A fuel cell system and a method of its operation, a vehicle and a method for propelling the vehicle with the fuel cell system.

Abstract

A fuel cell system and a method of its operation, a vehicle and a method for propelling the vehicle with the fuel cell system. In a fuel cell system (1), an evaporator (41), a superheater (42) and a reformer (26) are provided inside a pressurised container (20) to provide a compact fuel processing unit 5 (17).

Description

[0001] A fuel cell system and a method of its operation, a vehicle and a method for propelling the vehicle with the fuel cell system.

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a fuel cell system and a vehicle comprising it, as well as a method of operating the fuel cell system and a method for propelling a vehicle with it. For example, the vehicle is an automobile or a marine vessel.

[0004] BACKGROUND OF THE INVENTION

[0005] In fuel cell systems using methanol, a reformer is used for catalytic reformation of a mix of methanol and water to a reformate gas, also called reformed gas or syngas, which contains the necessary hydrogen. Typically, the reformer is heated by a burner, consuming fuel and / or anode exhaust gas, in order to reach the catalytic temperature necessary for the catalytic reformation of the fuel. As an initial step, the mix of methanol and water is evaporated and, then, further heated in a superheater to a temperature closer to the catalytic reformation temperature.

[0006] US2003 / 0022950A1 discloses a fuel cell system, in which a mix of water and methanol or ethanol is evaporated in an evaporator, the resulting vapour further heated in a superheater prior to high-temperature reformation in a reformer. The reformer is heated by a burner, the exhaust gas of which is used for evaporator. The reformate gas is used for superheating the evaporated fuel, so that the superheater cools the reformate gas prior to entering the fuel cell. As an example, there is a direct coupling of the burner with the reformer by integrating the reformer with the burner as a plate heat exchanger. The disclosure is silent with respect to the type of heat exchanger used for the evaporation.

[0007] US4670357 discloses use of burner gas for the reformer. The exhaust gas of the burner is used for superheating the evaporated methanol / water mixture for reformation and additionally for providing heat to the reformer. Fuel cell coolant is used for heating the vaporizer. The types of heat exchanger are not disclosed. In the article “Evaporation of Methanol Solution for a Methanol Steam Reforming System” by Trinh et al. published in Energies 2021, 14, 4862. https: / / doi.org / 10.3390 / enl4164862, it was found that evaporator design influences the methanol -reforming reaction. Four different evaporators designs were investigated, namely planar heat exchangers containing a microchannel structure, cylindrical shell-and-tube evaporators, zirconia balls for internal evaporation, and combinations of cylindrical shell-tubes and zirconia balls.

[0008] US2001 / 0026777A1 discloses a system that vaporizes a liquid fuel and steam-reforms the fuel in a reforming section to generate hydrogen. A pressure regulating valve is opened during start-up of the system for limiting the rate of increase in pressure just after the generation of reformed gas has started.

[0009] As it appears, various different heating configurations are known, the varieties yielding different advantages, and the configuration and type of heat exchanger also influences the reformation process. An optimization of the reformation process is also beneficial for the overall production of electricity by the fuel cell system. Furthermore, for mass production, considerations have to be applied as to how systems even with known basic principles can be optimised for fast, simple and low cost manufacturing. Additionally, sizing and weight of fuel cell system is of concern, in particular for automotive applications, where space is limited and minimization of weight an important factor.

[0010] Although the prior art gives various suggestions for basic principles used in fuel cell systems and optimization thereof, there is still room for improvement, in particular with respect to mass production and optimization with respect to weight and size.

[0011] DESCRIPTION / SUMMARY OF THE INVENTION

[0012] It is therefore an objective of the invention to provide an improvement in the art. In particular, it is an objective to provide improvements of fuel cell systems with respect to simplification, minimization of size and weight, and being advantageous for mass production at low cost. This objective and further advantages are achieved with a fuel cell system and method of its operation as described below and in the claims. In short an evaporator, a superheater, and a reformer are provided inside a pressurised container to provide a compact fuel processing unit.

[0013] The system described herein provide a number of advantages. One of the advantages is compactness, which is advantageous in particular in automobiles. Another advantage in comparison with the prior art is a reduction of system components, in particular pipes and valves, which reduces complexity and simplifies production and maintenance. Due to the reduced number of components, the system results in a substantial cost reduction in production. In addition, the reduction of pipes and valves, improves longevity and operational reliability, especially when used under conditions with substantial vibrations, such as in automobiles and marine vessels. As it appears from the above, the improvement to an apparently simple design yields a number of advantages over prior art systems.

