularly useful for applications where the fuel is miscible in water and pre-mixed, such as a methanol-water mix for reforming.

BACKGROUND OF THE INVENTION

Reformers are devices which convert hydrogen-rich fuels into hydrogen gas and byproduct gases. Typically the reformer will have a burner to supply heat, and the fuel will be heated and introduced to a catalyst bed, where the chemical reaction of reforming takes place, liberating hydrogen from the fuel. In some cases the reformer also includes a purification step to separate the hydrogen from the reformed gas mixture, for example, to supply hydrogen for a fuel cell.

There have been a variety of patent disclosures regarding the startup and operation of reformers, and the burners utilized for such. In U.S. Pat. No. 4,946,557 B. Beshty disclose a reformer utilizing a burner, where the burner which can either accept a methanol-water mix, or a combustible gaseous mixture containing hydrogen and other gases. These gases are produced during operation of the reformer after startup has been completed.

In U.S. Pat. No. 6,451,465, Chalfant and Clingerman describe a reformer where the burner includes a combustion catalyst, and can operate on a liquid hydrocarbon such as methanol, as well as well as hydrogen produced by the reformer which has not been used by the fuel cell. Vaporization of the fuel entering the burner can be performed using an electric heater. Further description of the above, including control means, is further described by Doan and Clingerman in U.S. Pat. No. 6,602,624.

U.S. Pat. No. 6,669,463 by Beutel et. al involves a combustor for a fuel processor which integrates a burner and a catalyst. The device initiates light-off with the use of a spark plug, where a methanol-water mix can supply combustion heat. The heated catalyst is then used to react fuel cell anode exhaust with air under normal operation to supply reformer heat.

In U.S. Pat. No. 6,887,603 Kasahara et. al detail the use of a vaporizer as part of a catalytic combustor, where the combustor can operate with methanol or reformed gases. The combustor is integrated into a reformer for producing hydrogen.

US. 2003/0223926 A1 by Edlund et. al generically claim a reformer with burner operating on a pre-mix of carbon containing feedstock and at least 25% water. The claims further include the use of a vaporizer and an ignition source, as well as an atomization assembly. An annular burner assembly is detailed as part of the disclosure.

The above disclosures provide a variety of means for starting and operating a reformer, particularly using a liquid fuel or water-fuel mix. However, there still remains a need for further improvement for the burners for linear reformers, where the catalyst bed, burner, and other elements are linear elements and substantially parallel to each other, and the burner gases travel transversely to the linear elements for heat transfer. Specifically, there is a need for an improved burner arrangement allowing for startup and operation using a small electric heater, and the use of liquid fuel, for supplying startup heat in the reformer.

SUMMARY OF THE INVENTION

In linear reformers, the burner, heat exchanger, catalyst bed, and other parts are arranged such that the elements are in parallel with each other. Burner gases for supplying process heat can then flow perpendicular to the parallel arrangement of the parts. With respect to the burner, this arrangement favors a long fuel distributor, such as a tube with periodic holes for fuel distribution and mixing with burner air.

In the prior art, the techniques where a fuel mix, such as methanol-water are vaporized and sent to the burner, have difficulties upon application to the linear arrangement. Specifically, on cold startup, the long distributor tube for the burner will condense the vaporized methanol-water mix, preventing the proper mixing of the fuel and air for burner light-off. Further, when the primary combustion takes place using a catalytic element, the necessary light-off temperature for initiation of combustion may not take place without adding heat.

These difficulties are solved when the fuel distributor is combined with a heating element that maintains the distributor above the boiling point of the fuel mix. The heating element may additionally supply sufficient heat for bringing the catalytic burner element to the light-off point. A single heating element can be located within the burner distributor tube, or adjacent to it, to perform this task. Alternatively, two heaters can be employed—one to maintain the distributor above the boiling point, and another to heat the catalyst for light-off. Fuel may arrive at the burner distributor in the liquid phase for vaporization at the distributor itself, or it may arrive already vaporized.

