Fuel cell system for separating hydrogen from anode exhaust gas

Abstract

In a fuel cell system having an HT-PEM fuel cell (2), hydrogen is separated from an anode off-gas and recycled into the anode in order to improve efficiency. Instead of combusting the hydrogen in a reformer-heater, the reformer is electrically heated or heated by using a heat pump (12). Separation of H2 from the anode off-gas provides an option for collecting remaining CO2 after condensing water from the anode off-gas.

Description

Technical Field

[0001] The present invention relates to a fuel cell system, which includes a hydrogen separator for separating hydrogen H2 from anode exhaust gas and recycling the separated H2 gas back to the anode. Specifically, the present invention relates to a system as described in the preamble of the independent claims, its use, and its method of operation. Background Art

[0002] There are various options for feeding hydrogen, H2, or hydrocarbons to a fuel cell, including pressurized H2, methane, or alcohols such as methanol or ethanol. Typical gaseous fuels for fuel cells include ethane, propane, and natural gas. The advantage of alcohol fuels for fuel cells is that the existing liquid fuel infrastructure for diesel and gasoline can be largely reused, which also includes transporting the fuel to filling stations and storing the fuel in vehicles.

[0003] When methane or alcohols are used as fuels, they must be converted into H2 gas. The corresponding reforming reaction in a catalytic reformer is endothermic and requires energy. To supply this energy by heating the reformer, a reformer-heater is provided in the fuel cell system. Typically, the reformer-heater is a burner that burns fuel to provide heat energy. The term burner is common in the technical field, regardless of whether the burner uses a traditional flame or catalytic consumption of the fuel to generate the necessary heat energy. As an option, the burner consumes excess H2 gas from the anode exhaust gas of the fuel cell. When methanol is used, the temperature for reforming is typically 250 °C. The reformer heater adds heat energy at a rate sufficient to sustain the reforming process, specifically 49 kJ / mol, for the reaction in which methanol and water are reformed into CO2 and H2.

[0004] The reforming of the fuel produces syngas, which is a mixture of gases including H2 gas, carbon dioxide (CO2), carbon monoxide (CO), and some residue of water (H2O). For fuel cells with a polymer electrolyte membrane (PEM) at low temperatures (below 100 °C), which is why this type of fuel cell is called an LT-PEM fuel cell or simply a PEM fuel cell, the catalyst is sensitive to CO gas at these temperatures, such that before the syngas enters the fuel cell, the CO gas is converted into CO2 in a shift reactor. For typical high-temperature PEM fuel cells (HT-PEM fuel cells operating at higher temperatures (above 120 °C and even up to 200 °C)), the system has a stronger resistance to CO gas, and the shift reactor and other gas purification processes for this gas can be avoided.

[0005] As fuel cells become increasingly attractive for power production, especially in transportation such as electric drive vehicles and ships, there is a constant desire to increase the efficiency of power production, and even an improvement of just about one percent is attractive. Therefore, there is a need for improvements in the technical field.

[0006] For example, in US Patent Publication US2010 / 0266923A1, an electrochemical hydrogen separator is disclosed that is used to separate H2 gas from fuel cell anode exhaust gas and reintroduce the gas into the fuel cell in order to optimize the efficiency of the fuel cell. Monitoring the performance of the hydrogen separation device gives an indication of the performance of the fuel cell system. When H2 gas is separated from the anode exhaust stream and recycled to the fuel cell anode, it is consumed as fuel for a reformer-heater. As disclosed in US2010 / 0266923A1, this is not a problem for SOFC cells operating in the temperature range of 750°C - 950°C, because the excess heat of the fuel cell can be used not only to heat the electrochemical H2 separator (as shown in this disclosure), but also to heat the reformer.

[0007] However, for fuel cells operating at lower temperatures, fuel has traditionally been used to heat the reformer, such that H2 separation and reintroduction to the anode do not offer any significant efficiency advantage.

[0008] This consideration is supported by a study of the system disclosed in German patent application DE102013009244A1, where a membrane separator is used to separate H2 from the anode gas in order to capture the remaining CO2 in a storage tank after removing water by condensation. In this reference, a membrane is used to transfer H2 in an air stream to an H2O stream in order to provide a fuel air stream rich in H2 for a reformer-heater. This follows the traditional method of using H2 in a cycle to introduce it into a reformer-burner (either by flame or by catalytic combustion) in order to heat the reformer. As an additional option, DE102013009244A1 discloses the H2 enrichment of a methane air stream entering a catalytic reformer. However, in a more careful assessment, this does not seem to be the best option, since it can be expected that an elevated H2 level in the air stream at the inlet of the reformer will not increase the overall efficiency of reforming, but rather will decrease it, since the H2 concentration has been shifted to a rather high concentration level from the start in the reformer, such that the additional H2 production capacity in the reformer is not optimized up to the maximum concentration of H2 in the gas. Thus, it can be understood from the disclosure in DE102013009244A1 that the separation of H2 from the anode exhaust gas is not motivated by the overall goal of increasing the efficiency of the fuel cell system, but rather by the motivation to find some meaningful use for the H2 gas (which is precisely a by-product) separated from the anode exhaust gas before capturing carbon from the exhaust stream, and carbon capture is the main goal of DE102013009244A1.