[0014] The fuel cell system comprises a fuel cell, typically, as part of a stack of fuel cells, which is common practice. The fuel cell has a membrane and an anode side on one side of a separator, typically membrane, and a cathode side on the opposite side of the separator. In the following, the short terminology of anode and cathode will be used for the fuel cell.

[0015] Advantageously, the fuel cells ae of the type HT-PEM, which are high temperature (HT) fuel cells comprising a polymer electrolyte membranes (PEM). These fuel cells operate at a temperature in the range of 120-200°C, such as 150-180°C. Alternatively, other fuel cells that operate above 100°C are used, for example SOFC.

[0016] A coolant circuit containing coolant is flow-connected to the fuel cell for uptake of thermal energy from the fuel cell by the coolant and for maintaining a largely constant temperature of the fuel cell for proper operation.

[0017] For example, the HT-PEM fuel cell is operated at a temperature around 170°C, which is the temperature of the coolant at the outlet of the coolant channel in the fuel cell stack. Minor variations along the fuel cell stack, however, are normal, so that the operational temperature of the fuel cell stack is typically no more precise than a predetermined temperature + / - 10 degrees. For a set operational temperature of 170°C, which is the temperature by which the coolant leaves the fuel cell stack, the fuel cell stack would have temperature variations in the range of 160-180°C. In particular, the coolant that leaves the fuel cell at 170°C would enter the fuel cell stack at a lower temperature, for example 160°C, which is one of the reasons for the temperature variations within the stack. The coolant temperature is advantageous for evaporating liquid fuel, which also provides a decrease of the coolant temperature, as desired.

[0018] A liquid fuel supply is provided for supplying liquid fuel, and an evaporator for evaporating the liquid fuel prior to catalytic reformation of the evaporated fuel. For example, as a liquid fuel, a mix of water and alcohol, such as methanol or ethanol, is provided, which is evaporated for catalytic reformation the fuel into a reformate gas, also called syngas, which contains hydrogen gas for consumption by the fuel cell. The syngas also contains other gas by-products, such as CO2, water, and CO. An advantage of HT-PEM fuel cells, as compared to LT-PEM fuel cells is that the removal of CO is not necessary.

[0019] The coolant from the fuel cell coolant circuit is used for heating the liquid fuel and cause evaporation thereof. For a fuel cell operating at temperatures in the range of 150-180°C, the temperature need to be further increased for the catalytic reformation, and it is custom to use a so called superheater for further heating the evaporated fuel prior to reformation it the reformer.

[0020] For catalytically reforming the superheated fuel to reformed gas at a necessary catalytic temperature, for example in the range of 250°C-300°C, for reformation of a metha- nol / water mix, the reformer, in particular its catalyst, is heated by a reformer heater.

[0021] In order to provide a simplified system as compared to prior art systems, in which the evaporator, superheater and reformer are separate units, the system as described herein provides a compact technical solution, in which a fuel processing unit is provided that comprises a pressurised container that contains the evaporator, the superheater, and the reformer. However, the container does not contain the fuel cell, especially fuel cell stack.

[0022] The pressurized container has a fuel inlet connected to the liquid fuel supply by a fuel conduit. For example, the liquid fuel supply comprises a pipe-connected tank that contains a mixture of water and methanol. In an alternative embodiment, the liquid fuel supply comprises a first tank with water and a second tank with methanol and two pipe connections to the fuel processing unit and a mixing unit for controlling the correct mixing. This way, the fuel processing unit, especially the container, receives the fuel from a supply. Typically, the liquid fuel is stored in a tank, and a pump pumps the liquid fuel from the storage tank into the container. The pressurized container has a syngas outlet that is connected to the fuel cell stack by a syngas conduit. These features in particular justify the term of fuel processing unit, as the unit comprises a closed container that receives liquid fuel through an inlet and provides reformate gas at an outlet. The fuel processing, in particular evaporation, superheating and reformation, is done inside a single container, which has the advantages mentioned before concerning compactness, weight and production.