With this physical embodiment, a method for reformer startup may therefore be employed. The electric heating elements are heated up so that incoming liquid fuel remains vaporized in the burner distributor. At the same time, the catalytic burner element is preheated so that the arriving fuel will be ignited upon its arrival and mixture with incoming air. Once the operation of the burner combustion has been established, at a certain point it will be possible to turn off the electric heaters. The reformer will heat up to operating temperature, at which point the burner may then be fueled with combustible gases produced from the reforming reaction.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the general cross section of a burner arrangement for a linear reformer. The elements in FIG. 1 retain a similar cross-section at various positions along the linear axis of the reformer. The cross section in FIG. 1 is perpendicular to the linear axis.

The linear burner is enclosed within two sheet metal walls 10a and 10b, preferably constructed of higher temperature capable material such as stainless steel or any high temperature alloy. Incoming combustion air 6 is mixed with fuel 5 resulting in combustible mixture 11. Combustible mixture 11 arrives at catalytic burner element 12, and exits catalytic burner element 12 as heated flue gas 13. Catalytic burner element 12 can consist, for example, of a support structure upon which a catalytic material, such as platinum, is deposited. Support structures commonly used included extruded cordierite, as well as ceramic-coated metals.

Insulating blocks 7, 8, and 9 prevent metal walls 10a and 10b from becoming too hot, and guide the gases into catalytic burner element 12. Insulating blocks 7, 8, and 9 are preferably constructed of a low-density ceramic material.

Burner distributor tube 2 is disposed such that holes or aperatures 4 in burner distributor tube 2 are able to send combustible fuel 5 in mixing relation with incoming burner air 6, prior to arriving at catalytic burner element 12. An electric heater 1 is placed in the interior 3 of burner distributor tube 2, such that burner distributor tube 2 can be heated and combustible fuel 5 can be vaporized. Holes or aperatures 4 in burner distributor tube 22 (FIG. 2) are placed at multiple intervals along burner distributor tube 2 such that fuel is supplied along the linear axis of the burner. Electric heater 1 may be optionally placed adjacent and exterior to burner distributor tube 2, such that sufficient heat is transferred to burner distributor tube 2 to vaporize combustible fuel 5. Heat from electric heater 1 is also functional to heat adjacent catalytic burner element 12 to sufficient temperature for light-off of arriving mixed fuel and air 11. Optionally, an additional heater (not shown) may be used to separately heat up catalytic burner element 12 to the light-off temperature.

FIG. 2 shows the burner in a typical linear reformer arrangement in reformer assembly 23. Reformer assembly 23 is housed in housing 23a, typically constructed of temperature tolerant metal such as stainless steel or a high temperature alloy.

Combustion air for the burner arrives in inlet air plenum 21, via an air moving device such as a fan or blower (not shown). The air in plenum 21 then moves into the burner as preheated burner air 6, after receiving heat from heat exchange plates 18. Burner distributor 22, previously described in FIG. 1, supplies fuel 5. Fuel 5 mixes with preheated air 6 and forms combustible mixture 11, which then travels through catalytic combustor 12. Heated flue gas 13 then travels transversely past linear steam reforming catalyst element 14, such that heat is transferred to the steam reforming reaction within catalyst element 14. More specifically, catalyst element 14 may, by way of example, consist of a finned tube, with tube 14a and attached fins 14b, to facilitate heat transfer into the interior of tube 14a, which is filled with reforming catalyst 14c. Catalyst 14c is effective to perform the endothermic steam reforming reaction, for example, the conversion of methanol and steam to hydrogen and carbon dioxide. The catalyst element 14 may be configured in other ways as well, such as a microchannel catalyst bed arranged in a planar rather than a tubular fashion, with a main linear axis in parallel with the burner distributor 22. In another embodiment the flow direction of the reformed gases in the catalyst bed need not always follow the linear axis; however, the catalyst bed structure will have an overall construction such that it has an axis in parallel with the burner distributor 22. One such example is a helical arrangement of a catalyst-filled finned tube, where the helical axis of rotation is in parallel with burner distributor 22. Other arrangements may be envisioned by those skilled in the art.