[0009] In the article “Electrochemical hydrogen pumping using a high-temperature polybenzimidazole (PBI) membrane” published by Perry et al. in Journal of Power Sources 177 (2008), pages 478–484, the use of a high-temperature (>100 °C) polybenzimidazole (PBI) membrane for electrochemical hydrogen separation from a mixture of gases including N2, H2, CO, and CO2 is disclosed. Specifically, the electrochemical pump operates at 160 °C without external humidification, which is approximately 1.2 times the temperature required for pure hydrogen stoichiometry. It should be noted that such a hydrogen pump operates at a temperature similar to the coolant temperature of an HT-PEM fuel cell, while the coolant from an LT-PEM fuel cell (such as that disclosed in the above DE102013009244A) would not be able to deliver a high enough temperature.

[0010] For a fuel cell system in which a fuel cell operates at a temperature below the temperature required for reforming of the fuel, it would be useful to separate H2 from the anode exhaust gas and recycle the H2 back to the fuel cell. However, if on the one hand a method different from a burner can be found to heat the reformer, and on the other hand, the efficiency of such an arrangement would be higher than that of a comparable system in which H2 is burned in a reformer heater. SUMMARY OF THE INVENTION

[0011] The object of the present invention is to provide an improvement in technology. Specifically, the object is to provide a more efficient HT-PEM fuel cell system including a reformer. This object and other advantages are achieved by the fuel cell system and its method of operation described below and in the claims.

[0012] Briefly, in a fuel cell system having an HT-PEM fuel cell, hydrogen is separated from the anode exhaust gas and recycled to the anode in order to increase efficiency. Instead of burning hydrogen or fuel in a reformer-heater, the reformer is heated by an electrically driven reformer-heater (such as an electric heater or an electrically driven heat pump system). Separating H2 from the anode exhaust gas provides the option of collecting the remaining CO2 after condensing water.

[0013] The details are explained below.

[0014] It is common practice to provide an HT-PEM fuel cell, typically as part of a fuel cell stack. The fuel cell has a membrane and an anode side on one side of the membrane and a cathode side on the opposite side of the membrane. Hereinafter, the short terms anode and cathode will be used for the fuel cell.

[0015] The fuel cell system includes a fuel supplier for supplying an alcohol (such as ethanol but especially methanol) to the reformer after evaporation (usually after mixing with water) such that after reforming of the fuel, H2 gas can be fed to the fuel cell. Catalytic reforming of the fuel produces not only H2 but also other gaseous by-products such as CO2, water, CO. As discussed above, for an HT-PEM fuel cell, removal of CO is generally not necessary.

[0016] The anode of the fuel cell has an inlet that is fluidly connected to the reformate outlet via a syngas pipe and receives syngas from the reformer for reaction in the fuel cell; and the cathode receives oxygen, for example as part of air. In an HT-PEM fuel cell, hydrogen ions cross the ion-conducting membrane from the anode side to the cathode side and water is formed in the cathode. The water leaves the cathode as vapor together with other gaseous components (such as nitrogen from the supplied air).

[0017] The anode consumes a larger first portion of the received H2 to generate electricity, while a smaller second portion is released in the exhaust gas from the anode.

[0018] The operating temperature of the HT-PEM fuel cell is in the range of 120°C - 200°C, typically in the range of 150°C - 180°C. The operating temperature is lower than the minimum temperature required for catalytic reforming of the fuel. For ethanol, the minimum temperature is higher than 400°C, and for methanol, the minimum temperature is higher than 200°C. Typically, for methanol, the predetermined reformer temperature T ref is in the range of 250°C - 300°C, and the predetermined reformer temperature is relatively high.

[0019] Instead of burning H2 and / or fuel in a reformer burner according to the prior art, the reformer - heater of the reformer is electrically driven. For example, the reformer heater includes an electric heater, where electric power is used to heat a heating element by an electric current passing through the heating element. Alternatively, the reformer heater includes an electrically driven heat pump. The latter has been proven to have special advantages, as explained below.

[0020] The result of using an electrically driven reformer - heater is that the reformer burner does not require H2 gas and other fuels, and the H2 gas can be captured from the anode exhaust gas and recycled into the anode, thereby optimizing the performance of the system.