[0023] The pressurised container contains a first, second and third compartment, which are pressurised to above the pressure of the surroundings, for example at least 1.5 times, optionally at least 2 times, but typically no more than 4 times the pressure of the surroundings, and fluid-flow interconnected for forming a gas flow path inside the container for flow of evaporated fuel from the first compartment through the second compartment to the third compartment. The gas flow is determined, on the one hand, by the evaporation rate in the first compartment and, on the other hand, by the outflow rate of syngas from the third compartment.

[0024] Optionally, the gas flow through the three compartments is upwards, where the term upwards is here relatively to gravity and defines an orientation of the container. Accordingly, the container has an operational orientation relatively to gravity, wherein the third compartment is above the second compartment, and the second compartment is above the first compartment.

[0025] The first compartment comprises a receptacle at its bottom for accommodating the liquid fuel received from the liquid fuel supply, typically a tank. The first compartment contains a first heat exchanger having first heat exchanger walls confining a first inner flow volume that is connected to the coolant circuit, wherein an outer side of the first heat exchanger walls are in thermal contact with the liquid fuel for transfer of thermal energy from the coolant to the liquid fuel for evaporating the fuel. The second compartment is gas-flow connected to the first compartment for receiving the evaporated fuel from the first compartment in the flow through the container. The second compartment contains a second heat exchanger having second heat exchanger walls confining a second inner flow volume that has an upstream-connection and a downstream connection, wherein the upstream connection is connected to a downstream side of the reformer for receiving reformate gas from the reformer and the downstream side of the second heat exchanger is connected to the syngas outlet of the container, which in turn has a flow-connection to the fuel cell, so that the reformate gas, also called syngas, is flowing to the fuel cell for its electricity production. The second heat exchanger is superheating the evaporated gas by transfer of thermal energy from the reformate gas to the evaporated fuel prior to the reformate gas leaving the container through the syngas outlet and entering the fuel cell.

[0026] The third compartment contains the reformer, in particular the reformation catalyst, which is thermally connected to the reformer heater for receiving thermal energy from the reformer heater. The third compartment is gas-flow connected to the second compartment for receiving the superheated fuel from the second compartment in the flow, for example upwards flow, of the fuel through the container and for reforming the fuel into reformate gas.

[0027] In some embodiments, a reformer burner is integrated inside the container. In principle, it is possible to thermally connect the reformer burner directly to a plate or several plates to which the catalyst is attached.

[0028] Although, the so-called burner can be of the catalytic type, it is customary in the technical field to maintain the term “burner” for the oxidation of remaining of hydrogen gas and carbon monoxide in the anode exhaust gas, be it catalytic oxidation or by a flame.

[0029] In other embodiments, the reformer heater comprises a reformer burner outside the container. For example, a thermal connection between the reformer burner and the reformer comprises a thermal fluid circuit that is thermally connected to the reformer burner that bums anode exhaust gas or fuel or both. The thermal fluid circuit transports thermal energy from the reformer burner to the catalyst. Advantageously, the third compartment contains a third heat exchanger having third heat exchanger walls confining a third inner flow volume flow-connected to the circuit of thermal fluid. An outer side of the third heat exchanger walls is in thermal contact with the catalyst for transfer of thermal energy from the thermal fluid to the catalyst and heating it to no less than the catalytic temperature.

[0030] Whether the heat source for the thermal fluid is a burner, an electrical heater, a heat pump, or of other type, the thermal fluid in the thermal fluid circuit needs a temperature of no less than the catalytic temperature in order for the catalyst to gain the necessary temperature for the reaction from the thermal fluid.

[0031] For example, the circuit of thermal fluid is flow-connected to a heat pump, wherein the heat-pump is thermally connected to the coolant circuit of the fuel cell and arranged for transfer of thermal energy from the coolant to the thermal fluid and raising the temperature of the thermal fluid at no less than the catalytic temperature.

[0032] As an option, the heat pump comprises a compressor configured for receiving thermal fluid in gas form and compressing the thermal fluid to raise the temperature to no less than the catalytic temperature. Typically, the compression is adiabatic.

[0033] In operation, the fuel cell system is producing electrical energy by the fuel cell, especially the fuel cell stack, in particular a HT-PEM fuel cell as part of a fuel cell stack. The operation temperature of the fuel cell, for example in the range of 150-180°C, is maintained by the coolant circuit. Liquid fuel is supplied from the liquid supply to the receptacle in the first compartment, for example by using a liquid fuel pump. Flow of coolant is provided through the first inner volume of the first heat exchanger, which leads to evaporation of the liquid fuel due to transfer of thermal energy from the coolant to the liquid fuel. The catalyst is heated by the reformer heater to a temperature no less than the catalytic temperature. By receiving superheated fuel gas from the second compartment, the catalyst is reforming it into reformate gas.

