GB2458112A

GB2458112A - Heat and Process Water Recovery System

Info

Publication number: GB2458112A
Application number: GB0803952A
Authority: GB
Inventors: Michael Rendall; George Carins
Original assignee: Voller Energy Ltd
Current assignee: Voller Energy Ltd
Priority date: 2008-03-03
Filing date: 2008-03-03
Publication date: 2009-09-09
Also published as: WO2009109744A3; GB0803952D0; WO2009109744A2

Abstract

An integrated fuel processing and fuel cell system comprises a fuel processing device 2 for reforming a raw material fuel 3, having a reforming device 2 and a combustion unit 7 for generating the reaction heat for reforming the raw material fuel 3 and process water 42, an air intake from ambient for oxidant supply to the combustion unit 7 and to a cathode 8 of a fuel cell device 24 for generating electricity through an electrochemical reaction between the reformed fuel and the oxidant supply. In an embodiment, four heat exchangers are provided in series and a common media is circulated through the four heat exchangers to raise the temperature of the media higher than the operational temperature of the fuel cell device 24.

Description

* 2458112

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Heat and Process Water Recovery System

Technical Field

The present invention relates to a fuel cell power system, particularly to a fuel cell power system equipped with a heat recovery system which extracts waste heat from the reformer/fuel cell system.

Background Art

Fuel cell systems convert fuels into usable electrical power and heat via a controlled electrochemical reaction. Compared to conventional generation technologies fuel cell systems offer high overall efficiencies, low noise, low vibration, and low emissions. There are several different types of fuel cell technologies, including proton exchange membrane type (further split into low temperature and high temperature types), solid oxide, molten carbonate, alkaline and phosphoric acid. The most common of these is the proton exchange membrane type (PEM).

A fuel cell power system generates electricity through the electrochemical reaction between a hydrogen rich gas (reformate) and an oxidant gas such as air. In a PEM fuel cell system, the reformate is supplied to one electrode (anode) of a fuel cell. The oxidant such as air is supplied to the other electrode of the fuel cell (cathode). A membrane separates the anode and the cathode but allows the permeation of ions (protons) from the anode to the cathode. Electrons are collected on the anode and conducted through an external electric circuit to the cathode where they react with the protons and the oxidant molecules. This process produces electricity and heat Since the provision of high purity hydrogen for widespread application of fuel cells is generally impractical, generation of the reformate stream from common fuels is usually used for commercial application of PEM fuel cells.

Typically, such gas streams are produced via processing of a hydrocarbon input in a fuel processor (often referred to as a "reformer") followed by one or more gas purification stages. The reformer typically generates the required fuel cell suitable gas at a relatively high temperature. In order to integrate both subsystems, the fuel cell module and the reforming device, temperature control is crucial in order to get a high system performance in terms of power output, reliability and longevity. Additionally, effective temperature control is important should water need to be recovered by the system for use in the fuel processing or gas purification systems, for example in the case when the fuel processing system used is steam or auto thermal reforming.

However, a separate cooling and control of the liquids and gases within the system does not necessarily lead to a high quality heat source. As those skilled in the art will appreciate, high quality or high grade heat for hot water or space heating purposes is defined by its flow and return temperature.

The higher the temperature of a heat source, the more effectively it can be used for heating, for example via a circulating water flow passed through a space or water heat exchanger. Additionally, the lower the temperature of the return flow fluid back into the system compared to the temperature of the fluid exiting the system and consequently, the higher the temperature difference therebetween, the more thermal power can be extracted.

Furthermore, the heat should come from a single source in order to allow a simple installation, e.g. for a heating system in a house or temporary building, a vehicle or a boat. In addition, high temperature coolant flow makes the fuel cell system more efficient, as less power for fans or pumps is needed to dissipate the heat to ambient in particular where no heat recovery is needed and the fuel cell system is in a sole electricity generation mode.