Once heated flue gas 13 travels past the catalyst bed 14, it arrives in heated space 16. In the event that it is desirable to purify the reformed gases exiting catalyst bed 14, a hydrogen-purifying element may be optionally placed in heated space 16. A typical example is a membrane purifier using a palladium alloy, which allows only hydrogen to permeate the membrane, effectively purifying the reformed gases.

After exiting heated space 16, flue gas 13 travels past boiler assembly 15, transferring heat at exiting as cooler flue gas 17. Cooler flue gas 17 further transfers heat via heat exchange plates 18 to effectively heat incoming burner air 6. Heat exchange plates 18 are separated by thermally insulating gaskets 19 to form a counterflow heat exchanger. After traveling through the heat exchanger exit gases arrive at exhaust plenum 20.

Boiler assembly 15 as shown consists of a serpentine assembly containing three boiler tubes, 15a, 15b, and 15c. Boiler tubes consist of metal tubes such as 15-b2, with attached fins 15-b1, to assist with heat transfer from the flue gas 13 to the fuel inside the tubes. Fuel arrives first in tube 15a, and is subsequently transferred to tube 15b via a connection (not shown), and subsequently to tube 15c. In this fashion, as serpentine arrangement of tubes 15 can therefore pull heat from heated flue gas 13 in counterflow fashion. This allows the fuel to be boiled and preheated prior to arrival in catalyst bed 14 via a connection between boiler tube 15c and catalyst bed 14 (not shown).

Flue gas heat exchanger plates 18 and gaskets 19 are more clearly shown in FIGS. 3 and 4. In FIG. 3 a typical set of heat exchanger plates 18 are shown with gas flow apertures 18b shown. The heat exchanger plates are preferably staggered when they are stacked, as shown in FIG. 3, so that the heat exchange gases are continually making 90 degree turns to flow past the plates, facilitating heat exchange. Between each plate is a thermally insulating gasket 19 (FIG. 2), further illustrated in FIG. 4. Typical construction of the gasket includes materials such as an alumina-silica felt. Air traveling to the burner travels through aperture 25a, while exiting flue gas 17 travels through aperture 25b. Gasket material creates an effective seal between the two aperatures via separation section 26. Heat exchanger plates 18 are typically constructed of aluminum, however the plates most proximal to the burner may be constructed of a higher temperature material such as stainless steel to shield the aluminum plates from excessive temperature.

Other configurations of the reformer may be desirable. For example, if a palladium-based purifier is not desired, the reformer may be effective as a hydrogen supplying steam reformer as long as carbon monoxide levels in the reformed gases are reduced. In such cases, it may be desirable to include a low-temperature shift stage to the reformer, downstream of the first catalyst bed 14.

One such embodiment is described in FIG. 5. Reformed gases from catalyst bed 14 exit the catalyst bed 14 via connection line 30 to cooldown stage 28. Cooldown stage 28 may, for example, consist of a finned tube for transferring excess heat 29 to plenum 35. Plenum 35 is located within the plates 18 of the counterflow heat exchanger at a position where the amount of heat shed 29 from cooldown stage 28 is at the desired level. Moving the cooldown stage 28 and plenum 35 closer to the air inlet plenum 21 (by adjusting the number of heat exchange plates 18 above and below plenum 35) allows the amount of heat shed 29 at cooldown stage 28 to increase, as the air in plenum 35 will be cooler. Placement within the heat exchanger can thus be adjusted until the desired exit temperature at cooldown stage 29 via connection line 31 is achieved to low temperature shift bed 32 in plenum 36. A desirable inlet temperature to low temperature shift bed 32 can be between 150 to 250 Celsius when using a typical CuZnO low temperature shift catalyst 33 in shift bed 32. Reformed gases with reduced carbon monoxide levels exit the shift bed 32 via exit line 34, where they may be sent to a fuel cell or further processed prior to being sent to a fuel cell. Further processing might include a methanation step to convert carbon monoxide to methane, selective oxidation of carbon monoxide, or a hydrogen purification step using pressure swing absorption. Other steps might include using the available heat from the reformed gases to pre-heat the incoming fuel arriving at the boiler assembly 15, preferably in counterflow fashion.