[0034] In operation, the fuel is evaporated and a flow of the evaporated fuel, for example an upwards flow against gravity, through the container from the first compartment through the second compartment and through the third compartment. For providing thermal energy for the superheating of the evaporated gas by the second heat exchanger in the second compartment, a flow of reformate-gas from the third compartment into the second inner flow volume of the second heat exchanger is provided. After the superheating, the reformate gas flows from a downstream side of the second heat exchanger through the syngas outlet of the container to the fuel cell stack.

[0035] Advantageously, the gas pressure inside the pressurised container is adjusted by regulating the evaporation rate of the fuel in the first container through adjustment of coolant flow through the first heat exchanger. The more coolant flows through the first heat exchanger, the more thermal energy is taken up by the liquid fuel and the more liquid fuel is evaporated, which regulates the pressure in the container.

[0036] As already indicated above, as an option, the circuit of thermal fluid is flow-connected to a heat pump that is flow connected to the coolant circuit, and there is a transfer of thermal energy from the coolant to the thermal fluid by the heat pump, which raises the temperature of the thermal fluid to no less than the catalytic temperature.

[0037] As an option, the heat pump comprises a compressor, receiving thermal fluid in gas form and compressing it, typically adiabatically compressing it, to raise the temperature of the gaseous thermal fluid to no less than the catalytic temperature.

[0038] In practical embodiments, during operation, the compressor is pumping the thermal fluid through the third inner volume of the third heat exchanger. The thermal fluid is cooled by transfer of thermal energy to the catalyst, for example leading to condensation of the thermal fluid. Downstream of the third heat exchanger, the thermal fluid is expanded again for reducing its pressure and temperature to a first temperature below a coolant temperature in the coolant circuit in order to provide a thermal fluid in liquid form. The thermal fluid in liquid form flows through an evaporator that is thermally connected to the coolant circuit, and by transfer of thermal energy from the coolant to the thermal fluid through the evaporator, the temperature of the thermal fluid is raised and the thermal fluid evaporating prior to the gaseous thermal fluid entering the compressor in this circuit. Optionally, at least one of, the first, second, and third heat exchanger is a pillow plate heat exchanger. For example, all are pillow plate heat exchangers. Advantageously, they are connected to each other edge-to-edge one above the other to form a single rigid heat exchanger constructions.

[0039] The fuel cell system as explained herein is compact and therefore particularly useful electrical power production in vehicles and for propelling the vehicle by electricity. For example, the vehicle is an automobile or truck. Alternatively, the vehicle is a marine vessel.

[0040] SHORT DESCRIPTION OF THE DRAWINGS

[0041] The invention will be explained in more detail with reference to the drawing, where FIG. 1 illustrates a fuel cell system with a fuel processing unit;

[0042] FIG. 2 illustrates a fuel processing unit in more detail;

[0043] FIG. 3 illustrates fuel cell system with a fuel processing unit and a heat pump.

[0044] DETAILED DESCRIPTION / PREFERRED EMBODIMENT

[0045] FIG. 1 illustrates a fuel cell system 1 comprising a fuel cell, which is exemplified as a HT-PEM fuel cell 2, typically as part of a fuel cell stack. The fuel cell has a cathode 3 and an anode 4, separated by a proton-conducting separator 5. During operation, the cathode 3 receives air from the surroundings, pressurised by a pump 6, which provides the necessary oxygen for the reaction with hydrogen into water, which is released from the cathode through a cathode gas exhaust 7 as steam together with the remains of the gases from the air, as the fuel cell 2 is operating at temperature well above the boiling point of water. In order to maintain the fuel cell 2 at an operation temperature, for example in the range of 150-180°C, and prevent overheating, coolant, for example coolant oil, is pumped in a coolant circuit 8 by a corresponding pump 9 through the fuel cell 2. The temperature of the coolant is adjustable by a corresponding cooler 10. For example, the coolant is entering the fuel cell 2 at a temperature in the order of 10 kelvin lower than the operational temperature of the fuel cell 2. For electricity-producing reaction of hydrogen with oxygen into water, the anode 4 received H2-rich syngas from a fuel processing container 17, which includes a reformer and which is explained in more detail below. The flow of the syngas into the fuel cell 2 is controlled by a corresponding flow control unit 11.