EP1653546A1, "Fuel Cell Cogeneration System", to Ebara Ballard Corporation, describes a heat recovery system with in series connected heat exchanger for a reformer fuel cell system but the maximum hot water temperature is limited to the outlet temperature of the fuel cell stack. No further heat recovery steps with respect to an increased hot water storage temperature are disclosed therein. Apart from heating up the hot water storage tank, excess heat is used for oxidant supply humidification.

EP 1542301 Al, "Fuel Cell Cogeneration System", to Matsushita Electric Industrial Corporation, describes a system with in series connected heat exchanger taking advantage of the temperature gradient within a hot water storage tank. According to that application, hot water in the upper area of a hot water tank can be used to heat up the fuel cell device in order to speed up the start up time. However, that application is limited with respect to the hot water storage temperature as it requires a heat exchanger up stream the hot water storage tank which needs to be operated even below the stack temperature and therefore is not ideal for heat recovery of a system with a low temperature fuel cell which typically operates at 67 °C. The additional heat exchanger in the flue gas pathway described therein dissipates heat into the coolant upstream the fuel cell device heat exchanger and can therefore not contribute to the temperature increase of the coolant entering the hot water storage tank.

In most fuel cell cogeneration systems, particularly in PEM systems, most of the heat is generated at quite low temperatures (40 °C to 60 °C).

Additionally, the heat is generated by multiple heat sources leading to higher costs and complexity with regard to an implementation into heating systems.

In comparison, conventional heating systems can typically generate a single hot media at a flow temperature of up to 75 °C, which makes is useful for hot water production or space heating as it allows an efficient heat transfer between the heating circuit and ambient. In addition, temperatures above 70 °C advantageously avoid bacterial growth in water circuits, especially with regards to the fatal Legionella pneumophila.

Statements of Invention

The present invention has been devised to provide for an increased flow temperature of the cooling media in order to tackle the above mentioned problem and combines different heat sources into one heating circuit for an easy installation into existing hot water and heating systems.

The invention solves the problem by a combination of at least two heat sources in one media circuit and by a series connection of at least two heat exchanging devices. A cooling media flowing through the in series linked heat exchanger devices takes up heat from the respective heat sources in a way that the temperature of the cooling media is being increased through each subsequent heat exchanger.

According to one aspect, the present invention provides a fuel cell power system, comprising a fuel processing device for processing input fuel into a reformed gas, a fuel cell device for converting the reformed gas into electricity, and two or more heat exchangers connected in series to increase the temperature of a heat exchanger media so that the temperature of a heat exchanger media is higher than the operational temperature of the fuel cell device.

A flue gas heat exchanger may be provided coupled to the fuel processing device for cooling flue gas from the fuel processing device, wherein the flue gas heat exchanger is provided as the last heat exchanger in the series of connected heat exchangers.

According to another aspect, the present invention provides a fuel cell power system, comprising a fuel processing device for processing input fuel into a reformed gas, a fuel cell device for converting the reformed gas into electricity, a reformat heat exchanger coupled to the fuel processing device for cooling reformed gas from the fuel processing device, a flue gas heat

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exchanger coupled to the fuel processing device for cooling flue gas from the fuel processing device, a cathode off gas heat exchanger coupled to the fuel cell device for cooling cathode off gas from the fuel cell device, and a fuel cell device heat exchanger coupled to the fuel cell device for heating and cooling the fuel cell device, wherein the reformat heat exchanger, flue gas heat exchanger, cathode off gas heat exchanger and fuel cell device heat exchanger are arranged in series to transfer heat to the same heat exchanger media.

A valve may be provided to bypass the fuel cell device heat exchanger.

According to yet another aspect, the present invention provides a fuel cell power system, comprising a fuel processing device for processing input fuel into a reformed gas, a fuel cell device for converting the reformed gas into electricity, a reformat heat exchanger coupled to the fuel processing device for cooling reformed gas from the fuel processing device, a fuel cell device heat exchanger coupled to the fuel cell device for heating and cooling the fuel cell device, and a combined gas heat exchanger coupled to the fuel processing device and the fuel cell device for cooling combined flue gas from the fuel processing device and cathode off gas from the fuel cell device, wherein the reformat heat exchanger and the fuel cell device heat exchanger are arranged in series to transfer heat to the same heat exchanger media.