The embodiment in FIG. 5 is flexible in regard to which processes are inserted into plenum 35 or plenum 36. Heat may be removed from the reformed gases in either plenum, and various catalytic processes can be introduced into either plenum, either endothermic or exothermic. The desired temperature of the particular process will dictate the position of the heat exchanger, such as cooldown stage 29, to achieve the desired process temperature by coupling the heat exchanger to either the incoming air for the burner or the cooling gases exhausting the unit. The heat exchanger such as heat exchanger 29 may also be combined with the catalyst bed such as shift bed 32 into a single integrated unit in either plenum. The variations and processes are apparent to those skilled in the art.

EXAMPLE 1

A linear reformer was constructed generally with the layout shown in FIG. 2. The exhaust heat exchanger comprised of 20 slotted aluminum plates less than 0.032″ thick, with 50% open area, with offset openings between successive plates. The two plates closest to the burner were constructed of stainless steel. Thin spacer gaskets constructed of alumina-silica felt were placed between the plates to form a seal and to space the plates.

The reformer further consisted of a 200 cell per inch extruded cordierite catalytic burner with a platinum coating for catalytic activity. The catalyst bed consisted of a finned tubes filled with platinum-based catalyst, and the boiler assembly consisted of a serpentine of 4 finned ¼″ diameter tubes. Gases exiting the catalyst bed were routed to a hydrogen purifier which resided in the flue gas stream downstream of the catalyst bed. The purifier, catalyst bed, boiler, catalytic burner, and burner distributor were all on a common parallel axis.

The burner distributor consisted of a 5/16 metal tube with 10 round aperatures 0.030″ in diameter. The distributor was 7″ long and had a ⅛″, 125 watt heater in the center of the distributor tube. A fuel pump was used to pump a 65/35 volume percent methanol water mix to the burner distributor.

Operation of the reformer was initiated by turning on the electric heater for 4 minutes, blowing a small amount of air through the burner to additionally move some heat into the catalytic burner material. Once the burner distributor and catalytic burner material were sufficiently hot, small amounts of methanol/water mix were pumped through a diverting valve into the burner distributor. As the exit flue gas temperature from the catalytic burner increased, the fuel pumping rate and air flow rate were increased. The electric heater was turned off once the burner was hot enough to no longer require the electric heat. Temperatures increased in the reformer enabling fuel to be sent to the catalyst bed rather than the burner distributor. At this point the diverter from the fuel pump was switched to sending fuel to the catalyst bed, and the reformer produced hydrogen from the catalyst bed. This hydrogen was subsequently sent to the burner distributor for self-sustaining operation of the reformer without sending any additional methanol/water mix directly to the burner distributor. Hydrogen production of the reformer was achieved within 15 minutes.

Claims

1. A burner for a reformer for liberating hydrogen from a hydrogen containing feedstock, operable on both gaseous and liquid fuels, comprising: a substantially linear burner distributor with at least two fuel distribution apertures for distribution of fuel;a supply of air in a substantially linear mixing cavity which is substantially parallel with the axis of the burner distributor, where the at least two fuel distribution apertures supply burner fuel, and the fuel and air mix to form a catalytically combustible mixture;a catalytic burner element; andan at least one electric heater in heat transferring relation to at least one of said burner distributor and the catalytic burner element;

2. The burner as claimed in claim 1, where the burner distributor is a porous tubular element.

3. The burner as claimed in claim 1, where the electric heater is contained within a burner distributor cavity, such that liquid fuel arriving at the burner distributor comes into direct contact with said electric heater prior to exiting the distribution apertures.