[0021] Therefore, for separation, a hydrogen separator is connected to the downstream side of the anode to receive the anode exhaust gas and separate H2 gas from the anode exhaust gas. The hydrogen separator is connected on its downstream side to a syngas pipeline extending between the downstream side of the reformer and the upstream side of the anode. In this way, the H2 separated from the anode exhaust gas can be fed back into the anode after being mixed with the syngas from the reformer.

[0022] Different types of H2 separators can be used, such as those involving pressure swing adsorption technology, amine adsorption, and electrochemical separation. The latter is particularly advantageous and will be discussed in more detail below.

[0023] In this regard, a comparison should be made with the above - mentioned reference DE102013009244A1. For this comparison, it is observed that Figure 3 of DE102013009244A1 illustrates the only example of directly recycling H2 into the anode. However, contrary to the system described herein, the anode in it does not receive syngas. Instead, in DE102013009244A1, the recycled H2O vapor receives additional H2 from the syngas together with the recycled H2 across an H2 separation membrane. After the resulting H2 - rich recycled vapor is split into corresponding separate pipelines, it is used not only to feed the anode but also to feed the reformer - burner. This is a different system from the one described herein and has different functions.

[0024] In contrast, in the HT-PEM system described herein that utilizes an electrically driven reformer-heater in place of a reformer-burner, the H2 separator acts only on the anode exhaust gas and not on the syngas from the reformer, which is in contrast to DE102013009244A1. Accordingly, the required capacity of the H2 separator in the system described herein can be designed to be much smaller than the H2 membrane separator in DE102013009244A1. This is another advantage over DE102013009244A1.

[0025] Compared to, for example, the LT-PEM fuel cell disclosed in the above-mentioned reference DE102013009244A1, a high concentration of H2O vapor is not required in the gas supply to the anode of the HT-PEM fuel cell. Accordingly, the principle of using a recycled H2O vapor stream on one side of the H2 separation membrane to force H2 transport through the H2 separation membrane in DE102013009244A1 does not appear to be practical for the HT-PEM fuel cell system, and even a high concentration of vapor is not desirable as it may even have an adverse effect on the function of the HT-PEM fuel cell, particularly the catalysts used therein.

[0026] In contrast, it has been found that the electrochemical separation of hydrogen is better than the membrane separation system of DE102013009244A1.

[0027] As an option for the electrochemical separation of hydrogen, a hydrogen pump can be used as the H2 separator, the type of which is disclosed in the article “Electrochemical hydrogen pumping using a high-temperature polybenzimidazole (PBI) membrane” by Perry et al. in Journal of Power Sources, Vol. 177 (2008), pp. 478–484 and the references therein. As already mentioned in the introduction, this article discloses the electrochemical hydrogen separation from a gas mixture comprising N2, H2, CO and CO2 using a high-temperature (>100 °C) polybenzimidazole (PBI) membrane. Specifically, the electrochemical pump operates at 160 °C without external humidification, which is approximately 1.2 times the temperature of the stoichiometric requirement for pure hydrogen. Operating the hydrogen pump over a wide range of hydrogen flow rates requires a relatively low voltage (less than 1 V).

[0028] It should be noted that such a hydrogen pump operates at a temperature of 160 °C, which is similar to the coolant temperature of an HT-PEM fuel cell, while the coolant from an LT-PEM fuel cell (such as that disclosed in DE102013009244A above) will be below 100 °C and thus not able to deliver a high enough temperature.

[0029] Compared to the passive membranes in DE102013009244A, a significant advantage of electrochemical H2 separation is the possibility of monitoring the performance of the H2 separator (in particular the power consumption, which can give an indication of the performance of the fuel cell system). In some embodiments of the present invention described herein, such monitoring of the performance of the fuel cell system is carried out. For example, H2 generation can be monitored and the fuel feed λ value determined.

[0030] H2 is separated from the anode exhaust gas by the H2 separator, and after removing water (usually by condensation), the remaining gas contains almost only CO2. As an option, the remaining gas is liquefied and stored in a tank as a carbon capture measure.

[0031] As mentioned above, the advantage of HT-PEM fuel cells is that they are resistant to CO in the reformer gas, such that a shift gas reactor can be avoided. Thus, a relatively small and lightweight reformer can be used, which is advantageous due to the correspondingly smaller size of the electrically driven reformer heater (such as a heat pump system). Although heat pumps can be advantageous for various types of fuel cell systems from different perspectives, it appears that in particular HT-PEM fuel cell systems can benefit from the use of a heat pump or an electric heater to heat the reformer.