Another valve may be provided to cause the heat exchanger media to be circulated within the system and bypass external heat sinks. The valve may be a 3/2 way valve.

The fuel processing device may be a steam reformer. The fuel cell device may be a proton exchange membrane, PEM, fuel cell. Internal batteries may be provided for providing power for start-up. The input fuel may be liquefied petroleum gas, LPG.

The system may be a standalone unit not connected to an electrical grid.

The recovered heat can advantageously be used for water and space heating purposes and the recovered process water for internal usage.

Alternatively, when the fuel cell system is operated only in electricity generation mode, the recovered heat can simply be dissipated to the environment without being further used or stored.

Description of Drawings

Specific embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a block diagram of an example integrated fuel cell system which does not form a specific embodiment of the present invention; Figure 2 is a block diagram of the components of an integrated fuel cell system according to a first embodiment of the present invention; Figure 3 is a block diagram of the components of an integrated fuel cell system according to a second embodiment of the present invention, with an additional bypass path to a heat exchanger for an accelerated start up; Figure 4 is a block diagram of the components of an integrated fuel cell system according to a third embodiment of the present invention, with maximized water recovery;

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Figure 5 is a block diagram of the components of an integrated fuel cell system according to a fourth embodiment of the present invention, with an additional valve for accelerated heat up of the fuel cell device; and Figure 6 is a block diagram of the components of an integrated fuel cell system according to a fifth embodiment of the present invention, with an additional heat exchanger to maximise heat and water recovery.

Example Integrated Fuel Cell System The effects of the present invention can be best described with reference to a general example of an integrated fuel processor and fuel cell power system as illustrated in the schematic block diagram of Figure 1. The integrated system I depicted in Figure 1 includes a fuel processor 70 having a reforming device 2 (such as a steam reforming device) for processing input fuel into a reformat (reformed gas) using heat generated by a combustion unit (burner) 7. The system I also includes a fuel cell device 24, which in this embodiment is a low temperature polymer electrolyte membrane (PEM) fuel cell stack. The system 1 generates regulated electricity 41 through an electrochemical reaction between a hydrogen-rich reformat 20 and an oxidant gas 15 such as air. The reforming device 2 processes input fuel into a reformat (reformed gas). The reformat is supplied to an anode electrode 23 of the fuel cell device 24. The oxidant such as air 5 from ambient 19 is supplied to a cathode electrode 8 of the fuel cell. This process produces unregulated electricity 40 and heat. The electricity is passed through a power conditioning unit 25 in order to produce regulated electric power 41. Unused fuel in the anode 23 leaves the fuel cell device 24 as anode off gas 33 and is passed back into the combustion device 7 for providing a part of the reaction heat for the fuel reforming process carried out by the reforming device 2.

Figure 1 shows the different heat sources of the integrated system, in particular the combustion unit 7, the reforming device 2, and the fuel cell

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device 24. Figure 1 also shows the main heat sources being captured with four heat exchangers, a cathode off gas heat exchanger 28, a fuel cell device heat exchanger 27, a reformat heat exchanger 21 and a flue gas heat exchanger 17. As a result, in the example shown in Figure 1, five separate heating/cooling circuits are provided.

In a first heating/cooling circuit, the heat of the fuel cell device is transferred into a heat exchanger media 26 (such as water) and circulated with pump 39 through heat exchanger 27 and subsequently dissipated via a second cooling circuit into another heat exchanger media 54 (such as water). As those skilled in the art will appreciate, not only does the temperature of the fuel cell device 24 need to be maintained, but the temperature difference between the inlet and outlet of the coolant media 26 needs to be kept within certain operating parameters (e.g. as predefined by the manufacturer). This can only be maintained by the introduction of the separate first heating/cooling circuit (formed by media 26 circulated by pump 39) and the second heating/cooling circuit (formed in this example by media 54).

