Gas separation method and apparatus using partial pressure swing adsorption

Detailed description of the invention

(Cross-reference of related patent applications) Both of these applications are incorporated herein by reference in their entirety, U.S. Patent Application No. 11 / 188,118 filed July 25, 2005 and U.S. Patent Application No. 11 / 188,120 filed July 25, 2005. Claim the interests of.

(Background of invention) The present invention generally relates to the field of gas separation, and more specifically to a fuel cell system having recovery of anode exhaust fuel by partial pressure swing adsorption or temperature swing adsorption.

A fuel cell is an electrochemical device that converts the energy stored in fuel into electrical energy with high efficiency. High temperature fuel cells include solid oxide (solid electrolyte type) fuel cells and molten carbonate fuel cells. These fuel cells can operate using hydrogen fuel and / or hydrocarbon fuel. There are types of fuel cells, such as solid oxide regenerated fuel cells, which are capable of vice versa, such as being able to use electrical energy as an input to reduce oxidized fuel to unoxidized fuel. is there.

(Outline of the invention) Embodiments of the present invention are pressure swing adsorption (ie, concentration swing). Adsorption)) is used to provide a system and method for separating hydrogen from the fuel discharge stream of a fuel cell stack and returning the hydrogen to the fuel intake stream of the fuel cell stack. The first four embodiments described below cover "various partial pressure swing adsorption gas separation methods and devices" that can be used to separate hydrogen from the fuel discharge stream, the fifth and sixth embodiments. The form is intended for fuel cell systems that use "partial pressure swing adsorption methods and devices for hydrogen separation".

(Detailed description of preferred embodiment) The first embodiment of the present invention is a four-step pressure-divided swing adsorption (ie, concentrated swing adsorption) for gas separation, such as recovering fuel from the fuel (ie, anode side) exhaust of a solid oxide fuel cell stack. ) Provide a cycle. Two adsorption beds filled with an adsorbent such as activated carbon are used to adsorb carbon dioxide and water (ie, water vapor) from the fuel exhaust, allowing hydrogen and carbon monoxide to pass through the adsorption bed. The adsorption bed is regenerated using air that has been dried to a moderate relative humidity (such as about 30% to about 50% relative humidity), preferably countercurrent (backflow). For example, dry air for regeneration can be generated in a temperature swing adsorption cycle using silica gel or activated alumina. The cleaning process is used to recover additional hydrogen and prevent air from contaminating the recovered fuel. The duration of the adsorption and regeneration (ie, feed and purge) steps is preferably at least 5 times, for example 10 to 50 times, the duration of the cleaning step.

This provides a reliable and energy efficient cycle for optimal gas separation. For example, the cycle is a partial pressure swing adsorption with a countercurrent purging step and a parallel flow cleaning step that regains maximum hydrogen and eliminates carbon dioxide and air to the maximum (also referred to herein as concentrated swing adsorption). It is a high efficiency cycle based on. Since the adsorption bed is preferably regenerated with air, it is not desirable to push the air remaining on the adsorption bed back into the fuel cell stack at the end of regeneration. In addition, at the beginning of the regeneration process, the flow-removed adsorption bed contains hydrogen in the gas phase. It is desirable to recover this hydrogen. The cleaning process removes the air remaining on the adsorption floor at the end of the regeneration process to prevent this air from returning to the fuel cell stack, and the hydrogen remaining on the adsorption floor at the start of the regeneration process is used as the fuel inlet of the fuel cell stack. Used to supply to.

Although the system and method of the first embodiment are described and exemplified for an adsorption system that separates carbon dioxide from hydrogen in the fuel discharge stream of a solid oxide fuel cell, the system and method of the first embodiment is described. Also for "separating any multi-component gas stream" that is not part of a fuel cell system or is part of a fuel cell system other than a solid oxide fuel cell system, such as a molten carbon dioxide fuel cell system. Note that it can be used. Therefore, the systems and methods of the first embodiment should not be considered limited to separating hydrogen from carbon dioxide. The adsorbent on the adsorption bed can be selected based on the gas being separated.

FIG. 1 shows the gas separation device 1 of the first embodiment. The device 1 includes a first supply gas intake conduit (inlet conduit) 3 that supplies a supply gas intake stream (inlet stream, intake stream, intake stream, inlet stream) during operation. When device 1 is used to separate hydrogen from the fuel outlet of the fuel cell stack, conduit 3 is operably connected to the anode outlet of the fuel cell stack. As used herein, two elements are "operably connected" when the two elements are directly or indirectly connected and a fluid is directly or indirectly connected from one element to the other. It means that it can flow. The device 1 also includes a second purge gas intake conduit 5 that supplies the purge gas intake flow during operation.

The device includes a third supply gas collection conduit 7 that collects at least one separated component of the supply gas during operation. If device 1 is used to separate hydrogen from the fuel drain of the fuel cell stack and recirculate that hydrogen to the fuel inlet of the fuel cell stack, conduit 7 is the fuel inlet of the fuel cell stack. It is operably connected to the mouth (ie, directly to the fuel inlet of the stack or to a fuel inlet conduit operably connected to the fuel inlet of the stack). The device also includes a fourth purge gas collection conduit 9 that collects the supply gas exhaust stream during the cleaning process and collects the purge gas exhaust flow during the supply / purge process during operation.

Therefore, when device 1 is used to separate hydrogen from the fuel outflow of the fuel cell stack, the first conduit 3 constitutes an intake conduit for hydrogen, carbon dioxide, carbon monoxide, and steam. The second conduit 5 constitutes a dry air intake conduit, the third conduit 7 constitutes a hydrogen and carbon monoxide removal / recirculation conduit, and the fourth conduit 9 constitutes a carbon dioxide and water vapor removal conduit. To do.

Device 1 also includes at least two adsorption beds 11 and 13. The adsorption bed is optional that adsorbs at least most (eg, at least 80-95%) of one or more desired components of the supply gas and allows most of one or more other components to pass through. Can contain suitable adsorbents. For example, the material of the adsorption bed may consist of zeolite, activated carbon, silica gel, or activated alumina adsorbent. Activated carbon is suitable for separating hydrogen and carbon monoxide from water vapor and carbon dioxide in the fuel discharge stream of the fuel cell stack. Zeolites likewise adsorb carbon dioxide. However, zeolites adsorb water very strongly and for regeneration a very dry gas, which is difficult to obtain, should be used. Therefore, zeolite beds can preferably be used to separate water vapor-free gas streams, but not necessarily. This is because devices that use a zeolite bed to separate water vapor-containing gases can exhibit slow performance degradation.