[0046] For reformation of fuel, for example water mixed with methanol or ethanol, a catalytic reaction is used at elevated temperatures, for example in the order of 250°C. For achieving this high temperature, a reformer heater 12 is used, which in the illustrated embodiment comprises a burner, which consumes the exhaust gas from the anode, also called anode waste gas, AWG, received through a corresponding AWG conduit 13. AWG which contains some remains of hydrogen gas, for example in the order of 10% of the AWG when calculated in mole fraction of the AWG. The AWG also contains a few percentages of CO, which are also converted to heat in the burner of the reformer heater 12. The term burner is common in the technical field, despite the burner not necessarily working with a burner flame, as the term burner is also used for catalytic oxidation of the hydrogen and CO portion of the AWG. The exhaust gas from the burner, the main components of the resulting gas is water steam and CO2 as well as nitrogen gas from air that has been supplied by a pump 14.

[0047] The reformer heater, for example burner 12, provides heat to a thermal fluid circuit 15 that is used to transfer the required thermal energy from the reformer heater to a catalyst used in the reformation process in the reformer. A pump 16 in the thermal fluid circuit 15 is used for the transport through the fluid in the thermal fluid circuit 15.

[0048] The fuel cell system 1 comprises a fuel processing unit 17, which receives liquid fuel, typically water mixed with methanol or ethanol, pumped by a fuel pump 18 from a fuel tank 19 into a pressurised container of the fuel processing unit 17. In an alternative embodiment, the liquid fuel supply comprises a first tank with water and a second tank with methanol and two pipe connections to the fuel processing unit 17 and a mixing unit for controlling the correct mixing. The fuel processing unit 17 delivers the reformation gas, also called syngas, to the anode 4.

[0049] FIG. 2 illustrates a fuel processing unit 17 in more detail. It comprises a pressurised container 20 that has a first compartment 21 at the bottom, a second compartment 22 above the first compartment 21, and a third compartment 23 above the second compartment 22. The first compartment 21 is used to receive liquid fuel through a fuel inlet 25 and evaporate the liquid fuel 24, for example methanol mixed with water. The second compartment 22 is used for superheating the evaporated fuel 24 A, and the third compartment 23 contains the catalyst 26A of the reformer 26 for the reformation process of the evaporated fuel 25 into reformed gas 27, also called syngas. For example, the catalyst is provided as granules, filling the space for the gas flow in the third compartment 23. In such embodiment, advantageously, a grid 50 is used to support the granules.

[0050] The evaporated fuel 24A is obtained by heating the liquid fuel 24 at the bottom of the first compartment 21 by thermal energy transfer from the coolant coming through the fuel cell coolant circuit 8. The coolant enters a first heat exchanger 31 in the first compartment 21 through an inlet 31 A, flows as indicated by arrow 34 through the first heat exchanger 31 and leaves the first heat exchanger 31 through an outlet 3 IB. Through thermally conducting walls 31C of the first heat exchanger 31, the liquid fuel 24 receives thermal energy from the coolant. As an example, for efficient heat transfer, the outlet 3 IB of the first heat exchanger 31 is located higher than the inlet 31 A of the first heat exchanger 31, although this can also be different. In the present example, the coolant is oil, However, the coolant could be a different fluid, especially different liquid, optionally using gas / liquid condensation.

[0051] With reference to FIG. 1, a control valve 49 A and a flow restrictor 49B are used for controlling and adjusting the flow of the coolant through the first heat exchanger 31.

[0052] Determined, on the one hand, by the evaporation rate in the first compartment 21 and. on the other hand, by the outflow rate of syngas 27 from the third compartment 23, the evaporated fuel 24A flows upwards relative to gravity through the second heat exchanger 32 in the second compartment 22 prior to entering the third compartment 23 that contains the catalytic reformer 26. The catalyst 26A of the reformer 26 is heated by the third heat exchanger 33. One site of the heat-conducting walls 33C of the third heat exchanger 33 is heated by the thermal fluid from the thermal fluid circuit 15. The opposite side of the walls 33C of the third heat exchanger 33 is in thermal contact with the catalyst 26A for the heat transfer from the thermal fluid to the catalyst 26A. As an example, for efficient heat transfer, the outlet 33B of the third heat exchanger 33 is located higher than the inlet 33A of the third heat exchanger 33. With reference to FIG. 1, the thermal fluid for heating the catalyst 26A of the reformer 26 has a temperature sufficiently high for the reformation process, typically in the range of 230-300°C.