[0032] Examples are given below where an HT-PEM fuel cell operates at a temperature of approximately 170 °C, which is the temperature of the coolant at the outlet of the fuel cell stack. However, a slight temperature variation along the fuel cell stack is normal, such that the operating temperature of the fuel cell stack is usually not more precise than the predetermined temperature + / - 10 degrees. For a set operating temperature of 170 °C (which is the temperature of the coolant leaving the fuel cell stack), the fuel cell stack will have a temperature variation in the range of 160 °C - 180 °C. Specifically, the coolant leaving the fuel cell at T2 = 170 °C will enter the fuel cell stack at a lower temperature T1 (e.g., T1 = 160 °C), which is one of the reasons for the temperature variation within the stack.

[0033] The minimum temperature required for the reforming of methanol is 200 °C, and generally, the predetermined temperature T ref is in the range of 250 °C - 300 °C, and a temperature of T ref = 250 °C is useful.

[0034] The above object is also achieved by providing a method, the method comprising

[0035] - using the electric power in an electrically driven reformer heater to heat a catalytic reformer to a predetermined reformer temperature T by the reformer-heater ref , the predetermined reformer temperature being not lower than the minimum temperature required to catalytically reform the fuel into a syngas containing hydrogen H2; for example, for the reforming of methanol, the predetermined reformer temperature T ref is in the range of 250 °C - 300 °C;

[0036] - operating a fuel cell, for example, operating an HT-PEM fuel cell at an operating temperature in the range of 120 °C - 200 °C, optionally in the range of 150 °C - 180 °C;

[0037] - maintaining the operating temperature of the fuel cell by a cooling circuit comprising a coolant flow;

[0038] - reforming a fuel comprising an alcohol (such as methanol) into a syngas containing hydrogen H2 by a reformer, feeding the syngas into the anode of the fuel cell, and generating electricity by the fuel cell by consuming a first portion of the H2, and releasing a second portion of the H2 from the anode as part of the anode exhaust gas;

[0039] - receiving the anode exhaust gas by an H2 separator, separating the remaining portion of the H2 from the anode exhaust gas, and recycling the separated H2 to the anode after mixing with the syngas from the reformer.

[0040] Compared with the prior art, the reformer-heater in the system presented herein comprises an electrically driven reformer-heater. In some embodiments, the reformer-heater is an electric heater, where electric power is converted into heat through ohmic resistance; this type of heating is also referred to as ohmic heating. For the reforming of methanol into syngas, surprisingly, compared with the reformer-heater with respect to the fuel and / or anode exhaust gas, when H2 is recycled, the HT-PEM fuel cell system with an electric heater described herein is proven to have a 1% increase in efficiency.

[0041] Alternatively, the electrically driven reformer-heater includes an electrically driven heat pump, which increases the efficiency by more than 5% in such HT-PE fuel cell systems as described herein, which is very surprising but well-founded below. The heat pump does not burn fuel or recycle hot gas. Instead, for example, the electricity generated by the fuel cell is consumed. In this way, since the fuel cell needs to generate additional electricity, the drive of the heat pump indirectly consumes H2. However, this has an advantage over the reformer-burner because the fuel cell is a more efficient fuel consumer compared to the reformer-burner. Therefore, instead of being consumed in the reformer-burner with relatively low efficiency, the fuel is consumed by the more efficient fuel cell. This implies a higher efficiency option for the whole system. Additionally, as will be more apparent below, the waste heat from the fuel cell is reused for heating the reformer.

[0042] By using H2 separation and recycling, an efficiency gain of 7.5% can be achieved. For an electric heater, most of the heat is consumed again. However, when the HT-PEM fuel cell is driven at 170 °C, the heat pump can raise the temperature to 250 °C with medium energy consumption, and the net gain of the system exceeds 5%. These estimates include the electricity consumption of the H2 separator. Since the heat pump system is most suitable for the HT-PEM system, it will be explained in more detail below.

[0043] In a practical implementation, the heat pump is thermally connected to the cooling circuit to extract thermal energy from the coolant and reduce the temperature of the coolant, which is beneficial for the efficiency of the fuel cell system because heat is usually waste but useful in the systems described herein. The thermal energy from the coolant located downstream of the fuel cell is extracted from the coolant and transferred to the heating fluid in the heating circuit, which is connected to the reformer to transfer the thermal energy from the heating fluid to the reformer. To counteract the effect of the lower temperature in the cooling circuit, the temperature of the heating fluid in the heating circuit must be raised by the heat pump to the temperature required for reforming, and this temperature is higher than the temperature of the coolant.

[0044] Referring to the example of an HT-PEM operating at 170 °C and the example of a predetermined reformer temperature T ref = 250 °C for the reforming of methanol, the temperature of the heating fluid must be raised to a temperature not lower than 250 °C and may even be slightly higher to maintain the temperature in the reformer at 250 °C.