Device 1 also includes a plurality of valves that direct the gas flow. For example, the device may include three four-way valves with a "double LL" flow path, namely a supply valve 15, a regeneration valve 17, and a product valve 19. The supply valve 15 is connected to the first conduit 3, to the two suction beds 11 and 13, and to the regeneration valve 17 by the conduit 21. The regeneration valve 17 is connected to the second conduit 5, the fourth vessel 9, the supply valve 15 by the vessel 21, and the product valve 19 by the vessel 23. The product valve 19 is connected to the third conduit 7, the two suction beds 11 and 13, and to the regeneration valve 17 by the conduit 23. A four-way valve can be used to divert two streams at once. Such valves are available in a variety of sizes, for example from AT Controls, Inc., Cincinnati, Ohio, http://www.a-tcontrols.com. .. If desired, each four-way valve may be replaced by two three-way valves or four two-way valves, or by a completely different flow distribution system containing a manifold.

Therefore, the valves 15, 17, and 19 preferably have the purge gas intake flow countercurrent (backflow) with the supply gas intake flow during the purge process and parallel to the supply gas intake flow during the cleaning process. Operates to be fed to the suction beds 11 and 13. In other words, the first conduit 3 is operably connected to the first suction bed 11 and the second suction bed 13 to direct the supply gas intake flow in the first suction bed 11 and the first suction bed 11. It is supplied to the adsorption bed 13 of 2. The second conduit 5 has a first adsorption bed 11 and a second adsorption bed in a direction in which the purge gas intake flow is different from the first direction (such as in the opposite direction) during the first and second supply / purge steps. The first adsorption bed and the second adsorption are supplied to each of the thirteen and during the first and second cleaning steps, the purge gas intake stream is in the first direction (ie, in the same direction as the supply gas supply stream). It is operably connected to the first suction bed 11 and the second suction bed 13 via valves 17 and 19 so as to be supplied to the floor.

Figures 2A-2D show the steps of the system 1 operation cycle. In FIG. 2A, a supply gas intake flow such as a fuel discharge flow of the fuel cell stack is supplied to the first adsorption bed 11, and dry air is supplied to the second adsorption bed 13 in order to regenerate the second adsorption bed 13. The device 1 in the first supply / purge process to which the purge gas such as is supplied is shown.

The supply gas intake flow is supplied from the conduit 3 to the first adsorption bed 11 via the valve 15. For feed gases containing hydrogen, carbon monoxide, carbon dioxide, and water vapor, the majority of hydrogen and carbon monoxide (eg, at least 80-95%) passes through the first adsorption bed 11 and carbon dioxide. Most (eg, at least 80-95%) and most of the water vapor are adsorbed on the first adsorption bed. The supply gas exhaust stream containing at least one separated component of the supply gas such as hydrogen and carbon monoxide passes through the valve 19 and is collected on the first output side such as the third conduit 7.

The purge gas intake flow such as dry air is supplied from the second conduit 5 to the second adsorption bed 13 via the valve 17, the conduit 23 and the valve 19. The purge gas exhaust stream passes through the conduit 21, valve 15 and valve 17 and is collected on the second output side, such as the fourth conduit 9.

In the first supply / purge step, the valve position is such that the valve 15 directs the feed to the first adsorption bed 11 and the valve 19 allows the hydrogen product to escape into the conduit 7. The valve 17 is positioned to flush dry air countercurrently through the second adsorption bed to remove previously adsorbed carbon dioxide. A part of the water in the supply gas flow is adsorbed by an adsorbent such as activated carbon at the introduction port of the first adsorption bed 11, and is removed from the adsorption bed 11 when it is regenerated in the subsequent step. Carbon monoxide passes through the first adsorption bed 11 as the carbon dioxide wave advances.

FIG. 2B shows device 1 in the first cleaning step performed after the first supply / purge step. In this step, the supply valve 15 and the regeneration valve 17 switch the flow direction from the previous step, while the product valve 19 does not switch the flow direction.

The purge gas intake flow is supplied from the conduit 5 to the first adsorption bed 11 via the valve 17, the valve 15, and the conduit 21. Preferably, this purge gas intake flow is supplied to the first adsorption bed 11 in the same direction as the supply gas flow in the previous step. The purge gas exhaust stream containing at least one component of the supply gas such as hydrogen trapped in the void volume of the first adsorption bed is collected on the first output side such as conduit 7.

The supply gas intake flow is supplied from the conduit 3 to the second adsorption bed 13 via the valve 15. The supply gas exhaust flow containing a part of the purge gas such as air trapped in the void volume of the second adsorption bed 13 passes through the valve 19, the valve 17 and the conduit 23, and is different from the first output side conduit. Collected on the output side such as 9.

Therefore, in the first cleaning step, the hydrogen trapped in the void volume of the first adsorption bed 11 is washed away to the product by the incoming air and the desorbed carbon dioxide. The air trapped in the void volume of the second adsorption bed 13 is purged (removed) from the adsorption bed 13 by the incoming supply gas. This step continues to recover the hydrogen trapped from the previous supply step and prevents the air from the previous purging step from contaminating the hydrogen-containing product after the next valve switch, thereby overall the process. Improve efficiency. This cleaning step is as short as less than 1/5 of the time of the previous supply / purge step, for example 1/10 to 1/50 of the time of the previous step. For example, in the case of a supply / purge step of about 90 seconds, the cleaning step may be about 4 seconds.

FIG. 2C shows device 1 in a second supply / purge step performed after the first cleaning step. In this step, a supply gas flow such as a fuel discharge flow of the fuel cell stack is supplied to the second adsorption floor 13, and a purge gas such as dry air is supplied to the first adsorption floor 11 to provide the first adsorption. Regenerate floor 11. Therefore, in this step, the flow paths of the valve 17 and the valve 19 are switched. This process is generally similar to the first supply / purge process, but with the adsorption beds replaced.