[0053] As indicated in FIG. 2, the second heat exchanger 32 is heated by the reformed gas 27. For this purpose, the reformed gas 27 is extracted, as indicated by arrow 28, from the inner volume 17A of the fuel processing unit 17, advantageous, as indicated, at the top 23 A of the third compartment 23, where the reformed gas has the highest temperature and has passed the reformer 26. The reformed gas 27 enters the second heat exchanger

[0054] 32 and leaves it again through the syngas outlet 45 after heat of thermal energy through the walls 32C of the second heat exchanger 32 and uptake of the thermal energy by the evaporated fuel.

[0055] As explained, the three exchangers 31, 32, 33 have three different separate flow fields for heating media, one first heat exchanger 31 for the coolant in the lower, first compartment 21, one second heat exchanger 32 for the reformed gas in the second compartment 22 in the middle, and one third heat exchanger 33 in the upper third compartment 23 for the high-temperature thermal fluid. However, despite the three separated flow fields for the three different heating media, the three heat exchangers 31, 32, 33 are not necessarily provided as three physically separate heat exchangers but can as an option be provided as one single metal unit or a vertically-oriented face-to-face arrangement of single units, which is also illustrated in FIG. 2.

[0056] A useful type of heat exchanger for the first, second, and third heat exchanger 31, 32,

[0057] 33 is the type that is called “pillow plate” in the technical field. An assembly of multiple, for example five, pillow plates, the faces of which are oriented towards each other in a vertically oriented face-to-face configuration is illustrated in FIG. 2 as an upright oriented stack. Such heat exchangers have advantages in ease of manufacturing and in long-term mechanically stability, despite pressurization of the heating media.

[0058] Advantageously, as illustrated, the first, second, and third heat exchangers 31, 32, 33 are all pillow plate heat exchangers connected to each other edge-to-edge one above the other to form a single rigid heat exchange constructions. An assembly as illustrated in FIG. 2 reduces the number of pipes and valves and, thus, reduces the risk for leakage and breakage and reduces the need for maintenance.

[0059] FIG. 3 illustrates a fuel cell system 1 similar to the one in FIG. 1, and the reference numbers for the same components are not repeated here. Different from the embodiment in FIG. 1 is the fact that the reformer heater 12 does not comprise a burner, so that the AWG is used in a further processing device 40 for different purpose, for example recycling of the rest-hydrogen of the AWG into the anode and potentially using water separation followed by carbon capture, liquefying the resulting CO2.

[0060] Instead of the burner of FIG. 1, the fuel cell system 1 of FIG. 3 comprises a heat pump 48 that has a thermal connection, such as pipe connection 36, to the fuel cell coolant circuit 8, where the coolant has a temperature, for example, as indicated, in the range of 150-180°C. Different types of heat pumps can be employed, and FIG. 3 illustrates an example thereof. In this example of FIG. 3, thermal energy from the coolant in the coolant circuit 8 is transferred to an evaporator 37 that causes evaporation of the thermal fluid from a liquid state to a gaseous state. The thermal fluid in gaseous state enters a compressor 38 which raises the pressure and corresponding temperature of the gaseous thermal fluid, so that the thermal fluid attains a temperature high enough for heating the catalyst 26A in the reformer 26 inside the fuel processing unit 17. For example, the thermal fluid is heated in the evaporator 37 from a temperature just below the evaporation point at a certain pressure to a second temperature just above the evaporation point at a certain pressure. The gas by the compressor, for example from a few Bar (1 bar = 0.1 MPa), exemplified as 4 BarA (0.4 MPa), by a compression raising the pressure tenfold. Inside the fuel processing unit 17, in particular inside the reformer 26, the thermal fluid is cooled by thermal energy transfer to the catalyst 26A and then leaves the fuel processing unit 17. Typically, the heat exchange in the reformer 26 leads to condensation of the thermal fluid. By expansion in an expansion valve 39, the thermal fluid attains lower pressure and lower temperature.

[0061] The fuel cell system as explained herein is compact and therefore particularly useful electrical power production in vehicles and for propelling the vehicle by electricity. For example, the vehicle is an automobile or truck. Alternatively, the vehicle is a marine vessel. A further alternative is a stationary power station.