[0045] Currently, compared to similar systems using a reformer-burner, it is expected that heat pumps used in systems with LT-PEM fuel cells operating below 100 °C will not improve system efficiency. Thus, heat pumps do not seem attractive for such systems. However, from the perspective of improving energy efficiency, it cannot be excluded that future developments will make the use of heat pumps in such LT-PEM fuel cell systems attractive. In any case, heat pumps may enter such LT-PEM fuel cell systems due to other advantages (such as simplicity and profit considerations). Therefore, there is reason to extend the idea of using a heat pump to heat the reformer in an HT-PEM fuel cell system to systems with other types of fuel cells, such as LT-PEM fuel cell systems.

[0046] For example, a heat pump includes a multi-stage gas piston compressor that uses a working medium for heat pumping. There are various working media, and some high-efficiency heat pumps use vapor or helium as the working medium.

[0047] Examples of heat pumps that can raise the temperature are found on the commercial market. For example, the German company Spilling GmbH produces heat pumps that use a multi-stage vapor compressor in a modular design, have up to 6 cylinders, and are capable of heating up to 280 °C, with a coefficient of performance COP higher than 2. For temperatures below 250 °C, the COP is higher. For example, for a source temperature of 175 °C to an output temperature of 215 °C, the COP is as high as 8 or higher. For higher output temperatures, such as 250 °C, the COP is lower but can be expected to be 5.

[0048] Using current state-of-the-art heat pump technology, it is possible to use heat pumps that can raise the temperature from T2 = 170 °C to T ref = 250 °C, which makes them particularly suitable for methanol reforming and HT-PEM cells. As already mentioned above, for such HT-PEM systems where the reformer is heated using a heat pump and the H2 gas from the anode is recycled, compared to current state-of-the-art fuel cell systems where the reformer is heated by a fuel burner as a reformer-heater, a total efficiency improvement of more than 5% has been found. This highly beneficial increase in efficiency is possible, especially because the fuel cell operates at a relatively high temperature that is lower but relatively close to the temperature T ref for reforming. In these calculations, it has been assumed that COP = 5. For a simple scaling, it has been found that COP = 4 results in a 4% efficiency gain, COP = 3 results in a 3% efficiency gain, and COP = 2 results in a 2% efficiency gain. Thus, even when the COP is lower than the expected COP = 5, such as in the range of 2 to 4, a gain is provided when using a heat pump compared to when using a burner and when recycling H2 to the anode.

[0049] Of particular interest is the use in larger fuel cell systems, such as those designed for ships. In addition, there is particular interest in fuel cell systems for stationary power plants with a power generation capacity of at least 1 MW.

[0050] Large-sized multi-stage compressor heat pumps can be used, such that the efficiency gain balances the depreciation of the additional investment relatively quickly. For example, the above-mentioned company Spilling GmbH offers heat pumps with a capacity in the range of 1 MW to 15 MW and a weight of 15,000 kg - 45,000 kg. Undoubtedly, such heat pumps require large installations, such as ships, especially container ships, or power plants, or large-scale energy storage systems, which need to be discussed in combination with, for example, the so-called Power-to-X (PtX) options for converting and storing green energy.

[0051] Another possible candidate for the heat pump is among the machines offered by Energy Engineering, where the heat pump uses a Stirling cycle, has a closed single-phase system, performs compression and expansion through a double-acting piston, and has an expected COP of 2.5. The heat pump can raise the temperature by 200 degrees, however, limited by a minimum source temperature of 100 °C, which makes it suitable for HT-PEM but not for LT-PEM. The heat supply capacity is in the range of 0.3 MW to 10 MW and has a weight of 10,000 kg.

[0052] In the fuel cell system presented herein, a coolant flow is provided through the fuel cell, where the coolant entering the fuel cell is at a first temperature T1, for example 160 °C, and the coolant leaving the fuel cell is at a second increased temperature T2, for example 170 °C, and the second temperature is higher than the first temperature T1. To maintain the stable and optimal operating temperature of the fuel cell, the heat pump receiving the coolant downstream of the fuel cell should not reduce the temperature of the coolant at the downstream end of the heat pump system to a third temperature T3 that is lower than the first temperature T1. This can be achieved by appropriately adjusting the flow rate and design of the heat pump (for example, by selecting a heat pump with appropriate specifications), as discussed above.