The supply gas intake flow is supplied from the conduit 3 to the second adsorption bed 13 via the valve 15. Preferably, the supply gas intake flow is supplied to the second suction bed 13 in the direction opposite (that is, countercurrent) to the direction in which the purge gas intake flow is supplied to the second suction bed 13 in the first purge step. To. The supply gas exhaust stream containing at least one separated component of the supply gas such as hydrogen and carbon monoxide is collected on the first output side, such as the third conduit 7. The purge gas intake flow is supplied from the conduit 5 to the first adsorption bed 11 via the valve 17, the valve 19, and the conduit 23. Preferably, the purge gas intake flow is supplied to the first adsorption bed 11 in the direction opposite (that is, countercurrent) to the direction in which the supply gas intake flow is supplied to the first adsorption bed 11 in the first supply step. To. The purge gas exhaust flow is collected from the first adsorption bed 11 on an output side different from the first output side such as the fourth conduit 9.

FIG. 2D shows device 1 in a second cleaning step performed after the second feed / purge step. In this step, the supply valve 15 and the regeneration valve 17 switch the flow direction from the previous step, but the product valve 19 does not. This process is similar to the first cleaning process, but the adsorption beds have been replaced.

The purge gas intake flow is supplied from the conduit 5 to the second adsorption bed 13 via the valve 17, the valve 15, and the conduit 21. Preferably, this flow is supplied to the adsorption bed 13 in the same direction as the supply gas intake flow in the previous two steps. The purge gas exhaust stream containing at least one component of the supply gas such as hydrogen trapped in the void volume of the second adsorption bed 13 is collected on the first output side such as the third conduit 7.

The supply gas intake flow is supplied from the conduit 3 to the first adsorption bed 11 via the valve 15. The supply gas exhaust flow containing a part of the purge gas such as air captured in the void volume of the first adsorption bed 11 is collected on an output side different from the first output side such as the fourth conduit 9. .. After that, the first supply / purge step shown in FIG. 2A is repeated. Generally, the above four steps are repeated multiple times in the same order.

It should be noted that the supply gas intake flow is preferably supplied to the first adsorption bed 11 and the second adsorption bed 13 in the same direction in the above steps. In the first and second cleaning steps, the purge gas intake stream is supplied to the first and second adsorption beds, respectively, in the same direction as the supply gas intake stream. In contrast, in the first and second supply / purge steps, the purge gas intake flow is different from the supply gas intake flow, such as in the opposite direction of the supply gas intake flow, to the first and second adsorption beds, respectively. Is supplied to.

The countercurrent (backflow) purge gas intake flow is advantageous because it is considered to reduce the amount of carbon dioxide in the hydrogen generation distribution during the purge process as compared with the parallel flow. Some water will be adsorbed near the inlet of the carbon adsorption bed during the feeding process. During the purging or regeneration process, the adsorption bed is countercurrently purged with dry air. Activated carbon is used to adsorb carbon dioxide, and activated carbon does not adsorb much water at moderately low relative humidity, so to prevent water accumulation in the adsorption bed, the regeneration purge should be up to about 30-50% relative humidity. It may be dried. During the feeding process, carbon monoxide is a product (ie, by advancing a wave of carbon dioxide moderately deep inside the adsorption bed) by efficiently using the adsorption bed to remove carbon dioxide. Pushed into (with hydrogen). The countercurrent regeneration process reduces the level of carbon dioxide in the hydrogen stream as compared to the parallel flow regeneration process. The double cleaning process maximizes the recovery of hydrogen from the hydrogen product and the elimination of air.

As described above, in the partial pressure swing adsorption method, the supply gas intake stream is not pressurized before being supplied to the first and second adsorption beds. Further, the above four steps are preferably carried out without heating the adsorption bed from the outside.

During operation, the first suction bed 11 performs the following functions. The first adsorption bed 11 receives the supply gas intake flow from the first conduit 3 in the first supply / purge step and supplies at least one separated component of the supply gas to the third conduit 7. The first adsorption bed 11 receives the purge gas intake flow from the second conduit 5 in the first cleaning step, and is a purge gas containing at least one component of the supply gas captured in the void volume of the first adsorption bed. The exhaust flow is supplied to the third conduit 7. In the second supply / purge step, the first adsorption bed 11 receives the purge gas intake flow from the second conduit 5 and outputs the purge gas exhaust flow differently from the third conduit 7 such as the fourth vessel 9. Supply to the side. Further, the first adsorption bed 11 receives the supply gas intake flow from the first conduit 3 in the second cleaning step, and supplies a part of the purge gas trapped in the void volume of the first adsorption bed. The gas exhaust flow is supplied to an output side different from the third conduit 7 such as the fourth conduit 9.

During operation, the second suction bed 13 performs the following functions. The second adsorption bed 13 receives the purge gas intake flow from the second conduit 5 in the first supply / purge step, and receives the purge gas exhaust flow on the output side different from the third conduit 7 such as the fourth conduit 9. Supply to. The second adsorption bed 13 receives the supply gas intake flow from the first conduit 3 in the first cleaning step, and is a supply gas containing a part of the purge gas trapped in the void volume of the second adsorption bed 13. The exhaust flow is supplied to an output side different from the third conduit 7 such as the fourth conduit 9. The second adsorption bed 13 receives the supply gas intake flow from the first conduit 3 in the second supply / purge step, and a third supply gas exhaust flow containing at least one separated component of the supply gas. Supply to conduit 7. Further, the second adsorption bed 13 receives the purge gas intake flow from the second conduit 5 in the second cleaning step, and at least one component of the supply gas captured in the void volume of the second adsorption bed 13. Supply the purge gas exhaust flow including

Therefore, at least most of the carbon dioxide and most of the water vapor in the supply gas intake stream is taken up by the first adsorption bed 11 and the second adsorption bed 13 in each period of the first and second supply / purge steps. Be adsorbed. The adsorbed carbon dioxide and water vapor are removed from the first and second adsorption beds by the purge gas intake stream during the respective periods of the second and first supply / purge steps. The removed carbon dioxide and water vapor are collected by the purge gas exhaust stream on the second output side during the second and first supply / purge steps.

Regeneration (ie, parsing) of the adsorption bed is CO₂Note that it involves cooling the adsorption bed as it desorbs. This is CO₂It is considered that the adsorption equilibrium of is shifted to a lower partial pressure and the regeneration is delayed. This and the increasing front velocity during regeneration (velocity front) may be taken into account when setting the flow rate of purge gas (ie, dry air). For example, the flow rate measured by measuring the volume of the intake air for regeneration may be, for example, about 1.5 times higher than the exhaust flow rate of hydrogen and carbon monoxide. By allowing the desorption of carbon dioxide during regeneration, the exhaust flow rate for regeneration is considered to exceed the intake flow rate of the supply.