As discussed above, the reforming device 2 generates the required reformat 20 from a raw material fuel 3 using heat generated in a combustion device 7. Due to the high operating temperature of the reforming device and the low operating temperature of the PEM fuel cell stack, the reformat 20 needs to be cooled in heat exchanger 21 in order to match the return temperature of the fuel cell device coolant 26. The heat from the reformat 20 is transferred into media 52 by way of a third cooling circuit. The cooling of the reformat also results in condensation of water vapor contained in the reformat. The water 42 from the reformat is separated from the reformed gas in a gas/liquid separator 22. The water 42 is then fed into a buffer tank 12 for supply back into the reforming device 2 after being treated in a water purifier treatment device 13.

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The combustion device 7 is supplied with fuel 9 and oxidant 14. The oxidant is taken from ambient 19 fed by an air intake into an air compressor 6 to be pressurized in order to overcome the backpressure of downstream devices. In addition to the heat for the reforming device 2, the combustion device 7 produces a hot flue gas 16, which mainly comprises of water vapor, carbon dioxide and nitrogen. The water vapor 42 is condensed and circulated into the reforming device 2 by means of heat exchanger 17, gas/liquid separator 18, water buffer tank 12 and purifier device 13. The heat from the flue gas cooling is transferred into media 50 by way of a fourth cooling circuit.

The cathode off gas 37 of the fuel cell device is cooled in a cathode off gas heat exchanger 28 which results in further generation of liquid water which is separated in liquid/gas separator 36 and fed back into the buffer tank 12. The heat from cathode off gas heat exchanger 28 is transferred into media 56 by way of a fifth cooling circuit.

As those skilled in the art will appreciate, the temperatures, in particular of media 26 and the reformat 20, need to be controlled precisely in order to achieve a high performance, reliability and longevity of the fuel cell device, and to avoid system degradation and damage. For example, if the temperature of the reformat provided to the fuel cell device is significantly higher than the operating temperature of the fuel cell device, this would lead to unwanted condensation which may lead to blockages in the system. As another example, if the temperature of the fuel cell device is much higher than the temperature of the reformat, then the reformat would be wanned up as it enters the fuel cell device which leads to the undesirable effect of moisture in the fuel cell device drying up due to the decreased relative humidity of the reformat.

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In addition, in order to recover enough water for the reforming device 2, the flue gas 16 and the cathode off gas 37 need to be cooled.

The following table outlines the thermal power dissipated by heat exchangers 17, 21, 27 and 28 for a fuel cell device having a gross electric power of 1.2 kWel, and the respective media temperatures leaving the heat exchangers in order to meet the requirements in terms of cooling and process water recovery.

Heat exchanger Associated Dissipated Media temperature leaving Heat thermal respective heat exchanger exchanger power Media Fluegas(17) 52 540W 45°C Reformat (21) 50 206W 60°C Fuel cell device 54 993 W 60 °C (27) Cathode off gas 56 280W 40°C (28) Table 1: Thermal power to be dissipated in different heat exchangers and media flow temperatures, calculated with process simulation software chemcad from chemstations Inc. As described above and shown in Table 1 and Figure 1, the heat is dissipated at quite low temperatures (40 °C to 60 °C). Of course, as those skilled in the art will appreciate, the above values are provided by way of example, and the temperatures of media leaving the respective heat

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exchangers may vary (and the dissipated thermal power will likewise vary), for example if the power of the fuel cell device is changed.

In the example illustrated in Figure 1, the media are cooled and controlled separately to obtain a precise temperature control in order to get a high system performance in terms of power output, reliability and longevity.

Embodiments of the present invention will now be described which provide for improvements over the example illustrated in Figure 1. In particular, two or more of the heating/cooling circuits described above may be combined and/or other elements may be added to the heat and water recovery system.