[0053] For an example of a fuel cell system including a reformer for reforming an alcohol (such as methanol), methanol is mixed with water and supplied to the reformer as an evaporated vapor. The heat for evaporation is advantageously taken from the coolant in the coolant circuit. For example, the necessary thermal energy can be obtained at the low-temperature branch of the coolant circuit, the temperature of which is closer to the coolant temperature T1 fed into the fuel cell, for example T1 = 160 °C, or the necessary thermal energy can be obtained at the high-temperature branch in the coolant circuit, which has the coolant temperature T2 at the outlet of the fuel cell, for example T2 = 170 °C. Considering that the heat pump has to raise the temperature to the reforming temperature Tref , for example, at 250 °C, it is preferably to feed the coolant with the highest available temperature to the heat pump. As a result, the evaporator must be connected to the low-temperature branch of the cooling circuit, downstream of the location where the heat pump system extracts thermal energy from the cooling circuit.

[0054] However, in this case, since the evaporator absorbs heat from the coolant, the coolant from the heat pump with a temperature T3 at the inlet of the evaporator should have a temperature T3 slightly higher than the coolant temperature T1 used at the cooling inlet of the fuel cell, for example, 2 to 4 degrees higher. Therefore, when using an evaporator, the heat pump should reduce the temperature of the coolant, for example, from level T2 to a temperature T3 higher than temperature T1, at which point the coolant is fed into the fuel cell.

[0055] Optionally, another heat exchanger is used between the evaporator and the fuel cell to finely adjust the temperature of the coolant before it enters the fuel cell. Description of the Drawings

[0056] The present invention will be explained in more detail with reference to the accompanying drawings, in which

[0057] Figure 1 is a schematic overview of a fuel cell system. Detailed Description of the Invention

[0058] Figure 1 Illustrating a fuel cell system 1, the fuel cell system comprising a plurality of fuel cells 2 usually arranged in parallel as a fuel cell stack, as shown. Methanol as fuel from a fuel tank 3 is combined and mixed with water from a water tank 4 and evaporated in an evaporator 5. The evaporated mixture of methanol and water is fed into an inlet 6A of a catalytic reformer 6, which produces syngas as a reforming product. This syngas contains carbon dioxide (CO2), carbon monoxide (CO), and hydrogen (H2) as well as some residues of water. The syngas is fed (as indicated by arrow 21A) from a reforming product outlet 6B into an inlet 22 of the anode of the fuel cell 2, and H2 is used by the fuel cell 2 for power generation.

[0059] In an exemplary case, the fuel cell 2 is an HT-PEM fuel cell, which is insensitive to CO and does not require a shift reactor compared to an LT-PEM cell, and the water vapor content in the syngas does not need to be high either.

[0060] As an alternative to methanol, other alcohols can be used, for which the reformer temperature will have to be adjusted accordingly.

[0061] For example, the HT-PEM fuel cell 2 is driven at a temperature in the range of 170°C - 180°C, such that the coolant in the cooling circuit 7 (pumped to the fuel cell stack by the coolant pump 8 in the directions indicated by the arrows 17A and 17B) is heated from T1 = 160°C to T2 = 170°C. The fuel HT-PEM cell 2 can be driven at slightly different temperatures in the range of 120°C - 200°C, but typically in the range of 150°C - 180°C. Advantageously, the polymer electrolyte membrane PEM in the HT-PEM fuel cell is based on an inorganic acid, typically a polymer membrane, for example, polybenzimidazole (PBI) doped with phosphoric acid.

[0062] The reformer 6 is heated by a reformer-heater 27 (indicated by the dash-dotted line in Figure 1 ), and the components of the reformer-heater will be explained in more detail below.

[0063] The coolant flowing from the fuel cell 2 (from the fuel cell 2 at temperature T2), as indicated by the arrow 17B, transfers the thermal energy in the heat exchanger 9 to the transfer fluid in the transfer circuit 10, where the transfer fluid is pumped by the transfer pump 11.

[0064] The transfer circuit 10 is thermally connected to an electrically driven heat pump 12. The heat pump 12 transfers the thermal energy from the transfer fluid in the transfer circuit 10 to the heating fluid circulating in the heating circuit 13, and the heating circuit 13 is driven by a corresponding heating fluid pump 14 that heats the reformer 6.

[0065] The advantage of the transfer circuit 10 is that it is easy to adjust the inlet temperature into the heat pump 12 and the temperature of the coolant in the cooling circuit 7 downstream of the transfer heat exchanger 9.

[0066] In the shown system, the coolant in the low-temperature branch 7A of the cooling circuit 7 (downstream of the transfer heat exchanger 9) is used to heat the mixture of fuel and water in the evaporator 5. After that, the temperature of the coolant should be T1, for example, T1 = 160°C, to maintain the stable operating temperature of the fuel cell 2. The regulating heat exchanger 18 can be used to finely adjust the temperature to T1. According to the heat demand in the evaporator 5 (which varies with the load of the fuel cell 2 and the corresponding fuel consumption), the temperature of the coolant in the cooling circuit 7 can be adjusted by adjusting the transfer of thermal energy in the transfer heat exchanger 9 upstream of the evaporator 5. The power consumption of the heat pump 12 is adjusted according to the temperature of the transfer fluid in the transfer circuit 10 and the heat demand in the reformer 2.