The device 1 may have the following non-limiting features. The material of the adsorption bed preferably comprises activated carbon for separating hydrogen from the fuel exhaust of the fuel cell stack. For example, a 6x16 or 4x10 mesh of Calgon BPL activated carbon may be used. The adsorption beds 11 and 13 are cylindrical adsorption beds 2-12 inches in diameter and 1-6 feet long, for example 6 inches in diameter and 3 feet in length, depending on the size of the fuel cell stack and the flow of gas. It may be. The duration of the feed / purge process may exceed 1 minute and the duration of the cleaning process may be several seconds. For example, the duration of supply / purge may be 1-3 minutes (eg, 1.5 minutes) and the duration of cleaning may be 3-5 seconds (eg, 4 seconds).

The methods of the first embodiment include high hydrogen recovery (by cleaning process), high carbon dioxide separation (by cleaning and countercurrent regeneration process), high degree of air removal (by cleaning process), 30-50%. Regeneration with relatively low dryness purge gas, such as air with relative humidity, low energy requirements, high robustness (ie, easily adjustable and adaptable to changing operating conditions) It is intended to provide easy operation with few moving parts, high expandability, and low or moderate cost of capital.

Dry air for the purging step can be obtained by any suitable method. For example, dry air can be easily obtained by utilizing a temperature swing adsorption cycle using a water vapor adsorption bed such as an adsorption bed of silica gel or activated alumina. Silica gel has somewhat higher water treatment capacity than alumina. However, when it is very dry, it will crack if it comes in contact with water vapor. If this is likely to occur, a protective layer of silica gel that does not burn can be used, or activated alumina can be used.

The temperature swing adsorption cycle uses two adsorption beds (ie, adsorption beds other than adsorption beds 11 and 13 shown in FIG. 1). One adsorption bed is used in adsorption mode while the other is being regenerated (heated and cooled). The cycle process is as follows.

In the first adsorption step, 10 mol H₂Silica gel with a working capacity of O / kg can be used. In the worst case, air is saturated with water at 30 ° C. The partial pressure of water in saturated air at 30 ° C is 0.042 bar. For example, 0.28 mol / min of water must be removed to generate a dry air flow rate of 144 slpm from this moist air. At the specified working capacity, silica gel is consumed at a rate of 0.028 kg / min. An adsorption bed containing 2 kg of silica gel can remain in the stream for 72 minutes. Specific gravity of silica gel is 0.72 (45lb / ft)³(Corresponding to the bulk specific gravity), the adsorption bed dries the feed with a volume of 4300 suction beds during this time (12,000 liters of temperature-corrected wet feed is dried by the adsorption bed with a volume of 2.8 liters). Will be). The dry air is supplied to the device 1 via the conduit 5.

In the second heating step, the adsorption bed is countercurrently heated by a warm supply (eg, 80 ° C., other suitable moderately warm or hot temperature). The adsorption bed is heated after the volume of about 1000 adsorption beds has passed through it. Some more energy is required to heat metal parts as well.

In the third cooling step, the adsorption bed is cooled in parallel with the moist air supply (in the same direction as the adsorption). It takes a volume of about 800 adsorption beds to cool the adsorption beds. This deposits water at the adsorption bed inlet, exhausting some of the adsorption capacity and reducing it to the volume of about 3500 adsorption beds. While the first adsorption bed is in the adsorption process, the second adsorption bed is placed in the heating or cooling process. While the second adsorption bed is in the adsorption process, the first adsorption bed is placed in the heating or cooling process.

It should be understood that the above calculations are very conservative and approximate. The calculation is based on available regenerative air saturated with water at 30 ° C. In general, the air will be drier. Regeneration requirements for carbon adsorption beds are lenient (eg 30-50% RH). In fact, it is not necessary to dry the regenerated air on cool or dry days. Moreover, if the dryer is shut down for a short period of time, the process will not be compromised.

In a second embodiment of the invention, the device 31 operates with a countercurrent purge, but without a cleaning step. FIG. 3 shows a device 31 that utilizes a simple cycle with countercurrent purging but no cleaning. Two four-way valves 15 and 17 are used instead of three. The device 31 and the method of using the device are similar to the device 1 and method of the first embodiment, except that the first and second cleaning steps are omitted.

The advantage of countercurrent purging is that carbon dioxide is removed from the adsorption bed outlet during the supply process, resulting in higher hydrogen purity. However, without cleaning, about 5% of hydrogen is not recovered and air contaminates some hydrogen-containing products in the conduit 7.

In the third embodiment of the present invention, the device 41 operates by a parallel flow purge accompanied by a cleaning step. FIG. 4 shows a device 41 that utilizes parallel flow purging and cleaning. Device 41 also uses two four-way valves instead of three. The apparatus 41 and method of the third embodiment are, in many respects, first, except that the purge gas intake stream is supplied to the adsorption bed in the purge step in the same direction as the supply gas intake stream in the previous supply step. It is similar to device 1 and method of the embodiment. The negative side of this parallel flow cycle is the CO that remains on the adsorption bed.₂However, in the adsorption process, it is most concentrated near the output side end and contaminates the hydrogen-containing product supplied to the conduit 7 to some extent.

In the fourth embodiment of the present invention, the air purge gas is not pre-dried. In this embodiment, the device may include two or three carbon dioxide adsorption beds. Some of the three adsorption bed cycles do not require dry air. For example, a carbon adsorption bed used for carbon dioxide adsorption slowly accumulates water from both the fuel exhaust of the fuel cell stack and the wet regenerated air. Adsorption beds can be used for many cycles, although their capacity is reduced before they are fully regenerated. The adsorption bed will last longer when regenerated countercurrently than when regenerated concurrently. This is because the water accumulated during the supply process is partially removed by the reclaimed air and vice versa. In any case, the adsorption bed accumulates water over time.

In this embodiment, as in the first embodiment, three adsorption beds are used in two active adsorption and regeneration cycles, but the third adsorption bed is by thermal swing regeneration or drying. Regenerated more thoroughly by gas parsing.