These combination options are shown in the embodiments described hereinafter.

First Embodiment A first embodiment of a fuel cell cogeneration system of the present invention is illustrated in the schematic block diagram of Figure 2. The system 100 of the present embodiment comprises a fuel processor 70 having a combustion unit 7 and a reforming device 2 for reforming a raw material fuel 3 and process water 42 using reaction heat generated by the combustion unit 7. A raw material fuel clean up device 4 is provided for removing compounds (especially sulphur compounds) from the raw material fuel 3 before passing clean fuel 9 to the reforming device 2 and passing clean fuel 10 to the combustion unit 7. The system 100 also includes an air intake from ambient 19 for oxidant supply 14 to the combustion unit 7 and to a cathode 8 of a fuel cell device 24 for generating electricity through an electrochemical reaction between the reformed fuel and the oxidant supply, and an air compressor 6 to force air through to the combustion unit 7 and the cathode 8 of the fuel cell device 24. The process water 42 is collected in a water buffer tank 12 and purified in a water treatment unit 13, in particular to remove calcium ions in the process water 42.

Downstream the combustion unit 7, exhaust flue gas 16 is passed through a flue gas heat exchanger 17 and a gas/water separator 18 and released to ambient 19. The water 42 from the gas/water separator 18 is collected in water tank 12.

Downstream the reforming device 2, the reformat 20 is passed through a reformat heat exchanger 21 and gas liquid separator 22. From the gas liquid separator 22, the reformat 20 is passed to an anode 23 of the fuel cell device 24. The water 42 from separator 22 is collected in water tank 12.

Unused fuel in the anode 23 leaves the fuel cell device 24 as anode off gas 33 and is passed into the combustion unit 7 for providing a part of the reaction heat for the reforming process in the reforming device 2. The fuel cell device 24 converts the fuel 20 supplied to the anode 23 with oxidant 15 supplied to the cathode 8 into unregulated electric power 40 and heat. The electricity is fed into a power conditioning device 25 and is converted into regulated electric power 41. The generated heat of the fuel cell device 24 is transferred into heat exchanger media 26 (which in this embodiment is water), and circulated by pump 39 through a fuel cell device heat exchanger 27, forming a first cooling circuit. The heat is transferred in the fuel cell device heat exchanger 27 into another heat exchanger media 56 (which is in this embodiment is also water).

The cathode off gas 37 is passed through a cathode off gas heat exchanger 28 which also transfers the heat into the heat exchanger media 56 and subsequently passes the cathode off gas 37 through gas/water separator 36 before the gas is released to ambient 19. The water 42 gained from the gas/water separator 36 is passed into the process water buffer tank 12 for storage.

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As shown in Figure 2, the heat exchanger media 56 is circulated by pump 31 through the four heat exchangers: the cathode off gas heat exchanger 28, the fuel cell device heat exchanger 27, the reformat heat exchanger 21 and the flue gas heat exchanger 17, forming a second heating/cooling circuit. In this way, it is possible to take up waste heat from various heat sources into one heat exchanger media. At the same time, the temperatures of the heat exchanger media 26 and reformat 20 are matched appropriately to avoid the above-mentioned problems of system degradation or damage. (As further evidence of the significance of controlling the relative temperatures and the effect on system operation, the reader is referred to the experimental data provided in the Appendix.) Additionally, the cathode off gas and the flue gas are cooled down significantly in order to recover process water. Furthermore, the heat exchanger media 56 advantageously reaches a high temperature for space and water heating purposes. As a further advantageous effect, the temperature of the heat exchanger media 56 leaving the fuel cell system 100 will be high enough to avoid any bacterial growth.