[0067] An example of a heat pump is used to raise the temperature of the transfer fluid from a temperature in the range of 120°C - 200°C to at least T of the heating fluid refa temperature of = 220 °C, optionally raising the temperature of the transfer fluid from a temperature in the range of 150 °C - 180 °C to at least T of the heating fluid ref = a temperature of 250 °C.

[0068] By using a reformer heater 27 as presented herein, the reformer heater comprising a heat exchanger 9, a transfer loop 10 with its pump 11, and a heating loop 13 with its pump 14, and a heat pump 12, the reformer - burner does not require fuel or H2, such that the H2 gas remaining in the anode exhaust gas duct 18 can be separated by an H2 separator 19 (the separator being, for example, an electrochemical H2 separator), and fed by an H2 duct 20 into a syngas duct 21, the syngas duct connecting the reformate outlet 6B of the reformer 6 with the inlet 22 of the anode of the fuel cell 2. The H2 gas flow (as indicated by arrow 20A) in the H2 duct 20 downstream of the separator 19 is added to the syngas (as indicated by arrow 21A) flowing from the reformer (6) in the syngas duct 21, and produces a combined flow, as indicated by the thick arrow 21B in the syngas duct 21 upstream of the anode inlet 22 of the fuel cell 2.

[0069] Additionally, since the H2 gas has been separated from the anode exhaust gas in the exhaust duct 18 by the H2 separator 19, the remaining gas (mainly water vapor and CO2 gas) can in principle be discarded. However, optionally, water is separated from the CO2 gas in a condenser 15, and collected in a water reservoir 16 for possible reuse in mixing with the fuel. Optionally, the remaining CO2 in the CO2 duct 23 is collected as a liquid in a CO2 tank 26, for example, after compression in a compressor 24 and condensation in a heat exchanger 25.

[0070] It should be noted that the additional elements of H2 separation and H2 recirculation into the fuel cell rather than the burner, as well as water recirculation and potential carbon capture, all benefit from the use of the heat pump 12, such that the overall result of these elements added together is not just an aggregation, but a synergistic combination of the elements, thus forming an overall improved and environmentally friendly system.

Claims

1. A fuel cell system (1), comprising - a fuel supplier (3) for supplying fuel, - a reformer (6) for catalytically reforming the fuel into synthesis gas containing hydrogen H2, - a fuel cell (2) having an anode with an anode inlet (22), the anode inlet being fluidly connected to a reformate outlet (6B) of the reformer (6) for receiving the H2 and using the H2 to generate electricity, - Reformer - Heater (27), the Reformer - Heater being adapted to heat the reformer (6) to a predetermined reformer temperature T ref , the predetermined reformer temperature being not lower than the minimum temperature required for the catalytic reforming of the fuel - a cooling circuit (7) containing a coolant flow for maintaining the operating temperature of the fuel cell (2), - the system includes an H2 separator (19) connected to an anode exhaust duct (18) located downstream of the anode for receiving anode exhaust gas and separating H2 from the anode exhaust gas, wherein the H2 separator (19) is fluidly connected to a synthesis gas duct (21) connecting the reformate outlet (6B) to the inlet (22) of the anode for recycling the separated H2 gas into the anode after mixing with the synthesis gas from the reformer (6), It is characterized in that The fuel includes alcohols, and the fuel cell (2) is an HT-PEM fuel cell, the operating temperature of the HT-PEM fuel cell being in the range of 120°C - 200°C and lower than the predetermined reformer temperature T ref , and the reformer-heater is an electrically driven reformer-heater (27).

2. The system according to claim 1, wherein the H2 separator is an electrochemical H2 separator (19).

3. The system according to any one of the preceding claims, wherein the system downstream of the H2 separator (19) includes a water separator (15) and a CO2 liquefier (24, 25) for separating water from the anode exhaust gas after H2 separation, and further includes a CO2 storage tank (26) for storing the remaining CO2 in liquid form.

4. The system according to any one of the preceding claims, wherein the electrically driven reformer heater (27) comprises an electrically driven heat pump (12), the electrically driven heat pump being thermally connected to the cooling circuit (7) for extracting thermal energy from the coolant and reducing the temperature of the coolant, and transferring the extracted thermal energy to a heating fluid in a heating circuit (13) for heating the heating fluid and providing a heating fluid having a temperature not lower than the predetermined reformer temperature T ref of the heating fluid, wherein the heating circuit (13) is connected to the reformer (6) for transferring thermal energy from the heating fluid to the reformer (6).