Further, if the atmosphere is reasonably dry (ie, RH <50% at 30 ° C.), a partial pressure adsorption cycle with two adsorption beds can be used with exactly the same configuration as in the first embodiment. The purge gas does not deposit a large amount of water on the carbon, but flushes the air countercurrently during regeneration, thereby removing the adsorbed water from the fuel emission supply of the fuel cell stack. Therefore, if dry air is available from the atmosphere, no separate air drying step is required.

The fifth and sixth embodiments of the present invention exemplify how the adsorption devices of the first to fourth embodiments are used together with a fuel cell system such as a solid electrolyte fuel cell system. Note that other fuel cell systems may also be used.

In the system of the fifth embodiment, a fuel humidifier is used to humidify the fuel intake stream supplied to the fuel cell stack. In the system of the sixth embodiment, the fuel humidifier may be omitted. A portion of the fuel discharge stream of the fuel cell stack is directly recirculated to the fuel intake stream to humidify the fuel intake stream. Another portion of the fuel discharge stream of the fuel cell stack is fed to the adsorption device of any of the first four embodiments, and then the separated hydrogen and carbon monoxide are fed to the fuel intake stream.

FIG. 5 shows the fuel cell system 100 of the fifth embodiment. System 100 is outlined to show one solid oxide fuel cell in a stack containing a ceramic electrolyte such as yttria-stabilized zirconia (YSZ), an anode electrode such as nickel-YSZ cermet and a cathode electrode such as lanthanum strontium manganate. Includes a fuel cell stack 101, such as a solid oxide fuel cell stack (shown).

The system further includes a partial pressure swing adsorption (PPSA) unit 1 of any of the first four embodiments comprising multiple adsorption beds (not shown for clarity). PPSA unit 1 acts as a regenerative dryer and carbon dioxide scrubber (carbon dioxide remover).

The system 100 further includes a first conduit 3 that operably connects the fuel outlet 103 of the fuel cell stack 101 to the first inlet 2 of the partial pressure swing suction unit 1. For example, the first inlet 2 may include an inlet to one of the supply valve 15 and / or the suction beds 11, 13 as shown in FIG. System 100 further includes a second conduit 5 that operably connects a purge gas source, such as a dry air source or air source 6, to a second inlet 4 of the partial pressure swing adsorption unit 1. The purge gas source 6 includes an air blower or a compressor, and may optionally include a plurality of temperature swing cycle adsorption beds.

The system also includes a third conduit 7 that connects the exhaust port 8 of the partial pressure swing suction unit 1 to the fuel intake port 105 of the fuel cell stack 101. It is preferable that the system 100 does not have a compressor that compresses the fuel discharge flow of the fuel cell stack supplied to the partial pressure swing adsorption unit 1 during operation.

System 100 also includes a fourth conduit 9 that removes emissions from unit 1. The conduit 9 may be connected to a catalyst burner 107 or an air vent.

System 100 also includes a blower or heat driven compressor 109. The blower or heat-driven compressor includes an inlet operably connected to the partial pressure swing absorption unit 1 and an outlet operably connected to the fuel intake 105 of the fuel cell stack 101. For example, conduit 7 connects a blower or compressor 109 to unit 1. During operation, the blower or compressor 109 controlsably supplies the desired amounts of hydrogen and carbon monoxide separated from the fuel discharge stream of the fuel cell stack to the fuel intake stream of the fuel cell stack. Preferably, device 109 supplies hydrogen and carbon monoxide to the fuel inlet conduit 111 operably connected to the fuel intake 105 of the fuel cell stack 101. Alternatively, device 109 supplies hydrogen and carbon monoxide directly to the fuel intake 105 of the fuel cell stack 101.

System 100 also has a condenser 113 and a water separation with an inlet operably connected to the fuel outlet 103 of the fuel cell stack and an outlet operably connected to the inlet 2 of the partial pressure swing adsorption unit 1. Includes vessel 115 and. The condenser 113 and the water separator 115 may constitute a single device for condensing and separating water from the fuel discharge stream, or may include separate devices. For example, the condenser 113 may include a heat exchanger in which the fuel discharge stream is cooled by a cooling countercurrent or parallel air stream to condense water. The air flow may include an air intake flow to the fuel cell stack 101, or may include a separate cooling air flow. The water separator 115 may include a water tank that collects the separated water. The water separator 115 may have a drain pipe 117 that is used to remove the collected water and / or to reuse the collected water.

System 100 further has a first inlet operably connected to a hydrocarbon fuel source, such as a hydrocarbon fuel inlet conduit 111, and a second inlet operably connected to a fuel cell stack fuel outlet 103. Includes a fuel humidifier 119 having a first outlet operably connected to the fuel inlet 105 of the fuel cell stack, a condenser 113 and a second outlet operably connected to the water separator 115. During operation, the fuel humidifier 119 uses the water vapor contained in the fuel discharge stream of the fuel cell stack to humidify the hydrocarbon fuel intake stream from the conduit 111 containing the recycled hydrogen and carbon monoxide. Fuel humidifiers are, for example, Nafion® membrane humidifiers, as described in US Pat. No. 6,106,964 and US Patent Application No. 10 / 368,425, both of which are incorporated herein by reference in their entirety. Such as polymer film humidifiers, enthalpy wheels, or multiple water adsorption beds may be included. For example, one suitable type of humidifier is Nafion®-based, Perma Pure, which transfers water vapor and enthalpy. Includes permeable membranes available from LLC. The humidifier passively transfers water vapor and enthalpy from the fuel discharge stream to the fuel intake stream to provide a ratio of water vapor to carbon in the fuel intake stream from 2 to 2.5. The temperature of the fuel intake stream may be raised to about 80-90 ° C in the humidifier.

System 100 also includes a reheat heat exchanger 121 that exchanges heat between the stack fuel discharge stream and the hydrocarbon fuel intake stream supplied by the humidifier 119. The heat exchanger helps raise the temperature of the fuel intake stream, allows the fuel drainage stream to be further cooled in the condenser, and lowers the temperature of the fuel drainage stream so as not to damage the humidifier.

If the fuel cell is an external fuel reforming type battery, the system 100 includes a fuel reformer 123. The reformer 123 reforms the hydrocarbon fuel intake stream into a fuel stream containing hydrogen and carbon monoxide. The fuel flow is then supplied to stack 101. The combustor 123 generates heat within the fuel cell stack 101 as described in U.S. Patent Application No. 11 / 002,681 filed December 2, 2004, which is incorporated herein by reference in its entirety. And / or by the heat generated in the burner / combustor as an option, it can be heated radiatively, convectively, and / or conductively. Alternatively, if the stack 101 includes an internal reforming type battery where reforming occurs primarily within the stack's fuel cell, the external reformer 123 may be omitted.