The temperature rise of the heat exchanger media 56 according to the present embodiment is set out in Table 2, and can be compared to the thermal power data set out in Table 1 above. The table of figures for the present embodiment are calculated based on a fuel cell having a gross electric power of 1.2 kWei and where the heat exchanger media 56 (which in this embodiment is water) is circulated at 1 kg/mm, has a specific heat capacity of 4.2 kJfkg*K and enters the fuel cell cogeneration system 100 at 50 °C. Those skilled in the art will appreciate that the embodiments are not limited to these particular values and variations are possible. For example, if a higher heat fuel cell device is used (such as a 2 kW1 fuel cell), this would require a faster flow for the heat exchanger media and if a different media is used, then the specific heat capacity will likewise be different.

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Heat Heat Dissipated Heat exchanger Heat exchanger exchanger exchanger thermal media 56 inlet media 56 outlet sequence power temperature temperature I Cathode off 280W 50C 54C gas (28) 2 Fuel Cell 993 W 54 C 68 C Device (27) 3 Reformat 206 W 68 C 71 C (21) 4 Flue Gas 540W 71 C 79 C (17) Table 2: Temperature rise of heat exchanger media 56 according to the first embodiment As an advantageous effect of the invention, the heat exchanger media 56 according to the present embodiment reaches a temperature of 79 °C and solves the problem associated with cogeneration systems using a low temperature fuel cell with respect to their low operating temperature resulting in ineffective usage of waste heat. As set out in Table 2, a flow temperature of 79 °C and a return temperature of 50 °C equates to a usable thermal power of 2019 W. As opposed to the example fuel cell cogeneration system 1 illustrated in Figure 1, where thermal power is only produced up to 60 °C (referring to Table 1), the present embodiment makes waste heat from a combined heat and power (CHP) system more attractive for space and water heating for domestic, marine, recreational and construction industry application.

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Alternatively, if there is no any heat required for space and/or hot water generation, or if the integrated system 100 is only used to produce electric power, the waste heat from the integrated system 100 can be simply transferred into a primary coolant like water or dissipated into ambient air.

Second Embodiment Figure 3 illustrates an integrated fuel processing and fuel cell system according to a second embodiment of the present invention. The system of the second embodiment is essentially the same as the first embodiment with the addition of a valve 60 between the fuel cell device 8 and the fuel cell device heat exchanger 27. The valve 60, which may be a 3/2 way valve, provides a bypass path 26' for bypassing the fuel cell device heat exchanger 27, which can advantageously lead to an accelerated heat up of the fuel cell device during a start-up phase. Another benefit of the second embodiment is that in the case of a low return temperature of the heat exchanger media 56 (for example return temperatures << 50 °C), the fuel cell device 24 will be protected from being cooled excessively.

Third Embodiment Figure 4 illustrates an integrated fuel processing and fuel cell system 300 according to a third embodiment of the present invention. In comparison to the first and second embodiments, which both maximize the flow temperature of media 56, the system 300 of the third embodiment only combines the heat from the reformat heat exchanger 21 and the fuel cell device heat exchanger 27 in heat exchanger media 56. As discussed above, the reformat heat exchanger 21 and fuel cell device heat exchanger 27 are responsible for heating and cooling the reformat 20 and the fuel cell device heat exchanger media 26. Most of the heat (thermal energy) is still gathered in heat exchanger media 56. However, due to the fact that the cathode off gas cannot be cooled below the return temperature of heat exchanger media 56, and that the flue gas 16 cannot be cooled below the temperature of heat

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exchanger media 56 downstream the reformat heat exchanger 21 (according to the 2' thermodynamic law), it is advantageous to remove the cathode off gas heat exchanger 28 and flue gas heat exchanger 17 from the second heating/cooling circuit 56 and to cool the combined cathode off gas and flue gas 81 separately with an additional heat exchanger media 80, forming a third heating/cooling circuit. The cooled combined cathode off gas and flue gas 81 is passed through a gas/water separator 18 before the gas 81 is released to ambient 19. The water 42 gained from the gas/water separator 18 is passed into the process water buffer tank 12 as described above.

According to the third embodiment, this arrangement provides a higher water recovery rate but less thermal power recovery.