5. The system according to claim 4, wherein the fuel (2) comprises methanol and water, and wherein the system (1) comprises an evaporator (5) for receiving and evaporating the fuel for reforming in the reformer (6), wherein the cooling circuit (7) is configured to maintain the operating temperature of the HT-PEM fuel cell (2) in the range of 150°C - 180°C, and wherein the predetermined reformer temperature T ref is in the range of 250°C - 300°C.

6. The system according to claim 4 or 5, wherein the heat pump (12) comprises an electrically driven multi-stage gas piston compressor, and wherein the COP for heating the reformer to the predetermined reformer temperature T by means of the heat pump ref is not less than 2.

7. A method for operating a fuel cell system, wherein the method includes -The reformer-heater (27) heats the catalytic reformer (6) to a predetermined reformer temperature T ref , where the predetermined reformer temperature is not lower than the minimum temperature required to catalytically reform the fuel into syngas containing hydrogen H2, - maintaining the operating temperature of the fuel cell (2) by a cooling circuit (7) containing a coolant flow; - reforming the fuel into synthesis gas containing hydrogen H2 by the reformer, feeding the synthesis gas into the anode of the fuel cell (2), and generating electricity by the fuel cell (2) by consuming a first portion of the H2, and releasing a second portion of the H2 as part of the anode exhaust gas from the anode; - receiving the anode exhaust gas by an H2 separator (19), separating H2 from the anode exhaust gas and recycling the separated H2 into the anode; It is characterized in that The fuel includes alcohols, and the system includes a fuel evaporator (5), and the fuel cell (2) is an HT-PEM fuel cell, and the reformer-heater is an electrically driven reformer-heater (27), and the method includes: receiving and evaporating the fuel in the evaporator (5), and feeding the evaporated fuel into the reformer (6), operating the fuel cell at an operating temperature in the range of 120 °C to 200 °C, and maintaining a predetermined reformer temperature T by the reformer heater (27) ref , the predetermined reformer temperature being not lower than the minimum temperature required for the catalytic reforming of the fuel.

8. The method according to claim 7, wherein the method comprises: adding the separated H2 gas to the synthesis gas from the reformer (6) in a synthesis gas duct (21), the synthesis gas duct connecting the reformate outlet (6B) of the reformer (6) to the gas inlet (22) of the anode of the fuel cell (2).

9. The method according to claim 7 or 8, wherein the H2 separator is an electrochemical H2 separator (19).

10. The method according to claim 7, 8 or 9, wherein the method comprises: Separating H2O from the anode exhaust gas after H2 separation, and capturing carbon by liquefying the remaining CO2 and storing the CO2 as a liquid in a storage tank.

11. A method according to any one of claims 7 to 10, wherein the reformer heater (27) comprises an electrically driven heat pump (12) thermally connected to the cooling circuit (7), and wherein the method comprises: The heat pump (12) is driven by electricity, and thermal energy is extracted from the coolant in the cooling circuit (7), and the temperature of the coolant is reduced by the heat pump (12), and the extracted thermal energy is transferred to the heating fluid in the heating circuit (13), and the heating fluid is heated, and the heating fluid with a temperature not lower than the predetermined reformer temperature T ref is provided, and the thermal energy is transferred from the heating fluid to the reformer (6).

12. The method according to claim 11, wherein the method comprises: The operating temperature of the fuel cell (2) is maintained in the range of 150°C - 180°C by the cooling circuit, and the reformer is heated to a temperature in the range of 250°C - 300°C by using the heat pump (12).

13. The method according to claim 11 or 12, wherein the method comprises: A coolant flow through the fuel cell (2) is provided, the coolant entering the fuel cell (2) at a first temperature T1 and leaving the fuel cell (2) at a second increased temperature T2 higher than the first temperature T1, for example T1 = 160°C and T2 = 170°C, and wherein the heat pump (12) receives the coolant after the fuel cell (2) has increased the temperature to T2, and wherein the method comprises: extracting thermal energy from the coolant by using the heat pump (12) and reducing the temperature of the coolant to a third temperature T3 which is lower than T2 but not lower than the first temperature T1.

14. The method according to claim 13, wherein the method comprises: The heat pump (12) reduces the temperature of the coolant to a third temperature T3 which is lower than T2 but higher than the first temperature T1, and feeds the coolant located downstream of the reformer heater (27) into the evaporator (5), and transfers thermal energy from the coolant to the fuel in order to evaporate the fuel in the evaporator (5) before the fuel enters the reformer (6), and reduces the temperature from the third temperature T3 to a fourth temperature T4 by this transfer of thermal energy in the evaporator (5), wherein the fourth temperature T4 is not lower than the first temperature T1.

15. Use of a system according to any one of claims 1 to 6 or a method according to any one of claims 7 to 14 for generating electricity on an electrically driven ship.

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