Optionally, the system 100 also includes an air preheater heat exchanger 125. The heat exchanger 125 uses the heat of the fuel exhaust of the fuel cell stack to heat the air intake stream supplied to the fuel cell stack 101. If desired, the heat exchanger 125 may be omitted.

System 100 also preferably includes air heat exchanger 127. The heat exchanger 127 also uses the heat of the exhaust air (ie, oxidant or cathode) of the fuel cell stack to heat the air intake stream supplied to the fuel cell stack 101. If the preheater heat exchanger 125 is omitted, the air intake stream is supplied directly to the heat exchanger 127 by a blower or other air suction device.

The system 100 of the fifth embodiment operates as follows. The fuel intake stream is supplied to the fuel cell stack 101 via the fuel introduction conduit 111. The fuel may be any suitable fuel, such as, but not limited to, a natural gas containing methane with methane, hydrogen and other gases, a hydrocarbon fuel such as propane or other biogas, or one. Carbon fuel such as carbon oxide, oxygenated carbon-containing gas such as methanol, water vapor, H₂Other carbon-containing gases, including hydrogen-containing gases such as gases or mixtures thereof, and the like. The mixture may be, for example, a synthetic gas obtained by reforming coal or natural gas.

The fuel intake stream passes through the humidifier 119, where humidity is added to the fuel intake stream. The humidified fuel intake stream then passes through the fuel heat exchanger 121, where the humidified fuel intake stream is heated by the fuel discharge stream of the fuel cell stack. The heated and humidified fuel intake stream is then preferably supplied to an external reformer, the reformer 123. For example, reformer 123 may include the reformer described in US Patent Application No. 11 / 002,681, filed December 2, 2004, which is incorporated herein by reference in its entirety. The fuel reformer 123 partially or wholly reforms the hydrocarbon fuel to contain carbon and free hydrogen (free hydrogen, free). It may be any suitable device capable of forming a fuel containing hydrogen). For example, the fuel reformer 123 may include a catalyst-coated passage in which a humidified biogas, such as natural gas, is reformed via a steam-methane reforming reaction to free hydrogen (free hydrogen). Free hydrogen), carbon monoxide, carbon dioxide, steam and optionally the remaining amount of unreformed biogas. Free hydrogen and carbon monoxide are then supplied to the fuel (ie, anode) inlet 105 of the fuel cell stack 101. Therefore, with respect to the fuel intake flow, the humidifier 119 is located upstream of the heat exchanger 121, the heat exchanger 121 is located upstream of the reformer 123, and the reformer 123 is located upstream of the stack 101.

Air or other oxygen-containing gas (ie, oxidant) intake stream is preferably supplied to stack 101 via heat exchanger 127, where air (ie, cathode) is discharged from the fuel cell stack. Heated by the stream. If desired, the air intake stream may pass through the condenser 113 and / or the air preheat exchanger 125 to further raise the temperature of the air before it is supplied into the stack 101.

When fuel and air are supplied to the fuel cell stack 101, the stack 101 operates to generate an electrical and hydrogen-containing fuel discharge stream. The fuel discharge flow (that is, the anode discharge flow of the stack) is supplied to the partial pressure swing suction unit 1 from the fuel discharge port 103 of the stack. At least a portion of the hydrogen contained in the fuel discharge stream is separated within the unit 1 using partial pressure swing adsorption. Next, the hydrogen separated from the fuel discharge stream in the unit 1 is returned to the fuel intake stream. Preferably, the hydrogen is returned to the fuel introduction conduit 111 upstream of the humidifier 119.

The fuel discharge flow is supplied to unit 1 as follows. The fuel discharge stream contains some unreacted hydrocarbon gases such as hydrogen, steam, carbon monoxide, carbon dioxide, methane, other reaction by-products and impurities. For example, fuel exhaust has a flow rate of 160-225 slpm (eg about 186-about 196 slpm) and about 45-about 55% (eg about 48-50%) hydrogen, about 40-about 50%. It may contain carbon dioxide (eg, about 45-47%), about 2-about 4% (eg, about 3%) water, and about 1% -about 2% carbon monoxide.

This exhaust stream is first supplied to the heat exchanger 121, where the temperature is preferably lowered to less than 200 ° C., at which time the temperature of the fuel intake stream is raised. If an air preheater heat exchanger 125 is present, the fuel discharge stream is supplied through the heat exchanger 125 to further reduce its temperature, at which time the temperature of the air intake stream is raised. The temperature of the fuel discharge stream can be reduced to, for example, 90-110 ° C.

Next, the fuel discharge flow is supplied to the fuel humidifier 119, where a part of the water vapor in the fuel discharge flow is transferred to the fuel intake flow to humidify the fuel intake flow. The fuel effluent is then supplied to the capacitor 113, where it is further cooled to condense additional water vapor from the fuel effluent. The fuel discharge stream is cooled in the capacitor by the air intake stream of the fuel cell stack, by a different air intake stream, or by another coolant stream. The water condensed from the fuel discharge stream is collected in the water separator 115 in a liquid state. Water is discharged from the separator 115 via conduit 117 and then drained or reused.

Next, the remaining fuel exhaust flow gas is supplied as a supply gas intake flow from the separator 115 to the introduction port 2 of the partial pressure swing adsorption unit 1 via the conduit 3. Further, a purge gas intake stream such as a dry air stream is supplied from the blower or compressor 6 to the unit 1 and to the inlet 4 via the conduit 5. If desired, the air stream may be dried using an additional adsorption bed in the temperature swing adsorption cycle before being fed to the adsorption beds 11 and 13 of the unit 1. In this case, the heated air used in the temperature swing adsorption cycle to dry the silica gel or alumina in the adsorption bed may be removed from the unit 1 via the ventilation conduit 139.