Fourth Embodiment Figure 5 illustrates an integrated fuel processing and fuel cell system 400 according to a fourth embodiment of the present invention. The system 400 illustrated in Figure 5 is essentially the same as the second embodiment, with the addition of an additional valve 61 between the flue gas heat exchanger 17 and the pump 31, which enables the heat exchanger media 56 to be circulated within the system. This arrangement provides for an accelerated heat up of the fuel cell device 24.

During the start up of the system the combustion device 7 will be started first as the reforming device needs to be heated up to a quite high operating temperature (typically 850 °C). Along with the operation of the combustion device 7, flue gas is generated and passed through flue gas heat exchanger 17 to ambient 19. The heat of the flue gas is transferred into heat exchanger media 56. The heat exchanger media 56 is circulated by pump 31 through the cathode off gas heat exchanger 28 and fuel cell device heat exchanger 27. In the fuel cell device heat exchanger 27, the heat is transferred into heat exchanger media 26 which is circulated by pump 39

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through the fuel cell device 24. Under the condition that the temperature of the fuel cell device is below the temperature of the heat exchanger media 56, heat is transferred into the heat exchanger media 26 which eventually leads to the warm up of the fuel cell device 24.

Under normal operation of the heat and water recovery system described above, the fuel cell device is generating heat and therefore the effect of the system is to provide cooling of the fuel cell device via the use of the heat exchangers arranged in series. However, during a system start-up operation, the fuel cell device must instead be heated up to operational temperature. In such an operation, the combustion unit 7 will typically be in start-up operation and heat from the combustion unit 7 may advantageously be used to assist heating up of the fuel cell device 24 via the first heating/cooling circuit formed by the heat exchanger media 56 transferring heat to the fuel cell device heating/cooling circuit formed by the heat exchanger media 26. As a further alternative, the flow direction of the heat exchanger media 56 can be reversed so that heat from flue gas heat exchanger 17 is passed to the fuel cell device heat exchanger via the reformat heat exchanger 21.

Fifth Embodiment Figure 6 illustrates an integrated fuel processing and fuel cell system 500 according to a fifth embodiment of the present invention. The system 500 of the fifth embodiment is similar to the second embodiment, with an additional heat exchanger 97 provided downstream of the flue gas heat exchanger 17 and the cathode off gas heat exchanger 37, to provide both maximum heat and water recovery. The additional heat exchanger 97 receives a combined cooled flue gas 16 from the flue gas heat exchanger 17 and cooled cathode off gas 37 from the cathode off gas heat exchanger 28.

The cooled combined cathode off gas and flue gas 81 is passed through a gas/water separator 18 before the gas 81 is released to ambient 19. The water

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42 gained from the gas/water separator 18 is passed into the process water buffer tank 12 as described above.

The effect on the heat recovery is described above with respect to the first embodiment. As the additional heat exchanger 97 further cools the gas stream, additional water recovery is obtained via gas/liquid separator 18.

Alternative Embodiments It will be understood that embodiments of the present invention are described herein by way of example only, and that various changes and modifications may be made without departing from the scope of the invention.

For example, in the embodiments described above, an air compressor is provided to take air from ambient and provide pressurised air to the combustion unit and the fuel cell device. As those skilled in the art will appreciate, the air compressor may be provided as two or more separate units, and may instead comprise a blower or pump. As yet a further alternative, the air compressor may be further arranged as an air conditioner to filter the air to remove unwanted particles.

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Appendix The schemaUc relationship between reforniate temperature & Gross Power -15 -10.5 5 10 15 T(R.f)-T(Stk ml.f)IC Figure A-i: The diagram shows experimental data regarding the dependency of the temperature difference between reformat and fuel cell device coolant inlet (TgerTstk Inlet in °C) temperature and power loss of the fuel cell device (PGrossPqdT) in W). The power loss is significant if both the reformat temperature is higher than the fuel cell device coolant inlet temperature (TRer TstkInl> 0) and if the fuel cell device coolant inlet temperature is lower than the reformat temperature (TRCI-TStk Inlet < 0). The reformat is shown as reference number 20 and the fuel cell device coolant is shown as reference number 26 in Figures 1 to 6.