4. The burner as claimed in claim 3, where the electric heater and burner distributor are tubular and concentric with each other.

5. The burner as claimed in claim 4, where the heater further supplies sufficient heat to achieve a fuel and air light-off temperature within the catalytic burner element.

6. The burner as claimed in claim 1 including an electric pre-heater to add heat to the fuel arriving at the burner distributor, prior to the introduction of the fuel into the burner distributor.

7. A linear reformer for liberating hydrogen from a hydrogen containing feedstock, operable on both gaseous and liquid fuels, comprising: a burner distributor with at least two fuel distribution apertures for distribution of fuel;a supply of air, where the at least two fuel distribution apertures supply burner fuel, and the fuel and air mix to form a catalytically combustible mixture;a catalytic burner element;an at least one electric heater in heat transferring relation to at least one of said burner distributor and the catalytic burner element;a catalyst bed;a boiler for boiling and heating a feedstock;an exhaust heat exchanger effective for pre-heating the supply of air to the burner;

8. The reformer as claimed in claim 7, where the exhaust heat exchanger comprises: at least three heat exchange plates with openings allowing for the passage of two counterflow heat exchange gases; andinsulating gaskets between the plates, where the gaskets form a gas barrier between the counterflow heat exchange gases, and where the gaskets and plates form a stacked assembly.

9. The reformer as claimed in claim 7, where the heat exchanger plates are stacked such that the heat exchange gases change direction between successive openings in heat exchange plates.

10. A linear reformer for liberating hydrogen from a hydrogen containing feedstock, operable on both gaseous and liquid fuels, comprising: a burner distributor with at least two fuel distribution apertures for distribution of fuel;a supply of air, where the at least two fuel distribution apertures supply burner fuel, and the fuel and air mix to form a catalytically combustible mixture;a catalytic burner element;an at least one electric heater in heat transferring relation to at least one of said burner distributor and the catalytic burner element;a catalyst bed;a boiler for boiling and heating a feedstock;an at least one exhaust heat exchanger assembly effective for pre-heating the supply of air to the burner; at least three heat exchange plates with openings allowing for the passage of two counterflow heat exchange gases;insulating gaskets between the plates, where the gaskets form a gas barrier between the counterflow heat exchange gases, and where the gaskets and plates form a stacked assembly; and

11. The reformer as claimed in claim 10, where the exhaust heat exchanger comprises at least two heat exchanger assemblies, and at least one plenum in between two of the exhaust heat exchanger assemblies for each respective heat exchange gas, and where the reformed gases from the catalyst bed travel to said plenum for at least one further processing step including at least one of heat exchange and a catalytic process.

12. The reformer as claimed in claim 11 where the further processing step comprises reducing the temperature of the reformed gases and introducing the gases to low temperature shift bed, and where the temperature reduction is accomplished by shedding heat to either the air incoming into the burner or the exhaust flue gas with a heat exchanger, and the heat exchanger and catalyst bed are contained within one or both of the plenums defined between the exhaust heat exchanger assemblies.

13. The reformer as claimed in claim 10, including a hydrogen purifier to separate the hydrogen from the reformed gases produced in the catalyst bed.

14. The reformer as claimed in claim 13, where the purifier utilizes a metallic membrane to separate the hydrogen.

15. A method for initiating operation of a reformer for the production of hydrogen from a hydrogen-containing feedstock, comprising in sequence: preheating a multi-apertured linear burner distributor with an electric heater sufficient to vaporize liquid fuel;preheating a catalytic burner with an electric heater sufficient to achieve light-off temperature for a given fuel and air mix;pumping liquid fuel into the preheated burner distributor;adding oxidant air to the vaporized fuel;operating the fuel pump and air supply sufficient to achieve operation of the catalytic combustion burner;turning off said electric heaters when no longer needed for efficient burner operation; andoperating the burner using liquid fuel until sufficient heat has built up in the reformer to initiate steam reforming, and subsequently utilizing reformed gases as a fuel supply for the burner.