Thus, the fuel effluent includes hydrogen, carbon monoxide, water vapor, carbon dioxide, potential impurities and unreacted hydrocarbon fuels. During the separation step in Unit 1, at least most of the carbon dioxide and much of the water vapor in the fuel effluent is adsorbed on at least one of the adsorption beds 11 and 13 and hydrogen and carbon monoxide in the fuel effluent. At least most of the can pass through at least one adsorption bed. Specifically, the unpressurized fuel discharge flow is supplied to the first suction bed 11 and remains in the fuel discharge flow in the first suction bed 11 until the first suction bed 11 is saturated. At least most of the carbon dioxide is adsorbed. At this time, the second adsorption bed 13 is regenerated and adsorbed carbon dioxide and the adsorbed carbon dioxide by supplying air having a relative humidity of 50% or less at about 30 ° C so as to pass through the second adsorption bed 13. Water vapor is desorbed. After the first adsorption bed 11 is saturated with carbon dioxide, the unpressurized fuel discharge stream is supplied into the second adsorption bed 13 and in the second adsorption bed until the second adsorption bed is saturated. At least most of the carbon dioxide remaining in the fuel discharge stream is adsorbed. At this time, air having a relative humidity of 50% or less at about 30 ° C is supplied so as to pass through the first adsorption bed, so that the first adsorption bed is regenerated and the adsorbed carbon dioxide and water vapor are removed. Release.

The hydrogen and carbon monoxide separated from the fuel discharge stream (ie, the supply gas exhaust stream) are then removed from the unit 1 via the exhaust port 8 and the conduit 7, and the hydrocarbon fuel intake stream of the fuel introduction conduit 111. Is supplied to. Preferably, a blower or compressor 109 arranged in fluid communication with the conduit 7 is used to controlably supply the desired amounts of hydrogen and carbon monoxide from the fuel discharge stream to the fuel intake stream. The blower or compressor 109 may be operated by a computer or operator to provide a controllable amount of hydrogen and carbon monoxide to the fuel intake stream, and this amount may be varied based on any suitable parameter. .. The parameters are i) the detected or observed state of the system 100 (ie, the change in the operating state of the system that requires a change in the amount of hydrogen or CO in the fuel intake stream), ii) the hydrogen or CO in the fuel intake stream. The user's electricity demand changes, such as previous calculations provided to the computer or known state of the operator, and / or iii) stacks of electricity that require temporary adjustment. The operating parameters of the stack 101 include "desired future changes, current changes, or changes in the near past, etc. Therefore, the blower or compressor shall fuel intake based on the criteria described above and / or other criteria. The amount of hydrogen and carbon monoxide supplied to the stream may be changed in a controllable manner. Hydrogen and carbon monoxide are cooled to below 200 ° C, allowing hydrogen and carbon monoxide to be controlled in conduit 111. A low temperature blower can be used to supply.

The purge gas exhaust stream contains trace amounts of hydrogen and / or hydrocarbon gas trapped within the void volume of the adsorption bed. In other words, some of the trapped hydrogen or hydrocarbon gas cannot be removed into the conduit 7 by the cleaning process. Therefore, it is preferable that the conduit 9 supplies the purge gas exhaust flow to the burner 107. The air exhaust flow of the stack 101 is also supplied to the burner 107 via the heat exchanger 127. Then, the hydrogen or hydrocarbon gas remaining in the purge gas exhaust stream is burned in the burner in order to avoid polluting the environment. The heat from the burner 107 may be used to heat the reformer 123, or is supplied to other parts of the system 100 or to devices that consume heat outside the system 100, such as a building heating system. May be done.

Thus, with respect to the fuel discharge flow, the heat exchanger 121 is located upstream of the heat exchanger 125, the heat exchanger 125 is located upstream of the humidifier 119, and the humidifier 119 is of the compressor 113 and the water separator 115. Located upstream, the water separator 115 is located upstream of PPSA unit 1, PPSA unit 1 is located upstream of the blower or compressor 109, and the blower or compressor 109 is located upstream of the fuel introduction conduit 111.

FIG. 6 shows a system 200 according to a sixth embodiment of the present invention. The system 200 is similar to the system 100 and contains a large number of components in common. Those components that are common to both systems 100 and 200 are given the same reference numerals in FIGS. 5 and 6 and are not further described.

One difference between the systems 100 and 200 is that the system 200 does not necessarily have a humidifier 119, if not necessarily. Instead, some of the water vapor-containing stack fuel discharge stream is recirculated directly to the stack fuel intake stream. The water vapor in the fuel discharge stream is sufficient to humidify the fuel intake stream.

The system 200 includes a fluid splitter device (fluid distributor) 201, such as a multi-directional valve (eg, a three-way valve) or another fluid diversion device controlled by a computer or operator. The device 201 includes an inlet 203 operably connected to the fuel outlet 103 of the fuel cell stack, a first outlet 205 operably connected to the condenser 113 and the water separator 115, and the fuel in the fuel cell stack. Includes a second outlet 207 operably connected to the inlet 105. For example, the second outlet 207 may be operably connected to a fuel introduction conduit 111 operably connected to the inlet 105. However, the second discharge port 207 may supply a part of the fuel discharge flow to the fuel intake flow further downstream.

Preferably, the system 200 includes a second blower or compressor 209 that supplies the fuel discharge stream to the fuel intake stream. Specifically, the exhaust port 207 of the valve 201 is operably connected to the intake port of the blower or compressor 209, and the exhaust port of the blower or compressor 209 is connected to the hydrocarbon fuel introduction conduit 111. During operation, the blower or compressor 209 controlsably supplies a desired amount of fuel discharge flow from the fuel cell stack to the fuel intake flow from the fuel cell stack.

The method of operating the system 200 is similar to the method of operating the system 100. One difference is that the fuel discharge stream is separated by device 201 into at least two streams. The first fuel discharge stream is recirculated to the fuel intake stream, and the second flow is directed to PPSA unit 1, where at least some of the hydrogen and carbon monoxide contained in the second fuel discharge stream is directed. Separated using partial pressure swing adsorption. The hydrogen and carbon monoxide separated from the second fuel discharge stream are then supplied to the fuel intake stream. For example, 50-70% of the fuel discharge stream (eg, about 60%) may be supplied to the second blower or compressor 209, and the rest may be supplied to PPSA unit 1.

Preferably, the fuel discharge stream is first supplied through the heat exchangers 121 and 125 before being supplied to the valve 201. The fuel discharge stream is cooled in the heat exchanger 125 to 200 ° C or less (such as 90-180 ° C) before being supplied to valve 201 where it is separated into two streams. This allows the cold blower 209 to be used to controlfully recirculate the desired amount of the first fuel discharge stream into the fuel intake stream. This is because such blowers are adapted to move gas streams with temperatures below 200 ° C.