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Experimental data from 29.02-08

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13:40:48 13:48.00 13:55:12 14:02:24 14:09:38 14:18:48 14:24:00 14:31:12 14:3824 Time (hh:mm:ss) Figure A-2: The diagrams shows the temperature of the reformat entering the anode of the fuel cell device (media 20 in Figures 1 to 6) and fuel cell device coolant inlet temperature (media 26 in Figures 1 to 6). The results are achieved with an implementation of an embodiment of the described invention. The temperatures, in particular those when the system operated at steady (-time 14:15:00 to 14:35:00), are very close together, which meets the system operating requirements.

Claims

Claims: 1. A fuel cell power system, comprising a fuel processing device for processing input fuel into a reformed gas, a fuel cell device for converting the reformed gas into electricity, and two or more heat exchangers connected in series to increase the temperature of a heat exchanger media so that the temperature of a heat exchanger media is higher than the operational temperature of the fuel cell device.
2. A fuel cell power system according to claim 1, wherein the temperature of the reformed gas provided to the fuel cell device is maintained within the operating requirements of the fuel cell device.
3. A fuel cell power system according to claim 1 or 2, wherein the two or more heat exchangers comprise a flue gas heat exchanger coupled to the fuel processing device for cooling flue gas from the fuel processing device, wherein the flue gas heat exchanger is provided as the last heat exchanger in the series of connected heat exchangers.
4. A fuel cell power system, comprising: a fuel processing device for processing input fuel into a reformed gas; a fuel cell device for converting the reformed gas into electricity; a reformat heat exchanger coupled to the fuel processing device for cooling reformed gas from the fuel processing device; a flue gas heat exchanger coupled to the fuel processing device for cooling flue gas from the fuel processing device; a cathode off gas heat exchanger coupled to the fuel cell device for cooling cathode off gas from the fuel cell device; and a fuel cell device heat exchanger coupled to the fuel cell device for heating and cooling the fuel cell device, wherein the reformat heat exchanger, flue gas heat exchanger, cathode off gas heat exchanger and fuel cell device heat exchanger are arranged in series to transfer heat to the same heat exchanger media.
5. A fuel cell power system according to claim 4, further comprising a valve operable to bypass the fuel cell device heat exchanger.
6. A fuel cell power system, comprising: a fuel processing device for processing input fuel into a reformed gas; a fuel cell device for converting the reformed gas into electricity; a reformat heat exchanger coupled to the fuel processing device for cooling reformed gas from the fuel processing device; a fuel cell device heat exchanger coupled to the fuel cell device for heating and cooling the fuel cell device; and a combined gas heat exchanger coupled to the fuel processing device and the fuel cell device for cooling combined flue gas from the fuel processing device and cathode off gas from the fuel cell device, wherein the reformat heat exchanger and the fuel cell device heat exchanger are arranged in series to transfer heat to the same heat exchanger media.
7. A fuel cell power system according to any one of claims 4 to 6, further comprising a valve operable to cause the heat exchanger media to be circulated within the system and bypass external heat sinks.
8. A fuel cell power system according to claim 5 or 7, wherein the valve is a 3/2 way valve.
9. A fuel cell power system according to any preceding claim, wherein the fuel processing device is a steam reformer.I
10. A fuel cell power system according to any preceding claim, wherein the fuel cell device is a proton exchange membrane, PEM, fuel cell.
11. A fuel cell power system according to any preceding claim, further comprising internal batteries for providing power for start-up.
12. A fuel cell power system according to any preceding claim, wherein the input fuel is liquefied petroleum gas, LPG.
13. A fuel cell power system according to any preceding claim, wherein the system is a standalone unit not connected to an electrical grid.
14. A fuel cell power system substantially as herein described with reference to Figure 2, 3, 4, 5 or 6.