Claims

CLAIMS1. A fuel cell system (1) comprising- a fuel cell (2),- a liquid fuel supply (19) for supplying liquid fuel,- an evaporator (41) for evaporating the liquid fuel,- a superheater (42) for heating the evaporated fuel,- a reformer (26) comprising a catalyst (26A) for catalytically reforming the superheated fuel to reformed syngas (27) at a catalytic temperature;- a fuel processing unit (17) comprising a pressurised container (20) that contains the evaporator (41), the superheater (42), and the reformer (26) but not the fuel cell (2), wherein the pressurized container (20) has a fuel inlet (25) and a syngas outlet (45), wherein the fuel inlet (25) is flow-connected to the liquid fuel supply (19) by a fuel conduit and the syngas outlet (45) is flow-connected to the fuel cell (2) by a syngas conduit; wherein the pressurised container (20) contains a first, second and third compartment (21, 22, 23), which are pressurised to above the pressure of the surroundings and gas-flow interconnected for forming a gas flow path (44) inside the container (20) for flow of evaporated fuel from the first compartment (21) through the second compartment (22) to the third compartment (23); wherein the first compartment (21) comprises a receptacle (46) for accommodating the liquid fuel received through the fuel inlet (25); wherein the second compartment (22) is gas-flow connected to the first compartment (21) for receiving the evaporated fuel (24 A) from the first compartment (21) along the gas flow path (44) through the container (20), and wherein the third compartment (23) is gas-flow connected to the second compartment (22) for receiving the superheated evaporated fuel (24A) from the second compartment (23) for reforming the evaporated fuel (24 A) into syngas (27), characterized in that the fuel cell system further comprises a coolant circuit (8) containing coolant and flow-connected to the fuel cell (2) for uptake of thermal energy from the fuel cell by the coolant and a reformer heater (12, 15, 48) for heating the reformer (26) to a temperature at which catalytic reformation of the superheated fuel occurs;wherein the first compartment (21) contains a first heat exchanger (31) having first heat exchanger walls (31C) confining a first inner flow volume that is flow-connected to the coolant circuit (8), wherein an outer side of the first heat exchanger walls (31C) is in thermal contact with the liquid fuel (24) for transfer of thermal energy from the coolant to the liquid fuel (24) for evaporating the fuel; wherein the second compartment (22) contains a second heat exchanger (32) having second heat exchanger walls (32C) confining a second inner flow volume that has an upstream connection and a downstream connection, wherein the upstream connection is connected to a downstream side of the reformer (26) for receiving syngas from the reformer (26) and the downstream connection is connected to the syngas outlet (45) of the container (20), wherein the second heat exchanger (32) is configured for superheating the evaporated fuel (24A) by transfer of thermal energy from the syngas (27) to the evaporated fuel (24A) prior to the syngas (27) leaving the container (20) through the syngas outlet (45) and entering the fuel cell (2); wherein the third compartment (23) contains the reformer (26) with the reformation catalyst (26A) that is thermally connected to the reformer heater (12, 15, 48).

2. The fuel cell system according to claim 1, wherein the third compartment (23) contains a third heat exchanger (33) having third heat exchanger walls (33C) confining a third inner flow volume flow-connected to a circuit (15) of thermal fluid having a temperature of no less than the catalytic temperature, wherein an outer side of the third heat exchanger walls (33) is in thermal contact with the superheated evaporated fuel and the catalyst (26A) for transfer of thermal energy from the thermal fluid to the superheated evaporated fuel and the catalyst (26A) and for heating them to no less than the catalytic temperature.

3. The fuel cell system of claim 2, wherein the circuit (15) of thermal fluid is flow- connected to a heat-pump (48), wherein the heat-pump (48) is thermally connected to the coolant circuit (8) and arranged for transfer of thermal energy from the coolant to the thermal fluid for raising the temperature of the thermal fluid to no less than the catalytic temperature.

4. The fuel cell system of claim 3, wherein the heat-pump (48) comprises a compressor (38) configured for receiving the thermal fluid in gas form and adiabatically compressing the thermal fluid to raise the temperature to no less than the catalytic temperature.