The second blower or compressor 209 may be controlled by a computer or operator, or the amount of fuel discharge stream supplied to the fuel intake stream may be varied depending on the conditions described above with respect to the fifth embodiment. Good. Further, the second blower or compressor may be operated in step with the first blower or compressor 109. Therefore, the operator or computer may use any suitable criteria, such as those described above for the fifth embodiment, for the hydrogen and carbon monoxide supplied to the fuel intake stream by the first blower or compressor 109. The amount and the amount of fuel discharge flow supplied to the fuel intake flow by the second blower or compressor 209 can be changed individually. In addition, the computer or operator can use the amount of hydrogen and carbon monoxide supplied to the fuel intake stream by the first blower or compressor 109 and the fuel supplied to the fuel intake stream by the second blower or compressor 209. Both amounts can be optimized based on the criteria described above, taking into account both the amount of effluent and.

In a seventh embodiment of the invention, instead of PPSA unit 1, a temperature swing adsorption (TSA) unit is used to separate hydrogen from the fuel discharge stream. The TSA unit also does not require the supply gas to be pressurized.

The TSA unit also includes multiple adsorption beds of material that preferentially adsorb carbon dioxide and water vapor over hydrogen and carbon monoxide. The fuel effluent is fed to at least one first adsorption bed maintained at room temperature or other low temperature, from which most of the carbon dioxide and water vapor are adsorbed. When the first adsorption bed is saturated with carbon dioxide and water vapor, the fuel effluent is switched to at least one second adsorption bed. Next, by raising the temperature of the first adsorption bed, the first adsorption bed is purged and the adsorbed carbon dioxide and water vapor are released. For example, the first adsorption bed may be heated by the heat supplied by the fuel cell stack, such as by supplying a high temperature stack cathode exhaust that exchanges heat with the first adsorption bed. After parsing, the first adsorption bed is cooled by heat exchange with the ambient air. The cycle continues with continuous fuel recovery and circulation with multiple adsorption beds. This embodiment is also susceptible to carbon dioxide sequestration.

Rather than supplying air for heat exchange with the adsorption bed (ie, adjacent to the adsorption bed), the hot cathode exhaust may be directed directly into the adsorption bed to release carbon dioxide and water vapor. .. The cold ambient air is then passed directly through the adsorption bed, which is conditioned for the next cycle. If desired, a small amount of nitrogen may be purged through the adsorption bed before and after the adsorption bed is readjusted to further adsorb carbon dioxide and water. Nitrogen is obtained from a small temperature swing adsorber that uses air as the working fluid.

If desired, TSA effluent, such as effluent containing carbon dioxide and water vapor, may be discharged or removed via a vacuum pump after the purge gas has been shut down. Vacuum removes more residual carbon dioxide and water (a process similar to pressure swing adsorption, commonly referred to as vacuum swing adsorption), thereby being achieved utilizing cooling air or heat exchange. A cheaper and faster means of cooling the adsorption bed may be provided. The use of vacuum is also susceptible to carbon dioxide sequestration.

By recirculating at least a portion of hydrogen from the fuel discharge (ie, tail) gas stream to the fuel intake stream, it is believed that highly efficient operation of the fuel cell system can be obtained. Furthermore, the fuel usage efficiency as a whole is also improved. If the fuel utilization per pass is about 75% (ie, about 75% of the fuel is used each time it passes through the stack), then in the methods of the fifth and sixth embodiments, electricity The efficiency (ie, AC electrical efficiency) is between about 50% and about 60%, for example between about 54% and about 60%. The utilization rate per pass is about 75%, and if about 60% to about 85% (for example, about 80%) of fuel exhaust gas hydrogen is recycled and returned to the fuel cell stack, about 88 An effective fuel utilization rate of about 95% can be obtained from%. Higher efficiency can be obtained by increasing the fuel utilization rate per pass to more than 75%, for example 76-80%, and using adsorption to eliminate up to about 95% of carbon dioxide. In the steady state, in the methods of the fifth and sixth embodiments, if steam methane reforming is used to generate the supply gas to the fuel cell, it is not necessary to generate steam. The fuel discharge stream contains enough water vapor to humidify the fuel intake stream into the stack to a vapor-carbon ratio of 2 to 2.5. It improves net fuel utilization and eliminates the need for heat to generate steam, thus improving overall electrical efficiency. On the other hand, if hydrogen is not recycled, the AC electricity efficiency is about 45% even if the fuel utilization rate in the stack is about 75% to 80%.

The fuel cell system described herein may optionally have other embodiments and configurations. For example, U.S. Patent Application No. 10 / 300,021 filed November 20, 2002, U.S. Patent Application No. 60 / 461,190 filed April 9, 2003, all of which are incorporated herein by reference. , And other components may be added as desired, as described in US Patent Application No. 10 / 446,704 filed May 29, 2003. Further, any system element or method step described in any embodiment of the present specification and / or any system element or method step shown in any drawing of the present specification may be described in the other described above. It should be understood that it can be used even if it is not explicitly stated in the system and / or method of the appropriate embodiment.

The above description of the present invention is provided for purposes of illustration and description. This description is not intended to be comprehensive, nor is it intended to limit the invention to the disclosed form. Modifications and modifications are possible in the light of the teachings described above, or modifications and modifications may be obtained by practicing the present invention. The above description has been selected to illustrate the principles of the invention and its practical applications. The scope of the present invention shall be defined by the appended claims and their equivalents.

<figref num="1">It is the schematic of the partial pressure swing adsorption system of embodiment of this invention.</figref><figref num="2A">It is the schematic of the partial pressure swing adsorption system of embodiment of this invention.</figref><figref num="2B">It is the schematic of the partial pressure swing adsorption system of embodiment of this invention.</figref><figref num="2C">It is the schematic of the partial pressure swing adsorption system of embodiment of this invention.</figref><figref num="2D">It is the schematic of the partial pressure swing adsorption system of embodiment of this invention.</figref><figref num="3">It is the schematic of the partial pressure swing adsorption system of embodiment of this invention.</figref><figref num="4">It is the schematic of the partial pressure swing adsorption system of embodiment of this invention.</figref><figref num="5">It is the schematic of the fuel cell system of embodiment of this invention which incorporates a partial pressure swing adsorption system.</figref><figref num="6">It is the schematic of the fuel cell system of embodiment of this invention which incorporates a partial pressure swing adsorption system.</figref>