5. The fuel cell system according to anyone of the claims 2-4, wherein the pressurised container (20) has an operational orientation relatively to gravity, in which the third compartment (23) is above the second compartment (22), and the second compartment (22) is above the first compartment (21) for an upwards directed flow of evaporated fuel from the first compartment (21) through the second compartment (22) to the third compartment (23).

6. The fuel cell system according to claims 5, wherein the first, second, and third heat exchanger (31, 32, 33) are all pillow plate heat exchangers connected to each other edge-to-edge one above the other to form a single rigid heat exchange construction.

7. A method of operating a fuel cell system according to any preceding claim, the method comprising- operating the fuel cell system (1) and producing electrical energy by the fuel cell (2),- maintaining the fuel cell (2) at a predetermined operation temperature by the coolant circuit (8),- supplying liquid fuel from the fuel supply (19) to the receptacle (46) in the first compartment (21),- providing flow (34) of coolant through the first inner volume of the first heat exchanger (31) and evaporating the liquid fuel (24) by transfer of thermal energy from the coolant to the liquid fuel (24),- heating the catalyst (26A) by the reformer heater (12, 15, 48) to a temperature no less than the catalytic temperature, receiving superheated fuel from the second compartment and reforming it into syngas (27);- providing a flow of the evaporated fuel (26A) through the container along a gas flow path (44) from the first compartment (21) through the second compartment (22) and through the third compartment (23), and a flow (28) of syngas (27) from the third compartment (23) into the second inner flow volume of the second heat exchanger (22) in the second compartment (23) and superheating the evaporated fuel (26 A) in the second compartment (23) by the second heat exchanger (32);- providing a flow of the syngas from a downstream side of the second heat exchanger (22) through the syngas outlet (45) of the container (20) to the fuel cell (2).

8. The method according to claim 7, wherein the method comprises regulating the pressure inside the container (20) by regulating the evaporation rate of the liquid fuel (26) in the receptacle (46) of the first compartment (21) through adjustment of coolant flow through the first heat exchanger (31).

9. The method according to claim 7 or 8, wherein the third compartment (23) contains a third heat exchanger (33) having third heat exchanger walls (33C) confining a third inner flow volume flow-connected to a circuit (15) of thermal fluid, wherein the method comprises heating the thermal fluid to a temperature of no less than the catalytic temperature and transferring thermal energy from the thermal fluid through the third heat exchanger walls (33C) to the superheated evaporated fuel and the catalyst (26A) and heating them to no less than the catalytic temperature.

10. The method according to claim 9, wherein the circuit (15) of thermal fluid is flow- connected to a heat pump (48), wherein the heat-pump (48) is thermally connected to coolant circuit (8) and wherein the method comprises transferring thermal energy from the coolant to the thermal fluid by the heat pump (48) and raising the temperature of the thermal fluid to no less than the catalytic temperature.

11. The method according to claim 10, wherein the heat pump (48) comprises a compressor (38) and the method comprises receiving thermal fluid in gas form by the compressor (38) and adiabatically compressing the thermal fluid to raise the temperature to no less than the catalytic temperature.

12. The method according to claim 11, further comprising pumping the thermal fluid by the compressor (38) through the third inner volume of the third heat exchanger (33), cooling the thermal fluid by transfer of thermal energy from the thermal fluid through the third heat exchanger walls (33C) to the catalyst (26A), expanding the thermal fluid downstream of the third heat exchanger (33) for reducing the pressure and temperature of the thermal fluid to a first temperature below a coolant temperature in the coolant circuit (8), causing flow of the thermal fluid in liquid form through an evaporator (37)that is thermally connected to the coolant circuit (36), and by transfer of thermal energy from the coolant to the thermal fluid through the evaporator (37), raising the temperature of the thermal fluid and evaporating the thermal fluid prior to the gaseous thermal fluid entering the compressor (38).

13. The method according to anyone of the claims 9-12, wherein the first, second, and third heat exchanger (31, 32, 33) are all pillow plate heat exchangers connected to each other edge-to-edge one above the other to form a single rigid heat exchange construction.

14. A vehicle comprising a fuel cell system according to anyone of the claims 1-6.

15. A vehicle according to claim 14, where the vehicle is a marine vessel.

16. A method of propelling a vehicle by electricity, wherein the method comprises producing electricity by a method according to anyone of the claims 7-13 and feeding at least a portion of the electrical power into engines propelling the vehicle.

17. A method according to claim 16, where the vehicle is a marine vessel.

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